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Sample records for fracture mechanics investigation

  1. Fracture Mechanics

    CERN Document Server

    Zehnder, Alan T

    2012-01-01

    Fracture mechanics is a vast and growing field. This book develops the basic elements needed for both fracture research and engineering practice. The emphasis is on continuum mechanics models for energy flows and crack-tip stress- and deformation fields in elastic and elastic-plastic materials. In addition to a brief discussion of computational fracture methods, the text includes practical sections on fracture criteria, fracture toughness testing, and methods for measuring stress intensity factors and energy release rates. Class-tested at Cornell, this book is designed for students, researchers and practitioners interested in understanding and contributing to a diverse and vital field of knowledge. Alan Zehnder joined the faculty at Cornell University in 1988. Since then he has served in a number of leadership roles including Chair of the Department of Theoretical and Applied Mechanics, and Director of the Sibley School of Mechanical and Aerospace Engineering.  He teaches applied mechanics and his research t...

  2. Fracture mechanics

    CERN Document Server

    Perez, Nestor

    2017-01-01

    The second edition of this textbook includes a refined presentation of concepts in each chapter, additional examples; new problems and sections, such as conformal mapping and mechanical behavior of wood; while retaining all the features of the original book. The material included in this book is based upon the development of analytical and numerical procedures pertinent to particular fields of linear elastic fracture mechanics (LEFM) and plastic fracture mechanics (PFM), including mixed-mode-loading interaction. The mathematical approach undertaken herein is coupled with a brief review of several fracture theories available in cited references, along with many color images and figures. Dynamic fracture mechanics is included through the field of fatigue and Charpy impact testing. Explains computational and engineering approaches for solving crack-related problems using straightforward mathematics that facilitate comprehension of the physical meaning of crack growth processes; Expands computational understandin...

  3. Fracture mechanics

    Science.gov (United States)

    Shannon, John L., Jr.

    1986-01-01

    The application of fracture mechanics to the design of ceramic structures will require the precise measurement of crack growth and fracture resistance of these materials over their entire range of anticipated service temperatures and standardized test methods for making such measurements. The development of a standard test for measuring the plane strain fracture toughness is sought. Stress intensity factor coefficients were determined for three varieties of chevron-notch specimens, and fracture toughness measurements were made on silicon nitrides, silicon carbides, and aluminum oxides to assess the performance of each specimen variety. It was determined that silicon nitride and silicon carbides have flat crack growth resistance curves, but aluminum oxide does not. Additionally, batch-to-batch differences were noticed for the aluminum oxide. Experiments are continuing to explain the rising crack growth resistance and batch-to-batch variations for the aluminum oxide.

  4. Investigation of the fracture mechanics of boride composites

    Science.gov (United States)

    Kaufman, L.; Clougherty, E. V.; Nesor, H.

    1971-01-01

    Fracture energies of WC-6Co, Boride 5 (ZrB2+SiC), Boride 8(ZrB2+SiC+C) and Boride 8-M2(ZrB2+SiC+C) were measured by slow bend and impact tests of notched charpy bars. Cobalt bonded tungsten carbide exhibited impact energies of 0.76 ft-lb or 73.9 in-lb/square inch. Boride 5 and the Boride 8 exhibit impact energies one third and one quarter of that observed for WC-6Co comparing favorably with measurements for SiC and Si3N4. Slow bend-notched bar-fracture energies for WC-6Co were near 2.6 in-lb/square inch or 1/20 the impact energies. Slow bend energies for Boride 8-M2, Boride 8 and Boride 5 were 58%, 42% and 25% of the value observed for WC-6Co. Fractograph showed differences for WC-6Co where slow bend testing resulted in smooth transgranular cleavage while samples broken by impact exhibited intergranular failures. By contrast the boride fractures showed no distinction based on testing method. Fabrication studies were conducted to effect alteration of the boride composites by alloying and introduction of graphite cloth.

