WorldWideScience

Sample records for acid brittleness

  1. Effects of Temperature and Humidity History on Brittleness of α-Sulfonated Fatty Acid Methyl Ester Salt Crystals.

    Science.gov (United States)

    Watanabe, Hideaki; Morigaki, Atsunori; Kaneko, Yukihiro; Tobori, Norio; Aramaki, Kenji

    2016-01-01

    α-Sulfonated fatty acid methyl ester salts (MES), which were made from vegetable sources, are attractive candidates for eco-friendly washing detergents because they have various special features like excellent detergency, favorable biodegradability, and high stability against enzymes. To overcome some disadvantages of powder-type detergents like caking, sorting, and dusting, we studied how temperature and humidity history, as a model for long-term storage conditions, can affect crystalline structures and reduce the brittleness of MES powder. We characterized the crystalline structure of MES grains using small-angle X-ray scattering, wide-angle X-ray scattering, differential scanning calorimetry, and Fourier transform infrared spectroscopy measurements and determined the yield values, which measure the brittleness of MES grains, in shear stress using dynamic viscoelasticity measurements. This study confirmed that MES crystals form three pseudo-polymorphs via thermal or humidity conditioning: metastable crystals (αsubcell), anhydrous crystals (β subcell), and dihydrate crystals (β' subcell). Further, we found that the yield value increases upon phase transition from the β subcell to the β' subcell and from the β' subcell to the αsubcell. Therefore, controlling the thermal and humidity conditioning of MES grains is an effective way to decrease the brittleness of MES powders and can be used to overcome the above mentioned disadvantages of powder-type detergents in the absence of co-surfactants.

  2. [Cosmetology and brittle nails].

    Science.gov (United States)

    Abimelec, P

    2000-12-15

    The knowledge of manicure techniques and nail cosmetics compositions are a prerequisite to the understanding of their potential side effects. The brittle nail syndrome is a common problem that roughly affect 20% of women. We will review the etiologic hypothesis, describe the various presentations, and suggest a treatment for this perplexing problem.

  3. Fracture of brittle solids

    CERN Document Server

    Lawn, Brian

    1993-01-01

    This is an advanced text for higher degree materials science students and researchers concerned with the strength of highly brittle covalent-ionic solids, principally ceramics. It is a reconstructed and greatly expanded edition of a book first published in 1975. The book presents a unified continuum, microstructural and atomistic treatment of modern day fracture mechanics from a materials perspective. Particular attention is directed to the basic elements of bonding and microstructure that govern the intrinsic toughness of ceramics. These elements hold the key to the future of ceramics as high-technology materials--to make brittle solids strong, we must first understand what makes them weak. The underlying theme of the book is the fundamental Griffith energy-balance concept of crack propagation. The early chapters develop fracture mechanics from the traditional continuum perspective, with attention to linear and nonlinear crack-tip fields, equilibrium and non-equilibrium crack states. It then describes the at...

  4. Brittle diabetes: Psychopathology and personality.

    Science.gov (United States)

    Pelizza, Lorenzo; Pupo, Simona

    The term "brittle" is used to describe an uncommon subgroup of patients with type I diabetes whose lives are disrupted by severe glycaemic instability with repeated and prolonged hospitalization. Psychosocial problems are the major perceived underlying causes of brittle diabetes. Aim of this study is a systematic psychopathological and personological assessment of patients with brittle diabetes in comparison with subjects without brittle diabetes, using specific parameters of general psychopathology and personality disorders following the multi-axial format of the current DSM-IV-TR (Diagnostic and Statistical manual of Mental Disorders - IV Edition - Text Revised) diagnostic criteria for mental disorders. Patients comprised 42 subjects with brittle diabetes and a case-control group of 42 subjects with stable diabetes, matched for age, gender, years of education, and diabetes duration. General psychopathology and the DSM-IV-TR personality disorders were assessed using the Symptom Checklist-90-Revised (SCL-90-R) and the Structured Clinical Interview for axis II personality Disorders (SCID-II). The comparison for SCL-90-R parameters revealed no differences in all primary symptom dimensions and in the three global distress indices between the two groups. However, patients with brittle diabetes showed higher percentages in borderline, histrionic, and narcissistic personality disorder. In this study, patients with brittle diabetes show no differences in terms of global severity of psychopathological distress and specific symptoms of axis I DSM-IV-TR psychiatric diagnoses in comparison with subjects without brittle diabetes. Differently, individuals with brittle diabetes are more frequently affected by specific DSM-IV-TR cluster B personality disorders.

  5. Insulating and sheathing materials of electric and optical cables - Common test methods - Part 5-1: Methods specific to filling compounds - Drop-point - Separation of oil - Lower temperature brittleness - Total acid number - Absence of corrosive components - Permittivity at 23 °C - DC resistivity at 23 °C and 100 °C

    CERN Document Server

    International Electrotechnical Commission. Geneva

    2004-01-01

    Specifies the test methods for filling compounds of electric cables used with telecommunication equipment. Gives the methods for drop-point, separation of oil, lower temperature brittleness, total acid number, absence of corrosive components, permittivity at 23 °C, d.c. resistivity at 23°C and 100°C.

  6. Syndromes with congenital brittle bones

    Directory of Open Access Journals (Sweden)

    Plotkin Horacio

    2004-08-01

    Full Text Available Abstract Background There is no clear definition of osteogenesis imperfecta (OI. The most widely used classification of OI divides the disease in four types, although it has been suggested that there may be at least 12 forms of OI. These forms have been named with numbers, eponyms or descriptive names. Some of these syndromes can actually be considered congenital forms of brittle bones resembling OI (SROI. Discussion A review of different syndromes with congenital brittle bones published in the literature is presented. Syndromes are classified in "OI" (those secondary to mutations in the type I pro-collagen genes, and "syndromes resembling OI" (those secondary to mutations other that the type I pro-collagen genes, identified or not. A definition for OI is proposed as a syndrome of congenital brittle bones secondary to mutations in the genes codifying for pro-collagen genes (COL1A1 and COL1A2. Summary A debate about the definition of OI and a possible clinical and prognostic classification are warranted.

  7. Protection of brittle film against cracking

    Science.gov (United States)

    Musil, J.; Sklenka, J.; Čerstvý, R.

    2016-05-01

    This article reports on the protection of the brittle Zrsbnd Sisbnd O film against cracking in bending by the highly elastic top film (over-layer). In experiments the Zrsbnd Sisbnd O films with different elemental composition and structure were used. Both the brittle and highly elastic films were prepared by magnetron sputtering using a dual magnetron. The brittle film easily cracks in bending. On the other hand, the highly elastic film exhibits enhanced resistance to cracking in bending. Main characteristic parameters of both the brittle and highly elastic films are given. Special attention is devoted to the effect of the structure (crystalline, amorphous) of both the brittle and highly elastic top film on the resistance of cracking of the brittle film. It was found that (1) both the X-ray amorphous and crystalline brittle films easily crack in bending, (2) the highly elastic film can have either X-ray amorphous or crystalline structure and (3) both the X-ray amorphous and crystalline, highly elastic top films perfectly protect the brittle films against cracking in bending. The structure, mechanical properties and optical transparency of the brittle and highly elastic sputtered Zrsbnd Sisbnd O films are described in detail. At the end of this article, the principle of the low-temperature formation of the highly elastic films is also explained.

  8. Benchmarking numerical models of brittle thrust wedges

    NARCIS (Netherlands)

    Buiter, Susanne J H; Schreurs, Guido; Albertz, Markus; Gerya, Taras V.; Kaus, Boris; Landry, Walter; le Pourhiet, Laetitia; Mishin, Yury; Egholm, David L.; Cooke, Michele; Maillot, Bertrand; Thieulot, Cedric|info:eu-repo/dai/nl/270177493; Crook, Tony; May, Dave; Souloumiac, Pauline; Beaumont, Christopher

    2016-01-01

    We report quantitative results from three brittle thrust wedge experiments, comparing numerical results directly with each other and with corresponding analogue results. We first test whether the participating codes reproduce predictions from analytical critical taper theory. Eleven codes pass the

  9. Strength evaluation code STEP for brittle materials

    Energy Technology Data Exchange (ETDEWEB)

    Ishihara, Masahiro [Japan Atomic Energy Research Inst., Oarai, Ibaraki (Japan). Oarai Research Establishment; Futakawa, Masatoshi

    1997-12-01

    In a structural design using brittle materials such as graphite and/or ceramics it is necessary to evaluate the strength of component under complex stress condition. The strength of ceramic materials is said to be influenced by the stress distribution. However, in the structural design criteria simplified stress limits had been adopted without taking account of the strength change with the stress distribution. It is, therefore, important to evaluate the strength of component on the basis of the fracture model for brittle material. Consequently, the strength evaluation program, STEP, on a brittle fracture of ceramic materials based on the competing risk theory had been developed. Two different brittle fracture modes, a surface layer fracture mode dominated by surface flaws and an internal fracture mode by internal flaws, are treated in the STEP code in order to evaluate the strength of brittle fracture. The STEP code uses stress calculation results including complex shape of structures analyzed by the generalized FEM stress analysis code, ABAQUS, so as to be possible to evaluate the strength of brittle fracture for the structures having complicate shapes. This code is, therefore, useful to evaluate the structural integrity of arbitrary shapes of components such as core graphite components in the HTTR, heat exchanger components made of ceramics materials etc. This paper describes the basic equations applying to the STEP code, code system with a combination of the STEP and the ABAQUS codes and the result of the verification analysis. (author)

  10. Fracturing and brittleness index analyses of shales

    Science.gov (United States)

    Barnhoorn, Auke; Primarini, Mutia; Houben, Maartje

    2016-04-01

    The formation of a fracture network in rocks has a crucial control on the flow behaviour of fluids. In addition, an existing network of fractures , influences the propagation of new fractures during e.g. hydraulic fracturing or during a seismic event. Understanding of the type and characteristics of the fracture network that will be formed during e.g. hydraulic fracturing is thus crucial to better predict the outcome of a hydraulic fracturing job. For this, knowledge of the rock properties is crucial. The brittleness index is often used as a rock property that can be used to predict the fracturing behaviour of a rock for e.g. hydraulic fracturing of shales. Various terminologies of the brittleness index (BI1, BI2 and BI3) exist based on mineralogy, elastic constants and stress-strain behaviour (Jin et al., 2014, Jarvie et al., 2007 and Holt et al., 2011). A maximum brittleness index of 1 predicts very good and efficient fracturing behaviour while a minimum brittleness index of 0 predicts a much more ductile shale behaviour. Here, we have performed systematic petrophysical, acoustic and geomechanical analyses on a set of shale samples from Whitby (UK) and we have determined the three different brittleness indices on each sample by performing all the analyses on each of the samples. We show that each of the three brittleness indices are very different for the same sample and as such it can be concluded that the brittleness index is not a good predictor of the fracturing behaviour of shales. The brittleness index based on the acoustic data (BI1) all lie around values of 0.5, while the brittleness index based on the stress strain data (BI2) give an average brittleness index around 0.75, whereas the mineralogy brittleness index (BI3) predict values below 0.2. This shows that by using different estimates of the brittleness index different decisions can be made for hydraulic fracturing. If we would rely on the mineralogy (BI3), the Whitby mudstone is not a suitable

  11. High Speed Dynamics in Brittle Materials

    Science.gov (United States)

    Hiermaier, Stefan

    2015-06-01

    Brittle Materials under High Speed and Shock loading provide a continuous challenge in experimental physics, analysis and numerical modelling, and consequently for engineering design. The dependence of damage and fracture processes on material-inherent length and time scales, the influence of defects, rate-dependent material properties and inertia effects on different scales make their understanding a true multi-scale problem. In addition, it is not uncommon that materials show a transition from ductile to brittle behavior when the loading rate is increased. A particular case is spallation, a brittle tensile failure induced by the interaction of stress waves leading to a sudden change from compressive to tensile loading states that can be invoked in various materials. This contribution highlights typical phenomena occurring when brittle materials are exposed to high loading rates in applications such as blast and impact on protective structures, or meteorite impact on geological materials. A short review on experimental methods that are used for dynamic characterization of brittle materials will be given. A close interaction of experimental analysis and numerical simulation has turned out to be very helpful in analyzing experimental results. For this purpose, adequate numerical methods are required. Cohesive zone models are one possible method for the analysis of brittle failure as long as some degree of tension is present. Their recent successful application for meso-mechanical simulations of concrete in Hopkinson-type spallation tests provides new insight into the dynamic failure process. Failure under compressive loading is a particular challenge for numerical simulations as it involves crushing of material which in turn influences stress states in other parts of a structure. On a continuum scale, it can be modeled using more or less complex plasticity models combined with failure surfaces, as will be demonstrated for ceramics. Models which take microstructural

  12. Numerical experiments in revisited brittle fracture

    DEFF Research Database (Denmark)

    Bourdin, Blaise; Francfort, Gilles A; Marigo, Jean-Jacques

    2000-01-01

    The numerical implementation of the model of brittle fracture developed in~ Francfort and Marigo (1998) is presented. Various computational methods based on variational approximations of the original functional are proposed. They are tested on several antiplanar and planar examples that are beyon...... the reach of the classical computational tools of fracture mechanics.......The numerical implementation of the model of brittle fracture developed in~ Francfort and Marigo (1998) is presented. Various computational methods based on variational approximations of the original functional are proposed. They are tested on several antiplanar and planar examples that are beyond...

  13. Benchmarking numerical models of brittle thrust wedges

    NARCIS (Netherlands)

    Buiter, Susanne J H; Schreurs, Guido; Albertz, Markus; Gerya, Taras V.; Kaus, Boris; Landry, Walter; le Pourhiet, Laetitia; Mishin, Yury; Egholm, David L.; Cooke, Michele; Maillot, Bertrand; Thieulot, Cedric; Crook, Tony; May, Dave; Souloumiac, Pauline; Beaumont, Christopher

    2016-01-01

    We report quantitative results from three brittle thrust wedge experiments, comparing numerical results directly with each other and with corresponding analogue results. We first test whether the participating codes reproduce predictions from analytical critical taper theory. Eleven codes pass the s

  14. Aspects of brittle failure assessment for RPV

    Energy Technology Data Exchange (ETDEWEB)

    Zecha, H.; Hermann, T.; Hienstorfer, W. [TUeV SUeD Energietechnik GmbH Baden-Wuerttemberg, Filderstadt (Germany); Schuler, X. [Materialpruefungsanstalt, Univ. Stuttgart (Germany)

    2009-07-01

    This paper describes the process of pressurized thermal shock analysis (PTS) and brittle failure assessment for the reactor pressure vessel (RPV) of the nuclear power plants NECKAR I/II. The thermo-hydraulic part of the assessment provides the boundary conditions for the fracture mechanics analysis. In addition to the one dimensional thermo-hydraulic simulations CFD, analyses were carried out for selected transients. An extensive evaluation of material properties is necessary to provide the input data for a reliable fracture mechanics assessment. For the core weld and the flange weld it has shown that brittle crack initiation can be precluded for all considered load cases. For the cold and hot leg nozzle detailed linear-elastic and elasticplastic Finite Element Analyses (FEA) are performed to verify the integrity of the RPV. (orig.)

  15. Towards an Approach to Overcome Software Brittleness

    Energy Technology Data Exchange (ETDEWEB)

    OSBOURN,GORDON C.

    1999-11-01

    Development of bug-free, high-surety, complex software is quite difficult using current tools. The brittle nature of the programming constructs in popular languages such as C/C++ is one root cause. Brittle commands force the designer to rigidly specify the minutiae of tasks, e.g. using ''for(index=0;index>total;index++)'', rather than specifying the goals or intent of the tasks, e.g. ''ensure that all relevant data elements have been examined''. Specification of task minutiae makes code hard to comprehend, which in turn encourages design errors/limitations and makes future modifications quite difficult. This report describes an LDRD project to seed the development of a surety computer language, for stand-alone computing environments, to be implemented using the swarm intelligence of autonomous agents. The long term vision of this project was to develop a language with the following surety capabilities: (1) Reliability -- Autonomous agents can appropriate y decide when to act and when a task is complete, provide a natural means for avoiding brittle task specifications, and can overcome many hardware glitches. (2) Safety, security -- Watchdog safety and security agents can monitor other agents to prevent unauthorized or dangerous actions. (3) An immune system -- The small chunks of agent code can have an encryption scheme to enable detection and elimination of unauthorized and corrupted agents. This report describes the progress achieved during this small 9 month project and describes lessons learned.

  16. Fabrication of brittle materials -- current status

    Energy Technology Data Exchange (ETDEWEB)

    Scattergood, R.O.

    1988-12-01

    The research initiatives in the area of precision fabrication will be continued in the upcoming year. Three students, T. Bifano (PhD), P. Blake (PhD) and E. Smith (MS), finished their research programs in the last year. Sections 13 and 14 will summarize the essential results from the work of the Materials Engineering students Blake and Smith. Further details will be presented in forthcoming publications that are now in preparation. The results from Bifano`s thesis have been published in adequate detail and need not be summarized further. Three new students, S. Blackley (MS), H. Paul (PhD), and S. Smith (PhD) have joined the program and will continue the research efforts in precision fabrication. The programs for these students will be outlined in Sections 15 and 16. Because of the success of the earlier work in establishing new process models and experimental techniques for the study of diamond turning and diamond grinding, the new programs will, in part, build upon the earlier work. This is especially true for investigations concerned with brittle materials. The basic understanding of material response of nominally brittle materials during machining or grinding operations remains as a challenge. The precision fabrication of brittle materials will continue as an area of emphasis for the Precision Engineering Center.

  17. Metallurgical viewpoints on the brittleness of beryllium

    Energy Technology Data Exchange (ETDEWEB)

    Lagerberg, G.

    1960-02-15

    At present the development and use of beryllium metal for structural applications is severely hampered by its brittleness. Reasons for this lack of ductility are reviewed in discussing the deformation behaviour of beryllium in relation to other hexagonal metals. The ease of fracturing in beryllium is assumed to be a consequence of a limited number of deformation modes in combination with high deformation resistance. Models for the nucleation of fracture are suggested. The relation of ductility to elastic constants as well as to grain size, texture and alloying additions is discussed.

  18. Brittle and semi-brittle behaviours of a carbonate rock: influence of water and temperature

    Science.gov (United States)

    Nicolas, A.; Fortin, J.; Regnet, J. B.; Dimanov, A.; Guéguen, Y.

    2016-07-01

    Inelastic deformation can either occur with dilatancy or compaction, implying differences in porosity changes, failure and petrophysical properties. In this study, the roles of water as a pore fluid, and of temperature, on the deformation and failure of a micritic limestone (white Tavel limestone, porosity 14.7 per cent) were investigated under triaxial stresses. For each sample, a hydrostatic load was applied up to the desired confining pressure (from 0 up to 85 MPa) at either room temperature or at 70 °C. Two pore fluid conditions were investigated at room temperature: dry and water saturated. The samples were deformed up to failure at a constant strain rate of ˜10-5 s-1. The experiments were coupled with ultrasonic wave velocity surveys to monitor crack densities. The linear trend between the axial crack density and the relative volumetric strain beyond the onset of dilatancy suggests that cracks propagate at constant aspect ratio. The decrease of ultrasonic wave velocities beyond the onset of inelastic compaction in the semi-brittle regime indicates the ongoing interplay of shear-enhanced compaction and crack development. Water has a weakening effect on the onset of dilatancy in the brittle regime, but no measurable influence on the peak strength. Temperature lowers the confining pressure at which the brittle-semi-brittle transition is observed but does not change the stress states at the onset of inelastic compaction and at the post-yield onset of dilatancy.

  19. Research on basic characteristics of complex system brittleness

    Institute of Scientific and Technical Information of China (English)

    JIN Hong-zhang; GUO Jian; WEI Qi; LIN De-ming; LI Qi

    2004-01-01

    Tbe goal of this paper is to research one new characteristic of complex system. Brittleness, which is one new characteritic of complex system, is presented in this paper. The linguistic and qualitative descriptions of complex system are also given in this paper.Otherwise, the qualitative description of complex system is presented at first. On the basis of analyzing the existing brittleness problems, linguistic description and mathematic description of brittleness are given as well. Three kinds of phenomena to judge brittleness of complex system are also given, based on catastrophe theory. Basic characteristics of brittleness are given on the basis of its mathematic description. Two critical point sets are defined by using catastrophe theory. The definition of brittleness and its related theory can serve the control of complex system, and provide theoretical basis for the design and control of complex system.

  20. Brittle Destruction of Carbon Based Materials

    Science.gov (United States)

    Koza, Y.; Amouroux, S.; Bazylev, B. N.; Berthe, E.; Kuehnlein, W.; Linke, J.; Penkalla, H. J.; Singheiser, L.

    Erosion mechanisms for different carbon based materials (graphite, carbon fiber composites (CFCs), Si-doped CFC) have been studied under brittle destruction under intense transient thermal loads (ELMs, plasma disruptions, VDEs) with respect to material erosion in different particle emission regimes, characterization of emitted particles, and behavior of preheated samples. Furthermore, the experimental data were compared with 3-D numerical simulation on the onset of brittle destruction. From a morphological point of view, the resulting erosion patterns on the test samples and ejected particles differ significantly for the three materials. The isotropic graphite shows a homogeneous erosion profile with flat craters, while the CFC forms no crater and only preferential erosion in localized spots in the PAN fiber area while the pitch fiber strands remain almost undamaged. The particles originating from graphite samples which have been collected on TEM grids are composed of nano sized amorphous carbon. CFCs have been the source for sub Î 1/4 m sized agglomerated fragments of crystalline carbon or silicon particles with âe 1/4 50 nm diameter. Preheating of the test samples to 500 or 800°C results in a remarkable increase of the erosion depth and weight loss compared to the samples loaded at room temperature and identical heat fluxes. In particular, melting phenomena in the Si-doped CFC materials became essential at elevated temperatures.

  1. Brittle dynamic damage due to earthquake rupture

    Science.gov (United States)

    Bhat, Harsha; Thomas, Marion

    2016-04-01

    The micromechanical damage mechanics formulated by Ashby and Sammis, 1990, and generalized by Deshpande and Evans 2008 has been extended to allow for a more generalized stress state and to incorporate an experimentally motivated new crack growth (damage evolution) law that is valid over a wide range of loading rates. This law is sensitive to both the crack tip stress field and its time derivative. Incorporating this feature produces additional strain-rate sensitivity in the constitutive response. The model is also experimentally verified by predicting the failure strength of Dionysus-Pentelicon marble over wide range of strain rates. We then implement this constitutive response to understand the role of dynamic brittle off-fault damage on earthquake ruptures. We show that off-fault damage plays an important role in asymmetry of rupture propagation and is a source of high-frequency ground motion in the near source region.

  2. Fluid-driven fractures in brittle hydrogels

    Science.gov (United States)

    O'Keeffe, Niall; Linden, Paul

    2016-11-01

    Hydraulic fracturing is a process in which fluid is injected deep underground at high pressures that can overcome the strength of the surrounding matrix. This results in an increase of surface area connected to the well bore and thus allows extraction of natural gas previously trapped in a rock formation. We experimentally study the physical mechanisms of these fluid-driven fractures in low permeability reservoirs where the leak-off of fracturing fluid is considered negligible. This is done through the use of small scale experiments on transparent and brittle, heavily cross-linked hydrogels. The propagation of these fractures can be split into two distinct regimes depending on whether the dominant energy dissipation mechanism is viscous flow or material toughness. We will analyse crack growth rates, crack thickness and tip shape in both regimes. Moreover, PIV techniques allow us to explore the flow dynamics within the fracture, which is crucial in predicting transport of proppants designed to prevent localisation of cracks.

  3. Benchmarking numerical models of brittle thrust wedges

    Science.gov (United States)

    Buiter, Susanne J. H.; Schreurs, Guido; Albertz, Markus; Gerya, Taras V.; Kaus, Boris; Landry, Walter; le Pourhiet, Laetitia; Mishin, Yury; Egholm, David L.; Cooke, Michele; Maillot, Bertrand; Thieulot, Cedric; Crook, Tony; May, Dave; Souloumiac, Pauline; Beaumont, Christopher

    2016-11-01

    We report quantitative results from three brittle thrust wedge experiments, comparing numerical results directly with each other and with corresponding analogue results. We first test whether the participating codes reproduce predictions from analytical critical taper theory. Eleven codes pass the stable wedge test, showing negligible internal deformation and maintaining the initial surface slope upon horizontal translation over a frictional interface. Eight codes participated in the unstable wedge test that examines the evolution of a wedge by thrust formation from a subcritical state to the critical taper geometry. The critical taper is recovered, but the models show two deformation modes characterised by either mainly forward dipping thrusts or a series of thrust pop-ups. We speculate that the two modes are caused by differences in effective basal boundary friction related to different algorithms for modelling boundary friction. The third experiment examines stacking of forward thrusts that are translated upward along a backward thrust. The results of the seven codes that run this experiment show variability in deformation style, number of thrusts, thrust dip angles and surface slope. Overall, our experiments show that numerical models run with different numerical techniques can successfully simulate laboratory brittle thrust wedge models at the cm-scale. In more detail, however, we find that it is challenging to reproduce sandbox-type setups numerically, because of frictional boundary conditions and velocity discontinuities. We recommend that future numerical-analogue comparisons use simple boundary conditions and that the numerical Earth Science community defines a plasticity test to resolve the variability in model shear zones.

  4. Semi-brittle flow of granitoid fault rocks in experiments

    NARCIS (Netherlands)

    Pec, Matej; Stünitz, Holger; Heilbronner, Renée; Drury, Martyn

    2016-01-01

    Field studies and seismic data show that semi-brittle flow of fault rocks probably is the dominant deformation mechanism at the base of the seismogenic zone at the so-called frictional-viscous transition. To understand the physical and chemical processes accommodating semi-brittle flow, we have perf

  5. Effect of substrate roughness on the contact damage of thin brittle films on brittle substrates

    Energy Technology Data Exchange (ETDEWEB)

    Weidner, Mirko [School of Materials Science and Engineering, University of New South Wales NSW 2052, Sydney (Australia); Institute for Materials Science, Technische Universitaet Darmstadt, Petersenstrasse 23, 64287 Darmstadt (Germany); Borrero-Lopez, Oscar [School of Materials Science and Engineering, University of New South Wales NSW 2052, Sydney (Australia); Departamento de Ingenieria Mecanica, Energetica y de los Materiales, Universidad de Extremadura, 06071, Badajoz (Spain); Hoffman, Mark, E-mail: mark.hoffman@unsw.edu.a [School of Materials Science and Engineering, University of New South Wales NSW 2052, Sydney (Australia); Bendavid, Avi; Martin, Phil J. [CSIRO Materials Science and Engineering, P.O. Box 218, Lindfield NSW 2070 (Australia)

    2010-07-01

    The effect of substrate and surface roughness on the contact fracture of diamond-like carbon coatings on brittle soda-lime glass substrates has been investigated. The average surface roughness (R{sub a}) of the examined samples ranged from 15 nm to 571 nm. Contact damage was simulated by means of spherical nanoindentation, and fracture was subsequently assessed by focused ion beam microscopy. It was found that, in the absence of sub-surface damage in the substrate, fracture occurs in the coating in the form of radial, and ring/cone cracks during loading, and lateral cracks during unloading. Increasing the surface roughness results in a decrease in the critical load for crack initiation during loading, and in the suppression of fracture modes during unloading from high loads. When sub-surface damage (lateral cracks) is present in the substrate, severe spalling takes place during loading, causing a large discontinuity in the load-displacement curve. The results have implications concerning the design of damage-tolerant coated systems consisting of a brittle film on a brittle substrate.

  6. Brittle and compaction creep in porous sandstone

    Science.gov (United States)

    Heap, Michael; Brantut, Nicolas; Baud, Patrick; Meredith, Philip

    2015-04-01

    Strain localisation in the Earth's crust occurs at all scales, from the fracture of grains at the microscale to crustal-scale faulting. Over the last fifty years, laboratory rock deformation studies have exposed the variety of deformation mechanisms and failure modes of rock. Broadly speaking, rock failure can be described as either dilatant (brittle) or compactive. While dilatant failure in porous sandstones is manifest as shear fracturing, their failure in the compactant regime can be characterised by either distributed cataclastic flow or the formation of localised compaction bands. To better understand the time-dependency of strain localisation (shear fracturing and compaction band growth), we performed triaxial deformation experiments on water-saturated Bleurswiller sandstone (porosity = 24%) under a constant stress (creep) in the dilatant and compactive regimes, with particular focus on time-dependent compaction band formation in the compactive regime. Our experiments show that inelastic strain accumulates at a constant stress in the brittle and compactive regimes leading to the development of shear fractures and compaction bands, respectively. While creep in the dilatant regime is characterised by an increase in porosity and, ultimately, an acceleration in axial strain to shear failure (as observed in previous studies), compaction creep is characterised by a reduction in porosity and a gradual deceleration in axial strain. The overall deceleration in axial strain, AE activity, and porosity change during creep compaction is punctuated by excursions interpreted as the formation of compaction bands. The growth rate of compaction bands formed during creep is lower as the applied differential stress, and hence background creep strain rate, is decreased, although the inelastic strain required for a compaction band remains constant over strain rates spanning several orders of magnitude. We find that, despite the large differences in strain rate and growth rate

  7. CONSERVATION LAWS IN FINITE MICROCRACKING BRITTLE SOLIDS

    Institute of Scientific and Technical Information of China (English)

    Wang Defa; Chen Yiheng; Fukui Takuo

    2005-01-01

    This paper addresses the conservation laws in finite brittle solids with microcracks.The discussion is limited to the 2-D cases. First, after considering the combination of the PseudoTraction Method and the indirect Boundary Element Method, a versatile method for solving multicrack interacting problems in finite plane solids is proposed, by which the fracture parameters (SIF and path-independent integrals) can be calculated with a desirable accuracy. Second, with the aid of the method proposed, the roles the conservation laws play in the fracture analysis for finite microcracking solids are studied. It is concluded that the conservation laws do play important roles in not only the fracture analysis but also the analysis of damage and stability for the finite microcracking system. Finally, the physical interpretation of the M-integral is discussed further.An explicit relation between the M-integral and the crack face area, I.e., M = GS, has been discovered using the analytical method, which can shed some light on the Damage Mechanics issues from a different perspective.

  8. Modeling failure in brittle porous ceramics

    Science.gov (United States)

    Keles, Ozgur

    Brittle porous materials (BPMs) are used for battery, fuel cell, catalyst, membrane, filter, bone graft, and pharmacy applications due to the multi-functionality of their underlying porosity. However, in spite of its technological benefits the effects of porosity on BPM fracture strength and Weibull statistics are not fully understood--limiting a wider use. In this context, classical fracture mechanics was combined with two-dimensional finite element simulations not only to account for pore-pore stress interactions, but also to numerically quantify the relationship between the local pore volume fraction and fracture statistics. Simulations show that even the microstructures with the same porosity level and size of pores differ substantially in fracture strength. The maximum reliability of BPMs was shown to be limited by the underlying pore--pore interactions. Fracture strength of BMPs decreases at a faster rate under biaxial loading than under uniaxial loading. Three different types of deviation from classic Weibull behavior are identified: P-type corresponding to a positive lower tail deviation, N-type corresponding to a negative lower tail deviation, and S-type corresponding to both positive upper and lower tail deviations. Pore-pore interactions result in either P-type or N-type deviation in the limit of low porosity, whereas S-type behavior occurs when clusters of low and high fracture strengths coexist in a fracture data.

  9. Theory of friction based on brittle fracture

    Science.gov (United States)

    Byerlee, J.D.

    1967-01-01

    A theory of friction is presented that may be more applicable to geologic materials than the classic Bowden and Tabor theory. In the model, surfaces touch at the peaks of asperities and sliding occurs when the asperities fail by brittle fracture. The coefficient of friction, ??, was calculated from the strength of asperities of certain ideal shapes; for cone-shaped asperities, ?? is about 0.1 and for wedge-shaped asperities, ?? is about 0.15. For actual situations which seem close to the ideal model, observed ?? was found to be very close to 0.1, even for materials such as quartz and calcite with widely differing strengths. If surface forces are present, the theory predicts that ?? should decrease with load and that it should be higher in a vacuum than in air. In the presence of a fluid film between sliding surfaces, ?? should depend on the area of the surfaces in contact. Both effects are observed. The character of wear particles produced during sliding and the way in which ?? depends on normal load, roughness, and environment lend further support to the model of friction presented here. ?? 1967 The American Institute of Physics.

  10. Benchmarking analogue models of brittle thrust wedges

    Science.gov (United States)

    Schreurs, Guido; Buiter, Susanne J. H.; Boutelier, Jennifer; Burberry, Caroline; Callot, Jean-Paul; Cavozzi, Cristian; Cerca, Mariano; Chen, Jian-Hong; Cristallini, Ernesto; Cruden, Alexander R.; Cruz, Leonardo; Daniel, Jean-Marc; Da Poian, Gabriela; Garcia, Victor H.; Gomes, Caroline J. S.; Grall, Céline; Guillot, Yannick; Guzmán, Cecilia; Hidayah, Triyani Nur; Hilley, George; Klinkmüller, Matthias; Koyi, Hemin A.; Lu, Chia-Yu; Maillot, Bertrand; Meriaux, Catherine; Nilfouroushan, Faramarz; Pan, Chang-Chih; Pillot, Daniel; Portillo, Rodrigo; Rosenau, Matthias; Schellart, Wouter P.; Schlische, Roy W.; Take, Andy; Vendeville, Bruno; Vergnaud, Marine; Vettori, Matteo; Wang, Shih-Hsien; Withjack, Martha O.; Yagupsky, Daniel; Yamada, Yasuhiro

    2016-11-01

    We performed a quantitative comparison of brittle thrust wedge experiments to evaluate the variability among analogue models and to appraise the reproducibility and limits of model interpretation. Fifteen analogue modeling laboratories participated in this benchmark initiative. Each laboratory received a shipment of the same type of quartz and corundum sand and all laboratories adhered to a stringent model building protocol and used the same type of foil to cover base and sidewalls of the sandbox. Sieve structure, sifting height, filling rate, and details on off-scraping of excess sand followed prescribed procedures. Our analogue benchmark shows that even for simple plane-strain experiments with prescribed stringent model construction techniques, quantitative model results show variability, most notably for surface slope, thrust spacing and number of forward and backthrusts. One of the sources of the variability in model results is related to slight variations in how sand is deposited in the sandbox. Small changes in sifting height, sifting rate, and scraping will result in slightly heterogeneous material bulk densities, which will affect the mechanical properties of the sand, and will result in lateral and vertical differences in peak and boundary friction angles, as well as cohesion values once the model is constructed. Initial variations in basal friction are inferred to play the most important role in causing model variability. Our comparison shows that the human factor plays a decisive role, and even when one modeler repeats the same experiment, quantitative model results still show variability. Our observations highlight the limits of up-scaling quantitative analogue model results to nature or for making comparisons with numerical models. The frictional behavior of sand is highly sensitive to small variations in material state or experimental set-up, and hence, it will remain difficult to scale quantitative results such as number of thrusts, thrust spacing

  11. Scattering mechanical performances for brittle bulk metallic glasses

    Directory of Open Access Journals (Sweden)

    J. W. Qiao

    2014-11-01

    Full Text Available Scattering mechanical performances of brittle La- and Mg-based BMGs are found in the present study. Upon dynamic loading, there exist largely scattered fracture strengths even if the strain rates are under the same order, and the BMG systems are the same. The negative strain rate dependence for La- and Mg-based BMGs is obtained, i.e., a decreased fracture strength is dominating from quasi-static to dynamic compression. At cryogenic temperatures, distinguishingly low fracture strengths are available for these two brittle BMGs, and decreased tolerance to accommodate strains makes BMGs more and more brittle. It is concluded that the scattering mechanical performances of brittle BMGs should be carefully evaluated before actual applications.

  12. Brittleness Generation Mechanism and Failure Model of High Strength Lightweight Aggregate Concrete

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The brittleness generation mechanism of high strength lightweight aggregate concrete(HSLWAC) was presented, and it was indicated that lightweight aggregate was the vulnerable spot,initiating brittleness. Based on the analysis of the brittleness failure by the load-deflection curve, the brittleness presented by HSLWAC was more prominent compared with ordinary lightweight aggregate concrete of the same strength grade. The model of brittleness failure was also established.

  13. Brittle and semibrittle creep in a low porosity carbonate rock

    Science.gov (United States)

    Nicolas, Aurélien; Fortin, Jérôme; Regnet, Jean-Baptiste; Dimanov, Alexandre; Guéguen, Yves

    2016-04-01

    The mechanical behavior of limestones at room temperature is brittle at low confining pressure and becomes semi-brittle with the increase of the confining pressure. The brittle behavior is characterized by a macroscopic dilatancy due to crack propagation, leading to a stress drop when cracks coalesce at failure. The semi-brittle behavior is characterized by diffuse deformation due to intra-crystalline plasticity (dislocation movements and twinning) and microcracking. The aim of this work is to examine the influence of pore fluid and time on the mechanical behavior. Constant strain rate triaxial deformation experiments and stress-stepping creep experiments were performed on white Tavel limestone (porosity 14.7%). Elastic wave velocity evolutions were recorded during each experiment and inverted to crack densities. Constant strain rate triaxial experiments were performed for confining pressure in the range of 5-90 MPa. For Pc≤55 MPa our results show that the behavior is brittle. In this regime, water-saturation decreases the differential stress at the onset of crack propagation and enhances macroscopic dilatancy. For Pc≥70 MPa, the behavior is semi-brittle. Inelastic compaction is due to intra-crystalline plasticity and micro-cracking. However, in this regime, our results show that water-saturation has no clear effect at the onset of inelastic compaction. Stress stepping creep experiments were performed in a range of confining pressures crossing the brittle-ductile transition. In the brittle regime, the time-dependent axial deformation is coupled with dilatancy and a decrease of elastic wave velocities, which is characteristic of crack propagation and/or nucleation. In the semi-brittle regime, the first steps are inelastic compactant because of plastic pore collapse. But, following stress steps are dilatant because of crack nucleation and/or propagation. However, our results show that the axial strain rate is always controlled by plastic phenomena, until the last

  14. Fracture Energy-Based Brittleness Index Development and Brittleness Quantification by Pre-peak Strength Parameters in Rock Uniaxial Compression

    Science.gov (United States)

    Munoz, H.; Taheri, A.; Chanda, E. K.

    2016-12-01

    Brittleness is a fundamental mechanical rock property critical to many civil engineering works, mining development projects and mineral exploration operations. However, rock brittleness is a concept yet to be investigated as there is not any unique criterion available, widely accepted by rock engineering community able to describe rock brittleness quantitatively. In this study, new brittleness indices were developed based on fracture strain energy quantities obtained from the complete stress-strain characteristics of rocks. In doing so, different rocks having unconfined compressive strength values ranging from 7 to 215 MPa were examined in a series of quasi-static uniaxial compression tests after properly implementing lateral-strain control in a closed-loop system to apply axial load to rock specimen. This testing method was essential to capture post-peak regime of the rocks since a combination of class I-II or class II behaviour featured post-peak stress-strain behaviour. Further analysis on the post-peak strain localisation, stress-strain characteristics and the fracture pattern causing class I-II and class II behaviour were undertaken by analysing the development of field of strains in the rocks via three-dimensional digital image correlation. Analysis of the results demonstrated that pre-peak stress-strain brittleness indices proposed solely based on pre-peak stress-strain behaviour do not show any correlation with any of pre-peak rock mechanical parameters. On the other hand, the proposed brittleness indices based on pre-peak and post-peak stress-strain relations were found to competently describe an unambiguous brittleness scale against rock deformation and strength parameters such as the elastic modulus, the crack damage stress and the peak stress relevant to represent failure process.

  15. The nature of temper brittleness of high-chromium ferrite

    Energy Technology Data Exchange (ETDEWEB)

    Sarrak, V.I.; Suvorova, S.O.; Golovin, I.S.; Mishin, V.M.; Kislyuk, I.V. [Central Scientific-Research Institute for Ferrous Metallurgy, Moscow (Russian Federation)

    1995-03-01

    The reasons for development of {open_quotes}475{degrees}C brittleness{close_quotes} of high-chromium ferritic steels are considered from the standpoint of fracture mechanics. It is shown that the general rise in the curve of temperature-dependent local flow stress has the decisive influence on the position of the ductile-to-brittle transformation temperature and the increase in it as the result of a hold at temperatures of development of brittleness. The established effect is related to the change in the parameters determining dislocation mobility, that is, the activation energy of dislocation movement in high-chromium ferrite and the resistance to microplastic deformation, both caused by processes of separation into layers of high-chromium ferrite and decomposition of the interstitial solid solution.

  16. Brittle and ductile friction and the physics of tectonic tremor

    Science.gov (United States)

    Daub, E.G.; Shelly, D.R.; Guyer, R.A.; Johnson, P.A.

    2011-01-01

    Observations of nonvolcanic tremor provide a unique window into the mechanisms of deformation and failure in the lower crust. At increasing depths, rock deformation gradually transitions from brittle, where earthquakes occur, to ductile, with tremor occurring in the transitional region. The physics of deformation in the transition region remain poorly constrained, limiting our basic understanding of tremor and its relation to earthquakes. We combine field and laboratory observations with a physical friction model comprised of brittle and ductile components, and use the model to provide constraints on the friction and stress state in the lower crust. A phase diagram is constructed that characterizes under what conditions all faulting behaviors occur, including earthquakes, tremor, silent transient slip, and steady sliding. Our results show that tremor occurs over a range of ductile and brittle frictional strengths, and advances our understanding of the physical conditions at which tremor and earthquakes take place. Copyright ?? 2011 by the American Geophysical Union.

  17. Cuttability Assessment of Selected Rocks Through Different Brittleness Values

    Science.gov (United States)

    Dursun, Arif Emre; Gokay, M. Kemal

    2016-04-01

    Prediction of cuttability is a critical issue for successful execution of tunnel or mining excavation projects. Rock cuttability is also used to determine specific energy, which is defined as the work done by the cutting force to excavate a unit volume of yield. Specific energy is a meaningful inverse measure of cutting efficiency, since it simply states how much energy must be expended to excavate a unit volume of rock. Brittleness is a fundamental rock property and applied in drilling and rock excavation. Brittleness is one of the most crucial rock features for rock excavation. For this reason, determination of relations between cuttability and brittleness will help rock engineers. This study aims to estimate the specific energy from different brittleness values of rocks by means of simple and multiple regression analyses. In this study, rock cutting, rock property, and brittleness index tests were carried out on 24 different rock samples with different strength values, including marble, travertine, and tuff, collected from sites around Konya Province, Turkey. Four previously used brittleness concepts were evaluated in this study, denoted as B 1 (ratio of compressive to tensile strength), B 2 (ratio of the difference between compressive and tensile strength to the sum of compressive and tensile strength), B 3 (area under the stress-strain line in relation to compressive and tensile strength), and B 9 = S 20, the percentage of fines (University of Science and Technology (NTNU) model as well as B 9p (B 9 as predicted from uniaxial compressive, Brazilian tensile, and point load strengths of rocks using multiple regression analysis). The results suggest that the proposed simple regression-based prediction models including B 3, B 9, and B 9p outperform the other models including B 1 and B 2 and can be used for more accurate and reliable estimation of specific energy.

  18. A Weibull characterization for tensile fracture of multicomponent brittle fibers

    Science.gov (United States)

    Barrows, R. G.

    1977-01-01

    Necessary to the development and understanding of brittle fiber reinforced composites is a means to statistically describe fiber strength and strain-to-failure behavior. A statistical characterization for multicomponent brittle fibers is presented. The method, which is an extension of usual Weibull distribution procedures, statistically considers the components making up a fiber (e.g., substrate, sheath, and surface) as separate entities and taken together as in a fiber. Tensile data for silicon carbide fiber and for an experimental carbon-boron alloy fiber are evaluated in terms of the proposed multicomponent Weibull characterization.

  19. Damage and dissipation mechanisms in the dynamic fracture of brittle materials: Velocity driven transition from nominally brittle to quasi-brittle

    Directory of Open Access Journals (Sweden)

    Bonamy D.

    2010-06-01

    Full Text Available We present the results of recent dynamic fracture experiments [Scheibert et al., Phys. Rev. Lett. 104 (2010 045501] on polymethylmethacrylate, the archetype of nominally brittle materials, over a wide range of crack velocities. By combining velocity measurements and finite element calculations of the stress intensity factor, we determine the dynamic fracture energy as a function of crack speed. We show that the slope of this curve exhibits a discontinuity at a well-defined critical velocity, below the one associated to the onset of micro-branching instability. This transition is associated with the appearance of conics patterns on the fracture surfaces. In many amorphous materials, these are the signature of damage spreading through the nucleation, growth and coalescence of micro-cracks. We end with a discussion of the relationship between the energetic and fractographic measurements. All these results suggest that dynamic fracture at low velocities in amorphous materials is controlled by the brittle/quasi-brittle transition studied here.

  20. Fracture in brittle matrix particle composites with varying particle content

    NARCIS (Netherlands)

    Vliet, M.R.A. van; Mier, J.G.M. van

    1999-01-01

    Fracture in brittle matrix particle and fibre composites can be conveniently modelled by means of lattice models where the particle and/or fibre structure is incorporated directly in the model. The particles, fibres and matrix, as well as the interfacial transition zone are assumed to behave as a

  1. Finite element modelling of fibre-reinforced brittle materials

    NARCIS (Netherlands)

    Kullaa, J.

    1997-01-01

    The tensile constitutive behaviour of fibre-reinforced brittle materials can be extended to two or three dimensions by using the finite element method with crack models. The three approaches in this study include the smeared and discrete crack concepts and a multi-surface plasticity model. The tensi

  2. Scaling properties of crack branching and brittle fragmentation

    Directory of Open Access Journals (Sweden)

    Uvarov S.

    2011-01-01

    Full Text Available The present study is focused on the correlation of scaling properties of crack branching and brittle fragmentation with damage accumulation and a change in the fracture mechanism. The experimental results obtained from the glass fragmentation tests indicate that the size distribution of fragments has a fractal character and is described by a power law.

  3. Fracture mechanics applied to the machining of brittle materials

    Energy Technology Data Exchange (ETDEWEB)

    Hiatt, G.D.; Strenkowski, J.S.

    1988-12-01

    Research has begun on incorporating fracture mechanics into a model of the orthogonal cutting of brittle materials. Residual stresses are calculated for the machined material by a combination of Eulerian and Lagrangian finite element models and then used in the calculation of stress intensity factors by the Green`s Function Method.

  4. Fracture in brittle matrix particle composites with varying particle content

    NARCIS (Netherlands)

    Vliet, M.R.A. van; Mier, J.G.M. van

    1999-01-01

    Fracture in brittle matrix particle and fibre composites can be conveniently modelled by means of lattice models where the particle and/or fibre structure is incorporated directly in the model. The particles, fibres and matrix, as well as the interfacial transition zone are assumed to behave as a co

  5. Continuous intraperitoneal insulin infusion in patients with 'brittle' diabetes

    DEFF Research Database (Denmark)

    DeVries, J H; Eskes, S A; Snoek, Frank J

    2002-01-01

    AIMS: To evaluate the effects of continuous intraperitoneal insulin infusion (CIPII) using implantable pumps on glycaemic control and duration of hospital stay in poorly controlled 'brittle' Dutch diabetes patients, and to assess their current quality of life. METHODS: Thirty-three patients were...

  6. Analytical model of micromachining of brittle materials with sharp particles

    NARCIS (Netherlands)

    Moktadir, Z.; Wensink, H.; Kraft, M.

    2005-01-01

    We present an analytical model for the powder blasting of brittle materials with sharp particles. We developed a continuum equation, which describes the surface evolution during the powder blasting, into which we introduced surface energetics as the major relaxation mechanism. The experimental and t

  7. Brittle, flowing structures focused on subtle crustal heterogeneities

    Science.gov (United States)

    Soden, A. M.; Shipton, Z. K.; Lunn, R. J.; Pytharouli, S.; Kirkpatrick, J. D.

    2011-12-01

    Fundamental to the development of groundwater flow models are geological models that accurately account for the spatial distribution and geometrical attributes of fracture systems in three dimensions, at both seismic and sub-seismic resolution. Accurate characterization of fracture populations in crystalline rock is of particular importance, as these are the principal targets for nuclear waste repositories and enhanced geothermal systems. Fracture models are populated using average properties from site specific outcrop and borehole data, geophysical imaging and empirical scaling relationships such as the decrease of fracture density with distance from a fault surface However, host rock heterogeneity is likely to be of equal importance in influencing fracture attributes. Our study focuses on brittle structures associated with a regional NE-SW ductile shear zone in NE Brazil. Detailed field mapping shows two phases of brittle structure overprinting a ductile shear zone: 1) a brittle fault zone, which is largely "sealed" to flow, 2) a later set of open fractures. The earliest brittle fault is 1.4 - 2.6m wide zone of chaotic breccia bound by two sub-vertical fault walls. Extremely indurated breccias branching from the fault core have an orientation consistent with sinistral motion on the fault. The breccia is composed of centimeter to meter scale clasts in a fine-grained matrix. The host rock is intensely fractured by centimeter-scale fractures up to 60 m away from the fault. Veining is predominantly concentrated within 15 meters of the fault wall, and joints beyond this are unmineralised. The latest brittle deformation is represented by meter-scale open discrete fractures and fracture zones, up to 80 meters from the main fault. The fractures are unmineralised suggesting formation at relatively shallow depths. Fracture zones vary from decimeters long en echelon fractures to intensely fractured zones where the host rock is completely fragmented. This final phase of

  8. Brittleness index and seismic rock physics model for anisotropic tight-oil sandstone reservoirs

    Institute of Scientific and Technical Information of China (English)

    Huang Xin-Rui; Huang Jian-Ping; Li Zhen-Chun; Yang Qin-Yong; Sun Qi-Xing; Cui Wei

    2015-01-01

    Brittleness analysis becomes important when looking for sweet spots in tight-oil sandstone reservoirs. Hence, appropriate indices are required as accurate brittleness evaluation criteria. We construct a seismic rock physics model for tight-oil sandstone reservoirs with vertical fractures. Because of the complexities in lithology and pore structure and the anisotropic characteristics of tight-oil sandstone reservoirs, the proposed model is based on the solid components, pore connectivity, pore type, and fractures to better describe the sandstone reservoir microstructure. Using the model, we analyze the brittleness sensitivity of the elastic parameters in an anisotropic medium and establish a new brittleness index. We show the applicability of the proposed brittleness index for tight-oil sandstone reservoirs by considering the brittleness sensitivity, the rock physics response characteristics, and cross-plots. Compared with conventional brittleness indexes, the new brittleness index has high brittleness sensitivity and it is the highest in oil-bearing brittle zones with relatively high porosity. The results also suggest that the new brittleness index is much more sensitive to elastic properties variations, and thus can presumably better predict the brittleness characteristics of sweet spots in tight-oil sandstone reservoirs.

  9. Microstructural Modeling of Brittle Materials for Enhanced Performance and Reliability.

    Energy Technology Data Exchange (ETDEWEB)

    Teague, Melissa Christine [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Teague, Melissa Christine [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Rodgers, Theron [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Rodgers, Theron [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Grutzik, Scott Joseph [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Grutzik, Scott Joseph [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Meserole, Stephen [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Meserole, Stephen [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2017-08-01

    Brittle failure is often influenced by difficult to measure and variable microstructure-scale stresses. Recent advances in photoluminescence spectroscopy (PLS), including improved confocal laser measurement and rapid spectroscopic data collection have established the potential to map stresses with microscale spatial resolution (%3C2 microns). Advanced PLS was successfully used to investigate both residual and externally applied stresses in polycrystalline alumina at the microstructure scale. The measured average stresses matched those estimated from beam theory to within one standard deviation, validating the technique. Modeling the residual stresses within the microstructure produced general agreement in comparison with the experimentally measured results. Microstructure scale modeling is primed to take advantage of advanced PLS to enable its refinement and validation, eventually enabling microstructure modeling to become a predictive tool for brittle materials.

  10. Brittle to ductile transition in densified silica glass.

    Science.gov (United States)

    Yuan, Fenglin; Huang, Liping

    2014-05-22

    Current understanding of the brittleness of glass is limited by our poor understanding and control over the microscopic structure. In this study, we used a pressure quenching route to tune the structure of silica glass in a controllable manner, and observed a systematic increase in ductility in samples quenched under increasingly higher pressure. The brittle to ductile transition in densified silica glass can be attributed to the critical role of 5-fold Si coordination defects (bonded to 5 O neighbors) in facilitating shear deformation and in dissipating energy by converting back to the 4-fold coordination state during deformation. As an archetypal glass former and one of the most abundant minerals in the Earth's crest, a fundamental understanding of the microscopic structure underpinning the ductility of silica glass will not only pave the way toward rational design of strong glasses, but also advance our knowledge of the geological processes in the Earth's interior.

  11. Plasto-damage modelling for semi-brittle geomaterials

    OpenAIRE

    Alizadeh Ali; Gatmiri Behrouz

    2016-01-01

    This paper presents an elastoplastic damage model for constitutive modelling of semi-brittle geomaterials showing two irreversible mechanisms. On one hand, the model deals with the plastic behaviour of a porous medium by a new variant of Barcelona Basic Model. On the other hand, the model combines the micromechanical definition of damage and phenomenological concepts in the framework of Continuum Damage Mechanics (CDM) for damage modelling. A second order tensorial damage variable is adopted ...

  12. Rate-dependent deformation of rocks in the brittle regime

    Science.gov (United States)

    Baud, P.; Brantut, N.; Heap, M. J.; Meredith, P. G.

    2013-12-01

    Rate-dependent brittle deformation of rocks, a phenomenon relevant for long-term interseismic phases of deformation, is poorly understood quantitatively. Rate-dependence can arise from chemically-activated, subcritical crack growth, which is known to occur in the presence of aqueous fluids. Here we attempt to establish quantitative links between this small scale process and its macroscopic manifestations. We performed a series of brittle deformation experiments in porous sandstones, in creep (constant stress) and constant strain rate conditions, in order to investigate the relationship between their short- and long-term mechanical behaviors. Elastic wave velocities measurements indicate that the amount of microcracking follows the amount of inelastic strain in a trend which does not depend upon the timescale involved. The comparison of stress-strain curves between constant strain rate and creep tests allows us to define a stress difference between the two, which can be viewed as a difference in energy release rate. We empirically show that the creep strain rates are proportional to an exponential function of this stress difference. We then establish a general method to estimate empirical micromechanical functions relating the applied stresses to mode I stress intensity factors at microcrack tips, and we determine the relationship between creep strain rates and stress intensity factors in our sandstone creep experiments. We finally provide an estimate of the sub-critical crack growth law parameters, and find that they match -within the experimental errors and approximations of the method- the typical values observed in independent single crack tests. Our approach provides a comprehensive and unifying explanation for the origin and the macroscopic manifestation of time-dependent brittle deformation in brittle rocks.

  13. A Geometrically Nonlinear Phase Field Theory of Brittle Fracture

    Science.gov (United States)

    2014-10-01

    tension. Int J Fract Mech 4:257–266 Voyiadjis G, Mozaffari N (2013) Nonlocal damage model using the phase field method: theory and applications. Int J... model of fracture. Computer simula- tions enable descriptions of fracture in brittle solids under complex loading conditions and for nonlinear and...Simple models based on the notion of theo- retical strength (Gilman1960;Clayton 2009, 2010) can provide insight into directionality of fracture

  14. Interpreting finite element results for brittle materials in endodontic restorations.

    Science.gov (United States)

    Pérez-González, Antonio; Iserte-Vilar, José L; González-Lluch, Carmen

    2011-06-02

    Finite element simulation has been used in last years for analysing the biomechanical performance of post-core restorations in endodontics, but results of these simulations have been interpreted in most of the works using von Mises stress criterion. However, the validity of this failure criterion for brittle materials, which are present in these restorations, is questionable. The objective of the paper is to analyse how finite element results for brittle materials of endodontic restorations should be interpreted to obtain correct conclusions about the possible failure in the restoration. Different failure criteria (Von Mises, Rankine, Coulomb-Mohr, Modified Mohr and Christensen) and material strength data (diametral tensile strength and flexural strength) were considered in the study. Three finite element models (FEM) were developed to simulate an endodontic restoration and two typical material tests: diametral tensile test and flexural test. Results showed that the Christensen criterion predicts similar results as the Von Mises criterion for ductile components, while it predicts similar results to all other criteria for brittle components. The different criteria predict different failure points for the diametral tensile test, all of them under multi-axial stress states. All criteria except Von Mises predict failure for flexural test at the same point of the specimen, with this point under uniaxial tensile stress. From the results it is concluded that the Christensen criterion is recommended for FEM result interpretation in endodontic restorations and that the flexural test is recommended to estimate tensile strength instead of the diametral tensile test.

  15. THEORETICAL STATISTICAL SOLUTION AND NUMERICAL SIMULATION OF HETEROGENEOUS BRITTLE MATERIALS

    Institute of Scientific and Technical Information of China (English)

    陈永强; 姚振汉; 郑小平

    2003-01-01

    The analytical stress-strain relation with heterogeneous parameters is derived for the heterogeneous brittle materials under a uniaxial extensional load,in which the distributions of the elastic modulus and the failure strength are assumed to be statistically independent.This theoretical solution gives an approximate estimate of the equivalent stress-strain relations for 3-D heterogeneous materials.In one-dimensional cases it may provide comparatively accurate results.The theoretical solution can help us to explain how the heterogeneity influences the mechanical behaviors.Further,a numerical approach is developed to model the non-linear behavior of three-dimensional heterogeneous brittle materials.The lattice approach and statistical techniques are applied to simulate the initial heterogeneity of heterogeneous materials.The load increment in each loading stage is adaptively determined so that the better approximation of the failure process can be realized.When the maximum tensile principal strain exceeds the failure strain,the elements are considered to be broken,which can be carried out by replacing its Young's modulus with a very small value.A 3-D heterogeneous brittle material specimen is simulated during a full failure process.The numerical results are in good agreement with the analytical solutions and experimental data.

  16. The effect of shockwave profile shape on dynamic brittle failure

    Directory of Open Access Journals (Sweden)

    Gray G.T.

    2012-08-01

    Full Text Available The role of shock wave loading profile is investigated for the failure processes in a brittle material. The dynamic damage response of ductile metals has been demonstrated to be critically dependent on the shockwave profile and the stress-state of the shock. Changing from a square to triangular (Taylor profile with an identical peak compressive stress has been reported to increase the “spall strength” by over a factor of two and suppress damage mechanisms. The spall strength of tungsten heavy alloy (WHA based on plate impact square-wave loading has been extensively reported in the literature. Here a triangular wave loading profile is achieved with a composite flyer plate of graded density in contrast to the square-wave loading. Counter to the strong dependence in wave profile in ductile metals, for WHA, both square and triangle wave profiles the failure is by brittle cleavage fracture with additional energy dissipation through crack branching in the more brittle tungsten particles, largely indistinguishable between wave profiles. The time for crack nucleation is negligible compared to the duration of the experiment and the crack propagation rate is limited to the sound speed as defined by the shock velocity.

  17. Nanoscale Morphology in Tensile Fracture of a Brittle Amorphous Ribbon

    Institute of Scientific and Technical Information of China (English)

    Xifeng LI; Kaifeng ZHANG; Guofeng WANG

    2008-01-01

    The paper reports on the observation of nanoscale morphology on the tensile fracture surface of a brittle amorphous Fe-based ribbon. The formation of nanoscale damage cavity structure is a main characteristic morphology on the fracture surfaces. Approaching the ribbon boundary, these damage cavities assemble and form the nanoscale periodic corrugations, which are neither Wallner lines nor crack front waves. The periodic corrugations result from the interactions between the reflected elastic waves by the boundaries of amorphous ribbon and the stress fields of the crack tip.

  18. Nonlocal effects on dynamic damage accumulation in brittle solids

    Energy Technology Data Exchange (ETDEWEB)

    Chen, E.P.

    1995-12-01

    This paper presents a nonlocal analysis of the dynamic damage accumulation processes in brittle solids. A nonlocal formulation of a microcrack based continuum damage model is developed and implemented into a transient dynamic finite element computer code. The code is then applied to the study of the damage accumulation process in a concrete plate with a central hole and subjected to the action of a step tensile pulse applied at opposite edges of the plate. Several finite element discretizations are used to examine the mesh size effect. Comparisons between calculated results based on local and nonlocal formulations are made and nonlocal effects are discussed.

  19. What controls the strength and brittleness of shale rocks?

    Science.gov (United States)

    Rybacki, Erik; Reinicke, Andreas; Meier, Tobias; Makasi, Masline; Dresen, Georg

    2014-05-01

    With respect to the productivity of gas shales, in petroleum science the mechanical behavior of shales is often classified into rock types of high and low 'brittleness', sometimes also referred to as 'fraccability'. The term brittleness is not well defined and different definitions exist, associated with elastic properties (Poisson's ratio, Young's modulus), with strength parameters (compressive and tensile strength), frictional properties (cohesion, friction coefficient), hardness (indentation), or with the strain or energy budget (ratio of reversible to the total strain or energy, respectively). Shales containing a high amount of clay and organic matter are usually considered as less brittle. Similarly, the strength of shales is usually assumed to be low if they contain a high fraction of weak phases. We performed mechanical tests on a series of shales with different mineralogical compositions, varying porosity, and low to high maturity. Using cylindrical samples, we determined the uniaxial and triaxial compressive strength, static Young's modulus, the tensile strength, and Mode I fracture toughness. The results show that in general the uniaxial compressive strength (UCS) linearly increases with increasing Young's modulus (E) and both parameters increase with decreasing porosity. However, the strength and elastic modulus is not uniquely correlated with the mineral content. For shales with a relatively low quartz and high carbonate content, UCS and E increase with increasing quartz content, whereas for shales with a relatively low amount for carbonates, but high quartz content, both parameters increase with decreasing fraction of the weak phases (clays, kerogen). In contrast, the average tensile strength of all shale-types appears to increase with increasing quartz fraction. The internal friction coefficient of all investigated shales decreases with increasing pressure and may approach rather high values (up to ≡ 1). Therefore, the mechanical strength and

  20. Estimation Criteria for Rock Brittleness Based on Energy Analysis During the Rupturing Process

    Science.gov (United States)

    Ai, Chi; Zhang, Jun; Li, Yu-wei; Zeng, Jia; Yang, Xin-liang; Wang, Ji-gang

    2016-12-01

    Brittleness is one of the most important mechanical properties of rock: it plays a significant role in evaluating the risk of rock bursts and in analysis of borehole-wall stability during shale gas development. Brittleness is also a critical parameter in the design of hydraulic fracturing. However, there is still no widely accepted definition of the concept of brittleness in rock mechanics. Although many criteria have been proposed to characterize rock brittleness, their applicability and reliability have yet to be verified. In this paper, the brittleness of rock under compression is defined as the ability of a rock to accumulate elastic energy during the pre-peak stage and to self-sustain fracture propagation in the post-peak stage. This ability is related to three types of energy: fracture energy, post-peak released energy and pre-peak dissipation energy. New brittleness evaluation indices B 1 and B 2 are proposed based on the stress-strain curve from the viewpoint of energy. The new indices can describe the entire transition of rock from absolute plasticity to absolute brittleness. In addition, the brittle characteristics reflected by other brittleness indices can be described, and the calculation results of B 1 and B 2 are continuous and monotonic. Triaxial compression tests on different types of rock were carried out under different confining pressures. Based on B 1 and B 2, the brittleness of different rocks shows different trends with rising confining pressure. The brittleness of red sandstone decreases with increasing confining pressure, whereas for black shale it initially increases and then decreases in a certain range of confining pressure. Granite displays a constant increasing trend. The brittleness anisotropy of black shale is discussed. The smaller the angle between the loading direction and the bedding plane, the greater the brittleness. The calculation B 1 and B 2 requires experimental data, and the values of these two indices represent only

  1. Challenges in the Japan Beyond-Brittle Project (JBBP) for EGS development beyond the brittle-ductile transition

    Science.gov (United States)

    Asanuma, H.; Muraoka, H.; Tsuchiya, N.; Ito, H.

    2013-12-01

    Development using Engineered Geothermal System (EGS) technologies is considered to be the best solution to the problems of the localized distribution of geothermal resources. However, it is considered that a number of problems, including low water recovery rate, difficulty in design of the reservoir, and induced earthquake, would appear in Japanese EGS. These problems in the development of EGS reservoirs cannot be readily solved in Japan because they are intrinsically related to the physical characteristics and tectonic setting of the brittle rock mass. Therefore, we have initiated the Japan Beyond-Brittle Project (JBBP), which will take a multidisciplinary scientific approach, including geology, geochemistry, geophysics, water-rock interactions, rock mechanics, seismology, drilling technology, well-logging technology, and reservoir engineering. The science and technology required for the creation and control of geothermal reservoirs in superheated rocks in the ductile zone is at the frontier of modern research in most of the related disciplines. Solutions to the associated problems will not easily be found without international collaboration among researchers and engineers. For this reason, in March, 2013 we held a five-day ICDP-supported workshop in Japan to review and discuss various scientific and technological issues related to the JBBP. Throughout the discussions at the workshop on characteristics of the beyond-brittle rock mass and creation and control of EGS reservoirs in the ductile zone, it has concluded that there are two end-member reservoir models that should be considered (Fig. 1). The JBBP reservoir type-1 would be created near the top of the brittle-ductile transition (BDT) and connected to pre-existing hydrothermal systems, which would increase productivity and provide sustainability. The JBBP reservoir type-2 would be hydraulically or thermally created beyond the BDT, where pre-existing fractures are less permeable, and would be hydraulically

  2. Fracture and ductile vs. brittle behavior -- Theory, modeling and experiment

    Energy Technology Data Exchange (ETDEWEB)

    Beltz, G.E. [ed.] [Univ. of California, Santa Barbara, CA (United States); Selinger, R.L.B. [ed.] [Catholic Univ., Washington, DC (United States); Kim, K.S. [ed.] [Brown Univ., Providence, RI (United States); Marder, M.P. [ed.] [Univ. of Texas, Austin, TX (United States)

    1999-08-01

    The symposium brought together the many communities that investigate the fundamentals of fracture, with special emphasis on the ductile/brittle transition across a broad spectrum of material classes, fracture at interfaces, and modelling fracture over various length scales. Theoretical techniques discussed ranged from first-principles electronic structure theory to atomistic simulation to mesoscale and continuum theories, along with studies of fractals and scaling in fracture. Experimental and theoretical talks were interspersed throughout all sessions, rather than being segregated. The contributions to this volume generally follow the topical outline upon which the symposium was organized. The first part, dealing with ductile vs. brittle behavior in metals, concerns itself with investigations of high-strength steel, magnesium alloys, ordered intermetallics, and Fe-Cr-Al alloys. The development of analytical methods based on micromechanical models, such as dislocation mechanics and cohesive/contact zone models, are covered in a follow-up section. Nonmetals, including silicon, are considered in Parts 3 and 4. Fractals, chaos, and scaling theories are taken up in Part 5, with a special emphasis on fracture in heterogeneous solids. Modelling based on large populations of dislocations has substantially progressed during the past three years; hence, a section devoted to crystal plasticity and mesoscale dislocation modelling appears next. Finally, the technologically significant area of interfacial fracture, with applications to composites and intergranular fracture, is taken up in Part 7. Separate abstracts were prepared for most of the papers in this book.

  3. Brittle Creep of Tournemire Shale: Orientation, Temperature and Pressure Dependences

    Science.gov (United States)

    Geng, Zhi; Bonnelye, Audrey; Dick, Pierre; David, Christian; Chen, Mian; Schubnel, Alexandre

    2017-04-01

    Time and temperature dependent rock deformation has both scientific and socio-economic implications for natural hazards, the oil and gas industry and nuclear waste disposal. During the past decades, most studies on brittle creep have focused on igneous rocks and porous sedimentary rocks. To our knowledge, only few studies have been carried out on the brittle creep behavior of shale. Here, we conducted a series of creep experiments on shale specimens coming from the French Institute for Nuclear Safety (IRSN) underground research laboratory located in Tournemire, France. Conventional tri-axial experiments were carried under two different temperatures (26˚ C, 75˚ C) and confining pressures (10 MPa, 80 MPa), for three orientations (σ1 along, perpendicular and 45˚ to bedding). Following the methodology developed by Heap et al. [2008], differential stress was first increased to ˜ 60% of the short term peak strength (10-7/s, Bonnelye et al. 2016), and then in steps of 5 to 10 MPa every 24 hours until brittle failure was achieved. In these long-term experiments (approximately 10 days), stress and strains were recorded continuously, while ultrasonic acoustic velocities were recorded every 1˜15 minutes, enabling us to monitor the evolution of elastic wave speed anisotropy. Temporal evolution of anisotropy was illustrated by inverting acoustic velocities to Thomsen parameters. Finally, samples were investigated post-mortem using scanning electron microscopy. Our results seem to contradict our traditional understanding of loading rate dependent brittle failure. Indeed, the brittle creep failure stress of our Tournemire shale samples was systematically observed ˜50% higher than its short-term peak strength, with larger final axial strain accumulated. At higher temperatures, the creep failure strength of our samples was slightly reduced and deformation was characterized with faster 'steady-state' creep axial strain rates at each steps, and larger final axial strain

  4. Brittle fracture in casing pipes; Sproeda brott i mantelroer

    Energy Technology Data Exchange (ETDEWEB)

    Nilsson, Stefan; Thoernblom, Kristian; Saellberg, Sven-Erik; Bergstroem, Gunnar [Swedish National Testing and Research Inst., Goeteborg (Sweden)

    2005-05-01

    Rapid Crack Propagation (RCP) has been observed in the casing pipe of large diameter district heating pipes on several occasions. An RCP crack is driven by hoop stresses in the casing pipe wall. It is a problem during installation work in cold weather. The casing pipe material is more brittle in low temperatures, and a temperature decrease will cause a hoop stress build-up since the thermal contraction of the casing pipe is constrained by the steel pipe and the PUR foam. RCP fracture has been documented at temperatures around -18 deg C but has likely, at some instances, occurred already at few degrees below 0 deg C. Three different polyethylene materials were evaluated with respect to the risk for brittle fracture of the casing pipe. One unimodal material of PE80 quality which have been used in casing to a large extent previously, one modern unimodal PE80 material which is used today and, finally, a bimodal PE80 material of a quality which currently is the dominant choice among pipe producers. Modern materials are in general much more resistant to brittle fracture, since it is an important design property for the raw material producers. Tests were done on casing of both large (up to 630 mm in diameter) and small (160 mm) dimension. A handling test was made where the pipes were cooled down and worked on with power tools in a manner similar to actual field work. An RCP fracture occurred at -25 deg C during cutting with angle grinder on a pipe with a diameter of 500 mm on the modern unimodal PE80 material. The same material also fractured during impact testing according to EN 253 at -20 deg C on both small and large diameter pipes. The bimodal PE80 resin passed both tests without fracture. A series of impact tests were done on pipes with diameter 160 mm with the purpose of determining critical temperatures and temperature stress levels with respect to brittle fracture. The results show that the bimodal material is so resistant that there is no real risk for RCP in

  5. Determination of the Influence of c-BN+h-BN Coating Structure on Brittleness

    Institute of Scientific and Technical Information of China (English)

    Maciej Kupczyk; Adam Lejwoda; Przemyslaw Cieszkowski; Przemyslaw Libuda

    2004-01-01

    In the article is presented the brittleness study of boron nitride coatings deposited on cutting edges made of cemented carbides by the pulse-plasma method (PPD). Influences of the structure (density, pores, microcracks) of coating material on the brittleness and on selected technological parameters of boron nitride formation by PPD method particularly taking into account discharge voltage on brittleness are shown. Differences between values of both a1(300) and a1(500)coefficients characterized susceptibility to coatings cracking of investigated coating manufactured using different values of discharge voltage were defined. Results of an investigations have been confirmed usefulness of Palmqvist's method for measurement of coating susceptibility to brittle cracking.

  6. Research progress on ultra-precision machining technologies for soft-brittle crystal materials

    Science.gov (United States)

    Gao, Hang; Wang, Xu; Guo, Dongming; Chen, Yuchuan

    2016-12-01

    Soft-brittle crystal materials are widely used in many fields, especially optics and microelectronics. However, these materials are difficult to machine through traditional machining methods because of their brittle, soft, and anisotropic nature. In this article, the characteristics and machining difficulties of soft-brittle and crystals are presented. Moreover, the latest research progress of novel machining technologies and their applications for softbrittle crystals are introduced by using some representative materials (e.g., potassium dihydrogen phosphate (KDP), cadmium zinc telluride (CZT)) as examples. This article reviews the research progress of soft-brittle crystals processing.

  7. Determination of the Influence of c-BN+h-BN Coating Structure on Brittleness

    Institute of Scientific and Technical Information of China (English)

    MaciejKupczyk; AdamLejwoda; PrzemyslawCieszkowski; PrzemyslawLibuda

    2004-01-01

    In the article is presented the brittleness study of boron nitride coatings deposited on cutting edges made of cemented carbides by the pulse-plasma method (PPD). Influences of the structure (density, pores, microcracks) of coating material on the brittleness and on selected technological parameters of boron nitride formation by PPD method particularly taking into account discharge voltage on brittleness are shown. Differences between values of both a1(300) and a1(500)coefficients characterized susceptibility to coatings cracking of investigated coating manufactured using different values of discharge voltage were defined. Results of an investigations have been confirmed usefulness of Palmqyist's method for measurement of coating susceptibility to brittle cracking.

  8. Dynamic brittle material response based on a continuum damage model

    Energy Technology Data Exchange (ETDEWEB)

    Chen, E.P.

    1994-12-31

    The response of brittle materials to dynamic loads was studied in this investigation based on a continuum damage model. Damage mechanism was selected to be interaction and growth of subscale cracks. Briefly, the cracks are activated by bulk tension and the density of activated cracks are described by a Weibull statistical distribution. The moduli of a cracked solid derived by Budiansky and O`Connell are then used to represent the global material degradation due to subscale cracking. This continuum damage model was originally developed to study rock fragmentation and was modified in the present study to improve on the post-limit structural response. The model was implemented into a transient dynamic explicit finite element code PRONTO 2D and then used for a numerical study involving the sudden stretching of a plate with a centrally located hole. Numerical results characterizing the dynamic responses of the material were presented. The effect of damage on dynamic material behavior was discussed.

  9. Plasto-damage modelling for semi-brittle geomaterials

    Directory of Open Access Journals (Sweden)

    Alizadeh Ali

    2016-01-01

    Full Text Available This paper presents an elastoplastic damage model for constitutive modelling of semi-brittle geomaterials showing two irreversible mechanisms. On one hand, the model deals with the plastic behaviour of a porous medium by a new variant of Barcelona Basic Model. On the other hand, the model combines the micromechanical definition of damage and phenomenological concepts in the framework of Continuum Damage Mechanics (CDM for damage modelling. A second order tensorial damage variable is adopted for the model. Damaged effective stress variables are employed for formulation of elastoplastic behaviour laws and the plastic yield surface is a damage dependent one. The model has been validated by comparing the numerical results with experimental results of argillites.

  10. Meso-scopic deformation in brittle granular materials

    Science.gov (United States)

    Neal, William D.; Appleby-Thomas, Gareth J.; Collins, Gareth S.

    2014-05-01

    Compaction is the process of removing void-space from a porous material. In brittle particulate systems, the majority of densification is caused by particle fracture. This preliminary study aimed to investigate the differences in fracture behaviour between quasi-statically and shock loaded glass-microsphere beds. Macro-scale quasi-static (20 μm s-1) and dynamic compaction curves were measured that show subtle qualitative differences in stress-density space. Samples were recovered from a quasi-static and dynamic experiment at a similar order of stress. Differences in fracture behaviour were observed that may explain the differences in crush curves. Results suggest that the primary total-fracture process occurs relatively instantaneously at low stresses in the quasi-static regime. The sphere fracture process is slow relative to the stress-wave therefore causing a different fracture pattern in the shock regime.

  11. New criterion of material resistance for brittle fracture

    Directory of Open Access Journals (Sweden)

    M. Maj

    2010-01-01

    Full Text Available Wide variety of cast material applications and efforts to find optimum fields for casting operation are the reasons why it is so important to collect as many data on the properties of materials as possible. The problem of primary importance is to know how these materials will behave under the normally and rapidly changing loads, in other words – to know their fatigue strength. This study gives a short characteristic of fatigue tests and compares various data collected during measurements of the low-cycle fatigue strength coefficient K with the values of constant KIc, representing fracture toughness. The results of the investigations described here have revealed some important correlations that exist between the total elongation A5 and the proposed brittleness criterion B, conventional stress K, and fracture toughness KIc. The development of measurements seems to be of great importance and opens the field for further studies on practical implementation of this method.

  12. On Failure in Polycrystalline and Amorphous Brittle Materials

    Science.gov (United States)

    Bourne, N. K.

    2009-12-01

    The performance of behaviour of brittle materials depends upon discrete deformation mechanisms operating during the loading process. The critical mechanisms determining the behaviour of armour ceramics have not been isolated using traditional ballistics. It has recently become possible to measure strength histories in materials under shock. The data gained for the failed strength of the armour are shown to relate directly to the penetration measured into tiles. Further the material can be loaded and recovered for post-mortem examination. Failure is by micro-fracture that is a function of the defects and then cracking activated by plasticity mechanisms within the grains and failure at grain boundaries in the amorphous intergranular phase. Thus it is the shock-induced plastic yielding of grains at the impact face that determines the later time penetration through the tile.

  13. Simulations of ductile flow in brittle material processing

    Energy Technology Data Exchange (ETDEWEB)

    Luh, M.H.; Strenkowski, J.S.

    1988-12-01

    Research is continuing on the effects of thermal properties of the cutting tool and workpiece on the overall temperature distribution. Using an Eulerian finite element model, diamond and steel tools cutting aluminum have been simulated at various, speeds, and depths of cut. The relative magnitude of the thermal conductivity of the tool and the workpiece is believed to be a primary factor in the resulting temperature distribution in the workpiece. This effect is demonstrated in the change of maximum surface temperatures for diamond on aluminum vs. steel on aluminum. As a preliminary step toward the study of ductile flow in brittle materials, the relative thermal conductivities of diamond on polycarbonate is simulated. In this case, the maximum temperature shifts from the rake face of the tool to the surface of the machined workpiece, thus promoting ductile flow in the workpiece surface.

  14. Modeling Strain Rate Effect for Heterogeneous Brittle Materials

    Institute of Scientific and Technical Information of China (English)

    MA Guowei; DONG Aiai; LI Jianchun

    2006-01-01

    Rocks are heterogeneous from the point of microstructure which is of significance to their dynamic failure behavior.Both the compressive and tensile strength of rock-like materials is regarded different from the static strength.The present study adopts smoothed particle hydrodynamics (SPH) which is a virtual particle based meshfree method to investigate strain rate effect for heterogeneous brittle materials.The SPH method is capable of simulating rock fracture,free of the mesh constraint of the traditional FEM and FDM models.A pressure dependent J-H constitutive model involving heterogeneity is employed in the numerical modeling.The results show the compressive strength increases with the increase of strain rate as well as the tensile strength,which is important to the engineering design.

  15. A proposal for an international brittle fracture acceptance criterion for nuclear material transport cask applications

    Energy Technology Data Exchange (ETDEWEB)

    Sorenson, K.B.; Salzbrenner, R.J.; Nickell, R.E.

    1989-01-01

    This paper presents a fundamental basis for a brittle fracture acceptance criterion, examine several existing criteria and propose examples for consideration as international brittle fracture acceptance criteria. The proposed criteria are intended to stimulate discussion in order to advance the development of a consensus approach. 8 refs., 1 fig., 1 tab.

  16. A combined analytical-experimental tensile test technique for brittle materials

    Science.gov (United States)

    Chu, M. L.; Scavuzzo, R. J.; Srivatsan, T. S.

    1992-01-01

    A semiconventional tensile test technique is developed for impact ices and other brittle materials. Accurate results have been obtained on ultimate strength and modulus of elasticity in a refrigerated ice test. It is noted that the technique can be used to determine the physical properties of impact ices accreted inside icing wind tunnels or other brittle materials.

  17. Microstructural features of intergranular brittle fracture and cold cracking in high strength aluminum alloys

    NARCIS (Netherlands)

    Lalpoor, M.; Eskin, D. G.; ten Brink, Gert; Katgerman, L.

    2010-01-01

    Intergranular brittle fracture has been mainly observed and reported in steel alloys and precipitation hardened At-alloys where intergranular precipitates cover a major fraction of the grain boundary area. 7xxx series aluminum alloys suffer from this problem in the as-cast condition when brittle

  18. SAFOD Brittle Microstructure and Mechanics Knowledge Base (BM2KB)

    Science.gov (United States)

    Babaie, Hassan A.; Broda Cindi, M.; Hadizadeh, Jafar; Kumar, Anuj

    2013-07-01

    Scientific drilling near Parkfield, California has established the San Andreas Fault Observatory at Depth (SAFOD), which provides the solid earth community with short range geophysical and fault zone material data. The BM2KB ontology was developed in order to formalize the knowledge about brittle microstructures in the fault rocks sampled from the SAFOD cores. A knowledge base, instantiated from this domain ontology, stores and presents the observed microstructural and analytical data with respect to implications for brittle deformation and mechanics of faulting. These data can be searched on the knowledge base‧s Web interface by selecting a set of terms (classes, properties) from different drop-down lists that are dynamically populated from the ontology. In addition to this general search, a query can also be conducted to view data contributed by a specific investigator. A search by sample is done using the EarthScope SAFOD Core Viewer that allows a user to locate samples on high resolution images of core sections belonging to different runs and holes. The class hierarchy of the BM2KB ontology was initially designed using the Unified Modeling Language (UML), which was used as a visual guide to develop the ontology in OWL applying the Protégé ontology editor. Various Semantic Web technologies such as the RDF, RDFS, and OWL ontology languages, SPARQL query language, and Pellet reasoning engine, were used to develop the ontology. An interactive Web application interface was developed through Jena, a java based framework, with AJAX technology, jsp pages, and java servlets, and deployed via an Apache tomcat server. The interface allows the registered user to submit data related to their research on a sample of the SAFOD core. The submitted data, after initial review by the knowledge base administrator, are added to the extensible knowledge base and become available in subsequent queries to all types of users. The interface facilitates inference capabilities in the

  19. Brittle-tough transitions during crack growth in toughened adhesives

    Science.gov (United States)

    Thoules, Michael

    2008-03-01

    The use of structural adhesives in automotive applications relies on an effective understanding of their performance under crash conditions. In particular, there is considerable potential for mechanics-based modeling of the interaction between an adhesive layer and the adherends, to replace current empirical approaches to design. Since energy dissipation during a crash, mediated by plastic deformation of the structure, is a primary consideration for automotive applications, traditional approaches of fracture mechanics are not appropriate. Cohesive-zone models that use two fracture parameters - cohesive strength and toughness - have been shown to provide a method for quantitative mechanics analysis. Combined numerical and experimental techniques have been developed to deduce the toughness and strength parameters of adhesive layers, allowing qualitative modeling of the performance of adhesive joints. These techniques have been used to study the failure of joints, formed from a toughened adhesive and sheet metal, over a wide range of loading rates. Two fracture modes are observed: quasi-static crack growth and dynamic crack growth. The quasi-static crack growth is associated with a toughened mode of failure; the dynamic crack growth is associated with a more brittle mode of failure. The results of the experiments and analyses indicate that the fracture parameters for quasi-static crack growth in this toughened system are essentially rate independent, and that quasi-static crack growth can occur even at the highest crack velocities. Effects of rate appear to be limited to the ease with which a transition to dynamic fracture could be triggered. This transition appears to be stochastic in nature, and it does not appear to be associated with the attainment of any critical value for crack velocity or loading rate. Fracture-mechanics models exist in the literature for brittle-ductile transitions in rate-dependent polymers, which rely on rate dependent values of toughness

  20. Aggregations of brittle stars can perform similar ecological roles as mussel reefs

    KAUST Repository

    Geraldi, NR

    2016-11-29

    Biogenic habitats, such as coral reefs, facilitate diverse communities. In aquatic systems, aggregations of mobile benthic species may play a similar ecological role to that of typically sessile biogenic habitats; however, this has rarely been considered. We quantified the abundance of sessile horse mussels Modiolus modiolus and aggregating brittle stars Ophiothrix fragilis and tested for correlations between the density of mussels (live and dead) and brittle stars each with (1) abundance, biomass, diversity, and assemblage structure of associated benthic macrofauna; and (2) percent organic matter of the sediment. We found that the abundance of live M. modiolus was positively associated with the abundance and biomass of macrofauna. The positive association between M. modiolus and macrofaunal abundance was further amplified with an increase in brittle stars and a decrease in dead mussel shells. Macrofaunal biomass was lower with a higher percentage of dead mussel shells, and macrofaunal diversity increased with greater abundances of live M. modiolus and brittle stars. Sediment organic matter was positively related to brittle star density, but not to the abundance of live or dead mussels. The positive relationship between brittle stars and sediment organic matter suggests that brittle stars could enhance rates of benthic- pelagic coupling. Given the importance of understanding the functional role of threatened habitats, it is essential that the underlying community patterns be understood through robust observational studies to then derive testable hypotheses to determine drivers. These findings provide novel insight into the ecological role of aggregations of mobile species, which is essential to prioritize conservation and restoration strategies.

  1. Comparison of ductile-to-brittle transition curve fitting approaches

    Energy Technology Data Exchange (ETDEWEB)

    Cao, L.W. [School of Materials Science and Engineering, Beihang University (BUAA), Beijing 100191 (China)] [Department of Mechanical Engineering, University of Bristol, Bristol BS8 1TR (United Kingdom); Wu, S.J., E-mail: wusj@buaa.edu.cn [School of Materials Science and Engineering, Beihang University (BUAA), Beijing 100191 (China); Flewitt, P.E.J. [Interface Analysis Centre, University of Bristol, Bristol BS2 8BS (United Kingdom)] [School of Physics, HH Wills Laboratory, University of Bristol, BS8 1TL (United Kingdom)

    2012-05-15

    Ductile-to-brittle transition (DBT) curve fitting approaches are compared over the transition temperature range for reactor pressure vessel steels with different kinds of data, including Charpy-V notch impact energy data and fracture toughness data. Three DBT curve fitting methods have been frequently used in the past, including the Burr S-Weibull and tanh distributions. In general there is greater scatter associated with test data obtained within the transition region. Therefore these methods give results with different accuracies, especially when fitting to small quantities of data. The comparison shows that the Burr distribution and tanh distribution can almost equally fit well distributed and large data sets extending across the test temperature range to include the upper and lower shelves. The S-Weibull distribution fit is poor for the lower shelf of the DBT curve. Overall for both large and small quantities of measured data the Burr distribution provides the best description. - Highlights: Black-Right-Pointing-Pointer Burr distribution offers a better fit than that of a S-Weibull and tanh fit. Black-Right-Pointing-Pointer Burr and tanh methods show similar fitting ability for a large data set. Black-Right-Pointing-Pointer Burr method can fit sparse data well distributed across the test temperature. Black-Right-Pointing-Pointer S-Weibull method cannot fit the lower shelf well and show poor fitting quality.

  2. A Maxwell elasto-brittle rheology for sea ice modelling

    Science.gov (United States)

    Dansereau, Véronique; Weiss, Jérôme; Saramito, Pierre; Lattes, Philippe

    2016-07-01

    A new rheological model is developed that builds on an elasto-brittle (EB) framework used for sea ice and rock mechanics, with the intent of representing both the small elastic deformations associated with fracturing processes and the larger deformations occurring along the faults/leads once the material is highly damaged and fragmented. A viscous-like relaxation term is added to the linear-elastic constitutive law together with an effective viscosity that evolves according to the local level of damage of the material, like its elastic modulus. The coupling between the level of damage and both mechanical parameters is such that within an undamaged ice cover the viscosity is infinitely large and deformations are strictly elastic, while along highly damaged zones the elastic modulus vanishes and most of the stress is dissipated through permanent deformations. A healing mechanism is also introduced, counterbalancing the effects of damaging over large timescales. In this new model, named Maxwell-EB after the Maxwell rheology, the irreversible and reversible deformations are solved for simultaneously; hence drift velocities are defined naturally. First idealized simulations without advection show that the model reproduces the main characteristics of sea ice mechanics and deformation: strain localization, anisotropy, intermittency and associated scaling laws.

  3. Numerical modeling of macroscale brittle rock crushing during impacts

    Energy Technology Data Exchange (ETDEWEB)

    Badr, Salah A.; Abdelhaffez, Gamal S. [King Abdulaziz Univ., Jeddah (Saudi Arabia)

    2014-02-01

    Several machines, such as crushers use the physical effect of compression to cause fragmentation 'crushing' of brittle rocks. As a consequence of the complex fragmentation process, crushers are still sized by empirical approaches. This paper present the results of a numerical study to understand some aspects of rock crushing phenomenon in terms of energy consumption. The study uses the discrete element approach of PFC2D code to simulate a stamp mill. The stamp mill has a simple crushing mechanism of a fixed kinetic energy delivered by a rigid ram impact. A single rock fragment crushing process dependent on the number of stamp mill ram blows is numerically examined. Both amount and type of energy generated by a ram blow are monitored besides the type of fractures generated. The model results indicate that the ram impact energy is mainly consumed in form of friction energy (up to 61 %) while strain energy stays at about 5 % of delivered energy. The energy consumed by crushing the rock represents only 32 % to 45 % of stamp mill energy and tends to decrease as the number of impacts increases. The rock fragmented matrix tends to convert into more friction energy with reduced number of new fractures as number of blows increase. The fragmentation caused by tensile is more often compared to those caused by shear, this behaviour increased with increasing number of ram blows. (orig.)

  4. Ductile streaks in precision grinding of hard and brittle materials

    Indian Academy of Sciences (India)

    V C Venkatesh; S Izman; S Sharif; T T Mon; M Konneh

    2003-10-01

    Ductile streaks produced during diamond grinding of hard and brittle materials have aided the subsequent process of polishing. Two novel techniques were used to study the formation of ductile mode streaks during diamond grinding (primary process) of germanium, silicon, and glass. In the first technique, aspheric surfaces were generated on Ge and Si at conventional speeds (5000 rpm). In the second technique, diamond grinding of plano surfaces on glass and Si surfaces using high speed (100,000 rpm) was carried out. Form accuracy, surface finish and ductile mode grinding streaks are discussed in this paper. It was found that resinoid diamond wheels gave more ductile streaks than metal-bonded wheels but better form accuracy was obtained with the latter. Ductile streaks were obtained more easily with pyrex rather than with BK 7 glass thus necessitating very little time for polishing. Ductile streaks appeared in abundance on germanium rather than silicon. Both the novel grinding techniques were used on CNC machining centres.

  5. Prediction of rock brittleness using nondestructive methods for hard rock tunneling

    Institute of Scientific and Technical Information of China (English)

    Rennie B. Kaunda; Brian Asbury

    2016-01-01

    The material and elastic properties of rocks are utilized for predicting and evaluating hard rock brit-tleness using artificial neural networks (ANN). Herein hard rock brittleness is defined using Yagiz’ method. A predictive model is developed using a comprehensive database compiled from 30 years’ worth of rock tests at the Earth Mechanics Institute (EMI), Colorado School of Mines. The model is sensitive to density, elastic properties, and P-and S-wave velocities. The results show that the model is a better predictor of rock brittleness than conventional destructive strength-test based models and mul-tiple regression techniques. While the findings have direct implications on intact rock, the methodology can be extrapolated to rock mass problems in both tunneling and underground mining where rock brittleness is an important control.

  6. Polymer Reinforced, Non-Brittle, Light-Weight Cryogenic Insulation for Reduced Life Cycle Costs Project

    Data.gov (United States)

    National Aeronautics and Space Administration — InnoSense LLC (ISL) proposes to fabricate a composite aerogel foam. This material is designed to be impact resistant, non-brittle, non-water-retaining and insulating...

  7. Prediction of rock brittleness using nondestructive methods for hard rock tunneling

    Directory of Open Access Journals (Sweden)

    Rennie B. Kaunda

    2016-08-01

    Full Text Available The material and elastic properties of rocks are utilized for predicting and evaluating hard rock brittleness using artificial neural networks (ANN. Herein hard rock brittleness is defined using Yagiz' method. A predictive model is developed using a comprehensive database compiled from 30 years' worth of rock tests at the Earth Mechanics Institute (EMI, Colorado School of Mines. The model is sensitive to density, elastic properties, and P- and S-wave velocities. The results show that the model is a better predictor of rock brittleness than conventional destructive strength-test based models and multiple regression techniques. While the findings have direct implications on intact rock, the methodology can be extrapolated to rock mass problems in both tunneling and underground mining where rock brittleness is an important control.

  8. Correlation between the electric and acoustic signals emitted during compression of brittle materials

    Directory of Open Access Journals (Sweden)

    Ermioni D. Pasiou

    2017-04-01

    Full Text Available An experimental protocol is described including a series of uni¬axial compression tests of three brittle materials (marble, mortar and glass. The Acoustic Emission (AE technique and the Pressure Stimulated Currents (PSC one are used since the recordings of both techniques are strongly related to the formation of cracking in brittle materials. In the present paper, the correlation of these techniques is investigated, which is finally proven to be very satisfactory.

  9. Development of a brittle fracture acceptance criterion for the International Atomic Energy Agency (IAEA)

    Energy Technology Data Exchange (ETDEWEB)

    Sorenson, K.B.; Salzbrenner, R. (Sandia National Labs., Albuquerque NM (United States)); Nickell, R.E.

    1993-01-01

    An effort has been undertaken to develop a brittle fracture acceptance criterion for structural components of nuclear material transportation casks. The need for such a criterion was twofold. First, new generation cask designs have proposed the use of ferritic steels and other materials to replace the austenitic stainless steel commonly used for structural components in transport casks. Unlike austenitic stainless steel which fails in a high-energy absorbing, ductile tearing mode, it is possible for these candidate materials to fail via brittle fracture when subjected to certain combinations of elevated loading rates and low temperatures. Second, there is no established brittle fracture criterion accepted by the regulatory community that covers a broad range of structural materials. Although the existing IAEA Safety Series no.37 addressed brittle fracture, its the guidance was dated and pertained only to ferritic steels. Consultant's Services Meetings held under the auspices of the IAEA have resulted in a recommended brittle fracture criterion. The brittle fracture criterion is based on linear elastic fracture mechanics, and is the result of a consensus of experts from six participating IAEA-member countries. The brittle fracture criterion allows three approaches to determine the fracture toughness of the structural material. The three approaches present the opportunity to balance material testing requirements and the conservatism of the material's fracture toughness which must be used to demonstrate resistance to brittle fracture. This work has resulted in a revised Appendix IX to Safety Series no.37 which will be released as an IAEA Technical Document within the coming year. (author).

  10. Development of a brittle fracture acceptance criterion for the International Atomic Energy Agency (IAEA)

    Energy Technology Data Exchange (ETDEWEB)

    Sorenson, Ken B.; Salzbrenner, Richard [Sandia National Labs., Albuquerque, NM (United States); Nickell, Robert E. [Applied Science and Technology, Inc., Poway, CA (United States)

    1992-01-01

    An effort has been undertaken to develop a brittle fracture acceptance criterion for structural components of nuclear material transportation casks. The need for such a criterion was twofold. First, new generation cask designs have proposed the use of ferritic steels and other materials to replace the austenitic stainless steel commonly used for structural components in transport casks. Unlike austenitic stainless steel which fails in a high-energy absorbing, ductile tearing mode, it is possible for these candidate materials to fail via brittle fracture when subjected to certain combinations of elevated loading rates and low temperatures. Second, there is no established brittle fracture criterion accepted by the regulatory community that covers a broad range of structural materials. Although the existing IAEA Safety Series {number sign}37 addressed brittle fracture, its the guidance was dated and pertained only to ferritic steels. Consultant's Services Meetings held under the auspices of the IAEA have resulted in a recommended brittle fracture criterion. The brittle fracture criterion is based on linear elastic fracture mechanics, and is the result of a consensus of experts from six participating IAEA-member countries. The brittle fracture criterion allows three approaches to determine the fracture toughness of the structural material. The three approaches present the opportunity to balance material testing requirements and the conservatism of the material's fracture toughness which must be used to demonstrate resistance to brittle fracture. This work has resulted in a revised Appendix IX to Safety Series {number sign}37 which will be released as an IAEA Technical Document within the coming year.

  11. Brittle materials at high-loading rates: an open area of research

    Science.gov (United States)

    Forquin, Pascal

    2017-01-01

    Brittle materials are extensively used in many civil and military applications involving high-strain-rate loadings such as: blasting or percussive drilling of rocks, ballistic impact against ceramic armour or transparent windshields, plastic explosives used to damage or destroy concrete structures, soft or hard impacts against concrete structures and so on. With all of these applications, brittle materials are subjected to intense loadings characterized by medium to extremely high strain rates (few tens to several tens of thousands per second) leading to extreme and/or specific damage modes such as multiple fragmentation, dynamic cracking, pore collapse, shearing, mode II fracturing and/or microplasticity mechanisms in the material. Additionally, brittle materials exhibit complex features such as a strong strain-rate sensitivity and confining pressure sensitivity that justify expending greater research efforts to understand these complex features. Currently, the most popular dynamic testing techniques used for this are based on the use of split Hopkinson pressure bar methodologies and/or plate-impact testing methods. However, these methods do have some critical limitations and drawbacks when used to investigate the behaviour of brittle materials at high loading rates. The present theme issue of Philosophical Transactions A provides an overview of the latest experimental methods and numerical tools that are currently being developed to investigate the behaviour of brittle materials at high loading rates. This article is part of the themed issue 'Experimental testing and modelling of brittle materials at high strain rates'.

  12. Brittleness and Packing Density Effects on Blast-hole Cuttings Yield of Selected Rocks

    Directory of Open Access Journals (Sweden)

    B. Adebayo

    2016-06-01

    Full Text Available This paper evaluates brittleness and packing density to analysis their effects on blast-hole cutting yield for three selected rocks in Nigeria. Brittleness test (S20 was carried out in accordance with Norwegian Soil and Rock Engineering and the Brittleness Index (BI for the selected rocks were estimated. The packing density determined from the photomicrograph of the rock samples. The grain size of 45 blast-holes drill cuttings collected from three selected while drilling of these rocks were determined using standard method of America Society for Testing and Materials (ASTM D 2487. The brittleness values are 50%, 44% and 42% for micro granite, porphyritic granite and medium biotite granite respectively. The result of BI varied from 10.32 – 11.59 and they are rated as moderately brittle rocks. The values of packing density varied from 92.20 – 94.55%, 91.00 -92.96% and 92.92 – 94.96% for all the rocks. The maximum weights of blast-hole particle size retained at 75 µm are 106.00g, 103.28 g and 99.76 g for medium biotite granite, micro granite and porhyritic granite respectively. Packing density values have correlation to some extent with (S20 values hence, this influence the yield of blast-hole cuttings as drilling progresses. The minimum weight of blast-hole cuttings particle size retained at 150 µm agrees with brittleness index classification for micro granite.

  13. Brittle materials at high-loading rates: an open area of research

    Science.gov (United States)

    2017-01-01

    Brittle materials are extensively used in many civil and military applications involving high-strain-rate loadings such as: blasting or percussive drilling of rocks, ballistic impact against ceramic armour or transparent windshields, plastic explosives used to damage or destroy concrete structures, soft or hard impacts against concrete structures and so on. With all of these applications, brittle materials are subjected to intense loadings characterized by medium to extremely high strain rates (few tens to several tens of thousands per second) leading to extreme and/or specific damage modes such as multiple fragmentation, dynamic cracking, pore collapse, shearing, mode II fracturing and/or microplasticity mechanisms in the material. Additionally, brittle materials exhibit complex features such as a strong strain-rate sensitivity and confining pressure sensitivity that justify expending greater research efforts to understand these complex features. Currently, the most popular dynamic testing techniques used for this are based on the use of split Hopkinson pressure bar methodologies and/or plate-impact testing methods. However, these methods do have some critical limitations and drawbacks when used to investigate the behaviour of brittle materials at high loading rates. The present theme issue of Philosophical Transactions A provides an overview of the latest experimental methods and numerical tools that are currently being developed to investigate the behaviour of brittle materials at high loading rates. This article is part of the themed issue ‘Experimental testing and modelling of brittle materials at high strain rates’. PMID:27956517

  14. A new approach to rock brittleness and its usability at prediction of drillability

    Science.gov (United States)

    Özfırat, M. Kemal; Yenice, Hayati; Şimşir, Ferhan; Yaralı, Olgay

    2016-07-01

    Rock brittleness is one of the most important issues in rock drilling and cutting. The relations between drillability and brittleness will assist engineers in excavation works. The demand for representative rock parameters related to planning of underground excavations is increasing, as these parameters constitute fundamental input for obtaining the most reliable cost and time estimates. In rock cutting mechanics, the effects of the rock and brittleness on the efficiency of drilling and excavation are examined by many researchers. In this study, 41 different rock types were tested in laboratory to investigate the relations between the drilling rate index and different brittleness values. Firstly, the relations defined in literature are tested. Strength tests are made according to International Society for Rock Mechanics standards. In addition Norwegian University of Science and Technology standards are used to determine drilling rate index. Then, a new brittleness index is proposed which is the arithmetic average of uniaxial compressive strength and tensile strength. Considering the regression analysis carried out, it was seen that the proposed formula showed good correlation for these samples handled in this study. As a result of this study, a high correlation is obtained between the proposed index and drilling rate index values (R:0.84). The results are found to be at least reliable as well as other brittleness equations given in literature.

  15. Quantitative comparisons of analogue models of brittle wedge dynamics

    Science.gov (United States)

    Schreurs, Guido

    2010-05-01

    Analogue model experiments are widely used to gain insights into the evolution of geological structures. In this study, we present a direct comparison of experimental results of 14 analogue modelling laboratories using prescribed set-ups. A quantitative analysis of the results will document the variability among models and will allow an appraisal of reproducibility and limits of interpretation. This has direct implications for comparisons between structures in analogue models and natural field examples. All laboratories used the same frictional analogue materials (quartz and corundum sand) and prescribed model-building techniques (sieving and levelling). Although each laboratory used its own experimental apparatus, the same type of self-adhesive foil was used to cover the base and all the walls of the experimental apparatus in order to guarantee identical boundary conditions (i.e. identical shear stresses at the base and walls). Three experimental set-ups using only brittle frictional materials were examined. In each of the three set-ups the model was shortened by a vertical wall, which moved with respect to the fixed base and the three remaining sidewalls. The minimum width of the model (dimension parallel to mobile wall) was also prescribed. In the first experimental set-up, a quartz sand wedge with a surface slope of ˜20° was pushed by a mobile wall. All models conformed to the critical taper theory, maintained a stable surface slope and did not show internal deformation. In the next two experimental set-ups, a horizontal sand pack consisting of alternating quartz sand and corundum sand layers was shortened from one side by the mobile wall. In one of the set-ups a thin rigid sheet covered part of the model base and was attached to the mobile wall (i.e. a basal velocity discontinuity distant from the mobile wall). In the other set-up a basal rigid sheet was absent and the basal velocity discontinuity was located at the mobile wall. In both types of experiments

  16. Study on electroplating technology of diamond tools for machining hard and brittle materials

    Science.gov (United States)

    Cui, Ying; Chen, Jian Hua; Sun, Li Peng; Wang, Yue

    2016-10-01

    With the development of the high speed cutting, the ultra-precision machining and ultrasonic vibration technique in processing hard and brittle material , the requirement of cutting tools is becoming higher and higher. As electroplated diamond tools have distinct advantages, such as high adaptability, high durability, long service life and good dimensional stability, the cutting tools are effective and extensive used in grinding hard and brittle materials. In this paper, the coating structure of electroplating diamond tool is described. The electroplating process flow is presented, and the influence of pretreatment on the machining quality is analyzed. Through the experimental research and summary, the reasonable formula of the electrolyte, the electroplating technologic parameters and the suitable sanding method were determined. Meanwhile, the drilling experiment on glass-ceramic shows that the electroplating process can effectively improve the cutting performance of diamond tools. It has laid a good foundation for further improving the quality and efficiency of the machining of hard and brittle materials.

  17. ADOLESCENT ROMANCE AND DELINQUENCY: A FURTHER EXPLORATION OF HIRSCHI'S "COLD AND BRITTLE" RELATIONSHIPS HYPOTHESIS.

    Science.gov (United States)

    Giordano, Peggy C; Lonardo, Robert A; Manning, Wendy D; Longmore, Monica A

    2010-11-28

    Hirschi argued that delinquent youth tend to form relatively "cold and brittle" relationships with peers, depicting these youths as deficient in their attachments to others. The current analysis explores connections between delinquency and the character of adolescent romantic ties, drawing primarily on the first wave of the Toledo Adolescent Relationships Study, and focusing on 957 teens with dating experience. We examine multiple relationship qualities/dynamics in order to explore both the "cold" and "brittle" dimensions of Hirschi's hypothesis. Regarding the "cold" assumption, results suggest that delinquency is not related to perceived importance of the romantic relationship, level of intimate self-disclosure or feelings of romantic love, and more delinquent youth actually report more frequent contact with their romantic partners. Analyses focused on two dimensions tapping the "brittle" description indicate that while durations of a focal relationship do not differ according to level of respondent delinquency, more delinquent youths report higher levels of verbal conflict.

  18. Composition and size dependent brittle-to-malleable transitions of Mg-based bulk metallic glasses

    Energy Technology Data Exchange (ETDEWEB)

    Yin, Jian, E-mail: yinjiandonic@yahoo.com; Ma, Xiujun; Zhou, Zhijian

    2014-05-01

    Mg-based bulk metallic glasses (BMGs) were often treated as brittle materials. However, some Mg-based BMGs were recently reported to show malleability. In order to identify the reasons for the achievement of the brittle-to-malleable transitions in the Mg-based BMGs, we systematically investigated the mechanical properties of four Mg-based BMGs (Mg{sub 65}Cu{sub 25}Gd{sub 10}, Mg{sub 65}Cu{sub 20}Ni{sub 5}Gd{sub 10}, Mg{sub 75}Ni{sub 15}Gd{sub 10}, and Mg{sub 75}Ni{sub 15}Gd{sub 5}Nd{sub 5} BMGs) using the uniaxial compression tests on the samples with sizes of ∅1×2 mm{sup 2} and ∅2×4 mm{sup 2}. The corresponding fracture morphology was observed by scanning electron microscopy (SEM). These Mg-based BMGs displayed the composition or size dependent brittle-to-malleable transitions, accompanied by the fracture mode transition from the cleavage fracture to the shear fracture. It appeared that the Mg-based BMGs were sensitive to cleavage cracks upon loading. The brittle-to-malleable transitions of the Mg-based BMGs were related to not only the stability of shear banding but also the nucleation and propagation of cleavage cracks. It was demonstrated that the suppression of the nucleation and propagation of cleavage cracks could favor the transition from the cleavage fracture to the shear fracture and encourage the brittle-to-malleable transition for the Mg-based BMGs. The underlying mechanism for the brittle-to-malleable transitions of the Mg-based BMGs was discussed with respect to both the composition and size effects.

  19. Prediction of Brittle Failure for TBM Tunnels in Anisotropic Rock: A Case Study from Northern Norway

    Science.gov (United States)

    Dammyr, Øyvind

    2016-06-01

    Prediction of spalling and rock burst is especially important for hard rock TBM tunneling, because failure can have larger impact than in a drill and blast tunnel and ultimately threaten excavation feasibility. The majority of research on brittle failure has focused on rock types with isotropic behavior. This paper gives a review of existing theory and its application before a 3.5-m-diameter TBM tunnel in foliated granitic gneiss is used as a case to study brittle failure characteristics of anisotropic rock. Important aspects that should be considered in order to predict brittle failure in anisotropic rock are highlighted. Foliation is responsible for considerable strength anisotropy and is believed to influence the preferred side of v-shaped notch development in the investigated tunnel. Prediction methods such as the semi- empirical criterion, the Hoek- Brown brittle parameters, and the non-linear damage initiation and spalling limit method give reliable results; but only as long as the angle between compression axis and foliation in uniaxial compressive tests is relevant, dependent on the relation between tunnel trend/plunge, strike/dip of foliation, and tunnel boundary stresses. It is further demonstrated that local in situ stress variations, for example, due to the presence of discontinuities, can have profound impact on failure predictions. Other carefully documented case studies into the brittle failure nature of rock, in particular anisotropic rock, are encouraged in order to expand the existing and relatively small database. This will be valuable for future TBM planning and construction stages in highly stressed brittle anisotropic rock.

  20. Influence of Composition and Deformation Conditions on the Strength and Brittleness of Shale Rock

    Science.gov (United States)

    Rybacki, E.; Reinicke, A.; Meier, T.; Makasi, M.; Dresen, G. H.

    2015-12-01

    Stimulation of shale gas reservoirs by hydraulic fracturing operations aims to increase the production rate by increasing the rock surface connected to the borehole. Prospective shales are often believed to display high strength and brittleness to decrease the breakdown pressure required to (re-) initiate a fracture as well as slow healing of natural and hydraulically induced fractures to increase the lifetime of the fracture network. Laboratory deformation tests were performed on several, mainly European black shales with different mineralogical composition, porosity and maturity at ambient and elevated pressures and temperatures. Mechanical properties such as compressive strength and elastic moduli strongly depend on shale composition, porosity, water content, structural anisotropy, and on pressure (P) and temperature (T) conditions, but less on strain rate. We observed a transition from brittle to semibrittle deformation at high P-T conditions, in particular for high porosity shales. At given P-T conditions, the variation of compressive strength and Young's modulus with composition can be roughly estimated from the volumetric proportion of all components including organic matter and pores. We determined also brittleness index values based on pre-failure deformation behavior, Young's modulus and bulk composition. At low P-T conditions, where samples showed pronounced post-failure weakening, brittleness may be empirically estimated from bulk composition or Young's modulus. Similar to strength, at given P-T conditions, brittleness depends on the fraction of all components and not the amount of a specific component, e.g. clays, alone. Beside strength and brittleness, knowledge of the long term creep properties of shales is required to estimate in-situ stress anisotropy and the healing of (propped) hydraulic fractures.

  1. Plug shear failure in nailed timber connections:avoiding brittle and promoting ductile failures

    OpenAIRE

    Johnsson, Helena

    2004-01-01

    Mechanical timber connections can fail both in a brittle and a ductile manner depending on the joint layout. Plug shear failure in nailed timber connections is a brittle failure mode, which shall be avoided in timber structures. This failure mode occurs in nailed connections loaded in tension parallel to the grain, for instance in the lower chord of a timber truss. The failure mode is not described in the Swedish building code of today, but there is an informative annex in the upcoming Euroco...

  2. Damage Model of Brittle Coal-Rock and Damage Energy Index of Rock Burst

    Institute of Scientific and Technical Information of China (English)

    尹光志; 张东明; 魏作安; 李东伟

    2003-01-01

    Based on the mechanical experiment of brittle coal-rock and the damage mechanical theory, a damage model was established. Coal-Rock damage mechanical characteristic was researched. Furthermore, interior energy transformation mechanism of rock was analyzed from the point of view of damage mechanics and damage energy release rate of brittle coal rock was derived. By analyzing the energy transformation of rock burst, a new conception, damage energy index of rock burst, was put forward. The condition of rock burst was also established.

  3. The Influence of Brittle Daniels System Characteristics on the Value of Load Monitoring Information

    DEFF Research Database (Denmark)

    Thöns, Sebastian; Schneider, Ronald

    This paper addresses the influence of deteriorating brittle Daniels system characteristics on the value of structural health monitoring (SHM). The value of SHM is quantified as the difference between the life cycle benefits with and without SHM. A value of SHM analysis is performed within...

  4. Microcosmic analysis of ductile shearing zones of coal seams of brittle deformation domain in superficial lithosphere

    Institute of Scientific and Technical Information of China (English)

    JU; Yiwen; WANG; Guiliang; JIANG; Bo; HOU; Quanlin

    2004-01-01

    The ductile shearing zones of coal seams in a brittle deformation domain in superficial lithosphere are put forward based on the study on bedding shearing and ductile rheology of coal seams. The macrocosmic and microcosmic characteristics include wrinkle fold, mymonitized zones and ductile planar structure of coal seams, etc., while the microcosmic characteristics may also include different optic-axis fabrics and the anisotropy of vitrinite reflectance as well as the change of chemical structure and organic geochemistry components. The forming mechanism is analyzed and the strain environment of ductile shearing zones of coal seams discussed. The result indicates that, in the superficial brittle deformation domain, the coal seams are easy to be deformed, resulting in not only brittle deformation but also ductile shearing deformation under the action of force. Because of simple shearing stress, the interlayer gliding or ductile rheology may take place between coal seams and wall rocks. Therefore, many ductile shearing zones come into being in superficial lithosphere (<5 km). The research on ductile shearing zone of brittle deformation domain in superficial lithosphere is significant not only theoretically for the study of ductile shearing and ductile rheology of the lithosphere but also practically for the structural movement of coal seams, the formation and accumulation of coal-bed methane, and the prevention and harness of gas burst in coal mine.

  5. Two-dimensional isotropic damage elastoplastic model for quasi-brittle material

    OpenAIRE

    Beneš, P. (Pavel); Vavřík, D. (Daniel)

    2014-01-01

    Micro-mechanical model for isotropic damage of quasi-brittle material including frictionis presented. Damage is assumed to be isotropic and scalar damage variable is employed . Operatorsplitting method is applied. The article contains derived expressions for derivations necessary forcomputation of coefficients in two dimensions for strain and damage normality rules.

  6. Long-term follow-up of children thought to have temporary brittle bone disease

    Directory of Open Access Journals (Sweden)

    Paterson CR

    2011-06-01

    Full Text Available Colin R Paterson1, Elizabeth A Monk21Department of Medicine (retired, 2School of Accounting and Finance, University of Dundee, Dundee, ScotlandBackground: In addition to nonaccidental injury, a variety of bone disorders may underlie the finding of unexplained fractures in young children. One controversial postulated cause is temporary brittle bone disease, first described in 1990.Methods: Eighty-five patients with fractures showing clinical and radiological features of temporary brittle bone disease were the subject of judicial hearings to determine whether it was appropriate for them to return home. Sixty-three patients did, and follow-up information was available for 61 of these. The mean follow-up period was 6.9 years (range 1–17, median 6.Results: We found that none of the children had sustained any further injuries that were thought to represent nonaccidental injury; no child was re-removed from home. Three children had fractures. In each case there was general agreement that the fractures were accidental. Had the original fractures in these children been the result of nonaccidental injury, it would have been severe and repeated; the average number of fractures was 9.1.Conclusion: The fact that no subsequent suspicious injuries took place after return home is consistent with the view that the fractures were unlikely to have been caused by nonaccidental injury, and that temporary brittle bone disease is a distinctive and identifiable disorder.Keywords: fractures, osteogenesis imperfecta, temporary brittle bone disease, nonaccidental injury

  7. Study on the cutting mechanism and the brittle ductile transition model of isotropic pyrolyric graphite

    Science.gov (United States)

    Wang, Minghai; Wang, Hujun; Liu, Zhonghai

    2011-05-01

    Isotropic pyrolyric graphite (IPG) is a new kind of brittle material, it can be used for sealing the aero-engine turbine shaft and the ethylene high-temperature equipment. It not only has the general advantages of ordinal carbonaceous materials such as high temperature resistance, lubrication and abrasion resistance, but also has the advantages of impermeability and machinability that carbon/carbon composite doesn't have. Therefore, it has broad prospects for development. Mechanism of brittle-ductile transition of IPG is the foundation of precision cutting while the plastic deformation of IPG is the essential and the most important mechanical behavior of precision cutting. Using the theory of strain gradient, the mechanism of this material removal during the precision cutting is analyzed. The critical cutting thickness of IPG is calculated for the first time. Furthermore, the cutting process parameters such as cutting depth, feed rate which corresponding to the scale of brittle-ductile transition deformation of IPG are calculated. In the end, based on the theory of micromechanics, the deformation behaviors of IPG such as brittle fracture, plastic deformation and mutual transformation process are all simulated under the Sih.G.C fracture criterion. The condition of the simulation is that the material under the pressure-shear loading conditions .The result shows that the best angle during the IPG precision cutting is -30°. The theoretical analysis and the simulation result are validated by precision cutting experiments.

  8. A map of competing buckling-driven failure modes of substrate-supported thin brittle films

    Energy Technology Data Exchange (ETDEWEB)

    Jia, Zheng [Department of Mechanical Engineering and Maryland NanoCenter, University of Maryland, College Park, MD 20742 (United States); Peng, Cheng [Department of Mechanical Engineering and Materials Science, Rice University, Houston, TX 77005 (United States); Lou, Jun, E-mail: jlou@rice.edu [Department of Mechanical Engineering and Materials Science, Rice University, Houston, TX 77005 (United States); Li, Teng, E-mail: lit@umd.edu [Department of Mechanical Engineering and Maryland NanoCenter, University of Maryland, College Park, MD 20742 (United States)

    2012-08-31

    Our in situ experiments of polyimide-supported thin indium tin oxide (ITO) films reveal buckling-driven film cracking in some samples and buckling-driven interfacial delamination in other samples. Although studies of individual buckling-driven failure mode exist, it still remains unclear what governs the competition between these two different failure modes in a given film/substrate structure. Through theoretical analysis and numerical simulations, we delineate a map of competing buckling-driven failure modes of substrate-supported thin brittle films in the parameter space of interfacial adhesion and interfacial imperfection size. Such a map can offer insight on the mechanical durability of functional thin films. For example, interestingly, we show that strongly bonded thin brittle films are more prone to buckling-driven cracking, a more detrimental failure mode for thin brittle ITO transparent conductors widely used in displays and flexible electronics. - Highlights: Black-Right-Pointing-Pointer Map of buckling-driven failure modes of thin brittle films on substrates. Black-Right-Pointing-Pointer We study key parameters that govern buckling-driven failure modes. Black-Right-Pointing-Pointer The map offers insights on optimal design of functional thin films.

  9. Interaction between cracking, delamination and buckling in brittle elastic thin films

    NARCIS (Netherlands)

    Vellinga, W. P.; Van den Bosch, M.; Geers, M. G. D.

    2008-01-01

    A discrete lattice based model for the interaction of cracking, delamination and buckling of brittle elastic coatings is presented. The model is unique in its simultaneous incorporation of the coating and of disorder in the interface and material properties, leading to realistic 3D bending (and buck

  10. Modelling dynamic tensile failure of quasi-brittle materials using stress-enhanced non local models

    NARCIS (Netherlands)

    Pereira, L.; Weerheijm, J.; Sluys, L.J.

    2015-01-01

    The development of realistic numerical tools to efficiently model the response of concrete structures subjected to close-in detonations and high velocity impacts has been one of the major quests in defense research. Under these loading conditions, quasi-brittle materials undergo a multitude of failu

  11. Modelling dynamic tensile failure of quasi-brittle materials using stress-enhanced nonlocal models

    NARCIS (Netherlands)

    Magalhaes Pereira, L.F.; Weerheijm, J.; Sluys, L.J.

    2015-01-01

    The development of realistic numerical tools to efficiently model the response of concrete structures subjected to close-in detonations and high velocity impacts has been one of the major quests in defense research. Under these loading conditions, quasi-brittle materials undergo a multitude of failu

  12. Brittle fracture phase-field modeling of a short-rod specimen

    Energy Technology Data Exchange (ETDEWEB)

    Escobar, Ivana [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Tupek, Michael R. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Bishop, Joseph E. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2015-09-01

    Predictive simulation capabilities for modeling fracture evolution provide further insight into quantities of interest in comparison to experimental testing. Based on the variational approach to fracture, the advent of phase-field modeling achieves the goal to robustly model fracture for brittle materials and captures complex crack topologies in three dimensions.

  13. A kinematic measurement for ductile and brittle failure of materials using digital image correlation

    Directory of Open Access Journals (Sweden)

    M.M. Reza Mousavi

    2016-12-01

    Full Text Available This paper addresses some material level test which is done on quasi-brittle and ductile materials in the laboratory. The displacement control experimental program is composed of mortar cylinders under uniaxial compression shows quasi-brittle behavior and seemingly round-section aluminum specimens under uniaxial tension represents ductile behavior. Digital Image Correlation gives full field measurement of deformation in both aluminum and mortar specimens. Likewise, calculating the relative displacement of two points located on top and bottom of virtual LVDT, which is virtually placed on the surface of the specimen, gives us the classical measure of strain. However, the deformation distribution is not uniform all over the domain of specimens mainly due to imperfect nature of experiments and measurement devices. Displacement jumps in the fracture zone of mortar specimens and strain localization in the necking area for the aluminum specimen, which are reflecting different deformation values and deformation gradients, is compared to the other regions. Since the results are inherently scattered, it is usually non-trivial to smear out the stress of material as a function of a single strain value. To overcome this uncertainty, statistical analysis could bring a meaningful way to closely look at scattered results. A large number of virtual LVDTs are placed on the surface of specimens in order to collect statistical parameters of deformation and strain. Values of mean strain, standard deviation and coeffcient of variations for each material are calculated and correlated with the failure type of the corresponding material (either brittle or ductile. The main limiters for standard deviation and coeffcient of variations for brittle and ductile failure, in pre-peak and post-peak behavior are established and presented in this paper. These limiters help us determine whether failure is brittle or ductile without determining of stress level in the material.

  14. Role of Brittle Behaviour of Soft Calcarenites Under Low Confinement: Laboratory Observations and Numerical Investigation

    Science.gov (United States)

    Lollino, Piernicola; Andriani, Gioacchino Francesco

    2017-07-01

    The strength decay that occurs in the post-peak stage, under low confinement stress, represents a key factor of the stress-strain behaviour of rocks. However, for soft rocks this issue is generally underestimated or even neglected in the solution of boundary value problems, as for example those concerning the stability of underground cavities or rocky cliffs. In these cases, the constitutive models frequently used in limit equilibrium analyses or more sophisticated numerical calculations are, respectively, rigid-plastic or elastic-perfectly plastic. In particular, most of commercial continuum-based numerical codes propose a variety of constitutive models, including elasticity, elasto-plasticity, strain-softening and elasto-viscoplasticity, which are not exhaustive in simulating the progressive failure mechanisms affecting brittle rock materials, these being characterized by material detachment and crack opening and propagation. As a consequence, a numerical coupling with mechanical joint propagation is needed to cope with fracture mechanics. Therefore, continuum-based applications that treat the simulation of the failure processes of intact rock masses at low stress levels may need the adoption of numerical techniques capable of implementing fracture mechanics and rock brittleness concepts, as it is shown in this paper. This work is aimed at highlighting, for some applications of rock mechanics, the essential role of post-peak brittleness of soft rocks by means of the application of a hybrid finite-discrete element method. This method allows for a proper simulation of the brittle rock behaviour and the related mechanism of fracture propagation. In particular, the paper presents two ideal problems, represented by a shallow underground cave and a vertical cliff, for which the evolution of the stability conditions is investigated by comparing the solutions obtained implementing different brittle material responses with those resulting from the assumption of perfectly

  15. A unified phase-field theory for the mechanics of damage and quasi-brittle failure

    Science.gov (United States)

    Wu, Jian-Ying

    2017-06-01

    Being one of the most promising candidates for the modeling of localized failure in solids, so far the phase-field method has been applied only to brittle fracture with very few exceptions. In this work, a unified phase-field theory for the mechanics of damage and quasi-brittle failure is proposed within the framework of thermodynamics. Specifically, the crack phase-field and its gradient are introduced to regularize the sharp crack topology in a purely geometric context. The energy dissipation functional due to crack evolution and the stored energy functional of the bulk are characterized by a crack geometric function of polynomial type and an energetic degradation function of rational type, respectively. Standard arguments of thermodynamics then yield the macroscopic balance equation coupled with an extra evolution law of gradient type for the crack phase-field, governed by the aforesaid constitutive functions. The classical phase-field models for brittle fracture are recovered as particular examples. More importantly, the constitutive functions optimal for quasi-brittle failure are determined such that the proposed phase-field theory converges to a cohesive zone model for a vanishing length scale. Those general softening laws frequently adopted for quasi-brittle failure, e.g., linear, exponential, hyperbolic and Cornelissen et al. (1986) ones, etc., can be reproduced or fit with high precision. Except for the internal length scale, all the other model parameters can be determined from standard material properties (i.e., Young's modulus, failure strength, fracture energy and the target softening law). Some representative numerical examples are presented for the validation. It is found that both the internal length scale and the mesh size have little influences on the overall global responses, so long as the former can be well resolved by sufficiently fine mesh. In particular, for the benchmark tests of concrete the numerical results of load versus displacement

  16. Analysis of fracture process zone in brittle rock subjected to shear-compressive loading

    Institute of Scientific and Technical Information of China (English)

    ZHOU De-quan; CHEN Feng; CAO Ping; MA Chun-de

    2005-01-01

    An analytical expression for the prediction of shear-compressive fracture process zone(SCFPZ) is derived by using a proposed local strain energy density criterion, in which the strain energy density is separated into the dilatational and distortional strain energy density, only the former is considered to contribute to the brittle fracture of rock in different loading cases. The theoretical prediction by this criterion shows that the SCFPZ is of asymmetric mulberry leaf in shape, which forms a shear-compression fracture kern. Dilatational strain energy density along the boundary of SCFPZ reaches its maximum value. The dimension of SCFPZ is governed by the ratio of KⅡ to KⅠ . The analytical results are then compared with those from literatures and the tests conducted on double edge cracked Brazilian disk subjected to diametrical compression. The obtained results are useful to the prediction of crack extension and to nonlinear analysis of shear-compressive fracture of brittle rock.

  17. Superior room-temperature ductility of typically brittle quasicrystals at small sizes

    Science.gov (United States)

    Zou, Yu; Kuczera, Pawel; Sologubenko, Alla; Sumigawa, Takashi; Kitamura, Takayuki; Steurer, Walter; Spolenak, Ralph

    2016-08-01

    The discovery of quasicrystals three decades ago unveiled a class of matter that exhibits long-range order but lacks translational periodicity. Owing to their unique structures, quasicrystals possess many unusual properties. However, a well-known bottleneck that impedes their widespread application is their intrinsic brittleness: plastic deformation has been found to only be possible at high temperatures or under hydrostatic pressures, and their deformation mechanism at low temperatures is still unclear. Here, we report that typically brittle quasicrystals can exhibit remarkable ductility of over 50% strains and high strengths of ~4.5 GPa at room temperature and sub-micrometer scales. In contrast to the generally accepted dominant deformation mechanism in quasicrystals--dislocation climb, our observation suggests that dislocation glide may govern plasticity under high-stress and low-temperature conditions. The ability to plastically deform quasicrystals at room temperature should lead to an improved understanding of their deformation mechanism and application in small-scale devices.

  18. Overcoming the brittleness of glass through bio-inspiration and micro-architecture

    Science.gov (United States)

    Mirkhalaf, M.; Dastjerdi, A. Khayer; Barthelat, F.

    2014-01-01

    Highly mineralized natural materials such as teeth or mollusk shells boast unusual combinations of stiffness, strength and toughness currently unmatched by engineering materials. While high mineral contents provide stiffness and hardness, these materials also contain weaker interfaces with intricate architectures, which can channel propagating cracks into toughening configurations. Here we report the implementation of these features into glass, using a laser engraving technique. Three-dimensional arrays of laser-generated microcracks can deflect and guide larger incoming cracks, following the concept of ‘stamp holes’. Jigsaw-like interfaces, infiltrated with polyurethane, furthermore channel cracks into interlocking configurations and pullout mechanisms, significantly enhancing energy dissipation and toughness. Compared with standard glass, which has no microstructure and is brittle, our bio-inspired glass displays built-in mechanisms that make it more deformable and 200 times tougher. This bio-inspired approach, based on carefully architectured interfaces, provides a new pathway to toughening glasses, ceramics or other hard and brittle materials.

  19. Neutron irradiation effects on the ductile-brittle transition of ferritic/martensitic steels

    Energy Technology Data Exchange (ETDEWEB)

    Klueh, R.L.; Alexander, D.J. [Oak Ridge National Lab., TN (United States)

    1997-08-01

    Ferritic/martensitic steels such as the conventional 9Cr-1MoVNb (Fe-9Cr-1Mo-0.25V-0.06Nb-0.1C) and 12Cr-1MoVW (Fe-12Cr-1Mo-0.25V-0.5W-0.5Ni-0.2C) steels have been considered potential structural materials for future fusion power plants. The major obstacle to their use is embrittlement caused by neutron irradiation. Observations on this irradiation embrittlement is reviewed. Below 425-450{degrees}C, neutron irradiation hardens the steels. Hardening reduces ductility, but the major effect is an increase in the ductile-brittle transition temperature (DBTT) and a decrease in the upper-shelf energy, as measured by a Charpy impact test. After irradiation, DBTT values can increase to well above room temperature, thus increasing the chances of brittle rather than ductile fracture.

  20. Alternating brittle and ductile response of coherent twin boundaries in nanotwinned metals

    Energy Technology Data Exchange (ETDEWEB)

    Sinha, Tanushree; Kulkarni, Yashashree, E-mail: ykulkarni@uh.edu [Department of Mechanical Engineering, University of Houston, Houston, Texas 77204 (United States)

    2014-11-14

    Nanotwinned metals have opened exciting avenues for the design of high strength and high ductility materials. In this work, we investigate crack propagation along coherent twin boundaries in nanotwinned metals using molecular dynamics. Our simulations reveal that alternating twin boundaries exhibit intrinsic brittleness and ductility owing to the opposite crystallographic orientations of the adjoining twins. This is a startling consequence of the directional anisotropy of an atomically sharp crack along a twin boundary that favors cleavage in one direction and dislocation emission from the crack tip in the opposite direction. We further find that a blunt crack exhibits ductility in all cases albeit with very distinct deformation mechanisms and yield strength associated with intrinsically brittle and ductile coherent twin boundaries.

  1. Mechanical Properties Degradation at Room Temperature in ZRY-4 by Hydrogen Brittleness

    Directory of Open Access Journals (Sweden)

    Bertolino G.

    2002-01-01

    Full Text Available A hot rolled Zircaloy-4 alloy, annealed with a final cold rolling, presenting rounded grains, was studied. Hydrogen cathodic charge with a homogenization heat treatment was used to pre-charge the specimens with different hydrogen contents. Hydrogen embrittlement susceptibility analysis was held using J integral and J-R curve results from CT specimens (compact tension specimens tested at room temperature. As J IC values showed scatter, toughness was evaluated for deltaa = 1mm. Toughness clearly tended to decrease as hydrogen content increased abruptly for low H contents and gradually for high contents. A few specimens with high hydrogen content failed in brittle mode, or presented instability and posterior crack arrest. Fractographic observations showed that, despite the records had presented no signs of brittle fracture, certain specimens showed cleavage-like zones. More cleavage-like area percentage was present the higher the hydrogen content was.

  2. Crack Arrest in Brittle Ceramics Subjected to Thermal Shock and Ablation

    Science.gov (United States)

    Wang, Yan-Wei; Yu, He-Long; Tang, Hong-Xiang; Feng, Xue

    2014-09-01

    Ceramics are suitable for high temperature applications, especially for aerospace materials. When serving in high temperature environments, ceramics usually have to deal with the challenge of both thermal shock and ablation. We report the crack arrest in brittle ceramics during thermal shock and ablation. In our experiment, the specimens of Al2O3 are subjected to oxygen-propane flame heating until the temperature arises up to 1046°C and then are cooled down in air. The crack occurs, however, it does not propagate when arrested by the microstructures (e.g., micro-bridges) of the crack tip. Such micro-bridge enhances the toughness of the brittle ceramics and prevents the crack propagation, which provides a hint for design of materials against the thermal shock.

  3. Semi-brittle rheology and ice dynamics in DynEarthSol3D

    Science.gov (United States)

    Logan, Liz C.; Lavier, Luc L.; Choi, Eunseo; Tan, Eh; Catania, Ginny A.

    2017-01-01

    We present a semi-brittle rheology and explore its potential for simulating glacier and ice sheet deformation using a numerical model, DynEarthSol3D (DES), in simple, idealized experiments. DES is a finite-element solver for the dynamic and quasi-static simulation of continuous media. The experiments within demonstrate the potential for DES to simulate ice failure and deformation in dynamic regions of glaciers, especially at quickly changing boundaries like glacier termini in contact with the ocean. We explore the effect that different rheological assumptions have on the pattern of flow and failure. We find that the use of a semi-brittle constitutive law is a sufficient material condition to form the characteristic pattern of basal crevasse-aided pinch-and-swell geometry, which is observed globally in floating portions of ice and can often aid in eroding the ice sheet margins in direct contact with oceans.

  4. Damage initiation in brittle and ductile materials as revealed from a fractoluminescence study

    Directory of Open Access Journals (Sweden)

    Alexandre Chmel

    2014-10-01

    Full Text Available A set of heterogeneous and homogeneous materials differing in their brittle and ductile characteristics (granite, marble, silica ceramics, silicon carbide, organic glass were subjected to impact damaging by a falling weight. Multiple chemical bond ruptures produced by elastic waves propagating from a damaged zone were accompanied by the photon emission generated throughout the sample (tribo- or fractoluminescence, FL. The statistical analysis of the FL time series detected with high resolution (10 ns showed that the energy release distributions in brittle solids follow the power law typical for the correlated nucleation of primary defects. At the same time, the formation of damaged sites in ductile materials (marble and organic glass was found to be fully random.

  5. Numerical Simulation on Failure Process in Brittle and Heterogeneous Matrix Filled with Randomly Distributed Particles

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yafang; TANG Chun'an; LIU Hao

    2006-01-01

    Based on an essential assumption of meso-heterogeneity of material, the macro characteristic of composite reinforced with particles, the crack initiation, propagation and the failure process in composite were studied by using a numerical code. The composite is subjected to a uniaxial tension, and stiff or soft particles are distributed at random manner but without overlapping or contacting. The effect of reinforcement particle properties on the fracture process and mechanism of composite with brittle matrix, furthermore, the influence of the particle volumetric fraction is also investigated. Numerical results present the different failure mode and re-produce the crack initiation, propagation and coalescence in brittle and heterogeneous matrix. The mechanism of such failure was also elucidated.

  6. Hypervelocity impact on brittle materials of semi-infinite thickness: fracture morphology related to projectile diameter

    Science.gov (United States)

    Taylor, Emma A.; Kay, Laurie; Shrine, Nick R. G.

    Hypervelocity impact on brittle materials produces features not observed on ductile targets. Low fracture toughness and high yield strength produce a range of fracture morphologies including cracking, spallation and shatter. For sub-mm diameter projectiles, impact features are characterised by petaloid spallation separated by radial cracks. The conchoidal or spallation diameter is a parameter in current cratering equations. An alternative method for interpreting hypervelocity impacts on glass targets of semi-infinite thickness is tested against impact data produced using the Light Gas Gun (LGG) facility at the University of Kent at Canterbury (UKC), U.K. Spherical projectiles of glass and other materials with diameters 30-300 μm were fired at ~5 km s^-1 at a glass target of semi-infinite thickness. The data is used to test a power law relationship between projectile diameter and crack length. The results of this work are compared with published cratering/spallation equations for brittle materials.

  7. Characteristics of machined surface controlled by cutting tools and conditions in machining of brittle material

    Institute of Scientific and Technical Information of China (English)

    Yong-Woo KIM; Soo-Chang CHOI; Jeung-Woo PARK; Deug-Woo LEE

    2009-01-01

    One of the ultra-precision machining methods was adapted for brittle material as well as soft material by using multi-arrayed diamond tips and high speed spindle. Conventional machining method is too hard to control surface roughness and surface texture against brittle material because the particles of grinding tools are irregular size and material can be fragile. Therefore, we were able to design tool paths and machine controlled pattern on surface by multi-arrayed diamond tips with uniform size made in MEMS fabrication and high speed spindle, and the maximum speed was about 3×105 r/min. We defined several parameters that can affect the machining surface. Those were multi-array of diamond tips (n×n), speed of air spindle and feeding rate. The surface roughness and surface texture can be controlled by those parameters for micro machining.

  8. Quasi-Brittle Fracture Modeling of Preflawed Bitumen Using a Diffuse Interface Model

    Directory of Open Access Journals (Sweden)

    Yue Hou

    2016-01-01

    Full Text Available Fundamental understandings on the bitumen fracture mechanism are vital to improve the mixture design of asphalt concrete. In this paper, a diffuse interface model, namely, phase-field method is used for modeling the quasi-brittle fracture in bitumen. This method describes the microstructure using a phase-field variable which assumes one in the intact solid and negative one in the crack region. Only the elastic energy will directly contribute to cracking. To account for the growth of cracks, a nonconserved Allen-Cahn equation is adopted to evolve the phase-field variable. Numerical simulations of fracture are performed in bituminous materials with the consideration of quasi-brittle properties. It is found that the simulation results agree well with classic fracture mechanics.

  9. Application of percolation model on the brittle to ductile transition for polystyrene and polyolefin elastomer blends

    Directory of Open Access Journals (Sweden)

    2007-01-01

    Full Text Available The percolation model was applied in the study of brittle to ductile transition (BDT of polystyrene (PS and polyolefin elastomer (POE blends. Based on the interparticle distance and percolation model, stress volume (Vs can be expressed by volume fraction (Vr and ratio of the diameter of stress volume and the diameter of the domain (S/d. The percolation threshold (Vsc varied from π/6 to 0.65. From the results of the Charpy impact strength of the blends, the percolation threshold for the brittle to ductile transition of PS/POE blend is 14 wt% POE, corresponding to Vsc~0.5, which is consistent with the calculated value of π/6. Morphology observations show that the percolation point is correlated with the phase inversion of the blend.

  10. Steadiness and stop of brittle fracture driven by the forces in different distances

    Institute of Scientific and Technical Information of China (English)

    和雪松; 李世愚; 滕春凯

    2005-01-01

    Based on the principle of fracture mechanics, the stop criterion of brittle fracture is proposed and the equation of minimal crack stop is given. By using the zero frequency Green function, the steadiness and stop of brittle fracture driven by the concentrated force and simple distributed forces in different locales are analyzed. The critical loading, unsteady boundary line and location of stop points under some typical conditions are calculated. The steady growth caused by the near forces is significant in interpreting the creep and the forming of some tectonics. Whereas the unsteady propagation caused by the forces in different distances from the crack is significant in interpreting the occurring and stop of earthquakes. It is suggested that the strong earthquakes may be the result of compound of the near-field and far-field forces. The results of this paper are also valuable for investigation of the mechanism of induced earthquake.

  11. Prevention of brittle fracture of steel structures by controlling the local stress and strain fields

    Directory of Open Access Journals (Sweden)

    Moyseychik Evgeniy Alekseevich

    Full Text Available In the article the author offers a classification of the methods to increase the cold resistance of steel structural shapes with a focus on the regulation of local fields of internal stresses and strains to prevent brittle fracture of steel structures. The need of a computer thermography is highlighted not only for visualization of temperature fields on the surface, but also to control the fields of residual stresses and strains in a controlled element.

  12. Fracture propagation in brittle materials as a standard dissipative process: General theorems and crack tracking algorithms

    Science.gov (United States)

    Salvadori, A.; Fantoni, F.

    2016-10-01

    The present work frames the problem of three-dimensional quasi-static crack propagation in brittle materials into the theory of standard dissipative processes. Variational formulations are stated. They characterize the three dimensional crack front "quasi-static velocity" as minimizer of constrained quadratic functionals. An implicit in time crack tracking algorithm that computationally handles the constraint via the penalty method algorithm is introduced and proof of concept is provided.

  13. Pinch and swell structures: evidence for brittle-viscous behaviour in the middle crust

    Directory of Open Access Journals (Sweden)

    R. Gardner

    2015-04-01

    Full Text Available The flow properties of middle to lower crustal rocks are commonly represented by viscous flow. However, examples of pinch and swell structures found in a mid-crustal high strain zone at St. Anne Point (Fiordland, New Zealand suggest pinch and swell structures are initiated by brittle failure of the more competent layer in conjunction with material softening. On this basis we develop a flexible numerical model using brittle-viscous flow where Mohr–Coulomb failure is utilised to initiate pinch and swell structure development. Results show that pinch and swell structures develop in a competent layer in both Newtonian and non-Newtonian flow provided the competent layer has enough viscosity contrast and initially fails brittlely. The degree of material softening after initial failure is shown to impact pinch and swell characteristics with high rates of material softening causing the formation of thick necks between swells by limiting the successful localisation of strain. The flow regime and yielding characteristics of the matrix do not impact pinch and swell structure formation itself, so long as the matrix is less competent. To aid analysis of the structures and help derive the flow properties of rocks in the field, we define three stages of pinch and swell development and offer suggestions for measurements to be made in the field. Our study suggests that Mohr–Coulomb behaviour combined with viscous flow is an appropriate way to represent the heterogeneous rocks of the middle to lower crust. This type of mid-crustal rheological behaviour has significant influence on the localization of strain at all scales. For example, inclusion of Mohr–Coulomb brittle failure with viscous flow in just some mid-crustal layers within a crustal scale model will result in strain localisation throughout the whole crustal section allowing the development of through-going high strain structures from the upper crust into the middle and lower crust. This

  14. From boron carbide to glass: Absorption of an elongated high-speed projectile in brittle materials

    Science.gov (United States)

    Rumyantsev, B. V.

    2016-09-01

    Penetration into boron carbide of an elongated high-speed projectile in the form of a copper jet produced by an explosion of a cumulative charge is studied. The efficiency of absorption of a copper jet in different brittle materials for evaluating their protective ability is compared. Conditions for the absence of the influence of the lateral unloading wave on the penetration zone, which provide the minimum penetration depth, are determined.

  15. Micromechanisms of brittle fracture: STM, TEM and electron channeling analysis. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Gerberich, W.W.

    1997-01-01

    The original thrust of this grant was to apply newly developed techniques in scanning tunneling and transmission electron microscopy to elucidate the mechanism of brittle fracture. This grant spun-off several new directions in that some of the findings on bulk structural materials could be utilized on thin films or intermetallic single crystals. Modeling and material evaluation efforts in this grant are represented in a figure. Out of this grant evolved the field the author has designated as Contact Fracture Mechanics. By appropriate modeling of stress and strain distribution fields around normal indentations or scratch tracks, various measures of thin film fracture or decohesion and brittle fracture of low ductility intermetallics is possible. These measures of fracture resistance in small volumes are still evolving and as such no standard technique or analysis has been uniformly accepted. For brittle ceramics and ceramic films, there are a number of acceptable analyses such as those published by Lawn, Evans and Hutchinson. For more dissipative systems involving metallic or polymeric films and/or substrates, there is still much to be accomplished as can be surmised from some of the findings in the present grant. In Section 2 the author reviews the funding history and accomplishments associated mostly with bulk brittle fracture. This is followed by Section 3 which covers more recent work on using novel techniques to evaluate fracture in low ductility single crystals or thin films using micromechanical probes. Basically Section 3 outlines how the recent work fits in with the goals of defining contact fracture mechanics and gives an overview of how the several examples in Section 4 (the Appendices) fit into this framework.

  16. Sample Size Induced Brittle-to-Ductile Transition of Single-Crystal Aluminum Nitride

    Science.gov (United States)

    2015-08-01

    exhibit many distinctive physical and mechanical properties, compared to metallic and polymeric materials, but the propensity toward brittle fracture ...copper grid by a FIB micro-probe. (d) Side view of the sliced specimen after a final milling. The TEM foil is welded on the Cu grid using tungsten ...their respective height and fractured micropillars are shown by cross mark (). (b) The measured ultimate (failure) strength and plasticity vs. the

  17. Controlling factors for the brittle-to-ductile transition in tungsten single crystals

    Science.gov (United States)

    Gumbsch; Riedle; Hartmaier; Fischmeister

    1998-11-13

    Materials performance in structural applications is often restricted by a transition from ductile response to brittle fracture with decreasing temperature. This transition is currently viewed as being controlled either by dislocation mobility or by the nucleation of dislocations. Fracture experiments on tungsten single crystals reported here provide evidence for the importance of dislocation nucleation for the fracture toughness in the semibrittle regime. However, it is shown that the transition itself, in general, is controlled by dislocation mobility rather than by nucleation.

  18. Formulation and computational aspects of plasticity and damage models with application to quasi-brittle materials

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Z.; Schreyer, H.L. [New Mexico Engineering Research Institute, Albuquerque, NM (United States)

    1995-09-01

    The response of underground structures and transportation facilities under various external loadings and environments is critical for human safety as well as environmental protection. Since quasi-brittle materials such as concrete and rock are commonly used for underground construction, the constitutive modeling of these engineering materials, including post-limit behaviors, is one of the most important aspects in safety assessment. From experimental, theoretical, and computational points of view, this report considers the constitutive modeling of quasi-brittle materials in general and concentrates on concrete in particular. Based on the internal variable theory of thermodynamics, the general formulations of plasticity and damage models are given to simulate two distinct modes of microstructural changes, inelastic flow and degradation of material strength and stiffness, that identify the phenomenological nonlinear behaviors of quasi-brittle materials. The computational aspects of plasticity and damage models are explored with respect to their effects on structural analyses. Specific constitutive models are then developed in a systematic manner according to the degree of completeness. A comprehensive literature survey is made to provide the up-to-date information on prediction of structural failures, which can serve as a reference for future research.

  19. Síndrome das unhas frágeis Brittle nail syndrome

    Directory of Open Access Journals (Sweden)

    Izelda Maria Carvalho Costa

    2007-06-01

    Full Text Available A síndrome das unhas frágeis é queixa comum, caracterizada por aumento da fragilidade das lâminas ungueais. Afeta quase 20% da população geral, sendo mais comum em mulheres. Clinicamente se manifesta com onicosquizia e onicorrexe - distúrbios nos fatores de adesão intercelular das unhas se manifestam como a primeira, ao passo que alterações da matriz apresentamse com onicorrexe. Mesmo sendo tão usual e afetando os pacientes de maneira importante em seu cotidiano, o tratamento das unhas frágeis avançou pouco nas últimas décadas e ainda se baseia principalmente no uso da biotina.Brittle nail syndrome is a common condition, characterized by increased fragility of the nail plates. It affects almost 20% of the population, being more usual in women. Clinical manifestations of brittle nails are onychoschizia and onychorexis - disorders of intercellular adhesive factors are expressed as the first, while disorders of the nail matrix manifest as onychorexis. Despite being so common and causing much more than only cosmetic problems to the patient, the treatment of brittle nails has had little improvement over the past decades and is still mainly based on the daily use of biotin.

  20. TENSILE STRENGTH FOR SPLITTING FAILURE OF BRITTLE PARTICLES WITH CONSIDERATION OF POISSON'S RATIO

    Institute of Scientific and Technical Information of China (English)

    Guoming Hu; Yanmin Wang; Pingbo Xie; Zhidong Pan

    2004-01-01

    The core mechanism of comminution could be reduced to the breakage of individual particles that occurs through contact with other particles or with the grinding media, or with the solid walls of the mill. When brittle particles are loaded in compression or by impact, substantial tensile stresses are induced within the particles. These tensile stresses are responsible for splitting failure of brittle particles. Since many engineering materials have Poisson's ratios very close to 0.3, the influence of Poisson's ratio on the tensile strength is neglected in many studies. In this paper, the state of stress in a spherical particle due to two diametrically opposed forces is analyzed theoretically. A simple equation for the tensile stress at the centre of the particle is obtained. It is found reasonable to propose this tensile stress at the instant of failure as the tensile strength of the particle. Moreover, this tensile strength is a function of the Poisson's ratio of the material. As the state of stress along the z-axis in an irregular specimen tends to be similar to that in a spherical particle compressed diametrically with the same force, this tensile strength has some validity for irregular particles as well.Therefore, it could be used as the tensile strength for brittle particles in general. The effect of Poisson's ratio on the tensile strength is discussed.

  1. 3D modelling of salt tectonics with a brittle overburden in an extensional regime

    Science.gov (United States)

    Eichheimer, Philipp; Reuber, Georg; Kaus, Boris

    2016-04-01

    Most previous numerical models of salt tectonics only considered 2D cases or did not taken a brittle sedimentary overburden into account, both of which are likely to be important in nature. To get insights into the dynamics of diapiric rise of salt we here present time-dependent high resolution 3D models of salt tectonics in the presence of a brittle overburden and sedimentation. We focus on the internal deformation of an embedded anhydrite layer within a nonlinear viscous salt layer. As salt in nature tends to rise upwards to the surface along fault zones, the salt layer is overlain by a brittle overburden to simulate faulting. The resulting complex folding of the anhydrite layer obtained in our models is consistent with natural observations, e.g. Gorleben [1]. Regarding field examples we vary the shape of the anhydrite layer to understand different modes of deformation [2]. We test the effect of overburden rheology, extension and sedimentation rates on the 3D salt dome patterns and on its internal deformation. [1] O. Bornemann. Zur Geologie des Salzstocks Gorleben nach den Bohrergebnissen. Bundesamt für Strahlenschutz (1991). [2] Z. Chemia, H. Koyi, and H. Schmeling. Numerical modelling of rise and fall of a dense layer in salt diapirs. Geophysical Journal International 172.2 (2008): 798-816.

  2. Strain Rate Dependent Ductile-to-Brittle Transition of Graphite Platelet Reinforced Vinyl Ester Nanocomposites

    Directory of Open Access Journals (Sweden)

    Brahmananda Pramanik

    2014-01-01

    Full Text Available In previous research, the fractal dimensions of fractured surfaces of vinyl ester based nanocomposites were estimated applying classical method on 3D digital microscopic images. The fracture energy and fracture toughness were obtained from fractal dimensions. A noteworthy observation, the strain rate dependent ductile-to-brittle transition of vinyl ester based nanocomposites, is reinvestigated in the current study. The candidate materials of xGnP (exfoliated graphite nanoplatelets reinforced and with additional CTBN (Carboxyl Terminated Butadiene Nitrile toughened vinyl ester based nanocomposites that are subjected to both quasi-static and high strain rate indirect tensile load using the traditional Brazilian test method. High-strain rate indirect tensile testing is performed with a modified Split-Hopkinson Pressure Bar (SHPB. Pristine vinyl ester shows ductile deformation under quasi-static loading and brittle failure when subjected to high-strain rate loading. This observation reconfirms the previous research findings on strain rate dependent ductile-to-brittle transition of this material system. Investigation of both quasi-static and dynamic indirect tensile test responses show the strain rate effect on the tensile strength and energy absorbing capacity of the candidate materials. Contribution of nanoreinforcement to the tensile properties is reported in this paper.

  3. A study of fracture in brittle laminar composites that contain weak interlayers

    Science.gov (United States)

    Scott, Colin Stuart

    Ceramics have material properties that make them useful for many industrial applications. They are strong, hard, and chemically inert. Their refractoriness gives them an advantage over metals and polymers for use at high temperature. Unfortunately, the inherent brittleness of ceramics limits their use in structural applications. One way to improve the toughness of ceramics is to combine them with other materials to make composites. The correct combination of materials can lead to synergism, and a significant improvement in properties. In this work, brittle laminates that contain weak interlayers are considered. The weak interlayers lead to crack deflection, and can result in non-catastrophic failure of the material. The requirements for consistent crack deflection and non-catastrophic failure are not fully understood. This work is an attempt to explain the observed fracture behaviour in brittle laminar composites that contain weak interlayers. A combination of experimental work, fracture mechanics modeling and finite element modeling has been used to predict the requirements necessary for non-catastrophic failure. The work shows the size of flaws in the surface of the composite, in the weak interlayer, and in subsequent strong layers in the material, all play an important role in the fracture behaviour. Control and understanding of the effect of the various flaw sizes can be used to achieve non-catastrophic failure and increased work of fracture in these composites.

  4. A new anisotropic damage model for brittle solids based on the effective damage concept

    Energy Technology Data Exchange (ETDEWEB)

    Yazdani, S. [North Dakota State Univ., Fargo, ND (United States)

    1995-12-31

    The presence of microdefects within the structure of a brittle solid plays a dominant role on the manner in which the material responds to externally applied stresses. When a loading state involves a confining pressure of a sufficient magnitude such that nucleation of new microdefects and the propagation of existing ones are inhibited, brittle solids display a ductile response. However, when the same materials are stressed in a low pressure regime, responses become very brittle with little or no ductility. During the process of damage, material bonds are severed, leading to the alteration of elastic properties. It is, therefore, plausible to employ the changes in compliance or stiffness as measures of damage as they relate directly to the physics of the problem. The paper starts with a review of the fundamental concepts based on the laws of thermodynamics, considers anisotropic damage formulation, including both elastic and inelastic damage processes, and proposes new damage response tensors to allow for the rotation of principal stress axis. Damage is recorded in the material compliance tensor involving an effective damage parameter whose increment is obtained from the consistency condition of a damage potential known as {open_quotes}damage surface.{close_quotes} Finally, the paper illustrates the model for a cementitious material in different loading paths.

  5. Final report of experimental laboratory-scale brittle fracture studies of glasses and ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Jardine, L.J.; Mecham, W.J.; Reedy, G.T.; Steindler, M.J.