  5. Investigation of Mechanical Properties and Fracture Simulation of Solution-Treated AA 5754

    Science.gov (United States)

    Kumar, Pankaj; Singh, Akhilendra

    2017-06-01

    In this work, mechanical properties and fracture toughness of as-received and solution-treated aluminum alloy 5754 (AA 5754) are experimentally evaluated. Solution heat treatment of the alloy is performed at 530 °C for 2 h, and then, quenching is done in water. Yield strength, ultimate tensile strength, impact toughness, hardness, fatigue life, brittle fracture toughness (K_{Ic} ) and ductile fracture toughness (J_{Ic} ) are evaluated for as-received and solution-treated alloy. Extended finite element method has been used for the simulation of tensile and fracture behavior of material. Heaviside function and asymptotic crack tip enrichment functions are used for modelling of the crack in the geometry. Ramberg-Osgood material model coupled with fracture energy is used to simulate the crack propagation. Fracture surfaces obtained from various mechanical tests are characterized by scanning electron microscopy.

  6. Fracture Mechanics of Concrete

    DEFF Research Database (Denmark)

    Ulfkjær, Jens Peder

    Chapter 1 Chapter l contains the introduction to this thesis. The scope of the thesis is partly to investigate different numerical and analytical models based on fracture mechanical ideas, which are able to predict size effects, and partly to perform an experimental investigation on high-strength......Chapter 1 Chapter l contains the introduction to this thesis. The scope of the thesis is partly to investigate different numerical and analytical models based on fracture mechanical ideas, which are able to predict size effects, and partly to perform an experimental investigation on high......-strength concrete. Chapter 2 A description of the factors which influence the strength and cracking of concrete and high strength concrete is made. Then basic linear fracture mechanics is outlined followed by a description and evaluation of the models used to describe concrete fracture in tension. The chapter ends...... with a description of the different types of size effects. Three examples which discuss the two terms 'size effect' and 'brittleness' and the importance of a stiff test rig. Finally some brittleness numbers are defined. Chapter 3 In chapter 3 the most well-known numerical methods which use the fictitious crack...

  7. Experimental Investigation and Fracture Mechanical Modelling of Debonded Sandwich Panels Loaded with Lateral Pressure

    DEFF Research Database (Denmark)

    Jolma, Perttu; Segercrantz, Sebastian; Berggreen, Carl Christian

    2005-01-01

    For the determination of debonded sandwich panel residual strength with lateral loading a parametric finite element model is developed. The parametric model allows an arbitrary positioning of the debond within the panel and consists of both solid and shell elements. A fracture mechanical approach...

  8. Fracture mechanics safety approaches

    Energy Technology Data Exchange (ETDEWEB)

    Roos, E.; Schuler, X.; Eisele, U. [Materials Testing Inst. (MPA), Univ. of Stuttgart (Germany)

    2004-07-01

    Component integrity assessments require the knowledge of reliable fracture toughness parameters characterising the initiation of the failure process in the whole relevant temperature range. From a large number of fracture mechanics tests a statistically based procedure was derived allowing to quantify the initiation of fracture toughness as a function of temperature as a closed function as well as the temperature dependence of the cleavage instability parameters. Alternatively to the direct experimental determination one also can use a correlation between fracture toughness and notch impact energy. (orig.)

  9. Fracture mechanical investigation of a thermo shock scenario for a VVER-440 RPV

    Energy Technology Data Exchange (ETDEWEB)

    Altstadt, E.; Abendroth, Martin [Forschungszentrum Dresden-Rossendorf (Germany)

    2008-07-01

    The paper describes the modelling and evaluation of a pressurized thermal shock (PTS) scenario in a VVER-440 reactor pressure vessel due to an emergency cooling. An axially oriented semi-elliptical crack is assumed to be located in the core welding seam. Two variants of fracture mechanical evaluation are performed: the analysis of a sub-cladding crack and of a surface crack. Three-dimensional finite element (FE) models are used to compute the global transient temperature and stress-strain fields. By using a three-dimensional submodel, which includes the crack, the local crack stress-strain field is obtained. Within the subsequent postprocessing using the J-integral technique the stress intensity factors K{sub I} along the crack front are obtained. The FE results are compared to analytical calculations proposed in the VERLIFE code. The stress intensity factors are compared to the fracture toughness curve of the weld material. (orig.)

  10. Dynamic fracture mechanics

    Science.gov (United States)

    Kobayashi, A. S.; Ramulu, M.

    1985-01-01

    Dynamic fracture and crack propagation concepts for ductile materials are reviewed. The equations for calculating dynamic stress integrity and the dynamic energy release rate in order to study dynamic crack propagation are provided. The stress intensity factor versus crack velocity relation is investigated. The uses of optical experimental techniques and finite element methods for fracture analyses are described. The fracture criteria for a rapidly propagating crack under mixed mode conditions are discussed; crack extension and fracture criteria under combined tension and shear loading are based on maximum circumferential stress or energy criteria such as strain energy density. The development and use of a Dugdale model and finite element models to represent crack and fracture dynamics are examined.