    1982-10-01

    An experimental program was conducted to characterize the fragments generated when brittle glasses and ceramics are impacted. The direct application of the results is to radioactive waste forms for which the effects of accidental impacts must be known or predictable. Two major measurable experimental responses used for characterization of these effects are (1) the size distribution of the fragments, including the sizes that are respirable, and (2) the increase in surface area of the brittle test specimen. This report describes the glass and ceramic materials characterized, the procedures and techniques used for the characterization of size distributions and surface areas, and the results of the two key responses of the impact tests. Five alternative methods of determining size distributions were compared. Also examined were the effects of diametral and axial specimen impact configurations and the use of mechanical stops to eliminate secondary crushing during testing. Microscopic characterizations of Pyrex and SRL 131 simulated waste glass and SYNROC fragments were also performed. Preliminary correlations of impact energy with key size-distribution parameters, fragment surface areas, and respirable fines were proposed as useful for future verification and for use with modeling and scale-up studies of brittle fracture of larger realistic waste forms. The impact fragments of all specimens could be described by lognormal size distributions.

  6. Rock Drilling Performance Evaluation by an Energy Dissipation Based Rock Brittleness Index

    Science.gov (United States)

    Munoz, H.; Taheri, A.; Chanda, E. K.

    2016-08-01

    To reliably estimate drilling performance both tool-rock interaction laws along with a proper rock brittleness index are required to be implemented. In this study, the performance of a single polycrystalline diamond compact (PDC) cutter cutting and different drilling methods including PDC rotary drilling, roller-cone rotary drilling and percussive drilling were investigated. To investigate drilling performance by rock strength properties, laboratory PDC cutting tests were performed on different rocks to obtain cutting parameters. In addition, results of laboratory and field drilling on different rocks found elsewhere in literature were used. Laboratory and field cutting and drilling test results were coupled with values of a new rock brittleness index proposed herein and developed based on energy dissipation withdrawn from the complete stress-strain curve in uniaxial compression. To quantify cutting and drilling performance, the intrinsic specific energy in rotary-cutting action, i.e. the energy consumed in pure cutting action, and drilling penetration rate values in percussive action were used. The results show that the new energy-based brittleness index successfully describes the performance of different cutting and drilling methods and therefore is relevant to assess drilling performance for engineering applications.

  7. Experimental study on the physical and chemical properties of the deep hard brittle shale

    Directory of Open Access Journals (Sweden)

    Jian Xiong

    2016-03-01

    Full Text Available In the hard brittle shale formation, rock composition, physical and chemical properties, mechanics property before and after interacting with fluid have direct relation with borehole problems, such as borehole wall collapse, mud loss, hole shrinkage. To achieve hard brittle shale micro-structure, physical–chemical properties and mechanics property, energy-dispersive X-ray diffraction (XRD, cation exchange capacity experiment and hardness test are conducted. The result of laboratory experiments indicates that, clay mineral and quartz is dominated in mineral composition. In clay mineral, illite and illite/semectite mixed layers are abundant and there is no sign of montmorillonite. Value of cation exchange capacity (CEC ranges from 102.5–330 mmol/kg and average value is 199.56 mmol/kg. High value of CEC and content of clay mineral means hard brittle shale has strong ability of hydration. The image of XRD shows well developed micro-cracks and pores, which make rock failure easily, especially when fluid invades rock inside. Shale sample soaked with anti-high temperature KCL drilling fluid on shorter immersing time has stronger strength, whereas shale sample soaked with plugging and film forming KCL drilling fluid on longer immersing time has stronger strength.

  8. Microstructures relevant to brittle fracture initiation at the heat-affected zone of weldment of a low carbon steel

    Science.gov (United States)

    Ohya, Kenji; Kim, Jongseop; Yokoyama, Ken'ichi; Nagumo, Michihiko

    1996-09-01

    Charpy toughness of the heat-affected zone (HAZ) of weldment of a low carbon steel has been investigated by means of an instrumented Charpy test and fractographic analysis. Microstructures were varied with thermal cycles simulating double-pass welding. The ductile-brittle transition temperature is the most deteriorated at an intermediate second-cycle heating temperature. The origin of the difference in the transition temperatures has been analyzed to exist in the brittle fracture initiation stage. Fractographic examination correlating with microstructural features has revealed that the brittle fracture initiation site is associated with the intersection of bainitic ferrite areas with different orientations rather than the martensite-austenite constituents. The role of the constraint of plastic deformation on the brittle fracture initiation is discussed.

  9. Sequencing and analysis of the gastrula transcriptome of the brittle star Ophiocoma wendtii

    Directory of Open Access Journals (Sweden)

    Vaughn Roy

    2012-09-01

    Full Text Available Abstract Background The gastrula stage represents the point in development at which the three primary germ layers diverge. At this point the gene regulatory networks that specify the germ layers are established and the genes that define the differentiated states of the tissues have begun to be activated. These networks have been well-characterized in sea urchins, but not in other echinoderms. Embryos of the brittle star Ophiocoma wendtii share a number of developmental features with sea urchin embryos, including the ingression of mesenchyme cells that give rise to an embryonic skeleton. Notable differences are that no micromeres are formed during cleavage divisions and no pigment cells are formed during development to the pluteus larval stage. More subtle changes in timing of developmental events also occur. To explore the molecular basis for the similarities and differences between these two echinoderms, we have sequenced and characterized the gastrula transcriptome of O. wendtii. Methods Development of Ophiocoma wendtii embryos was characterized and RNA was isolated from the gastrula stage. A transcriptome data base was generated from this RNA and was analyzed using a variety of methods to identify transcripts expressed and to compare those transcripts to those expressed at the gastrula stage in other organisms. Results Using existing databases, we identified brittle star transcripts that correspond to 3,385 genes, including 1,863 genes shared with the sea urchin Strongylocentrotus purpuratus gastrula transcriptome. We characterized the functional classes of genes present in the transcriptome and compared them to those found in this sea urchin. We then examined those members of the germ-layer specific gene regulatory networks (GRNs of S. purpuratus that are expressed in the O. wendtii gastrula. Our results indicate that there is a shared ‘genetic toolkit’ central to the echinoderm gastrula, a key stage in embryonic development, though

  10. Deciphering the brittle evolution of SW Norway through a combined structural, mineralogical and geochronological approach

    Science.gov (United States)

    Scheiber, Thomas; Viola, Giulio; Fredin, Ola; Zwingmann, Horst; Wilkinson, Camilla Maya; Ganerød, Morgan

    2016-04-01

    SW Norway has experienced a complex brittle history after cessation of the Caledonian orogeny, and the recent discoveries of major hydrocarbon reserves in heavily fractured and weathered basement offshore SW Norway has triggered a renewed interest in understanding this complex tectonic evolution. In this contribution we present results from a multidisciplinary study combining lineament analysis, field work, paleo-stress inversion, mineralogical characterization and radiometric dating in the Bømlo area of SW Norway in order to develop a tectonic model for the brittle evolution of this important region. The study area mainly consists of the Rolvsnes granodiorite (U-Pb zircon age of ca. 466 Ma), which is devoid of penetrative ductile deformation features. The first identified brittle faults are muscovite-bearing top-to-the-NNW thrusts and E-W striking dextral strike-slip faults decorated with stretched biotite. These are mechanically compatible and are assigned to the same NNW-SSE transpressional regime. Ar-Ar muscovite and biotite dates of ca. 450 Ma (Late Ordovician) indicate fault activity in the course of a Taconian-equivalent orogenic event. During the subsequent Silurian Laurentia-Baltica collision variably oriented, lower-grade chlorite and epidote-coated faults formed in response to a ENE-WSW compressional stress regime. A large number of mainly N-S striking normal faults consist of variably thick fault gouge cores with illite, quartz, kaolinite, calcite and epidote mineralizations, accommodating mainly E-W extension. K-Ar dating of illites separated from representative fault gouges and zones of altered granodiorite constrain deformation ranging from the Permian to the Late Jurassic, indicating a long history of crustal extension where faults were repeatedly activated. In addition, a set of ca. SW-NE striking faults associated with alteration zones give Cretaceous dates, either representing a young phase of NW-SE extension or reactivation of previously formed

  11. Hemolytic and cytotoxic effects of saponin like compounds isolated from Persian Gulf brittle star (Ophiocoma erinaceus)

    Institute of Scientific and Technical Information of China (English)

    Elaheh Amini; Mohammad Nabiuni; Javad Baharara; Kazem Parivar; Javad Asili

    2014-01-01

    Objective: To isolate and characterize the saponin from Persian Gulf brittle star (Ophiocomaerinaceus Methods: In an attempt to prepare saponin from brittle star, collected samples were minced and extracted with ethanol, dichloromethane, n-buthanol. Then, concentrated n-butanol extract were loaded on HP-20 resin and washed with dionized water, 80% ethanol and 100%ethanol respectively. Subsequently, detection of saponin was performed by foaming property, fourier transform infrared spectroscopy and hemolytic analysis on thin layer chromatography. The cytotoxic activity on HeLa cells was evaluated through 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazoliumbromide (MTT) assay and under invert microscopy.Results:) and to evaluate its hemolytic and cytotoxic potential. method. The presence of C-H bond, C-O-C and OH in fourier transform infrared spectrum of fraction 80% ethanol is characteristic feature in the many of saponin compounds. Hemolytic assay revealed HD50 value was 500 µg/mL. MTT assay exhibited that saponin extracted in IC50 value of 25 µg/mL inducsd potent cytotoxic activity against HeLa cells in 24 h and 12.5 µg/mL in 48 h, meanwhile in lower concentration did not have considerable effect against HeLa cells.Conclusions:The existence of saponin in Ophiocoma erinaceus were approved by phytochemical These findings showed that only 80% ethanol fraction Persian Gulf brittle star contained saponin like compounds with hemolytic activity which can be detected simply by phytochemical that can be appreciable for future anticancer research.

  12. An experimental study on semi-brittle and plastic rheology of Panzhihua gabbro

    Institute of Scientific and Technical Information of China (English)

    HE; Changrong(何昌荣); ZHOU; Yongsheng(周永胜); SANG; Zunan(桑祖南)

    2003-01-01

    We have carried out a systematic experimental study on semi-brittle and plastic deformation of fine-grained Panzhihua gabbro under dry condition with temperature range of 700-1100℃, confining pressure of 450-500 MPa, and strain rate of 1×10-4-3.1×10-6 s-1, using a triaxial testing system with a Griggs type solid medium pressure vessel. In terms of the parameters in the flow law and microstructure after deformation, the rate-dependent deformation can be categorized into three modes: (i) In temperature range of 700-800℃, the deformation is accommodated by semi-brittle flow, with activation energy Q = 612 ± 12 kJ/mol, and stress exponent n = 14.6. The deformation in microscopic scale corresponds to the dislocation glide accompanied with microfracturing. (ii) In temperature range of 900-950℃, the predominant deformation mechanisms in this phase are mechanical twinning and dislocation glide, with activation energy Q =720 ± 61 kJ/mol, and stress exponent n = 6.4. (iii) In temperature range of 1000-1150℃, the major deformation mechanisms are dislocation glide and dislocation climb with minor processes of partial melting, with activation energy Q = 699 ± 55 kJ/mol and stress exponent n = 4.1. The microstructure and deformation mechanism of our experiments are comparable to the results of clinopyroxene and diabase as observed in previous studies. The flow stress of a mafic lower crust is calculated based on the rheological parameters of dry fine-grained gabbro, which implies that a lower curst with mafic granulite may be brittle, and it is possible to fracture and produce frictional slips. This may be an important implication for earthquake nucleation in the lower crust.

  13. What do we know about the initiation and early stages of brittle faulting in crystalline rocks?

    Science.gov (United States)

    Crider, J. G.

    2011-12-01

    The styles of initiation and subsequent growth of faults control fault length-slip scaling, the internal structure of fault zones, and fault-rock properties, influencing seismogenic behavior and fluid flow along the faults. Observations by many researchers over the last several decades have illustrated that faults in the upper crust initiate on pre-existing (inherited) or precursory (early-formed) structures and grow by the mechanical interaction and linkage of these structures. These pre-existing and precursory structures are typically mode I fractures (joints, veins, dikes) but may also be semi-brittle shear zones (such as deformation bands in porous sandstone). Research in the granitic outcrops of the central Sierra Nevada (California) has provided significant insight into the geometry and fundamental mechanics of the early stages of fault development. This work has shown that faults in plutonic rocks initiate on pre-existing or precursory joints or dikes and that the discontinuous nature of early mode I fractures has a strong influence on the subsequent development of the fault zone. In basalt, we have similarly observed the important influence of preexisting joints, and, at a broader scale, precursory, semi-brittle shear zones in the form of fault-tip monoclines. In metamorphic rocks, foliation appears to control the initial development of faults, influencing fault orientation, or enabling precursory structures such as kink bands. Kink bands, like deformation bands in porous sandstone, accommodate only small strains before locking, but then become strong inclusions in the material, serving to localize brittle fractures. The quasi-static mechanics of isotropic, isothermal linear-elastic materials in two and three dimensions provides first order understanding of controls on interaction and linkage of early structures, including the concentration of stresses and local stress reorientation. Fruitful research directions important to faulting in crystalline rock

  14. Tectonic tremor and brittle seismic events triggered along the Eastern Denali Fault in northwest Canada

    Science.gov (United States)

    Zimmerman, J. P.; Aiken, C.; Peng, Z.

    2013-12-01

    Deep tectonic tremor has been observed in a number of plate-bounding tectonic environments around the world. It can occur both spontaneously (i.e. ambient) and as a result of small stress perturbations from passing seismic waves (i.e. triggered). Because tremor occurs beneath the seismogenic zone (> 15 km), it is important to understand where and how tremor occurs to discern its relationship with shallower earthquakes. In this study, we search for triggered tremor and brittle seismic events along the Eastern Denali Fault (EDF) in northwest Canada, an intraplate strike-slip region where previously tremor has not been observed. We retrieve seismic data for 19 distant earthquakes from 9 broadband stations monitored by the Canadian National Seismograph Network (CNSN). We apply high-pass or band-pass filters to the seismic data to suppress signals from distant events and search for local sources. Triggered tremor signals exhibit high-frequency contents, have long duration (> 15 s), are coincident with passing surface waves of the distant earthquakes, and are observable among nearby stations. Using this simple approach, we have identified 4 mainshocks that triggered tremor in our study region: the 2011/03/11 Mw9.1 Tohoku, 2012/04/11 Mw8.6 Sumatra, 2012/10/28 Mw7.7 Haida Gwaii, and 2013/01/05 Mw7.5 Craige earthquakes. Our initial locations indicate that the tremor source occurs on or near the southeastern portion of the EDF near the fault trace. In addition to the triggered tremor sources, we also identified many 'brittle' events with very short durations triggered by the Rayleigh waves of the 2012/10/28 Mw7.7 Haida Gwaii earthquake. While we were unable to locate these brittle events, they appear to be seismically similar to triggered icequakes observed in Antarctica (Peng et al., 2013) and occur during the dilatational strain changes caused by the Rayleigh waves.

  15. THE VISCOUS TO BRITTLE TRANSITION IN CRYSTAL- AND BUBBLE-BEARING MAGMAS

    Directory of Open Access Journals (Sweden)

    Mattia ePistone

    2015-11-01

    Full Text Available The transition from viscous to brittle behaviour in magmas plays a decisive role in determining the style of volcanic eruptions. While this transition has been determined for one- or two-phase systems, it remains poorly constrained for natural magmas containing silicic melt, crystals, and gas bubbles. Here we present new experimental results on shear-induced fracturing of three-phase magmas obtained at high-temperature (673-1023 K and high-pressure (200 MPa conditions over a wide range of strain-rates (5·10-6 s-1 to 4·10-3 s-1. During the experiments bubbles are deformed (i.e. capillary number are in excess of 1 enough to coalesce and generate a porous network that potentially leads to outgassing. A physical relationship is proposed that quantifies the critical stress required for magmas to fail as a function of both crystal (0.24 to 0.65 and bubble volume fractions (0.09 to 0.12. The presented results demonstrate efficient outgassing for low crystal fraction ( 0.44 promote gas bubble entrapment and inhibit outgassing. The failure of bubble-free, crystal-bearing systems is enhanced by the presence of bubbles that lower the critical failure stress in a regime of efficient outgassing, while the failure stress is increased if bubbles remain trapped within the crystal framework. These contrasting behaviours have direct impact on the style of volcanic eruptions. During magma ascent, efficient outgassing reduces the potential for an explosive eruption and favours brittle behaviour, contributing to maintain low overpressures in an active volcanic system resulting in effusion or rheological flow blockage of magma at depth. Conversely, magmas with high crystallinity experience limited loss of exsolved gas, permitting the achievement of larger overpressures prior to a potential sudden transition to brittle behaviour, which could result in an explosive volcanic eruption.

  16. New perspectives on the transition between discrete fracture, fragmentation, and pulverization during brittle failure of rocks

    Science.gov (United States)

    Griffith, W. A.; Ghaffari, H.; Barber, T. J.; Borjas, C.

    2015-12-01

    The motions of Earth's tectonic plates are typically measured in millimeters to tens of centimeters per year, seemingly confirming the generally-held view that tectonic processes are slow, and have been throughout Earth's history. In line with this perspective, the vast majority of laboratory rock mechanics research focused on failure in the brittle regime has been limited to experiments utilizing slow loading rates. On the other hand, many natural processes that pose significant risk for humans (e.g., earthquakes and extraterrestrial impacts), as well as risks associated with human activities (blow-outs, explosions, mining and mine failures, projectile penetration), occur at rates that are hundreds to thousands of times faster than those typically simulated in the laboratory. Little experimental data exists to confirm or calibrate theoretical models explaining the connection between these dramatic events and the pulverized rocks found in fault zones, impacts, or explosions; however the experimental data that does exist is thought-provoking: At the earth's surface, the process of brittle fracture passes through a critical transition in rocks at high strain rates (101-103s-1) between regimes of discrete fracture and distributed fragmentation, accompanied by a dramatic increase in strength. Previous experimental works on this topic have focused on key thresholds (e.g., peak stress, peak strain, average strain rate) that define this transition, but more recent work suggests that this transition is more fundamentally dependent on characteristics (e.g., shape) of the loading pulse and related microcrack dynamics, perhaps explaining why for different lithologies different thresholds more effectively define the pulverization transition. In this presentation we summarize some of our work focused on this transition, including the evolution of individual defects at the microscopic, microsecond scale and the energy budget associated with the brittle fragmentation process as a

  17. Brittle versus ductile deformation as the main control of the deep fluid circulation in continental crust

    Science.gov (United States)

    Violay, Marie; Madonna, Claudio; Burg, Jean-Pierre

    2016-04-01

    The Japan Beyond-Brittle Project (JBBP) and the Taupo Volcanic Zone-Deep geothermal drilling project in New Zealand (TVZ-DGDP) proposed a new concept of engineered geothermal development where reservoirs are created in ductile rocks. This system has several advantages including (1) a simpler design and control of the reservoir due to homogeneous rock properties and stress states in the ductile domain ,(2) possible extraction of supercritical fluids (3) less probability for induced earthquakes. However, it is at present unknwon what and how porosity and permeability can be engineered in such environments. It has been proposed that the magmatic chamber is surrounded by a hot and ductile carapace through which heat transfer is conductive because the plastic behaviour of the rock will close possible fluid pathways. Further outward, as temperature declines, the rock will encounter the brittle-ductile transition with a concomitant increase in porosity and permeability. The thickness of the conduction-dominated, ductile boundary zone between the magmatic chamber and the convecting geothermal fluid directly determines the rate of heat transfer. To examine the brittle to ductile transition in the context of the Japanese crust, we conducted deformation experiments on very-fine-grain granite in conventional servocontrolled, gas-medium triaxial apparatus (from Paterson instrument). Temperature ranged from 600° C to 1100° C and effective confining pressure from 100 to 150 MPa. Dilatancy was measured during deformation. The method consisted in monitoring the volume of pore fluid that flows into or out of the sample at constant pore pressure. Permeability was measured under static conditions by transient pressure pulse method. Mechanical and micro-structural observations at experimental constant strain rate of 10-5 s-1 indicated that the granite was brittle and dilatant up to 900 ° C. At higher temperatures the deformation mode becomes macroscopically ductile, i

  18. Film-induced brittle intergranular cracking of silver-gold alloys

    Energy Technology Data Exchange (ETDEWEB)

    Friedersdorf, F. [Bethlehem Steel Corp., PA (United States). Homer Research Labs.; Sieradzki, K. [Arizona State Univ., Tempe, AZ (United States)

    1996-05-01

    Dealloying of a binary noble alloy produces a porous layer rich in the more noble element. Application of a tensile load initiates a brittle intergranular (IG) crack in the dealloyed layer that advances into the unattacked material. This study showed that the crack penetration depth (C{sub d}) is proportional to the thickness of the dealloyed layer (t). For a given value of t, the grain-boundary crack penetration distance was shown to decrease as the dealloying potential increased. The dependence of C{sub d} on t and the dealloying potential, as opposed to the applied potential at the time of fracture, supported the film-induced cleavage model.

  19. Mechanical Behavior of Low Porosity Carbonate Rock: From Brittle Creep to Ductile Creep.

    Science.gov (United States)

    Nicolas, A.; Fortin, J.; Gueguen, Y.

    2014-12-01

    Mechanical compaction and associated porosity reduction play an important role in the diagenesis of porous rocks. They may also affect reservoir rocks during hydrocarbon production, as the pore pressure field is modified. This inelastic compaction can lead to subsidence, cause casing failure, trigger earthquake, or change the fluid transport properties. In addition, inelastic deformation can be time - dependent. In particular, brittle creep phenomena have been deeply investigated since the 90s, especially in sandstones. However knowledge of carbonates behavior is still insufficient. In this study, we focus on the mechanical behavior of a 14.7% porosity white Tavel (France) carbonate rock (>98% calcite). The samples were deformed in a triaxial cell at effective confining pressures ranging from 0 MPa to 85 MPa at room temperature and 70°C. Experiments were carried under dry and water saturated conditions in order to explore the role played by the pore fluids. Two types of experiments have been carried out: (1) a first series in order to investigate the rupture envelopes, and (2) a second series with creep experiments. During the experiments, elastic wave velocities (P and S) were measured to infer crack density evolution. Permeability was also measured during creep experiments. Our results show two different mechanical behaviors: (1) brittle behavior is observed at low confining pressures, whereas (2) ductile behavior is observed at higher confining pressures. During creep experiments, these two behaviors have a different signature in term of elastic wave velocities and permeability changes, due to two different mechanisms: development of micro-cracks at low confining pressures and competition between cracks and microplasticity at high confining pressure. The attached figure is a summary of 20 triaxial experiments performed on Tavel limestone under different conditions. Stress states C',C* and C*' and brittle strength are shown in the P-Q space: (a) 20°C and dry

  20. Modeling and mesoscopic damage constitutive relation of brittle short-fiber-reinforced composites

    Institute of Scientific and Technical Information of China (English)

    刘洪秋; 梁乃刚; 夏蒙棼

    1999-01-01

    Aimed at brittle composites reinforced by randomly distributed short-fibers with a relatively large aspect ratio, stiffness modulus and strength, a mesoscopic material model was proposed. Based on the statistical description,damage mechanisms, damage-induced anisotropy, damage rate effect and stress redistribution, the constitutive relation were derived. By taking glass fiber reinforced polypropylene polymers as an example, the effect of initial orientation distribution of fibers, damage-induced anisotropy, and damage-rate effect on macro-behaviors of composites were quantitatively analyzed. The theoretical predictions compared favorably with the experimental results.

  1. Experiments of Brittle-Plastic Transition and Instability Modes of Juyongguan Granite at Different Temperatures and Pressures

    Institute of Scientific and Technical Information of China (English)

    Zhou Yongsheng; Jiang Haikun; He Changrong

    2003-01-01

    Three groups of experiments on brittle-plastic transition and instability modes of granite wereperformed in a triaxial vessel with solid pressure medium at high temperature and highpressure. The results of experiments show that brittle faulting is the major failure mode attemperature < 300℃, but crystal-plastic deformation is dominate at temperature > 800℃, andthere is a transition with increasing temperature from semi-brittle faulting to cataclnstic flowand semi-brittle flow at temperatures of 300 ~ 800℃. So, temperature is the most influentialfactor in brittle-plastic transition of granite and confining pressure is the second factor. Theresults also show that progressive failure of granite occurs at lower pressure or hightemperature where there is crystal plasticity, and sudden instability occurs at room temperatureand high pressure ( > 300MPa) or high temperature and great pressure(550℃600MPa ~ 650℃700MPa), and a broad regime of quasi-sudden instability exists between the T-P condition ofprogressive failure and sudden instability. So, instability modes of granite dependsimnitaneonsly on the pressure and temperature.

  2. Porosity evolution at the brittle-ductile transition in the continental crust: Implications for deep hydro-geothermal circulation.

    Science.gov (United States)

    Violay, M; Heap, M J; Acosta, M; Madonna, C

    2017-08-09

    Recently, projects have been proposed to engineer deep geothermal reservoirs in the ductile crust. To examine their feasibility, we performed high-temperature (up to 1000 °C), high-pressure (130 MPa) triaxial experiments on granite (initially-intact and shock-cooled samples) in which we measured the evolution of porosity during deformation. Mechanical data and post-mortem microstuctural characterisation (X-ray computed tomography and scanning electron microscopy) indicate that (1) the failure mode was brittle up to 900 °C (shear fracture formation) but ductile at 1000 °C (no strain localisation); (2) only deformation up to 800 °C was dilatant; (3) deformation at 900 °C was brittle but associated with net compaction due to an increase in the efficiency of crystal plastic processes; (4) ductile deformation at 1000 °C was compactant; (5) thermally-shocking the granite did not influence strength or failure mode. Our data show that, while brittle behaviour increases porosity, porosity loss is associated with both ductile behaviour and transitional behaviour as the failure mode evolves from brittle to ductile. Extrapolating our data to geological strain rates suggests that the brittle-ductile transition occurs at a temperature of 400 ± 100 °C, and is associated with the limit of fluid circulation in the deep continental crust.

  3. A New Method to Evaluate Rock Mass Brittleness Based on Stress-Strain Curves of Class I

    Science.gov (United States)

    Xia, Y. J.; Li, L. C.; Tang, C. A.; Li, X. Y.; Ma, S.; Li, M.

    2017-05-01

    Brittleness is a key controlling parameter for rock engineering projects such as hydrocarbon production and other applications. In this paper, commonly used methods based on stress-strain curves of Class I for the calculation of rock brittleness are reviewed. In order to describe the rock brittleness more reasonable, the new index B i was proposed based on the stress drop rate obtained from post-peak stress-strain curve and the ratio of elastic energy released during failure to the total energy stored before the peak strength. Then the validity of B i is verified with experimental tests conducted on rock specimens drilled from the interlayer and oil layer through a well of Shengli Oilfield. Moreover, numerical simulation is performed to analyze the effects of primary mechanical parameters on the brittleness of rock masses. Based on experimental tests and numerical simulation results, the acoustic emission modes influenced by brittleness index B i are summarized. At last, correlation between acoustic emission mechanism and index B i is verified by comparing the acoustic emission modes of limestone under different levels of confining pressure and various types of coal.

  4. Brittle Creep Failure, Critical Behavior, and Time-to-Failure Prediction of Concrete under Uniaxial Compression

    Directory of Open Access Journals (Sweden)

    Yingchong Wang

    2015-01-01

    Full Text Available Understanding the time-dependent brittle deformation behavior of concrete as a main building material is fundamental for the lifetime prediction and engineering design. Herein, we present the experimental measures of brittle creep failure, critical behavior, and the dependence of time-to-failure, on the secondary creep rate of concrete under sustained uniaxial compression. A complete evolution process of creep failure is achieved. Three typical creep stages are observed, including the primary (decelerating, secondary (steady state creep regime, and tertiary creep (accelerating creep stages. The time-to-failure shows sample-specificity although all samples exhibit a similar creep process. All specimens exhibit a critical power-law behavior with an exponent of −0.51 ± 0.06, approximately equal to the theoretical value of −1/2. All samples have a long-term secondary stage characterized by a constant strain rate that dominates the lifetime of a sample. The average creep rate expressed by the total creep strain over the lifetime (tf-t0 for each specimen shows a power-law dependence on the secondary creep rate with an exponent of −1. This could provide a clue to the prediction of the time-to-failure of concrete, based on the monitoring of the creep behavior at the steady stage.

  5. Pressure induced stiffening, thermal softening of bulk modulus and brittle nature of mercury chalcogenides

    Science.gov (United States)

    Varshney, Dinesh; Shriya, Swarna; Sapkale, Raju; Varshney, Meenu; Ameri, M.

    2015-07-01

    The pressure and temperature dependent elastic properties of mercury chalcogenides (HgX; X = S, Se and Te) with pressure induced structural transition from ZnS-type (B3) to NaCl-type (B1) structure have been analyzed within the framework of a model interionic interaction potential with long-range Coulomb and charge transfer interactions, short-range overlap repulsion and van der Waals (vdW) interactions as well as zero point energy effects. Emphasis is on the evaluation of the Bulk modulus with pressure and temperature dependency to yield the Poisson's ratio ν, the Pugh ratio ϕ, anisotropy parameter, Shear and Young's modulus, Lamé's constant, Klein man parameter, elastic wave velocity and Debye temperature. The Poisson's ratio behavior infers that HgX are brittle in nature. To our knowledge this is the first quantitative theoretical prediction of the pressure dependence of elastic and thermodynamical properties explicitly the ductile (brittle) nature of HgX and still awaits experimental confirmations.

  6. PREDICTION OF CHARACTERISTIC LENGTH AND FRACTURE TOUGHNESS IN DUCTILE-BRITTLE TRANSITION

    Energy Technology Data Exchange (ETDEWEB)

    Lam, P

    2008-04-15

    Finite element method was used to analyze the three-point bend experimental data of A533B-1 pressure vessel steel obtained by Sherry, Lidbury, and Beardsmore [1] from -160 to -45 C within the ductile-brittle transition regime. As many researchers have shown, the failure stress ({sigma}{sub f}) of the material could be approximated as a constant. The characteristic length, or the critical distance (r{sub c}) from the crack tip, at which {sigma}{sub f} is reached, is shown to be temperature dependent based on the crack tip stress field calculated by the finite element method. With the J-A{sub 2} two-parameter constraint theory in fracture mechanics, the fracture toughness (J{sub C} or K{sub JC}) can be expressed as a function of the constraint level (A{sub 2}) and the critical distance r{sub c}. This relationship is used to predict the fracture toughness of A533B-1 in the ductile-brittle transition regime with a constant {sigma}{sub f} and a set of temperature-dependent r{sub c}. It can be shown that the prediction agrees well with the test data for wide range of constraint levels from shallow cracks (a/W= 0.075) to deep cracks (a/W= 0.5), where a is the crack length and W is the specimen width.

  7. Electromagnetic and neutron emissions from brittle rocks failure: Experimental evidence and geological implications

    Indian Academy of Sciences (India)

    A Carpinteri; G Lacidogna; O Borla; A Manuello; G Niccolini

    2012-02-01

    It has been observed energy emission in the form of electromagnetic radiation, clearly indicating charge redistribution, and neutron bursts, necessarily involving nuclear reactions, during the failure process of quasi-brittle materials such as rocks, when subjected to compression tests. The material used is Luserna stone, which presents a very brittle behaviour during compression failure. The observed phenomenon of high-energy particle emission, i.e., electrons and neutrons, can be explained in the framework of the superradiance applied to the solid state, where individual atoms lose their identity and become part of different plasmas, electronic and nuclear. Since the analysed material contains iron, it can be conjectured that piezonuclear reactions involving fission of iron into aluminum, or into magnesium and silicon, should have occurred during compression damage and failure. These complex phenomenologies are confirmed by Energy Dispersive X-ray Spectroscopy (EDS) tests conducted on Luserna stone specimens, and found additional evidences at the Earth’s Crust scale, where electromagnetic and neutron emissions are observed just in correspondence with major earthquakes. In this context, the effects of piezonuclear reactions can be also considered from a geophysical and geological point of view.

  8. Brittle and Ductile Behavior in Deep-Seated Landslides: Learning from the Vajont Experience

    Science.gov (United States)

    Paronuzzi, Paolo; Bolla, Alberto; Rigo, Elia

    2016-06-01

    This paper analyzes the mechanical behavior of the unstable Mt. Toc slope before the 1963 catastrophic collapse, considering both the measured data (surface displacements and microseismicity) and the updated geological model of the prehistoric rockslide. From February 1960 up to 9 October 1963, the unstable mass behaved as a brittle-ductile `mechanical system,' characterized by remarkable microseismicity as well as by considerable surface displacements (up to 4-5 m). Recorded microshocks were the result of progressive rock fracturing of distinct resisting stiff parts made up of intact rock (indentations, undulations, and rock bridges). The main resisting stiff part was a large rock indentation located at the NE extremity of the unstable mass that acted as a mechanical constraint during the whole 1960-1963 period, inducing a progressive rototranslation toward the NE. This large constraint failed in autumn 1960, when an overall slope failure took place, as emphasized by the occurrence of the large perimetrical crack in the upper slope. In this circumstance, the collapse was inhibited by a reblocking phenomenon of the unstable mass that had been previously destabilized by the first reservoir filling. Progressive failure of localized intact rock parts progressively propagated westwards as a consequence of the two further filling-drawdown cycles of the reservoir (1962 and 1963). The characteristic brittle-ductile behavior of the Vajont landslide was made possible by the presence of a very thick (40-50 m) and highly deformable shear zone underlying the upper rigid rock mass (100-120 m thick).

  9. Modeling and analysis of ductility of brittle materials using indentation method

    Science.gov (United States)

    Sun, Guoyan; Lu, Zhe; Bai, Jianming; Yu, Fangsu

    2014-08-01

    Nowadays, many optical elements are fabricated by means of glass molding using hard and brittle inserts such as Silicon Carbide (SiC) and Silicon Nitride (Si3N4). However, for those hard-to-machine materials, the most feasible solution is still with ultra-precision grinding and following polishing. Hence, it is necessary and meaningful to study their plastic properties for the development of optical fabrication and ultra-precision manufacturing process. However, the conventional methods including compression test and indentation fracture mechanics are not sufficient to obtain the accurate parameters and still lack of reliable supporting of the machining process. To solve this problem, this paper presents a novel way to correlate the plastic properties to the indentation data using dimensional analysis for the two sorts of hard and brittle materials of SiC and Si3N4. Through integrating the data obtained by the indentation tests and the modeling method presented in this paper, stress-strain behavior, yield stress σy, yield strain epsilony and strain hardening exponent n could be determined. The processing performance of these two materials reflected by the above parameters are consistent with the conclusions drawing from the indentation crack development under varying loads during the indentation test, which verifies the effectiveness and feasibility of the presented modeling method.

  10. KrF excimer laser precision machining of hard and brittle ceramic biomaterials.

    Science.gov (United States)

    Huang, Yao-Xiong; Lu, Jian-Yi; Huang, Jin-Xia

    2014-06-01

    KrF excimer laser precision machining of porous hard-brittle ceramic biomaterials was studied to find a suitable way of machining the materials into various desired shapes and sizes without distorting their intrinsic structure and porosity. Calcium phosphate glass ceramics (CPGs) and hydroxyapatite (HA) were chosen for the study. It was found that KrF excimer laser can cut both CPGs and HA with high efficiency and precision. The ablation rates of CPGs and HA are respectively 0.081 µm/(pulse J cm(-2)) and 0.048 µm/(pulse  J cm(-2)), while their threshold fluences are individually 0.72 and 1.5 J cm(-2). The cutting quality (smoothness of the cut surface) is a function of laser repetition rate and cutting speed. The higher the repetition rate and lower the cutting speed, the better the cutting quality. A comparison between the cross sections of CPGs and HA cut using the excimer laser and using a conventional diamond cutting blade indicates that those cut by the excimer laser could retain their intrinsic porosity and geometry without distortion. In contrast, those cut by conventional machining had distorted geometry and most of their surface porosities were lost. Therefore, when cutting hard-brittle ceramic biomaterials to prepare scaffold and implant or when sectioning them for porosity evaluation, it is better to choose KrF excimer laser machining.

  11. Nano finish grinding of brittle materials using electrolytic in-process dressing (ELID) technique

    Indian Academy of Sciences (India)

    M Rahman; A Senthil Kumar; H S Lim; K Fatima

    2003-10-01

    Recent developments in grinding have opened up new avenues for finishing of hard and brittle materials with nano-surface finish, high tolerance and accuracy. Grinding with superabrasive wheels is an excellent way to produce ultraprecision surface finish. However, superabrasive diamond grits need higher bonding strength while grinding, which metal-bonded grinding wheels can offer. Truing and dressing of the wheels are major problems and they tend to glaze because of wheel loading. When grinding with superabrasive wheels, wheel loading can be avoided by dressing periodically to obtain continuous grinding. Electrolytic inprocess dressing (ELID) is the most suitable process for dressing metal-bonded grinding wheels during the grinding process. Nano-surface finish can be achieved only when chip removal is done at the atomic level. Recent developments of ductile mode machining of hard and brittle materials show that plastically deformed chip removal minimizes the subsurface damage of the workpiece. When chip deformation takes place in the ductile regime, a defect-free nano-surface is possible and it completely eliminates the polishing process. ELID is one of the processes used for atomic level metal removal and nano-surface finish. However, no proper and detailed studies have been carried out to clarify the fundamental characteristics for making this process a robust one. Consequently, an attempt has been made in this study to understand the fundamental characteristics of ELID grinding and their influence on surface finish.

  12. Research on Ultrasonic Vibration Grinding of the Hard and Brittle Materials

    Institute of Scientific and Technical Information of China (English)

    YANG Xin-hong; HAN Jie-cai; ZHANG Yu-min; ZUO Hong-bo; ZHANG Xue-jun

    2006-01-01

    It is well known that grinding techniques are main methods to machine hard and brittle materials such as engineering ceramics. But the conventional grinding has many shortcomings such as poorer surface finish, quicker wear and tear of grinding tools, lower efficiency and so on. Ultrasonic vibration grinding (UVG) which combines ultrasonic machining and grinding emerged as a developing and promising technique in recent years. In this paper, experimental studies on UVG were conducted on several kinds of hard and brittle material by altering processing parameters such as vibration frequency and its amplitude, diamond abrasive grit size, cutting depth, feeding speed and rotary speed of tools. The experimental results show that alteration in any of above mentioned parameters will bring effects on the processed surface finish of these materials. Of them, the diamond abrasive grit size has the greatest. Moreover, conventional grinding experiments were also carried out on these materials. By comparison, it was found that the UVG is superior to the conventional method in terms of the ground surface quality, the working efficiency and the wear rate of tools.

  13. Life Predicted in a Probabilistic Design Space for Brittle Materials With Transient Loads

    Science.gov (United States)

    Nemeth, Noel N.; Palfi, Tamas; Reh, Stefan

    2005-01-01

    Analytical techniques have progressively become more sophisticated, and now we can consider the probabilistic nature of the entire space of random input variables on the lifetime reliability of brittle structures. This was demonstrated with NASA s CARES/Life (Ceramic Analysis and Reliability Evaluation of Structures/Life) code combined with the commercially available ANSYS/Probabilistic Design System (ANSYS/PDS), a probabilistic analysis tool that is an integral part of the ANSYS finite-element analysis program. ANSYS/PDS allows probabilistic loads, component geometry, and material properties to be considered in the finite-element analysis. CARES/Life predicts the time dependent probability of failure of brittle material structures under generalized thermomechanical loading--such as that found in a turbine engine hot-section. Glenn researchers coupled ANSYS/PDS with CARES/Life to assess the effects of the stochastic variables of component geometry, loading, and material properties on the predicted life of the component for fully transient thermomechanical loading and cyclic loading.

  14. Micromechanics of rock damage: Advances in the quasi-brittle field

    Directory of Open Access Journals (Sweden)

    Qizhi Zhu

    2017-02-01

    Full Text Available Constitutive models play an essential role in numerical modeling and simulation of nonlinear deformation, progressive damage and failure of rock-like materials and structures. Recent advances in the quasi-brittle field show that upscaling methods by homogenization have provided a new efficient way to derive macroscopic formulations of rocks from their microstructure information and local properties and then to model nonlinear mechanical behaviors identified at laboratory. This paper aims first at relating the mechanical phenomena on sample scale to their respective mechanisms on microscale. Main focus is put on unilateral effects due to crack's opening/closure transition, material anisotropy induced by crack growth in some preferred directions and multiphysical coupling at microcracks. After a brief introduction to the linear homogenization method and its application to crack problems, we present some recent advances achieved in the combined homogenization/thermodynamics framework, including anisotropic unilateral damage-friction coupling, theoretical failure prediction in conjunction with deformation analyses, poromechanical coupling, analytical solutions and numerical implementation with application to typical brittle rocks.

  15. Crack deflection in brittle media with heterogeneous interfaces and its application in shale fracking

    Science.gov (United States)

    Zeng, Xiaguang; Wei, Yujie

    Driven by the rapid progress in exploiting unconventional energy resources such as shale gas, there is growing interest in hydraulic fracture of brittle yet heterogeneous shales. In particular, how hydraulic cracks interact with natural weak zones in sedimentary rocks to form permeable cracking networks is of significance in engineering practice. Such a process is typically influenced by crack deflection, material anisotropy, crack-surface friction, crustal stresses, and so on. In this work, we extend the He-Hutchinson theory (He and Hutchinson, 1989) to give the closed-form formulae of the strain energy release rate of a hydraulic crack with arbitrary angles with respect to the crustal stress. The critical conditions in which the hydraulic crack deflects into weak interfaces and exhibits a dependence on crack-surface friction and crustal stress anisotropy are given in explicit formulae. We reveal analytically that, with increasing pressure, hydraulic fracture in shales may sequentially undergo friction locking, mode II fracture, and mixed mode fracture. Mode II fracture dominates the hydraulic fracturing process and the impinging angle between the hydraulic crack and the weak interface is the determining factor that accounts for crack deflection; the lower friction coefficient between cracked planes and the greater crustal stress difference favor hydraulic fracturing. In addition to shale fracking, the analytical solution of crack deflection could be used in failure analysis of other brittle media.

  16. Visco-poroelastic damage model for brittle-ductile failure of porous rocks

    Science.gov (United States)

    Lyakhovsky, Vladimir; Zhu, Wenlu; Shalev, Eyal

    2015-04-01

    The coupling between damage accumulation, dilation, and compaction during loading of sandstones is responsible for different structural features such as localized deformation bands and homogeneous inelastic deformation. We distinguish and quantify the role of each deformation mechanism using new mathematical model and its numerical implementation. Formulation includes three different deformation regimes: (I) quasi-elastic deformation characterized by material strengthening and compaction; (II) cataclastic flow characterized by damage increase and compaction; and (III) brittle failure characterized by damage increase, dilation, and shear localization. Using a three-dimensional numerical model, we simulate the deformation behavior of cylindrical porous Berea sandstone samples under different confining pressures. The obtained stress, strain, porosity changes and macroscopic deformation features well reproduce the laboratory results. The model predicts different rock behavior as a function of confining pressures. The quasi-elastic and brittle regimes associated with formation of shear and/or dilatant bands occur at low effective pressures. The model also successfully reproduces cataclastic flow and homogeneous compaction under high pressures. Complex behavior with overlap of common features of all regimes is simulated under intermediate pressures, resulting with localized compaction or shear enhanced compaction bands. Numerical results elucidate three steps in the formation of compaction bands: (1) dilation and subsequent shear localization, (2) formation of shear enhanced compaction band, and (3) formation of pure compaction band.

  17. Analytical and numerical analysis of frictional damage in quasi brittle materials

    Science.gov (United States)

    Zhu, Q. Z.; Zhao, L. Y.; Shao, J. F.

    2016-07-01

    Frictional sliding and crack growth are two main dissipation processes in quasi brittle materials. The frictional sliding along closed cracks is the origin of macroscopic plastic deformation while the crack growth induces a material damage. The main difficulty of modeling is to consider the inherent coupling between these two processes. Various models and associated numerical algorithms have been proposed. But there are so far no analytical solutions even for simple loading paths for the validation of such algorithms. In this paper, we first present a micro-mechanical model taking into account the damage-friction coupling for a large class of quasi brittle materials. The model is formulated by combining a linear homogenization procedure with the Mori-Tanaka scheme and the irreversible thermodynamics framework. As an original contribution, a series of analytical solutions of stress-strain relations are developed for various loading paths. Based on the micro-mechanical model, two numerical integration algorithms are exploited. The first one involves a coupled friction/damage correction scheme, which is consistent with the coupling nature of the constitutive model. The second one contains a friction/damage decoupling scheme with two consecutive steps: the friction correction followed by the damage correction. With the analytical solutions as reference results, the two algorithms are assessed through a series of numerical tests. It is found that the decoupling correction scheme is efficient to guarantee a systematic numerical convergence.

  18. An Improved Approach to Fracture Toughness Assessment of Brittle Coating on Ductile Substrate Systems under Indentation

    Science.gov (United States)

    Demidova, Natalia V.

    Fracture toughness is an important material property that determines the structural integrity of a component with pre-existing or service-generated flaws. In the present research, an indentation-based method and the associated fracture mechanics model are proposed for fracture toughness assessment of brittle coating/ductile substrate systems. The proposed models consider well-developed radial/median cracks generated under sharp indentation, despite that the crack formation process may have gone through crack initiation and propagation phases. For generality, the geometry of a well-developed crack is assumed to be semi-elliptical in shape. The driving force of the crack is considered to stem from the residual plastic zone expansion under the indenter, as well as the far-field Boussinesq (elastic) stress. Three well-defined configurations are studied. For the first configuration, a crack with a depth of less than 7% of the coating thickness is considered. In this case, the problem is treated as the one for the monolithic material with the coating material properties. For the second configuration, a crack that runs deeper than 7% of the coating thickness but is still within the coating layer is analyzed. In this case, the composite hardness is introduced into the analysis to account for the influence of the substrate material properties; and furthermore, an interface correction factor is proposed to take into account the presence of the coating/substrate interface and its influence on the stress intensity factor of the well-developed elliptical cracks. For the third configuration, a crack penetrating into the substrate is considered. In this case, based on the condition of deformation compatibility across the coating/substrate interface, the bulk modulus for the coating/substrate system is introduced into the analysis. A series of indentation tests are conducted on a WC/10Co/4Cr coating/1080 low carbon steel substrate specimen, which is a brittle coating on a ductile

  19. The control of brittleness and development of desirable mechanical properties in polycrystalline systems by grain boundary engineering

    Energy Technology Data Exchange (ETDEWEB)

    Watanabe, Tadao; Tsurekawa, Sadahiro

    1999-11-12

    Grain boundaries can be effectively controlled to produce or enhance their beneficial effects and also to diminish or reduce their detrimental effects on bulk properties in polycrystalline materials. Particular attention has been paid to the control of intergranular brittleness which remains a serious problem of material processing and development. Recent studies are presented and discussed, which have been successfully performed to control intergranular brittleness of intrinsically brittle materials such as the refractory metal molybdenum and the ordered intermetallic alloy Ni{sub 3}Al and to produce superplasticity in an Al-Li alloy, by grain boundary engineering through controlling a new microstructural factor termed the grain boundary character distribution (GBCD). The optimization of GBCD and the grain boundary connectivity has been found to be a key to produce desirable bulk mechanical properties in both structural and functional polycrystalline materials.

  20. Mixed brittle-plastic deformation behaviour in a slate belt. Examples from the High-Ardenne slate belt (Belgium, Germany)

    Science.gov (United States)

    Sintubin, Manuel; van Baelen, Hervé; van Noten, Koen; Muchez, Philippe

    2010-05-01

    In the High-Ardenne slate belt, part of the Rhenohercynian external fold-and-thrust belt at the northern extremity of the Late Palaeozoic Variscan orogen (Belgium, Germany, France), particular quartz vein occurrences can be observed in predominantly fine-grained siliciclastic metasediments. Detailed structural, petrographical and geochemical studies has revealed that these vein occurrences can be related to a mixed brittle-plastic deformation behaviour in a low-grade metamorphic mid-crustal environment. The first type of quartz veins are bedding-perpendicular, lens-shaped extension veins that are confined to the sandstone layers within the multilayer sequence. Fluid inclusion studies demonstrate high fluid pressures suggesting that the individual sandstone bodies acted as isolated high-pressure compartments in an overpressured basin. Hydraulic fracturing occurred during the tectonic inversion (from extension to compression) in the earliest stages of the Variscan orogeny. The vein fill shows a blocky character indicating crystal growth in open cavities. Both the typical lens shape of the veins and the subsequent cuspate-lobate folding of the bed interfaces in between the quartz veins suggest plastic deformation of cohesionless fluid-filled fissures. Metamorphic grade of the host rock and fluid temperature and pressure clearly indicates mid-crustal conditions below the brittle-plastic transition. This first type of quartz veins exemplifies mixed brittle-plastic deformation behaviour, possibly related to a transient deepening of the brittle-plastic transition. This is in contrast with contemporaneous bedding-perpendicular crack-seal veins observed in higher - upper-crustal - structural levels in the slate belt, reflecting pure brittle deformation behaviour. The second type are discordant quartz veins confined to extensional low-angle detachment shear zones. These very irregular veins transect a pre-existing pervasive cleavage fabric. They show no matching walls and

  1. Estimation of brittle fracture behavior of SA508 carbon steel by considering temperature dependence of damage model

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Shin Beom; Jeong, Jae Uk; Choi, Jae Boong [Sungkyunkwan Univ., Seoul (Korea, Republic of); Chang, Yoon Suk [Kyunghee Univ., Seoul (Korea, Republic of); Kim, Min Chul [Korea Institute of Nuclear Safety, Daejeon (Korea, Republic of); Lee, Bong Sang [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2012-05-15

    The aim of this study was to determine the brittle fracture behavior of reactor pressure vessel steel by considering the temperature dependence of a damage model. A multi island genetic algorithm was linked to a Weibull stress model, which is the model typically used for brittle fracture evaluation, to improve the calibration procedure. The improved calibration procedure and fracture toughness test data for SA508 carbon steel at the temperatures -60 .deg. C, -80 .deg. C, and -100 .deg. C were used to decide the damage parameters required for the brittle fracture evaluation. The model was found to show temperature dependence, similar to the case of NUREG/CR 6930. Finally, on the basis of the quantification of the difference between 2- and 3-parameter Weibull stress models, an engineering equation that can help obtain more realistic fracture behavior by using the simpler 2-parameter Weibull stress model was proposed.

  2. Ultraprecision, high stiffness CNC grinding machines for ductile mode grinding of brittle materials

    Science.gov (United States)

    McKeown, Patrick A.; Carlisle, Keith; Shore, Paul; Read, R. F.

    1990-10-01

    Under certain controlled conditions it is now possible to machine brittle materials such as glasses and ceramics using single or multi-point diamond tools (grinding), so that material is removed by plastic flow, leaving crack-free surfaces. This process is called 'shear' or 'ductile' mode grinding. It represents a major breakthrough in modern manufacturing engineering since it promises to enable: - complex optical components, both transmission and reflecting to be generated by advanced CNC machines with very little (or even zero) subsequent polishing. - complex shaped components such as turbine blades, nozzle guide vanes, etc. to be finish machined after near net shape forming, to high precision in advanced ceramics such as silicon nitride, without inducing micro-cracking and thus lowering ultimate rupture strength and fatigue life. Ductile mode "damage free" grinding occurs when the volume of materials stressed by each grit of the grinding wheel is small enough to yield rather than exhibit brittle fracture, i.e. cracking. In practice, this means maintaining the undeformed chip thickness to below the ductile-brittle transition value; this varies from material to material but is generally in the order of 0.1 pm or 100 nm, (hence the term "nanogrinding" is sometimes used) . Thus the critical factors for operating successfully in the ductile regime are machine system accuracy and dynamic stiffness between each grit and the workpiece. In detail this means: (i) High precision 'truing' of the diamond grits, together with dressing of the wheel bond to ensure adequate ' openness'; (ii) Design and build of the grinding wheel spindle with very high dynamic stiffness; error motions, radial and axial, must be considerably less than 100 nfl. (iii) Design and build of the workpiece carriage motion system with very high dynamic stiffness; error motions, linear or rotary, must be well within 100 nm. (iv) Smooth, rumble-free, high-stiffness servo-drives controlling the motions

  3. Slip transfer across fault discontinuities within granitic rock at the brittle-ductile transition

    Science.gov (United States)

    Nevitt, J. M.; Pollard, D. D.; Warren, J. M.

    2011-12-01

    Fault mechanics are strongly influenced by discontinuities in fault geometry and constitutive differences between the brittle and ductile regions of the lithosphere. This project uses field observations, laboratory analysis and numerical modeling to investigate deformational processes within a contractional step at the brittle-ductile transition, and in particular, how slip is transferred between faults via ductile deformation across the step. The Bear Creek field area (central Sierra Nevada, CA) is comprised of late Cretaceous biotite-hornblende granodiorite and experienced a period of faulting at the brittle-ductile transition. Abundant echelon faults in Bear Creek, some of which were seismically active, provide many textbook examples of contractional steps, which are characterized by well-developed ductile fabrics. The occurrence of hydrothermal alteration halos and hydrothermal minerals in fracture fill documents the presence of water, which we suggest played a weakening role in the constitutive behavior of the granodiorite. Furthermore, the mechanism that accomplishes slip transfer in contractional steps appears to be related to water-enhanced ductile deformation. We focus our investigation on Outcrop SG10, which features a 10cm thick aplite dike that is offset 0.45m through a contractional step between two sub-parallel left-lateral faults. Within the step, the aplite undergoes dramatic thinning (stretch ~1/10) and the granodiorite is characterized by a well-developed mylonitic foliation, in which quartz and biotite plastically flow around larger grains of feldspars, hornblende and opaque minerals. Electron backscatter diffraction (EBSD) analysis gives a more quantitative depiction of the active micromechanics and reveals how slip is accommodated at the crystal scale throughout the step. We use Abaqus, a commercial finite element software, to test several constitutive laws that may account for the deformation observed both macro- and microscopically throughout

  4. Capsules with evolving brittleness to resist the preparation of self-healing concrete

    Directory of Open Access Journals (Sweden)

    Gruyaert, E.

    2016-09-01

    Full Text Available Capsules for self-healing concrete have to possess multifunctional properties and it would be an enormous advantage in the valorization process when they could also be mixed in. Therefore, we aimed to develop capsules with evolving brittleness. Capsules with high initial flexibility were prepared by adding a plasticizer to an ethyl cellulose matrix. During hardening of the concrete, the plasticizing agent should leach out to the moist environment yielding more brittle capsules which break upon crack appearance. The tested capsules could easily be mixed in during concrete production. However, incompatibility issues between the capsule wall and the inner polymeric healing agent appeared. Moreover, the capsules became insufficiently brittle and the bond strength to the cementitious matrix was too weak. Consequently, multilayer capsules were tested. These capsules had a high impact resistance to endure concrete mixing and were able to break upon crack formation.Las cápsulas para la auto-reparación del hormigón tienen que poseer propiedades multifuncionales. Una enorme ventaja en el proceso para su valorización se obtendría si aquellas pudieran resistir con éxito el mezclado. Por lo tanto, nos propusimos desarrollar cápsulas cuya fragilidad evoluciona. Cápsulas con una alta flexibilidad inicial se prepararon mediante la adición de un plastificante a una matriz de etil celulosa. Durante el endurecimiento del hormigón, el agente plastificante debe filtrarse hacia el medio ambiente húmedo produciendo cápsulas más frágiles que se rompen con el surgimiento de fisuras. Las cápsulas pudieron ser fácilmente mezcladas durante la producción de hormigón. Sin embargo, aparecieron problemas de incompatibilidad entre la pared de la cápsula y el agente de curación polimérico interior. Por otra parte, las cápsulas se comportaron insuficientemente frágiles y con una baja adherencia hacia la matriz cementicia. En consecuencia, se probaron las c

  5. De Novo Adult Transcriptomes of Two European Brittle Stars: Spotlight on Opsin-Based Photoreception.

    Directory of Open Access Journals (Sweden)

    Jérôme Delroisse

    Full Text Available Next generation sequencing (NGS technology allows to obtain a deeper and more complete view of transcriptomes. For non-model or emerging model marine organisms, NGS technologies offer a great opportunity for rapid access to genetic information. In this study, paired-end Illumina HiSeqTM technology has been employed to analyse transcriptomes from the arm tissues of two European brittle star species, Amphiura filiformis and Ophiopsila aranea. About 48 million Illumina reads were generated and 136,387 total unigenes were predicted from A. filiformis arm tissues. For O. aranea arm tissues, about 47 million reads were generated and 123,324 total unigenes were obtained. Twenty-four percent of the total unigenes from A. filiformis show significant matches with sequences present in reference online databases, whereas, for O. aranea, this percentage amounts to 23%. In both species, around 50% of the predicted annotated unigenes were significantly similar to transcripts from the purple sea urchin, the closest species to date that has undergone complete genome sequencing and annotation. GO, COG and KEGG analyses were performed on predicted brittle star unigenes. We focused our analyses on the phototransduction actors involved in light perception. Firstly, two new echinoderm opsins were identified in O. aranea: one rhabdomeric opsin (homologous to vertebrate melanopsin and one RGR opsin. The RGR-opsin is supposed to be involved in retinal regeneration while the r-opsin is suspected to play a role in visual-like behaviour. Secondly, potential phototransduction actors were identified in both transcriptomes using the fly (rhabdomeric and mammal (ciliary classical phototransduction pathways as references. Finally, the sensitivity of O.aranea to monochromatic light was investigated to complement data available for A. filiformis. The presence of microlens-like structures at the surface of dorsal arm plate of O. aranea could potentially explain phototactic

  6. Understanding ductile-to-brittle transition of metallic glasses from shear transformation zone dilatation

    Directory of Open Access Journals (Sweden)

    M.Q. Jiang

    2015-08-01

    Full Text Available A theoretical model that takes into account the free-volume aided cooperative shearing of shear transformation zones (STZs is developed to quantitatively understand the ductile-to-brittle transition (DBT of metallic glasses. The STZ dilatational strain is defined as the ratio of STZ-activated free volume to STZ volume itself. The model demonstrates that the STZ dilatational strain will increase drastically and exceed the characteristic shear strain of STZ as temperature decreases below a critical value. This critical temperature is in good agreement with the experimentally measured DBT temperature. Our results suggest that the DBT of metallic glasses is underpinned by the transition of atomic-cluster motions from STZ-type rearrangements to dilatational processes (termed tension transformation zones (TTZs.

  7. Fracture Testing at Small-Length Scales: From Plasticity in Si to Brittleness in Pt

    Science.gov (United States)

    Jaya, B. Nagamani; Jayaram, Vikram

    2016-01-01

    The field of micro-/nano-mechanics of materials has been driven, on the one hand by the development of ever smaller structures in devices, and, on the other, by the need to map property variations in large systems that are microstructurally graded. Observations of `smaller is stronger' have also brought in questions of accompanying fracture property changes in the materials. In the wake of scattered articles on micro-scale fracture testing of various material classes, this review attempts to provide a holistic picture of the current state of the art. In the process, various reliable micro-scale geometries are shown, challenges with respect to instrumentation to probe ever smaller length scales are discussed and examples from recent literature are put together to exhibit the expanse of unusual fracture response of materials, from ductility in Si to brittleness in Pt. Outstanding issues related to fracture mechanics of small structures are critically examined for plausible solutions.

  8. A dimensional analysis approach to fatigue in quasi-brittle materials

    Directory of Open Access Journals (Sweden)

    Marco Paggi

    2009-10-01

    Full Text Available In this study, a generalized Barenblatt and Botvina dimensional analysis approach to fatigue crack growth is proposed in order to highlight and explain the deviations from the classical power-law equations used to characterize the fatigue behaviour of quasi-brittle materials. According to this theoretical approach, the microstructural-size (related to the volumetric content of fibres in fibre-reinforced concrete, the crack-size, and the size-scale effects on the Paris’ law and the Wöhler equation are presented within a unified mathematical framework. Relevant experimental results taken from the literature are used to confirm the theoretical trends and to determine the values of the incomplete self-similarity exponents. All these information are expected to be useful for the design of experiments, since the role of the different dimensionless numbers governing the phenomenon of fatigue is herein elucidated.

  9. Successful Treatment of Brittle Diabetes Following Total Pancreatectomy by Islet Allotransplantation: A Case Report

    Directory of Open Access Journals (Sweden)

    Angela Koh

    2013-07-01

    Full Text Available Context Allotransplantation of islets can successfully treat subjects with type 1 diabetes complicated by severehypoglycemia and erratic glycemic control. Insulin independence is often lost over time due to several factors, includingrecurrent autoimmunity. Brittle diabetes (frequent hypoglycemia and labile glycemic control is common afterpancreatectomy. This is ameliorated by auto-islet transplantation in pancreatectomized patients who have better glycemiccontrol, even without insulin independence. Case report We herein report a case where islet allotransplantation was carriedout in a patient who had undergone total pancreatectomy. Following two islet infusions, he became insulin independent withexcellent glycemic control and remains so currently, more than four years after his second islet infusion. Side effects fromimmunosuppressive therapy were minimal. Discussion Islet allotransplantation can be considered in selected individualspost-pancreatectomy. The absence of autoimmunity may be advantageous for long term graft function relative to isletallotransplantation in type 1 diabetic recipients.

  10. The Pore Collapse “Hot-Spots” Model Coupled with Brittle Damage for Solid Explosives

    Directory of Open Access Journals (Sweden)

    L. R. Cheng

    2014-01-01

    Full Text Available This paper is devoted to the building of a numerical pore collapse model with “hot-spots” formation for the impacted damage explosives. According to damage mechanical evolution of brittle material, the one-dimensional elastic-viscoplastic collapse model was improved to incorporate the impact damage during the dynamic collapse of pores. The damage of explosives was studied using the statistical crack mechanics (SCRAM. The effects of the heat conduction and the chemical reaction were taken into account in the formation of “hot-spots.” To verify the improved model, numerical simulations were carried out for different pressure states and used to model a multiple-impact experiment. The results show that repeated weak impacts can lead to the collapse of pores and the “hot-spots” may occur due to the accumulation of internal defects accompanied by the softening of explosives.

  11. Nucleating and propagating of nanocrack in dislocation-free zone in brittle materials

    Institute of Scientific and Technical Information of China (English)

    褚武扬; 高克玮; 陈奇志; 王燕斌; 肖纪美

    1995-01-01

    Nudeating and propagating of nanocrack forming in dislocation-free zone (DFZ) for a brittle material, TiAl alloy, was studied through in situ tensile test in TEM and analyzed using micro-fracture mechanics. The results show that many of dislocations can be emitted from a crack tip when the applied stress intensity KIa is larger than the stress intensity for dislocation emission KIe = 1.4MPa·m1/2 and a DFZ is formed after reaching equilibrium. The stress in a certain site in the DFZ, which is an elastic zone and is thinned gradually through dislocation multiplication and motion in the plastic zone, may be equal to the cohesive strength, resulting in initiating of a nanocrack in the DFZ or sometimes at the notch tip. The nanocrack forming in the DFZ is stable and can propagate into a cleavage microcrack through multiplication and movement of dislocations in the plastic zone under constant displacement condition.

  12. A MIXED MODE FRACTURE CRITERION BASED ON THE MAXIMUM TANGENTIAL STRESS IN BRITTLE INCLUSION

    Institute of Scientific and Technical Information of China (English)

    Ji Changjiang; Li Zhonghua; Sun Jun

    2005-01-01

    A closed-form solution for predicting the tangential stress of an inclusion located in mixed mode Ⅰ and Ⅱ crack tip field was developed based on the Eshelby equivalent inclusion theory. Then a mixed mode fracture criterion, including the fracture direction and the critical load, was established based on the maximum tangential stress in the inclusion for brittle inclusioninduced fracture materials. The proposed fracture criterion is a function of the inclusion fracture stress, its size and volume fraction, as well as the elastic constants of the inclusion and the matrix material. The present criterion will reduce to the conventional one as the inclusion having the same elastic behavior as the matrix material. The proposed solutions are in good agreement with detailed finite element analysis and measurement.

  13. Brittle-ductile behavior of a nanocrack in nanocrystalline Ni: A quasicontinuum study

    Institute of Scientific and Technical Information of China (English)

    Shao Yu-Fei; Yang Xin; Zhao Xing; Wang Shao-Qing

    2012-01-01

    The effects of stacking fault energy,unstable stacking fault energy,and unstable twinning fault energy on the fracture behavior of nanocrystalline Ni are studied via quasicontinuum simulations.Two semi-empirical potentials for Ni are used to vary the values of these generalized planar fault energies.When the above three energies are reduced,a brittle-to-ductile transition of the fracture behavior is observed.In the model with higher generalized planar fault energies,a nanocrack proceeds along a grain boundary,while in the model with lower energies,the tip of the nanocrack becomes blunt.A greater twinning tendency is also observed in the more ductile model.These results indicate that the fracture toughness of nanocrystalline face-centered-cubic metals and alloys might be efficiently improved by controlling the generalized planar fault energies.

  14. Morphological study of elastic-plastic-brittle transitions in disordered media

    Science.gov (United States)

    Kale, Sohan; Ostoja-Starzewski, Martin

    2014-10-01

    We use a spring lattice model with springs following a bilinear elastoplastic-brittle constitutive behavior with spatial disorder in the yield and failure thresholds to study patterns of plasticity and damage evolution. The elastic-perfectly plastic transition is observed to follow percolation scaling with the correlation length critical exponent ν ≈1.59 , implying the universality class corresponding to the long-range correlated percolation. A quantitative analysis of the plastic strain accumulation reveals a dipolar anisotropy (for antiplane loading) which vanishes with increasing hardening modulus. A parametric study with hardening modulus and ductility controlled through the spring level constitutive response demonstrates a wide spectrum of behaviors with varying degree of coupling between plasticity and damage evolution.

  15. Stability and roughness of crack paths in 2D heterogeneous brittle materials

    Science.gov (United States)

    Katzav, Eytan; Adda-Bedia, Mokhtar; Derrida, Bernard

    2007-03-01

    We present a recent study on the stability of propagating cracks in heterogeneous two-dimensional brittle materials and on the roughness of the surfaces created by this irreversible process. We introduce a stochastic model describing the propagation of the crack tip based on an elastostatic description of crack growth in the framework of linear elastic fracture mechanics. The model recovers the stability of straight cracks and allows for the study of the roughening of fracture surfaces. We show that in a certain limit, the problem becomes exactly solvable and yields analytic predictions for the power spectrum of the paths. This result suggests a surprising alternative to the conventional power law analysis often used in the analysis of experimental data and thus calls for a revised interpretation of the experimental results.

  16. Phase-Transformation Ductilization of Brittle High-Entropy Alloys via Metastability Engineering.

    Science.gov (United States)

    Huang, Hailong; Wu, Yuan; He, Junyang; Wang, Hui; Liu, Xiongjun; An, Ke; Wu, Wei; Lu, Zhaoping

    2017-08-01

    High-entropy alloys (HEAs) in which interesting physical, chemical, and structural properties are being continuously revealed have recently attracted extensive attention. Body-centered cubic (bcc) HEAs, particularly those based on refractory elements are promising for high-temperature application but generally fail by early cracking with limited plasticity at room temperature, which limits their malleability and widespread uses. Here, the "metastability-engineering" strategy is exploited in brittle bcc HEAs via tailoring the stability of the constituent phases, and transformation-induced ductility and work-hardening capability are successfully achieved. This not only sheds new insights on the development of HEAs with excellent combination of strength and ductility, but also has great implications on overcoming the long-standing strength-ductility tradeoff of metallic materials in general. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Volume Change of Heterogeneous Quasi-brittle Materials in Uniaxial Compression

    Institute of Scientific and Technical Information of China (English)

    WANG Xuebin

    2006-01-01

    The volumetric strain was categorized into elastic and plastic parts. The former composed of axial and lateral strains is uniform and determined by Hooke's law; however, the latter consisting of axial and lateral strains is a function of thickness of shear band determined by gradient-dependent plasticity by considering the heterogeneity of quasi-brittle materials. The non-uniform lateral strain due to the fact that shear band was formed in the middle of specimen was averaged within specimen to precisely assess the volumetric strain. Then, the analytical expression for volumetric strain was verified by comparison with two earlier experimental results for concrete and rock. Finally, a detailed parametric study was carried out to investigate effects of constitutive parameters (shear band thickness, elastic and softening moduli) and geometrical size of specimen(height and width of specimen) on the volume dilatancy.

  18. Generalized Continuum: from Voigt to the Modeling of Quasi-Brittle Materials

    Directory of Open Access Journals (Sweden)

    Jamile Salim Fuina

    2010-12-01

    Full Text Available This article discusses the use of the generalized continuum theories to incorporate the effects of the microstructure in the nonlinear finite element analysis of quasi-brittle materials and, thus, to solve mesh dependency problems. A description of the problem called numerically induced strain localization, often found in Finite Element Method material non-linear analysis, is presented. A brief historic about the Generalized Continuum Mechanics based models is presented, since the initial work of Voigt (1887 until the more recent studies. By analyzing these models, it is observed that the Cosserat and microstretch approaches are particular cases of a general formulation that describes the micromorphic continuum. After reporting attempts to incorporate the material microstructure in Classical Continuum Mechanics based models, the article shows the recent tendency of doing it according to assumptions of the Generalized Continuum Mechanics. Finally, it presents numerical results which enable to characterize this tendency as a promising way to solve the problem.

  19. Displacement Forecasting Method in Brittle Crack Surrounding Rock Under Excavation Unloading Incorporating Opening Deformation

    Science.gov (United States)

    Li, X. J.; Yang, W. M.; Wang, L. G.; Butler, I. B.

    2014-11-01

    Splitting failure, which is recognized as a special engineering geology phenomenon, occurs continually in the brittle rock mass of caverns during underground excavation. In this paper, a splitting model of linear slippage crack groups is built with fracture mechanics, energy analysis, and crack extension theories. Considering intrinsic cracks in rock mass and change of outer stress, intrinsic cracks propagate into macroscopical splitting cracks that are approximately parallel to the side wall of caverns. The splitting criterion of cavern rock mass and the method for predicting displacement in view of splitting opening displacement are proposed. In the end, the forecasting method is applied to the Jinping-I Hydropower Station, underground caverns engineering in China, the splitting failure zone and forecasting displacement are accordant with the monitoring data. The new forecasting displacement method is proven to contribute to the construction of similar underground caverns.

  20. Brittle Cornea Syndrome Associated with a Missense Mutation in the Zinc-Finger 469 Gene

    DEFF Research Database (Denmark)

    Christensen, Anne Elisabeth; Knappskog, Per Morten; Midtbø, Marit

    2010-01-01

    Purpose: To investigate the diverse clinical manifestations, identify the causative mutation and explain the association with red hair in a family with brittle cornea syndrome (BCS). Methods: Eight family members in three generations underwent ophthalmic, dental, and general medical examination......, dental anomalies, hearing loss and minor cardiac defects. The morphologies of the skin biopsies were normal except that in some areas slightly thinner collagen fibrils were seen in one of the affected individuals. Molecular genetic analysis revealed a novel missense mutation of ZNF469, c.10016G....... Reduced BMD and atypical dental crown morphology have not been reported previously. We confirm that BCS is associated with mutations in ZNF469. The association with red hair in some individuals with BCS is likely to occur by chance....

  1. MAGNETIC STRIPS TO SIMULATE LAYERED BRITTLE SOLIDS IN CLEAVAGE AND FRACTURE EXPERIMENTS

    Institute of Scientific and Technical Information of China (English)

    Francisco G.Emmerich; Alfredo G.Cunha; Carlos M.A.Girelli; Arnobio I.Vassem

    2008-01-01

    A characteristic of the fracture and cleavage experiments is that they are usually intrinsically destructive.Cracks do not completely heal in an unstressed system,even in crystals such as mica.Here,we used magnetic solids composed of magnetic strips for the non-destructive cleavage and brittle fracture experiments.Between the magnetic strips materials with different mechanical characteristics can be inserted,such as Teflon or foam strips,to change the mechanical properties of the solid.For the cleavage experiments,we developed an apparatus where parameters such as the main involved force can be measured easily.By inserting flaws,the magnetic solid can be used in dynamic fracture experiments,with the advantages of simulating macroscopically a non-destructive experiment in an easier way,that happen in real materials with much higher velocities.The apparatus and the used magnetic solid may be useful for demonstrations of fractures in classes.

  2. Cracks in random brittle solids:. From fiber bundles to continuum mechanics

    Science.gov (United States)

    Patinet, S.; Vandembroucq, D.; Hansen, A.; Roux, S.

    2014-10-01

    Statistical models are essential to get a better understanding of the role of disorder in brittle disordered solids. Fiber bundle models play a special role as a paradigm, with a very good balance of simplicity and non-trivial effects. We introduce here a variant of the fiber bundle model where the load is transferred among the fibers through a very compliant membrane. This Soft Membrane fiber bundle mode reduces to the classical Local Load Sharing fiber bundle model in 1D. Highlighting the continuum limit of the model allows to compute an equivalent toughness for the fiber bundle and hence discuss nucleation of a critical defect. The computation of the toughness allows for drawing a simple connection with crack front propagation (depinning) models.

  3. Nominally brittle cracks in inhomogeneous solids: From microstructural disorder to continuum-level scale

    Directory of Open Access Journals (Sweden)

    Jonathan eBarés

    2014-11-01

    Full Text Available We analyze the intermittent dynamics of cracks in heterogeneous brittle materials and the roughness of the resulting fracture surfaces by investigating theoretically and numerically crack propagation in an elastic solid of spatially-distributed toughness. The crack motion split up into discrete jumps, avalanches, displaying scale-free statistical features characterized by universal exponents. Conversely, the ranges of scales are non-universal and the mean avalanche size and duration depend on the loading microstructure and specimen parameters according to scaling laws which are uncovered. The crack surfaces are found to be logarithmically rough. Their selection by the fracture parameters is formulated in term of scaling laws on the structure functions measured on one-dimensional roughness profiles taken parallel and perpendicular to the direction of crack growth.

  4. Brittle intermetallic compound makes ultrastrong low-density steel with large ductility

    Science.gov (United States)

    Kim, Sang-Heon; Kim, Hansoo; Kim, Nack J.

    2015-02-01

    Although steel has been the workhorse of the automotive industry since the 1920s, the share by weight of steel and iron in an average light vehicle is now gradually decreasing, from 68.1 per cent in 1995 to 60.1 per cent in 2011 (refs 1, 2). This has been driven by the low strength-to-weight ratio (specific strength) of iron and steel, and the desire to improve such mechanical properties with other materials. Recently, high-aluminium low-density steels have been actively studied as a means of increasing the specific strength of an alloy by reducing its density. But with increasing aluminium content a problem is encountered: brittle intermetallic compounds can form in the resulting alloys, leading to poor ductility. Here we show that an FeAl-type brittle but hard intermetallic compound (B2) can be effectively used as a strengthening second phase in high-aluminium low-density steel, while alleviating its harmful effect on ductility by controlling its morphology and dispersion. The specific tensile strength and ductility of the developed steel improve on those of the lightest and strongest metallic materials known, titanium alloys. We found that alloying of nickel catalyses the precipitation of nanometre-sized B2 particles in the face-centred cubic matrix of high-aluminium low-density steel during heat treatment of cold-rolled sheet steel. Our results demonstrate how intermetallic compounds can be harnessed in the alloy design of lightweight steels for structural applications and others.

  5. Testing constitutive equations for brittle-ductile deformation associated with faulting in granitic rock

    Science.gov (United States)

    Nevitt, Johanna M.; Warren, Jessica M.; Pollard, David D.

    2017-08-01

    Uncertainty in constitutive equations for brittle-ductile deformation limits our understanding of earthquake nucleation and propagation at the base of the seismogenic lithosphere. To reduce this uncertainty, we investigate exhumed strike-slip faults and related deformation features in the Lake Edison granodiorite (central Sierra Nevada, CA) that developed at 250-500°C and 250 MPa. The Seven Gables outcrop contains a 10 cm wide contractional fault step separating 2 m-scale left-lateral faults. Within the step, an 4 cm thick leucocratic dike is stretched and rotated, thus constraining the kinematics of deformation, and the dike and surrounding granodiorite are strongly mylonitized. Petrographic and electron backscatter diffraction analyses reveal evidence for brittle and plastic deformation mechanisms, including dislocation creep, diffusion creep, microfracturing, and cataclasis. We present a 2-D finite element model of the Seven Gables outcrop that tests a series of candidate constitutive equations: Von Mises elastoplasticity, Drucker-Prager elastoplasticity, power law creep viscoelasticity, two-layer elastoviscoplasticity, and coupled elastoviscoplasticity. Models based on Von Mises yielding most accurately match the outcrop deformation. Frictional plastic yield criteria (i.e., Drucker-Prager) are incapable of reproducing the outcrop deformation due to the elevated mean compressive stress and reduced plastic yielding within the model fault step. Furthermore, the power law creep viscoelastic model requires a high strain rate ( 10-4 s-1) to resolve slip on faults and fails to localize strain within the step region. Comparing model results and elastic stress fields with field observations suggests that deformation localizes in regions of elevated mean compressive stress and Mises equivalent stress.

  6. A damage mechanics approach for quantifying stress changes due to brittle failure of porous rocks

    Science.gov (United States)

    Jacquey, Antoine B.; Cacace, Mauro; Blöcher, Guido; Milsch, Harald; Scheck-Wenderoth, Magdalena

    2016-04-01

    Natural fault zones or man-made injection or production of fluid impact the regional stress distribution in Earth's crust and can be responsible for localized stress discontinuities. Understanding the processes controlling fracturing of the porous rocks and mechanical behaviour of fault zones is therefore of interest for several applications including geothermal energy production. In this contribution, we will present a thermodynamically consistent visco-poroelastic damage model which can deal with the multi-scale and multi-physics nature of the physical processes controlling the deformation of porous rocks during and after brittle failure. Deformation of a porous medium is crucially influenced by the changes in the effective stress. Considering a strain-formulated yield cap and the compaction-dilation transition, three different regimes can be identified: quasi-elastic deformation, cataclastic compaction with microcracking (damage accumulation) and macroscopic brittle failure with dilation. The governing equations for deformation, damage accumulation/healing and fluid flow have been implemented in a fully-coupled finite-element-method based framework (MOOSE). The MOOSE framework provides a powerful and flexible platform to solve multiphysics problems implicitly and in a tightly coupled manner on unstructured meshes which is of interest for such non-linear context. To illustrate the model, simulation of a compaction experiment of a sandstone leading to shear failure will be presented which allows to quantify the stress drop accompanying the failure. Finally, we will demonstrate that this approach can also be used at the field scale to simulate hydraulic fracturing and assess the resulting changes in the stress field.

  7. Energy transport processes in a brittle ductile intrusive model of the Taupo Volcanic Zone, New Zealand

    Science.gov (United States)

    Weir, Graham J.

    1998-08-01

    The implications of the findings of recent GPS and micro-seismic studies in the Taupo Volcanic Zone (TVZ), New Zealand, on models of processes transporting mass, heat and chemicals are discussed. It is argued that in addition to the well established process of groundwater convection extracting heat and chemicals by interacting with magmatic intrusives under the TVZ, that two other processes may be important. Firstly, the existence of a ductile layer with very low permeability between about 8 to 15 km depth will produce a region of `enhanced conduction' in which very high conductive fluxes of energy arise from a temperature distribution which varies exponentially with depth. Secondly, water may transport up through the ductile layer, as a result of extensional processes in the ductile region. If extension is occurring at about 8 mm/yr, then geothermal heat transfer in the TVZ of about 4200 MW is made up from about 1200 MW from the cooling of intrusives in the brittle region in the upper 8 km; of about an additional 1900 MW of conducted heat entering the brittle region from the ductile region; and about an additional 1100 MW from water transport through the ductile region. Provided this water flow has a chloride concentration similar to that emitted from nearby volcanoes, then the total chloride transport from the TVZ is about 3.5 kg/s, as suggested by average enthalpy to chloride ratios in the TVZ of about 1.2 MJ/g. The present high heat and mass transport processes in the TVZ are assumed to result from the passive filling of volume created from extensional processes under the TVZ, plus conductive and/or convective heating processes below 15 km depth.

  8. High-definition micropatterning method for hard, stiff and brittle polymers.

    Science.gov (United States)

    Zhao, Yiping; Truckenmuller, Roman; Levers, Marloes; Hua, Wei-Shu; de Boer, Jan; Papenburg, Bernke

    2017-02-01

    Polystyrene (PS) is the most commonly used material in cell culture devices, such as Petri dishes, culture flasks and well plates. Micropatterning of cell culture substrates can significantly affect cell-material interactions leading to an increasing interest in the fabrication of topographically micro-structured PS surfaces. However, the high stiffness combined with brittleness of PS (elastic modulus 3-3.5GPa) makes high-quality patterning into PS difficult when standard hard molds, e.g. silicon and nickel, are used as templates. A new and robust scheme for easy processing of large-area high-density micro-patterning into PS film is established using nanoimprinting lithography and standard hot embossing techniques. Including an extra step through an intermediate PDMS mold alone does not result in faithful replication of the large area, high-density micropattern into PS. Here, we developed an approach using an additional intermediate mold out of OrmoStamp, which allows for high-quality and large-area micro-patterning into PS. OrmoStamp was originally developed for UV nanoimprint applications; this work demonstrates for the first time that OrmoStamp is a highly adequate material for micro-patterning of PS through hot embossing. Our proposed processing method achieves high-quality replication of micropatterns in PS, incorporating features with high aspect ratio (4:1, height:width), high density, and over a large pattern area. The proposed scheme can easily be adapted for other large-area and high-density micropatterns of PS, as well as other stiff and brittle polymers.

  9. Intraplate brittle deformation and states of paleostress constrained by fault kinematics in the central German platform

    Science.gov (United States)

    Navabpour, Payman; Malz, Alexander; Kley, Jonas; Siegburg, Melanie; Kasch, Norbert; Ustaszewski, Kamil

    2017-01-01

    The structural evolution of Central Europe reflects contrasting tectonic regimes after the Variscan orogeny during Mesozoic - Cenozoic time. The brittle deformation related to each tectonic regime is localized mainly along major fault zones, creating complex fracture patterns and kinematics through time with diverging interpretations on the number and succession of the causing events. By contrast, fracture patterns in less deformed domains often provide a pristine structural inventory. We investigate the brittle deformation of a relatively stable, wide area of the central German platform using fault-slip data to identify the regional stress fields required to satisfy the data. In a non-classical approach, and in order to avoid local stress variations and misinterpretations, the fault-slip data are scaled up throughout the study area into subsets of consistent kinematics and chronology for sedimentary cover and crystalline basement rocks. Direct stress tensor inversion was performed through an iterative refining process, and the computed stress tensors were verified using field-based observations. Criteria on relative tilt geometry and indicators of kinematic change suggest a succession of events, which begins with a post-Triassic normal faulting regime with σ3 axis trending NE-SW. The deformation then follows by strike-slip and thrust faulting regimes with a change of σ1 axis from N-S to NE-SW, supposedly in the Late Cretaceous. Two younger events are characterized by Cenozoic normal and oblique thrust faulting regimes with NW-SE-trending σ3 and σ1 axes, respectively. The fracture patterns of both the cover and basement rocks appear to record the same states of stress.

  10. The "brittle response" to Parkinson's disease medications: characterization and response to deep brain stimulation.

    Directory of Open Access Journals (Sweden)

    Daniel Martinez-Ramirez

    Full Text Available OBJECTIVE: Formulate a definition and describe the clinical characteristics of PD patients with a "brittle response" (BR to medications versus a "non-brittle response" (NBR, and characterize the use of DBS for this population. METHODS: An UF IRB approved protocol used a retrospective chart review of 400 consecutive PD patients presenting to the UF Center for Movement Disorders and Neurorestoration. Patient records were anonymized and de-identified prior to analysis. SPSS statistics were used to analyze data. RESULTS: Of 345 included patients, 19 (5.5% met criteria for BR PD. The BR group was comprised of 58% females, compared to 29% in the NBR group (P = .008. The former had a mean age of 63.4 compared to 68.1 in the latter. BR patients had lower mean weight (63.5 vs. 79.6, P = <.001, longer mean disease duration (12.6 vs. 8.9 years, P = .003, and had been on LD for more years compared to NBR patients (9.8 vs. 5.9, P = .001. UPDRS motor scores were higher (40.4 vs. 30.0, P = .001 in BR patients. No differences were observed regarding the Schwab and England scale, PDQ-39, and BDI-II. Sixty-three percent of the BR group had undergone DBS surgery compared to 18% (P = .001. Dyskinesias were more common, severe, and more often painful (P = <.001 in the BR group. There was an overall positive benefit from DBS. CONCLUSION: BR PD occurred more commonly in female patients with a low body weight. Patients with longer disease duration and longer duration of LD therapy were also at risk. The BR group responded well to DBS.

  11. Time-resolved study of femtosecond laser induced micro-modifications inside transparent brittle materials

    Science.gov (United States)

    Hendricks, F.; Matylitsky, V. V.; Domke, M.; Huber, Heinz P.

    2016-03-01

    Laser processing of optically transparent or semi-transparent, brittle materials is finding wide use in various manufacturing sectors. For example, in consumer electronic devices such as smartphones or tablets, cover glass needs to be cut precisely in various shapes. The unique advantage of material processing with femtosecond lasers is efficient, fast and localized energy deposition in nearly all types of solid materials. When an ultra-short laser pulse is focused inside glass, only the localized region in the neighborhood of the focal volume absorbs laser energy by nonlinear optical absorption. Therefore, the processing volume is strongly defined, while the rest of the target stays unaffected. Thus ultra-short pulse lasers allow cutting of the chemically strengthened glasses such as Corning Gorilla glass without cracking. Non-ablative cutting of transparent, brittle materials, using the newly developed femtosecond process ClearShapeTM from Spectra-Physics, is based on producing a micron-sized material modification track with well-defined geometry inside. The key point for development of the process is to understand the induced modification by a single femtosecond laser shot. In this paper, pump-probe microscopy techniques have been applied to study the defect formation inside of transparent materials, namely soda-lime glass samples, on a time scale between one nanosecond to several tens of microseconds. The observed effects include acoustic wave propagation as well as mechanical stress formation in the bulk of the glass. Besides better understanding of underlying physical mechanisms, our experimental observations have enabled us to find optimal process parameters for the glass cutting application and lead to better quality and speed for the ClearShapeTM process.

  12. Mutations in PRDM5 in Brittle Cornea Syndrome Identify a Pathway Regulating Extracellular Matrix Development and Maintenance

    NARCIS (Netherlands)

    Wright, Emma M. M. Burkitt; Spencer, Helen L.; Daly, Sarah B.; Manson, Forbes D. C.; Zeef, Leo A. H.; Urquhart, Jill; Zoppi, Nicoletta; Bonshek, Richard; Tosounidis, Ioannis; Mohan, Meyyammai; Madden, Colm; Dodds, Annabel; Chandler, Kate E.; Banka, Siddharth; Au, Leon; Clayton-Smith, Jill; Khan, Naz; Biesecker, Leslie G.; Wilson, Meredith; Rohrbach, Marianne; Colombi, Marina; Giunta, Cecilia; Black, Graeme C. M.

    2011-01-01

    Extreme corneal fragility and thinning, which have a high risk of catastrophic spontaneous rupture, are the cardinal features of brittle cornea syndrome (BCS), an autosomal-recessive generalized connective tissue disorder. Enucleation is frequently the only management option for this condition,

  13. Differential growth forms of the sponge Biemna fortis govern the abundance of its associated brittle star Ophiactis modesta

    Science.gov (United States)

    Dahihande, Azraj S.; Thakur, Narsinh L.

    2017-08-01

    Marine intertidal regions are physically stressful habitats. In such an environment, facilitator species and positive interactions mitigate unfavorable conditions to the benefit of less tolerant organisms. In sponge-brittle star association, sponges effectively shelter brittle stars from biotic and abiotic stresses. The sponge, Biemna fortis (Topsent, 1897) was examined from two intertidal regions Anjuna and Mhapan along the Central West Coast of India for associated brittle star Ophiactis modesta (Brock, 1888) during 2013-2014. The study sites varied in suspended particulate matter (SPM). B. fortis at the high SPM habitat (Anjuna) had partially buried growth form and at the low SPM habitat (Mhapan) had massive growth form. O. modesta was abundantly associated with the massive growth form (50-259 individuals per 500 ml sponge) but rarely occurred in association with partially buried growth form (6-16 individuals per 500 ml sponge). In laboratory choice assay O. modesta showed equal preference to the chemical cues from both the growth forms of B. fortis. In addition, O. modesta showed significant preference to B. fortis compared to other sympatric sponges. These observations highlight the involvement of chemical cues in host recognition by O. modesta. Massive growth forms transplanted to the high SPM habitat were unable to survive but partially buried growth forms transplanted to the low SPM habitat were able to survive. Differential growth forms of the host sponge B. fortis at different abiotic stresses affect the abundance of the associated brittle star O. modesta.

  14. Ductile-brittle transition behavior of V-4Cr-4Ti irradiated in the dynamic helium charging experiment

    Energy Technology Data Exchange (ETDEWEB)

    Chung, H.M.; Nowicki, L.J.; Busch, D.E. [Argonne National Lab., Chicago, IL (United States)] [and others

    1995-04-01

    The objective of this work is to determine the effect of simultaneous displacement damage and dynamically charged helium on the ductile-brittle transition behavior of V-4Cr-4Ti specimens irradiated to 18-31 dpa at 425-600{degrees}C in the Dynamic Helium Charging Experiment (DHCE).

  15. Fracture process of a low carbon low alloy steel relevant to charpy toughness at ductile-brittle fracture transition region

    Science.gov (United States)

    Tani, T.; Nagumo, M.

    1995-02-01

    The fracture process that determines the Charpy energy at the ductile-brittle transition region was investigated by means of the instrumented Charpy test and fractographic analysis with a low carbon low alloy steel subjected to different control-rolling conditions. The decomposition of a Charpy energy into the energies dissipated in the course of the notch-tip blunting, stable crack growth, and brittle crack propagation is unique irrespective of the testing temperatures and specimen series. Toughness level can be divided into four regions according to the pre-dominating fracture process. The temperature dependence of toughness and effects of the an-isotropy of a specimen originates in the brittle fracture initiation stage rather than the resistance against the notch-tip blunting or stable crack growth. From fractographic examination referring to the stress analyses, it is discussed that the brittle fracture initiation is controlled by the local deformation microstructures in the plastic zone together with the stress field ahead of the notch or the stable crack front.

  16. Mutations in PRDM5 in Brittle Cornea Syndrome Identify a Pathway Regulating Extracellular Matrix Development and Maintenance

    NARCIS (Netherlands)

    Wright, Emma M. M. Burkitt; Spencer, Helen L.; Daly, Sarah B.; Manson, Forbes D. C.; Zeef, Leo A. H.; Urquhart, Jill; Zoppi, Nicoletta; Bonshek, Richard; Tosounidis, Ioannis; Mohan, Meyyammai; Madden, Colm; Dodds, Annabel; Chandler, Kate E.; Banka, Siddharth; Au, Leon; Clayton-Smith, Jill; Khan, Naz; Biesecker, Leslie G.; Wilson, Meredith; Rohrbach, Marianne; Colombi, Marina; Giunta, Cecilia; Black, Graeme C. M.

    2011-01-01

    Extreme corneal fragility and thinning, which have a high risk of catastrophic spontaneous rupture, are the cardinal features of brittle cornea syndrome (BCS), an autosomal-recessive generalized connective tissue disorder. Enucleation is frequently the only management option for this condition, resu

  17. Brittleness Source Identification Model for Cascading Failure of Complex Power Grid Based on Brittle Risk Entropy%基于脆性风险熵的复杂电网连锁故障脆性源辨识模型

    Institute of Scientific and Technical Information of China (English)

    刘文颖; 王佳明; 谢昶; 王维洲

    2012-01-01

    The essence of cascading failure in complex power system, which is the main reason of large-scale blackouts, is brittleness process when the brittleness source is excited. To study how large-scale blackouts take place and the defense measures, meanwhile, find out the high-risk lines, the author proposed a brittleness source identification model for cascading failure based on brittleness theory of complex system. From the view that brittleness is the nature of power system, the model used power flow entropy to measure the condition of power grid, and analyzed the mechanism of cascading failure by brittleness relevance and entropy increase from component and macroscopic aspects respectively. Take the identifying method of brittleness sources and brittleness relevance degree of grid components into consideration, a determining process of high-risk lines was given. Through simulation of cascading failure, brittle risk entropy was applied to assess the impact of component outage from power grid operation and the load removed, and this can provide a basis for defensive strategy making. Taking Gansu power network as an example, the feasibility and effectiveness of the proposed defense model were validated.%复杂电网连锁故障是引发系统大停电的主要原因,其实质是脆性源被激发后系统脆性的传播过程.为研究复杂电网大停电的机理及防御措施,同时找出电网的薄弱环节,提出了一种基于复杂系统脆性理论的连锁故障脆性源辨识模型.模型从电力系统本身具有的脆性出发,用潮流熵来衡量电网所处的状态,通过脆性关联及熵增分别从元件和宏观上阐述连锁故障的传播机理.提出了脆性源的辨识方法,并综合元件脆性关联度的分析给出了对连锁故障影响较大的系统薄弱环节的判定流程,通过对连锁故障过程的模拟,用脆性风险熵来评估元件退出运行对电网状态的影响及造成的负荷切除,为连锁故障防御策

  18. Failure processes in soft and quasi-brittle materials with nonhomogeneous microstructures

    Science.gov (United States)

    Spring, Daniel W.

    Material failure pervades the fields of materials science and engineering; it occurs at various scales and in various contexts. Understanding the mechanisms by which a material fails can lead to advancements in the way we design and build the world around us. For example, in structural engineering, understanding the fracture of concrete and steel can lead to improved structural systems and safer designs; in geological engineering, understanding the fracture of rock can lead to increased efficiency in oil and gas extraction; and in biological engineering, understanding the fracture of bone can lead to improvements in the design of bio-composites and medical implants. In this thesis, we numerically investigate a wide spectrum of failure behavior; in soft and quasi-brittle materials with nonhomogeneous microstructures considering a statistical distribution of material properties. The first topic we investigate considers the influence of interfacial interactions on the macroscopic constitutive response of particle reinforced elastomers. When a particle is embedded into an elastomer, the polymer chains in the elastomer tend to adsorb (or anchor) onto the surface of the particle; creating a region in the vicinity of each particle (often referred to as an interphase) with distinct properties from those in the bulk elastomer. This interphasial region has been known to exist for many decades, but is primarily omitted in computational investigations of such composites. In this thesis, we present an investigation into the influence of interphases on the macroscopic constitutive response of particle filled elastomers undergoing large deformations. In addition, at large deformations, a localized region of failure tends to accumulate around inclusions. To capture this localized region of failure (often referred to as interfacial debonding), we use cohesive zone elements which follow the Park-Paulino-Roesler traction-separation relation. To account for friction, we present a new

  19. Brittle-to-viscous behaviour of quartz gouge in shear experiments

    Science.gov (United States)

    Richter, Bettina; Stunitz, Holger; Heilbronner, Renée

    2016-04-01

    In order to study the microstructure development across the brittle-viscous transition and to derive the corresponding flow laws, we performed shear experiments on quartz gouge in a Griggs-type deformation apparatus. The starting material is a crushed quartz single crystal (sieved grain size water added. The experiments were conducted at temperatures between 500 ° C and 1000 ° C at confining pressures of 0.5 GPa, 1.0 GPa or 1.5 GPa. Four strain-rate-stepping experiments were conducted at strain rates between ˜2.5 x 10-6 s-1 and ˜2.5 x 10-4 s-1. Other experiments were conducted at constant strain rates of ˜2.5 x 10-6 s-1, ˜2.5 x 10-5 s-1, ˜2.5 x 10-4 s-1 and ˜2.5 x 10-3 s-1. At high confining pressure, the strength of the samples decreases with increasing temperature for all strain rates. The largest decrease occurred between 650 ° C and 700 ° C at shear strain rates of ˜2.5 x 10-5 s-1. At the same time, the pressure dependence of strength is positive for T ≤ 650 ° C while an inverse pressure dependence is observed at T > 650 ° C. For T one dominated by cataclastic flow to one dominated by crystal plasticity. The microstructure reveals a less abrupt transition in terms of operating processes, because brittle and viscous processes are equally active around 650 ° C. With increasing temperature the volume fraction of recrystallised grains increases, and at 900 ° C - 1000 ° C recrystallisation is nearly complete at strains of γ ˜ 3. The crystallographic preferred orientation of the c-axis evolves from a random distribution at low temperatures towards two peripheral maxima at intermediate temperatures. At high temperatures the c-axis show a single Y-maximum. At high temperature, the stress exponent is n = 2.1 ± 0.2. The activation energy Q is 193 ± 12 kJ/mol at strain rates of 10-5 s-1, at faster strain rates the activation energy drops down to Q = 119 ± 12 kJ/mol. This small stress exponent at high temperatures indicates a combination of

  20. Brittle ductile transition in experimentally deformed basalt under oceanic crust conditions

    Science.gov (United States)

    Violay, M.; Gibert, B.; Mainprice, D.; Evans, B.; Pezard, P. A.; Flovenz, O.

    2009-04-01

    The mid-ocean ridge system is the largest continuous volcanic feature on Earth, with significant interactions between tectonic activity, volcanism and sea-water circulation. Iceland is the biggest landmass straddling a mid-ocean ridge. The associated tectonic and volcanic settings resulting from the active rifting provide in this geodynamic context a major heat source for the geothermal exploitation. High-pressure, high-temperature, conventional triaxial compression experiments have been conducted in a Paterson Press to explore the brittle-ductile transition of oceanic crustal rocks under in situ conditions at depth (3-10 Km). The study provides some insights into the prospect of producing geothermal fluids from deep wells drilled into a reservoir at temperatures and pressures of supercritical water (T>400°C). We present a series of 20 axial compression deformation experiments performed on jacketed basalt cores of 10 mm diameter and 20 mm long. The experiments were performed at 100 and 300 MPa, with temperatures ranging from 400°C to 900°C, and pore pressures ranging from 0 to 100 MPa, a constant strain rate of 1 × 10- 5 s- 1 and up to strains of 15%. Two different types of basalts were selected for their simple compositions, low alteration degree and very low porosity (3%). The two samples differed in their percentage of glass, being zero in one case and 15% in the other. For the vitreous sample at a confining pressure of 100 and 300 MPa, our experiments show that deformation takes place by three deformation modes; (1) brittle fracture at 400°C with a maximal strength of 900 MPa, corresponding to failure by localized rupture, (2) strain-hardening at small strains and followed by slipping on a localized fracture plane at a constant strength around 250 MPa at higher strains, for temperatures ranging from 500°C to 700°C, (3) distributed ductile flow at differential stresses from 50 to 100 MPa and temperature from 800 to 900°C. For the non glassy sample, the

  1. Brittle Solvers: Lessons and insights into effective solvers for visco-plasticity in geodynamics

    Science.gov (United States)

    Spiegelman, M. W.; May, D.; Wilson, C. R.

    2014-12-01

    Plasticity/Fracture and rock failure are essential ingredients in geodynamic models as terrestrial rocks do not possess an infinite yield strength. Numerous physical mechanisms have been proposed to limit the strength of rocks, including low temperature plasticity and brittle fracture. While ductile and creep behavior of rocks at depth is largely accepted, the constitutive relations associated with brittle failure, or shear localisation, are more controversial. Nevertheless, there are really only a few macroscopic constitutive laws for visco-plasticity that are regularly used in geodynamics models. Independent of derivation, all of these can be cast as simple effective viscosities which act as stress limiters with different choices for yield surfaces; the most common being a von Mises (constant yield stress) or Drucker-Prager (pressure dependent yield-stress) criterion. The choice of plasticity model, however, can have significant consequences for the degree of non-linearity in a problem and the choice and efficiency of non-linear solvers. Here we describe a series of simplified 2 and 3-D model problems to elucidate several issues associated with obtaining accurate description and solution of visco-plastic problems. We demonstrate that1) Picard/Successive substitution schemes for solution of the non-linear problems can often stall at large values of the non-linear residual, thus producing spurious solutions2) Combined Picard/Newton schemes can be effective for a range of plasticity models, however, they can produce serious convergence problems for strongly pressure dependent plasticity models such as Drucker-Prager.3) Nevertheless, full Drucker-Prager may not be the plasticity model of choice for strong materials as the dynamic pressures produced in these layers can develop pathological behavior with Drucker-Prager, leading to stress strengthening rather than stress weakening behavior.4) In general, for any incompressible Stoke's problem, it is highly advisable to

  2. Dependence of the brittle ductile transition on strain-rate-dependent critical homologous temperature

    Science.gov (United States)

    Davis, Paul M.

    2017-05-01

    Earthquakes mainly occur in crust or mantle that is below a critical temperature for the tectonic strain-rate, \\dot{e}_t, such that stress builds up to the breaking point before it can relax due to creep. Then long-range stress correlation gives rise to power law seismicity including large events. The limiting temperature depends on pressure, which is taken into account by finding a critical homologous temperature THc = T/TM above which earthquakes are rarely observed (where T, TM are temperature and average melting temperature of constituent minerals). We find that THc for ocean plates is ∼0.55. For California earthquakes, it is also close to 0.55. The uppermost mantle layer of oceanic plates of thickness ∼50 km is composed of harzburgite and depleted peridotite from which basalt has been removed to form ocean crust. Thus it has a higher melting temperature than the peridotite of the surrounding mantle, or the lower halves of plates. Thicknesses of seismicity in deep subduction zones, determined from 2-D polynomial fits to a relocated catalogue, are ∼50 km, which suggests that the earthquake channel is confined to this layer. We construct models to find homologous temperatures in slabs, and find that seismicity thicknesses are also, on average, confined to TH ≤ 0.55 ± 0.05. The associated rheology is compared with that obtained from flexure models of ocean lithosphere. The brittle-ductile transition occurs where viscosity drops from high values in the cold cores of slabs to values of 1022-1023 Pa s, that is, where creep strain-rates become comparable to tectonic rates. The cut-off for deep earthquakes is not sharp. However they appear unlikely to occur if homologous temperature is high TH > 0.55. Exceptions to the rule are anomalously deep earthquakes such as those beneath the Iceland and the Hawaiian hotspots, and the Newport Inglewood Fault. These are smaller events with short-range stress correlation, and can be explained if strain-rates are two to

  3. Deformation mechanisms of NiAl cyclicly deformed near the brittle-to-ductile transformation temperature

    Science.gov (United States)

    Antolovich, Stephen D.; Saxena, Ashok; Cullers, Cheryl

    1992-01-01

    One of the ongoing challenges of the aerospace industry is to develop more efficient turbine engines. Greater efficiency entails reduced specific strength and larger temperature gradients, the latter of which means higher operating temperatures and increased thermal conductivity. Continued development of nickel-based superalloys has provided steady increases in engine efficiency and the limits of superalloys have probably not been realized. However, other material systems are under intense investigation for possible use in high temperature engines. Ceramic, intermetallic, and various composite systems are being explored in an effort to exploit the much higher melting temperatures of these systems. NiAl is considered a potential alternative to conventional superalloys due to its excellent oxidation resistance, low density, and high melting temperature. The fact that NiAl is the most common coating for current superalloy turbine blades is a tribute to its oxidation resistance. Its density is one-third that of typical superalloys and in most temperature ranges its thermal conductivity is twice that of common superalloys. Despite these many advantages, NiAl requires more investigation before it is ready to be used in engines. Binary NiAl in general has poor high-temperature strength and low-temperature ductility. On-going research in alloy design continues to make improvements in the high-temperature strength of NiAl. The factors controlling low temperature ductility have been identified in the last few years. Small, but reproducible ductility can now be achieved at room temperature through careful control of chemical purity and processing. But the mechanisms controlling the transition from brittle to ductile behavior are not fully understood. Research in the area of fatigue deformation can aid the development of the NiAl system in two ways. Fatigue properties must be documented and optimized before NiAl can be applied to engineering systems. More importantly though

  4. Microstructures and composition of brittle faults in claystones: Constraints on the barrier behavior

    Science.gov (United States)

    Kneuker, Tilo; Hammer, Jörg; Jahn, Steffen; Zulauf, Gernold

    2017-04-01

    Investigations of fault rocks are crucial to evaluate the barrier properties of clay rich formations used for the storage of hydrocarbons, carbon dioxide gas or for the storage of heat generating radioactive waste. Claystones are considered as a geological barrier. However, their barrier capability can be reduced if the claystones are cut by brittle faults. Our study is focusing on the microfabrics and element mobility of artificially and naturally fractured claystones using a multi-method approach. Particular attention was paid to small scale lithological heterogeneities occurring in the clayey sequence. The microfabrics were investigated using SEM and optical microscopy. Geochemical and phase analyses were carried out using XRD, XRF and ICP-MS. In addition, organic (TOC) and inorganic carbon (TIC), total sulphur (TS) as well as the cation exchange capacity (CEC) were determined. Macroscopic observations of fault zones on outcrops and drill cores indicate closely spaced planar and undulating discontinuities, including slickenside striations. The investigated fault zones are often accompanied by calcite veins and calcite enriched zones. The fault core is formed by a mm to cm thick clayey, fine grained, cohesionless fault gouge including reworked calcite fragments. Duplex-like domains are separated by discrete microshears, along which the rocks disintegrate. Calcareous fossils, common in undeformed claystones, appear in these zones fragmented and rotated. In contrast to calcite, quartz is more resistant to solution-precipitation processes. Rarely intracrystalline fracturing was observed. The calcite mineralization in veins, and solution-precipitation processes of calcite, documented by stylolites, reflect enhanced palaeo-permeability and activity of Ca2+- and CO2-rich fluids inside some of the fault zones, mainly along fault parallel shear planes. Elevated Sr and Ba concentrations are bound to the tectonic, secondary calcite veins within and outside the investigated

  5. Oblique impact cratering experiments in brittle targets: Implications for elliptical craters on the Moon

    Science.gov (United States)

    Michikami, Tatsuhiro; Hagermann, Axel; Morota, Tomokatsu; Haruyama, Junichi; Hasegawa, Sunao

    2017-01-01

    Most impact craters observed on planetary bodies are the results of oblique impacts of meteoroids. To date, however, there have only been very few laboratory oblique impact experiments for analogue targets relevant to the surfaces of extraterrestrial bodies. In particular, there is a lack of laboratory oblique impact experiments into brittle targets with a material strength on the order of 1 MPa, with the exception of ice. A strength on the order of 1 MPa is considered to be the corresponding material strength for the formation of craters in the 100 m size range on the Moon. Impact craters are elliptical if the meteoroid's trajectory is below a certain threshold angle of incidence, and it is known that the threshold angle depends largely on the material strength. Therefore, we examined the threshold angle required to produce elliptical craters in laboratory impact experiments into brittle targets. This work aims to constrain current interpretations of lunar elliptical craters and pit craters with sizes below a hundred meters. We produced mortar targets with compressive strength of 3.2 MPa. A spherical nylon projectile (diameter 7.14 mm) was shot into the target surface at a nominal velocity of 2.3 km/s, with an impact angle of 5°-90° from horizontal. The threshold angle of this experiment ranges from 15° to 20°. We confirmed that our experimental data agree with previous empirical equations in terms of the cratering efficiency and the threshold impact angle. In addition, in order to simulate the relatively large lunar pit craters related to underground cavities, we conducted a second series of experiments under similar impact conditions using targets with an underground rectangular cavity. Size and outline of craters that created a hole are similar to those of craters without a hole. Moreover, when observed from an oblique angle, a crater with a hole has a topography that resembles the lunar pit craters. The relation between the impact velocity of meteoroids on

  6. Developing an Experimental Simulation Method for Rock Avalanches: Fragmentation Behavior of Brittle Analogue Material

    Science.gov (United States)

    Thordén Haug, Øystein; Rosenau, Matthias; Leever, Karen; Oncken, Onno

    2013-04-01

    Gravitational mass movement on earth and other planets show a scale dependent behavior, of which the physics is not fully understood. In particular, the runout distance for small to medium sized landslides (volume granular material down a chute. Though such granular avalanche models provide important insights into avalanche dynamics, they imply that the material fully disintegrate instantaneously. Observations from nature, however, suggests that a transition from solid to "liquid" occurs over some finite distance downhill, critically controlling the mobility and energy budget of the avalanche. Few experimental studies simulated more realistically the material failing during sliding and those were realized in a labscale centrifuge, where the range of volumes/scales is limited. To develop a new modeling technique to study the scale dependent runout behavior of rock avalanches, we designed, tested and verified several brittle materials allowing fragmentation to occur under normal gravity conditions. According to the model similarity theory, the analogue material must behave dynamically similar to the rocks in natural rock avalanches. Ideally, the material should therefore deform in a brittle manner with limited elastic and ductile strains up to a certain critical stress, beyond which the material breaks and deforms irreversibly. According to scaling relations derived from dimensional analysis and for a model-to-prototype length ratio of 1/1000, the appropriate yield strength for an analogue material is in the order of 10 kPa, friction coefficient around 0.8 and stiffness in the order of MPa. We used different sand (garnet, quartz) in combination with different matrix materials (sugar, salt, starch, plaster) to cement it. The deformation behavior and strength of the samples was tested using triaxial compression tests at atmospheric confining pressures. Proper material properties were obtained using well-sorted, well-rounded, medium grained quartz sand with gypsum

  7. One- / Two-Dimensional versus Three-Dimensional Rupture Propagation in Brittle Solids

    Science.gov (United States)

    Uenishi, K.

    2016-12-01

    Source dynamics of normal earthquakes is usually considered in the framework of 3D rupture in brittle solids. However, our understanding of mechanical details of actual 3D rupture is limited and most of the frequently utilized rupture criteria in earthquake science have been derived from 1D (or at most 2D) experiments. Typically, criteria based on 1D frictional observations of sliding materials are quite often employed in seismological simulations, but we are not sure whether these rupture criteria are really valid for the generation and complex propagation process of 3D rupture. Indeed, our recent experimental observations on dynamic rupture of monolithic brittle solids using a high-speed digital video camera system indicate rather complicated histories of rupture development in 3D solid materials but at the same time they show simple final rupture patterns (rupture networks). For example, by concurrently applying high-voltage electric discharge impulses, a controlled and geometrically plain dynamic rupture pattern can be really obtained in cylindrical concrete specimens, but the simple final rupture pattern is formed not by unidirectional rupture propagation but by multi-directional one. Another example of plain final rupture patterns can be found by dynamic experiments of ice spheres that impinge upon a flat polycarbonate or ice plate. Rupture of the ice spheres induced by the mechanical impact (free fall) shows two representative rupture patterns: (i) The ice sphere is mainly divided into three or four large segments of comparable size (similar to orange segments); and (ii) Only some portions near the bottom of the ice sphere are ruptured into pieces upon collision and a relatively large "top"-shaped part remains unbroken. Both experimental observations indicate generation of remarkably simple and frequently flat rupture surfaces in 3D specimens even without the clear existence of planes of weakness, but it seems difficult to explain the dynamic rupture

  8. New Methods in Exploring Old Topics: Case Studying Brittle Diabetes in the Family Context

    Directory of Open Access Journals (Sweden)

    Moritz Philipp Günther

    2016-01-01

    Full Text Available Background. In questing for a more refined quantitative research approach, we revisited vector autoregressive (VAR modeling for the analysis of time series data in the context of the so far poorly explored concept of family dynamics surrounding instable diabetes type 1 (or brittle diabetes. Method. We adopted a new approach to VAR analysis from econometrics referred to as the optimized multivariate lag selection process and applied it to a set of raw data previously analyzed through standard approaches. Results. We illustrated recurring psychosomatic circles of cause and effect relationships between emotional and somatic parameters surrounding glycemic control of the child’s diabetes and the affective states of all family members. Conclusion. The optimized multivariate lag selection process allowed for more specific, dynamic, and statistically reliable results (increasing R2 tenfold in explaining glycemic variability, which were derived from a larger window of past explanatory variables (lags. Such highly quantitative versus historic more qualitative approaches to case study analysis of psychosomatics surrounding diabetes in adolescents were reflected critically.

  9. Deleterious Mutations in the Zinc-Finger 469 Gene Cause Brittle Cornea Syndrome

    Science.gov (United States)

    Abu, Almogit; Frydman, Moshe; Marek, Dina; Pras, Eran; Nir, Uri; Reznik-Wolf, Haike; Pras, Elon

    2008-01-01

    Brittle cornea syndrome (BCS) is an autosomal-recessive disorder characterized by a thin cornea that tends to perforate, causing progressive visual loss and blindness. Additional systemic symptoms such as joint hypermotility, hyperlaxity of the skin, and kyphoscoliosis place BCS among the connective-tissue disorders. Previously, we assigned the disease gene to a 4.7 Mb interval on chromosome 16q24. In order to clone the BCS gene, we first narrowed the disease locus to a 2.8 Mb interval and systematically sequenced genes expressed in connective tissue in this chromosomal segment. We have identified two frameshift mutations in the Zinc-Finger 469 gene (ZNF469). In five unrelated patients of Tunisian Jewish ancestry, we found a 1 bp deletion at position 5943 (5943 delA), and in an inbred Palestinian family we detected a single-nucleotide deletion at position 9527 (9527 delG). The function of ZNF469 is unknown. However, a 30% homology to a number of collagens suggests that it could act as a transcription factor involved in the synthesis and/or organization of collagen fibers. PMID:18452888

  10. Enrichment of pathogenic alleles in the brittle cornea gene, ZNF469, in keratoconus

    Science.gov (United States)

    Lechner, Judith; Porter, Louise F.; Rice, Aine; Vitart, Veronique; Armstrong, David J.; Schorderet, Daniel F.; Munier, Francis L.; Wright, Alan F.; Inglehearn, Chris F.; Black, Graeme C.; Simpson, David A.; Manson, Forbes; Willoughby, Colin E.

    2014-01-01

    Keratoconus, a common inherited ocular disorder resulting in progressive corneal thinning, is the leading indication for corneal transplantation in the developed world. Genome-wide association studies have identified common SNPs 100 kb upstream of ZNF469 strongly associated with corneal thickness. Homozygous mutations in ZNF469 and PR domain-containing protein 5 (PRDM5) genes result in brittle cornea syndrome (BCS) Types 1 and 2, respectively. BCS is an autosomal recessive generalized connective tissue disorder associated with extreme corneal thinning and a high risk of corneal rupture. Some individuals with heterozygous PRDM5 mutations demonstrate a carrier ocular phenotype, which includes a mildly reduced corneal thickness, keratoconus and blue sclera. We hypothesized that heterozygous variants in PRDM5 and ZNF469 predispose to the development of isolated keratoconus. We found a significant enrichment of potentially pathologic heterozygous alleles in ZNF469 associated with the development of keratoconus (P = 0.00102) resulting in a relative risk of 12.0. This enrichment of rare potentially pathogenic alleles in ZNF469 in 12.5% of keratoconus patients represents a significant mutational load and highlights ZNF469 as the most significant genetic factor responsible for keratoconus identified to date. PMID:24895405

  11. Fracture toughness from atomistic simulations: Brittleness induced by emission of sessile dislocations

    Energy Technology Data Exchange (ETDEWEB)

    Farkas, D. [Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Dept. of Materials Science and Engineering

    1998-08-04

    Using atomistic simulations of crack response for intermetallic materials the author shows that when the emitted dislocations are sessile and stay in the immediate vicinity of the crack tip the emitted dislocations can actually lead to brittle failure. She present the results of an atomistic simulation study of the simultaneous dislocation emission and crack propagation process in this class of materials. She used a molecular statics technique with embedded atom (EAM) potentials developed for NiAl. The crystal structure of NiAl is the CsCl type (B2) with a lattice parameter of 0.287 nm, which is reproduced by the potential together with the cohesive energy and elastic constants. The compound stays ordered up to the melting point, indicating a strong tendency towards chemical ordering with a relatively high energy of the antiphase boundary (APB). As a result of this relatively large energy the dislocations of 1/2<111> type Burgers vectors imply a high energy and the deformation process occurs via the larger <100> type dislocations.

  12. Thrust-wrench fault interference in a brittle medium: new insights from analogue modelling experiments

    Science.gov (United States)

    Rosas, Filipe; Duarte, Joao; Schellart, Wouter; Tomas, Ricardo; Grigorova, Vili; Terrinha, Pedro

    2015-04-01

    We present analogue modelling experimental results concerning thrust-wrench fault interference in a brittle medium, to try to evaluate the influence exerted by different prescribed interference angles in the formation of morpho-structural interference fault patterns. All the experiments were conceived to simulate simultaneous reactivation of confining strike-slip and thrust faults defining a (corner) zone of interference, contrasting with previously reported discrete (time and space) superposition of alternating thrust and strike-slip events. Different interference angles of 60°, 90° and 120° were experimentally investigated by comparing the specific structural configurations obtained in each case. Results show that a deltoid-shaped morpho-structural pattern is consistently formed in the fault interference (corner) zone, exhibiting a specific geometry that is fundamentally determined by the different prescribed fault interference angle. Such angle determines the orientation of the displacement vector shear component along the main frontal thrust direction, determining different fault confinement conditions in each case, and imposing a complying geometry and kinematics of the interference deltoid structure. Model comparison with natural examples worldwide shows good geometric and kinematic similarity, pointing to the existence of matching underlying dynamic process. Acknowledgments This work was sponsored by the Fundação para a Ciência e a Tecnologia (FCT) through project MODELINK EXPL/GEO-GEO/0714/2013.

  13. The effect of dopants on the brittle-to-ductile transition in silicon single crystals

    Science.gov (United States)

    Hong, Youn Jeong; Tanaka, Masaki; Maeno, Keiki; Higashida, Kenji

    2010-07-01

    The brittle-to-ductile transition (BDT) in boron, antimony and arsenic doped Cz silicon crystals has been experimentally studied, respectively. The BDT temperatures in antimony and arsenic doped silicon wafers are lower than that in a non-doped wafer while the BDT temperature in a boron doped wafer is almost the same as that in the non-doped wafer. The activation energy was obtained from the strain rate dependence of the BDT temperature. It was found that the values of the activation energy in the antimony and arsenic doped wafers are lower than that in the non-doped and boron doped wafers, indicating that the dislocation velocity in the antimony and arsenic doped silicon is faster than that in the non-doped while the dislocation velocity in the boron doped is the same as that in the non-doped. The effect of increasing in dislocation velocity on the BDT temperature was calculated by two-dimensional discrete dislocation dynamics simulations, indicating that the increasing in dislocation velocity decreases the BDT temperature in silicon single crystals.

  14. Reliability Analysis of Brittle Material Structures - Including MEMS(?) - With the CARES/Life Program

    Science.gov (United States)

    Nemeth, Noel N.

    2002-01-01

    Brittle materials are being used, or considered, for a wide variety of high tech applications that operate in harsh environments, including static and rotating turbine parts. thermal protection systems, dental prosthetics, fuel cells, oxygen transport membranes, radomes, and MEMS. Designing components to sustain repeated load without fracturing while using the minimum amount of material requires the use of a probabilistic design methodology. The CARES/Life code provides a general-purpose analysis tool that predicts the probability of failure of a ceramic component as a function of its time in service. For this presentation an interview of the CARES/Life program will be provided. Emphasis will be placed on describing the latest enhancements to the code for reliability analysis with time varying loads and temperatures (fully transient reliability analysis). Also, early efforts in investigating the validity of using Weibull statistics, the basis of the CARES/Life program, to characterize the strength of MEMS structures will be described as as well as the version of CARES/Life for MEMS (CARES/MEMS) being prepared which incorporates single crystal and edge flaw reliability analysis capability. It is hoped this talk will open a dialog for potential collaboration in the area of MEMS testing and life prediction.

  15. Insensitivity to Flaws Leads to Damage Tolerance in Brittle Architected Meta-Materials

    Science.gov (United States)

    Montemayor, L. C.; Wong, W. H.; Zhang, Y.-W.; Greer, J. R.

    2016-01-01

    Cellular solids are instrumental in creating lightweight, strong, and damage-tolerant engineering materials. By extending feature size down to the nanoscale, we simultaneously exploit the architecture and material size effects to substantially enhance structural integrity of architected meta-materials. We discovered that hollow-tube alumina nanolattices with 3D kagome geometry that contained pre-fabricated flaws always failed at the same load as the pristine specimens when the ratio of notch length (a) to sample width (w) is no greater than 1/3, with no correlation between failure occurring at or away from the notch. Samples with (a/w) > 0.3, and notch length-to-unit cell size ratios of (a/l) > 5.2, failed at a lower peak loads because of the higher sample compliance when fewer unit cells span the intact region. Finite element simulations show that the failure is governed by purely tensile loading for (a/w) < 0.3 for the same (a/l); bending begins to play a significant role in failure as (a/w) increases. This experimental and computational work demonstrates that the discrete-continuum duality of architected structural meta-materials may give rise to their damage tolerance and insensitivity of failure to the presence of flaws even when made entirely of intrinsically brittle materials. PMID:26837581

  16. Deformation mechanisms of NiAl cyclicly deformed near the brittle-to-ductile transition temperature

    Science.gov (United States)

    Cullers, Cheryl L.; Antolovich, Stephen D.

    1993-01-01

    The intermetallic compound NiAl is one of many advanced materials which is being scrutinized for possible use in high temperature, structural applications. Stoichiometric NiAl has a high melting temperature, excellent oxidation resistance, and good thermal conductivity. Past research has concentrated on improving monotonic properties. The encouraging results obtained on binary and micro-alloyed NiAl over the past ten years have led to the broadening of NiAl experimental programs. The purpose of this research project was to determine the low cycle fatigue properties and dislocation mechanisms of stoichiometric NiAl at temperatures near the monotonic brittle-to-ductile transition. The fatigue properties were found to change only slightly in the temperature range of 600 to 700 K; a temperature range over which monotonic ductility and fracture strength increase markedly. The shape of the cyclic hardening curves coincided with the changes observed in the dislocation structures. The evolution of dislocation structures did not appear to change with temperature.

  17. An ESPI experimental study on the phenomenon of fracture in glass. Is it brittle or plastic?

    Science.gov (United States)

    Ferretti, Daniele; Rossi, Marco; Royer-Carfagni, Gianni

    2011-07-01

    The crack opening displacement (COD) in annealed soda-lime (float) glass has been measured with an electronic speckle pattern interferometry (ESPI) apparatus using coherent laser light. Specimens, naturally pre-cracked with a particular technique, were loaded under strain-driven bending until crack propagated; at regular intervals loading was paused to let the crack reach subcritical equilibrium and the COD measured. By using a post-processing algorithm comparing four images lighted with phase-shifted laser beams, surface displacements could be measured at a resolution of 0.01 μm. Glass transparency has allowed to see through that the propagating crack front is not sharp but curved, jagged and merged in an opaque neighborhood. Numerical simulations show that the measured CODs cannot be reproduced if cohesive surface forces à la Barenblatt-Dugdale bridge the crack lips; instead a plastic-like region must form in a bulk neighborhood of the tip, where inelastic strains are associated with volume increase rather than deviatoric distortion. For this, a Gurson-Tvergaard model of porous plasticity, accounting for the formation of microvoids/microcracks, has been found more efficient than classical von Mises plasticity. This study confirms the formation at the crack tip of a process zone, whose occurrence in brittle materials like glass is still a subject of controversy.

  18. Temporary brittle bone disease: relationship between clinical findings and judicial outcome

    Directory of Open Access Journals (Sweden)

    Colin R. Paterson

    2011-10-01

    Full Text Available There is a wide differential diagnosis for the child with unexplained fractures including non-accidental injury, osteogenesis imperfecta and vitamin D deficiency rickets. Over the last 20 years we and others have described a self-limiting syndrome characterised by fractures in the first year of life. This has been given the provisional name temporary brittle bone disease. This work had proved controversial mostly because the fractures, including rib fractures and metaphyseal fractures, were those previously regarded as typical or even diagnostic of non-accidental injury. Some have asserted that the condition does not exist. Over the years 1985 to 2000 we investigated 87 such cases with fractures with a view to determining the future care of the children. In 85 of these the judiciary was involved. We examined the clinical and radiological findings in the 33 cases in which there was a judicial finding of abuse, the 24 cases in which the parents were exonerated and the 28 cases in which no formal judicial finding was made. The three groups of patients were similar in terms of demographics, age at fracturing and details of the fractures. The clinical similarities between the three groups of patients contrasts with the very different results of the judicial process.

  19. A fiber-bundle model for the continuum deformation of brittle material

    CERN Document Server

    Nanjo, K Z

    2016-01-01

    The deformation of brittle material is primarily accompanied by micro-cracking and faulting. However, it has often been found that continuum fluid models, usually based on a non-Newtonian viscosity, are applicable. To explain this rheology, we use a fiber-bundle model, which is a model of damage mechanics. In our analyses, yield stress was introduced. Above this stress, we hypothesize that the fibers begin to fail and a failed fiber is replaced by a new fiber. This replacement is analogous to a micro-crack or an earthquake and its iteration is analogous to stick-slip motion. Below the yield stress, we assume that no fiber failure occurs, and the material behaves elastically. We show that deformation above yield stress under a constant strain rate for a sufficient amount of time can be modeled as an equation similar to that used for non-Newtonian viscous flow. We expand our rheological model to treat viscoelasticity and consider a stress relaxation problem. The solution can be used to understand aftershock tem...

  20. Mechanical properties and material removal characteristics of soft-brittle HgCdTe single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Irwan, R. [School of Mechanical and Mining Engineering, the University of Queensland, Brisbane, QLD 4072 (Australia); Huang, H., E-mail: han.huang@uq.edu.au [School of Mechanical and Mining Engineering, the University of Queensland, Brisbane, QLD 4072 (Australia); Zheng, H.Y.; Wu, H. [Singapore Institute of Manufacturing Technology, 71 Nanyang Drive, Singapore 638075 (Singapore)

    2013-01-01

    Mechanical properties and material removal characteristics of mercury cadmium telluride (Hg{sub 0.84}C{sub 0.16}Te) single crystals were investigated by the use of indentation and single point diamond turning. The nanoindentation tests showed that the average values of elastic modulus and hardness were 40 and 0.55 GPa, respectively. The fracture toughness estimated by Vickers indentation fracture toughness test was 0.200 MPa m{sup 1/2}, in the predicted range of 0.204-0.235 MPa m{sup 1/2} by the Bifano model. The diamond turning experiments revealed that there was a threshold value in depth of cut that was responsible for the transition from ductile to brittle removal modes during the cutting of the Hg{sub 0.84}C{sub 0.16}Te single crystals. The measured critical depth of cut was between 1.5 and 2 {mu}m, in agreement with that of 1.541 {mu}m calculated by the Bifano model.

  1. Standard test method for splitting tensile strength for brittle nuclear waste forms

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    1989-01-01

    1.1 This test method is used to measure the static splitting tensile strength of cylindrical specimens of brittle nuclear waste forms. It provides splitting tensile-strength data that can be used to compare the strength of waste forms when tests are done on one size of specimen. 1.2 The test method is applicable to glass, ceramic, and concrete waste forms that are sufficiently homogeneous (Note 1) but not to coated-particle, metal-matrix, bituminous, or plastic waste forms, or concretes with large-scale heterogeneities. Cementitious waste forms with heterogeneities >1 to 2 mm and 5 mm can be tested using this procedure provided the specimen size is increased from the reference size of 12.7 mm diameter by 6 mm length, to 51 mm diameter by 100 mm length, as recommended in Test Method C 496 and Practice C 192. Note 1—Generally, the specimen structural or microstructural heterogeneities must be less than about one-tenth the diameter of the specimen. 1.3 This test method can be used as a quality control chec...

  2. New Methods in Exploring Old Topics: Case Studying Brittle Diabetes in the Family Context

    Science.gov (United States)

    Günther, Moritz Philipp; Winker, Peter; Wudy, Stefan A.; Brosig, Burkhard

    2016-01-01

    Background. In questing for a more refined quantitative research approach, we revisited vector autoregressive (VAR) modeling for the analysis of time series data in the context of the so far poorly explored concept of family dynamics surrounding instable diabetes type 1 (or brittle diabetes). Method. We adopted a new approach to VAR analysis from econometrics referred to as the optimized multivariate lag selection process and applied it to a set of raw data previously analyzed through standard approaches. Results. We illustrated recurring psychosomatic circles of cause and effect relationships between emotional and somatic parameters surrounding glycemic control of the child's diabetes and the affective states of all family members. Conclusion. The optimized multivariate lag selection process allowed for more specific, dynamic, and statistically reliable results (increasing R2 tenfold in explaining glycemic variability), which were derived from a larger window of past explanatory variables (lags). Such highly quantitative versus historic more qualitative approaches to case study analysis of psychosomatics surrounding diabetes in adolescents were reflected critically. PMID:26634215

  3. Detection of Cracking Levels in Brittle Rocks by Parametric Analysis of the Acoustic Emission Signals

    Science.gov (United States)

    Moradian, Zabihallah; Einstein, Herbert H.; Ballivy, Gerard

    2016-03-01

    Determination of the cracking levels during the crack propagation is one of the key challenges in the field of fracture mechanics of rocks. Acoustic emission (AE) is a technique that has been used to detect cracks as they occur across the specimen. Parametric analysis of AE signals and correlating these parameters (e.g., hits and energy) to stress-strain plots of rocks let us detect cracking levels properly. The number of AE hits is related to the number of cracks, and the AE energy is related to magnitude of the cracking event. For a full understanding of the fracture process in brittle rocks, prismatic specimens of granite containing pre-existing flaws have been tested in uniaxial compression tests, and their cracking process was monitored with both AE and high-speed video imaging. In this paper, the characteristics of the AE parameters and the evolution of cracking sequences are analyzed for every cracking level. Based on micro- and macro-crack damage, a classification of cracking levels is introduced. This classification contains eight stages (1) crack closure, (2) linear elastic deformation, (3) micro-crack initiation (white patch initiation), (4) micro-crack growth (stable crack growth), (5) micro-crack coalescence (macro-crack initiation), (6) macro-crack growth (unstable crack growth), (7) macro-crack coalescence and (8) failure.

  4. Effect of Brittle off-fault Damage on Earthquake Rupture Dynamics

    Science.gov (United States)

    Thomas, Marion Y.; Bhat, Harsha S.; Klinger, Yann

    2017-04-01

    In the shallow brittle crust, following earthquake ruptures, geophysical observations show a dramatic drop of seismic wave speeds in the shallow off-fault medium. Seismic ruptures generate, or reactivate, damage around faults that alter the constitutive response of the surrounding medium, which in turn modifies the earthquake itself, the seismic radiation and the near-fault ground motion. This numerical study aims to assess the interplay between earthquake ruptures and dynamically evolving off-fault medium and to underline the damage-related features pertinent to interpret geophysical observations. We present a micro-mechanics based constitutive model that account for dynamic evolution of elastic moduli at high-strain rates. We consider 2-D inplane models, with a 1-D right lateral fault featuring slip-weakening friction law. We demonstrate that the response of the damaged elastic solid is different in the compressional and tensional quadrant. We observe that dynamic damage induces a reduction in elastic moduli and produces slip rate oscillations which result in high frequency content in the radiated ground motion, consistent with strong motion records. We underline the importance of incorporating off-fault medium history in earthquake rupture processes. We find that dynamic damage generation is sensitive to material contrast and that it introduces an additional asymmetry beyond that of a bimaterial fault, in agreement with experimental studies.

  5. Insensitivity to Flaws Leads to Damage Tolerance in Brittle Architected Meta-Materials

    Science.gov (United States)

    Montemayor, L. C.; Wong, W. H.; Zhang, Y.-W.; Greer, J. R.

    2016-02-01

    Cellular solids are instrumental in creating lightweight, strong, and damage-tolerant engineering materials. By extending feature size down to the nanoscale, we simultaneously exploit the architecture and material size effects to substantially enhance structural integrity of architected meta-materials. We discovered that hollow-tube alumina nanolattices with 3D kagome geometry that contained pre-fabricated flaws always failed at the same load as the pristine specimens when the ratio of notch length (a) to sample width (w) is no greater than 1/3, with no correlation between failure occurring at or away from the notch. Samples with (a/w) > 0.3, and notch length-to-unit cell size ratios of (a/l) > 5.2, failed at a lower peak loads because of the higher sample compliance when fewer unit cells span the intact region. Finite element simulations show that the failure is governed by purely tensile loading for (a/w) structural meta-materials may give rise to their damage tolerance and insensitivity of failure to the presence of flaws even when made entirely of intrinsically brittle materials.

  6. A micromechanical basis for partitioning the evolution of grainbridging in brittle materials

    Energy Technology Data Exchange (ETDEWEB)

    Foulk III, J.W.; Cannon, R.M.; Johnson, G.C.; Klein, P.A.; Ritchie, R.O.

    2006-10-09

    A micromechanical model is developed for grain bridging inmonolithic ceramics. Specifically, bridge formation of a single,non-equiaxed grain spanning adjacent grains is addressed. A cohesive zoneframework enables crack initiation and propagation along grainboundaries. The evolution of the bridge is investigated through avariance in both grain angle and aspect ratio. We propose that thebridging process can be partitioned into five distinct regimes ofresistance: propagate, kink, arrest, stall, and bridge. Although crackpropagation and kinking are well understood, crack arrest and subsequent"stall" have been largely overlooked. Resistance during the stall regimeexposes large volumes of microstructure to stresses well in excess of thegrain boundary strength. Bridging can occur through continued propagationor reinitiation ahead of the stalled crack tip. The driving forcerequired to reinitiate is substantially greater than the driving forcerequired to kink. In addition, the critical driving force to reinitiateis sensitive to grain aspect ratio but relatively insensitive to grainangle. The marked increase in crack resistance occurs prior to bridgeformation and provides an interpretation for the rapidly risingresistance curves which govern the strength of many brittle materials atrealistically small flaw sizes.

  7. Size effect on brittle and ductile fracture of two-dimensional interlinked carbon nanotube network

    Science.gov (United States)

    Jing, Yuhang; Aluru, N. R.

    2017-09-01

    The mechanical properties of two-dimensional (2D) interlinked carbon nanotube (CNT) network are investigated using ab initio calculation and molecular dynamics simulations (MD) with Reaxff force field. The simulation results show that bulk 2D interlinked CNT network has good mechanical properties along the axial direction which can be comparable to that of single-walled CNT and graphene, but has better ductility along the radial direction than single-walled CNT and graphene. In addition, the mechanical properties of 2D interlinked CNT network ribbon along the radial direction depend strongly on the size of the ribbon. The Young's modulus and Poisson's ratio decrease as the size increases while the fracture strain increases with the size increasing. By analyzing the atomic structural (both bond length and atomic von Mises stress) evolution of the ribbons, the mechanism of a brittle-to-ductile transition is revealed. The exploration of the mechanical properties of the 2D interlinked CNT network paves the way for application of the relevant devices that can benefit from the high Young's modulus, high tensile strength, and good ductility.

  8. Enrichment of pathogenic alleles in the brittle cornea gene, ZNF469, in keratoconus.

    Science.gov (United States)

    Lechner, Judith; Porter, Louise F; Rice, Aine; Vitart, Veronique; Armstrong, David J; Schorderet, Daniel F; Munier, Francis L; Wright, Alan F; Inglehearn, Chris F; Black, Graeme C; Simpson, David A; Manson, Forbes; Willoughby, Colin E

    2014-10-15

    Keratoconus, a common inherited ocular disorder resulting in progressive corneal thinning, is the leading indication for corneal transplantation in the developed world. Genome-wide association studies have identified common SNPs 100 kb upstream of ZNF469 strongly associated with corneal thickness. Homozygous mutations in ZNF469 and PR domain-containing protein 5 (PRDM5) genes result in brittle cornea syndrome (BCS) Types 1 and 2, respectively. BCS is an autosomal recessive generalized connective tissue disorder associated with extreme corneal thinning and a high risk of corneal rupture. Some individuals with heterozygous PRDM5 mutations demonstrate a carrier ocular phenotype, which includes a mildly reduced corneal thickness, keratoconus and blue sclera. We hypothesized that heterozygous variants in PRDM5 and ZNF469 predispose to the development of isolated keratoconus. We found a significant enrichment of potentially pathologic heterozygous alleles in ZNF469 associated with the development of keratoconus (P = 0.00102) resulting in a relative risk of 12.0. This enrichment of rare potentially pathogenic alleles in ZNF469 in 12.5% of keratoconus patients represents a significant mutational load and highlights ZNF469 as the most significant genetic factor responsible for keratoconus identified to date.

  9. A 3D mechanistic model for brittle materials containing evolving flaw distributions under dynamic multiaxial loading

    Science.gov (United States)

    Hu, Guangli; Liu, Junwei; Graham-Brady, Lori; Ramesh, K. T.

    2015-05-01

    We present a validated fully 3D mechanism-based micromechanical constitutive model for brittle solids under dynamic multiaxial loading conditions. Flaw statistics are explicitly incorporated through a defect density, and evolving flaw distributions in both orientation and size. Interactions among cracks are modeled by means of a crack-matrix-effective-medium approach. A tensorial damage parameter is defined based upon the crack length and orientation development under local effective stress fields. At low confining stresses, the wing-cracking mechanism dominates, leading to the degradation of the modulus and peak strength of the material, whereas at high enough confining stresses, the cracking mechanism is completely shut-down and dislocation mechanisms become dominant. The model handles general multiaxial stress states, accounts for evolving internal variables in the form of evolving flaw size and orientation distributions, includes evolving anisotropic damage and irreversible damage strains in a thermodynamically consistent fashion, incorporates rate-dependence through the micromechanics, and includes dynamic bulking based on independent experimental data. Simulation results are discussed and compared with experimental results on one specific structural ceramic, aluminum nitride. We demonstrate that this 3D constitutive model is capable of capturing the general constitutive response of structural ceramics.

  10. Rice Brittleness Mutants: A Way to Open the 'Black Box' of Monocot Cell Wall Biosynthesis

    Institute of Scientific and Technical Information of China (English)

    Baocai Zhang; Yihua Zhou

    2011-01-01

    Rice is a model organism for studying the mechanism of cell wall biosynthesis and remolding in Gramineae.Mechanical strength is an important agronomy trait of rice(Oryza sativa L.)plants that affects crop lodging and grain yield.As a prominent physical property of cell walls,mechanical strength reflects upon the structure of different wall polymers and how they interact.Studies on the mechanisms that regulate the mechanical strength therefore consequently results in uncovering the genes functioning in cell wall biosynthesis and remodeling.Our group focuses on the study of isolation of brittle culm(bc)mutants and characterization of their corresponding genes.To date,several bc mutants have been reported.The identified genes have covered several pathways of cell wall biosynthesis,revealing many secrets of monocot cell wall biosynthesis.Here,we review the progress achieved in this research field and also highlight the perspectives in expectancy.All of those lend new insights into mechanisms of cell wall formation and are helpful for harnessing the waste rice straws for biofuel production.

  11. How tough is Brittle Bone? Investigating Osteogenesis Imperfecta in Mouse Bone††

    Science.gov (United States)

    Carriero, A.; Zimmermann, E. A.; Paluszny, A.; Tang, S. Y.; Bale, H.; Busse, B.; Alliston, T.; Kazakia, G.

    2015-01-01

    The multiscale hierarchical structure of bone is naturally optimized to resist fractures. In osteogenesis imperfecta, or brittle bone disease, genetic mutations affect the quality and/or quantity of collagen, dramatically increasing bone fracture risk. Here we reveal how the collagen defect results in bone fragility in a mouse model of osteogenesis imperfecta (oim), which has homotrimeric α1(I) collagen. At the molecular level we attribute the loss in toughness to a decrease in the stabilizing enzymatic crosslinks and an increase in non-enzymatic crosslinks, which may break prematurely inhibiting plasticity. At the tissue level, high vascular canal density reduces the stable crack growth, and extensive woven bone limits the crack-deflection toughening during crack growth. This demonstrates how modifications at the bone molecular level have ramifications at larger length scales affecting the overall mechanical integrity of the bone; thus, treatment strategies have to address multiscale properties in order to regain bone toughness. In this regard, findings from the heterozygous oim bone, where defective as well as normal collagen are present, suggest that increasing the quantity of healthy collagen in these bones helps to recover toughness at the multiple length scales. PMID:24420672

  12. Evaluation of Crashworthiness for SAE Materials under Ductile to Brittle Transition Temperature (DBTT

    Directory of Open Access Journals (Sweden)

    Amol Bhanage

    2014-10-01

    Full Text Available The concept of crashworthy coaches came into existence after a crash. This demands, avoid vehicle deformation of other/central parts. For this, the behaviour of plastic deformation of the material is necessary to be known. So, these results are required to study the crashworthy behaviour of the structure. In this research, Comparative study has been taken on the automotive materials of SAE 1026, SAE 4140, SAE 5120 and SAE8620. This paper presents the results of fracture toughness, impact energy and stress required for crack propagation from Charpy v-notch impact test and tensile test. The mechanical behaviour of SAE 1026, SAE 4140, SAE 5120 and SAE 8620 are important to describe response during actual loading condition properties used in the crash analysis of the component. The Charpy impact test was conducted at temperature ranging from room temperature 24°C, 0°C, -20°C, - 40°C, -60°C. Specimens oriented in T-L direction are tested. The materials SAE 1026, SAE 4140, SAE 5120 and SAE8620 shown that the ductile to brittle transition temperature, based on 19.5 J, 10.5 J, 113 J, 59.5 J, absorbed energy is about 1.2°C, -3°C, -38°C, -10°C respectively.

  13. The effect of dopants on the brittle-to-ductile transition in silicon single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Youn Jeong; Tanaka, Masaki; Maeno, Keiki; Higashida, Kenji, E-mail: hong@kyudai-mse.or [Department of Materials Science and Engineering, Kyushu University, 744 Motooka, Fukuoka, 819-0395 (Japan)

    2010-07-01

    The brittle-to-ductile transition (BDT) in boron, antimony and arsenic doped Cz silicon crystals has been experimentally studied, respectively. The BDT temperatures in antimony and arsenic doped silicon wafers are lower than that in a non-doped wafer while the BDT temperature in a boron doped wafer is almost the same as that in the non-doped wafer. The activation energy was obtained from the strain rate dependence of the BDT temperature. It was found that the values of the activation energy in the antimony and arsenic doped wafers are lower than that in the non-doped and boron doped wafers, indicating that the dislocation velocity in the antimony and arsenic doped silicon is faster than that in the non-doped while the dislocation velocity in the boron doped is the same as that in the non-doped. The effect of increasing in dislocation velocity on the BDT temperature was calculated by two-dimensional discrete dislocation dynamics simulations, indicating that the increasing in dislocation velocity decreases the BDT temperature in silicon single crystals.

  14. Effect of disorder on shrinkage-induced fragmentation of a thin brittle layer

    Science.gov (United States)

    Halász, Zoltán; Nakahara, Akio; Kitsunezaki, So; Kun, Ferenc

    2017-09-01

    We investigate the effect of the amount of disorder on the shrinkage-induced cracking of a thin brittle layer attached to a substrate. Based on a discrete element model we study how the dynamics of cracking and the size of fragments evolve when the amount of disorder is varied. In the model a thin layer is discretized on a random lattice of Voronoi polygons attached to a substrate. Two sources of disorder are considered: structural disorder captured by the local variation of the stiffness and strength disorder represented by the random strength of cohesive elements between polygons. Increasing the amount of strength disorder, our calculations reveal a transition from a cellular crack pattern, generated by the sequential branching and merging of cracks, to a disordered ensemble of cracks where the merging of randomly nucleated microcracks dominate. In the limit of low disorder, the statistics of fragment size is described by a log-normal distribution; however, in the limit of high disorder, a power-law distribution is obtained.

  15. Fracture Modes in Curved Brittle Layers Subject to Concentrated Cyclic Loading in Liquid Environments.

    Science.gov (United States)

    Kim, Jae-Won; Thompson, Van P; Rekow, E Dianne; Jung, Yeon-Gil; Zhang, Yu

    2009-03-01

    Damage response of brittle curved structures subject to cyclic Hertzian indentation was investigated. Specimens were fabricated by bisecting cylindrical quartz glass hollow tubes. The resulting hemi-cylindrical glass shells were bonded internally and at the edges to polymeric supporting structures and loaded axially in water on the outer circumference with a spherical tungsten carbide indenter. Critical loads and number of cycles to initiate and propagate near-contact cone cracks and far-field flexure radial cracks to failure were recorded. Flat quartz glass plates on polymer substrates were tested as a control group. Our findings showed that cone cracks form at lower loads, and can propagate through the quartz layer to the quartz/polymer interface at lower number of cycles, in the curved specimens relative to their flat counterparts. Flexural radial cracks require a higher load to initiate in the curved specimens relative to flat structures. These radial cracks can propagate rapidly to the margins, the flat edges of the bisecting plane, under cyclic loading at relatively low loads, owing to mechanical fatigue and a greater spatial range of tensile stresses in curved structures.

  16. Role of indenter material and size in veneer failure of brittle layer structures.

    Science.gov (United States)

    Bhowmick, Sanjit; Meléndez-Martínez, Juan José; Hermann, Ilja; Zhang, Yu; Lawn, Brian R

    2007-07-01

    The roles of indenter material and size in the failure of brittle veneer layers in all-ceramic crown-like structures are studied. Glass veneer layers 1 mm thick bonded to alumina layers 0.5 mm thick on polycarbonate bases (representative of porcelain/ceramic-core/dentin) are subject to cyclic contact loading with spherical indenters in water (representative of occlusal biting environment). Two indenter materials-glass and tungsten carbide-and three indenter radii-1.6, 5.0, and 12.5 mm-are investigated in the tests. A video camera is used to follow the near-contact initiation and subsequent downward propagation of cone cracks through the veneer layer to the core interface, at which point the specimen is considered to have failed. Both indenter material and indenter radius have some effect on the critical loads to initiate cracks within the local Hertzian contact field, but the influence of modulus is weaker. The critical loads to take the veneer to failure are relatively insensitive to either of these indenter variables, since the bulk of the cone crack propagation takes place in the contact far field. Clinical implications of the results are considered, including the issue of single-cycle overload versus low-load cyclic fatigue and changes in fracture mode with loading conditions.

  17. Impact of sediment organic matter quality on the fate and effects of fluoranthene in the infaunal brittle star Amphiura filiformis

    DEFF Research Database (Denmark)

    Selck, Henriette; Granberg, Maria E; Forbes, Valery E.

    2005-01-01

    Hydrophobic contaminants, such as polycyclic aromatic hydrocarbons (PAHs) readily adsorb to organic matter. The aim of this study was to determine the importance of the quality of sedimentary organic matter for the uptake, biotransformation and toxicity of the PAH, fluoranthene (Flu...... to equilibrium partitioning between organism lipid content and organic content of the sediment. Biotransformation of Flu by brittle stars was very limited and unaffected by organic matter quality. A. filiformis contributed to the downward transport of Flu from the surface sediment to the burrow lining....... The limited breakdown of parent Flu by brittle stars and/or microorganisms was relatively higher in burrows compared to surface sediment, and highest in the presence of labile organic matter. Tissue concentrations were higher in disk than in arms, but the proportion of metabolic products relative to parent...

  18. Calcium Binding Restores Gel Formation of Succinylated Gelatin and Reduces Brittleness with Preservation of the Elastically Stored Energy.

    Science.gov (United States)

    Baigts Allende, Diana; de Jongh, Harmen H J

    2015-08-12

    To better tailor gelatins for textural characteristics in (food) gels, their interactions are destabilized by introduction of electrostatic repulsions and creation of affinity sites for calcium to "lock" intermolecular interactions. For that purpose gelatins with various degrees of succinylation are obtained. Extensive succinylation hampers helix formation and gel strength is slightly reduced. At high degrees of succinylation the helix propensity, gelling/melting temperatures, concomitant transition enthalpy, and gel strength become calcium-sensitive, and relatively low calcium concentrations largely restore these properties. Although succinylation has a major impact on the brittleness of the gels formed and the addition of calcium makes the material less brittle compared to nonmodified gelatin, the modification has no impact on the energy balance in the gel, where all energy applied is elastically stored in the material. This is explained by the unaffected stress relaxation by the network and high water-holding capacity related to the small mesh sizes in the gels.

  19. Damage law identification of a quasi brittle ceramic from a b ending test using digital image correlation

    Directory of Open Access Journals (Sweden)

    Meille S.

    2010-06-01

    Full Text Available The quasi brittle ceramics show a non linear mechanical behaviour resulting most of the time in a dissymetry between their tensile and compressive stress-strain laws. The characterization of their fracture strengths might be biased if elastic linear formulae are used to analyze classical tests like bending tests. Based on Digital Image Correlation (DIC, a methodology is proposed to characterize materials with dissymmetric behaviours. Applying specific DIC decomposition functions for bending, compressive and tensile tests, a stress-strain model and its damage law are identified for aluminium titanate, a damageable micro cracked ceramic. This identification method using DIC can obviously be applied to other quasi brittle materials.

  20. The Ductile to Brittle Transition Behavior of the Modified 9Cr-1Mo Steel and Its Laser Welds

    Institute of Scientific and Technical Information of China (English)

    H.C. Wu; R.K. Shiue; C. Chen

    2004-01-01

    The ductile to brittle transition temperature (DBTT) of the modified 9Cr-1Mo steel and its laser welds was studied. The increase in grain size of the weld structure ascended the DBTT of the steel significantly. The transformation of retained austenite at martensite interlath boundaries into untempered and/or twinned martensite could also contribute to increased DBTTs of the steel and its welds tempered at 540℃.

  1. Simulation of seismic waves at the Earth crust (brittle-ductile transition) based on the Burgers model

    OpenAIRE

    Carcione, J.M.; Poletto, F.; B. Farina; A. Craglietto

    2014-01-01

    The Earth crust presents two dissimilar rheological behaviours depending on the in-situ stress-temperature conditions. The upper, cooler, part is brittle while deeper zones are ductile. Seismic waves may reveal the presence of the transition but a proper characterization is required. We first obtain a stress–strain relation including the effects of shear seismic attenuation and ductility due to shear deformations and plastic flow. The anelastic behaviour i...

  2. Simulation of seismic waves at the Earth crust (brittle-ductile transition based on the Burgers model

    Directory of Open Access Journals (Sweden)

    J. M. Carcione

    2014-06-01

    Full Text Available The Earth crust presents two dissimilar rheological behaviours depending on the in-situ stress-temperature conditions. The upper, cooler, part is brittle while deeper zones are ductile. Seismic waves may reveal the presence of the transition but a proper characterization is required. We first obtain a stress–strain relation including the effects of shear seismic attenuation and ductility due to shear deformations and plastic flow. The anelastic behaviour is based on the Burgers mechanical model to describe the effects of seismic attenuation and steady-state creep flow. The shear Lamé constant of the brittle and ductile media depends on the in-situ stress and temperature through the shear viscosity, which is obtained by the Arrhenius equation and the octahedral stress criterion. The P- and S-wave velocities decrease as depth and temperature increase due to the geothermal gradient, an effect which is more pronounced for shear waves. We then obtain the P-S and SH equations of motion recast in the velocity-stress formulation, including memory variables to avoid the computation of time convolutions. The equations correspond to isotropic anelastic and inhomogeneous media and are solved by a direct grid method based on the Runge–Kutta time stepping technique and the Fourier pseudospectral method. The algorithm is tested with success against known analytical solutions for different shear viscosities. A realistic example illustrates the computation of surface and reverse-VSP synthetic seismograms in the presence of an abrupt brittle-ductile transition.

  3. A two-scale model for frictional cracks in 3D fractured brittle media with the extended finite element method

    Science.gov (United States)

    Liu, F.; Borja, R. I.

    2009-12-01

    Stress concentration induced by the heterogeneity in brittle geomaterials is generally considered as the driving force in the evolution of the microstructure (such as the crack and pore microstructure). Specifically, modeling heterogeneity is key to properly predicting the nucleation, coalescence and propagation of micro-cracks in brittle solids. In this paper, we propose a two-scale model for frictional cracks in fractured brittle media. The major crack in the study domain is modeled at a macro level, while the micro-cracks are modeled at a finer scale. The macro-scale behavior is described by a standard boundary value problem. The finer-scale problem is modeled using the notion of representative elementary volume (REV) consisting of a solid volume with distributed micro-cracks. Periodic boundary condition and small strain formulation are assumed in the finer-scale analysis. The scale bridging mechanism is borrowed from the standard homogenization technique. The proposed model is implemented with the extended finite element method. The macro stress at each Gauss point in the finite element formulation is computed as the volume average of finer-scale stresses in each corresponding REV. The macro tangent operator is computed using a perturbation method. For 3D problems, six independent linear perturbation analyses are carried out for each numerical integration point. Our numerical examples capture the nucleation and coalescence of micro-cracks, which can be used to infer the potential propagation direction of the major crack.