  11. Investigation of the mechanical properties and failure modes of hybrid natural fiber composites for potential bone fracture fixation plates.

    Science.gov (United States)

    Manteghi, Saeed; Mahboob, Zia; Fawaz, Zouheir; Bougherara, Habiba

    2017-01-01

    The purpose of this study is to investigate the mechanical feasibility of a hybrid Glass/Flax/Epoxy composite material for bone fracture fixation such as fracture plates. These hybrid composite plates have a sandwich structure in which the outer layers are made of Glass/Epoxy and the core from Flax/Epoxy. This configuration resulted in a unique structure compared to prior composites proposed for similar clinical applications. In order to evaluate the mechanical properties of this hybrid composite, uniaxial tension, compression, three-point bending and Rockwell Hardness tests were conducted. In addition, water absorption tests were performed to investigate the rate of water absorption for the specimens. This study confirms that the proposed hybrid composite plates are significantly more flexible axially compared to conventional metallic plates. Furthermore, they have considerably higher ultimate strength in tension, compression and flexion. Such high strength will ensure good stability of bone-implant construct at the fracture site, immobilize adjacent bone fragments and carry clinical-type forces experienced during daily normal activities. Moreover, this sandwich structure with stronger and stiffer face sheets and more flexible core can result in a higher stiffness and strength in bending compared to tension and compression. These qualities make the proposed hybrid composite an ideal candidate for the design of an optimized fracture fixation system with much closer mechanical properties to human cortical bone.

  12. Fracture Criterion for Fracture Mechanics of Magnets

    Institute of Scientific and Technical Information of China (English)

    潘灏; 杨文涛

    2003-01-01

    The applicability and limitation of some fracture criteria in the fracture mechanics of magnets are studied.It is shown that the magnetic field intensity factor can be used as a fracture criterion when the crack in a magnet is only affected by a magnetic field. For some magnetostrictive materials in which the components of magnetostriction strain do not satisfy the compatibility equation of deformation, the stress intensity factor can no longer be effectively applicable as a fracture criterion when the crack in a magnet is affected by a magnetic field and mechanical loads simultaneously.

  13. Phase Field Fracture Mechanics.

    Energy Technology Data Exchange (ETDEWEB)

    Robertson, Brett Anthony [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2015-11-01

    For this assignment, a newer technique of fracture mechanics using a phase field approach, will be examined and compared with experimental data for a bend test and a tension test. The software being used is Sierra Solid Mechanics, an implicit/explicit finite element code developed at Sandia National Labs in Albuquerque, New Mexico. The bend test experimental data was also obtained at Sandia Labs while the tension test data was found in a report online from Purdue University.

  14. Nonlinear fracture mechanics investigation on the ductility of reinforced concrete beams

    Directory of Open Access Journals (Sweden)

    A. Carpinteri

    Full Text Available In the present paper, a numerical algorithm based on the finite element method is proposed for the prediction of the mechanical response of reinforced concrete (RC beams under bending loading. The main novelty of such an approach is the introduction of the Overlapping Crack Model, based on nonlinear fracture mechanics concepts, to describe concrete crushing. According to this model, the concrete dam- age in compression is represented by means of a fictitious interpenetration. The larger is the interpenetration, the lower are the transferred forces across the damaged zone. The well-known Cohesive Crack Model in tension and an elastic-perfectly plastic stress versus crack opening displacement relationship describing the steel reinforcement behavior are also integrated into the numerical algorithm. The application of the proposed Cohesive-Overlapping Crack Model to the assessment of the minimum reinforcement amount neces- sary to prevent unstable tensile crack propagation and to the evaluation of the rotational capacity of plastic hinges, permits to predict the size-scale effects evidenced by several experimental programs available in the literature. According to the obtained numerical results, new practical design formulae and diagrams are proposed for the improvement of the current code provisions which usually disregard the size effects.