  4. A shale rock physics model for analysis of brittleness index, mineralogy and porosity in the Barnett Shale

    Science.gov (United States)

    Guo, Zhiqi; Li, Xiang-Yang; Liu, Cai; Feng, Xuan; Shen, Ye

    2013-04-01

    We construct a rock physics workflow to link the elastic properties of shales to complex constituents and specific microstructure attributes. The key feature in our rock physics model is the degrees of preferred orientation of clay and kerogen particles defined by the proportions of such particles in their total content. The self-consistent approximation method and Backus averaging method are used to consider the isotropic distribution and preferred orientation of compositions and pores in shales. Using the core and well log data from the Barnett Shale, we demonstrate the application of the constructed templates for the evaluation of porosity, lithology and brittleness index. Then, we investigate the brittleness index defined in terms of mineralogy and geomechanical properties. The results show that as clay content increases, Poisson's ratio tends to increase and Young's modulus tends to decrease. Moreover, we find that Poisson's ratio is more sensitive to the variation in the texture of shales resulting from the preferred orientation of clay particles. Finally, based on the constructed rock physics model, we calculate AVO responses from the top and bottom of the Barnett Shale, and the results indicate predictable trends for the variations in porosity, lithology and brittleness index in shales.

  5. Numerical simulation of triaxial compression test for brittle rock sample using a modified constitutive law considering degradation and dilation behavior

    Institute of Scientific and Technical Information of China (English)

    谭鑫

    2015-01-01

    The understanding of the rock deformation and failure process and the development of appropriate constitutive models are the basis for solving problems in rock engineering. In order to investigate progressive failure behavior in brittle rocks, a modified constitutive model was developed which follows the principles of the continuum damage mechanics method. It incorporates non-linear Hoek-Brown failure criterion, confining pressure-dependent strength degradation and volume dilation laws, and is able to represent the nonlinear degradation and dilation behaviors of brittle rocks in the post-failure region. A series of triaxial compression tests were carried out on Eibenstock (Germany) granite samples. Based on a lab data fitting procedure, a consistent parameter set for the modified constitutive model was deduced and implemented into the numerical code FLAC3D. The good agreement between numerical and laboratory results indicates that the modified constitutive law is well suited to represent the nonlinear mechanical behavior of brittle rock especially in the post-failure region.

  6. Predicting the Relationship Between System Vibration with Rock Brittleness Indexes in Rock Sawing Process

    Science.gov (United States)

    Mikaeil, Reza; Ataei, Mohammad; Ghadernejad, Saleh; Sadegheslam, Golsa

    2014-03-01

    The system vibration is a very significant measure of the sawing performance, because it indicates the amount of energy required to saw the rock. The maintenance cost of system is also dependant on system vibration. A few increases in system vibration cause a huge increase in the maintenance cost of the system. In this paper, the vibration of system in terms of RMSa was investigated and models for estimation of vibration by means of rock brittleness indexes and operational specifications were designed via statistical models and multiple curvilinear regression analysis. In this study, the relationships between rock brittleness indexes and operational specifications were investigated by regression analysis in statistical package for social science (SPSS) and the results of determination coefficients have been presented. In the second part, the diagrams show that a point lying on the line indicates an exact estimation. In the plot for model, the points are scattered uniformly about the diagonal line, suggesting that the models are good. It is very useful to evaluate the vibration of system and select the suitable operational characteristics by only some mechanical properties of rock. Drgania układu uważane są za miernik wydajności procesu urabiania, ponieważ pokazują ilość energii niezbędnej do urabiania skały. Od poziomu drgań zależą także koszty eksploatacji systemu. Nieznaczny nawet wzrost poziomu drgań prowadzi do znacznego zwiększenia kosztów eksploatacyjnych urządzenia. W pracy tej przeprowadzono analizę drgań (ich wartości skutecznych) i opracowano model estymacji poziomu drgań w oparciu o współczynnik kruchości skał i parametry eksploatacyjne urządzenia. W pracy wykorzystano modele statystyczne i wielokrotną analizę metodą regresji krzywoliniowej. W pracy obecnej związek pomiędzy współczynnikiem kruchości skał a parametrami eksploatacyjnymi urządzenia badano z wykorzystaniem analizy metodą regresji dostępnej w

  7. SAFOD Brittle Microstructure and Mechanics Knowledge Base (SAFOD BM2KB)

    Science.gov (United States)

    Babaie, H. A.; Hadizadeh, J.; di Toro, G.; Mair, K.; Kumar, A.

    2008-12-01

    We have developed a knowledge base to store and present the data collected by a group of investigators studying the microstructures and mechanics of brittle faulting using core samples from the SAFOD (San Andreas Fault Observatory at Depth) project. The investigations are carried out with a variety of analytical and experimental methods primarily to better understand the physics of strain localization in fault gouge. The knowledge base instantiates an specially-designed brittle rock deformation ontology developed at Georgia State University. The inference rules embedded in the semantic web languages, such as OWL, RDF, and RDFS, which are used in our ontology, allow the Pellet reasoner used in this application to derive additional truths about the ontology and knowledge of this domain. Access to the knowledge base is via a public website, which is designed to provide the knowledge acquired by all the investigators involved in the project. The stored data will be products of studies such as: experiments (e.g., high-velocity friction experiment), analyses (e.g., microstructural, chemical, mass transfer, mineralogical, surface, image, texture), microscopy (optical, HRSEM, FESEM, HRTEM]), tomography, porosity measurement, microprobe, and cathodoluminesence. Data about laboratories, experimental conditions, methods, assumptions, equipments, and mechanical properties and lithology of the studied samples will also be presented on the website per investigation. The ontology was modeled applying the UML (Unified Modeling Language) in Rational Rose, and implemented in OWL-DL (Ontology Web Language) using the Protégé ontology editor. The UML model was converted to OWL-DL by first mapping it to Ecore (.ecore) and Generator model (.genmodel) with the help of the EMF (Eclipse Modeling Framework) plugin in Eclipse. The Ecore model was then mapped to a .uml file, which later was converted into an .owl file and subsequently imported into the Protégé ontology editing environment

  8. Dynamic response of brittle materials from penetration and split Hopkinson pressure bar experiments

    Science.gov (United States)

    Frew, Danny Joe

    This research began with a study on the penetration of limestone targets with ogive-nose rod projectiles. Three sets of experiments were conducted with geometrically similar, steel rod projectiles that had length-to-diameter ratios of 10 and 7.1, 12.7, and 25.4-mm-diameters. Results from these penetration experiments and previously developed penetration models suggested that the limestone target exhibited strain-rate sensitivity. In order to investigate this hypothesis, an experimental/analytical program to study the dynamic material response of limestone was begun. As a first step, it was decided to focus on the dynamic material responses of brittle materials, such as limestone, under a state of one-dimensional stress. A split Hopkinson pressure bar (SHPB) facility was built at the Geotechnical and Structures Laboratory, U.S. Army Waterways Experiment Station. Early in the experimental program it became clear that new modifications had to be made to the traditional SHPB apparatus and experimental techniques. In addition, it was decided to model the responses of the SHPB apparatus and the sample under test in order to guide the experimental designs and minimize the experimental trials. The conventional split Hopkinson pressure bar apparatus was modified by shaping the incident pulse such that the samples are in dynamic stress equilibrium and have nearly constant strain rate over most of the test duration. A thin disk of annealed or hard C11000 copper is placed on the impact surface of the incident bar in order to shape the incident pulse. After impact by the striker bar, the copper disk deforms plastically and spreads the pulse in the incident bar. An analytical model and data show that a wide variety of incident strain pulses can be produced by varying the geometry of the copper disks and the length and striking velocity of the striker bar. The pulse shaping model predictions are in good agreement with measurements. Analytic models predict that a ramp stress pulse

  9. Benchmarking the Sandbox: Quantitative Comparisons of Numerical and Analogue Models of Brittle Wedge Dynamics (Invited)

    Science.gov (United States)

    Buiter, S.; Schreurs, G.; Geomod2008 Team

    2010-12-01

    When numerical and analogue models are used to investigate the evolution of deformation processes in crust and lithosphere, they face specific challenges related to, among others, large contrasts in material properties, the heterogeneous character of continental lithosphere, the presence of a free surface, the occurrence of large deformations including viscous flow and offset on shear zones, and the observation that several deformation mechanisms may be active simultaneously. These pose specific demands on numerical software and laboratory models. By combining the two techniques, we can utilize the strengths of each individual method and test the model-independence of our results. We can perhaps even consider our findings to be more robust if we find similar-to-same results irrespective of the modeling method that was used. To assess the role of modeling method and to quantify the variability among models with identical setups, we have performed a direct comparison of results of 11 numerical codes and 15 analogue experiments. We present three experiments that describe shortening of brittle wedges and that resemble setups frequently used by especially analogue modelers. Our first experiment translates a non-accreting wedge with a stable surface slope. In agreement with critical wedge theory, all models maintain their surface slope and do not show internal deformation. This experiment serves as a reference that allows for testing against analytical solutions for taper angle, root-mean-square velocity and gravitational rate of work. The next two experiments investigate an unstable wedge, which deforms by inward translation of a mobile wall. The models accommodate shortening by formation of forward and backward shear zones. We compare surface slope, rate of dissipation of energy, root-mean-square velocity, and the location, dip angle and spacing of shear zones. All models show similar cross-sectional evolutions that demonstrate reproducibility to first order. However

  10. Microstructure evolution of fault rocks at the "brittle-to-plastic" transition

    Science.gov (United States)

    Heilbronner, R.; Pec, M.; Stunitz, H.

    2011-12-01

    In the continental crust, large earthquakes tend to nucleate at the "brittle-to-plastic" transition at depths of ~ 10 - 20 km indicating stress release by rupture at elevated PT. Experimental studies, field observations, and models predict peak strength of the lithosphere at depths where rocks deform by "semi-brittle" flow. Thus, the deformation processes taking place at these conditions are important aspects of the seismic cycle and fault rheology in general. We performed a series of experiments with crushed Verzasca gneiss powder (d ≤ 200 μm), "pre-dried" and 0.2 wt% H2O added, placed between alumina forcing blocks (45° pre-cut) and weld-sealed in Pt jackets. The experiments were performed at Pc = 500, 1000 and 1500 MPa, T = 300°C and 500°C. and shear strain rates of ~10-3 s-1 to ~10-5 s-1 in a solid medium deformation apparatus (Griggs rig). Samples deformed at Pc = 500 MPa attain peak strength (~ 1100-1400 MPa) at γ ~ 2, they weaken by ~20 MPa (300°C) to ~140 MPa (500°C) and reach a steady state. The 300°C experiments are systematically stronger by ~ 330 - 370 MPa than the 500°C experiments, and flow stress increases with increasing strain rate. At Pc = 1000 and 1500 MPa, peak strength (~1300-1600 MPa) is reached at γ = 1 to 1.5 followed by weakening of ~60 (300°C) and ~150 MPa (500°C). The strength difference between 300°C and 500°C samples is 270-330 MPa and does not increase with increasing confining pressure. The peak strength increase with confining pressure is modest (50-150 MPa), indicating that the rocks reach their maximal compressive strength. The microstructure develops as an S-C-C' fabric with dominant C' slip zones. At low strains, the gouge zone is pervasively cut by closely spaced C' shears containing fine-grained material (d < 100 nm). At peak strength, deformation localizes into less densely spaced, ~10 μm thick C'-C slip zones which develop predominantly in feldspars. In TEM, they show no porosity and consist of amorphous

  11. From brittle to ductile: a structure dependent ductility of diamond nanothread

    Science.gov (United States)

    Zhan, Haifei; Zhang, Gang; Tan, Vincent B. C.; Cheng, Yuan; Bell, John M.; Zhang, Yong-Wei; Gu, Yuantong

    2016-05-01

    As a potential building block for the next generation of devices/multifunctional materials that are spreading in almost every technology sector, one-dimensional (1D) carbon nanomaterial has received intensive research interests. Recently, a new ultra-thin diamond nanothread (DNT) has joined this palette, which is a 1D structure with poly-benzene sections connected by Stone-Wales (SW) transformation defects. Using large-scale molecular dynamics simulations, we found that this sp3 bonded DNT can transition from brittle to ductile behaviour by varying the length of the poly-benzene sections, suggesting that DNT possesses entirely different mechanical responses than other 1D carbon allotropes. Analogously, the SW defects behave like a grain boundary that interrupts the consistency of the poly-benzene sections. For a DNT with a fixed length, the yield strength fluctuates in the vicinity of a certain value and is independent of the ``grain size''. On the other hand, both yield strength and yield strain show a clear dependence on the total length of DNT, which is due to the fact that the failure of the DNT is dominated by the SW defects. Its highly tunable ductility together with its ultra-light density and high Young's modulus makes diamond nanothread ideal for the creation of extremely strong three-dimensional nano-architectures.As a potential building block for the next generation of devices/multifunctional materials that are spreading in almost every technology sector, one-dimensional (1D) carbon nanomaterial has received intensive research interests. Recently, a new ultra-thin diamond nanothread (DNT) has joined this palette, which is a 1D structure with poly-benzene sections connected by Stone-Wales (SW) transformation defects. Using large-scale molecular dynamics simulations, we found that this sp3 bonded DNT can transition from brittle to ductile behaviour by varying the length of the poly-benzene sections, suggesting that DNT possesses entirely different

  12. Brittle fault analysis from the immediate southern side of the Insubric fault

    Science.gov (United States)

    Pleuger, Jan; Mancktelow, Neil

    2013-04-01

    The Insubric segment of the Periadriatic fault is characterised in its central part between Lago Maggiore and Valle d'Ossola by two greenschist-facies mylonitic belts which together are about 1 km thick. The northern, external belt has a north-side-up kinematics generally with a minor dextral component and the southern internal belt is dextral, locally with a considerable south-side-up component. Overprinting relations locally show that the internal belt is younger than the external one (e.g. Schmid et al., 1987). The absolute age of dextral shearing is probably given by K-Ar white mica ages ranging mostly between from c. 27 to 23 Ma (Zingg and Hunziker, 1990). We analysed fault-slip data from various locations in the Southern Alps immediately south of the Insubric Fault. From the results, two different patterns of orientations of contraction (P-axes) and extension (T-axes) axes can be distinguished. One group (group 1) of analyses is compatible with dextral transpression (i.e. both P- and T-axes are subhorizontal) and the other (group 2) with roughly orogen-perpendicular extension (i.e. subvertical P-axes and subhorizontal T-axes). The orientations of subhorizontal axes (P- and T-axes in group 1, T-axes in group 2) show a tendency to follow the curved shape of the Insubric fault, i.e. P-axes of group 1 and T-axes of group 2 change from NNW-SSE in the east where the Insubric fault trends east-west to WNW-ESE in the west where the Insubric fault trends northeast-southwest. We speculate that group 1 formed at the same time as dextral shearing on in the internal mylonite belt while none of our fault analyses reflects the north-side-up reverse faulting that is observed in the external mylonite belt. The northwest-southeast extension documented in the analyses of group 2 is not associated with a continuous mylonitic belt or brittle fault plane along the Insubric fault. Instead, an uplift of the Southern Alps with respect to the northern block was accommodated by

  13. A visco-poroelastic damage model for modelling compaction and brittle failure of porous rocks

    Science.gov (United States)

    Jacquey, Antoine B.; Cacace, Mauro; Blöcher, Guido; Milsch, Harald; Scheck-Wenderoth, Magdalena

    2016-04-01

    Hydraulic stimulation of geothermal wells is often used to increase heat extraction from deep geothermal reservoirs. Initiation and propagation of fractures due to pore pressure build-up increase the effective permeability of the porous medium. Understanding the processes controlling the initiation of fractures, the evolution of their geometries and the hydro-mechanical impact on transport properties of the porous medium is therefore of great interest for geothermal energy production. In this contribution, we will present a thermodynamically consistent visco-poroelastic damage model which can deal with the multi-scale and multi-physics nature of the physical processes occurring during deformation of a porous rock. Deformation of a porous medium is crucially influenced by the changes in the effective stress. Considering a strain-formulated yield cap and the compaction-dilation transition, three different regimes can be identified: quasi-elastic deformation, cataclastic compaction with microcracking (damage accumulation) and macroscopic brittle failure with dilation. The governing equations for deformation, damage accumulation/healing and fluid flow have been implemented in a fully-coupled finite-element-method based framework (MOOSE). The MOOSE framework provides a powerful and flexible platform to solve multiphysics problems implicitly and in a tightly coupled manner on unstructured meshes which is of interest for such non-linear context. To validate and illustrate the model, simulations of the deformation behaviour of cylindrical porous Bentheimer sandstone samples under different confining pressures are compared to experiments. The first experiment under low confining pressure leads to shear failure, the second for high confining pressure leads to cataclastic compaction and the third one with intermediate confining pressure correspond to a transitional regime between the two firsts. Finally, we will demonstrate that this approach can also be used at the field

  14. Brittle Culm1, a COBRA-like protein, functions in cellulose assembly through binding cellulose microfibrils.

    Science.gov (United States)

    Liu, Lifeng; Shang-Guan, Keke; Zhang, Baocai; Liu, Xiangling; Yan, Meixian; Zhang, Lanjun; Shi, Yanyun; Zhang, Mu; Qian, Qian; Li, Jiayang; Zhou, Yihua

    2013-01-01

    Cellulose represents the most abundant biopolymer in nature and has great economic importance. Cellulose chains pack laterally into crystalline forms, stacking into a complicated crystallographic structure. However, the mechanism of cellulose crystallization is poorly understood. Here, via functional characterization, we report that Brittle Culm1 (BC1), a COBRA-like protein in rice, modifies cellulose crystallinity. BC1 was demonstrated to be a glycosylphosphatidylinositol (GPI) anchored protein and can be released into cell walls by removal of the GPI anchor. BC1 possesses a carbohydrate-binding module (CBM) at its N-terminus. In vitro binding assays showed that this CBM interacts specifically with crystalline cellulose, and several aromatic residues in this domain are essential for binding. It was further demonstrated that cell wall-localized BC1 via the CBM and GPI anchor is one functional form of BC1. X-ray diffraction (XRD) assays revealed that mutations in BC1 and knockdown of BC1 expression decrease the crystallite width of cellulose; overexpression of BC1 and the CBM-mutated BC1s caused varied crystallinity with results that were consistent with the in vitro binding assay. Moreover, interaction between the CBM and cellulose microfibrils was largely repressed when the cell wall residues were pre-stained with two cellulose dyes. Treating wild-type and bc1 seedlings with the dyes resulted in insensitive root growth responses in bc1 plants. Combined with the evidence that BC1 and three secondary wall cellulose synthases (CESAs) function in different steps of cellulose production as revealed by genetic analysis, we conclude that BC1 modulates cellulose assembly by interacting with cellulose and affecting microfibril crystallinity.

  15. Brittle Culm1, a COBRA-like protein, functions in cellulose assembly through binding cellulose microfibrils.

    Directory of Open Access Journals (Sweden)

    Lifeng Liu

    Full Text Available Cellulose represents the most abundant biopolymer in nature and has great economic importance. Cellulose chains pack laterally into crystalline forms, stacking into a complicated crystallographic structure. However, the mechanism of cellulose crystallization is poorly understood. Here, via functional characterization, we report that Brittle Culm1 (BC1, a COBRA-like protein in rice, modifies cellulose crystallinity. BC1 was demonstrated to be a glycosylphosphatidylinositol (GPI anchored protein and can be released into cell walls by removal of the GPI anchor. BC1 possesses a carbohydrate-binding module (CBM at its N-terminus. In vitro binding assays showed that this CBM interacts specifically with crystalline cellulose, and several aromatic residues in this domain are essential for binding. It was further demonstrated that cell wall-localized BC1 via the CBM and GPI anchor is one functional form of BC1. X-ray diffraction (XRD assays revealed that mutations in BC1 and knockdown of BC1 expression decrease the crystallite width of cellulose; overexpression of BC1 and the CBM-mutated BC1s caused varied crystallinity with results that were consistent with the in vitro binding assay. Moreover, interaction between the CBM and cellulose microfibrils was largely repressed when the cell wall residues were pre-stained with two cellulose dyes. Treating wild-type and bc1 seedlings with the dyes resulted in insensitive root growth responses in bc1 plants. Combined with the evidence that BC1 and three secondary wall cellulose synthases (CESAs function in different steps of cellulose production as revealed by genetic analysis, we conclude that BC1 modulates cellulose assembly by interacting with cellulose and affecting microfibril crystallinity.

  16. Cadmium Accumulation and Its Toxicity in Brittle Culm 1 (bc1, a Fragile Rice Mutant

    Directory of Open Access Journals (Sweden)

    Guo-sheng SHAO

    2007-09-01

    Full Text Available Cadmium (Cd accumulation and toxicity in rice plants were characterized and identified by using brittle culm 1 (bc1, a fragile rice mutant and its wild type (Shuangkezao, an indica rice as materials by hydroponics. The low Cd level didn't obviously affect the growth parameters in both rice genotypes, but under high Cd levels (1.0 and 5.0 μmol/L, the growth of both rice plants were substantially inhibited. Moreover, bc1 tended to suffer more seriously from Cd toxicity than Shuangkezao. Cd accumulation in both rice plants increased with the increase of Cd levels. There was a significant difference in Cd accumulation between the two rice genotypes with constantly higher Cd concentration in bc1, which also accumulated more Cd at 0, 0.1, and 1.0 μmol/L Cd levels. The same case was found in the two rice plants grown on Cd-contaminated soil. This suggested that cell wall might play an important role in Cd accumulation in rice plants by the physiological mechanisms. The malondialdehyde (MDA content, superoxide dismutase (SOD and peroxidase (POD activities in rice plants were affected differently under Cd treatments, and which implied that POD might play the main role in detoxifying active oxygen free radical. A significant difference in antioxidative system between the two rice genotypes was found with constantly higher MDA content, SOD and POD activities in bc1. In summary, bc1 accumulated more Cd and appeared to be more sensitive to Cd stress compared with its wild type.

  17. ADP-glucose pyrophosphorylase in shrunken-2 and brittle-2 mutants of maize.

    Science.gov (United States)

    Giroux, M J; Hannah, L C

    1994-05-25

    The Shrunken-2 (Sh2) and Brittle-2 (Bt2) genes of maize encode subunits of the tetrameric maize endosperm ADPglucose pyrophosphorylase. However, in all sh2 and bt2 mutants so far examined, measurable ADPglucose pyrophosphorylase activity remains. We have investigated the origin of the residual activity found in various sh2 and bt2 mutants as well as tissue specific expression and post-translational modification of the Sh2 and Bt2 proteins. Sh2 and Bt2 cDNAs were expressed in Escherichia coli and antibodies were prepared against the resulting proteins SH2 and BT2 specific antibodies were used to demonstrate that SH2 and BT2 are endosperm specific, are altered or missing in various sh2 or bt2 mutants, and have a mol. wt. of 54 and 51 kDa respectively in the wild type. The Sh2 and Bt2 transcripts are also endosperm specific. Ten sh2 and eight bt2 mutants show varying severity of phenotypes expressed at transcript, protein subunit and kernel level. Synthesis of multiple transcripts and proteins commonly occurs as a result of sh2 or bt2 mutation. While all mutants produce detectable enzymic activity, not all produce detectable transcripts and proteins. To examine the origin of the apparent non-SH2/BT2 endosperm enzymic activity, homologs of Sh2 and Bt2, designated Agp1 and Agp2 respectively, were isolated from an embryo cDNA library and found to hybridize to endosperm transcripts distinct from those of Sh2 and Bt2. Thus Agp1 and Agp2 or closely related genes may be responsible for the residual activity in some sh2 and bt2 mutants. Surprisingly, no evidence of post-translational modification of the SH2 and BT2 protein subunits was detected.

  18. Drilling on Mars---Mathematical Model for Rotary-Ultrasonic Core Drilling of Brittle Materials

    Science.gov (United States)

    Horne, Mera Fayez

    The results from the Phoenix mission led scientists to believe it is possible that primitive life exists below the Martian surface. Therefore, drilling in Martian soil in search for organisms is the next logical step. Drilling on Mars is a major engineering challenge due to the drilling depth requirement. Mars lacks a thick atmosphere and a continuous magnetic field that shield the planet's surface from solar radiation and solar flares. As a result, the Martian surface is sterile and if life ever existed, it must be found below the surface. In 2001, NASA's Mars Exploration Payload Advisory Group proposed that drilling should be considered as a priority investigation on Mars in an effort of finding evidence of extinct or extant life. On August 6, 2012, the team of engineers landed the spacecraft Curiosity on the surface of Mars by using a revolutionary hovering platform. The results from the Curiosity mission suggested the next logical step, which is drilling six meters deep in the red planet in search of life. Excavation tools deployed to Mars so far have been able to drill to a maximum depth of 6.5 cm. Thus, the drilling capabilities need to be increased by a factor or approximately 100 to achieve the goal of drilling six meters deep. This requirement puts a demand on developing a new and more effective technologies to reach this goal. Previous research shows evidence of a promising drilling mechanism in rotary-ultrasonic for what it offers in terms of high surface quality, faster rate of penetration and higher material removal rate. This research addresses the need to understand the mechanics of the drill bit tip and rock interface in rotary-ultrasonic drilling of brittle materials. A mathematical model identifying all contributing independent parameters, such as drill bit design parameters, drilling process parameters, ultrasonic wave amplitude and rocks' material properties, that have effect on rate of penetration is developed. Analytical and experimental

  19. Impact cratering experiments in brittle targets with variable thickness: Implications for deep pit craters on Mars

    Science.gov (United States)

    Michikami, T.; Hagermann, A.; Miyamoto, H.; Miura, S.; Haruyama, J.; Lykawka, P. S.

    2014-06-01

    High-resolution images reveal that numerous pit craters exist on the surface of Mars. For some pit craters, the depth-to-diameter ratios are much greater than for ordinary craters. Such deep pit craters are generally considered to be the results of material drainage into a subsurface void space, which might be formed by a lava tube, dike injection, extensional fracturing, and dilational normal faulting. Morphological studies indicate that the formation of a pit crater might be triggered by the impact event, and followed by collapse of the ceiling. To test this hypothesis, we carried out laboratory experiments of impact cratering into brittle targets with variable roof thickness. In particular, the effect of the target thickness on the crater formation is studied to understand the penetration process by an impact. For this purpose, we produced mortar targets with roof thickness of 1-6 cm, and a bulk density of 1550 kg/m3 by using a mixture of cement, water and sand (0.2 mm) in the ratio of 1:1:10, by weight. The compressive strength of the resulting targets is 3.2±0.9 MPa. A spherical nylon projectile (diameter 7 mm) is shot perpendicularly into the target surface at the nominal velocity of 1.2 km/s, using a two-stage light-gas gun. Craters are formed on the opposite side of the impact even when no target penetration occurs. Penetration of the target is achieved when craters on the opposite sides of the target connect with each other. In this case, the cross section of crater somehow attains a flat hourglass-like shape. We also find that the crater diameter on the opposite side is larger than that on the impact side, and more fragments are ejected from the crater on the opposite side than from the crater on the impact side. This result gives a qualitative explanation for the observation that the Martian deep pit craters lack a raised rim and have the ejecta deposit on their floor instead. Craters are formed on the opposite impact side even when no penetration

  20. Brittle/Ductile deformation at depth during continental crust eclogitization (Mont-Emilius klippe, Western Internal Alps).

    Science.gov (United States)

    Hertgen, Solenn; Yamato, Philippe; Morales, Luiz; Angiboust, Samuel

    2016-04-01

    Eclogitic rocks are important for understanding tectonics at large scale as they provide key constraints on both the evolution (P-T-t-ɛ paths) and the deformation modes of the crust along the subduction interface. We herein focus our study on eclogitized mafic dykes remnants exposed within granulites from the continental basement silver of the Mt. Emilius klippe (Western Internal Alps, Italy). These eclogites exhibit highly deformed garnetite and clinopyroxenite levels. In some places, these rocks with a ± mylonitic aspect can be found as clasts within meter-thick brecciated fault rocks formed close to metamorphic peak conditions in eclogite facies. Especially, the garnet-rich levels tend to behave in a brittle fashion while deformation within clinopyroxene-rich levels is mostly accommodated by creep. This is evidenced by the presence of elongated grains, subgrain boundaries and intense grain size reduction close to rigid garnets. Crystallographic preferred orientation (CPO) measurements in garnets indicate a quasi-random distribution. In most of the clinopyroxenes levels nevertheless, the CPO is relatively strong, with multiples of uniform distribution varying from 4 to 5.5 (value of 1 is random texture). This CPO is characterized by a strong alignment of poles (001) parallel to the lineation and (100) and [010] distributed along girdles cross-cutting the foliation plane. Our study thus attests that the materials along the subduction interface at P~2.0-2.5 GPa and T~500-550°C can locally be brittle where deformation is classically envisioned as ductile. In addition to this deformation analysis, we present a petrological study of these eclogites, from the outcrop to the microscopic scale, tracking the chemical evolution associated to the observed deformation. Based on all these data, we finally propose a tectono-metamorphic history for these rocks allowing to explain the co-existence of ductile and brittle features developed in the same metamorphic facies, and

  1. An Experimental and Numerical Study on Cracking Behavior of Brittle Sandstone Containing Two Non-coplanar Fissures Under Uniaxial Compression

    Science.gov (United States)

    Yang, Sheng-Qi; Tian, Wen-Ling; Huang, Yan-Hua; Ranjith, P. G.; Ju, Yang

    2016-04-01

    To understand the fracture mechanism in all kinds of rock engineering, it is important to investigate the fracture evolution behavior of pre-fissured rock. In this research, we conducted uniaxial compression experiments to evaluate the influence of ligament angle on the strength, deformability, and fracture coalescence behavior of rectangular prismatic specimens (80 × 160 × 30 mm) of brittle sandstone containing two non-coplanar fissures. The experimental results show that the peak strength of sandstone containing two non-coplanar fissures depends on the ligament angle, but the elastic modulus is not closely related to the ligament angle. With the increase of ligament angle, the peak strength decreased at a ligament angle of 60°, before increasing up to our maximum ligament angle of 120°. Crack initiation, propagation, and coalescence were all observed and characterized from the inner and outer tips of pre-existing non-coplanar fissures using photographic monitoring. Based on the results, the sequence of crack evolution in sandstone containing two non-coplanar fissures was analyzed in detail. In order to fully understand the crack evolution mechanism of brittle sandstone, numerical simulations using PFC2D were performed for specimens containing two non-coplanar fissures under uniaxial compression. The results are in good agreement with the experimental results. By analyzing the stress field, the crack evolution mechanism in brittle sandstone containing two non-coplanar fissures under uniaxial compression is revealed. These experimental and numerical results are expected to improve the understanding of the unstable fracture mechanism of fissured rock engineering structures.

  2. A pulse-shaping technique to investigate the behaviour of brittle materials subjected to plate-impact tests

    Science.gov (United States)

    Forquin, Pascal; Zinszner, Jean-Luc

    2017-01-01

    Owing to their significant hardness and compressive strengths, ceramic materials are widely employed for use with protective systems subjected to high-velocity impact loadings. Therefore, their mechanical behaviour along with damage mechanisms need to be significantly investigated as a function of loading rates. However, the classical plate-impact testing procedures produce shock loadings in the brittle sample material which cause unrealistic levels of loading rates. Additionally, high-pulsed power techniques and/or functionally graded materials used as flyer plates to smooth the loading pulse remain costly, and are generally difficult to implement. In this study, a shockless plate-impact technique based on the use of either a wavy-machined flyer plate or buffer plate that can be produced by chip-forming is proposed. A series of numerical simulations using an explicit transient dynamic finite-element code have been performed to design and validate the experimental testing configuration. The calculations, conducted in two-dimensional (2D) plane-strain or in 2D axisymmetric modes, prove that the `wavy' contact surface will produce a pulse-shaping effect, whereas the buffer plate will produce a homogenizing effect of the stress field along the transverse direction of the sample. In addition, `wavy-shape' geometries of different sizes provide an easy way to change the level of loading rate and rise time in an experimentally tested ceramic specimen. Finally, when a shockless compression loading method is applied to the sample, a Lagrangian analysis of data is made possible by considering an assemblage of ceramic plates of different thicknesses in the target, so the axial stress-strain response of the brittle sample material can be provided. This article is part of the themed issue 'Experimental testing and modelling of brittle materials at high strain rates'.

  3. Initiation of a Low-Angle Normal Fault Active Across the Upper Brittle-Plastic Transition, Chemehuevi Mountains, CA

    Science.gov (United States)

    LaForge, J.; John, B. E.; Grimes, C. B.; Stunitz, H.; Heilbronner, R.

    2016-12-01

    The Chemehuevi detachment fault system, part of the regionally developed Colorado River extensional corridor, hosts exceptional exposures of a denuded fault system related to Miocene extension. Here, we characterize the early history of extension associated with a small slip (1-2 km) low-angle normal fault, the Mohave Wash fault (MWF), initially active across the brittle-plastic transition. Strain localized in three principal ways across the 23-km down-dip exposure (T 400°C): a brittle fault zone, localized, disseminated quartz mylonites, and syntectonic dikes hosting mylonitic fabrics. Brittle deformation in these crystalline rocks was concentrated into a 10-62-m thick brittle fault zone hosting localized, unmineralized to chlorite-epidote-quartz mineralized zones of cataclasite series fault rocks ≤3 m thick and rare pseudotachylite. Mylonitic deformation played an increased role in deformation down dip (NE), with mylonites increasing in quantity and average thickness. At shallow structural levels, footwall mylonites are absent; at 9-18 km down dip, cm-scale quartz mylonites are common; ≥18 km down dip, meter-scale syntectonic intermediate-felsic dikes are mylonitic, are attenuated into parallelism with the MWF, and host well-developed L-S fabric; 23 km down dip, the footwall hosts meter-thick zones of disseminated mylonitic quartz of varying intensities. These mylonites host microstructures that record progressively higher deformation temperature down dip, with dislocation-creep in quartz indicative of T of 280-400°C to ≥500°C, and diffusion creep with grain boundary sliding in dikes suggestive of even higher T deformation. Dike emplacement in the system is syntectonic with MWF slip; mafic-intermediate composition dikes intruded damage zone fractures and cataclasites, and were in turn fractured; Pb/U zircon ages of intermediate-felsic dikes range from ca. 1.5 ± 1 Ma to 3.8 ± 1 Ma after the onset of regional extension, but predate rapid slip. Cross

  4. Laboratory tests and numerical simulations of brittle marble and squeezing schist at Jinping II hydropower station,China

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    Four 16.7 km-long tunnels with diameters ranging from 12.4 to 14.6 m are now under construction at Jinping II hydropower station along the Yalong River.The tunnels pass through Triassic rocks below Jinping Mountain.The tunnels are characterized with high overburden,long alignment and complex geological conditions.Brittle failure in marble and squeezing in schist are the primary problems in tunnelling.This paper introduces the studies of laboratory tests on Jinping II marble as well as numerical prediction o...

  5. A New Multiaxial High-Cycle Fatigue Criterion Based on the Critical Plane for Ductile and Brittle Materials

    Science.gov (United States)

    Wang, Cong; Shang, De-Guang; Wang, Xiao-Wei

    2015-02-01

    An improved high-cycle multiaxial fatigue criterion based on the critical plane was proposed in this paper. The critical plane was defined as the plane of maximum shear stress (MSS) in the proposed multiaxial fatigue criterion, which is different from the traditional critical plane based on the MSS amplitude. The proposed criterion was extended as a fatigue life prediction model that can be applicable for ductile and brittle materials. The fatigue life prediction model based on the proposed high-cycle multiaxial fatigue criterion was validated with experimental results obtained from the test of 7075-T651 aluminum alloy and some references.

  6. Effect of the features of functionalized structure on elastic properties and strength of partially-filled brittle porous materials

    Science.gov (United States)

    Konovalenko, Igor S.; Shilko, Evgeny V.; Konovalenko, Ivan S.; Vodopjyanov, Egor M.

    2016-11-01

    A two-scale mechanical model of brittle porous material partially filled with plastic filler (inclusions) was developed within the framework of the formalism of movable cellular automaton method. The model was applied to study the mechanical properties of mesoscopic samples with a linear distribution of the local porosity in the depth of the material. Calculation results showed essentially nonlinear dependence of their elastic and strength properties on the degree of pore space filling. It is found that depending on the sign of the gradient of porosity the value of shear strength of partially filled samples can significantly increase or remain constant with increase in the value of the degree of filling.

  7. Revealing stiffening and brittling of chronic myelogenous leukemia hematopoietic primary cells through their temporal response to shear stress

    Science.gov (United States)

    Laperrousaz, B.; Berguiga, L.; Nicolini, F. E.; Martinez-Torres, C.; Arneodo, A.; Maguer Satta, V.; Argoul, F.

    2016-06-01

    Cancer cell transformation is often accompanied by a modification of their viscoelastic properties. When capturing the stress-to-strain response of primary chronic myelogenous leukemia (CML) cells, from two data sets of CD34+ hematopoietic cells isolated from healthy and leukemic bone marrows, we show that the mean shear relaxation modulus increases upon cancer transformation. This stiffening of the cells comes along with local rupture events, detected as reinforced sharp local maxima of this modulus, suggesting that these cancer cells respond to a local mechanical stress by a cascade of local brittle failure events.

  8. THE EFFECT OF MATRIX TOUGHNESS ON THE BRITTLE-DUCTILE TRANSITION OF HDPE/CaCO3 BLENDS

    Institute of Scientific and Technical Information of China (English)

    FU Qiang; ZHANG Yulin; WANG Guiheng

    1994-01-01

    The effects of HDPE matrix toughness on the brittle-ductile transition of HDPE/CaCO3 blends are investigated. Not all HDPE can be toughened by CaCO3 particles. The ability of the matrix to yield plays a fundamental role in determing whether HDPE can be toughened or not.There exists a critical matrix toughness (Isc≈45J/m) below which HDPE can not be toughened observably by CaCO3 particle at given average size, and above which the critical matrix ligament thickness (τc) is proportional to matrix impact strength.

  9. Swedish Work on Brittle-Fracture Problems in Nuclear Reactor Pressure Vessels

    Energy Technology Data Exchange (ETDEWEB)

    Grounes, M.

    1966-03-15

    After a short review of the part of the Swedish nuclear energy program that is of interest in this context the Swedish reactor pressure vessels and the reasoning behind the choice of materials are surveyed. Problems and desirable aims for future reactors are discussed. Much work is now being done on new types of pressure vessel steels with high strength, low transition temperature and good corrosion resistance. These steels are of the martensitic austenitic type Bofors 2RMO (13 % Cr, 6 % Ni, 1. 5 % Mo) and of the ferritic martensitic austenitic type Avesta 248 SV (16 % Cr, 5 % Ni, 1 % Mo). An applied philosophy for estimating the brittle-fracture tendency of pressure vessels is described. As a criterion of this tendency we use the crack-propagation transition temperature, e. g. as measured by the Robertson isothermal crack-arrest test. An estimate of this transition temperature at the end of the reactor' s lifetime must take increases due to fabrication, welding, geometry, ageing and irradiation into account. The transition temperature vs. stress curve moves towards higher temperatures during the reactor' s lifetime. As long as this curve does not cross the reactor vessel stress vs. temperature curve the vessel is considered safe. The magnitude of the different factors influencing the final transition temperature are discussed and data for the Marviken reactor's pressure vessel are presented. At the end of the reactor's lifetime the estimated transition temperature is 115 deg C, which is below the maximum permissible value. A program for the study of strain ageing has been initiated owing to the uncertainty as to the extent of strain ageing at low strains. A study of a simple crack-arrest test, developed in Sweden, is in progress. An extensive irradiation-effects program on several steels is in progress. Results from tests on the Swedish carbon-manganese steels 2103/R3, SIS 142103 and SIS 142102, the low-alloy steels Degerfors DE-631A, Bofors NO

  10. 3D Imaging of Brittle/Ductile transition of the crust beneath the resurgent calderas

    Science.gov (United States)

    Tizzani, P.; Castaldo, R.; Pepe, S.; Solaro, G.

    2012-04-01

    Rheology is a crucial factor to understand the mechanical behaviour and evolution of the crust in young and tectonically active belts. The aim of this paper is to investigate the rheological properties of the crust beneath resurgent calderas as Long Valley caldera (California USA) and Campi Flegrei (Southern Italy). Through the rheological proprieties of the calderas area, we highlight the driving process that determine the cut off of the local seismicity [K. Ito, 1993]. In this context, we consider the thermal proprieties and mechanical heterogeneity of the crust in order to develop a 3D conductive time dependent thermal model of the upper crust beneath the two calderas. More specifically we integrate geophysical information (gravimetric, seismic and boreholes data) available for the considered area in FEM environment [Manconi A. et al., 2010]. We performed a numerical solution of Fourier equation to carry out an advance optimization of the real measured data. We produce a set of forward models and propose, in order to analyse and solve the statistical problem, the Monte Carlo optimization procedures as Genetic Algorithm [Manconi A. et al., 2009]. In particular we search for the heat production, the volume source distribution and the surface emissivity parameters that providing the best-fit of the geothermal profiles data measured at boreholes, by solving the non stationary heat flow equation (Campanian Ignimbrite eruption about 40 kyr for Campi Flegrei caldera and Bishop tuff eruption about 700 kyr for Long Valley caldera). The performed thermal fields allow us to obtain the rheological stratification of the crust beneath two resurgent calderas; the models suggest that the uprising of a ductile layer which connects the upper mantle to the volcanic feeding system could determine the stress conditions that controlled the distribution of seismicity. In fact, the computed 3D imaging of Brittle/Ductile transition well agrees with the seismic hypocentral distribution

  11. The brittle-viscous-plastic evolution of shear bands in the South Armorican Shear Zone

    Science.gov (United States)

    Bukovská, Zita; Jeřábek, Petr; Morales, Luiz F. G.; Lexa, Ondrej; Milke, Ralf

    2014-05-01

    microcracks and nearly absent in matrix grains in the well developed C bands. The chemical variation between primary and secondary new-formed micas was clearly identified by the Mg-Ti-Na content. The microstructural analysis documents a progressive decrease in quartz grain size and increasing interconnectivity of K-feldspar and white mica towards more mature shear bands. The contact-frequency analysis demonstrates that the phase distribution in shear bands tends to evolve from quartz aggregate distribution via randomization to K-feldspar aggregate distribution. The boundary preferred orientation is absent in quartz-quartz contacts either inside of outside the C bands, while it changes from random to parallel to the C band for the K-feldspar and and K-feldspar-quartz boundaries. The lack of crystallographic preferred orientation of the individual phases in the mixed matrix of the C planes suggests a dominant diffusion-assisted grain boundary sliding deformation mechanism. In the later stages of shear band development, the deformation is accommodated by crystal plasticity of white mica in micaceous bands. The crystallographic and microstructural data thus indicate two important switches in deformation mechanisms, from (i) brittle to Newtonian viscous behavior in the initial stages of shear band evolution and from (ii) Newtonian viscous to power law in the later evolutionary stages. The evolution of shear bands in the South Armorican Shear Zone thus document the interplay between deformation mechanisms and chemical reactions in deformed granitoids.

  12. Geometrical and mechanical properties of the fractures and brittle deformation zones based on the ONKALO tunnel mapping, 2400 - 4390 m tunnel chainage

    Energy Technology Data Exchange (ETDEWEB)

    Moenkkoenen, H.; Rantanen, T.; Kuula, H. [WSP Finland Oy, Helsinki (Finland)

    2012-05-15

    In this report, the rock mechanics parameters of fractures and brittle deformation zones have been estimated in the vicinity of the ONKALO area at the Olkiluoto site, western Finland. This report is an extension of the previously published report: Geometrical and Mechanical properties if the fractures and brittle deformation zones based on ONKALO tunnel mapping, 0-2400 m tunnel chainage (Kuula 2010). In this updated report, mapping data are from 2400-4390 m tunnel chainage. Defined rock mechanics parameters of the fractures are associated with the rock engineering classification quality index, Q', which incorporates the RQD, Jn, Jr and Ja values. The friction angle of the fracture surfaces is estimated from the Jr and Ja numbers. There are no new data from laboratory joint shear and normal tests. The fracture wall compressive strength (JCS) data are available from the chainage range 1280-2400 m. Estimation of the mechanics properties of the 24 brittle deformation zones (BDZ) is based on the mapped Q' value, which is transformed to the GSI value in order to estimate strength and deformability properties. A component of the mapped Q' values is from the ONKALO and another component is from the drill cores. In this study, 24 BDZs have been parameterized. The location and size of the brittle deformation are based on the latest interpretation. New data for intact rock strength of the brittle deformation zones are not available. (orig.)

  13. Numerical evaluation of the phase-field model for brittle fracture with emphasis on the length scale

    Science.gov (United States)

    Zhang, Xue; Vignes, Chet; Sloan, Scott W.; Sheng, Daichao

    2017-05-01

    The phase-field model has been attracting considerable attention due to its capability of capturing complex crack propagations without mesh dependence. However, its validation studies have primarily focused on the ability to predict reasonable, sharply defined crack paths. Very limited works have so far been contributed to estimate its accuracy in predicting force responses, which is majorly attributed to the difficulty in the determination of the length scale. Indeed, accurate crack path simulation can be achieved by setting the length scale to be sufficiently small, whereas a very small length scale may lead to unrealistic force-displacement responses and overestimate critical structural loads. This paper aims to provide a critical numerical investigation of the accuracy of phase-field modelling of brittle fracture with special emphasis on a possible formula for the length scale estimation. Phase-field simulations of a number of classical fracture experiments for brittle fracture in concretes are performed with simulated results compared with experimental data qualitatively and quantitatively to achieve this goal. Furthermore, discussions are conducted with the aim to provide guidelines for the application of the phase-field model.

  14. Atomistic Origin of Brittle Failure of Boron Carbide from Large-Scale Reactive Dynamics Simulations: Suggestions toward Improved Ductility

    Science.gov (United States)

    An, Qi; Goddard, William A.

    2015-09-01

    Ceramics are strong, but their low fracture toughness prevents extended engineering applications. In particular, boron carbide (B4C ), the third hardest material in nature, has not been incorporated into many commercial applications because it exhibits anomalous failure when subjected to hypervelocity impact. To determine the atomistic origin of this brittle failure, we performed large-scale (˜200 000 atoms /cell ) reactive-molecular-dynamics simulations of shear deformations of B4C , using the quantum-mechanics-derived reactive force field simulation. We examined the (0001 )/⟨10 1 ¯ 0 ⟩ slip system related to deformation twinning and the (01 1 ¯ 1 ¯ )/⟨1 ¯ 101 ⟩ slip system related to amorphous band formation. We find that brittle failure in B4C arises from formation of higher density amorphous bands due to fracture of the icosahedra, a unique feature of these boron based materials. This leads to negative pressure and cavitation resulting in crack opening. Thus, to design ductile materials based on B4C we propose alloying aimed at promoting shear relaxation through intericosahedral slip that avoids icosahedral fracture.

  15. Detecting Acoustic Emissions With/Without Dehydration of Serpentine Outside P-T Field of Conventional Brittle Failure

    Science.gov (United States)

    Jung, H.; Fei, Y.; Silver, P. G.; Green, H. W.

    2005-12-01

    It is currently thought that earthquakes cannot be triggered at depths greater than ~60 km by unassisted brittle failure or frictional sliding, but could be triggered by dehydration embrittlement of hydrous minerals (Raleigh and Paterson, 1965; Green and Houston, 1995; Kirby, 1995; Jung et al., 2004). Using a new multianvil-based system for detecting acoustic emissions with four channels at high pressure and high temperature that was recently developed (Jung et al., 2005), we tested this hypothesis by deforming samples of serpentine. We found that acoustic emissions were detected not only during/after the dehydration of serpentine, but even in the absence of dehydration. These emissions occurred at high pressure and high temperature, and thus outside pressure-temperature field of conventional brittle failure. Backscattered-electron images of microstructures of the post-run specimen revealed fault slip at elevated pressure, with offsets of up to ~500 μm, even without dehydration. Analysis of P-wave travel times from the four sensors confirmed that the acoustic emissions originated from within the specimen during fault slip. These observations suggest that earthquakes can be triggered by slip along a fault containing serpentine at significantly higher pressure and temperature conditions than that previously thought, even without dehydration. They are thus consistent with faulting mechanisms that appeal to dehydration embrittlement, as well as those that rely solely on the rheology of non-dehydrated serpentine.

  16. Atomistic Origin of Brittle Failure of Boron Carbide from Large-Scale Reactive Dynamics Simulations: Suggestions toward Improved Ductility.

    Science.gov (United States)

    An, Qi; Goddard, William A

    2015-09-01

    Ceramics are strong, but their low fracture toughness prevents extended engineering applications. In particular, boron carbide (B(4)C), the third hardest material in nature, has not been incorporated into many commercial applications because it exhibits anomalous failure when subjected to hypervelocity impact. To determine the atomistic origin of this brittle failure, we performed large-scale (∼200,000  atoms/cell) reactive-molecular-dynamics simulations of shear deformations of B(4)C, using the quantum-mechanics-derived reactive force field simulation. We examined the (0001)/⟨101̅0⟩ slip system related to deformation twinning and the (011̅1̅)/⟨1̅101⟩ slip system related to amorphous band formation. We find that brittle failure in B(4)C arises from formation of higher density amorphous bands due to fracture of the icosahedra, a unique feature of these boron based materials. This leads to negative pressure and cavitation resulting in crack opening. Thus, to design ductile materials based on B(4)C we propose alloying aimed at promoting shear relaxation through intericosahedral slip that avoids icosahedral fracture.

  17. Alternative modelling of brittle structures in a sub-area of the SKB candidate area at Forsmark, eastern Sweden.

    Energy Technology Data Exchange (ETDEWEB)

    Askling, Per; Tiren, Sven A.; Beckholmen, Monica; Straeng, Thomas (Geosigma AB, Uppsala (Sweden))

    2008-11-15

    One way to test the confidence of a presented model is to construct an alternative model. Such work is cognitive process of skill acquisition and also a process of understanding data in the sense of sorting and classifying data. This is of particular interest for the Swedish Radiation Safety Authority (SSM) in their technical review of SKB's on-going site investigation programme for potential repository sites. In this study, an alternative brittle deformation model of a selected part of the SKB candidate area in eastern Sweden was constructed. The input data set was obtained from SKB's database SICADA and is a selected set of data from five cored boreholes drilled from two drill-sites and comprises geophysical borehole logs, geological core-logs, hydrological logs (PFL; Posiva Flow Log) and borehole deviation measurements. Statistical cluster analysis applied on the geophysical borehole data were used to obtain the locations of bedrock with contrasting physical characteristics similar to those of brittle deformation zones. The cluster analysis is an objective procedure, contrasting with SKB's more subjective approach to the single-hole interpretation. Thus some differences are expected which could illustrate the effect of methodology that includes subjective 'expert judgement.' and indicate the possibility of alternative interpretations. The information about brittle structures in the geological boreholes logs was sorted and classification was made according to character of the structures (all fractures, open fractures, partly open fractures, frequency, orientate on/identification of fracture sets, sections of crush rock, and alteration). A separate study was performed to relate rock alteration with structures. The resolution applied in the fracture statistics is one metre, i.e. all studied entities were expressed per metre borehole length. All clusters were structurally characterized by the fractures inside the clusters (orientation and

  18. Using helium as background gas to avoid hydrogen brittleness for MgB2 film fabrication on niobium substrate by HPCVD

    Science.gov (United States)

    Guo, Xin; Ni, Zhimao; Chen, Lizhi; Hu, Hui; Yang, Can; Feng, Qingrong; Liu, Kexin

    2016-05-01

    Magnesium diboride has shown potential as an alternative material for the application of superconducting RF cavities. However, if MgB2 films are fabricated on niobium substrates with HPCVD method, hydrogen brittleness will cause cracks on MgB2 film when it is bent. In this work, we have investigated the possibility of depositing MgB2 film on niobium in other background gases rather than hydrogen to avoid hydrogen brittleness. Though MgB2 films fabricated in nitrogen and argon have impurities and show poor superconducting properties, the MgB2 film fabricated in helium has similar morphology and superconducting properties of that prepared in hydrogen and no cracks are observed after bending. The problem of hydrogen brittleness can be solved by using helium as the background gas when fabricating MgB2 films on niobium substrates.

  19. Combined structural analysis and dating of authigenic/synkinematic illite: A step towards unravelling brittle faulting processes in time and space

    Science.gov (United States)

    Viola, Giulio

    2017-04-01

    Faulting accommodates momentous deformation and its style reflects the complex interplay of often transient processes such as friction, fluid flow and rheological changes within generally dilatant systems. Brittle faults are thus unique archives of the stress state and the physical and chemical conditions at the time of both initial strain localization and subsequent slip(s) during structural reactivation. Opening those archives, however, may be challenging due to the commonly convoluted (if not even chaotic) nature of brittle fault architectures and fault rocks. This is because, once formed, faults are extremely sensitive to variations in stress field and environmental conditions and are prone to readily slip in a variety of conditions, also in regions affected by only weak, far-field stresses. The detailed, multi-scalar structural analysis of faults and of fault rocks has to be the starting point for any study aiming at reconstructing the complex framework of brittle deformation. However, considering that present-day exposures of faults only represent the end result of the faults' often protracted and heterogeneous histories, the obtained structural and mechanical results have to be integrated over the life span of the studied fault system. Dating of synkinematic illite/muscovite to constrain the time-integrated evolution of faults is therefore the natural addition to detailed structural studies. By means of selected examples it will be demonstrated how careful structural analysis integrated with illite characterization and K-Ar dating allows the high-resolution reconstruction of brittle deformation histories and, in turn, multiple constraints to be placed on strain localization, deformation mechanisms, fluid flow, mineral alteration and authigenesis within actively deforming brittle fault rocks. Complex and long brittle histories can thus be reconstructed and untangled in any tectonic setting.

  20. Geochronology Constraints on Transformation Age from Ductile to Brittle Deformation of the Shangma Fault and Its Tectonic Significance, Dabieshan, Central China

    Institute of Scientific and Technical Information of China (English)

    Wang Guocan; Wang Pu; Liu Chao; Wang An; Ye Runqing

    2008-01-01

    By a detailed investigation of geometry and kinematics of the Shangma (商麻) fault in Dabieshan (大别山),three different crust levels of extension movement have been recognized in sequence from the deep to the shallow:① low-angle ductile detachment shearing with top to the NW; ② low-angle normal fault with top to the NW or NWW in brittle or brittle-ductile transition domain; ③high-angle brittle normal fault with top to the W or NWW. Two samples were chosen for zircon U-Pb age dating to constrain the activity age of the Shangma fault. A bedding intrusive granitoid pegmatite vein that is parallel to the foliation of the low-angle ductile detachment shear zone of the country rock exhibits a lotus-joint type of boudinage deformation,showing syn-tectonic emplacing at the end of the ductile deformation period and deformation in the brittle-ductile transition domain. The zircon U-Pb dating of this granitoid pegmatite vein gives an age of (125.9±4.2) Ma,which expresses the extension in the brittle-ductile transition domain of the Shangma fault. The other sample,which is collected from a granite pluton cutting the foliation of the low-angle ductile detachment shear zone, gives a zircon U-Pb age of (118.8±4.1) Ma,constraining the end of the ductile detachment shearing. Then the transformation age from ductile to brittle deformation can be constrained between 126-119 Ma.Combined with the previous researches,the formation of the Luotian (罗田) dome,which is located to the east of the Shangma fault,can beconstrained during 150-126 Ma. This study gives a new time constraint to the evolution of the Dabie orogenic belt.

  1. Positron annihilation in pivalic acid. Temperature dependence of angular correlation curves

    DEFF Research Database (Denmark)

    Jain, P. C.; Eldrup, Morten Mostgaard; Pedersen, Niels Jørgen;

    1986-01-01

    Positron annihilation angular correlation curves have been measured as a function of temperature for trimethylacetic (pivalic) acid in both the brittle and plastic phases. A simple fitting of the data to a sum of three gaussians shows the presence of a narrow component due to para-positronium (p...

  2. On dependence of mechanical properties of brittle material on partial concentrations of different sized pores in its structure in a wide range of porosity

    Science.gov (United States)

    Konovalenko, Igor S.; Smolin, Alexey Yu.; Psakhie, Sergey G.

    2015-10-01

    2D and 3D models of mechanical behavior of brittle porous material under uniaxial compression loading were developed in the framework of the movable cellular automaton method. The considered material was characterized by pore size distribution function having two maxima. On the basis of simulation results the dependence of the strength properties of brittle porous material on its total porosity and partial porosities corresponding to pores with different size was revealed. The change in internal structure of material in a wide range of mentioned parameters was analyzed. The main structural factors influencing compression strength of the material at various combinations of values of porosity parameters were identified.

  3. Genome-wide quantitative trait locus mapping identifies multiple major loci for brittle rachis and threshability in Tibetan semi-wild wheat (Triticum aestivum ssp. tibetanum Shao.

    Directory of Open Access Journals (Sweden)

    Yun-Feng Jiang

    Full Text Available Tibetan semi-wild wheat (Triticum aestivum ssp. tibetanum Shao is a semi-wild hexaploid wheat resource that is only naturally distributed in the Qinghai-Tibet Plateau. Brittle rachis and hard threshing are two important characters of Tibetan semi-wild wheat. A whole-genome linkage map of T. aestivum ssp. tibetanum was constructed using a recombinant inbred line population (Q1028×ZM9023 with 186 lines, 564 diversity array technology markers, and 117 simple sequence repeat markers. Phenotypic data on brittle rachis and threshability, as two quantitative traits, were evaluated on the basis of the number of average spike rachis fragments per spike and percent threshability in 2012 and 2013, respectively. Quantitative trait locus (QTL mapping performed using inclusive composite interval mapping analysis clearly identified four QTLs for brittle rachis and three QTLs for threshability. However, three loci on 2DS, 2DL, and 5AL showed pleiotropism for brittle rachis and threshability; they respectively explained 5.3%, 18.6%, and 18.6% of phenotypic variation for brittle rachis and 17.4%, 13.2%, and 35.2% of phenotypic variation for threshability. A locus on 3DS showed an independent effect on brittle rachis, which explained 38.7% of the phenotypic variation. The loci on 2DS and 3DS probably represented the effect of Tg and Br1, respectively. The locus on 5AL was in very close proximity to the Q gene, but was different from the predicted q in Tibetan semi-wild wheat. To our knowledge, the locus on 2DL has never been reported in common wheat but was prominent in T. aestivum ssp. tibetanum accession Q1028. It remarkably interacted with the locus on 5AL to affect brittle rachis. Several major loci for brittle rachis and threshability were identified in Tibetan semi-wild wheat, improving the understanding of these two characters and suggesting the occurrence of special evolution in Tibetan semi-wild wheat.

  4. Geothermal Frontier: Penetrate a boundary between hydrothermal convection and heat conduction zones to create 'Beyond Brittle Geothermal Reservoir'

    Science.gov (United States)

    Tsuchiya, N.; Asanuma, H.; Sakaguchi, K.; Okamoto, A.; Hirano, N.; Watanabe, N.; Kizaki, A.

    2013-12-01

    EGS has been highlightened as a most promising method of geothermal development recently because of applicability to sites which have been considered to be unsuitable for geothermal development. Meanwhile, some critical problems have been experimentally identified, such as low recovery of injected water, difficulties to establish universal design/development methodology, and occurrence of large induced seismicity. Future geothermal target is supercritical and superheated geothermal fluids in and around ductile rock bodies under high temperatures. Ductile regime which is estimated beyond brittle zone is target region for future geothermal development due to high enthalpy fluids and relatively weak water-rock interaction. It is very difficult to determine exact depth of Brittle-Ductile boundary due to strong dependence of temperature (geotherm) and strain rate, however, ductile zone is considered to be developed above 400C and below 3 km in geothermal fields in Tohoku District. Hydrothermal experiments associated with additional advanced technology will be conducting to understand ';Beyond brittle World' and to develop deeper and hotter geothermal reservoir. We propose a new concept of the engineered geothermal development where reservoirs are created in ductile basement, expecting the following advantages: (a)simpler design and control the reservoir, (b)nearly full recovery of injected water, (c)sustainable production, (d)cost reduction by development of relatively shallower ductile zone in compression tectonic zones, (e)large quantity of energy extraction from widely distributed ductile zones, (f)establishment of universal and conceptual design/development methodology, and (g) suppression of felt earthquakes from/around the reservoirs. In ductile regime, Mesh-like fracture cloud has great potential for heat extraction between injection and production wells in spite of single and simple mega-fracture. Based on field observation and high performance hydrothermal

  5. Observations on the brittle to ductile transition temperatures of B2 nickel aluminides with and without zirconium

    Science.gov (United States)

    Raj, S. V.; Noebe, R. D.; Bowman, R.

    1989-01-01

    The effect of a zirconium addition (0.05 at. pct) to a stoichiometric NiAl alloy on the brittle-to-ductile transition temperature (BDTT) of this alloy was investigated. Constant velocity tensile tests were conducted to fracture between 300 and 1100 K under initial strain rate 0.00014/sec, and the true stress and true strain values were determined from plots of load vs time after subtracting the elastic strain. The inelastic strain was measured under a traveling microscope. Microstructural characterization of as-extruded and fractured specimens was carried out by SEM and TEM. It was found that, while the addition of 0.05 at. pct Zr strengthened the NiAl alloy, it increased its BDTT; this shift in the BDTT could not be attributed either to variations in grain size or to impurity contents. Little or no room-temperature ductility was observed for either alloy.

  6. Lower Greenschist Facies Oscillations Across the Brittle-Ductile Transition Induced by Alternating Reaction Softening and Hardening Events

    Science.gov (United States)

    Wintsch, R. P.; Yeh, M.

    2011-12-01

    Reaction textures associated with multiple fabrics in the Red River shear zone show evidence for both brittle and ductile deformation. Rocks on the eastern flank of the shear zone in the Diancang Shan block near Dali, Yunnan Province, China are dominated by porphyritic granodiorites and form the protoliths of the Red River fault rocks. The earliest fault-rocks are cataclasites in which fracture processes broke matrix feldspar grains. Grain-scale brittle fractures and crushed grains are well preserved in the >cm size relic K-feldspar phenocrysts, where multiple fractures are filled with newly precipitated quartz. Progressive deformation has displaced broken K-feldspar fragments into the evolving matrix establishing a cataclastic texture with abundant feldspar porphyroclasts. Ductile deformation is manifest in multiple generations of fabrics that wrap around these broken phenocrysts. The fabrics are defined primarily by muscovite and chlorite that form folia that may exceed the length of a thin section (several cm). Truncations and embayments of these minerals show that earlier magmatic feldspars and biotites have been dissolved and muscovite + chlorite + quartz have crystallized as reaction products. Reaction softening is clearly manifest by the replacement of K-feldspar and the crystallization of quartz as ribbons and muscovite in well aligned folia that define the mylonitic foliation. In some microstructural sites K-feldspar porphyroclasts themselves are truncated and engulfed by muscovite alone. These relationships suggest the simultaneous operation of the locally metasomatic ionic replacement reactions: K-feldspar + Na+ = Albite + K+ , and ΔV = -10% 3K-feldspar + 2H+ = muscovite + 6 quartz + 2K+ and ΔV = -16% 3Albite + K+ + 2H+ = muscovite + 6 quartz + 3Na+. ΔV = - 8% The latter two reactions produce muscovite and quartz, both much weaker than the reactant K-feldspar; these reactions constitute reaction softening. Moreover, the muscovite tends to align in

  7. Numerical simulation of rock progressive failure on samples with a pre-existed weak zone during brittle failure*

    Institute of Scientific and Technical Information of China (English)

    焦明若; 张国民; 唐春安; 傅宇方

    2002-01-01

    Considering the heterogeneity of geomechanical materials, seismicity during brittle rock failure under compressive loading on the sample with an original weak zone is simulated by using rock failure process analysis code (RFPA2D). The run-through process of weak zone, the forming of new fault and associated micro-seismicities are studied. The modeling demonstrates the total process of source development of earthquake from deformation, micro-failure to collapse and the behavior of temporal-spatial distribution of micro-seismicities. The stress, strain and the temporal-spatial distribution of micro-seismicities life-likely portrayed the phenomena of localization and temporal-spatial transitions, which is similar to those observed in our real crust. Also, the results obtained in simulations are in agreement with or similar to the reported experimental observations.

  8. Non-destructive morphological observations of the fleshy brittle star, Asteronyx loveni using micro-computed tomography (Echinodermata, Ophiuroidea, Euryalida

    Directory of Open Access Journals (Sweden)

    Massanori Okanishi

    2017-03-01

    Full Text Available The first morphological observation of a euryalid brittle star, Asteronyx loveni, using non-destructive X-ray micro-computed tomography (µCT was performed. The body of euryalids is covered by thick skin, and it is very difficult to observe the ossicles without dissolving the skin. Computed tomography with micrometer resolution (approximately 4.5–15.4 µm was used to construct 3D images of skeletal ossicles and soft tissues in the ophiuroid’s body. Shape and positional arrangement of taxonomically important ossicles were clearly observed without any damage to the body. Detailed pathways inside the vertebral ossicles, lateral arm plates, and arm spines for passage of nerves and water vascular structures were observed. Inter-vertebral muscles were also observed. Forms and 3D arrangements of many important taxonomical characters of the euryalids were scrutinized by µCT in high enough resolution for taxonomic description of ophiuroids.

  9. Stress Drop as a Result of Splitting, Brittle and Transitional Faulting of Rock Samples in Uniaxial and Triaxial Compression Tests

    Directory of Open Access Journals (Sweden)

    Cieślik Jerzy

    2015-03-01

    Full Text Available Rock samples can behave brittle, transitional or ductile depending on test pressure, rate of loading and temperature. Axial stiffness and its changes, relative and absolute dilatancy, yield, and fracture thresholds, residual strength are strongly pressure dependent. In this paper the stress drop as an effect of rock sample strength loss due to failure was analyzed. Uniaxial and triaxial experiments on three types of rock were performed to investigate the stress drop phenomenon. The paper first introduces short background on rock behavior and parameters defining a failure process under uniaxial and triaxial loading conditions. Stress drop data collected with experiments are analyzed and its pressure dependence phenomenon is described. Two methods for evaluation of stress drop value are presented.

  10. Mesoscale analysis of failure in quasi-brittle materials: comparison between lattice model and acoustic emission data.

    Science.gov (United States)

    Grégoire, David; Verdon, Laura; Lefort, Vincent; Grassl, Peter; Saliba, Jacqueline; Regoin, Jean-Pierre; Loukili, Ahmed; Pijaudier-Cabot, Gilles

    2015-10-25

    The purpose of this paper is to analyse the development and the evolution of the fracture process zone during fracture and damage in quasi-brittle materials. A model taking into account the material details at the mesoscale is used to describe the failure process at the scale of the heterogeneities. This model is used to compute histograms of the relative distances between damaged points. These numerical results are compared with experimental data, where the damage evolution is monitored using acoustic emissions. Histograms of the relative distances between damage events in the numerical calculations and acoustic events in the experiments exhibit good agreement. It is shown that the mesoscale model provides relevant information from the point of view of both global responses and the local failure process. © 2015 The Authors. International Journal for Numerical and Analytical Methods in Geomechanics published by John Wiley & Sons Ltd.

  11. Grain boundary chemistry and heat treatment effects on the ductile-to-brittle transition behavior of vanadium alloys

    Energy Technology Data Exchange (ETDEWEB)

    Kurtz, R.J.; Hamilton, M.L.; Li, H. [Pacific Northwest National Lab., Richland, WA (United States)

    1998-03-01

    One-third scale Charpy impact specimens of V-4Cr-4Ti were given the same heat treatments applied to equivalent specimens of V-5Cr-5Ti. Auger specimens of V-4Cr-4Ti were also heat treated with the Charpy specimens to enable grain boundary chemistry measurements. The microstructural, microchemical and Charpy impact response of V-4Cr-4Ti displayed trends similar to those observed for V-5Cr-5Ti. The results show that grain size plays an important role in determining the ductile-to-brittle transition temperature (DBTT) of these materials and that a threshold level of grain boundary segregant appears to be required to cause grain boundary embrittlement and intergranular fracture.

  12. A Study on the Mechanical Properties and Impact-Induced Initiation Characteristics of Brittle PTFE/Al/W Reactive Materials.

    Science.gov (United States)

    Ge, Chao; Maimaitituersun, Wubuliaisan; Dong, Yongxiang; Tian, Chao

    2017-04-26

    Polytetrafluoroethylene/aluminum/tungsten (PTFE/Al/W) reactive materials of three different component mass ratios (73.5/26.5/0, 68.8/24.2/7 and 63.6/22.4/14) were studied in this research. Different from the PTFE/Al/W composites published elsewhere, the materials in our research were fabricated under a much lower sintering temperature and for a much shorter duration to achieve a brittle property, which aims to provide more sufficient energy release upon impact. Quasi-static compression tests, dynamic compression tests at room and elevated temperatures, and drop weight tests were conducted to evaluate the mechanical and impact-induced initiation characteristics of the materials. The materials before and after compression tests were observed by a scanning electron microscope to relate the mesoscale structural characteristics to their macro properties. All the three types of materials fail at very low strains during both quasi-static and dynamic compression. The stress-strain curves for quasi-static tests show obvious deviations while that for the dynamic tests consist of only linear-elastic and failure stages typically. The materials were also found to exhibit thermal softening at elevated temperatures and were strain-rate sensitive during dynamic tests, which were compared using dynamic increase factors (DIFs). Drop-weight test results show that the impact-initiation sensitivity increases with the increase of W content due to the brittle mechanical property. The high-speed video sequences and recovered sample residues of the drop-weight tests show that the reaction is initiated at two opposite positions near the edges of the samples, where the shear force concentrates the most intensively, indicating a shear-induced initiation mechanism.

  13. Microstructural parameters governing cleavage fracture behaviors in the ductile-brittle transition region in reactor pressure vessel steels

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Won-Jon; Lee, Bong-Sang; Oh, Yong-Jun; Huh, Moo-Young; Hong, Jun-Hwa

    2004-08-15

    The fracture behaviors in the ductile-brittle transition region of reactor pressure vessel (RPV) steels with similar chemical compositions but different manufacturing processes were examined in view of cleavage fracture stress at crack-tip. The steels typically had a variation in grain size and carbide size distribution through the different manufacturing processes. Fracture toughness was evaluated by using a statistical method in accordance to the ASTM standard E1921. From the fractography of the tested specimens, it was found that fracture toughness of the steels increased with increasing distance from the crack-tip to the cleavage initiating location, namely cleavage initiation distance (CID, X{sub f}) and its statistical mean value (K{sub JC(med)}) was proportional to the cleavage fracture stress ({sigma}{sub f}) determined from finite-element (FE) calculation at cleavage initiating location. On the other hand, {sigma}{sub f} could also be calculated by applying the size of microstructural parameters, such as carbide, grain and bainite packet, into the Griffith's theory for brittle fracture. Among the parameters, the {sigma}{sub f} obtained from the mean diameter of the carbides above 1% of the total population was in good agreement with the {sigma}{sub f} value from the FE calculation for the five different steels. The results suggest that the fracture toughness of bainitic RPV steels in the transition region is mostly influenced by only some 1% of total carbides and the critical step for cleavage fracture of the RPV steels should be the propagation of this carbide size crack to the adjacent ferrite matrix.

  14. Static assessment of brittle/ductile notched materials: an engineering approach based on the Theory of Critical Distances

    Directory of Open Access Journals (Sweden)

    R. Louks

    2014-10-01

    Full Text Available Engineering components often contain notches, keyways or other stress concentration features. These features raise the stress state in the vicinity of their apex which can lead to unexpected failure of the component. The Theory of Critical Distances has been proven to predict accurate results, but, conventionally, requires two key ingredients to be implemented: the first is a stress-distance curve which can be obtained relatively easily by means of any finite element software, the second is two additional material parameters which are determined by running appropriate experiments. In this novel reformulation, one of these additional parameters, namely the critical distance, can be determined a priori, allowing design engineers to assess components whilst reducing the time and cost of the design process. This paper investigates reformulating the Theory of Critical Distances to be based on two readily available material parameters, i.e., the Ultimate Tensile Strength and the Fracture Toughness. An experimental data base was compiled from the technical literature. The investigated samples had a range of stress concentration features including sharp V-notches to blunt U-notches, and a range of materials that exhibit brittle, quasi-brittle and ductile mechanical behaviour. Each data set was assessed and the prediction error was calculated. The failure predictions were on average 30% conservative, whilst the non-conservative predictions account for less than 10% of the tested data and less than 2% of the non-conservative error results exceed -20%. It is therefore recommended that a safety factor of at least 1.2 is used in the implementation of this version of the Theory of Critical Distances.

  15. Quantifying the Relationship between Strike-slip Fault Spacing and Brittle Crust Thickness in Continental Settings based on Sandbox Experiments

    Science.gov (United States)

    Lin, J. C.; Zuza, A. V.; Yin, A.

    2015-12-01

    Parallel and evenly spaced strike-slip faults occur widely in continental settings. The fault spacing varies from 10s of km along transform fault systems (e.g., southern California and New Zealand) to 200-400 km in continental interiors (e.g., central Tibet, central Asia, and North China plains). In order to understand the role of the brittle crust rheology and thickness in controlling the fault spacing in continental settings, we performed a series of sandbox experiments using medium-grained dry sand under strike-slip simple-shear conditions. With a self-built sliding device, we determined the yield strength of the dry sand to follow a Coulomb fracture relationship: Tn = 0.5173Sn + 15.475(Pa), with R2 = 0.936, where Tn is the shear stress, Sn is the normal stress, R is the coefficient of linear correlation, and 15.475 Pa is the cohesive strength. In our experiments, we created parallel Riedel shears in a simple shear zone with sand layer thickness varying from 1 cm to 6 cm. The relationship between the fault spacing (S) and the sand layer thickness (T) fits a linear equation of S = 0.5528T + 4.765, with R2 = 0.975. Assuming that the cohesive strength of the continental crust is 1-5 MPa and neglecting the density difference between rock and sand, the scaling relationship between sand and crustal thickness can be approximated as 1:1 X 105 to 1:5 X 105, which means that our experiments simulate a range of crustal thicknesses from 1 km to 30 km. The relevance of the S-T relationship obtained from this study will be tested in areas of active strike-slip tectonics, where the thickness of the brittle crust can be determined by the thickness of the seismogenic zones.

  16. Ductile and brittle structural evolution of the Laxemar-Simpevarp area: an independent analysis based on local and regional constraints

    Energy Technology Data Exchange (ETDEWEB)

    Viola, Giulio (Geological Survey of Norway, Trondheim (Norway))

    2008-10-15

    This report discusses the main aspects of the ductile and brittle deformational evolution of the Laxemar-Simpevarp area. Based on the interpretation of existing potential field geophysical data, it is suggested that the structural ductile grain of the region is controlled by large, c. EW trending shear zones with an overall sinistral strike-slip kinematics. The Oskarshamn Shear Zone (OSZ) and the Mederhult lineament are two examples of these shear zones and it is proposed that the ductile lineaments mapped in Laxemar-Simpevarp are genetically linked to shearing accommodated by these shear zones. The structural interpretation of the geophysical imagery of the Laxemar-Simpevarp regional model area and the available meso-scale structural information indicate that the Laxemar-Simpevarp study area can be interpreted as the analogue of a large-scale S/C' structural pattern. In detail, the Aespoe shear zone and other similarly oriented ductile shears represent C' shear bands that deform sinistrally the intervening EW lineaments (the S surfaces), which locally are significantly crenulated/folded in response to their asymptotic bending into the C' shears. This geometric and kinematic interpretation implies that, in contrast to existing reconstructions and models, EW- and not NE-trending shear zones become the main structural ductile feature of the region. Shear forces acting parallel to these main zones can successfully explain all the ductile structures described and reported from the area. The greatest compressive stress at the time of ductile shearing would trend NE-SW. The brittle deformation history of the region is complex and results from the multiple reactivation of fracture- and fault sets caused by the many orogenic episodes that affected the area during 1.5 Gyr of geological brittle evolution. Fault-slip data from outcrops and oriented drill cores were used to compute paleo-stress states. In the general absence of time markers that help constrain

  17. The Stress-Strain State and Potential Crack Trajectories in 2D Elastic Brittle Materials from Steady-State Flow Experiments

    NARCIS (Netherlands)

    Küntz, M.; Dyskin, A.; Lavallée, P.

    1998-01-01

    A steady-state flow method is used to examine micromechanisms of brittle failure in 2D elastic cracked media submitted to uniaxial compressive stress. The steady-state flow experiments were conducted with an incompressible Newtonian fluid in a Hele Shaw cell. Thin linear rubber inclusions were

  18. New constraints on the rheology of granitic rock during faulting at the brittle-ductile transition: field observations, microstructural analysis and mechanical modeling

    Science.gov (United States)

    Nevitt, J. M.; Pollard, D. D.; Warren, J. M.

    2012-12-01

    Mechanical models of fault slip and related deformation are built upon the equations of motion, which require constitutive equations to define the relationship between stress and resulting strain or strain rate. Although the brittle-ductile transition plays a significant role in earthquake nucleation and propagation, constitutive equations governing rock behavior in this crustal interval remain largely unknown. Identifying appropriate constitutive equations will improve our understanding of earthquake mechanics, in addition to our knowledge of the strength of the lithosphere. Outcrops in the Bear Creek drainage (central Sierra Nevada, CA) provide excellent opportunities to investigate structures that develop under brittle-ductile conditions. There, late Cretaceous biotite-hornblende granodiorite contains an abundance of discontinuous left-lateral strike-slip faults, some of which were seismically active based on the presence of pseudotachylyte. The occurrence of both brittle (e.g., cataclastic rock, opening mode fractures) and ductile (e.g., foliation, ductile shear zones) features suggests that deformation likely occurred near the brittle-ductile transition. Microstructural observations indicate that the temperature during deformation was ~450°C, consistent with the brittle-ductile transition in continental crust. The Seven Gables outcrop contains a 4 cm wide aplite dike that is displaced 42 cm through a contractional step. Within the step, the aplite undergoes stretching (180% stretch) and rotation (45° CCW about an axis plunging 21°), while the granodiorite develops a locally strong mylonitic foliation. The aplite dike provides a valuable strain marker from which we deduce the kinematic evolution of faulting at this contractional step under brittle-ductile conditions. The geometry and kinematic model of the Seven Gables outcrop constrain the geometry and boundary conditions of a forward finite element model. The faults are modeled as planar features and obey

  19. The role of post-failure brittleness of soft rocks in the assessment of stability of intact masses: FDEM technique applications to ideal problems

    Science.gov (United States)

    Lollino, Piernicola; Andriani, Gioacchino Francesco; Fazio, Nunzio Luciano; Perrotti, Michele

    2016-04-01

    Strain-softening under low confinement stress, i.e. the drop of strength that occurs in the post-failure stage, represents a key factor of the stress-strain behavior of rocks. However, this feature of the rock behavior is generally underestimated or even neglected in the assessment of boundary value problems of intact soft rock masses. This is typically the case when the stability of intact rock masses is treated by means of limit equilibrium or finite element analyses, for which rigid-plastic or elastic perfectly-plastic constitutive models, generally implementing peak strength conditions of the rock, are respectively used. In fact, the aforementioned numerical techniques are characterized by intrinsic limitations that do not allow to account for material brittleness, either for the method assumptions or due to numerical stability problems, as for the case of the finite element method, unless sophisticated regularization techniques are implemented. However, for those problems that concern the stability of intact soft rock masses at low stress levels, as for example the stability of shallow underground caves or that of rock slopes, the brittle stress-strain response of rock in the post-failure stage cannot be disregarded due to the risk of overestimation of the stability factor. This work is aimed at highlighting the role of post-peak brittleness of soft rocks in the analysis of specific ideal problems by means of the use of a hybrid finite-discrete element technique (FDEM) that allows for the simulation of the rock stress-strain brittle behavior in a proper way. In particular, the stability of two ideal cases, represented by a shallow underground rectangular cave and a vertical cliff, has been analyzed by implementing a post-peak brittle behavior of the rock and the comparison with a non-brittle response of the rock mass is also explored. To this purpose, the mechanical behavior of a soft calcarenite belonging to the Calcarenite di Gravina formation, extensively

  20. Micro- and submicrostructural evidence for high-temperature brittle-ductile transition deformation of hornblende: Case study of high-grade mylonites from Diancangshan, western Yunnan

    Institute of Scientific and Technical Information of China (English)

    CAO; ShuYun; LIU; JunLai; HU; Ling

    2007-01-01

    OM (optical microscope)/TEM (transmission electron microscope) micro- and submicrostructural analysis of hornblende rocks sheared at high temperatures from the Diancangshan area, western Yunnan reveals evidence for deformation in the brittle-ductile transition of hornblende at middle crustal level (about 637℃ and 0.653 GPa) and mechanisms of deformation in the transitional regime are further discussed. Sheared hornblende rocks at middle crustal level have typical mylonitic microstructures, shown by coarse porphyroclasts and fine matrix grains. Different mineral phases in the rocks show distinct deformation characteristics. Hornblende and feldspar grains are intensely deformed with obvious grainsize reduction, but quartz grains are recrystallized dominantly by grain growth. Hornblende grains show typical brittle-ductile transition nature. Initial crystallographic orientations of porphyroclasts have strong effects on the behavior of grains during deformation. There are mainly two types of porphyroclasts, type I "hard" porphyroclasts and type II "soft" porphyroclasts, with [001] perpendicular and parallel to external shear stresses respectively. "Hard" porphyroclasts generally occur as competent grains that are rarely deformed or sometimes deformed by fracturing and dislocation tangling. "Soft" porphyroclasts are highly deformed primarily by dislocation tangling (as shown in the cores of the porphyroclasts), but twinning, dislocation glide and climb probably due to hydrolytic weakening also contribute to dynamic recrystallization of the porphyroclasts into fine grains in the matrix. The micro- and submicrostructures of the two types of porphyroclasts and fine-grained matrix provide powerful evidence for the behavior of brittle-ductile transition of hornblende grains. It is concluded that twinning nucleation is one of the most important processes that operate during dynamic recrystallization of hornblende crystals at the brittle-ductile transition. (100) [001] twin

  1. Ductile and brittle structural evolution of the Laxemar-Simpevarp area: an independent analysis based on local and regional constraints

    Energy Technology Data Exchange (ETDEWEB)

    Viola, Giulio (Geological Survey of Norway, Trondheim (Norway))

    2008-10-15

    This report discusses the main aspects of the ductile and brittle deformational evolution of the Laxemar-Simpevarp area. Based on the interpretation of existing potential field geophysical data, it is suggested that the structural ductile grain of the region is controlled by large, c. EW trending shear zones with an overall sinistral strike-slip kinematics. The Oskarshamn Shear Zone (OSZ) and the Mederhult lineament are two examples of these shear zones and it is proposed that the ductile lineaments mapped in Laxemar-Simpevarp are genetically linked to shearing accommodated by these shear zones. The structural interpretation of the geophysical imagery of the Laxemar-Simpevarp regional model area and the available meso-scale structural information indicate that the Laxemar-Simpevarp study area can be interpreted as the analogue of a large-scale S/C' structural pattern. In detail, the Aespoe shear zone and other similarly oriented ductile shears represent C' shear bands that deform sinistrally the intervening EW lineaments (the S surfaces), which locally are significantly crenulated/folded in response to their asymptotic bending into the C' shears. This geometric and kinematic interpretation implies that, in contrast to existing reconstructions and models, EW- and not NE-trending shear zones become the main structural ductile feature of the region. Shear forces acting parallel to these main zones can successfully explain all the ductile structures described and reported from the area. The greatest compressive stress at the time of ductile shearing would trend NE-SW. The brittle deformation history of the region is complex and results from the multiple reactivation of fracture- and fault sets caused by the many orogenic episodes that affected the area during 1.5 Gyr of geological brittle evolution. Fault-slip data from outcrops and oriented drill cores were used to compute paleo-stress states. In the general absence of time markers that help constrain

  2. Dynamic earthquake sequence simulations with fault constitutive law accounting for brittle-plastic transition and pressure solution-precipitation creep

    Science.gov (United States)

    Noda, Hiroyuki; Shimamoto, Toshihiko

    2015-04-01

    Fault mechanical behavior is presumably dictated by a pressure-sensitive friction law in the brittle regime where cataclastic deformation dominates, and by a pressure-insensitive flow law in the plastic regime where milonytes are generated. A fault constitutive law in the transitional regime is of great importance in considering earthquake cycles as evidenced by field observations of repeating brittle and ductile deformations [e.g., Sibson 1980]. Shimamoto and Noda [2014] proposed an empirical method of connecting the friction law and the flow law without introducing a new parameter, and demonstrated 2-D dynamic earthquake sequence simulations for a strike-slip fault [e.g., Lapusta et al., 2000] with the friction-to-flow law. A logarithmic rate- and state-dependent friction law (aging law) and a rate- and state-dependent flow law (power law) [Noda and Shimamoto, 2010] with a quartzite steady-state flow law (power exponent n = 4) [Hirth et al., 2001] were adopted for the friction law and the flow law, respectively. Our numerical models are realization of conceptual fault models [e.g., Scholz, 1988]. "Christmas tree" stress profiles appear as a result of evolution of the system, and fluctuate with time. During the interseismic periods, creep fronts penetrated into the locked depth, slow slip events were generated, and then nucleation of dynamic rupture took place either in the shallower or deeper creeping region. The dynamic ruptures spanned the locked depth, reaching the ground surface and extending downwards even deeper than the depth of maximum pre-stress where the deformation mode was in the transitional regime preseismically where S-C mylonitic texture was expected [Shimamoto, 1989]. The coseismic deformation was in the frictional regime because the pure flow law predicts tremendously high flow stress at high strain rate and "the weaker wins". Our simulations reproduced repeating overprint of brittle and ductile deformations. We attempt here to include pressure

  3. Seismicity and Attenuation Correlation Analysis in the Bucaramanga Nest (Colombia). A Test for the Brittle-Ductile Interaction Hypothesis

    Science.gov (United States)

    Tarela, E.; Pujades, L. G.; Ugalde, A.

    2008-12-01

    Technical advances are nowadays starting to provide data sets covering large enough time windows and allowing studying the time evolution of several seismic parameters with some perspective. We study here, at a local scale, the following items: 1) the time evolution of two of these parameters, the seismicity and the coda-wave-attenuation, 2) their relationship in order to test the brittle-ductile interaction hypothesis of the lithosphere-asthenosphere complex system, and 3) its possible use as a mid-term predictor. Seismicity represents the brittle zone stress state, while the one of the ductile zone is characterized by the attenuation of coda waves, which here is measured through coda-Q quality factor. According to the model, the time series will present a similar variation rate during the calm period of the cycle. About two years before a major earthquake takes place in the region, the stress state of both the brittle and the ductile parts of the lithosphere-asthenosphere system would change and the correlation between the two parameters would break down because of this uncoupling. So, a correlation analysis of the two time series would lead to a mid- term prediction. The method is applied in a region with a complex and deep seismicity; this is, the Nest of Bucaramanga (Colombia). The seismic catalogue and waveforms for the attenuation analysis are obtained from Ingeominas; the catalogue includes 13629 events with local magnitude ML>3, fulfilling the magnitude completeness conditions. The seismic attenuation data are obtained from waveforms that have been selected between more than 17000 short period vertical seismograms, recorded at Barichara station, which is located right over the seismic nest. Over 3600 of these waveforms fulfil the magnitude completeness conditions, happened at hypocentral distances smaller than 150km and give coda Q fitting values with correlation coefficients r2≥0.7 So, for the time evolution we were able to average over 50 values of Q0

  4. Influence of lithologic variability on the rheology of granitic rock deformed near the brittle-ductile transition (Invited)

    Science.gov (United States)

    Nevitt, J. M.; Pollard, D. D.; Warren, J. M.

    2013-12-01

    Examining fault-related deformation under brittle-ductile conditions and across different lithologies has implications for seismic hazard analysis, since earthquakes are thought to nucleate near the brittle-ductile transition and fault slip distributions are influenced by lithologic variations. This presentation focuses on two outcrops containing lithologic heterogeneities - the Seven Gables (SG) outcrop and the Sheared Schlieren (SS) outcrop - to investigate the relationship between lithology and deformation. This is accomplished through a combination of field observations, micro-structural/-chemical analyses, and mechanics-based finite element models. The SG and SS outcrops are located in the Bear Creek field area (central Sierra Nevada, CA), which consists of a medium- to fine-grained biotite-hornblende granodiorite with a weak regional foliation trending approximately northwest. The field area contains abundant faults, which microstructural observations suggest were active near the brittle-ductile transition. Furthermore, leucocratic dikes, volcanic xenoliths, and schlieren are abundant throughout the granodiorite, making it lithologically heterogeneous at the decimeter- to meter-scale. The SG outcrop allows comparison of granodiorite rheology to that of a leucocratic dike, both of which are ductilely deformed within a contractional fault step. Both lithologies contain plagioclase, K-feldspar, and quartz, with the granodiorite also containing biotite, hornblende, and sphene. The 10 cm wide right step occurs between two left-lateral faults, measuring 1 and 2 m in length, respectively. A 4 cm thick leucocratic dike runs directly through the center of the step at an angle of 70° to the faults, as measured in the plane of the outcrop. Microstructural analysis indicates that the dominant quartz slip system within the center of the step is basal . The SS outcrop contains a schlieren that is ductilely sheared in the near-tip region of a left-lateral fault. The

  5. Unified nano-mechanics based probabilistic theory of quasibrittle and brittle structures: I. Strength, static crack growth, lifetime and scaling

    Science.gov (United States)

    Le, Jia-Liang; Bažant, Zdeněk P.; Bazant, Martin Z.

    2011-07-01

    Engineering structures must be designed for an extremely low failure probability such as 10 -6, which is beyond the means of direct verification by histogram testing. This is not a problem for brittle or ductile materials because the type of probability distribution of structural strength is fixed and known, making it possible to predict the tail probabilities from the mean and variance. It is a problem, though, for quasibrittle materials for which the type of strength distribution transitions from Gaussian to Weibullian as the structure size increases. These are heterogeneous materials with brittle constituents, characterized by material inhomogeneities that are not negligible compared to the structure size. Examples include concrete, fiber composites, coarse-grained or toughened ceramics, rocks, sea ice, rigid foams and bone, as well as many materials used in nano- and microscale devices. This study presents a unified theory of strength and lifetime for such materials, based on activation energy controlled random jumps of the nano-crack front, and on the nano-macro multiscale transition of tail probabilities. Part I of this study deals with the case of monotonic and sustained (or creep) loading, and Part II with fatigue (or cyclic) loading. On the scale of the representative volume element of material, the probability distribution of strength has a Gaussian core onto which a remote Weibull tail is grafted at failure probability of the order of 10 -3. With increasing structure size, the Weibull tail penetrates into the Gaussian core. The probability distribution of static (creep) lifetime is related to the strength distribution by the power law for the static crack growth rate, for which a physical justification is given. The present theory yields a simple relation between the exponent of this law and the Weibull moduli for strength and lifetime. The benefit is that the lifetime distribution can be predicted from short-time tests of the mean size effect on

  6. New type of brittle deformations: two-axial turn structure of fractures in the Kovdor carbonatite intrusion (NW Russia)

    Science.gov (United States)

    Zhirov, Dmitry

    2017-04-01

    The Earth's crust is known for a few types of structural fissuring and faults organization. First of all, this is an orthogonal or some kind of non-orthogonal fissuring network with a various number of systems. The hierarchic model is also popular since it stipulates a regular arrangement and collateral subordination of several ranks of elements relative to each other, and a general fault and/or shear zone. An axis-symmetric fissuring structure is developed in the central (ring)-type massifs and some other geological bodies. It is formed due to the progressive turn of adjoining fissure planes around the massif symmetry axis (mostly vertical) at a discrete angle (within 5-15° on the average depending on the scale and internal structural features). The investigation of the fault tectonics in the Kovdor carbonatite intrusion (NW Russia) has resulted in the identification of a new brittle deformations type. It is formed due to the simultaneous turn of fissure planes at discrete angles around two orthogonal guiding lines (axes), where one is represented by a vertical massif symmetry axis (L1), and the other axis (L2) lies horizontally in the fracture plane. Nonetheless, the rotation along the both axes is codirectional, i.e., when moving counterclockwise around the L1 axis, the L2 rotation is also counterclockwise. If we very tentatively consider a fissure as an ellipse, and take into account the whole assemblage of long and short axes, the overall picture of their spatial distribution generates a screw conoid or ordinary helicoid type structure. It will be shown as an S-shaped plane poles chain in the stereogram. A sequence of large scale fissures (longer than 100 meters), which are 25 to 100 meters apart from each other and regularly vary in strike and dip angle, is mapped in the open pit of the Kovdor apatite-magnetite deposit. The accuracy of positioning for each fissure is a few centimeters in measurement spots, with a deviation from its actual surface due to the

  7. Strain localization in brittle-ductile shear zones: fluid abundant vs fluid limited conditions (an example from Wyangala area, Australia

    Directory of Open Access Journals (Sweden)

    L. Spruzeniece

    2015-04-01

    Full Text Available This study focuses on physiochemical processes occurring in a brittle-ductile shear zone at both fluid-present and fluid-limited conditions. In the studied shear zone (Wyangala, SE Australia, a coarse-grained two feldspar-quartz-biotite granite is transformed into a medium grained orthogneiss at the shear zone margins and a fine-grained quartz-muscovite phyllonite in the central parts. The orthogneiss displays cataclasis of feldspar and crystal-plastic deformation of quartz. Quartz accommodates most of the deformation and is extensively recrystallized showing distinct crystallographic preferred orientation (CPO. Feldspar-to-muscovite, biotite-to-muscovite and albitization reactions occur locally at porphyroclasts' fracture surfaces and margins. However, the bulk rock composition shows very little change in respect to the wall rock composition. In contrast, in the shear zone centre quartz occurs as large, weakly deformed porphyroclasts, in sizes similar to that in the wall rock, suggesting that it has undergone little deformation. Feldspars and biotite are almost completely reacted to muscovite, which is arranged in a fine-grained interconnected matrix. Muscovite-rich layers contain significant amounts of fine-grained intermixed quartz with random CPO. These domains are interpreted to have accommodated most of the strain. Bulk rock chemistry data shows a significant increase in SiO2 and depletion in NaO content compared to the wall rock composition. We suggest that the high and low strain fabrics represent markedly different scenarios and cannot be interpreted as a simple sequential development with respect to strain. We suggest that the fabrics and mineralogical changes in the shear zone centre have formed due to fluid influx probably along an initially brittle fracture. Here, hydration reactions dramatically changed the rheological properties of the rock. In the newly produced muscovite-quartz layers creep cavitation associated with grain

  8. Estimation of brittleness index using dynamic and static elastic constants in the Haenam Basin, Southwestern Part of Korean Peninsula

    Science.gov (United States)

    Hwang, Seho; Shin, Jehyun; Kim, Jongman; Won, Byeongho; Song, Wonkyoung; Kim, Changryol; Ki, Jungseok

    2014-05-01

    shows a good correlation. The estimation of brittleness index using averaging the dynamic and static elastic constants shows the good trend, i.e., as Poisson's ratio decreases, Young's modulus increases. From the various tests such as well logging in the pilot borehole and laboratory test, we could understand the key to accurately predict the brittleness index is the measurement of S-wave velocity using dipole sonic log.

  9. 某型武器通信系统脆性建模与分析%Brittleness Modeling and Analysis on A Weapon's Communication System

    Institute of Scientific and Technical Information of China (English)

    胡俊

    2015-01-01

    某型武器通信系统进行脆性建模与分析的目的是找到该通信系统的脆性源,为改进装备维修保障工作提供依据.运用图论建立通信系统脆性模型,对模型进行分层重构.找到通信系统的脆性源,得到分层的系统脆性模型.分析结果表明:在某型武器通信系统中,通信控制机是其脆性源,对完善某型武器通信系统建构、改善通信控制机性能、开展通信控制机操作训练和故障诊断训练等具有很强的指导作用,同时也为建设某型通信控制机故障诊断训练系统提供理论依据.%Brittleness modeling and analysis that was adopted to a weapon's communication system aimed to find the brittle source of the communication system and to provide basis for improve the work of equipment's maintenance. Brittleness model of communication system was constructed by the graph theory, then the model was reconstructed hierarchically. And brittle source of communication system was found, hierarchical system brittle model was got at last. It was demonstrated by the analysis result that communication controller was brittle source of a weapon's communication system. As a result it has stronger directive function to consummate the construction of a weapon's communication system, improve the performance of communication controller, develop the operation training and fault diagnosis training of communication controller, theoretical support was afforded to construct a fault diagnosis training system of communication controller at the same time.

  10. Phase field modeling of brittle fracture for enhanced assumed strain shells at large deformations: formulation and finite element implementation

    Science.gov (United States)

    Reinoso, J.; Paggi, M.; Linder, C.

    2017-02-01

    Fracture of technological thin-walled components can notably limit the performance of their corresponding engineering systems. With the aim of achieving reliable fracture predictions of thin structures, this work presents a new phase field model of brittle fracture for large deformation analysis of shells relying on a mixed enhanced assumed strain (EAS) formulation. The kinematic description of the shell body is constructed according to the solid shell concept. This enables the use of fully three-dimensional constitutive models for the material. The proposed phase field formulation integrates the use of the (EAS) method to alleviate locking pathologies, especially Poisson thickness and volumetric locking. This technique is further combined with the assumed natural strain method to efficiently derive a locking-free solid shell element. On the computational side, a fully coupled monolithic framework is consistently formulated. Specific details regarding the corresponding finite element formulation and the main aspects associated with its implementation in the general purpose packages FEAP and ABAQUS are addressed. Finally, the applicability of the current strategy is demonstrated through several numerical examples involving different loading conditions, and including linear and nonlinear hyperelastic constitutive models.

  11. The role of crack tip plasticity on the propagation of fracture in rocks and other brittle solids

    Science.gov (United States)

    Borja, R. I.; Rahmani, H.; Liu, F.; Aydin, A.

    2009-12-01

    Small-scale plastic yielding around a crack tip plays a key role in the propagation of fractures in brittle materials such as rocks. Linear elastic fracture mechanics (LEFM) quantifies the asymptotic strain field around a crack tip under the assumptions of linear elasticity and infinitesimal deformation. However, no material can withstand an infinite stress, and plastic yielding is expected to take place near and around a crack tip. Plastic yielding governs the extension of an existing crack, as well as determines the direction of propagation of splay cracks. Unlike in LEFM, however, no closed-form solution is available for the asymptotic strain field near and around a crack tip in the presence of inelastic deformation. In this work, we resort to finite element modeling for capturing plastic yielding and asymptotic strain field near and around a crack tip. Novel features of the modeling include an enhanced finite element around the crack tip that captures the expected asymptotic strain field, and an elastoplastic constitutive law for near-tip yielding. Through numerical simulations, we infer the likely orientation of splay cracks from the prevailing crystal orientation and overall stress field around the crack tip. We also compare the angular variation of the crack-tip enrichment function in the presence of plastic yielding with the closed-form solution derived from LEFM for different loading conditions and elastoplastic bulk constitutive laws.

  12. Investigation of Macroscopic Brittle Creep Failure Caused by Microcrack Growth Under Step Loading and Unloading in Rocks

    Science.gov (United States)

    Li, Xiaozhao; Shao, Zhushan

    2016-07-01

    The growth of subcritical cracks plays an important role in the creep of brittle rock. The stress path has a great influence on creep properties. A micromechanics-based model is presented to study the effect of the stress path on creep properties. The microcrack model of Ashby and Sammis, Charles' Law, and a new micro-macro relation are employed in our model. This new micro-macro relation is proposed by using the correlation between the micromechanical and macroscopic definition of damage. A stress path function is also introduced by the relationship between stress and time. Theoretical expressions of the stress-strain relationship and creep behavior are derived. The effects of confining pressure on the stress-strain relationship are studied. Crack initiation stress and peak stress are achieved under different confining pressures. The applied constant stress that could cause creep behavior is predicted. Creep properties are studied under the step loading of axial stress or the unloading of confining pressure. Rationality of the micromechanics-based model is verified by the experimental results of Jinping marble. Furthermore, the effects of model parameters and the unloading rate of confining pressure on creep behavior are analyzed. The coupling effect of step axial stress and confining pressure on creep failure is also discussed. The results provide implications on the deformation behavior and time-delayed rockburst mechanism caused by microcrack growth on surrounding rocks during deep underground excavations.

  13. Finite element modeling of quasi-brittle cracks in 2D and 3D with enhanced strain accuracy

    Science.gov (United States)

    Cervera, M.; Barbat, G. B.; Chiumenti, M.

    2017-07-01

    This paper discusses the finite element modeling of cracking in quasi-brittle materials. The problem is addressed via a mixed strain/displacement finite element formulation and an isotropic damage constitutive model. The proposed mixed formulation is fully general and is applied in 2D and 3D. Also, it is independent of the specific finite element discretization considered; it can be equally used with triangles/tetrahedra, quadrilaterals/hexahedra and prisms. The feasibility and accuracy of the method is assessed through extensive comparison with experimental evidence. The correlation with the experimental tests shows the capacity of the mixed formulation to reproduce the experimental crack path and the force-displacement curves with remarkable accuracy. Both 2D and 3D examples produce results consistent with the documented data. Aspects related to the discrete solution, such as convergence regarding mesh resolution and mesh bias, as well as other related to the physical model, like structural size effect and the influence of Poisson's ratio, are also investigated. The enhanced accuracy of the computed strain field leads to accurate results in terms of crack paths, failure mechanisms and force displacement curves. Spurious mesh dependency suffered by both continuous and discontinuous irreducible formulations is avoided by the mixed FE, without the need of auxiliary tracking techniques or other computational schemes that alter the continuum mechanical problem.

  14. Multi-scale defect interactions in high-rate brittle material failure. Part I: Model formulation and application to ALON

    Science.gov (United States)

    Tonge, Andrew L.; Ramesh, K. T.

    2016-01-01

    Within this two part series we develop a new material model for ceramic protection materials to provide an interface between microstructural parameters and bulk continuum behavior to provide guidance for materials design activities. Part I of this series focuses on the model formulation that captures the strength variability and strain rate sensitivity of brittle materials and presents a statistical approach to assigning the local flaw distribution within a specimen. The material model incorporates a Mie-Grüneisen equation of state, micromechanics based damage growth, granular flow and dilatation of the highly damaged material, and pore compaction for the porosity introduced by granular flow. To provide initial qualitative validation and illustrate the usefulness of the model, we use the model to investigate Edge on Impact experiments (Strassburger, 2004) on Aluminum Oxynitride (AlON), and discuss the interactions of multiple mechanisms during such an impact event. Part II of this series is focused on additional qualitative validation and using the model to suggest material design directions for boron carbide.

  15. Method of superposition of dislocations for finding stress-strain state around fan-shaped structure in a brittle rock

    Science.gov (United States)

    Sadovskii, V. M.; Sadovskaya, O. V.

    2016-10-01

    The Tarasov fan-shaped mechanism, simulating the formation of shear ruptures in a brittle rock at stress conditions corresponding to seismogenic depths, is analyzed. For computation of the stress-strain state of a rock near the equilibrium fan-structure the original method is constructed. The fault is modeled as a narrow elongated layer, filled with the domino-blocks, between two elastic half-spaces. Displacements and stresses around the fan are represented in the integral form as a superposition of edge dislocations with an unknown function of distribution of the Burgers vector. To take into account the stresses of lateral thrust, the solution of plane problem of the elasticity is used for a tensile crack, on the surfaces of which the previously unknown normal stresses are distributed. The exact formulation of the problem leads to a system of two nonlinear singular integral equations, which is solved numerically by the method of successive approximations. The obtained solution is used, when setting the initial data in computations of the dynamics of the Tarasov fan-shaped mechanism. With the help of this solution the discontinuous nature of shear ruptures, observed in natural and laboratory experiments, is explained.

  16. Common genetic variants near the Brittle Cornea Syndrome locus ZNF469 influence the blinding disease risk factor central corneal thickness.

    Directory of Open Access Journals (Sweden)

    Yi Lu

    2010-05-01

    Full Text Available Central corneal thickness (CCT, one of the most highly heritable human traits (h(2 typically>0.9, is important for the diagnosis of glaucoma and a potential risk factor for glaucoma susceptibility. We conducted genome-wide association studies in five cohorts from Australia and the United Kingdom (total N = 5058. Three cohorts were based on individually genotyped twin collections, with the remaining two cohorts genotyped on pooled samples from singletons with extreme trait values. The pooled sample findings were validated by individual genotyping the pooled samples together with additional samples also within extreme quantiles. We describe methods for efficient combined analysis of the results from these different study designs. We have identified and replicated quantitative trait loci on chromosomes 13 and 16 for association with CCT. The locus on chromosome 13 (nearest gene FOXO1 had an overall meta-analysis p-value for all the individually genotyped samples of 4.6x10(-10. The locus on chromosome 16 was associated with CCT with p = 8.95x10(-11. The nearest gene to the associated chromosome 16 SNPs was ZNF469, a locus recently implicated in Brittle Cornea Syndrome (BCS, a very rare disorder characterized by abnormal thin corneas. Our findings suggest that in addition to rare variants in ZNF469 underlying CCT variation in BCS patients, more common variants near this gene may contribute to CCT variation in the general population.

  17. Modeling the Ductile Brittle Fracture Transition in Reactor Pressure Vessel Steels using a Cohesive Zone Model based approach

    Energy Technology Data Exchange (ETDEWEB)

    Pritam Chakraborty; S. Bulent Biner

    2013-10-01

    Fracture properties of Reactor Pressure Vessel (RPV) steels show large variations with changes in temperature and irradiation levels. Brittle behavior is observed at lower temperatures and/or higher irradiation levels whereas ductile mode of failure is predominant at higher temperatures and/or lower irradiation levels. In addition to such temperature and radiation dependent fracture behavior, significant scatter in fracture toughness has also been observed. As a consequence of such variability in fracture behavior, accurate estimates of fracture properties of RPV steels are of utmost importance for safe and reliable operation of reactor pressure vessels. A cohesive zone based approach is being pursued in the present study where an attempt is made to obtain a unified law capturing both stable crack growth (ductile fracture) and unstable failure (cleavage fracture). The parameters of the constitutive model are dependent on both temperature and failure probability. The effect of irradiation has not been considered in the present study. The use of such a cohesive zone based approach would allow the modeling of explicit crack growth at both stable and unstable regimes of fracture. Also it would provide the possibility to incorporate more physical lower length scale models to predict DBT. Such a multi-scale approach would significantly improve the predictive capabilities of the model, which is still largely empirical.

  18. Common genetic variants near the Brittle Cornea Syndrome locus ZNF469 influence the blinding disease risk factor central corneal thickness.

    Directory of Open Access Journals (Sweden)

    Yi Lu

    2010-05-01

    Full Text Available Central corneal thickness (CCT, one of the most highly heritable human traits (h(2 typically>0.9, is important for the diagnosis of glaucoma and a potential risk factor for glaucoma susceptibility. We conducted genome-wide association studies in five cohorts from Australia and the United Kingdom (total N = 5058. Three cohorts were based on individually genotyped twin collections, with the remaining two cohorts genotyped on pooled samples from singletons with extreme trait values. The pooled sample findings were validated by individual genotyping the pooled samples together with additional samples also within extreme quantiles. We describe methods for efficient combined analysis of the results from these different study designs. We have identified and replicated quantitative trait loci on chromosomes 13 and 16 for association with CCT. The locus on chromosome 13 (nearest gene FOXO1 had an overall meta-analysis p-value for all the individually genotyped samples of 4.6x10(-10. The locus on chromosome 16 was associated with CCT with p = 8.95x10(-11. The nearest gene to the associated chromosome 16 SNPs was ZNF469, a locus recently implicated in Brittle Cornea Syndrome (BCS, a very rare disorder characterized by abnormal thin corneas. Our findings suggest that in addition to rare variants in ZNF469 underlying CCT variation in BCS patients, more common variants near this gene may contribute to CCT variation in the general population.

  19. Coupled hydro-thermo-mechanical modeling of hydraulic fracturing in quasi-brittle rocks using BPM-DEM

    Directory of Open Access Journals (Sweden)

    Ingrid Tomac

    2017-02-01

    Full Text Available This paper presents an improved understanding of coupled hydro-thermo-mechanical (HTM hydraulic fracturing of quasi-brittle rock using the bonded particle model (BPM within the discrete element method (DEM. BPM has been recently extended by the authors to account for coupled convective–conductive heat flow and transport, and to enable full hydro-thermal fluid–solid coupled modeling. The application of the work is on enhanced geothermal systems (EGSs, and hydraulic fracturing of hot dry rock (HDR is studied in terms of the impact of temperature difference between rock and a flowing fracturing fluid. Micro-mechanical investigation of temperature and fracturing fluid effects on hydraulic fracturing damage in rocks is presented. It was found that fracture is shorter with pronounced secondary microcracking along the main fracture for the case when the convective–conductive thermal heat exchange is considered. First, the convection heat exchange during low-viscosity fluid infiltration in permeable rock around the wellbore causes significant rock cooling, where a finger-like fluid infiltration was observed. Second, fluid infiltration inhibits pressure rise during pumping and delays fracture initiation and propagation. Additionally, thermal damage occurs in the whole area around the wellbore due to rock cooling and cold fluid infiltration. The size of a damaged area around the wellbore increases with decreasing fluid dynamic viscosity. Fluid and rock compressibility ratio was found to have significant effect on the fracture propagation velocity.

  20. Dynamic optical interferometry applied to analyse out of plane displacement fields for crack propagation in brittle materials

    Science.gov (United States)

    Hedan, S.; Pop, O.; Valle, V.; Cottron, M.

    2006-08-01

    We propose in this paper, to analyse, the evolution of out-of-plane displacement fields for a crack propagation in brittle materials. As the crack propagation is a complex process that involves the deformation mechanisms, the out-of-plane displacement measurement gives pertinent information about the 3D effects. For investigation, we use the interferometric method. The optical device includes a laser source, a Michelson interferometer and an ultra high-speed CCD camera. To take into account the crack velocity, we dispose of a maximum frame rate of 1Mfps. The experimental tests have been carried out for a SEN (Single Edge Notch) specimen of PMMA material. The crack propagation is initiated by adding a dynamic energy given by the impact of a cutter on the initial crack. The obtained interferograms are analysed with a new phase extraction method entitled MPC [6]. This analysis, which has been developed specially for dynamic studies, gives the out-of-plane displacement with an accuracy of about 10 nm.

  1. A quasi-static algorithm that includes effects of characteristic time scales for simulating failures in brittle materials

    KAUST Repository

    Liu, Jinxing

    2013-04-24

    When the brittle heterogeneous material is simulated via lattice models, the quasi-static failure depends on the relative magnitudes of Telem, the characteristic releasing time of the internal forces of the broken elements and Tlattice, the characteristic relaxation time of the lattice, both of which are infinitesimal compared with Tload, the characteristic loading period. The load-unload (L-U) method is used for one extreme, Telem << Tlattice, whereas the force-release (F-R) method is used for the other, Telem T lattice. For cases between the above two extremes, we develop a new algorithm by combining the L-U and the F-R trial displacement fields to construct the new trial field. As a result, our algorithm includes both L-U and F-R failure characteristics, which allows us to observe the influence of the ratio of Telem to Tlattice by adjusting their contributions in the trial displacement field. Therefore, the material dependence of the snap-back instabilities is implemented by introducing one snap-back parameter γ. Although in principle catastrophic failures can hardly be predicted accurately without knowing all microstructural information, effects of γ can be captured by numerical simulations conducted on samples with exactly the same microstructure but different γs. Such a same-specimen-based study shows how the lattice behaves along with the changing ratio of the L-U and F-R components. © 2013 The Author(s).

  2. Experimental study of impact-cratering damage on brittle cylindrical column model as a fundamental component of space architecture

    Science.gov (United States)

    Fujiwara, Akira; Onose, Naomi; Setoh, Masato; Nakamura, Akiko M.; Hiraoka, Kensuke; Hasegawa, Sunao; Okudaira, Kyoko

    2014-10-01

    The cylindrical column of brittle material processed from soil and rock is a fundamental component of architectures on the surface of solid bodies in the solar system. One of the most hazardous events for the structure is damaging by hypervelocity impacts by meteoroids and debris. In such a background, cylindrical columns made of plaster of Paris and glass-bead-sintered ceramic were impacted by spherical projectiles of nylon, glass, and steel at velocity of about 1-4.5 km/s. Measured crater radii, depth, and excavated mass expressed by a function of the cylinder radius are similar irrespective of the target material, if those parameters are normalized by appropriate parameters of the crater produced on the flat-surface target. The empirical scaling relations of the normalized crater radii and depth are provided. Using them, crater dimensions and excavated mass of crater on cylindrical surface of any radius can be predicted from the existing knowledge of those for flat surface. Recommendation for the minimum diameter of a cylinder so as to resist against a given impact is provided.

  3. Evaluation of ductile-brittle transition behavior with neutron irradiation in nuclear reactor pressure vessel steels using small punch test

    Energy Technology Data Exchange (ETDEWEB)

    Kim, M. C.; Lee, B. S. [KAERI, Taejon (Korea, Republic of); Oh, Y. J. [Hanbat National Univ., Taejon (Korea, Republic of)

    2003-10-01

    A Small Punch (SP) test was performed to evaluate the ductile-brittle transition temperature before and after neutron irradiation in Reactor Pressure Vessel (RPV) steels produced by different manufacturing (refining) processes. The results were compared to the standard transition temperature shifts from the Charpy test and Master Curve fracture toughness test in accordance with the ASTM standard E1921. The samples were taken from 1/4t location of the vessel thickness and machined into a 10x10x0.5mm dimension. Irradiation of the samples was carried out in the research reactor at KAERI (HANARO) at about 290 .deg. C of the different fluence levels respectively. SP tests were performed in the temperature range of RT to -196 .deg. C using a 2.4mm diameter ball. For the materials before and after irradiation, SP transition temperatures (T{sub sp}), which are determined at the middle of the upper and lower SP energies, showed a linear correlation with the Charpy index temperature, T{sub 41J}. T{sub sp} from the irradiated samples was increased as the fluence level increased and was well within the deviation range of the unirradiated data. The TSP had a correlation with the reference temperature (T{sub 0}) from the master curve method using a pre-cracked Charpy V-notched (PCVN) specimen.

  4. Demonstration of freedom from brittle fracture - validation of the master curve methodology for deriving material fracture toughness

    Energy Technology Data Exchange (ETDEWEB)

    Norton, F. [BNFL (United Kingdom); Pisarski, H. [TWI (United Kingdom)

    2004-07-01

    ASTM A 350 LF5 steel is used in the manufacture of transport flasks. In order to satisfy regulatory requirements for demonstrating this materials' resistance to brittle fracture during flask operation, fracture mechanics data are required. The normal requirement for generating fracture toughness data is that testing must be carried out on material of equivalent thickness to the component under investigation and that the test must be carried out at the appropriate temperature and loading rate. Satisfying these requirements becomes very difficult for thick materials. In particular, routine dynamic testing of 300 mm thick steels could not be done on any known facility and would require a significant effort to develop one. The Master Curve proposed by Wallin(1) offers an alternative testing philosophy that enables the desired fracture toughness data to be generated by small scale testing. This report presents the results of a program of work to demonstrate that A350 LF5 steel is amenable to Master Curve techniques.

  5. EFFECTS OF INTERPARTICLE DISTANCE,TEMPERATURE AND INTERFACIAL ADHESION ON BRITTLE-DUCTILE TRANSITION FOR NYLON 6/ABS BLENDS

    Institute of Scientific and Technical Information of China (English)

    Shu-hao Qin; Jie Yu; Min He; Wei Yan

    2009-01-01

    The toughness of blends composed of nylon 6 and acrylonitrile-butadiene-styrene(ABS)compatibilized by using styrene-maleic anhydride(SMA)as a compatibilizer was measured over a wide temperature region.Results reveal that the combining effects of particle size and volume fraction of ABS on the toughness of nylon 6/ABS/SMA blends can be described through plotting brittle-ductile transition of the impact strength versus the interparticle distance(ID)on the assumption that ABS domains relieve the triaxial tension via internal cavitation or interfacial debonding.Moreover,the effect of interfacial adhesion on fracture behavior of nylon 6/ABS/SMA blends strongly depends upon the testing temperature.The difference of relation amomg temperature,fracture behavior and interfacial adhesion can be understood in terms of the deformation mechanisms,i.e.in the case of poor interfacial adhesion,the toughness lies on whether debonding existing at the interface relieves triaxial tension or not.It is believed that for good interfacial adhesion,internal cavitation followed by matrix shear yielding is a predominant factor for toughening.Furthermore,the fracture surface of these blends was probed to elucidate how interfacial adhesion affected the impact strength of the blends.

  6. Phase field modeling of brittle fracture for enhanced assumed strain shells at large deformations: formulation and finite element implementation

    Science.gov (United States)

    Reinoso, J.; Paggi, M.; Linder, C.

    2017-06-01

    Fracture of technological thin-walled components can notably limit the performance of their corresponding engineering systems. With the aim of achieving reliable fracture predictions of thin structures, this work presents a new phase field model of brittle fracture for large deformation analysis of shells relying on a mixed enhanced assumed strain (EAS) formulation. The kinematic description of the shell body is constructed according to the solid shell concept. This enables the use of fully three-dimensional constitutive models for the material. The proposed phase field formulation integrates the use of the (EAS) method to alleviate locking pathologies, especially Poisson thickness and volumetric locking. This technique is further combined with the assumed natural strain method to efficiently derive a locking-free solid shell element. On the computational side, a fully coupled monolithic framework is consistently formulated. Specific details regarding the corresponding finite element formulation and the main aspects associated with its implementation in the general purpose packages FEAP and ABAQUS are addressed. Finally, the applicability of the current strategy is demonstrated through several numerical examples involving different loading conditions, and including linear and nonlinear hyperelastic constitutive models.

  7. Eruption versus intrusion? Arrest of propagation of constant volume, buoyant, liquid-filled cracks in an elastic, brittle host

    Science.gov (United States)

    Taisne, B.; Tait, S.

    2009-06-01

    When a volume of magma is released from a source at depth, one key question is whether or not this will culminate in an eruption or in the emplacement of a shallow intrusion. We address some of the physics behind this question by describing and interpreting laboratory experiments on the propagation of cracks filled with fixed volumes of buoyant liquid in a brittle, elastic host. Experiments were isothermal, and the liquid was incompressible. The cracks propagated vertically because of liquid buoyancy but were then found to come to a halt at a configuration of static mechanical equilibrium, a result that is inconsistent with the prediction of the theory of linear elastic fracture mechanics in two dimensions. We interpret this result as due to a three-dimensional effect. At the curved crack front, horizontal cracking is necessary in order for vertical propagation to take place. As the crack elongates and thins, the former becomes progressively harder and, in the end, impossible to fracture. We present a scaling law for the final length and breadth of cracks as a function of a governing dimensionless parameter, constructed from the liquid volume, the buoyancy, and host fracture toughness. An important implication of this result is that a minimum volume of magma is required for a volcanic eruption to occur for a given depth of magma reservoir.

  8. 钻井完井液浸泡弱化页岩脆性机制%BRITTLENESS WEAKENING MECHANISMS OF SHALE SOAKED BY DRILLING & COMPLETION FLUID

    Institute of Scientific and Technical Information of China (English)

    康毅力; 佘继平; 林冲; 游利军

    2016-01-01

    页岩脆性是页岩地层钻井、水力压裂设计的关键参数之一,目前针对钻井过程中工作液浸泡对页岩脆性的影响还未引起关注。通过开展钻井完井液浸泡前后页岩三轴力学实验,利用脆性评价模型分析了页岩脆性变化特征。结果表明,延长组页岩脆性强于龙马溪组页岩;油基和水基钻井完井液浸泡均能导致页岩脆性降低,且油基钻井完井液浸泡后的页岩脆性降低幅度更大;龙马溪组页岩浸泡后脆性减弱幅度较延长组页岩大。页岩脆性弱化机制包括:(1)由层理面胶结强度不同引起的脆性强弱差异;(2)由毛管自吸作用导致的高孔压、高应力强度因子、低临界断裂韧性;(3)由碱液侵蚀导致的页岩溶蚀孔形成及矿物颗粒碎裂;(4)由黏土矿物水化膨胀产生的膨胀应力;(5)由钻井完井液滤液润滑导致的页岩破裂面摩擦系数降低。延长组页岩层理面强度较龙马溪组页岩低,导致延长组页岩脆性强于龙马溪组页岩。其次,和水基钻井完井液相比,油基钻井完井液具有更大的自吸量、更高的pH值、更强的润滑性,因此,油基钻井完井液浸泡降低页岩脆性幅度更大。另外,由于龙马溪组页岩具有更小的润湿角、更强的毛管自吸和碱液侵蚀作用,相同浸泡条件下,龙马溪组页岩脆性降低幅度更大。本研究可为页岩地层钻井液性能优化、井壁稳定控制、水力压裂设计等提供理论指导。%Brittleness is one key parameter during drilling and fracturing in shale formations, however, influencing mechanism of soaking by drilling&completion fluid on shale brittleness has not been focused. In this paper, triaxial mechanical tests of shales soaked by fluid were performed;and optimized brittleness evaluation model was employed to evaluate brittleness of shale. Results indicate that the brittleness of Yanchang shale is larger than that

  9. Chaotic state to self-organized critical state transition of serrated flow dynamics during brittle-to-ductile transition in metallic glass

    Energy Technology Data Exchange (ETDEWEB)

    Wang, C.; Wang, W. H.; Bai, H. Y., E-mail: hybai@aphy.iphy.ac.cn [Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Sun, B. A. [Centre for Advanced Structural Materials, Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Kowloon Tong, Kowloon (Hong Kong)

    2016-02-07

    We study serrated flow dynamics during brittle-to-ductile transition induced by tuning the sample aspect ratio in a Zr-based metallic glass. The statistical analysis reveals that the serrated flow dynamics transforms from a chaotic state characterized by Gaussian-distribution serrations corresponding to stick-slip motion of randomly generated and uncorrelated single shear band and brittle behavior, into a self-organized critical state featured by intermittent scale-free distribution of shear avalanches corresponding to a collective motion of multiple shear bands and ductile behavior. The correlation found between serrated flow dynamics and plastic deformation might shed light on the plastic deformation dynamic and mechanism in metallic glasses.

  10. DYNAMIC BREAKAGE AND FRAGMENTATION OF BRITTLE SINGLE PARTICLE OF VARIOUS SIZES AND STRENGTH%脆性单颗粒之动态损伤和破碎

    Institute of Scientific and Technical Information of China (English)

    周锦添; 武生智; 黄凯珠

    2003-01-01

    Breakage, comminution, crushing and fragmentation of brittle solids under dynamic impacts are an important applied mechanics and rock mechanics problem. In civil engineering applications, impact-induced-fragmentation relates to crushing of rock mass during mining process, tunneling, and aggregate production. The main objective of this paper is to outline some of our recent experimental, analytical and numerical efforts in studying the dynamic fragmentation process in brittle particle. First, an analytical solution of a solid sphere compressed dynamically between two rigid flat platens is derived analytically. Secondly, a sequence of double impact tests on spheres were conducted using an impactor Dynatup 8250 at HKUST, with both impact velocity and contact force at the impactor measured accurately. Finally, a newly developed computer program, DIFAR, is used to investigate the mechanism of dynamic fragmentation. The paper will summarize and discuss briefly all three aspects of our comprehensive approach.

  11. The skeletal proteome of the brittle star Ophiothrix spiculata identifies C-type lectins and other proteins conserved in echinoderm skeleton formation

    Directory of Open Access Journals (Sweden)

    Brian T. Livingston

    2016-07-01

    Full Text Available Determining the identity and functional role of proteins involved in biomineralization and the formation of skeletons is critical to our understanding of the process. Proteomics has allowed rapid characterization of the proteins occluded within mineralized tissue, but the large numbers of proteins detected makes it difficult to assign the relative importance of each protein. We have taken a comparative approach, examining the skeletal proteome of different species of echinoderms in order to identify the proteins that are conserved and likely to be important. Our previous study comparing the skeletal proteome of the brittle star Ophiocoma wendtii to the published proteomes of the sea urchin Strongylocentrotus purpuratus revealed some conservation of proteins, but indicated that the C-type lectin domain-containing spicule matrix proteins abundant in the sea urchin skeletal proteome were not conserved in the brittle star. Here we examine the skeletal proteome of a different species of brittle star, Ophiothrix spiculata. We have isolated the proteins from the skeleton of O. spiculata and performed LC/MS/MS to identify peptides present. Comparison to transcriptome and genome databases revealed the proteins present in the O. spiculata proteome. Despite being diverged for several million years, the two brittle stars have very similar proteins in their skeletons. Included is a fibrinogen C-like lectin and several C-type lectins proteins, which we describe in detail. The unusual number of C-type lectins found in the S. purpuatus skeleton and the repetitive regions seen in those spicule matrix proteins are not present in O. spiculata.

  12. Protective Effect of the Persian Gulf brittle star Ophiocoma Erinaceus extract on carbon tetrachloride (CCl4 induced liver damage in adult male Wistar rats

    Directory of Open Access Journals (Sweden)

    Aida Soheili

    2015-12-01

    Full Text Available Background and Aim:  Brittle star possess  bioactive compounds which confer the wound healing capacity and regenerative potency of damaged  arms and organisms to this creature. The aim of the current study was to assess the   protective  effect  of  the  star extract on liver damages induced by carbon tetrachloride in adult male Wistar rats. Materials and Methods: In this experimental study, 32 adult male rats were randomly divided into 4 equal groups: control, Sham exposed, experimental 1 (treated with %25 extract and experimental 2 (treated with %50 extract of star Ophiocoma Erinaceus. The control group received no treatment. The sham exposed groups received carbon tetrachloride .(50% in olive oil .0.5 ml/kg for 7 days. The experimental groups firstly received carbon tetrachloride, then received %25, %50 brittle star extract as intragastric for 7 days. Finally, the animals were sacrificed, and their bodies and livers were weighed. Then, the livers sections were prepared and were examined by means of light microscope. Finally, the obtained  quantitative data was analyzed using SPSS (V; 20, Mini Tab software, ANOVA, and Tukey. at the significant level of P<0.001. Results: Carbon tetrachloride significantly decreased the rats’ body weight, but it increased their livers weight (P<0.001. Histopathological evaluations showed .extensive liver damage. On the other hand, treatment with brittle star extract .ncreased liver weight, reduced. body weight and significantly altered other induced changes by carbon tetrachloride on liver structure such as hepatocytes number, Kupffer cells, and arteritis, which indicated  the improvement of damaged liver tissue (P<0.001. Conclusion: It was found that brittle star extract can exert protective effects on  liver damages induced by carbon tetrachloride on male Wistar rat.

  13. The local effect of Persian Gulf brittle star (Ophiocoma erinaceus alcoholic extract on cutaneous wound healing in Balb/C mouse

    Directory of Open Access Journals (Sweden)

    Javad Baharara

    2014-11-01

    Results: Significant changes in proliferation of inflammatory cells (on the 12th day, epithelium thickness (on the 6th day, more angiogenesis (on the 6th- 9th day, in the experimental wounds were compared with those in the control group. However, experimental group with positive control were not significantly different in these days. Conclusion: Findings of this research indicated that the topical application of brittle star extract posse positive impact on wound healing process.

  14. The electronic structure and grain boundary segregation by boron addition——A binding energy shifting criterion for the brittle-ductile fracture transition in Ni3Al

    Institute of Scientific and Technical Information of China (English)

    张云; 林栋梁

    1997-01-01

    The electronic structure and grain boundary segregation caused by boron addition to Ni3Al have been studied by X-ray photoelectron spectroscopy and Auger electron spectroscopy, respectively. The obtained results show that the Ni2p3/2 electron binding energy rises gradually in the sequence of pure Ni< Ni76Al24< Ni74Al26 < Ni25Al25, while it reduces monotonously with an increase in boron addition to Ni3Al. Besides, it is found that the gram boundary segregation of boron occurring in Ni3Al is a combined equilibrium and non-equilibrium type in nature. Based on the concept of the bonding environmental inhomogeneity, measured by the shift in Ni2p3/2 electron binding energy from the nickel atoms in the simple substance nickel to those in the intermetallic compound Ni3Al (ΔEB), being responsible for the brittle behavior of the alloy, a binding energy shifting criterion for the brittle-ductile fracture transition in Ni3Al is presented: when ΔEB>0, the brittle failure occurs in Ni3Al; when ΔEB<0, the ductile o

  15. 3D random Voronoi grain-based models for simulation of brittle rock damage and fabric-guided micro-fracturing

    Institute of Scientific and Technical Information of China (English)

    E. Ghazvinian; M.S. Diederichs; R. Quey

    2014-01-01

    A grain-based distinct element model featuring three-dimensional (3D) Voronoi tessellations (random poly-crystals) is proposed for simulation of crack damage development in brittle rocks. The grain boundaries in poly-crystal structure produced by Voronoi tessellations can represent flaws in intact rock and allow for numerical replication of crack damage progression through initiation and propagation of micro-fractures along grain boundaries. The Voronoi modelling scheme has been used widely in the past for brittle fracture simulation of rock materials. However the difficulty of generating 3D Voronoi models has limited its application to two-dimensional (2D) codes. The proposed approach is implemented in Neper, an open-source engine for generation of 3D Voronoi grains, to generate block geometry files that can be read directly into 3DEC. A series of Unconfined Compressive Strength (UCS) tests are simulated in 3DEC to verify the proposed methodology for 3D simulation of brittle fractures and to investigate the relationship between each micro-parameter and the model’s macro-response. The possibility of nu-merical replication of the classical U-shape strength curve for anisotropic rocks is also investigated in numerical UCS tests by using complex-shaped (elongated) grains that are cemented to one another along their adjoining sides. A micro-parameter calibration procedure is established for 3D Voronoi models for accurate replication of the mechanical behaviour of isotropic and anisotropic (containing a fabric) rocks.

  16. 3D random Voronoi grain-based models for simulation of brittle rock damage and fabric-guided micro-fracturing

    Directory of Open Access Journals (Sweden)

    E. Ghazvinian

    2014-12-01

    Full Text Available A grain-based distinct element model featuring three-dimensional (3D Voronoi tessellations (random poly-crystals is proposed for simulation of crack damage development in brittle rocks. The grain boundaries in poly-crystal structure produced by Voronoi tessellations can represent flaws in intact rock and allow for numerical replication of crack damage progression through initiation and propagation of micro-fractures along grain boundaries. The Voronoi modelling scheme has been used widely in the past for brittle fracture simulation of rock materials. However the difficulty of generating 3D Voronoi models has limited its application to two-dimensional (2D codes. The proposed approach is implemented in Neper, an open-source engine for generation of 3D Voronoi grains, to generate block geometry files that can be read directly into 3DEC. A series of Unconfined Compressive Strength (UCS tests are simulated in 3DEC to verify the proposed methodology for 3D simulation of brittle fractures and to investigate the relationship between each micro-parameter and the model's macro-response. The possibility of numerical replication of the classical U-shape strength curve for anisotropic rocks is also investigated in numerical UCS tests by using complex-shaped (elongated grains that are cemented to one another along their adjoining sides. A micro-parameter calibration procedure is established for 3D Voronoi models for accurate replication of the mechanical behaviour of isotropic and anisotropic (containing a fabric rocks.

  17. Rice Brittle culm 6 encodes a dominant-negative form of CesA protein that perturbs cellulose synthesis in secondary cell walls.

    Science.gov (United States)

    Kotake, Toshihisa; Aohara, Tsutomu; Hirano, Ko; Sato, Ami; Kaneko, Yasuko; Tsumuraya, Yoichi; Takatsuji, Hiroshi; Kawasaki, Shinji

    2011-03-01

    The brittle culm (bc) mutants of Gramineae plants having brittle skeletal structures are valuable materials for studying secondary cell walls. In contrast to other recessive bc mutants, rice Bc6 is a semi-dominant bc mutant with easily breakable plant bodies. In this study, the Bc6 gene was cloned by positional cloning. Bc6 encodes a cellulose synthase catalytic subunit, OsCesA9, and has a missense mutation in its highly conserved region. In culms of the Bc6 mutant, the proportion of cellulose was reduced by 38%, while that of hemicellulose was increased by 34%. Introduction of the semi-dominant Bc6 mutant gene into wild-type rice significantly reduced the percentage of cellulose, causing brittle phenotypes. Transmission electron microscopy analysis revealed that Bc6 mutation reduced the cell wall thickness of sclerenchymal cells in culms. In rice expressing a reporter construct, BC6 promoter activity was detected in the culms, nodes, and flowers, and was localized primarily in xylem tissues. This expression pattern was highly similar to that of BC1, which encodes a COBRA-like protein involved in cellulose synthesis in secondary cell walls in rice. These results indicate that BC6 is a secondary cell wall-specific CesA that plays an important role in proper deposition of cellulose in the secondary cell walls.

  18. Study on Testing of Brittleness Temperature of Plastics%塑料脆化温度测试的影响因素研究

    Institute of Scientific and Technical Information of China (English)

    宋蓓蓓; 郭乔; 胡生平; 吴博

    2013-01-01

    通过测试共聚PP和均聚PP在不同测试条件下的脆化温度,讨论了脆化温度测试的相关影响因素。结果表明,冷冻时间、试样厚度及退火处理等都会对测试结果产生影响。冷冻时间变长会使脆化温度测试结果偏高;试样厚度越大,测得的脆化温度越高;退火对结晶型材料影响较大,而且结晶度越高,退火的影响越大。%The influencing factors on the plastic's brittleness temperature testing results were studied by testing homo-polypropylene and co-polypropylene in different measurement conditions.The result shows that freezing time , the thickness of samples and annealing treatment affects testing results.The brittleness temperature results increase as the freezing time elongated.The thickness of the sample is greater ,the brittleness temperature is higher.Annea-ling has great effect on the crystalline material ,and higher the degree of crystallization results greater the influence of annealing.

  19. A brittle (normal?) shear zone cored in Site C0002 of Nankai Trough Seismogenic Zone Experiment (IODP Expedition 348)

    Science.gov (United States)

    Crespo-Blanc, Ana; Sample, James; Brown, Kevin; Otsubo, Makoto; Yamamoto, Yuzuru

    2016-04-01

    Integrated Ocean Discovery Program (IODP) Expedition 348, which belongs to the Nankai Trough Seismogenic Zone Experiment, conducted riser-drilling to make deeper an existing hole at Site C0002, up to 3058.5 meters below seafloor (mbsf). This site is located 80 km SE of the Kii Peninsula (Japan) in the Kumano forearc basin, in turn situated on top of the Nankai accretionary prism. Cuttings (875.5-3058.5 mbsf) and cores (2163.0-2217.5 mbsf) were collected in the upper Miocene to Pliocene turbiditic silty claystone with few intercalations of sandstone which characterize the accretionary prism lithological units. A remarkably preserved fault zone has been cored around 2205 mbsf (core section Hole C0002P-348-5R-4). It is characterized by 34 cm of fault breccia, in which an anastomosed cataclastic foliation is present. The rocks of the damaged zone are formed by silty claystone with an incipient scaly fabric and scarce levels of sandstones. Extra-large thin sections were made along the whole core section. In the brittle shear zone, they reveal a catalogue of deformation structures characteristic of a high structural level. In particular, almond-type structures and arrays of microfaults cutting the stratification are the most common structures and outline the cataclastic foliation. The occurrence of calcite veins in the recovered cores is limited to this fault zone, which is indicative of its role as fluid path, accompanied by carbonate cementation. Generally fault veins have lower δ18O values than carbonate cements in the sedimentary matrix, consistent with veins forming at higher temperatures and/or from a fluid more strongly depleted in 18O. A continuum of the relationships between calcite veins and cataclastic deformation is observed, from veins that precipitated early in the fault history, with calcite grains broken during subsequent deformation, to late veins which seal the almond-type structures within the claystones. The geometry of the calcite grains within the

  20. 100 Ma: the new frontier for quantitative global models of the coupled brittle-plates/viscous-mantle system.

    Science.gov (United States)

    Stotz, Ingo; Iaffaldano, Giampiero; Davies, Rhodri

    2014-05-01

    Over recent decades the body of geophysical datasets has grown substantially and rapidly. Ocean-floor observations now allow one to unravel past plate motions (for instance, in the North Atlantic and Indian Ocean over the past 20 Myr) at the unprecedented temporal resolution of about 1 Myr; and more data is anticipated in the near future. Similarly, our knowledge of continental evolution has grown due to advances in interpreting the records of orogeny and sedimentation. Altogether, these ever-growing datasets allow us to reconstruct the past evolution of Earth's lithospheric plates in greater detail than previously achieved. This is key to unravel the dynamics of geological processes, because reconstructed plate motions and their temporal changes are a powerful probe into the evolving balance of shallow- and deep-rooted forces. Such progress, however, is not yet matched by the ability to quantitatively model past plate-motion changes and, therefore to test hypotheses on the dominant geological controls. The main technical challenge is simulating the rheological behaviour of the plates/mantle system, which varies significantly from viscous to brittle. Classically, computer models for viscous mantle flow and for the piecewise motions of the brittle lithosphere have been developed separately. In recent years, coupling of these two independent classes of models has been pioneered, but only for neo-tectonic scenarios (i.e. past few Myr), and with some limitations as to accounting for the impact of evolving mantle-flow on plate motions. It is now timely to further advance the technical ability to simulate the coupled plates/mantle system through geological time (for instance throughout the Cenozoic and possibly the Cretaceous), and to use the growing body of geophysical data as a primary constraint on these quantitative models. In this project, we take steps in this direction. We build on previous work aimed at coupling two advanced codes for mantle flow and lithosphere

  1. Brittle cornea syndrome ZNF469 mutation carrier phenotype and segregation analysis of rare ZNF469 variants in familial keratoconus.

    Science.gov (United States)

    Davidson, Alice E; Borasio, Edmondo; Liskova, Petra; Khan, Arif O; Hassan, Hala; Cheetham, Michael E; Plagnol, Vincent; Alkuraya, Fowzan S; Tuft, Stephen J; Hardcastle, Alison J

    2015-01-06

    Brittle cornea syndrome 1 (BCS1) is a rare recessive condition characterized by extreme thinning of the cornea and sclera, caused by mutations in ZNF469. Keratoconus is a relatively common disease characterized by progressive thinning and ectasia of the cornea. The etiology of keratoconus is complex and not yet understood, but rare ZNF469 variants have recently been associated with disease. We investigated the phenotype of BCS1 carriers with known pathogenic ZNF469 mutations, and recruited families in which aggregation of keratoconus was observed to establish if rare variants in ZNF469 segregated with disease. Patients and family members were recruited and underwent comprehensive anterior segment examination, including corneal topography. Blood samples were donated and genomic DNA was extracted. The coding sequence and splice sites of ZNF469 were PCR amplified and Sanger sequenced. Four carriers of three BCS1-associated ZNF469 loss-of-function mutations (p.[Glu1392Ter], p.[Gln1930Argfs*6], p.[Gln1930fs*133]) were examined and none had keratoconus. One carrier had partially penetrant features of BCS1, including joint hypermobility. ZNF469 sequencing in 11 keratoconus families identified 9 rare (minor allele frequency [MAF] ≤ 0.025) variants predicted to be potentially damaging. However, in each instance the rare variant(s) identified, including two previously reported as potentially keratoconus-associated, did not segregate with the disease. The presence of heterozygous loss-of-function alleles in the ZNF469 gene did not cause keratoconus in the individuals examined. None of the rare nonsynonymous ZNF469 variants identified in the familial cohort conferred a high risk of keratoconus; therefore, genetic variants contributing to disease pathogenesis in these 11 families remain to be identified. Copyright 2015 The Association for Research in Vision and Ophthalmology, Inc.

  2. The Padul normal fault activity constrained by GPS data: Brittle extension orthogonal to folding in the central Betic Cordillera

    Science.gov (United States)

    Gil, Antonio J.; Galindo-Zaldívar, Jesús; Sanz de Galdeano, Carlos; Borque, Maria Jesús; Sánchez-Alzola, Alberto; Martinez-Martos, Manuel; Alfaro, Pedro

    2017-08-01

    The Padul Fault is located in the Central Betic Cordillera, formed in the framework of the NW-SE Eurasian-African plate convergence. In the Internal Zone, large E-W to NE-SW folds of western Sierra Nevada accommodated the greatest NW-SE shortening and uplift of the cordillera. However, GPS networks reveal a present-day dominant E-W to NE-SW extensional setting at surface. The Padul Fault is the most relevant and best exposed active normal fault that accommodates most of the NE-SW extension of the Central Betics. This WSW-wards dipping fault, formed by several segments of up to 7 km maximum length, favored the uplift of the Sierra Nevada footwall away from the Padul graben hanging wall. A non-permanent GPS network installed in 1999 constrains an average horizontal extensional rate of 0.5 mm/yr in N66°E direction. The fault length suggests that a (maximum) 6 magnitude earthquake may be expected, but the absence of instrumental or historical seismic events would indicate that fault activity occurs at least partially by creep. Striae on fault surfaces evidence normal-sinistral kinematics, suggesting that the Padul Fault may have been a main transfer fault of the westernmost end of the Sierra Nevada antiform. Nevertheless, GPS results evidence: (1) shortening in the Sierra Nevada antiform is in its latest stages, and (2) the present-day fault shows normal with minor oblique dextral displacements. The recent change in Padul fault kinematics will be related to the present-day dominance of the ENE-WSW regional extension versus NNW-SSE shortening that produced the uplift and northwestwards displacement of Sierra Nevada antiform. This region illustrates the importance of heterogeneous brittle extensional tectonics in the latest uplift stages of compressional orogens, as well as the interaction of folding during the development of faults at shallow crustal levels.

  3. On the toughening of brittle materials by grain bridging:promoting intergranular fracture through grain angle, strength, andtoughness

    Energy Technology Data Exchange (ETDEWEB)

    Foulk III, J.W.; Johnson, G.C.; Klein, P.A.; Ritchie, R.O.

    2007-11-15

    The structural reliability of many brittle materials such asstructural ceramics relies on the occurrence of intergranular, as opposedto transgranular, fracture in order to induce toughening by grainbridging. For a constant grain boundary strength and grain boundarytoughness, the current work examines the role of grain strength, graintoughness, and grain angle in promoting intergranular fracture in orderto maintain such toughening. Previous studies have illustrated that anintergranular path and the consequent grain bridging process can bepartitioned into five distinct regimes, namely: propagate, kink, arrest,stall and bridge. To determine the validity of the assumed intergranularpath, the classical penentration/deflection problem of a crack impingingon an interface is reexamined within a cohesive zone framework forintergranular and transgranular fracture. Results considering both modesof propagation, i.e., a transgranular and intergranular path, reveal thatcrack-tip shielding is a natural outcome of the cohesive zone approach tofracture. Cohesive zone growth in one mode shields the opposing mode fromthe stresses required for cohesive zone initiation. Although stablepropagation occurs when the required driving force is equivalent to thetoughness for either transgranular or intergranular fracture, the mode ofpropagation depends on the normalized grain strength, normalized graintoughness, and grain angle. For each grain angle, the intersection ofsingle path and multiple path solutions demarcates "strong" grains thatincrease the macroscopic toughness and "weak" grains that decrease it.The unstable transition to intergranular fracture reveals that anincreasinggrain toughness requires a growing region of the transgranularcohesive zone be at and near the peak cohesive strength. The inability ofthe body to provide the requisite stress field yields an overdriven andunstable configuration. The current results provide restrictions for theachievement of substantial toughening

  4. The effects of relative food item size on optimal tooth cusp sharpness during brittle food item processing.

    Science.gov (United States)

    Berthaume, Michael A; Dumont, Elizabeth R; Godfrey, Laurie R; Grosse, Ian R

    2014-12-01

    Teeth are often assumed to be optimal for their function, which allows researchers to derive dietary signatures from tooth shape. Most tooth shape analyses normalize for tooth size, potentially masking the relationship between relative food item size and tooth shape. Here, we model how relative food item size may affect optimal tooth cusp radius of curvature (RoC) during the fracture of brittle food items using a parametric finite-element (FE) model of a four-cusped molar. Morphospaces were created for four different food item sizes by altering cusp RoCs to determine whether optimal tooth shape changed as food item size changed. The morphospaces were also used to investigate whether variation in efficiency metrics (i.e. stresses, energy and optimality) changed as food item size changed. We found that optimal tooth shape changed as food item size changed, but that all optimal morphologies were similar, with one dull cusp that promoted high stresses in the food item and three cusps that acted to stabilize the food item. There were also positive relationships between food item size and the coefficients of variation for stresses in food item and optimality, and negative relationships between food item size and the coefficients of variation for stresses in the enamel and strain energy absorbed by the food item. These results suggest that relative food item size may play a role in selecting for optimal tooth shape, and the magnitude of these selective forces may change depending on food item size and which efficiency metric is being selected.

  5. Evaluation of ductile-brittle transition temperature before and after neutron irradiation for RPV steels using small punch tests

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Min-Chul [Korea Atomic Energy Research Institute, 150 Deokjin-dong, Yuseong-gu, Daejeon 305-353 (Korea, Republic of)]. E-mail: mckim@kaeri.re.kr; Oh, Yong Jun [Hanbat National University, Deogmyeong-dong, Yuseong-gu, Daejeon 305-719 (Korea, Republic of); Lee, Bong Sang [Korea Atomic Energy Research Institute, 150 Deokjin-dong, Yuseong-gu, Daejeon 305-353 (Korea, Republic of)

    2005-08-01

    Small punch (SP) tests were performed to evaluate the ductile-brittle transition temperature before and after a neutron irradiation of reactor pressure vessel (RPV) steels produced by different manufacturing (refining) processes. The results were compared to the standard transition temperature shifts from the conventional Charpy tests and the Master Curve fracture toughness tests in accordance with the American Society for Testing and Materials (ASTM) standard E1921. Small punch specimens were taken from a 1/4t location of the vessel thickness and machined into a 10 mm x 10 mm x 0.5 mm dimension. The specimens were irradiated in the research reactors at Korea Atomic Energy Research Institute Nuclear Research Institute in the Czech Republic at the different fluence levels of about 290 deg C. Small punch tests were performed in the temperature range of RT to -196 deg C using a 2.4 mm diameter ball. For the materials before and after irradiation, the small punch transition temperatures (T {sub SP}), which are determined at the middle of the upper small punch energies, showed a linear correlation with the Charpy index temperature, T {sub 41J}. T {sub SP} from the irradiated samples was increased with the fluence levels and was well within the deviation range of the unirradiated data. However, the transition temperature shift from the Charpy test ({delta}T {sub 41J}) shows a better correlation with the transition temperature shift ({delta}T {sub SP(E)}) when a specific small punch energy level rather than the middle energy level of the small punch curve is used to determine the transition temperature. T {sub SP} also had a correlation with the reference temperature (T {sub 0}) from the Master Curve method using a pre-cracked Charpy V-notched (PCVN) specimen.

  6. SG2PS (structural geology to postscript converter) - A graphical solution for brittle structural data evaluation and paleostress calculation

    Science.gov (United States)

    Sasvári, Ágoston; Baharev, Ali

    2014-05-01

    The aim of this work was to create an open source cross platform application to process brittle structural geological data with seven paleostress inversion algorithms published by different authors and formerly not available within a single desktop application. The tool facilitates separate processing and plotting of different localities, data types and user made groups, using the same single input file. Simplified data input is supported, requiring as small amount of data as possible. Data rotation to correct for bedding tilting, rotation with paleomagnetic declination and k-means clustering are available. RUP and ANG stress estimators calculation and visualization, resolved shear direction display and Mohr circle stress visualization are available. RGB-colored vector graphical outputs are automatically generated in Encapsulated PostScript and Portable Document Format. Stereographical displays on great circle or pole point plot, equal area or equal angle net and upper or lower hemisphere projections are implemented. Rose plots displaying dip direction or strike, with dip angle distribution of the input data set are available. This tool is ideal for preliminary data interpretation on the field (quick processing and visualization in seconds); the implemented methods can be regularly used in the daily academic and industrial work as well. The authors' goal was to create an open source and self-contained desktop application that does not require any additional third party framework (such as .NET) or the Java Virtual Machine. The software has a clear and highly modular structure enabling good code portability, easy maintainability, reusability and extensibility. A Windows installer is publicly available and the program is also fully functional on Linux. The Mac OS X port should be feasible with minimal effort. The install file with test and demo data sets, detailed manual, and links to the GitHub repositories are available on the regularly updated website www.sg2ps.eu.

  7. Carbon deposition during brittle rock deformation: Changes in electrical properties of fault zones and potential geoelectric phenomena during earthquakes

    Energy Technology Data Exchange (ETDEWEB)

    Mathez, E A; Roberts, J J; Duba, A G; Kronenberg, A K; Karner, S L

    2008-05-16

    To investigate potential mechanisms for geoelectric phenomena accompanying earthquakes, we have deformed hollow cylinders of Sioux quartzite to failure in the presence of carbonaceous pore fluids and investigated the resulting changes in electrical conductivity and carbon distribution. Samples were loaded at room temperature or 400 C by a hydrostatic pressure at their outer diameter, increasing pressure at a constant rate to {approx}290 MPa. Pore fluids consisted of pure CO, CO{sub 2}, CH{sub 4} and a 1:1 mixture of CO{sub 2} and CH{sub 4}, each with pore pressures of 2.0 to 4.1 MPa. Failure occurred by the formation of mode II shear fractures transecting the hollow cylinder walls. Radial resistivities of the cylinders fell to 2.9 to 3.1 M{Omega}-m for CO tests and 15.2 to 16.5 M{Omega}-m for CO{sub 2}:CH{sub 4} tests, compared with >23 M{Omega}-m for dry, undeformed cylinders. Carbonaceous fluids had no discernable influence on rock strength. Based on mapping using electron microprobe techniques, carbon occurs preferentially as quasi-continuous films on newly-formed fracture surfaces, but these films are absent from pre-existing surfaces in those same experiments. The observations support the hypothesis that electrical conductivity of rocks is enhanced by the deposition of carbon on fracture surfaces and imply that electrical properties may change in direct response to brittle deformation. They also suggest that the carbon films formed nearly instantaneously as the cracks formed. Carbon film deposition may accompany the development of microfracture arrays prior to and during fault rupture and thus may be capable of explaining precursory and coseismic geoelectric phenomena.

  8. Internal fabrics in magmatic plutons emplaced in extended brittle crust - insight from analogue models with AMS (Anisotropy of Magnetic Susceptibility)

    Science.gov (United States)

    Mirzaei, Masoud; Zavada, Prokop; Machek, Matej; Roxerova, Zuzana

    2016-04-01

    Magma emplacement in extended brittle crust was simulated by injecting plaster of Paris (magma) into a large sandbox with central deformable rubber sheet. Analog magma is during the experiments injected through small circular inlet cut in the center of the elastic sheet. Injection force oscillation during the steadily evacuating analog magma was recorded during the experiments and regularly showed 3-4 increases followed by a quick drop. The recorded oscillation amplitude is largest for static injection without extension of the sandbox, which formed a columnar body with concentric and zonal internal fabric. Experiments including normal or oblique 20% extension resulted in along rift axis elongated oblate ellipsoidal pluton with rift parallel ridges in the top part of the pluton. Inspection of horizontal profiles show bone-shaped internal zoning patterns limited by conjugate sets of shear zones. Orientation of these internal shear zones is correlated with the sand-clock fault pattern developed in the overburden sand pack. Another set of shear zones parallel with the long axes of the plutons (rift axis) are associated with successive emplacement of distinct plaster pulses during the buildup of the entire body. The innermost lastly emplaced pulses of plaster display weak vertical magnetic fabrics with vertical lineations, while the outer shells of already emplaced plaster reveal stronger and margin parallel oblate magnetic fabrics with subhorizontal lineations. We interpret the vertical innermost fabrics as a result of active ascent of plaster from the injection inlet, while the fabrics in the outer zones likely reflect push due to inflation of the inner domain reflected in the reworking of the magnetic fabric.

  9. Studies on Biological Characterization of Rice Brittle Culm Mutants and Their Biomass Degradation Efficiency%特异水稻脆茎突变体生物学特性及生物质降解效率的研究

    Institute of Scientific and Technical Information of China (English)

    冯永清; 邹维华; 李丰成; 张晶; 张会; 谢国生; 涂媛苑; 路铁刚; 彭良才

    2013-01-01

    yield. Meanwhile, the mutants had higher biomass yield. With respect to the brittle characters, all mutants exhibited a much higher biomass enzymatic digestibility upon various acid and alkali pretreatments. The data indicated that the mutants could be applied for energy crop breeding towards high yields of seeds and biomass in rice.

  10. Prediction of non-brittle fracture in the welded joint of C-Mn steel in the brittle-ductile transition domain; Prediction de la non-rupture fragile dans un joint soude en acier C-Mn dans le domaine de la transition fragile/ductile

    Energy Technology Data Exchange (ETDEWEB)

    Nguyen, Thai Ha

    2009-11-15

    This work concerns the nuclear safety, specifically the secondary circuit integrity of pressurized water reactors (PWR). The problem is that of the fracture of a thin tubular structure in ferritic steel with many welded joints. The ferritic steel and weld present a brittle/ductile tenacity transition. Moreover, the welds present geometry propitious to the appearance of fatigue cracks, due to vibrations and expansions. These cracks may cause the complete fracture of the structure. The objectives of this work are to establish a criterion of non-fracture by cleavage of thin welded structures in ferritic steel, applicable to actual structures. Therefore, the present study focuses on the fracture behaviour of welded thin structures in brittle/ductile transition. It aims at developing the threshold stress model initially proposed by Chapuliot, to predict the non-brittle-fracture of this welded structure. The model is identified for the welded joint in C-Mn steel for nuclear construction, specifically in the upper part of the transition. A threshold stress, below which the cleavage cannot take place, is identified using tensile tests at low temperature on axis-symmetrical notched specimens taken in welded joint. This threshold stress is used to define the threshold volume where the maximum principal stress exceeds the threshold stress during the test. The analysis by SEM of specimen fracture surfaces shows that the gross solidification molten zone in the weld is the most likely to cleave. The relation between the brittle fracture probability and the threshold volume in the gross solidification molten zone is established via a sensitivity function, using multi-materials simulations. The model thus identified is tested for the prediction of non-brittle-fracture of SENT specimens taken in the welded joint and tested in tension. The results obtained are encouraging with regards to the transferability of the model to the actual structure. (author)

  11. Growth, reproduction and possible recruitment variability in the abyssal brittle star Ophiocten hastatum (Ophiuroidea: Echinodermata) in the NE Atlantic

    Science.gov (United States)

    Gage, John D.; Anderson, Roslyn M.; Tyler, Paul A.; Chapman, Rachel; Dolan, Emily

    2004-06-01

    Growth was studied from skeletal growth markers in the cosmopolitan abyssal brittle star Ophiocten hastatm. Samples for analysis were taken at five sites located in the southern (2900 m) and central (2000 m) Rockall Trough, at ca. 3000 and 4000 m in the Porcupine Seabight, and at 4850 m on the Porcupine Abyssal Plain. Growth bands were assumed to reflect an annual cycle in skeletal growth. Band measurements on arm vertebrae, standardised to disc diameter, were used to provide size-at-age data and size-increment data that took into account overgrowth of early bands in older individuals. The Richards growth function marginally provides best fit to pooled size-at-age data, although the asymptote-less Tanaka function and the Gompertz growth function also provided good fit to size-at-age data which showed a rather linear growth pattern with little indication of a growth asymptote. Log e transformed size-increment data were linearised by applying the Ford-Walford method to approximate Gompertz growth so that growth could be compared at the five sites. Grouped linear regression and analysis of covariance showed no significant differences between growth at the sites and a common fitted regression. However, pairwise comparisons suggest growth differences with increasing bathymetric separation. Oocyte size frequencies measured from histological preparations of the gonad of specimens from the Porcupine Abyssal Plain indicate marked reproductive periodicity, with spawn-out in late winter that is likely followed by planktotrophic early development in spring with benthic settlement in summer. Although usually rare in the trawl and epibenthic sled samples, several years of successful recruitment followed by a period when recruitment was low or absent might explain size structure observed in a single unusually large sample from the Rockall Trough. This is consistent with previous observations during the late 1990s of a large population increase on the Porcupine Abyssal Plain

  12. The evolutionary fate of phenotypic plasticity and functional traits under domestication in manioc: changes in stem biomechanics and the appearance of stem brittleness.

    Science.gov (United States)

    Ménard, Léa; McKey, Doyle; Mühlen, Gilda S; Clair, Bruno; Rowe, Nick P

    2013-01-01

    Domestication can influence many functional traits in plants, from overall life-history and growth form to wood density and cell wall ultrastructure. Such changes can increase fitness of the domesticate in agricultural environments but may negatively affect survival in the wild. We studied effects of domestication on stem biomechanics in manioc by comparing domesticated and ancestral wild taxa from two different regions of greater Amazonia. We compared mechanical properties, tissue organisation and wood characteristics including microfibril angles in both wild and domesticated plants, each growing in two different habitats (forest or savannah) and varying in growth form (shrub or liana). Wild taxa grew as shrubs in open savannah but as lianas in overgrown and forested habitats. Growth form plasticity was retained in domesticated manioc. However, stems of the domesticate showed brittle failure. Wild plants differed in mechanical architecture between shrub and liana phenotypes, a difference that diminished between shrubs and lianas of the domesticate. Stems of wild plants were generally stiffer, failed at higher bending stresses and were less prone to brittle fracture compared with shrub and liana phenotypes of the domesticate. Biomechanical differences between stems of wild and domesticated plants were mainly due to changes in wood density and cellulose microfibril angle rather than changes in secondary growth or tissue geometry. Domestication did not significantly modify "large-scale" trait development or growth form plasticity, since both wild and domesticated manioc can develop as shrubs or lianas. However, "finer-scale" developmental traits crucial to mechanical stability and thus ecological success of the plant were significantly modified. This profoundly influenced the likelihood of brittle failure, particularly in long climbing stems, thereby also influencing the survival of the domesticate in natural situations vulnerable to mechanical perturbation. We

  13. The evolutionary fate of phenotypic plasticity and functional traits under domestication in manioc: changes in stem biomechanics and the appearance of stem brittleness.

    Directory of Open Access Journals (Sweden)

    Léa Ménard

    Full Text Available Domestication can influence many functional traits in plants, from overall life-history and growth form to wood density and cell wall ultrastructure. Such changes can increase fitness of the domesticate in agricultural environments but may negatively affect survival in the wild. We studied effects of domestication on stem biomechanics in manioc by comparing domesticated and ancestral wild taxa from two different regions of greater Amazonia. We compared mechanical properties, tissue organisation and wood characteristics including microfibril angles in both wild and domesticated plants, each growing in two different habitats (forest or savannah and varying in growth form (shrub or liana. Wild taxa grew as shrubs in open savannah but as lianas in overgrown and forested habitats. Growth form plasticity was retained in domesticated manioc. However, stems of the domesticate showed brittle failure. Wild plants differed in mechanical architecture between shrub and liana phenotypes, a difference that diminished between shrubs and lianas of the domesticate. Stems of wild plants were generally stiffer, failed at higher bending stresses and were less prone to brittle fracture compared with shrub and liana phenotypes of the domesticate. Biomechanical differences between stems of wild and domesticated plants were mainly due to changes in wood density and cellulose microfibril angle rather than changes in secondary growth or tissue geometry. Domestication did not significantly modify "large-scale" trait development or growth form plasticity, since both wild and domesticated manioc can develop as shrubs or lianas. However, "finer-scale" developmental traits crucial to mechanical stability and thus ecological success of the plant were significantly modified. This profoundly influenced the likelihood of brittle failure, particularly in long climbing stems, thereby also influencing the survival of the domesticate in natural situations vulnerable to mechanical

  14. Brittle reactivation of inherited late Neoproterozoic/Cambrian lithospheric-scale structures during extension and break-up of Madagascar from Africa

    Science.gov (United States)

    Giese, J.; Reiss, M. C.; Rindraharisaona, E. J.; Rumpker, G.; Schreurs, G.; Tilmann, F. J.; Yuan, X.

    2016-12-01

    We compare the temporal and structural evolution of the adjacent Morondava and Mahajanga sedimentary basins in western Madagascar in the light of reactivation of lithospheric and crustal-scale structures. Both basins formed during Mesozoic extension and break-up of Madagascar from Africa and are underlain and bordered by highly reworked Precambrian basement. Rifting in the Morondava basin was partly guided by brittle reactivation of inherited Neoproterozoic/Cambrian ductile structures [1]. Thus, brittle faults in both basin and basement trend parallel (I) to the borders of the basin, i.e. N-S and NW-SE, and (II) to shear zones in the basement to the east. In contrast, the border of the Mahajanga basin and most of the brittle faults within the basin run NE-SW, at a high angle to abundant N-S and WNW-ESE trending brittle lineaments in the basement to the east. Recent shear-wave splitting results from a seismic network across the entire island of southern Madagascar from SW to NE mimic the surface orientation of shear zones in the central part of the array and indicate that the Neoproterozoic/Cambrian structural trends follow lithospheric-scale anisotropies [2]. Further, this implies that these anisotropies persisted in this area since the latest stages of convergence during the East African orogeny and thus the location of rifting in the Morondava basin was likely controlled by the inherited lithospheric structure. NE-SW trending anisotropy has been identified in the seismic network below the Antananarivo domain of SE Madagascar, the same basement domain bordering and underlying (part of) the Mahajanga basin. The reason for this orientation of anisotropy at depth is not entirely clear, but [2] propose crystallographic preferred orientation of mantle minerals due to absolute plate motion. However, the contribution of inherited lithospheric scale tectonic structures is also feasible. [1] Giese, J., Seward, D., Schreurs, G., 2012. Tectonics 31, doi:10.1029/2011TC002921

  15. Fold-and-thrust belt evolution influenced by along and across strike thickness variations: new insights from brittle-ductile centrifuge analogue models

    Science.gov (United States)

    Santolaria Otin, Pablo; Harris, Lyal; Casas, Antonio; Soto, Ruth

    2014-05-01

    Using a new centrifuge analogue modelling approach, 38 models were performed to study the influence of along and across strike thickness variations of a ductile-brittle layered sequence on the kinematics and deformation style of fold-and-thrust belts. Four different series, changing the brittle-ductile thickness ratio in models with i) constant thickness, ii) across strike varying thickness, iii) along strike varying thickness and iv) along and across-strike varying thickness, were performed. The brittle sedimentary cover was simulated by "Moon Sand™", regular fine-grained quartz sand coated by polymer and synthetic rubber binders, allowing layers to be placed vertically in the centrifuge (impossible with normal sand). The ductile décollement (evaporites) was simulated by silicone putty (Crazy Aaron Enterprise's Thinking Putty™). Models were run step by step in a high-acceleration centrifuge attaining 900 g, what allows to drastically reduce the experimental time. In addition to surface observation and serial cross-sections at the end of the models, CT scans portray the progressive 3- and 4-dimensional evolution of several models. With constant thickness, the increase of the brittle-ductile ratio results in the decrease of the number of structures where shortening is accommodated and the development of structures does not follow a linear sequence. Across-strike thickness variations trigger the location of deformation towards the wedge front, precluding the emplacement of structures in the hinterland. Along-strike thickness changes result in the lateral variation of the number of structure and a differential displacement of the deformation front. The occurrence of oblique structures is enhanced in wedges with across and along strike thickness variations where, in addition, rotational domains are observed. Comparison with the South Pyrenean Central Unit, in the Southern Pyrenees, characterized by a west- and southward thinning of the pretectonic Mesozoic series

  16. Method,Measure,and Immunity of the ASME Standard for Anti-brittle Fracture Thoughts,Methods and Absolution Steps of ASME Code for Anti-Brittle Fracture%ASME标准防脆断的思路、措施和豁免判定步骤

    Institute of Scientific and Technical Information of China (English)

    程涛涛; 黄明松

    2015-01-01

    介绍ASME 标准中防止低温脆断的总体思路和措施,并对该措施进行分析,比较了ASME Ⅷ-Ⅰ和ASME Ⅷ-Ⅱ中对防低温脆断措施方面的主要区别,列出了ASME材料低温冲击试验豁免判定的具体操作步骤。%This paper introduces the general idea and measures of preventing the low temperature brittle frac-ture in ASME standard,and analyzes the measures;it contrasts the main differences between ASME Ⅷ-Ⅰand ASME Ⅷ-Ⅱin preventing the low temperature brittle fracture;it lists the specific steps of impact test exemption of ASME.

  17. Constraints on structural evolution from correlations between hydraulic properties and P-wave velocities during brittle faulting of rocks

    Science.gov (United States)

    Ahrens, Benedikt; Duda, Mandy; Renner, Jörg

    2017-04-01

    . Except during the development of a localized fault at the lowest imposed effective confining pressure, we found permeability and hydraulic diffusivity to increase during progressing brittle deformation associated with dilation. Thus, in-situ faulting of fluid-bearing rocks should in general exhibit self-stabilization. Contrary, diffusivity decreases during ongoing inelastic compaction by non-localized cataclastic flow at the highest explored effective pressure. Hydraulic properties exhibit systematic correlations with inelastic radial strain, a rather expected result for permeability, but stress ratio and mean stress seem to control hydraulic properties before inelastic deformation begins. For permeability, radial strain, a likely surrogate for characteristics of cracks aligned with the flow direction, constitutes a reference unifying results up to about peak stress from experiments performed at different effective pressures. Such a relation with radial strain appears to hold even more uniformly for P-wave velocity throughout almost all of the deformation stages. The observed correlation between hydraulic diffusivity and P-wave velocity in the direction of fluid flow suggests that monitoring changes in elastic wave velocities bears the potential to constrain changes in conditions for transient fluid flow.

  18. Resilience and brittleness in the offshore helicopter transportation system: The identification of constraints and sacrifice decisions in pilots' work

    Energy Technology Data Exchange (ETDEWEB)

    Gomes, Jose O. [Graduate Program in Informatics-NCE and IM, Federal University of Rio de Janeiro, Cidade Universitaria, Ilha do Fundao, Rio de Janeiro, RJ (Brazil); Woods, David D. [Ohio State University, Ohio (United States); Carvalho, Paulo V.R. [National Nuclear Energy Commission/Nuclear Engineering Institute, Cidade Universitaria-Ilha do Fundao, Rio de Janeiro RJ 21945-970 (Brazil)], E-mail: paulov@pesquisador.cnpq.br; Huber, Gilbert J.; Borges, Marcos R.S. [Graduate Program in Informatics-NCE and IM, Federal University of Rio de Janeiro, Cidade Universitaria, Ilha do Fundao, Rio de Janeiro, RJ (Brazil)

    2009-02-15

    Offshore transportation using helicopters is a complex socio-technical system. The resilience of this system is an emergent property related to performance variability in many nested levels, e.g. pilot activities, maintenance, management systems, helicopter design and so forth. This paper examines production/safety tradeoffs in pilots' work in the helicopter transportation system for the Campos Basin oil fields in Brazil to understand the resilience and brittleness of this system. The study team carried out and analyzed 63 h of interviews with pilots, co-pilots, managers and human resources personnel of some of the main helicopter-operating companies. About 80% of the oil extracted in Brazil comes from this Basin, a 3 h drive north of Rio de Janeiro city. The oil company hires nine helicopter-operating companies to transport about 40,000 people who work on ships and platforms every month. The main goal of this project is to discover how the transport system is resilient and brittle, given the workload demands and economic pressures. The analysis uncovered goal conflicts that arise at the boundaries of the organizations and how people in different roles cope with these conflicts, and their implications to overall system safety and resilience.

  19. Quantification of brittle-ductile failure behavior of ferritic reactor pressure vessel steels using the Small-Punch-Test and micromechanical damage models

    Energy Technology Data Exchange (ETDEWEB)

    Linse, T., E-mail: thomas.linse@tu-dresden.de [Technische Universität Dresden, Institute for Solid Mechanics, 01062 Dresden (Germany); Kuna, M. [Technische Universität Bergakademie Freiberg, Institute of Mechanics and Fluid Dynamics, Lampadiusstrasse 4, 09596 Freiberg (Germany); Viehrig, H.-W. [Helmholtz-Zentrum Dresden-Rossendorf, P.O. Box 510119, 01328 Dresden (Germany)

    2014-09-22

    Two German ferritic pressure vessel steels are examined in the brittle to ductile transition regime as a function of temperature and irradiation. The experiments are done by a miniaturized Small-Punch-Test in hot cells within the temperature range of −185 °C up to 70 °C. From the load–displacement curve of the SPT, the yield curves and parameters of both a non-local GURSON-TVERGAARD-NEEDLEMAN ductile damage model and a modified BEREMIN model are identified. The influence of temperature and irradiation on the model parameters is analyzed. All parameters are verified by comparison with results from standard test methods. The parameters, identified from SPT, are used to simulate the failure behavior in standard fracture mechanics specimens. In the upper shelf, the non-local GTN-model is applied to simulate crack resistance curves, from where the fracture toughness data could be successfully predicted. In the lower shelf, the WEIBULL-stress of the specimens was computed to find out the statistics of fracture toughness values. Finally, the modified BEREMIN model and the non-local ductile damage model were combined to evaluate the failure of fracture specimens in the brittle-ductile transition region. This way, an acceptable agreement with Master-curve data for non-irradiated steels could be achieved in the whole temperature range.

  20. Comparative study of sea ice dynamics simulations with a Maxwell elasto-brittle rheology and the elastic-viscous-plastic rheology in NEMO-LIM3

    Science.gov (United States)

    Raulier, Jonathan; Dansereau, Véronique; Fichefet, Thierry; Legat, Vincent; Weiss, Jérôme

    2017-04-01

    Sea ice is a highly dynamical environment characterized by a dense mesh of fractures or leads, constantly opening and closing over short time scales. This characteristic geomorphology is linked to the existence of linear kinematic features, which consist of quasi-linear patterns emerging from the observed strain rate field of sea ice. Standard rheologies used in most state-of-the-art sea ice models, like the well-known elastic-viscous-plastic rheology, are thought to misrepresent those linear kinematic features and the observed statistical distribution of deformation rates. Dedicated rheologies built to catch the processes known to be at the origin of the formation of leads are developed but still need evaluations on the global scale. One of them, based on a Maxwell elasto-brittle formulation, is being integrated in the NEMO-LIM3 global ocean-sea ice model (www.nemo-ocean.eu; www.elic.ucl.ac.be/lim). In the present study, we compare the results of the sea ice model LIM3 obtained with two different rheologies: the elastic-viscous-plastic rheology commonly used in LIM3 and a Maxwell elasto-brittle rheology. This comparison is focused on the statistical characteristics of the simulated deformation rate and on the ability of the model to reproduce the existence of leads within the ice pack. The impact of the lead representation on fluxes between ice, atmosphere and ocean is also assessed.

  1. Multiscale approach to description of deformation and fracture of brittle media with hierarchical porous structure on the basis of movable cellular automaton method

    Directory of Open Access Journals (Sweden)

    S. G. Psakhie

    2013-04-01

    Full Text Available An approach to multiscale description of deformation and fracture of brittle porous materials on the basis of movable cellular automaton method was proposed. The material characterized by pore size distribution function having two maxima was considered. The core of the proposed approach consists in finding the automaton effective response function by means of direct numerical simulation of representative volume of the porous material. A hierarchical two-scale model of mechanical behavior of ceramics under compression and shear loading was developed. Zirconia based ceramics with pore size greater than the average grain size was considered. At the first scale of the model only small pores (corresponding to the first maximum of the pore size distribution function were taking into account explicitly (by removing automata from the initial structure. The representative volume and effective elastic properties of the porous material at this scale were evaluated. At the second scale of the model, big pores were taking into account explicitly, the parameters of the matrix corresponded to the ones determined at the first scale. Simulation results showed that the proposed multiscale model allows qualitatively and quantitatively correct describing of deformation and fracture of brittle material with hierarchical porous structure.

  2. Determining the Maximum Depth of Hydrothermal Circulation Using Geothermal Mapping and Seismicity to Delineate the Depth to Brittle-Plastic Transition in Northern Honshu, Japan

    Directory of Open Access Journals (Sweden)

    Yota Suzuki

    2014-05-01

    Full Text Available This paper defines the maximum possible vertical extent of hydrothermal circulation in granitic crust, and thus the maximum depth within which geothermal reservoirs can be encountered. To evaluate prospective geothermal fields we constructed a geothermal database in northern Honshu, Japan that includes 571 points of thermal data of existing wells and hot springs. Depth-temperature curves were normalized by the Activity Index for three-dimensional extrapolation and a depth contour map of the 380 °C isotherm was plotted as an assumed brittle-plastic transition for granitic crust. Shallower-depth anomalies of the brittle-plastic transition on this map are closely coincident with the Quaternary volcanoes and their prospective geothermal fields. It should be noted that the bottom of the spatial distribution of seismicity in the volcanic fields shows strong correlation to the 380 °C isotherm. This result indicates reliability of the subsurface three-dimensional thermal map and suggests that the 380 °C isotherm strongly constrains the bottom surface of seismicity, fracturing and hydrothermal convection in granitic crust.

  3. True Triaxial Strength and Brittle Fracture of the Granodiorite at the SAFOD Drillhole Wall, and the Potential for Estimating the Maximum Horizontal Principal Stress

    Science.gov (United States)

    Lee, H.; Haimson, B.

    2007-12-01

    Salinian granodiorite core from the 1462-1470m segment of the SAFOD drillhole was used to derive its critical mechanical properties under true triaxial stress conditions, analyze shear localization and brittle fracture characteristics, and establish the strength criterion under dry conditions (Eos Trans. AGU, 87/52, Abstract T32C- 03). Here we report on a series of true triaxial tests on 'unjacketed' specimens simulating stress conditions prevailing at the drillhole wall and responsible for borehole failure in the form of breakouts. Owing to numerous random cracks inherent in the core, only 11 rectangular prismatic specimens (19×19×38 mm3) were successfully tested, employing the University of Wisconsin polyaxial cell. The two larger principal stresses, σ1 and σ2, were transmitted through metal pistons, while σ3 was applied by confining fluid pressure. Specimen sides facing σ3 were left 'unjacketed', i.e. in direct contact with the confining fluid, to simulate the condition of drilling-mud pressure applying the principal radial stress (σ3) to the exposed borehole wall. The loading path called for first bringing σ2 and σ3 to preset levels and then increasing σ1 at a constant strain rate (5x10-6/sec) until brittle failure occurred. Invariably, failure occurred at σ1 levels that were only about half as high as those in previously tested dry samples under the same σ2 and σ3 magnitudes. Instead of a shear fracture, or fault, steeply inclined in the direction of σ3, as previously observed in the dry specimens, brittle failure took the form of a localized cluster of through-going extensile cracks parallel and adjacent to the faces subjected to σ3. Since failure occurred at σ1 values close to those at dilatancy onset in dry specimens, we infer that as soon as microcracks reopened, confining fluid rushed into those daylighting at the σ3 faces and extended them along a path of least resistance, i.e. along a plane normal to σ3. Thus brittle failure under

  4. Acidic deposition ("acid rain")

    Science.gov (United States)

    Schreiber, R. Kent; LaRoe, Edward T.; Farris, Gaye S.; Puckett, Catherine E.; Doran, Peter D.; Mac, Michael J.

    1995-01-01

    Acidic deposition, or "acid rain," describes any form of precipitation, including rain, snow, and fog, with a pH of 5.5 or below (Note: pH values below 7 are acidic; vinegar has a pH of 3). It often results when the acidity of normal precipitation is increased by sulfates and nitrates that are emitted into the atmosphere from burning fossil fuels. This form of airborne contamination is considered harmful, both directly and indirectly, to a host of plant and animal species.Although acid rain can fall virtually anywhere, ecological damages in environmentally sensitive areas downwind of industrial and urban emissions are a major concern. This includes areas that have a reduced capacity to neutralize acid inputs because of low alkalinity soils and areas that contain species with a low tolerance to acid conditions. To determine the distribution of acidic deposition and evaluate its biological effects, research and monitoring are being conducted by the federal government with support from states, universities, and private industry.            The national extent of the acid rain problem has been estimated by sampling water from 3,000 lakes and 500 streams (Irving 1991), representing more than 28,000 lakes and 56,000 stream reaches with a total of 200,000 km (125,000 mi). Some particularly sensitive areas, such as the Adirondack Mountain region, have been more intensively sampled and the biota examined in detail for effects from acidity.         To identify trends in aquatic ecosystems, present and historical survey data on water chemistry and associated biota are compared. In lakes, the chemical and biological history and pH trends may be inferred or reconstructed in some cases by examining assemblages of fossil diatoms and aquatic invertebrates in the sediment layers. In terrestrial ecosystems, vegetation damage is surveyed and effects of acidic deposition to plants and animals are determined from laboratory and field exposure experiments. Natural

  5. Does Extension Play a Role in Ionian Tectonics? Potential Effects of Preexisting Bounding Faults, Local Brittle Failure, and Sulfur Pore Pressure on Crustal Stresses

    Science.gov (United States)

    McKinnon, William B.; Kirchoff, M.; Bland, M.

    2013-10-01

    The majority of mountains observed on Io are tectonic, upthrusted blocks. Their formation is generally thought to be related to Io’s heat-pipe volcanism, crustal subsidence, and accompanying lateral confinement. In previous work, we demonstrated that compressional thermal stresses from sustained local or regional shut down of Io’s heat-pipe volcanism could also play a vital role in mountain formation, and help explain the anticorrelation between Io’s mountains and volcanic centers [Kirchoff and McKinnon 2009, Formation of mountains on Io: Variable volcanism and thermal stresses, Icarus 201, 598-614; Kirchoff et al. 2011, Global distribution of volcanoes and mountains on Io: Control by asthenospheric heating and implications for mountain formation, Earth Planet. Sci. Lett. 301, 22-30]. Here we refine our previous model by using an “unconfined” horizontal boundary condition (zero average lateral stress), including brittle failure (crustal plasticity), and adding sulfur to our rheological model. The unconfined horizontal boundary condition accounts for stresses released on preexisting, more distant faults; including crustal plasticity allows us to more realistically represent stresses that would exceed the brittle failure limit otherwise, and addition of sulfur to the model composition of Io’s crust further improves the rheological model of the crust. Heated and melted at depth, liquid sulfur creates pore pressure in the lower crust and profoundly reduces the brittle failure limit. Including these modifications when the volcanic eruption rate decreases introduces a region of tensional failure in the upper crust and increases the size of the region in compressional failure in the lower crust. Finite element models show that increasing compression at depth imparts substantial bending stresses, which can drive surface faulting and block rotation. Such conditions further facilitate mountain formation at the surface, and highlight the difference between Io

  6. Investigation of the physico-chemical and mechanical properties of hard brittle shales from the Shahejie Formation in the Nanpu Sag, northern China

    Science.gov (United States)

    Xiangjun, Liu; Jian, Xiong; Lixi, Liang; Yi, Ding

    2017-06-01

    With increasing demand for energy and advances in exploration and development technologies, more attention is being devoted to exploration and development of deep oil and gas reservoirs. The Nanpu Sag contains huge reserves in deep oil and gas reservoirs and is a promising area. In this paper, the physico-chemical and mechanical properties of hard brittle shales from the Shahejie Formation in the Nanpu Sag in the Bohai Bay Basin of northern China were investigated using a variety of methods, including x-ray diffraction analysis, cation exchange capacity (CEC) analysis, contact angle measurements, scanning electron microscope observations, immersion experiments, ultrasonic testing and mechanical testing. The effects of the physico-chemical properties of the shales on wellbore instability were observed, and the effects of hydration of the shales on wellbore instability were also examined. The results show that the major mineral constituents of the investigated shales are quartz and clay minerals. The clay mineral contents range from 25.33% to 52.03%, and the quartz contents range from 20.03% to 46.45%. The clay minerals do not include montmorillonite, but large amounts of mixed-layer illite/smectite were observed. The CEC values of the shales range from 90 to 210 mmol kg-1, indicating that the shales are partly hydrated. The wettability of the shales is strongly water-wetted, indicating that water would enter the shales due to the capillary effect. Hydration of hard brittle shales can generate cracks, leading to changes in microstructure and increases in the acoustic value, which could generate damage in the shales and reduce their strength. With increasing hydration time, the shale hydration effect gradually becomes stronger, causing an increase in the range of the acoustic travel time and decreases in the ranges of cohesion and internal friction angles. For the hard brittle shales of the Nanpu Sag, drilling fluid systems should aim to enhance sealing ability

  7. Influence of operation factors on brittle fracture initiation and critical local normal stress in SE(B) type specimens of VVER reactor pressure vessel steels

    Science.gov (United States)

    Kuleshova, E. A.; Erak, A. D.; Kiselev, A. S.; Bubyakin, S. A.; Bandura, A. P.

    2015-12-01

    A complex of mechanical tests and fractographic studies of VVER-1000 RPV SE(B) type surveillance specimens was carried out: the brittle fracture origins were revealed (non-metallic inclusions and structural boundaries) and the correlation between fracture toughness parameters (CTOD) and fracture surface parameters (CID) was established. A computational and experimental method of the critical local normal stress determination for different origin types was developed. The values of the critical local normal stress for the structural boundary origin type both for base and weld metal after thermal exposure and neutron irradiation are lower than that for initial state due to the lower cohesive strength of grain boundaries as a result of phosphorus segregation.

  8. Evolution of supraglacial brittle and ductile structures and drainage systems at a partly debris-covered alpine valley glacier during a 15 yr period

    Science.gov (United States)

    Kellerer-Pirklbauer, Andreas; Kulmer, Bernd

    2016-04-01

    Based on five glacier stages (1998, 2003, 2006, 2009 and 2012) covering a period of 15 years, supraglacial crevasses and other structures as well as the drainage system at the tongue of Pasterze Glacier were mapped and interpreted. Pasterze Glacier is the largest glacier (c.16.5 km2) of the entire Eastern European Alps located in the Hohe Tauern Range, Central Austria at 47°05'N and 12°43'E. The glacier is in a stage of rapid recession and downwasting. The tongue is connected with the firn area by a mighty ice fall. 75% of the c.4.5 km long glacier tongue is covered by a supraglacial debris cover affecting glacier surface morphology related to differential ablation influencing the glacier's stress and strain field. High resolution orthoimagery and digital elevation models/DEM (both data sets with 20-50 cm grid resolution) were analysed. A structure glaciological mapping key was applied to discern relevant brittle (normal faults, thrust faults, strike-slip faults commonly associated with and en èchelon structures, and ice disintegration expressed as normal faults) and ductile structures (band ogives). Additionally, a geometric mapping key was used differentiating between chevron, splaying, transverse, and longitudinal crevasses as well as complex crevasse fields related to ice disintegration (commonly circular and semi-circular collapse features). The drainage system was mapped differentiating between supraglacial channels and moulins. Observations made during annual glacier measurement campaigns were additionally considered. Results indicate that the lower half of the glacier tongue was characterised during the observation period by ice disintegration (with semi-circular collapse features since 2003 near the glacier terminus and since 2009 in the central part) and thrust faults with downslope convexity (steady upslope migration of first occurrence during the observation period). In general, the crevasse density increased towards the left (NE), less debris

  9. ANALYSIS OF THE LOCALIZATION OF DAMAGE AND THE COMPLETE STRESS-STRAIN RELATION FOR MESOSCOPIC HETEROGENEOUS BRITTLE ROCK SUBJECTED TO COMPRESSIVE LOADS

    Institute of Scientific and Technical Information of China (English)

    周小平; 张永兴; 哈秋聆; 王建华

    2004-01-01

    A micromechanics-based model is established. The model takes the interaction among sliding cracks into account, and it is able to quantify the effect of various parameters on the localization condition of damage and deformation for brittle rock subjected to compressive loads. The closed-form explicit expression for the complete stress-strain relation of rock containing microcracks subjected to compressive loads was obtained. It is showed that the complete stress-strain relation includes linear elasticity,nonlinear hardening,rapid stress drop and strain softening.The behavior of rapid stress drop and strain softening is due to localization of deformation and damage. Theoretical predictions have shown to be consistent with the experimental results.

  10. Optimization of RNA isolation from Brittle Leaf Disease affected date palm leaves and construction of a subtractive cDNA library.

    Science.gov (United States)

    Saïdi, Mohammed Najib; Gargouri-Bouzid, Radhia; Rayanni, Mariem; Drira, Noureddine

    2009-01-01

    A simple and efficient method was described here for the isolation of high-quality RNA from date palm leaves affected with Brittle Leaf Disease (BLD) and containing high amount of phenolic compounds. The procedure was based on the use of a non-ionic detergent Nonidet-P40 (NP-40), Polyvinylpyrrolidone (PVP), and beta-mercaptoethanol in the extraction buffer in order to isolate cytoplasmic RNA and to prevent the oxidation of phenolic compounds. This method allowed the isolation of intact RNA, suitable for cDNA synthesis and library construction. Differential screening of the subtractive cDNA library from affected leaf RNA led to the identification of some BLD-induced genes.

  11. Synergetic effect of hardness and phosphorus grain-boundary segregation on the ductile-to-brittle transition temperature of 17-4 PH steel

    Science.gov (United States)

    Christien, F.; Le Gall, R.; Saindrenan, G.

    2003-11-01

    The influence of hardness and phosphorus grain-boundary segregation (PGBS) on the ductile-to-brittle transition temperature (DBTT) of a 17-4 PH martensitic steel was studied. Thermal treatments including long-time aging at low temperature were made to get different hardness levels and different PGBS amounts. A synergetic effect between PGBS and hardness on the DBTT of the steel is evidenced; in other words, the DBTT shift due to PGBS increases with hardness. If hardness is low enough, PGBS can even have no effect on the DBTT. A tentative interpretation of this synergetic effect is proposed, based on the assumption that the detrimental effect of PGBS on the grain-boundary cohesion increases with temperature.

  12. Fracture toughness evaluation of 20MnMoNi55 pressure vessel steel in the ductile to brittle transition regime: Experiment & numerical simulations

    Science.gov (United States)

    Gopalan, Avinash; Samal, M. K.; Chakravartty, J. K.

    2015-10-01

    In this work, fracture behaviour of 20MnMoNi55 reactor pressure vessel (RPV) steel in the ductile to brittle transition regime (DBTT) is characterised. Compact tension (CT) and single edged notched bend (SENB) specimens of two different sizes were tested in the DBTT regime. Reference temperature 'T0' was evaluated according to the ASTM E1921 standard. The effect of size and geometry on the T0 was studied and T0 was found to be lower for SENB geometry. In order to understand the fracture behaviour numerically, finite element (FE) simulations were performed using Beremin's model for cleavage and Rousselier's model for ductile failure mechanisms. The simulated fracture behaviour was found to be in good agreement with the experiment.

  13. Definition of Brittle Ductile Transition of the upper crust beneath the Campi Flegrei-Ischia Volcanic District and its impact on natural seismicity

    Science.gov (United States)

    Tizzani, Pietro; Castaldo, Raffaele; De Novellis, Vincenzo; Santilano, Alessandro; Gola, Gianluca; Pepe, Susi; D'Auria, Luca; Solaro, Giuseppe

    2016-04-01

    The thermo-rheology behaviour of the rocks is a crucial aspect to understand the mechanical behaviour of the crust of tectonically active area. As a consequence, several studies have been performed since last decades in order to clarify the role of thermic state in the evolution of volcanic areas. In this framework, the knowledge of the Brittle-Ductile transition inside the upper crust may provide insights to verify the roles that some hypothesized mechanisms, such as slab pull, crustal delamination might have played in the evolution of a tectonically active region. The goal of our study was the 3D imaging of the crust rheology beneath the active Campi Flegrei-Ischia Volcanic District and its impact on natural seismicity. Despite many works have been done on the internal structure of the active volcanoes, the determination of the 3D rheological stratification of the crust below the caldera has not yet been tackled. To fill this gap of knowledge, we proposed the definition of 3D geometry of the Brittle-Ductile transition calculated via numerical optimization modelling based on geological, geochemical, and geophysical available data. We first performed a 3D numerical modelling of thermal field by using the a priori geological and geophysical information starting to thermal proprieties and mechanical heterogeneities of the crust beneath the caldera. We developed a suitable 3D conductive/convective time-dependent thermal numerical model solving the Fourier equation and further we used the retrieved thermal model to image a 3D rheological stratification of the shallow crust below the volcanic district. Finally we demonstrate the role of the crustal rheology on seismicity cut off and its implication on maximum expected earthquakes magnitude.

  14. Episodes of brittle deformation within the Dien Bien Phu Fault zone, Vietnam: Evidence from K-Ar age dating of authigenic illite

    Science.gov (United States)

    Bui, Hoang Bac; Ngo, Xuan Thanh; Khuong, The Hung; Golonka, Jan; Nguyen, Tien Dung; Song, Yungoo; Itaya, Tetsumaru; Yagi, Koshi

    2017-01-01

    Constraining the timing of fault zone origin and movement history is of fundamental geotectonic importance to understand the evolution and processes of the brittle fault structures. The authors present in this paper authigenic illite K-Ar age data from the fault gouge samples, collected from the Dien Bien Phu Fault (DBPF) in the Dien Bien province, Vietnam as well as in a major strike-slip fault zone in South-East Asia; all of which played important roles in the structural formation and geotectonic development of northwestern Vietnam. The gouge fault samples were separated into four grain-size fractions (groups, from 26 to 29 Ma and 130 Ma. The timing of the fault movements is defined at 26 ± 0.24 Ma, 29 ± 0.61 Ma, 130.1 ± 1.27 Ma and 130.7 ± 1.29 Ma. This indicates that the Dien Bien Phu Fault underwent two movements, first in the Early Cretaceous, with an age of about 130 Ma and second in the Oligocene (Paleogene), with an age of about 26-29 Ma. The ductile deformation of the DBPF terminated during the Early Cretaceous. These studies also indicate slow exhumation of the Dien Bien granitoid complex during the Cretaceous times. The Oligocene ages indicate that the DBPF had been reactivated by the SE extrusion and clock-wise rotation of the Indochina block, caused by the collision of the Indian and Eurasian plates. This tectonic event led to the DBPF brittle-sinistral movement, causing the exhumation phase along the fault. This movement period (ca. 26-29 Ma) is coexistent with 600-700 km sinistral shearing along the Red River-Ailao Shan fault. This is the first report determining the absolute age constraints of multi-activated tectonic events, affecting the Dien Bien Phu Fault using the K-Ar dating method for the gouge samples.

  15. Orogen-parallel brittle extension as a major tectonic imprint in the Neogene evolution of the south-western Alpine arc

    Science.gov (United States)

    Beucher, Romain; Sue, Christian; Tricart, Pierre

    2017-04-01

    We present a new analysis of the late Alpine brittle deformation in the southern branch of the western Alpine arc, focusing on the stack of internal metamorphic nappes east of the Argentera external crystalline massif. The regional-scale fault network is dominated by a NW-SE-striking right-lateral fault system that follows the general curvature of the arc and controls the overall morphology of the area. A second fault set strikes N-S and is mainly represented by normal faults which accommodate orogen-parallel extension. Structural analysis and paleostress tensors derived from inversion of fault-slip data reveal a complex pattern of deformation involving extensional and strike-slip deformation events. The orogen-parallel extension previously described in the internal zones at the east of the Pelvoux massif is confirmed further south, and we show that it is combined with right-lateral strike-slip deformation that increases in intensity towards the south-west. The stability of the minimum stress axis (σ3) direction suggests that extensional and transcurrent regimes are contemporaneous and highlights regional interferences between inner brittle extension, parallel to the strike of the belt, and the strike-slip strain field driven by the counterclockwise rotation of the Apulia-Adria plate. The curved geometry of the belt constrains the direction of extension and the coupling relationship between the internal and external Alpine zones. We propose that the Neogene tectonic history is a result of the unique curved tectonic architecture of the south-western Alps with respect to the rotation of the Apulia-Adria indenting plate. The southern tip of the western Alpine arc represents a transitional zone between extension in the inner chain and strike-slip/compression in the outer parts.

  16. Modelling of the plasticity and brittle failure of the irradiated bainitic steels; Modelisation du comportement en plasticite et a rupture des aciers bainitiques irradies

    Energy Technology Data Exchange (ETDEWEB)

    Nguyen, C.N.

    2010-02-15

    Low alloy steels are used in various equipments of nuclear reactors. Subjected to neutron irradiation produced during the operation of reactors, these materials exhibit significant changes in their microstructure, especially with the formation of radiation defects as interstitial loops, void clusters and precipitates. These defects in interactions with dislocations lead to a hardening and embrittlement which are directly related to the received dose and neutron flux. The plastic behaviour of non-irradiated low alloy bainitic steels has been the object of several modelling based on observations from experiments and atomistic simulations. Some of them result from thesis supported by EDF and CEA, which describe different strategies for the micro-mechanical modelling of brittle failure. Improvements in this work come from the integration of new physical characteristics and the attention paid to the representativeness of the microstructure: whereas realistic microstructures in terms of morphology and crystal orientations have been adopted, a dislocation density based constitutive model in the large deformation framework is used to describe crystal plasticity. This choice is justified by the need to take into account, in the constitutive modelling, the interactions between dislocations and irradiation defects under severe loading conditions. The plasticity laws have been implemented in the finite elements code ZeBuLoN in order to perform computations of polycrystalline aggregates. Such aggregates are representative volume elements. They thus provide the database required for the application of brittle failure models to structures. This multi-scale character confers to the modelling the status of 'micro-mechanical local approach of failure'. (author)

  17. 脆性物体破碎效果实时仿真研究%Research on Real Time Simulation of Brittle Objects Fracturing

    Institute of Scientific and Technical Information of China (English)

    王全玉; 米庆; 刘昕

    2012-01-01

    Based on the analysis of brittle objects fragmentation in the real world, a new approach was proposed to simulate realtime fracturing effect in the virtual environment. Brittle objects were represented by triangular surface mesh model and the triangles were stored in a BSP tree structure in order to achieve rapid classification and retrieval. Plane was used to cut the model, then the polygons were reconstructed and a new complete triangular model was generated. Position, speed and angle of each preprocessed triangle were initialized in order to achieve real-time simulation, and collision detection was hired to avoid penetration of each fragment.%通过对现实世界中脆性物体破碎现象的分析,实现了一种在虚拟场景中实时模拟物体破碎效果的方法。该方法采用三角面片模型对破碎物体进行建模,采用BSP树结构存储以实现三角面片的快速分类及检索。对模型进行预处理并使用平面进行切割,对切割所产生的多边形进行三维重建,得到新的完整的三角面片模型。对预处理所得的各个三角面片设置其初始位置、速度、角度等以实现物体破碎过程的实时仿真,引入碰撞检测以免碎片相互贯穿。

  18. Hydrothermal quartz formation during fluctuations of brittle shear-zone activity and fluid flow: grain growth and deformation structures of the Pfahl shear zone (Germany)

    Science.gov (United States)

    Yilmaz, T.; Prosser, G.; Liotta, D.; Kruhl, J. H.

    2012-12-01

    The Bavarian Pfahl shear zone is a WNW-ESE trending dextral strike-slip shear zone at the SW margin of the Bohemian Massif (Central Europe). It was discontinuously active during decreasing PT-conditions, i.e. from ductile to brittle, from the late-Carboniferous to the late-Cretaceous - Paleocene times. Triassic hydrothermal activity produced a 150 km long and 30-100 m wide quartz dyke along the main fault, surrounded by sheared basement rocks. Within a zone of >10 m metasomatism transformed the wall rocks to mostly kaolinite, chlorite and phyllosilicates. The quartz dyke exhibits a layered to lenticular and partly symmetric structure with different types of quartz masses, transected by a complex quartz vein network. This already indicates pulses of fluid flux and fragmentation during the lifetime of the shear zone. Analyses by optical microscopy, cathodoluminescence (CL) and SEM-EDX reveal at least four subsequent stages of quartz crystallization and fragmentation. (i) The oldest generation of quartz is represented by a homogeneous dark grey to reddish quartz mass made up by ~10-20 μm-sized crystals. It contains mm- to cm-sized angular wall-rock fragments, completely altered to kaolinite, indicating intense wall-rock alteration prior to the earliest event of silica precipitation. This rules out the possibility that the quartz mass developed from silicification of the wall rocks. This first type of quartz occurs as cm- to dm-large angular fragments in (ii) a light grey to pink quartz mass formed by ~10-50 μm-sized crystals. The different colours result from variable types and amounts of inclusions. Quartz of both generations shows random crystallographic orientations and complex inclusion structures. It probably developed during two fragmentation events and possibly from a silica gel precursor that crystallized after precipitation. (iii) The third quartz generation formed as a set of mm- to dm-wide veins roughly parallel to the trend of the Pfahl zone

  19. Elastic-brittle-plastic mechanical model for rock with confining pressure%考虑围压影响的岩石弹脆塑力学模型

    Institute of Scientific and Technical Information of China (English)

    张春会; 徐晓攀; 王锡朝; 赵全胜

    2015-01-01

    To model effects of confining pressure on the post-peak mechanical properties for rock such as the degradation of strength and modulus, and dilatancy, the deformation process is simplified into three phases including linear-elastic, brittle degradation and perfect plasticity. Degradation index and dilatancy index are employed to reflect the effects of confining pressure on the peak-post mechanical properties for rock in this paper, and an elastic-brittle-plastic model with confining pressure is presented. Based on the transformation relationship between Hoek-Brown failure criterion and Mohr-Column fail-ure criterion, how to obtain the calculation parameters of the peak-post mechanical model in this paper is presented. The Fish function method within FLAC is adopted to realize the elastic-brittle-plastic me-chanical model model in this paper. In numerical case study the peak-post mechanical properties of rock under varied confining pressure including the degradation of strength and modulus, and dilatancy are modelled. The results show that the model can perfectly describe the deformation process and the effects of confining pressure on peak-post mechanical properties of rock.%为模拟围压对岩石峰后强度、模量退化和剪胀的影响,将岩石的变形过程简化为线弹性变形、脆性跌落和理想塑性3个阶段,利用退化指数和扩容指数描述围压对岩石峰后强度、模量退化和剪胀的影响,建立了考虑围压影响的岩石弹脆塑力学模型。通过Hoek-Brown和Mohr-Column准则之间参数的转换关系,给出了模型峰后力学参数的确定方法。在 FLAC 软件下,利用 Fish函数方法实现了建立的弹脆塑性力学模型。在数值算例中,利用本文模型分析了不同围压下岩石的峰后力学特性劣化和剪胀扩容特征,结果表明本文模型不仅能较好地模拟岩石峰前、峰后全程变形发展过程,而且能较好地考虑围压对岩石峰后力学特性的影响。

  20. Fold-related fractures - a brittle tectonic case study of the Helvetic zone in Vorarlberg (western Austria) and Upper Allgäu (Bavaria)

    Science.gov (United States)

    Zerlauth, M.

    2012-04-01

    Michael Zerlauth1,2 , Marcel Schulz1,2 , Hugo Ortner1 , Bernhard Fügenschuh1, Christian Zangerl2 1 Institut für Geologie und Paläontologie, Leopold Franzens Universität, 6020 Innsbruck, Austria 2 alpS-Gmbh, 6020 Innsbruck, Austria In the eastern Alps the Helvetic units exposed at the surface form a narrow belt restricted to the westernmost part of Austria and the northerly adjacent southernmost part of Bavaria. The Helvetic zone represents a Tertiary fold-and-thrust belt made up of Jurassic to Cretaceous shelf sediments deposited on the European margin of the Eurasian plate. In the course of an industry-funded project, the potential of these units for deep hydro-geothermal energy is investigated. Potential targets for hydrothermal exploration are more or less thick carbonate sequences that can be traced throughout the Helvetic zone, namely the Late Jurassic Quinten Limestone and the Early Cretaceous Schrattenkalk-Fm. In depths of at least 3000m below sea level, that have to be drilled to gain water with at least 90°C, uncemented fractures at any scale are the only cavities within these carbonates to be expected. Therefore, brittle structures are studied at differing scales of observation; aerial photos and surface outcrops are analyzed as well as thin sections. All the data obtained so far were collected in areas deformed homogenously: measuring stations were located outside large scale shear zones and either in fold-limbs or hinge zones. A constantly geometrical relationship between the orientation of the various fractures, the sedimentary layering and the trace of the axial planes can be inferred, as already stated by Hancock (1985). Besides extension fractures, veins and stylolithes, conjugated hybrid and shear fractures are quite common, indicating layer-parallel shortening normal to the axial planes as well as axial elongation. Hence, all of the structures observed can be genetically linked with thrusting and folding during regional N-S compressional

  1. Triclinic Transpression in brittle shear zones evaluated via combined numerical and analogue modeling: the case of The Torcal de Antequera Massif, SE Spain.

    Science.gov (United States)

    Barcos, Leticia; Díaz-Azpiroz, Manuel; Faccenna, Claudio; Balanyá, Juan Carlos; Expósito, Inmaculada; Giménez-Bonilla, Alejandro

    2013-04-01

    Numerical kinematic models have been widely used to understand the parameters controlling the generation and evolution of ductile transpression zones. However, these models are based on continuum mechanics and therefore, are not as useful to analyse deformation partitioning and strain within brittle-ductile transpression zones. The combination of numerical and analogue models will potentially provide an effective approach for a better understanding of these processes and, to a broader extent, of high strain zones in general. In the present work, we follow a combined numerical and analogue approach to analyse a brittle dextral transpressive shear zone. The Torcal de Antequera Massif (TAM) is part of a roughly E-W oriented shear zone at the NE end of the Western Gibraltar Arc (Betic Cordillera). This shear zone presents, according to their structural and kinematic features, two types of domains i) Domain type 1 is located at both TAM margins, and is characterized by strike-slip structures subparallel to the main TAM boundaries (E-W). ii) Domain type 2 corresponds to the TAM inner part, and it presents SE-vergent open folds and reverse shear zones, as well as normal faults accommodating fold axis parallel extension. Both domains have been studied separately applying a model of triclinic transpression with inclined extrusion. The kinematic parameters obtained in this study (?, ? and Wk) allows us to constrain geometrical transpression parameters. As such, the angle of oblique convergence (α, the horizontal angle between the displacement vector and the strike of the shear zone) ranges between 10-17° (simple shear dominated) for domain type 1 and between 31-35° (coaxial dominated) for domain type 2. According to the results obtained from the numerical model and in order to validate its possible utility in brittle shear zones we develop two analogue models with α values representative of both domains defined in the TAM: 15° for type 1 and 30° for type 2. In the

  2. XFEM-Based CZM for the Simulation of 3D Multiple-Cluster Hydraulic Fracturing in Quasi-Brittle Shale Formations

    Science.gov (United States)

    Haddad, Mahdi; Sepehrnoori, Kamy

    2016-12-01

    The cohesive zone model (CZM) honors the softening effects and plastic zone at the fracture tip in a quasi-brittle rock, e.g., shale, which results in a more precise fracture geometry and pumping pressure compared to those from linear elastic fracture mechanics. Nevertheless, this model, namely the planar CZM, assumes a predefined surface on which the fractures propagate and therefore restricts the fracture propagation direction. Notably, this direction depends on the stress interactions between closely spaced fractures and can be acquired by integrating CZM as the segmental contact interaction model with a fully coupled pore pressure-displacement model based on extended finite element method (XFEM). This integrated model, called XFEM-based CZM, simulates the fracture initiation and propagation along an arbitrary, solution-dependent path. In this work, we modeled a single stage of 3D hydraulic fracturing initiating from three perforation clusters in a single-layer, quasi-brittle shale formation using planar CZM and XFEM-based CZM including slit flow and poroelasticity for fracture and matrix spaces, respectively, in Abaqus. We restricted the XFEM enrichment zones to the stimulation regions as enriching the whole domain leads to extremely high computational expenses and unrealistic fracture growths around sharp edges. Moreover, we validated our numerical technique by comparing the solution for a single fracture with KGD solution and demonstrated several precautionary measures in using XFEM in Abaqus for faster solution convergence, for instance the initial fracture length and mesh refinement. We demonstrated the significance of the injection rate and stress contrast in fracture aperture, injection pressure, and the propagation direction. Moreover, we showed the effect of the stress distribution on fracture propagation direction comparing the triple-cluster fracturing results from planar CZM with those from XFEM-based CZM. We found that the stress shadowing effect of

  3. XFEM-Based CZM for the Simulation of 3D Multiple-Stage Hydraulic Fracturing in Quasi-brittle Shale Formations

    Science.gov (United States)

    Haddad, M.; Sepehrnoori, K.

    2015-12-01

    The Cohesive Zone Model (CZM) engages the plastic zone and softening effects at the fracture tip in a quasi-brittle rock, e.g. shale, which concludes a more precise fracture geometry and pumping pressure compared to those from Linear Elastic Fracture Mechanics. Nevertheless, this model, namely planar CZM, assumes a predefined surface on which the fractures propagate and therefore, restricts the fracture propagation direction. Notably, this direction depends on the stress interactions between closely spaced fractures and can be acquired integrating CZM as the segmental contact interaction model with a fully coupled pore pressure-displacement, extended finite element model (XFEM). This later model simulates the fracture initiation and propagation along an arbitrary, solution-dependent path. In this work, we modeled double- and triple-cluster 3D hydraulic fracturing in a single-layer, quasi-brittle shale formation using planar CZM and XFEM-based CZM including slit flow and poro-elasticity for fracture and matrix spaces, respectively, in Abaqus. Our fully-coupled pore pressure-stress Geomechanics model includes leak-off as a continuum-based fluid flow component coupled with the other unknowns in the problem. Having compared the triple-cluster fracturing results from planar CZM with those from XFEM-based CZM, we found that the stress shadowing effect of multiple hydraulic fractures on each other can cause these fractures to rationally propagate out of plane; this also demonstrates the advantages of the second method compared to the first one. We investigated the effect of this arbitrary propagation direction on not only the fractures' length, aperture, and the required injection pressure, but also fractures' connection to the wellbore. Depending on the spacing and the number of clusters per stage, this connection can be gradually disrupted with time due to the near-wellbore fracture closure which may embed proppant particles on the fracture wall, or screen out the

  4. Positive feedback between strain localization and fluid flow at the ductile-brittle transition leading to Pb-Zn-Fe-Cu-Ag ore deposits in Lavrion (Greece)

    Science.gov (United States)

    Scheffer, Christophe; Tarantola, Alexandre; Vanderhaeghe, Olivier

    2016-04-01

    At the crustal scale, the ductile-brittle transition (DBT) might correspond to a physical barrier that separates a deep reservoir of metamorphic and magmatic fluids from a shallow reservoir of surficial fluids. Rock rheology, and thus the location of the DBT, is mainly governed by lithology, temperature and the presence/absence of fluids. Accordingly, the position of the DBT potentially evolves during orogenic evolution owing to thermal evolution and fluid circulation. In turn rocks are transferred across it during burial and exhumation. These processes induce connections between fluid reservoirs which might play a role on ore deposition. In this contribution, we discuss the impact of lithological heterogeneities on deformation, fluid flow and ore deposition based on the example of the Lavrion low-angle top-to-the-SSW detachment accommodating gravitational collapse of the Hellenides orogenic belt in Greece. The Lavrion peninsula, localized along the western boundary of the Attic-Cycladic Metamorphic Core Complex, is characterized by Pb-Zn-Fe-Cu-Ag ore mineralization mainly concentrated along a lithological contact (marble/schists) below and within a detachment shear zone. The mylonitic marble below the detachment shear zone is composed of white layers of pure marble alternating with blue layers containing impurities (SiO2, Al2O3, organic matter…). Development of the mylonitic fabric in competent impure blue marble is associated with its preferred dolomitization related to focused fluid infiltration. This mylonitic marble is cross-cut by several cataclastic horizons preferentially developed within the more competent impure blue marble and newly-crystallized dolomitic horizon. These cataclasites are invaded by fluorite and calcite gangue minerals showing locally Mn, Pb, Zn, Fe oxides and/or hydroxides, sphalerite, Ag-galena, Ag-sulfur and native Ag. Oxygen and carbon stable isotopes performed on marble sections point out decarbonation with magmatic contribution and

  5. Spatio-temporal Model of Multiscale Fracture in Brittle Solids%固体材料脆性断裂的多尺度时空模型

    Institute of Scientific and Technical Information of China (English)

    PETROV Y V; BRATOV V

    2012-01-01

    通过实例分析了动态断裂过程所固有的典型动态作用,基于断裂孵化时间理论的时空结构方法提出了固体材料断裂的统一解释.此外,还提出了计及尺度效应的广义断裂模型,该模型可以用于预测准脆性非均质材料的多尺度断裂,并证明此模型基于实验室尺度的实验数据可以预测更高尺度(真实尺度)的宏观断裂.%We analyze examples illustrating typical dynamic effects inherent in dynamic fracture process, and we propose a unified interpretation for fracture of solids utilizing structural-temporal approach based on the concept of the fracture incubation time. Corresponding generalized model accounting for fracture scale level will also be presented. The model will be used to predict fracture of quasi-brittle heterogeneous materials on different scale levels. It will be demonstrated that can give a possibility to predict fracture on a higher (real) scale level and having experimental data obtained on a lower (laboratory) scale level.

  6. Evaluation of the ductile-to-brittle transition temperature of a silicon steel under various strain rate conditions with a servo-hydraulic high speed testing machine

    Science.gov (United States)

    Kwon, Junbeom; Huh, Hoon; Kim, Jae-song

    2017-07-01

    This paper is concerned with the construction of an empirical model of the Ductile-to-Brittle Transition Temperature (DBTT) for 3.4% silicon steel based on tensile test results at strain rates ranging from 0.001 s‒1 to 100 s‒1. Dynamic tensile tests are conducted using an in-house servo hydraulic tensile test machine at strain rates of 1 s‒1, 10 s‒1, and 100 s‒1 and quasi-static tensile tests are conducted using Instron 4206 at strain rates of 0.001 s‒1 and 0.01 s‒1 with an environmental chamber. Fracture elongations are measured by a DIC method during all tests using the high-speed camera for accurate measurement. The DBTT of 3.4% silicon steel is presented in terms of fracture strain with the variation of the temperature and the strain rate. It is demonstrated from the test results that the DBTT increases as the strain rate increases. An empirical model of the DBTT is constructed in terms of strain rate, temperature and fracture elongation. The parameters of the empirical model are calculated from experimental results obtained at various temperatures and strain rates.

  7. Petrophysical approach for S-wave velocity prediction based on brittleness index and total organic carbon of shale gas reservoir: A case study from Horn River Basin, Canada

    Science.gov (United States)

    Kim, Taeyoun; Hwang, Seho; Jang, Seonghyung

    2017-01-01

    When finding the "sweet spot" of a shale gas reservoir, it is essential to estimate the brittleness index (BI) and total organic carbon (TOC) of the formation. Particularly, the BI is one of the key factors in determining the crack propagation and crushing efficiency for hydraulic fracturing. There are several methods for estimating the BI of a formation, but most of them are empirical equations that are specific to particular rock types. We estimated the mineralogical BI based on elemental capture spectroscopy (ECS) log and elastic BI based on well log data, and we propose a new method for predicting S-wave velocity (VS) using mineralogical BI and elastic BI. The TOC is related to the gas content of shale gas reservoirs. Since it is difficult to perform core analysis for all intervals of shale gas reservoirs, we make empirical equations for the Horn River Basin, Canada, as well as TOC log using a linear relation between core-tested TOC and well log data. In addition, two empirical equations have been suggested for VS prediction based on density and gamma ray log used for TOC analysis. By applying the empirical equations proposed from the perspective of BI and TOC to another well log data and then comparing predicted VS log with real VS log, the validity of empirical equations suggested in this paper has been tested.

  8. Characterisation of the fracture properties in the ductile to brittle transition region of the weld material of a reactor pressure vessel

    Energy Technology Data Exchange (ETDEWEB)

    Scibetta, M. [SCK-CEN, Boeretang 200, 2400 Mol (Belgium); Ferreno, D., E-mail: ferrenod@unican.es [University of Cantabria, ETS Ingenieros de Caminos, Av/Los Castros s/n, 39005 Santander (Spain); Gorrochategui, I. [Centro Tecnologico de Componentes (CTC), Parque Cientifico y Tecnologico de Cantabria, Isabel Torres No 1, 39011 Santander (Spain); Nuclenor, SA, C/Hernan Cortes 26, 39003 Santander (Spain); Lacalle, R. [University of Cantabria, ETS Ingenieros de Caminos, Av/Los Castros s/n, 39005 Santander (Spain); Walle, E. van [SCK-CEN, Boeretang 200, 2400 Mol (Belgium); Martin, J. [Nuclenor, SA, C/Hernan Cortes 26, 39003 Santander (Spain); Gutierrez-Solana, F. [University of Cantabria, ETS Ingenieros de Caminos, Av/Los Castros s/n, 39005 Santander (Spain)

    2011-04-15

    This work presents the results of the fracture characterisation of the weld material of a nuclear vessel, currently in service, in the ductile to brittle transition region. The tests consisted of Charpy impact and tensile tests, performed in the framework of the surveillance programme of the plant. Moreover, in the context of this research, K{sub Jc} fracture toughness tests on pre-cracked Charpy V notch specimens (evaluated according to the Master Curve methodology) together with some mini-tensile tests, were performed; non-irradiated and several irradiated material conditions were characterised. The analysis of the experimental results revealed some inconsistencies concerning the material embrittlement as measured through Charpy and K{sub Jc} fracture tests: in order to obtain an adequate understanding of the results, an extended experimental scope well beyond the regulatory framework was developed, including Charpy tests and K{sub Jc} fracture tests, both performed on reconstituted specimens. Moreover, Charpy specimens irradiated in the high flux BR2 material test reactor were tested with the same purpose. With this extensive experimental programme, a coherent and comprehensive description of the irradiation behaviour of the weld material in the transition region was achieved. Furthermore it revealed better material properties in comparison with the initial expectations based on the information obtained in the framework of the surveillance programme.

  9. Perioperative glycemic control using an artificial endocrine pancreas in patients undergoing total pancreatectomy: tight glycemic control may be justified in order to avoid brittle diabetes.

    Science.gov (United States)

    Hanazaki, Kazuhiro; Yatabe, Tomoaki; Kobayashi, Masaki; Tsukamoto, Yuuki; Kinoshita, Yoshihiko; Munekage, Masaya; Kitagawa, Hiroyuki

    2013-01-01

    I dedicate this paper to the late Prof. Yukihiko Nosé with all my heart. In 2001, under the direction of Prof. Nosé and Prof. Brunicardi at Baylor College of Medicine, we published a review article entitled "Artificial endocrine pancreas" in JACS. Subsequently, we reported that perioperative tight glycemic control (TGC) using an artificial pancreas (AP) with a closed-loop system could stably maintain near-normoglycemia in total-pancreatectomized dogs. Based on this experimental study in Houston, since 2006, we have introduced perioperative TGC using an AP into clinical use in Kochi. As of 2011, this novel TGC method has provided safe and stable blood glucose levels in more than 400 surgical patients. In this paper, we report new clinical findings regarding perioperative TGC using an AP in total-pancreatectomized patients. TGC using an AP enables us to achieve stable glycemic control not only without hypoglycemia and hyperglycemia but also with less variation in blood glucose concentration from the target blood glucose range, even in patients with the most serious form of diabetes, so-called "brittle diabetes", undergoing total pancreatectomy. To the best of our knowledge, this is the first clinical report of TGC using an AP in patients undergoing total pancreatic resection.

  10. Characterization of ductile-brittle transition behavior in Mn-Mo-Ni low alloy steels for reactor pressure vessel by small punch test

    Energy Technology Data Exchange (ETDEWEB)

    Kim, M. C.; Lee, B. S.; Park, S. D.; Kim, K. B

    2004-12-01

    Small Punch (SP) tests were performed to evaluate the ductile-brittle transition behavior of Reactor Pressure Vessel (RPV) steels produced by different manufacturing (refining) processes. The results were compared to the standard test results, such as the conventional Charpy impact tests, JIC test and the Master Curve fracture toughness tests in accordance with the ASTM standard E1921. The SP transition temperatures (TSP), which are determined by the middle of the upper SP energy, showed a good correlation with the Charpy index temperatures. And the critical fracture strength, {sigma}{sup *}{sub f(sp)} from small punch test were found to have a linear relationship to the values from the pre-cracked specimens({sigma}{sup *}{sub f(PCVN)}). From the observation of thickness changes according to displacement, Equivalent strain(Eq) could be obtained as a function of ball displacement. It is found that relation between specimen thickness and ball displacement is not dependent on material properties and it is expressed as a function of ball displacement, and then SP equivalent strain(Eq) have close relationship with the fracture toughness(J{sub IC})

  11. Valproic Acid

    Science.gov (United States)

    ... acid is in a class of medications called anticonvulsants. It works by increasing the amount of a ... older (about 1 in 500 people) who took anticonvulsants such as valproic acid to treat various conditions ...

  12. Amino acids

    Science.gov (United States)

    ... this page: //medlineplus.gov/ency/article/002222.htm Amino acids To use the sharing features on this page, please enable JavaScript. Amino acids are organic compounds that combine to form proteins . ...

  13. Obeticholic Acid

    Science.gov (United States)

    Obeticholic acid is used alone or in combination with ursodiol (Actigall, Urso) to treat primary biliary cholangitis (PBC; a ... were not treated successfully with ursodiol alone. Obeticholic acid is in a class of medications called farnesoid ...

  14. Ascorbic Acid

    Science.gov (United States)

    Ascorbic acid is used to prevent and treat scurvy, a disease caused by a lack of vitamin C in ... Ascorbic acid comes in extended-release (long-acting) capsules and tablets, lozenges, syrup, chewable tablets, and liquid drops to ...

  15. Mefenamic Acid

    Science.gov (United States)

    Mefenamic acid is used to relieve mild to moderate pain, including menstrual pain (pain that happens before or during a menstrual period). Mefenamic acid is in a class of medications called NSAIDs. ...

  16. Acid mucopolysaccharides

    Science.gov (United States)

    ... this page: //medlineplus.gov/ency/article/003368.htm Acid mucopolysaccharides To use the sharing features on this page, please enable JavaScript. Acid mucopolysaccharides is a test that measures the amount ...

  17. Ethacrynic Acid

    Science.gov (United States)

    Ethacrynic acid, a 'water pill,' is used to treat swelling and fluid retention caused by various medical problems. It ... Ethacrynic acid comes as a tablet to take by mouth. It is usually taken once or twice a day ...

  18. Aminocaproic Acid

    Science.gov (United States)

    Aminocaproic acid is used to control bleeding that occurs when blood clots are broken down too quickly. This type ... the baby is ready to be born). Aminocaproic acid is also used to control bleeding in the ...

  19. Aspartic acid

    Science.gov (United States)

    ... body work. It plays a role in: Hormone production and release Normal nervous system function Plant sources of aspartic acid include: avocado, asparagus, and molasses. Animal sources of aspartic acid include: ...

  20. New constraints on 1.7 Gyr of brittle tectonic evolution in southwestern Finland derived from a structural study at the site of a potential nuclear waste repository (Olkiluoto Island)

    Science.gov (United States)

    Mattila, Jussi; Viola, Giulio

    2014-10-01

    The brittle deformation history of southwestern Finland was reconstructed through paleostress inversion of fault-slip data from outcrops and drill cores at the site of a planned nuclear waste repository. Seven distinct paleostress states have been resolved spanning 1.7 Ga of geological history. (1) NW-SE to NNW-SSE transpression acted soon after 1.75 Ga, when conditions leading to brittle deformation were first attained. (2) N-S to NE-SW transpression caused partial reactivation of (1). (3) NW-SE extension followed during the Gothian event and at the time of rapakivi magmatism. (4) Renewed NE-SW transtension occurred between 1.60 and 1.30 Ga, forming the NW-SE-elongated Satakunta graben. (5) A significant and so far unrecognised phase of NE-SW compression has been found to postdate both rapakivi granites and 1.27 Ga olivine diabase sills. (6) E-W transpression followed during the early stages of the Mesoproterozoic Sveconorwegian orogeny and predated (7) almost coaxial E-W extension of the late Sveconorwegian orogenic collapse. Our results prove that the shield's 'crust fragmentation' (i.e. generation of new fractures) was short lived in comparison to its 'jostling phase' (i.e. reactivation of old fractures). The shield thus reached structural maturity with respect to its saturation with brittle structures already in the late Mesoproterozoic. We predict that that future stress changes will most probably be accommodated by reactivation of the existing and inherited brittle structures rather than by formation of new deformation zones.

  1. Fracture mechanical modeling of brittle crack propagation and arrest of steel. 3. Application to duplex-type test; Kozai no zeisei kiretsu denpa teisi no rikigaku model. 3. Konseigata shiken eno tekiyo

    Energy Technology Data Exchange (ETDEWEB)

    Aihara, S.; Tsuchida, Y. [Nippon Steel Corp., Tokyo (Japan); Machida, S.; Yoshinari, H. [The University of Tokyo, Tokyo (Japan). Faculty of Engineering

    1996-12-31

    A proposal was made previously on a model of brittle crack propagation and arrest that considers the effect of crack opening suppression by using unbroken ligaments generated on steel plate surface and the effect that cracks precede in the central part of the plate thickness, based on a local limit stress theory for brittleness fracture. This paper discusses applicability of this model to a mixed type test, and elucidates causes for difference in the arrest tenacity of both types in a double tensile test of the standard size. The brittle crack propagation and arrest model based on the local limit stress theory was found applicable to a simulation of the mixed type test. Experimental crack propagation speed history and behavior of the arrest were reproduced nearly completely by using this model. When load stress is increased, the arrests in the mixed type test may be classified into arrests of both inside the steel plate and near the surface, cracks in the former position or arrest in the latter position, and rush of cracks into both positions. Furthermore, at higher stresses, the propagation speed drops once after cracks rushed into the test plate, but turns to a rise, leading to propagation and piercing. 8 refs., 15 figs., 3 tabs.

  2. Understanding the interplays between Earth's shallow- and deep- rooted processes through global, quantitative model of the coupled brittle-lithosphere/viscous mantle system

    Science.gov (United States)

    Stotz, Ingo; Iaffaldano, Giampiero; Rhodri Davies, D.

    2016-04-01

    The volume of geophysical datasets has grown substantially, over recent decades. Our knowledge of continental evolution has increased due to advances in interpreting the records of orogeny and sedimentation. Ocean-floor observations now allow one to resolve past plate motions (e.g. in the North Atlantic and Indian Ocean over the past 20 Myr) at temporal resolutions of about 1 Myr. Altogether, these ever-growing datasets permit reconstructing the past evolution of Earth's lithospheric plates in greater detail. This is key to unravelling the dynamics of geological processes, because plate motions and their temporal changes are a powerful probe into the evolving force balance between shallow- and deep-rooted processes. However, such a progress is not yet matched by the ability to quantitatively model past plate-motion changes and, therefore, to test hypotheses on the dominant controls. The main technical challenge is simulating the rheological behaviour of the lithosphere/mantle system, which varies significantly from viscous to brittle. Traditionally computer models for viscous mantle flow and on the one hand, and for the motions of the brittle lithosphere on the other hand, have been developed separately. Coupling of these two independent classes of models has been accomplished only for neo-tectonic scenarios and with some limitations as to accounting for the impact of time-evolving mantle-flow and lithospheric slabs. Here we present results in this direction that permit simulating the coupled plates/mantle system through geological time. We build on previous work aimed at coupling two sophisticated codes for mantle flow and lithosphere dynamics: TERRA and SHELLS. TERRA is a global spherical finite-element code for mantle convection. It has been developed by Baumgardner (1985) and Bunge et al. (1996), and further advanced by Yang (1997; 2000) and Davies et al. (2013), among others. SHELLS is a thin-sheet finite-element code for lithosphere dynamics, developed by

  3. Brittle-ductile deformation effects on zircon crystal-chemistry and U-Pb ages: an example from the Finero Mafic Complex (Ivrea-Verbano Zone, western Alps)

    Science.gov (United States)

    Langone, Antonio; José Alberto, Padrón-Navarta; Zanetti, Alberto; Mazzucchelli, Maurizio; Tiepolo, Massimo; Giovanardi, Tommaso; Bonazzi, Mattia

    2016-04-01

    A detailed structural, geochemical and geochronological survey was performed on zircon grains from a leucocratic dioritic dyke discordantly intruded within meta-diorites/gabbros forming the External Gabbro unit of the Finero Mafic Complex. This latter is nowadays exposed as part of a near complete crustal section spanning from mantle rocks to upper crustal metasediments (Val Cannobina, Ivrea-Verbano Zone, Italy). The leucocratic dyke consists mainly of plagioclase (An18-24Ab79-82Or0.3-0.7) with subordinate amounts of biotite, spinel, zircon and corundum. Both the leucocratic dyke and the surrounding meta-diorites show evidence of ductile deformation occurred under amphibolite-facies conditions. Zircon grains (up to 2 mm in length) occur mainly as euhedral grains surrounded by fine grained plagioclase-dominated matrix and pressure shadows, typically filled by oxides. Fractures and cracks within zircon are common and can be associated with grain displacement or they can be filled by secondary minerals (oxides and chlorite). Cathodoluminescence (CL) images show that zircon grains have internal features typical of magmatic growth, but with local disturbances. However EBSD maps on two selected zircon grains revealed a profuse mosaic texture resulting in an internal misorientation of ca. 10o. The majority of the domains of the mosaic texture are related to parting and fractures, but some domains show no clear relation with brittle features. Rotation angles related to the mosaic texture are not crystallographically controlled. In addition, one of the analysed zircons shows clear evidence of plastic deformation at one of its corners due to indentation. Plastic deformation results in gradual misorientations of up to 12o, which are crystallographically controlled. Trace elements and U-Pb analyses were carried out by LA-ICP-MS directly on petrographic thin sections and designed to cover the entire exposed surface of selected grains. Such investigations revealed a strong

  4. 龙马溪组硬脆性页岩水化实验研究%Hydration Experiment of Hard Brittle Shale of the Longmaxi Formation

    Institute of Scientific and Technical Information of China (English)

    刘向君; 熊健; 梁利喜

    2016-01-01

    The hydration of hard brittle shale has an important influence on the borehole stability. Therefore,the hydration experiments was done for different types of shale from the Longmaxi formation in the south region of Sichuan Basin,observa-tions were made to mineral composition,microstructure,hydration swelling stress,water absorption by self-priming and core immersion. And based on observations,the paper discusses the hard brittle shale hydration process and hydration mechanism. The result shows that the main clay mineral of shale is illite,the shape of the clay mineral particles is flake and directional alignment. There are lots of bedding and micro-crack in the shale,which provide the operation-space and flow channel for the hydration of shale. The hydration swelling stress and water absorption by self-priming of shale tend to ascent first before becoming stable. The fabric of the shale has an important influence on the ascend velocity or extent. The fractures in the surface of sample are parallel plane of bedding in the process of immersion. With the increase of immersion time,the sample would keep its integrality or spall to pieces. The fabric and cementation type of the shale have an important influence on the hydration swelling. The hydration of the shale is a result of coupling of physical-chemical action and mechanical action,the former decreasing the rock fracture toughness,and the later increasing the stress intensity factor for mode-I fracture. When the stress intensity factor is greater than the rock fracture toughness,the crack will extend or broaden.%硬脆性页岩水化对页岩气开发井壁稳定有重要的影响,为此,对龙马溪组硬脆性页岩进行水化实验研究,包括矿物组成、微观结构、水化应力、自吸吸水率及岩芯浸泡等方面实验研究,探讨分析了硬脆性页岩水化过程与机理。研究结果表明,页岩黏土矿物以伊利石为主,黏土矿物呈片状且定向排列,层理和微

  5. Fatty acids - trans fatty acids

    Science.gov (United States)

    The data supporting a negative effect of dietary trans fatty acids on cardiovascular disease risk is consistent. The primary dietary sources of trans fatty acids include partially hydrogenated fat and rudiment fat. The adverse effect of trans fatty acids on plasma lipoprotein profiles is consisten...

  6. High Performance Brittle Matrices and Brittle Matrix Composites. Book 1

    Science.gov (United States)

    1989-12-31

    purpose of forming metallic glasses (7]. However, in the past 10-15 years a significant amount of attention has also been focused on rapidly solidified crystalline alloys , especially...C.M., and Lewis, R.E., in Rapidly Solidified Crystalline Alloys , p. 157, Das, S.K., Kear, B.H., and Adam, C.M., (Eds.), TMS Publications, 1985. (10

  7. High Performance Brittle Matrices and Brittle Matrix Composites. Book 2

    Science.gov (United States)

    1989-12-31

    out using the Least Pth algorithm ( Bandler and Charalambous, 1972) coupled with a Simplex search method (Press et al., 1986). In the terminology of...the Division of Applied Sciences, Harvard University. REFERENCES Bandler J.W., Charalambous C., Practical Least Pth Optimization of Networks, IEEE

  8. Temporal correlation between coda Q-1 and seismicity—evidence for a structural unit in the brittle-ductile transition zone

    Science.gov (United States)

    Jin, Anshu; Aki, Keiiti

    1993-07-01

    Analysis of local earthquake coda waves recorded on Wood-Anderson (1940-1947) and Benioff (after 1947) short-period vertical seismographs at station Mt. Hamilton, Calif., revealed a large temporal variation in coda Q-1. A strong positive correlation was found between the temporal variation of coda Q-1 and the number of earthquakes with a magnitude of 4.0⩽ M⩽4.5 appearing in a series of 100 consecutive earthquakes with a magnitude M⩾3.0. A correlation coefficient of 0.84 was determined with a confidence level of 0.98. The amplitude and time constant of variation in coda Q-1 for central California are similar to those found earlier for southern California (Jin and Aki, 1989). The strong correlation between coda Q-1 and b-value reported by Jin and Aki (1989) was shown to be equivalent to a positive correlation between coda Q-1 and the fractional number of earthquakes with a magnitude 3.0⩽ M⩽3.5. A review of the literature reporting observed temporal correlation between coda Q-1 and b-value (both positive and negative) revealed that all the reported observations can be interpreted in terms of a positive correlation between the coda Q-1 and the fractional frequency of earthquakes in a magnitude range around a certain magnitude, Mc, characteristic to each region. This positive correlation has been attributed to the aseismic creep in the brittle-ductile transition zone. Aseismic creep in the transition zone may occur over fractures with a characteristic size for each region. The existence of fractures with a characteristic size would necessarily violate the scale independent self-similarity of earthquake phenomena. This is consistent with the growing literature demonstrating a departure from self-similarity in various seismic phenomena.

  9. Applying micromechanic failure models for description of failure modes in the ductile-brittle transition region; Einsatz mikromechanischer Schaedigungsmodelle im sproed-duktilen Uebergangsbereich

    Energy Technology Data Exchange (ETDEWEB)

    Bernauer, G.

    1997-07-01

    The work reported was to examine whether the modified Gurson model and the Beremin model can be applied to the brittle-ductile transition region of a ferritic steel, and whether the material`s behaviour can be characterized with a failure model integrating the two models mentioned above into one. Any possible improvements of this approach were to be found. The report at first gives a brief list of terminology and formulas used. Chapter 3 explains the microscopic processes typically observed in the transition region in connection with the failure modes of ductile fracture and cleavage fracture, and shows possible approaches for modelling. Chapter 4 defines the specimens and materials, and chapter 5 explains the experiments as well as the microscopic analyses of the fracture surfaces. Chapter 6 presents subsequent calculations representing the processes observed. Based on the stress distributions thus derived, the Beremin model is re-examined for further development. Chapter 7 summarizes the results obtained. (orig./CB) [Deutsch] Ziel der Arbeit ist, zu untersuchen, ob das modifizierte Gurson-Modell und das Beremin-Modell im sproed-duktilen Uebergangsbereich eines ferritischen Stahls einsetzbar sind und ob das Werkstoffverhalten mit einem aus beiden Modellen kombinierten Schaedigungsmodell berechnet werden kann. Gegebenenfalls sind Verbesserungen herbeizufuehren. Die vorliegende Arbeit beginnt mit einer kurzen Einfuehrung der verwendeten Begriffe und Formalismen. In Kap. 3 werden die mikroskopischen Vorgaenge bei den im Uebergangsbereich typischerweise auftretenden Versagensarten duktiler Bruch und Spaltbruch vorgestellt und verschiedene Moeglichkeiten ihrer Modellierung aufgezeigt. Nach der Vorstellung des Probenwerkstoffs werden in Kap. 4 die Experimente beschrieben und die mikroskopischen Untersuchungen der Bruchflaechen in Kap. 5 dargestellt. Die Nachrechnungen der Experimente werden in Kap. 6 vorgestellt. Auf der Grundlage der dadurch bereitgestellten

  10. The microstructural record of porphyroclasts and matrix of serpentinite mylonites – from brittle and crystal-plastic deformation to dissolution-precipitation creep

    Directory of Open Access Journals (Sweden)

    J. Bial

    2013-04-01

    Full Text Available We examine the microfabric development in high-pressure, low-temperature metamorphic serpentinite mylonites exposed in the Erro-Tobbio Unit (Voltri Massif, Italy using polarization microscopy and electron microscopy (SEM/EBSD, EMP. The mylonites are derived from mantle peridotites, were serpentinized at the ocean floor and underwent high pressure metamorphism during Alpine subduction. They contain diopside and olivine porphyroclasts embedded in a fine-grained matrix essentially consisting of antigorite. The porphyroclasts record brittle and crystal-plastic deformation of the original peridotites in the upper mantle at stresses of a few hundred MPa. After the peridotites became serpentinized, deformation occurred mainly by dissolution-precipitation creep resulting in a foliation with flattened olivine grains at phase boundaries with antigorite, crenulation cleavages and olivine and antigorite aggregates in strain shadows next to porphyroclasts. It is suggested that the fluid was provided by dehydration reactions of antigorite forming olivine and enstatite during subduction and prograde metamorphism. At sites of stress concentration around porphyroclasts antigorite reveals an associated SPO and CPO, characteristically varying grain sizes and sutured grain boundaries, indicating deformation by dislocation creep. Stresses were probably below a few tens of MPa in the serpentinites, which was not sufficiently high to allow for crystal-plastic deformation of olivine at conditions at which antigorite is stable. Accordingly, any intragranular deformation features of the newly precipitated olivine in strain shadows are absent. The porphyroclast microstructures are not associated with the microstructures of the mylonitic matrix, but are inherited from an independent earlier deformation. The porphyroclasts record a high-stress deformation in the upper mantle of the oceanic lithosphere probably related to rifting processes, whereas the antigorite matrix

  11. When Ontogeny Matters: A New Japanese Species of Brittle Star Illustrates the Importance of Considering both Adult and Juvenile Characters in Taxonomic Practice.

    Directory of Open Access Journals (Sweden)

    Alexander Martynov

    Full Text Available Current taxonomy offers numerous approaches and methods for species delimitation and description. However, most of them are based on the adult characters and rarely suggest a dynamic representation of developmental transformations of taxonomically important features. Here we show how the underestimation of ontogenetic changes may result in long term lack of recognition of a new species of one of the most common ophiacanthid brittle stars (Echinodermata: Ophiuroidea from the North Pacific. Based on vast material collected predominantly by various Japanese expeditions in the course of more than 50 years, and thorough study of appropriate type material, we revise the complex of three common species of the ophiuroid genus Ophiacantha which have been persistently confused with each other. The present study thus reveals the previously unrecognized new species Ophiacantha kokusai sp.nov. which is commonly distributed off the Pacific coast of Japan. The new species shows developmental differentiation from the closely related species Ophiacantha rhachophora H. L. Clark, 1911 and retains clearly expressed early juvenile features in the adult morphology. Another species, Ophiacantha clypeata Kyte, 1977, which had been separated from O. rhachophora, is in turn shown to be just a juvenile stage of another North Pacific species, Ophiacantha trachybactra H.L. Clark, 1911. For every species, detailed morphological data from both adult and juvenile specimens based on scanning electron microscopy are presented. A special grinding method showing complex internal features has been utilized for the first time. For all three species in this complex, a clear bathymetric differentiation is revealed: O. rhachophora predominantly inhabits shallow waters, 0-250 m, the new species O. kokusai lives deeper, at 250-600 m, and the third species, O. trachybactra, is found at 500-2,000 m. The present case clearly highlights the importance of considering developmental

  12. Applying micromechanic failure models for description of failure modes in the ductile-brittle transition region; Einsatz mikromechanischer Schaedigungsmodelle im sproed-duktilen Uebergangsbereich

    Energy Technology Data Exchange (ETDEWEB)

    Bernauer, G.

    1997-07-01

    The work reported was to examine whether the modified Gurson model and the Beremin model can be applied to the brittle-ductile transition region of a ferritic steel, and whether the material`s behaviour can be characterized with a failure model integrating the two models mentioned above into one. Any possible improvements of this approach were to be found. The report at first gives a brief list of terminology and formulas used. Chapter 3 explains the microscopic processes typically observed in the transition region in connection with the failure modes of ductile fracture and cleavage fracture, and shows possible approaches for modelling. Chapter 4 defines the specimens and materials, and chapter 5 explains the experiments as well as the microscopic analyses of the fracture surfaces. Chapter 6 presents subsequent calculations representing the processes observed. Based on the stress distributions thus derived, the Beremin model is re-examined for further development. Chapter 7 summarizes the results obtained. (orig./CB) [Deutsch] Ziel der Arbeit ist, zu untersuchen, ob das modifizierte Gurson-Modell und das Beremin-Modell im sproed-duktilen Uebergangsbereich eines ferritischen Stahls einsetzbar sind und ob das Werkstoffverhalten mit einem aus beiden Modellen kombinierten Schaedigungsmodell berechnet werden kann. Gegebenenfalls sind Verbesserungen herbeizufuehren. Die vorliegende Arbeit beginnt mit einer kurzen Einfuehrung der verwendeten Begriffe und Formalismen. In Kap. 3 werden die mikroskopischen Vorgaenge bei den im Uebergangsbereich typischerweise auftretenden Versagensarten duktiler Bruch und Spaltbruch vorgestellt und verschiedene Moeglichkeiten ihrer Modellierung aufgezeigt. Nach der Vorstellung des Probenwerkstoffs werden in Kap. 4 die Experimente beschrieben und die mikroskopischen Untersuchungen der Bruchflaechen in Kap. 5 dargestellt. Die Nachrechnungen der Experimente werden in Kap. 6 vorgestellt. Auf der Grundlage der dadurch bereitgestellten

  13. Closed-Form Solutions for a Circular Tunnel in Elastic-Brittle-Plastic Ground with the Original and Generalized Hoek-Brown Failure Criteria

    Science.gov (United States)

    Chen, Ran; Tonon, Fulvio

    2011-03-01

    The paper presents a closed-form solution for the convergence curve of a circular tunnel in an elasto-brittle-plastic rock mass with both the Hoek-Brown and generalized Hoek-Brown failure criteria, and a linear flow rule, i.e., the ratio between the minor and major plastic strain increments is constant. The improvement over the original solution of Brown et al. (J Geotech Eng ASCE 109(1):15-39, 1983) consists of taking into account the elastic strain variation in the plastic annulus, which was assumed to be fixed in the original solution by Brown et al. The improvement over Carranza-Torres' solution (Int J Rock Mech Min Sci 41(Suppl 1):629-639, 2004) consists of providing a closed-form solution, rather than resorting to numerical integration of an ordinary differential equation. The presented solution, by rigorously following the theory of plasticity, takes into account that the elastic strain components change with radial and circumferential stress changes within the plastic annulus. For the original Hoek-Brown failure criterion, disregarding the elastic strain change leads to underestimate the convergence by up to 55%. For a rock mass failing according to the generalized Hoek-Brown failure criterion, using the original failure criterion leads to a high probability (97%) of underestimating the convergence by up to 100%. As a consequence, the onset or degree of squeezing may be underestimated, and the loading on the support/reinforcement calculated with the convergence/confinement method may be largely underestimated.

  14. Geographic structure in the Southern Ocean circumpolar brittle star Ophionotus victoriae (Ophiuridae) revealed from mtDNA and single-nucleotide polymorphism data.

    Science.gov (United States)

    Galaska, Matthew P; Sands, Chester J; Santos, Scott R; Mahon, Andrew R; Halanych, Kenneth M

    2017-01-01

    Marine systems have traditionally been thought of as "open" with few barriers to gene flow. In particular, many marine organisms in the Southern Ocean purportedly possess circumpolar distributions that have rarely been well verified. Here, we use the highly abundant and endemic Southern Ocean brittle star Ophionotus victoriae to examine genetic structure and determine whether barriers to gene flow have existed around the Antarctic continent. Ophionotus victoriae possesses feeding planktotrophic larvae with presumed high dispersal capability, but a previous study revealed genetic structure along the Antarctic Peninsula. To test the extent of genetic differentiation within O. victoriae, we sampled from the Ross Sea through the eastern Weddell Sea. Whereas two mitochondrial DNA markers (16S rDNA and COI) were employed to allow comparison to earlier work, a 2b-RAD single-nucleotide polymorphism (SNP) approach allowed sampling of loci across the genome. Mitochondrial data from 414 individuals suggested three major lineages, but 2b-RAD data generated 1,999 biallelic loci that identified four geographically distinct groups from 89 samples. Given the greater resolution by SNP data, O. victoriae can be divided into geographically distinct populations likely representing multiple species. Specific historical scenarios that explain current population structure were examined with approximate Bayesian computation (ABC) analyses. Although the Bransfield Strait region shows high diversity possibly due to mixing, our results suggest that within the recent past, dispersal processes due to strong currents such as the Antarctic Circumpolar Current have not overcome genetic subdivision presumably due to historical isolation, questioning the idea of large open circumpolar populations in the Southern Ocean.

  15. 考虑脆性损伤和渗流的圆形水工隧洞解析解%Analytical solutions of circular hydraulic tunnel considering brittle damage and seepage

    Institute of Scientific and Technical Information of China (English)

    卞康; 肖明; 刘会波

    2012-01-01

    Considering the damage characteristic of the brittle rock, the brittle damage model is introduced; and the expression of damage variable under 3-dimension isotropic damage condition is derived. The analytical solutions of elastoplastic stress and plastic radius of the circular hydraulic tunnel are deduced, considering the seepage influence, damage influence and principal stress corresponding relations under different engineering conditions. The research about brittle characteristic shows that the plastic radius of surrounding rock will increase after considering brittle damage. The more distinct the brittle characteristic is, the more larger plastic radius will be. Whether the first principal stress of rock nearby the tunnel is radial stress or tangential stress, the consideration of seepage will expand the plastic zone of the surrounding rock. In the process of internal water pressure increase from zero, the plastic radius will gradually decrease accompany with the increase of internal water pressure, until the plastic zone disappears in the end; however, when the internal water pressure exceeds the critical pressure; the plastic zone appears again; the plastic zone will gradually increase.%针对脆性岩石的损伤特性引入脆性损伤模型,导出三维各向同性损伤情况下的损伤变量表达式.在考虑损伤、不同工况主应力对应关系和渗流作用影响下,推导出圆形水工隧洞洞周围岩的弹塑性应力和塑性半径的解析解.对岩石的脆性特性的研究表明,考虑脆性损伤时的洞周围岩塑性半径比不考虑时有一定程度提升;围岩脆性特征越明显,塑性半径越大.无论洞周围岩应力状态如何,考虑渗流影响后,洞周围岩塑性区范围均会有所扩展.在内水压从0逐渐增加过程中,塑性半径随内水压增加而逐渐减小,直至塑性区消失,在超出临界内压后,塑性区重新出现,塑性半径逐渐增大.

  16. Stress Conditions for No Crack at Boundary of Brittle Inclusions inside Forgings%锻件内部脆性夹杂物边界无裂纹形成的应力条件

    Institute of Scientific and Technical Information of China (English)

    牛龙江; 张永涛; 韩国盛; 王庆伟; 任运来

    2014-01-01

    The cracks occurred at boundary of brittle inclusion inside heavy forging are major defects to influence its fa-tigue life and impact properties of heavy forging .In hot working , the stress field around the brittle inclusion is one of the most influential factors for crack initiation .In order to research the influence of the stress field , the definition of average spherical stress intensity (ASSI) is given.ASSI is used to research the influence of the stress field on the crack at boundary of brittle inclusion .Hot compression tests are carried out by dedicated specimens and anvils on a Gleeble-3180 thermo-mechanical simulator .Crack-forming process at boundary of brittle inclusion is observed by a scanning electron micro-scope.Results show that in compression tests at 1 200℃ there are no cracks at boundary of brittle inclusion when the alge-braic value of the ASSI is smaller than -1.74.%大型锻件内部脆性夹杂物边界裂纹是影响大型锻件疲劳寿命与冲击性能的主要缺陷。热锻变形下,脆性夹杂物周围区域的应力场是影响边界裂纹形成的主要因素之一。为研究应力场的影响,给出了平均球应力度的定义,借助平均球应力度研究了应力场对脆性夹杂物边界裂纹的影响规律。在Gleeble-3180热模拟试验机上,利用专门的试件和型砧进行了热压缩变形试验,在扫描电镜上观察试件内部脆性夹杂物边界裂纹的形成规律。试验表明,在1220℃进行压缩变形的条件下,当脆性夹杂物周围区域的平均球应力度的代数值小于-1.74时,脆性夹杂物边界无裂纹形成。

  17. The "fault of the Pool" along the Congo River between Kinshasa and Brazzaville, R(D)Congo is no more a myth: Paleostress from small-scale brittle structures

    Science.gov (United States)

    Delvaux, Damien; Ganza, Gloire; Kongota, Elvis; Fukiabantu, Guilain; Mbokola, Dim; Boudzoumou, Florent; Miyouna, Timothée; Gampio, Urbain; Nkodia, Hardy

    2017-04-01

    Small-scale brittle structures such as shear fractures and tension joints are well developed in the indurated Paleozoic Inkisi red sandstones of the West-Congo Supergroup in the "pool" region of Kinshasa and Brazzaville, along the Congo River. They appear to be related to the evolution of intraplate stresses during the late Cretaceous-Paleogene period, possibly related to the opening of the South Atlantic. However, inferring paleostresses from such structures is difficult due to the lack of clear kinematic indicators, so we used mainly the geometry, architecture and sequence of the joint systems to infer paleostresses. A limited number of kinematic indicators for slip sense (displaced pebbles, irregularities on striated surfaces, slickensides) or extension (plume joints) confirm the general conclusions of the joint architecture analysis. We found evidence for two major brittle deformation systems, leading to almost orthogonal fracture sets. They both started by the development of plume joints, which progressively evolved into open tension joints, isolated shear fractures and long (up to several hundred meters) brittle shear zones. The first system started to develop under NE-SW extension and evolved into strike-slip with NNW-SSE horizontal compression while the second (and later), started to develop under NW-SE extension and evolved into strike-slip with NNE-SSW horizontal compression. The second brittle deformation episode was associated with fluid flow as shown by the presence of palygorskite-calcite veins in the most prominent fractures of the second fracture system. Along the NE-SW brittle shear zones which run parallel to the Congo River, carbonate-rich fault-gauge lenses are filled by sand derived from the crushed adjacent walls and calcite vein fragments injected at a high fluid pressure, with late precipitation of palygorskite. Our study demonstrates the existence of two fault systems between Kinshasa and Brazzaville, the first one orthogonal to the trend

  18. Biaxial prestressing of brittle materials

    Science.gov (United States)

    Greszczuk, L.; Miller, R.; Netter, W.

    1970-01-01

    Strengthening of chemically consolidated zirconia with tungsten fibers, graphite fibers, sapphire whiskers, and silicon carbide whiskers is investigated. Addition of silicon carbide whiskers gives the highest increase in strength of zirconia at room and elevated temperatures. Prestressing with tungsten cables increases tensile strength and ductility

  19. Acoustic Emission in Brittle Solids

    DEFF Research Database (Denmark)

    Swindlehurst, W. E.; Wilshaw, T. R.

    1976-01-01

    A signal/source correlation study of the stress waves emitted during unstable microscopic Hertzian fracture in glass is described. A theoretical analysis of the variation in excess strain energy with applied load is made and the results compared with experimental data covering a wide range of cra...

  20. Folic Acid

    Science.gov (United States)

    ... damage. 10 Do I need folic acid after menopause? Yes. Women who have gone through menopause still need 400 micrograms of folic acid every ... United States: 2003–2006 . American Journal of Clinical Nutrition; 91(1): 231–237. Hamner, H.C., Cogswell, ...

  1. Numerical Modeling of an Active Salt System in Canyonlands, Utah: The Role of Topography in Driving Plastic Flow and Brittle Extension

    Science.gov (United States)

    Kravitz, K.; Upton, P.; Mueller, K. J.

    2014-12-01

    The Needles District of Canyonlands, Utah contains a coupled array of extensional faults, salt diapirs and an elongate anticline produced by gravitational stresses associated with erosion and canyon cutting along the Colorado River and its tributaries. Three-dimensional numerical models using high-resolution topography have been produced using FLAC3D to test how plastic flow of evaporites and brittle extension of overburden are coupled during deformation and how they combine to form salt structures in the region. High resolution (50 m DEM) topographic models were built of the Needles District and of the region to the southwest of the Needles containing the Imperial Valley fault. The overburden in these models was described by a strain-softening Mohr-Coulomb rheology and is 400 m thick from the surface to the base of the Colorado River canyon. It overlays a flat, 340 m thick, viscous layer representing the salt, which outcrops in the Colorado river downstream of the grabens. The Needles District is dominated by horst and graben structures which extend updip from the Colorado River to the southeast. In models of the Needles, lateral displacement is dominantly to the northwest, toward the river canyon with the most displacement occurring in regions containing side canyons. In the canyon, salt flows upward to form an anticline that follows the sinuosity of the river, and diapirs appear adjacent to side canyons or where the canyon widens, which is observed in the field and the models. Without a salt layer, models show much smaller displacement rates that vary from northwest to southeast demonstrating the importance of a flat lying salt layer in propagating deformation toward the river. The region to the southwest is an area of broader subsidence bounded by a major fault (Imperial Valley fault) with fewer developed extensional faults near the river canyon. The Imperial Valley fault model shows similar patterns in which deformation is driven perpendicular to the river

  2. Brittle tectonothermal evolution in the Forsmark area, central Fennoscandian Shield, recorded by paragenesis, orientation and 40Ar/ 39Ar geochronology of fracture minerals

    Science.gov (United States)

    Sandström, Björn; Tullborg, Eva-Lena; Larson, Sven Åke; Page, Laurence

    2009-12-01

    In this paper, we show how studies of fracture mineral paragenesis, their orientation and 40Ar/ 39Ar geochronology can be applied in order to recognise the brittle tectonothermal evolution in an area. Samples were selected from nearly 18 km of drill cores from the upper 1 km of the Fennoscandian Shield obtained during the site investigation for a repository of spent nuclear fuel in Forsmark, central Sweden. Four major events of fracturing and/or reactivation of fractures associated with fracture mineralisation have been distinguished. The first event was characterised by precipitation of epidote, quartz and chlorite, along preferably sub-horizontal and gently-dipping fractures or steep, WNW-ESE to NW-SE fractures. Precipitation occurred between 1.8 and 1.1 Ga, possibly during the late stage of the Svecokarelian orogeny close to 1.8-1.7 Ga. The second event is associated with precipitation of hematite-stained adularia and albite, prehnite, laumontite, calcite and chlorite, preferably along steep, ENE-WSW to NNE-SSW and NNW-SSE fractures. Precipitation occurred around 1107 ± 7 to 1034 ± 3 Ma, probably due to effects from the Sveconorwegian orogeny. This event was followed by a period with dissolution of fracture minerals and subsequent precipitation of mainly calcite, quartz, pyrite and asphaltite during the Palaeozoic. The formation fluid emanated from an overlying organic-rich sedimentary cover. Precipitation occurred during reactivation of Proterozoic fractures, but formation of new fractures is also inferred, possibly due to far-field effects of the Caledonian orogeny, or elevated hydrostatic pressure due to its foreland basin. The latest event is dominated by clay minerals, chlorite and calcite along hydraulically conductive fractures. These minerals are prominent along sub-horizontal and gently-dipping fractures, but also occur in sets of steeply-dipping fractures. It is inferred that the hydraulically conductive fractures are Proterozoic structures in which

  3. Brittle deformation in Southern Granulite Terrane (SGT): A study of pseudotachylyte bearing fractures along Gangavalli Shear Zone (GSZ), Tamil Nadu, India.

    Science.gov (United States)

    mohan Behera, Bhuban; Thirukumaran, Venugopal; Biswal, Tapas kumar

    2016-04-01

    High grade metamorphism and intense deformation have given a well recognition to the Southern Granulite Terrane (SGT) in India. TTG-Charnockite and basic granulites constitute the dominant lithoassociation of the area. Dunite-peridotite-anorthosite-shonkinite and syenites are the intrusives. TTG-charnockite-basic granulite have undergone F1 (isoclinal recumbent), F2 (NE-SW) and F3 (NW-SE) folds producing several interference pattern. E-W trending Neoarchean and Palaeoproterozoic Salem-Attur Shear Zone exhibits a low angle ductile thrust as well as some foot print of late stage brittle deformation near Gangavalli area of Tamil Nadu. The thrust causes exhumation of basic granulites to upper crust. Thrusting along the decollement has retrograded the granulite into amphibolite rock. Subsequently, deformation pattern of Gangavalli area has distinctly marked by numerous vertical to sub-vertical fractures mostly dominating along 0-15 and 270-300 degree within charnockite hills that creates a maximum stress (σ1) along NNW and minimum stress (σ3) along ENE. However, emplacement of pseudotachylyte vein along N-S dominating fracture indicates a post deformational seismic event. Extensive fractures produce anastomose vein with varying thickness from few millimeters to 10 centimeters on the outcrop. ICP-AES study results an isochemical composition of pseudotachylyte vein that derived from the host charnockitic rock where it occurs. But still some noticeable variation in FeO-MgO and Na2O-CaO are obtained from different parts within the single vein showing heterogeneity melt. Electron probe micro analysis of thin sections reveals the existence of melt immiscibility during its solidification. Under dry melting condition, albitic rich melts are considered to be the most favorable composition for microlites (e.g. sheaf and acicular micro crystal) re-crystallization. Especially, acicular microlites preserved tachylite texture that suggest its formation before the final coagulation

  4. Fungal Root Microbiome from Healthy and Brittle Leaf Diseased Date Palm Trees (Phoenix dactylifera L.) Reveals a Hidden Untapped Arsenal of Antibacterial and Broad Spectrum Antifungal Secondary Metabolites.

    Science.gov (United States)

    Mefteh, Fedia B; Daoud, Amal; Chenari Bouket, Ali; Alenezi, Faizah N; Luptakova, Lenka; Rateb, Mostafa E; Kadri, Adel; Gharsallah, Neji; Belbahri, Lassaad

    2017-01-01

    In this study, we aimed to explore and compare the composition, metabolic diversity and antimicrobial potential of endophytic fungi colonizing internal tissues of healthy and brittle leaf diseased (BLD) date palm trees (Phoenix dactylifera L.) widely cultivated in arid zones of Tunisia. A total of 52 endophytic fungi were isolated from healthy and BLD roots of date palm trees, identified based on internal transcribed spacer-rDNA sequence analysis and shown to represent 13 species belonging to five genera. About 36.8% of isolates were shared between healthy and diseased root fungal microbiomes, whereas 18.4 and 44.7% of isolates were specific to healthy and BLD root fungal microbiomes, respectively. All isolates were able to produce at least two of the screened enzymes including amylase, cellulase, chitinase, pectinase, protease, laccase and lipase. A preliminary screening of the isolates using disk diffusion method for antibacterial activity against four Gram-positive and three Gram-negative bacteria and antifungal activities against three phytopathogenic fungi indicated that healthy and BLD root fungal microbiomes displayed interesting bioactivities against examined bacteria and broad spectrum bioactivity against fungal pathogens. Some of these endophytic fungi (17 isolates) were fermented and their extracts were evaluated for antimicrobial potential against bacterial and fungal isolates. Results revealed that fungal extracts exhibited antibacterial activities and were responsible for approximately half of antifungal activities against living fungi. These results suggest a strong link between fungal bioactivities and their secondary metabolite arsenal. EtOAc extracts of Geotrichum candidum and Thielaviopsis punctulata originating from BLD microbiome gave best results against Micrococcus luteus and Bacillus subtilis with minimum inhibitory concentration (MIC, 0.78 mg/mL) and minimum bactericidal concentration (6.25 mg/mL). G. candidum gave the best result against

  5. Development of fluid veins during deformation of fluid-rich rocks close to the brittle-ductile transition: comparison between experimental and physical models.

    Science.gov (United States)

    Michel, Rabinowicz; Micha, Bystricky; Martin, Schmocker; Michael, Toplis; Alexis, Rigo; Hugo, Perfettini

    2010-05-01

    are generally run with a bulk shear stress close to but lower than the fracturation threshold of the rock. It is thus inferred that the development of R1 and R2 bands simply results from embrittlement of the rock in the zones of compaction in response to the steep increase in local stress and the steep drop in fluid pressure during shearing, while the bulk stress applied to deform the experimental sample remains below the brittle threshold of the rock. Implications of this process for melt segregation in the mantle and fluid percolation in gouges are discussed

  6. Fungal Root Microbiome from Healthy and Brittle Leaf Diseased Date Palm Trees (Phoenix dactylifera L.) Reveals a Hidden Untapped Arsenal of Antibacterial and Broad Spectrum Antifungal Secondary Metabolites

    Science.gov (United States)

    Mefteh, Fedia B.; Daoud, Amal; Chenari Bouket, Ali; Alenezi, Faizah N.; Luptakova, Lenka; Rateb, Mostafa E.; Kadri, Adel; Gharsallah, Neji; Belbahri, Lassaad

    2017-01-01

    In this study, we aimed to explore and compare the composition, metabolic diversity and antimicrobial potential of endophytic fungi colonizing internal tissues of healthy and brittle leaf diseased (BLD) date palm trees (Phoenix dactylifera L.) widely cultivated in arid zones of Tunisia. A total of 52 endophytic fungi were isolated from healthy and BLD roots of date palm trees, identified based on internal transcribed spacer-rDNA sequence analysis and shown to represent 13 species belonging to five genera. About 36.8% of isolates were shared between healthy and diseased root fungal microbiomes, whereas 18.4 and 44.7% of isolates were specific to healthy and BLD root fungal microbiomes, respectively. All isolates were able to produce at least two of the screened enzymes including amylase, cellulase, chitinase, pectinase, protease, laccase and lipase. A preliminary screening of the isolates using disk diffusion method for antibacterial activity against four Gram-positive and three Gram-negative bacteria and antifungal activities against three phytopathogenic fungi indicated that healthy and BLD root fungal microbiomes displayed interesting bioactivities against examined bacteria and broad spectrum bioactivity against fungal pathogens. Some of these endophytic fungi (17 isolates) were fermented and their extracts were evaluated for antimicrobial potential against bacterial and fungal isolates. Results revealed that fungal extracts exhibited antibacterial activities and were responsible for approximately half of antifungal activities against living fungi. These results suggest a strong link between fungal bioactivities and their secondary metabolite arsenal. EtOAc extracts of Geotrichum candidum and Thielaviopsis punctulata originating from BLD microbiome gave best results against Micrococcus luteus and Bacillus subtilis with minimum inhibitory concentration (MIC, 0.78 mg/mL) and minimum bactericidal concentration (6.25 mg/mL). G. candidum gave the best result against

  7. Structure/Property Relationships of Poly(L-lactic Acid/Mesoporous Silica Nanocomposites

    Directory of Open Access Journals (Sweden)

    Javier Gudiño-Rivera

    2013-01-01

    Full Text Available Biodegradable poly(L-lactic acid (PLLA/mesoporous silica nanocomposites were prepared by grafting L-lactic acid oligomer onto silanol groups at the surface of mesoporous silica (SBA-15. The infrared results showed that the lactic acid oligomer was grafted onto the mesoporous silica. Surface characterization of mesoporous silica proved that the grafted oligomer blocked the entry of nitrogen into the mesopores. Thermal analysis measurements showed evidence that, once mixed with PLLA, SBA-15 not only nucleated the PLLA but also increased the total amount of crystallinity. Neat PLLA and its nanocomposites crystallized in the same crystal habit and, as expected, PLLA had a defined periodicity compared with the nanocomposites. This was because the grafted macromolecules on silica tended to cover the lamellar crystalline order. The g-SBA-15 nanoparticles improved the tensile moduli, increasing also the tensile strength of the resultant nanocomposites. Overall, the silica concentration tended to form a brittle material.

  8. Drawing Brittle Fracture Causes Analysis of Large Gauge High Carbon Steel 82B Wire Rod%大规格高碳硬线82B拉拔脆断原因分析

    Institute of Scientific and Technical Information of China (English)

    张寄东; 智建国; 吕刚; 宿成

    2011-01-01

    采用金相组织检验分析等方法,分析了大规格82B拉拔劈裂脆断问题.结果表明:劈裂断口试样的中心处,由于锰、铬偏析而出现异常的马氏体组织,导致其变形与基体不一致,在拉拔过程中中心马氏体断裂成为裂纹源.断口附近表面存在结疤和擦伤等表面缺陷,中心马氏体和表面缺陷共同导致大规格82B拉拔劈裂脆断.通过优化合金元素锰、铬的成分含量,同时改善炼钢、轧制、拉拔等工艺,有效地降低了劈裂脆断的发生率.%The causes of drawing cleavage brittle fracture of large gauge high carbon steel 82B wire rod are analyzed by carrying out metallographic structure inspection and analysis. They are found out as the result of Mn, Cr central segregation causing formation of martensite in the centre of the wire rod, and the center martensite fracture becomes one of the sources of crack in the process of drawing because of the difference of deformation rate between the central part and the other area. There are some defects of scar and scratches near the fracture surface. It is manifested, through deeper analyzing, the main cause of drawing cleavage brittle fracture is the combined action of central martensite and surface defect. The incidence rate of cleavage brittle fracture defect has been reduced effectively through optimizing the content of Mn and Cr and improving the technics of steelmaking, rolling and drawing.

  9. Brittleness of 6.5wt% Si Silicon Steel Prepared by Chemical Vapor Deposition Method%化学气相沉积法制备硅质量分数6.5%硅钢的脆性

    Institute of Scientific and Technical Information of China (English)

    高超; 苏芳臣; 相颖杰; 孙权; 陈建钧

    2015-01-01

    6.5wt% Si silicon steel was prepared by chemical vapor deposition (CVD)method and the effects of reaction temperature,oxygen content in atmosphere and SiCl4 content on the brittleness of 6.5wt%Si silicon steel were studied using SEM,EDS and self-developed three-point bending machine.The results show that the grain size of the silicon steel increased with the reaction temperature rising,and the brittleness of the silicon steel increased with the increase of the grain size.Grain boundary oxidation was observed in the silicon steel when oxygen content in atmosphere was 100 mg·kg-1 ,which increased the brittleness of the silicon steel.Kirkendall voids were found in the silicon steel with a relatively high SiCl4 content of 35vol%,which increased the brittleness of the steel.%采用化学气相沉积(CVD)法制备了硅质量分数为6.5%的硅钢,利用扫描电镜、能谱仪和自主设计研发的三点压弯机研究了反应温度、气氛含氧量和 SiCl4含量对硅钢脆性的影响.结果表明:硅钢的晶粒尺寸随反应温度的升高而长大,硅钢的脆性随着晶粒尺寸的增加而增大;气氛含氧量在100 mg·kg-1时所制备的硅钢产生了晶界氧化现象,使硅钢脆性增加;SiCl4含量较大时(体积分数35%)所制备的硅钢产生了 Kirkendall 空洞,导致其脆性加剧.

  10. Folic acid

    Science.gov (United States)

    ... taking a specific nutritional supplement, containing vitamin B3 (nicotinamide), a compound isolated from grains (azelaic acid), zinc, ... lung cancer in most people. A type of skin cancer called melanoma. Limited research suggests that taking ...

  11. Folic Acid

    Science.gov (United States)

    ... B-complex vitamin needed by the body to manufacture red blood cells. A deficiency of this vitamin ... prepared from dried yeast, fruit, and fresh leafy green vegetables to increase the folic acid in your ...

  12. The impact of gallic acid on iron gall ink corrosion

    Science.gov (United States)

    Rouchon-Quillet, V.; Remazeilles, C.; Bernard, J.; Wattiaux, A.; Fournes, L.

    Many old manuscripts suffer from iron-gall ink corrosion, threatening our graphic heritage. Corroded papers become brown and brittle with age. The chemical reactions involved in this corrosion are relatively well known: they include both acidic hydrolysis and oxidation catalysed by free iron(II). Yet, a great variety of iron-gall ink recipes, including a wide range of constituents can be found in the literature and the visual aspect of old inks, can be very different from one inscription to another, even if they have been written on the same sheet of paper. This suggests that even if the free iron(II) plays a dominant role in the paper alteration, the contribution of other ingredients should not be neglected. For this reason, we explored the impact gallic acid may have on the corrosion mechanisms and in particular on the oxidation reactions. These investigations were carried out on laboratory probes prepared with paper sheets immersed in different solutions, all containing the same amount of iron sulphate, and different gallic acid concentrations. These probes were then artificially aged and their degradation state was evaluated by bursting strength measurements, FTIR spectrometry and Mössbauer spectrometry. All these analyses lead us to conclude that gallic acid has an influence on the iron(III)/iron(II) ratio, probably because of its reducing properties.

  13. Physical, chemical and mineralogical evolution of the Tolhuaca geothermal system, southern Andes, Chile: Insights into the interplay between hydrothermal alteration and brittle deformation

    Science.gov (United States)

    Sanchez-Alfaro, Pablo; Reich, Martin; Arancibia, Gloria; Pérez-Flores, Pamela; Cembrano, José; Driesner, Thomas; Lizama, Martin; Rowland, Julie; Morata, Diego; Heinrich, Christoph A.; Tardani, Daniele; Campos, Eduardo

    2016-09-01

    In this study, we unravel the physical, chemical and mineralogical evolution of the active Tolhuaca geothermal system in the Andes of southern Chile. We used temperature measurements in the deep wells and geochemical analyses of borehole fluid samples to constrain present-day fluid conditions. In addition, we reconstructed the paleo-fluid temperatures and chemistry from microthermometry and LA-ICP-MS analysis of fluid inclusions taken from well-constrained parageneses in vein samples retrieved from a ~ 1000 m borehole core. Based on core logging, mineralogical observations and fluid inclusions data we identify four stages (S1-S4) of progressive hydrothermal alteration. An early heating event (S1) was followed by the formation of a clay-rich cap in the upper zone (chemical analyses of fluid inclusions and borehole fluids reveal a significant change in chemical conditions during the evolution of Tolhuaca. Whereas borehole (present-day) fluids are rich in Au, B and As, but Cu-poor (B/Na ~ 100.5, As/Na ~ 10- 1.1, Cu/Na ~ 10- 4.2), the paleofluids trapped in fluid inclusions are Cu-rich but poor in B and As (B/Na ~ 10- 1, As/Na ~ 10- 2.5, Cu/Na ~ 10- 2.5 in average). We interpret the fluctuations in fluid chemistry at Tolhuaca as the result of transient supply of metal-rich, magmatically derived fluids where As, Au and Cu are geochemically decoupled. Since these fluctuating physical and chemical conditions at the reservoir produced a mineralogical vertical segmentation of the system that affects the mechanical and hydrological properties of host rock, we explored the effect of the development of a low-cohesion low-permeability clay cap on the conditions of fault rupture and on the long-term thermal structure of the system. These analyses were performed by using rock failure condition calculations and numerical simulations of heat and fluid flows. Calculations of the critical fluid pressures required to produce brittle rupture indicate that within the clay-rich cap, the

  14. Ibotenic acid and thioibotenic acid

    DEFF Research Database (Denmark)

    Hermit, Mette B; Greenwood, Jeremy R; Nielsen, Birgitte

    2004-01-01

    with the conformations preferred by the ligands upon docking to mGlu1 and models of the other mGlu subtypes, we propose that unlike other subtypes, group III mGlu receptor binding sites require a ligand conformation at an energy level which is prohibitively expensive for ibotenic acid, but not for thioibotenic acid....... These studies demonstrate how subtle differences in chemical structures can result in profound differences in pharmacological activity....

  15. 高氮奥氏体钢的韧脆转变与层错能的关系%Study on relationship between ductile to brittle transition and stacking fault energy of high nitrogen containing austenitic stainless steel

    Institute of Scientific and Technical Information of China (English)

    马玉喜

    2011-01-01

    在60℃至室温范围内,采用夏比冲击试验测定材料的韧一脆转变温度,并通过对冲击断口的X-射线测试层错能等方法,对几种不同含氮量奥氏体不锈钢在低温下发生韧一脆转变的现象进行了研究.结果表明:在超高氮奥氏体钢中,随氮质量分数的增加该钢种发生韧一脆转变的温度上升,层错能减少,韧性越来越差.%The DBTT of super-high nitrogen containing austenitic stainless steels was tested at temperatures between room-temperature and -60 ℃ by Charpy-type test, and its ductility and brittleness transition were investigated under low temperature by XRD method. The results show that the ductile to brittle transition temperature (DBTT) of high nitrogen containing austenitic stainless steels depends on the nitrogen content in the steel, and the DBTT is shifted from low temperature to high temperature. In addition,with the increase of nitrogen content, the stacking fault energy is decreased and the ductility is getting worse.

  16. Embrittlement and conditions of the optimization of magnetic properties in the amorphous alloy Co69Fe3.7Cr3.8Si12.5B11 in the absence of a viscous-brittle transition

    Science.gov (United States)

    Kekalo, I. B.; Mogil'nikov, P. S.

    2016-07-01

    The influence of the holding time upon annealing on the temperature of the viscous-brittle transition (temperature of embrittlement) T f in a cobalt-based amorphous alloy of the composition Co69Fe3.7Cr3.8Si12.5B11 with a very low saturation magnetostriction λs (<10-7) has been studied. It has been established that the dependence of the embrittlement temperature T f on the of time of holding t a can be described by an Arrhenius equation and that the embrittlement at the annealing temperatures above and below 300°C is described by different kinetic parameters. In the alloy under study, irrespective of the holding time, embrittlement occurs in a very narrow range of annealing temperatures, which does not exceed 5 K. Based on the experimental data on the evolution of the hysteresis magnetic properties upon the isochronous annealings and upon the isothermal holding, the regime of heat treatment that ensures a very high (about 50000) magnitude of the permeability µ5 ( H = 5 mOe, f = 1 kHz) without the transition of the alloy into a brittle state has been determined.

  17. Quantification of the brittle-ductile failure behavior of reactor steels by means of the small punch tests and micromechanical damage models; Quantifizierung des sproed-duktilen Versagensverhaltens von Reaktorstaehlen mit Hilfe des Small-Punch-Tests und mikromechanischer Schaedigungsmodelle

    Energy Technology Data Exchange (ETDEWEB)

    Linse, Thomas

    2013-02-25

    This work comprises the development and implementation of a non-local ductile damage model, the application of methods for the identification of material parameters from experimental data as well as the calculation of fracture mechanics parameters in the brittle-ductile transition zone through numerical simulations of fracture mechanical tests using the identified parameters. The developed non-local ductile damage model is based on the Gurson-Tvergaard- Needleman model (GTN). The pathological mesh sensitivity of the GTN model is eliminated by introducing an additional length parameter by means of an implicit gradient formulation. To solve the coupled field problem, the non-local damage model is implemented in a finite element program in the form of a userdefined element. Force-displacement-curves of the small punch test (SPT), a miniaturised test, are evaluated for the determination of material parameters. Given the modest material requirements for the preparation of the required samples remnants of Charpy-specimens are reused. Two ferritic reactor steels, both irradiated and unirradiated, are examined. The experiments cover the full brittle-ductile transition region of the steels. Following the concept of the Local Approach, fracture toughness values are determined by numerical calculation of the stress and deformation state in fracture mechanics specimen only. Here, the yield curves and damage parameters previously determined from the SPT are used. The calculated fracture toughness values are compared with experimental results.

  18. Assessment of Ductile-to-Brittle Transition Behavior of Localized Microstructural Regions in a Friction-Stir Welded X80 Pipeline Steel with Miniaturized Charpy V-Notch Testing

    Science.gov (United States)

    Avila, Julian A.; Lucon, Enrico; Sowards, Jeffrey; Mei, Paulo Roberto; Ramirez, Antonio J.

    2016-06-01

    Friction-stir welding (FSW) is an alternative welding process for pipelines. This technology offers sound welds, good repeatability, and excellent mechanical properties. However, it is of paramount importance to determine the toughness of the welds at low temperatures in order to establish the limits of this technology. Ductile-to-brittle transition curves were generated in the present study by using a small-scale instrumented Charpy machine and miniaturized V-notch specimens (Kleinstprobe, KLST); notches were located in base metal, heat-affected, stirred, and hard zones within a FSW joint of API-5L X80 Pipeline Steel. Specimens were tested at temperatures between 77 K (-196 °C) and 298 K (25 °C). Based on the results obtained, the transition temperatures for the base material and heat-affected zone were below 173 K (-100 °C); conversely, for the stirred and hard zones, it was located around 213 K (-60 °C). Fracture surfaces were characterized and showed a ductile fracture mechanism at high impact energies and a mixture of ductile and brittle mechanisms at low impact energies.

  19. Acid Rain

    Science.gov (United States)

    Bricker, Owen P.; Rice, Karen C.; Dietrich, W.E.; Sposito, Garrison

    1997-01-01

    Acid deposition, or acid rain as it is more commonly referred to, has become a widely publicized environmental issue in the U.S. over the past decade. The term usually conjures up images of fish kills, dying forests, "dead" lakes, and damage to monuments and other historic artifacts. The primary cause of acid deposition is emission of S02 and NOx to the atmosphere during the combustion of fossil fuels. Oxidation of these compounds in the atmosphere forms strong acids - H2SO4 and HNO3 - which are returned to the Earth in rain, snow, fog, cloud water, and as dry deposition.Although acid deposition has only recently been recognized as an environmental problem in the U.S., it is not a new phenomenon (Cogbill & Likens 1974). As early as the middle of the 17th century in England, the deleterious effects of industrial emissions on plants, animals, and humans, and the atmospheric transport of pollutants between England and France had become issues of concern (Evelyn 1661, Graunt 1662). It is interesting that well over three hundred years ago in England, recommendations were made to move industry outside of towns and build higher chimneys to spread the pollution into "distant parts." Increasing the height of smokestacks has helped alleviate local problems, but has exacerbated others. In the U.S. the height of the tallest smokestack has more than doubled, and the average height of smokestacks has tripled since the 1950s (Patrick et al 1981). This trend occurred in most industrialized nations during the 20th century and has had the effect of transforming acid rain from a local urban problem into a problem of global scale.

  20. Perfluorooctanoic acid

    NARCIS (Netherlands)

    de Voogt, P.; Wexler, P.

    2014-01-01

    Perfluorooctanoic acid (PFOA, 335-67-1) is used in fluoropolymer production and firefighting foams and persists in the environment. Human exposure to PFOA is mostly through the diet. PFOA primarily affects the liver and can cause developmental and reproductive toxic effects in test animals.

  1. Research on Cutting Brittle Materials by Pre-mixed Abrasive Water Jet%前混合磨料水射流切割脆性材料研究

    Institute of Scientific and Technical Information of China (English)

    张沙; 龚烈航

    2011-01-01

    提出在有防爆要求的场合下,利用前混合磨料水射流冷切割技术对混凝土等脆性材料进行切割.对脆性材料的切割机制进行研究,建立切割冲蚀模型,分析受冲击区的应力.对混凝土试块进行切割实验,并对分析同切割深度的不同形态所产生的因为.研究表明:在切割初始阶段,高速磨料以较小角度冲击、磨削材料,形成较光滑的切割磨削区;随切深的增加,材料在磨料粒子大角度冲击下形成斜条纹状的变形磨削区.前混合磨料水射流对混凝土等建筑脆性材料具有良好的切割效果,在易燃易爆等应急场合进行切割作业具有独特优势.%To meet the occasion that has the requirement of explosion proof, the cold cutting technology of premixed abrasive water jet was proposed to use in the cut of brittle materials such as concretes. The mechanism of cutting brittle materials was studied, the impact model was established and the stress of impacting area was analyzed. Experiments of cutting concrete block were conducted and the reason for different forms on different cutting depth was analyzed. The results show that in the initial stage, the formation of a smooth cutting grinding zone is due to the impact and materials grinding by the high-speed abrasive particles with a small angle. With the increase of cutting depth, under the impact of abrasive particles with a large angle,an oblique stripe deformation of the grinding zone are formed. Good effect of cutting brittle materials such as concrete by premixed abrasive water jet shows that this clod cutting technology has a unique advantage in the schoolwork under urgent conditions.

  2. Hydroxycarboxylic acids and salts

    Energy Technology Data Exchange (ETDEWEB)

    Kiely, Donald E; Hash, Kirk R; Kramer-Presta, Kylie; Smith, Tyler N

    2015-02-24

    Compositions which inhibit corrosion and alter the physical properties of concrete (admixtures) are prepared from salt mixtures of hydroxycarboxylic acids, carboxylic acids, and nitric acid. The salt mixtures are prepared by neutralizing acid product mixtures from the oxidation of polyols using nitric acid and oxygen as the oxidizing agents. Nitric acid is removed from the hydroxycarboxylic acids by evaporation and diffusion dialysis.

  3. 大理岩脆-延-塑转换特性的细观模拟研究%MESOSCOPIC SIMULATION STUDY OF BRITTLE-DUCTILE-PLASTIC TRANSITION CHARACTER OF MARBLE

    Institute of Scientific and Technical Information of China (English)

    余华中; 阮怀宁; 褚卫江

    2013-01-01

      针对锦屏深埋大理岩峰后变形破坏的脆–延–塑转换特性,采用颗粒流程序(PFC)中的簇单元模型(CPM)对其进行细观模拟研究。经过对室内试验结果的反复模拟校准,获得描述锦屏深埋大理岩力学性质的一组细观物理力学性质参数。模型试验结果表明:试样的一系列宏观力学表现,包括弹性模量、泊松比、单轴与启裂抗压强度、应力–应变曲线、峰值与残余强度包络线、拉压强度比以及破坏形态等均与锦屏深埋大理岩的试验结果具有良好的一致性。对不同围压下裂纹发育规律的研究表明:不同应力状态下细观裂纹发育特征的显著差异是导致大理岩的变形破坏出现脆–延–塑转换特性的主要原因;张性裂纹的大量发育决定介质的脆性破坏模式,而剪切裂纹数目的快速增长则促使介质由脆性破坏模式逐渐向延–塑性破坏模式转换。%The deformation and failure characteristics of brittle-ductile-plastic transition,which is shown in the post-peak stage for Jinping deep marble,was simulated by clumped-particle model(CPM) of particle flow code(PFC),and studied from the micro view. After a long process of trial-and-error calibration of laboratory test results,a set of micro parameters for Jinping deep marble were obtained. It is shown that a series of macroscopic mechanical properties of the synthetic rock,including the elastic modulus,Poisson′s ratio,uniaxial compressive and crack initiation strengths,stress-strain curves,the peak and residual strength envelops,the ratio of tensile to uniaxial compressive strength,and the failure patterns of synthetic rock samples,all agree well with the test results of Jinping deep marble. Study of regularities of crack development in synthetic rock samples at different confining pressures indicates that:The significant difference of development features of microcracks at different confining pressures is

  4. Effect of curing way on brittleness and durability of prestress high concrete pipe piles%养护制度对预应力高强度混凝土管桩脆性及耐久性的影响

    Institute of Scientific and Technical Information of China (English)

    王成启; 王春明; 周郁兵; 张宜兵

    2014-01-01

    The brittleness and durability of prestress high concrete pipe piles on non-steam autoclaved and steam autoclaved were exper-imentally studied.Experimental results showed that the brittleness of non-steam autoclaved concrete was less than steam autoclaved con-crete's.Moreover,the chlorine-resistant and frost-resistance properties of non-steam autoclaved concrete were better than steam autoclaved concrete's.prestress high concrete pipe piles on non-steam autoclaved excels in anti hammer ,it was applicable in freeze-thaw and chlorine circumstance.%试验研究了常压蒸养护和高压蒸汽养护工艺生产的预应力高强度混凝土管桩混凝土的脆性和耐久性。研究结果表明,常压蒸养预应力高强度混凝土管桩混凝土的脆性小于高压蒸养混凝土;常压蒸养预应力高强度混凝土管桩混凝土抗氯盐侵蚀性能和抗冻性等耐久性高于高压蒸养混凝土。采用常压蒸养生产预应力高强度混凝土管桩有利于预应力高强度混凝土管桩的抗锤击性能,适用于北方冻融和海洋环境。

  5. Differential Effects of Dietary Fat Content and Protein Source on Bone Phenotype and Fatty Acid Oxidation in Female C57Bl/6 Mice

    Science.gov (United States)

    Sawin, Emily A.; Stroup, Bridget M.; Murali, Sangita G.; O’Neill, Lucas M.; Ntambi, James M.

    2016-01-01

    Background Glycomacropeptide (GMP) is a 64-amino acid glycophosphopeptide released from κ-casein during cheesemaking that promotes satiety, reduces body fat, increases bone mass and infers prebiotic and anti-inflammatory effects. The impact of adiposity and gender on bone health is unclear. Objective To determine how feeding female mice diets providing 60% Fat Kcal (high-fat) or 13% Fat Kcal (control) with either GMP or casein as the protein source impacts: body composition, ex vivo fatty acid oxidation, bone (femoral) biomechanical performance, and the relationship between body composition and bone. Methods Weanling female C57Bl/6 mice were fed high-fat (60% Fat Kcal) or control diets (13% Fat Kcal) with GMP or casein from 3 to 32 weeks of age with assessment of body weight and food intake. Body composition was assessed by dual-energy X-ray absorptiometry (DXA). Fatty acid oxidation was measured in liver, muscle, and fat tissues using 14C-palmitate. Plasma concentrations of hormones and cytokines were determined. Bone biomechanical performance was assessed by the 3-point bending test. Results Female mice fed high-fat diets showed increased fatty acid oxidation capacity in both gastrocnemius muscle and brown adipose tissue compared to mice fed the control diets with a lower fat content. Despite increased fat mass in mice fed the high-fat diets, there was little evidence of glucose impairment or inflammation. Mice fed the high-fat diets had significantly greater total body bone mineral density (BMD), femoral BMD, and femoral cross-sectional area than mice fed the control diets. Femora of mice fed the high-fat diets had increased yield load and maximum load before fracture, consistent with greater bone strength, but reduced post-yield displacement or ductility, consistent with bone brittleness. Female mice fed a high-fat GMP diet displayed increased fat oxidation capacity in subcutaneous fat relative to mice fed the high-fat casein diet. Regardless of dietary fat

  6. Hydrofluoric acid poisoning

    Science.gov (United States)

    Fluorhydric acid ... stomach, or intestine have holes (perforations) from the acid. ... Hydrofluoric acid is especially dangerous. The most common accidents involving hydrofluoric acid cause severe burns on the skin ...

  7. Dehydroabietic acid

    Directory of Open Access Journals (Sweden)

    Xiao-Ping Rao

    2009-10-01

    Full Text Available The title compound [systematic name: (1R,4aS,10aR-7-isopropyl-1,4a-dimethyl-1,2,3,4,4a,9,10,10a-octahydrophenanthrene-1-carboxylic acid], C20H28O2, has been isolated from disproportionated rosin which is obtained by isomerizing gum rosin with a Pd-C catalyst.. Two crystallographically independent molecules exist in the asymmetric unit. In each molecule, there are three six-membered rings, which adopt planar, half-chair and chair conformations. The two cyclohexane rings form a trans ring junction with the two methyl groups in axial positions. The crystal structure is stabilized by intermolecular O—H...O hydrogen bonds.

  8. Effect of oral intake of choline-stabilized orthosilicic acid on skin, nails and hair in women with photodamaged skin.

    Science.gov (United States)

    Barel, A; Calomme, M; Timchenko, A; De Paepe, K; Paepe, K De; Demeester, N; Rogiers, V; Clarys, P; Vanden Berghe, D

    2005-10-01

    Chronic exposure of the skin to sunlight causes damage to the underlying connective tissue with a loss of elasticity and firmness. Silicon (Si) was suggested to have an important function in the formation and maintenance of connective tissue. Choline-stabilized orthosilicic acid ("ch-OSA") is a bioavailable form of silicon which was found to increase the hydroxyproline concentration in the dermis of animals. The effect of ch-OSA on skin, nails and hair was investigated in a randomized, double blind, placebo-controlled study. Fifty women with photodamaged facial skin were administered orally during 20 weeks, 10 mg Si/day in the form of ch-OSA pellets (n=25) or a placebo (n=25). Noninvasive methods were used to evaluate skin microrelief (forearm), hydration (forearm) and mechanical anisotropy (forehead). Volunteers evaluated on a virtual analog scale (VAS, "none=0, severe=3") brittleness of hair and nails. The serum Si concentration was significantly higher after a 20-week supplementation in subjects with ch-OSA compared to the placebo group. Skin roughness parameters increased in the placebo group (Rt:+8%; Rm: +11%; Rz: +6%) but decreased in the ch-OSA group (Rt: -16%; Rm: -19%; Rz: -8%). The change in roughness from baseline was significantly different between ch-OSA and placebo groups for Rt and Rm. The difference in longitudinal and lateral shear propagation time increased after 20 weeks in the placebo group but decreased in the ch-OSA group suggesting improvement in isotropy of the skin. VAS scores for nail and hair brittleness were significantly lower after 20 weeks in the ch-OSA group compared to baseline scores. Oral intake of ch-OSA during the 20 weeks results in a significant positive effect on skin surface and skin mechanical properties, and on brittleness of hair and nails.

  9. A degradation study of PLLA containing lauric acid.

    Science.gov (United States)

    Renouf-Glauser, Annette C; Rose, John; Farrar, David; Cameron, Ruth E

    2005-05-01

    Addition of lauric acid to poly (L-lactide) (PLLA) has resulted in a new family of enhanced degradation biomaterials. Presented is PLLA4.5 (PLLA containing 4.5 wt% lauric acid), the fastest degrading of the family. Degradation was studied via mass changes, gel-permeation chromatography, wide- and small-angle X-ray scattering (WAXS and SAXS), simultaneous SAXS and tensile testing, and visual observation. The undegraded PLLA4.5 deformed by crazing, recognisable from the characteristic shape of the SAXS pattern. As water up-take and degradation proceeded, samples crystallised, decreasing the SAXS long period, until by 4 days the deformation mechanism had become that of crystal-mediated deformation. This resulted in a 'peanut-lemon'-shaped SAXS pattern, interpreted in terms of cavitation and fibrillated shear. Further degradation up to 12 days resulted in the same deformation mechanism at different sample displacements, with samples failing earlier during tensile testing until a ductile-brittle transition occurred. At 30-40 days water up-take and mass-loss increased significantly and global whitening of samples occurred, while the crystallinity and long period stabilised. Complete degradation had not occurred by the end of the study at 73 days. Through an understanding of how the changes in morphology during degradation affect the micromechanisms of deformation, it may be possible to design microstructures to give a tailored evolution of mechanical response in the body.

  10. Mechanical properties of PET composites using multi-walled carbon nanotubes functionalized by inorganic and itaconic acids

    Directory of Open Access Journals (Sweden)

    A. May-Pat

    2012-02-01

    Full Text Available Multi-walled carbon nanotubes (MWCNTs were oxidized by two different acid treatments and further functionalized with itaconic acid (IA. The functionalized MWCNTs were used to fabricate Poly(ethylene terephthalate (PET composites by melt mixing. The presence of functional groups on the surface of the treated MWCNTs was confirmed by infrared spectroscopy and thermogravimetric analysis. The MWCNTs oxidized with a concentrated mixture of HNO3 and H2SO4 exhibited more oxygen containing functional groups (OH, COOH but also suffer larger structural degradation than those oxidized by a mild treatment based on diluted HNO3 followed by H2O2. PET composites were fabricated using the oxidized-only and oxidized followed by functionalization with IA MWCNTs. PET composites fabricated with MWCNT oxidized by mild conditions showed improved tensile strength and failure strain, while harsh MWCNT oxidation render them overly brittle.

  11. Preparation of robust polyamide microcapsules by interfacial polycondensation of p-phenylenediamine and sebacoyl chloride and plasticization with oleic acid.

    Science.gov (United States)

    Rosa, Natacha; Martins, Gabriela V; Bastos, Margarida M S M; Gois, Joana R; Coelho, Jorge F J; Marques, Juliana; Tavares, Carlos J; Magalhães, Fernão D

    2015-01-01

    Microcapsules produced by interfacial polycondensation of p-phenylenediamine (PPD) and sebacoyl chloride (SC) were studied. The products were characterized in terms of morphology, mean diameter and effectiveness of dodecane encapsulation. The use of Tween 20 as dispersion stabilizer, in comparison with polyvinyl alcohol (PVA), reduced considerably the mean diameter of the microcapsules and originated smoother wall surfaces. When compared to ethylenediamine (EDA), microcapsules produced with PPD monomer were more rigid and brittle, prone to fracture during processing and ineffective retention of the core liquid. The use of diethylenetriamine (DETA) cross-linker in combination with PPD did not decrease capsule fragility. On the other hand, addition of a small fraction of oleic acid to the organic phase remarkably improved wall toughness and lead to successful encapsulation of the core-oil. Oleic acid is believed to act as a plasticizer. Its incorporation in the polymeric wall was demonstrated by FTIR and (1)H-NMR.

  12. Effect of gallic acid on the wear behavior of early carious enamel

    Energy Technology Data Exchange (ETDEWEB)

    Gao, S S; Huang, S B; Yu, H Y [State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041 (China); Qian, L M, E-mail: yhyang6812@scu.edu.c [Tribology Research Institute, National Traction Power Laboratory, Southwest Jiaotong University, Chengdu 610031 (China)

    2009-06-15

    The purpose of this research was to investigate the wear behavior of early carious enamel remineralized with gallic acid. Forty natural human premolar specimens with early caries lesions were prepared. A remineralization pH-cycling treatment agent of 4000 ppm gallic acid was used for 12 days to treat the early lesions. The changes in microhardness were monitored. Nanoscratch tests were used to evaluate wear resistance. The experimental data were analyzed by using a t-test. The widths of traces were measured by an AMBIOS XP-2 stylus profilometer. After remineralization, all samples re-hardened significantly. The coefficients of friction became higher, and the widths of scratches were larger than they were before remineralization. Gallic acid significantly improved the early carious enamel's hardness. The wear damage of the samples treated with gallic acid was more severe than that of the control group. There were more obvious cracks and delaminations on the traces of the treated group. Compared with the control group, the enamel remineralized with gallic acid had inferior wear resistance. After remineralization, the dominant damage mechanisms of early carious enamel had changed from plastic deformation and adhesive wear to a combination of brittle cracks and delamination of enamel.

  13. Study on Rumen Degradability Characteristics of Brittleness Mutation Rice by Cows%全株脆性突变水稻在奶牛瘤胃内降解特性的研究

    Institute of Scientific and Technical Information of China (English)

    吕宗友; 苏衍菁; 赵国琦; 严长杰

    2011-01-01

    通过本试验确定全株脆性突变水稻是否可作为优质饲料稻的中间育种材料,以便为进一步解决南方饲草缺乏和开发饲料资源打下基础.本试验选用3头装有永久性瘤胃瘘管的中国荷斯坦牛,采用尼龙袋法研究了全株脆性突变(:Brittl]eness Mutation,BM)水稻及其亲本中花11(Zhongghuall)在瘤胃内的降解特性.结果表明:(1)黄熟期全株BM水稻营养成分与对照亲本存在较大的差异.其中,全株BM水稻半纤维素含量极显著高于对照亲本(P<0.01),而NFE含量则极显著低于对照亲本(P<0.01);(2)24h后的各个时间点,全株BM水稻DM降解率极显著低于对照亲本(P<0.01),:NDF、ADF、半纤维素和纤维素的降解率则极显著高于对照亲本(P<0.01);(3)对于瘤胃有效降解率,全株BM水稻DM有效降解率极显著低于对照亲本(P<0.01),NDF、ADF和半纤维素有效降解率明显高于对照亲本;(4)通过透射电镜观察,与对照亲本相比,全株脆性突变水稻的厚壁组织细胞壁明显变薄.全株脆性突变水稻可以作为优质饲料稻选育的中间育种材料.%In the study we can get the conclution that the Brittleness Mutation rice can be used as middle breeding material of fine quality fodder-rice or not, and pave the way for the shorting of forage and exploitation feed resource. In the study three Holstein cows with a permanent rumen cannula were used to measure rumen degradability characteristics of Brittleness Mutation(BM)rice and its wild type japonica variety Zhonghua-11. The results shows that: (1)Compared with the wild type, at yellow mature stage hemi-cellulose content of whole crop BM-rice was significantly increased(P<0.01), but its NFE content was significantly decreased(P<O.01). (2)At different time after 24h, compared with the wild type, DM degradability of whole crop BM-rice was significantly decreased(P<O.Ol),but its NDF、ADF、Hemi-cellulose and cellulose degradability were significantly

  14. 多元化企业经营系统脆性控制模型及最优策略%Brittle control model and optimal strategy for diversified company

    Institute of Scientific and Technical Information of China (English)

    王德鲁; 宋学锋

    2011-01-01

    脆性的激发是导致企业全局性失败或经营困境的关键所在,脆性风险控制则是提高经营系统安全性的重要保障.在企业经营系统脆性风险扩散路径分析的基础上,建立了具有状态依赖的基本风险控制模型和考虑业务增长率与衰减率的改进控制模型,并评估和比较了免疫策略、隔离策略和综合控制3种方案的效果.同时,还进一步讨论了改进控制模型周期解的存在性以及周期控制方案下的最优策略问题.结果表明,不同的控制策略对脆性风险控制而言都能够得到相同的结果,但在相同的目标下,综合控制策略的总成本最小,而免疫策略和隔离策略总成本的大小则依赖于初始条件和临界参数;当任何一次控制方案都不能达到目标时,最佳选择就是采取周期性的综合控制策略.%The excitation of brittleness is the key to overall managerial difficulties, and brittle risk control is the important leverage to improve the security of management system. Based on the path analysis of brittle risk spread in firm' 8 business system, the basic state-dependent model and modified control model considering growth rate and decline rate of business are put forward, and the effect of three strategies such as immuniza tion , isolation and integrated control is evaluated and compared. In addition, the existence of periodic solu tions of improved model and optimal cycle control strategy are discussed. The results show that different control strategies can provide the same results in terms of risk control. Under the same objective, the total cost of inte grated control strategy is the lowest, while the total cost of immunization strategy and isolation strategy depends on the initial conditions and critical parameters. Moreover, the best option is to implement a cyclical compre hensive control strategy when none of the strategies can achieve the goal.

  15. The effects of three different food acids on the attrition-corrosion wear of human dental enamel

    Science.gov (United States)

    Zhang, Yichi; Arsecularatne, Joseph A.; Hoffman, Mark

    2015-07-01

    With increased consumption of acidic drinks and foods, the wear of human teeth due to attrition in acidic environments is an increasingly important issue. Accordingly, the present paper investigates in vitro the wear of human enamel in three different acidic environments. Reciprocating wear tests in which an enamel cusp slides on an enamel flat surface were carried out using acetic, citric and lactic acid lubricants (at pH 3-3.5). Distilled water was also included as a lubricant for comparison. Focused ion beam milling and scanning electron microscopy imaging were then used to investigate the enamel subsurfaces following wear tests. Nanoindentation was used to ascertain the changes in enamel mechanical properties. The study reveals crack generation along the rod boundaries due to the exposure of enamel to the acidic environments. The wear mechanism changes from brittle fracture in distilled water to ploughing or shaving of the softened layer in acidic environments, generating a smooth surface with the progression of wear. Moreover, nanoindentation results of enamel samples which were exposed to the above acids up to a duration of the wear tests show decreasing hardness and Young’s modulus with exposure time.

  16. Progress in the Brittle Fracture and Fatigue of High Strength Steels and Their Welds%高强度钢材及其焊缝脆性断裂与疲劳性能的研究进展

    Institute of Scientific and Technical Information of China (English)

    王元清; 林云; 周晖; 张延年; 石永久

    2012-01-01

    The advantages and disadvantages of high strength steel as well as its application in the domestic and foreign construction engineering and bridge engineering were briefly described, as well as a number of practical engineering problems analyzed. Summing up the related research of domestic and foreign high strength steels and their welds on their brittle fracture and fatigue, the article raised the need for study on the fracture toughness and fatigue performance of high strength steel used in construction and its connection weld and the change law of influence factor. Low temperature, weld defects, increasing thickness of steel and high-frequency dynamic load were found greatly reducing the resistance capacity of brittle fracture of high strength steel and fatigue life; Other than these external factors,for mechanical properties and toughness due to special metallurgical processes,the application of high strength steel was limited.%简单阐述了高强度钢材的优、缺点以及在国内外建筑工程和桥梁工程中的应用情况,并分析了其实际工程中存在的若干问题.总结了国内外对高强度钢材及其焊缝的脆性断裂与疲劳破坏的相关研究,引出研究高强度建筑用结构钢材及其连接焊缝的断裂韧性和疲劳性能以及影响因素变化规律的必要性,得出了如下结论:低温、焊缝缺陷、钢材厚度的增加和高频动荷载极大降低了高强度钢材的抗脆断能力及疲劳寿命;同时高强度钢材由于特殊冶金工艺而具有的力学性能和韧性加上这些外因限制了其使用范围.

  17. A MICROMECHANICAL MODEL FOR DAMAGE AND THERMAL CONDUCTIVITY OF BRITTLE ROCKS%脆性岩石损伤与热传导特性的细观力学模型

    Institute of Scientific and Technical Information of China (English)

    陈益峰; 李典庆; 荣冠; 姜清辉; 周创兵

    2011-01-01

    基于均匀化方法给出低孔隙率脆性岩石在热-力耦合荷载作用条件下的各向异性损伤模型和有效热传导特性模型.其中,损伤模型可考虑非等温条件下裂纹的法向压缩变形、刚度恢复以及裂纹的滑动剪胀特性,热传导特性模型可反映损伤过程中细观结构的演化以及裂纹形态、孔隙率和饱和度变化对岩石有效热传导特性的影响.讨论低孔隙率结晶岩裂纹形态和饱和度对其有效热传导特性的影响;采用瑞典(A)sp(o)闪长岩在三轴压缩条件下的应力-应变曲线验证损伤模型的有效性,并分析岩石在损伤演化过程中裂纹体积率、密度、形态、饱和度和有效热传导特性的演化规律.研究成果对于深部岩体的热-力耦合特性研究具有一定参考意义.%An anisotropic damage model and an effective thermal conductivity model were presented based on homogenization techniques for low-porosity brittle rocks subjected to mechanical and thermal loadings. The thermal effect, the recovery of normal stiffness and the mobilized dilatancy behavior were incorporated in the damage model. The thermal conductivity model took into account the effects of damage-induced microstructure evolution, crack shape, porosity and saturation degree on the effective thermal conductivity of brittle rocks. The influences of crack shape and saturation degree on the effective thermal conductivity of low-porosity crystallized rocks were particularly discussed. The damage model was validated by the triaxial test data on an intact Aspo diorite; and the evolutions of porosity, crack density, crack shape, saturation degree and the effective thermal conductivity during the mechanical loading were demonstrated. The results may provide a helpful reference for better understanding the coupled thermo-mechanical behaviors of deep rocks.

  18. Preliminary study of two-scale model for analyzing brittle rock based on asymptotic expansion method%基于渐近展开法的脆性岩石双尺度方法初步研究

    Institute of Scientific and Technical Information of China (English)

    彭从文; 朱向荣; 王金昌

    2011-01-01

    将渐近展开法与细观统计模型相结合,研究了脆性岩石双尺度计算方法.该方法在细观尺度定义材料属性,假定材料参数符合Weibull分布,采用弹性-理想脆性本构模型,脆断标准采用修正的Mohr-Coulomb准则和最大拉应力准则,通过宏细观尺度耦合计算,得到细观尺度材料损伤演化及其对结构宏观性状的影响.方法包括确定材料统计参数、确定细观尺度代表性体积单元(RVE)及求解边值方程等步骤.数值模型采用商业软件ABAQUS及其内嵌的UMAT用户子程序实现.该方法适用于岩石单轴受压或低围压应力状态,考虑到计算效率,计算时宜采用混合尺度,即模型重点(关键)部位采用双尺度,而其他区域采用单尺度计算.宏观尺度材料软化后未采用正则化方法,此时的计算结果有网格依赖性.%The asymptotic expansion method was combined with micro-based statistical model to develop a two-scale scheme for analyzing the behavior of brittle rock.The material properties were defined in micro-scale and the elastic-perfect brittle constitutive was adopted, the modified Mohr-Coulomb theory and the maximum tensile strength were selected as the fracture criterion.Through calculating in a global-local coupling way, the damage evolution of material in the micro-scale and its effects on the properties of rock in the macro-scale were derived.The scheme included three steps: determining material statistical parameters, determining representative volume element (RVE) and solving boundary equations.The numerical model was realized by the commercial software ABAQUS and its subroutine UMAT.This scheme can be used in the conditions that the rock is loaded with uniaxial compression or triaxial compression with low confining pressure.The regularization method is not used, so the result is mesh dependent after the rock is localized.

  19. Determination of sulfuric acid concentration for anti-cavitation characteristics of Al alloy by two step anodizing process to forming nano porous.

    Science.gov (United States)

    Lee, Seung-Jun; Kim, Seong-Kweon; Jeong, Jae-Yong; Kim, Seong-Jong

    2014-12-01

    Al alloy is a highly active metal but forms a protective oxide film having high corrosion resistance in atmosphere environment. However, the oxide film is not suitable for practical use, since the thickness of the film is not uniform and it is severly altered with formation conditions. This study focused on developing an aluminum anodizing layer having hardness, corrosion resistance and abrasion resistance equivalent to a commercial grade protective layer. Aluminum anodizing layer was produced by two-step aluminum anodizing oxide (AAO) process with different sulfuric acid concentrations, and the cavitation characteristics of the anodized coating layer was investigated. In hardness measurement, the anodized coating layer produced with 15 vol.% of sulfuric acid condition had the highest value of hardness but exhibited poor cavitation resistance due to being more brittle than those with other conditions. The 10 vol.% of sulfuric acid condition was thus considered to be the optimum condition as it had the lowest weight loss and damage depth.

  20. Amino acids in the sedimentary humic and fulvic acids

    Digital Repository Service at National Institute of Oceanography (India)

    Sardessai, S.

    to the coastal sedimentary humic acids implying higher association of amino acids with the carbonaceous and fine grained sedimentary humic acids. Both the humic and fulvic acids are composed of neutral, acidic, basic, aromatic and sulphur containing amino acids....

  1. [Teichoic acids from lactic acid bacteria].

    Science.gov (United States)

    Livins'ka, O P; Harmasheva, I L; Kovalenko, N K

    2012-01-01

    The current view of the structural diversity of teichoic acids and their involvement in the biological activity of lactobacilli has been reviewed. The mechanisms of effects of probiotic lactic acid bacteria, in particular adhesive and immunostimulating functions have been described. The prospects of the use of structure data of teichoic acid in the assessment of intraspecific diversity of lactic acid bacteria have been also reflected.

  2. Plasma amino acids

    Science.gov (United States)

    Amino acids blood test ... types of methods used to determine the individual amino acid levels in the blood. ... test is done to measure the level of amino acids in the blood. An increased level of a ...

  3. Uric acid test (image)

    Science.gov (United States)

    Uric acid urine test is performed to check for the amount of uric acid in urine. Urine is collected over a 24 ... testing. The most common reason for measuring uric acid levels is in the diagnosis or treatment of ...

  4. Influence of the residual stresses on crack initiation in brittle materials and structures; Prise en compte des contraintes residuelles dans un critere d'amorcage en rupture fragile

    Energy Technology Data Exchange (ETDEWEB)

    Henninger, C

    2007-11-15

    Many material assemblies subjected to thermo-mechanical loadings develop thermal residual stresses which modify crack onset conditions. Besides if one of the components has a plastic behaviour, plastic residual deformations may also have a contribution. One of the issues in brittle fracture mechanics is to predict crack onset without any pre-existing defect. Leguillon proposed an onset criterion based on both a Griffth-like energetic condition and a maximum stress criterion. The analysis uses matched asymptotics and the theory of singularity. The good fit between the model and experimental measurements led on homogeneous isotropic materials under pure mechanical loading incited us to take into account residual stresses in the criterion. The comparison between the modified criterion and the experimental measurements carried out on an aluminum/epoxy assembly proves to be satisfying concerning the prediction of failure of the interface between the two components. Besides, it allows, through inversion, identifying the fracture properties of this interface. The modified criterion is also applied to the delamination of the tile/structure interface in the plasma facing components of the Tore Supra tokamak. Indeed thermal and plastic residual stresses appear in the metallic part of these coating tiles. (author)

  5. Temporary expansion to shelf depths rather than an onshore-offshore trend: the shallow-water rise and demise of the modern deep-sea brittle star family Ophiacanthidae (Echinodermata: Ophiuroidea

    Directory of Open Access Journals (Sweden)

    Ben Thuy

    2013-07-01

    Full Text Available Hypotheses on the age and possible antiquity of the modern deep-sea fauna put forward to date almost all agree on the assumption that the deep-sea fauna is largely the result of colonisation from shallow-water environments. Here, the fossil record of the Ophiacanthidae, a modern deep-sea brittle star family with extensive fossil occurrences at shelf depths, is systematically traced against a calibrated phylogeny. Several lines of evidence suggest that the Ophiacanthidae originated and greatly diversified in the deep sea, with most extant clades having diverged by the end of the Triassic at the latest. During the Jurassic, the family temporarily invaded shelf environments, attaining relative abundances and diversities comparable to those found in coeval and modern deep-sea settings, and gradually declined in abundance subsequently, to become largely restricted to the deep-sea again. The pattern of temporary expansion to shelf environments suggested here underpins the potential of deep-sea environments to contribute significantly to shallow-water biodiversity; an aspect that has mostly been neglected so far. It is speculated that the large-scale ophiacanthid invasion of shelf environments around the Triassic-Jurassic boundary was initiated by a change from thermohaline to halothermal circulation, attenuating the thermal stratification of the water column and thus providing opportunities for enhan