  15. Mechanisms of intergranular fracture

    Energy Technology Data Exchange (ETDEWEB)

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

    1999-08-01

    The authors present a study of the atomistic mechanisms of crack propagation along grain boundaries in metals and alloys. The failure behavior showing cleavage crack growth and/or crack-tip dislocation emission is demonstrated using atomistic simulations for an embedded-atom model. The simulations follow the quasi-equilibrium growth of a crack as the stress intensity applied increases. Dislocations emitted from crack tips normally blunt the crack and inhibit cleavage, inducing ductile behavior. When the emitted dislocations stay near the crack tip (sessile dislocations), they do blunt the crack but brittle cleavage can occur after the emission of a sufficient number of dislocations. The fracture process occurs as a combination of dislocation emission/micro-cleavage portions that are controlled by the local atomistic structure of the grain boundary. The grain boundary is shown to be a region where dislocation emission is easier, a mechanism that competes with the lower cohesive strength of the boundary region.

  16. Fracture mechanics in pavement design

    CSIR Research Space (South Africa)

    Denneman, E

    2009-07-01

    Full Text Available effects. Examples of the use of fracture mechanics providing an alternative to these conventional design parameters are given in the paper. The paper shows that although much further development is required before fracture mechanics can be relied upon...

  17. Fractures and rock mechanics, Phase 2

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2001-03-01

    Knowledge of fracture occurrence and orientation in chalk is important for optimum field development planning and evaluation of well-bore stability. The combined geological and geotechnical studies carried out under the EFP-96 and EFP-98 programmes have investigated the influence of fractures on rock mechanics properties for chalk. Data for quantifying the effect of natural fractures in chalk have been supplied by triaxial testing in normal scale and large scale on samples from three chalk types, namely from Valhall Tor and Tyra Maastrichtian and an outcrop locality at Hillerslev. >From the latter locality special big cylindrical specimens were sampled for the large scale triaxial testing (500x500 mm) in order to get at true representation of the natural fracturing in the Hillerslev chalk. By comparing test results from normal scale to large scale on fractured and non fractured specimens it was found that the stiffness of the chalk is dependent on scale while the shear strength generally seems to depend on fractures and not on scale. Furthermore the studies revealed, that fractures have a significant reducing effect on the shear strength, that characterisation by the Geological Strength Index, GSI, on fractured test specimens igve a very good prediction of shear, that shear failure and yield surface characteristics for fractued and intact chalk can be provided using GSI, that up-scaling influence the elastic deformation properties in the low stress regime and that fractures influence the compressibility in the elastic stress regime, but not in the plastic stress regime. Finally, the practical application of some of the results on reservoir chalk has been addressed, especially the up-scaling of strength and deformation properties from normal scale tests to reservoir conditions. The up-scaling laws are relevant for borehole stability problems but not for compaction. Generally, the observations in the study are relevant for quantifying the effect of fracturing and

  18. Fracture Mechanics: Inspirations from Nature

    Directory of Open Access Journals (Sweden)

    David Taylor

    2014-10-01

    Full Text Available In Nature there are many examples of materials performing structural functions. Nature requires materials which are stiff and strong to provide support against various forces, including self-weight, the dynamic forces involved in movement, and external loads such as wind or the actions of a predator. These materials and structures have evolved over millions of years; the science of Biomimetics seeks to understand Nature and, as a result, to find inspiration for the creation of better engineering solutions. There has been relatively little fundamental research work in this area from a fracture mechanics point of view. Natural materials are quite brittle and, as a result, they have evolved several interesting strategies for preventing failure by crack propagation. Fatigue is also a major problem for many animals and plants. In this paper, several examples will be given of recent work in the Bioengineering Research Centre at Trinity College Dublin, investigating fracture and fatigue in such diverse materials as bamboo, the legs and wings of insects, and living cells.

  19. Investigation into the Mechanical Properties and Fracture Behavior of A356 Aluminum Alloy-Based ZrO2-Particle-Reinforced Metal-Matrix Composites

    Science.gov (United States)

    Abdizadeh, H.; Baghchesara, M. A.

    2013-11-01

    In the present study, an investigation has been carried out into the influence of ZrO2 content and casting temperature on the mechanical properties and fracture behavior of A356 Al/ZrO2 composites. A356 aluminum alloy matrix composites reinforced with 5, 10 and 15 vol.% ZrO2 were fabricated at 750, 850, and 95 0°C via the stir-casting method. Based on the results obtained, the optimum amount of reinforcement and casting temperature were determined by evaluating the density and mechanical properties of the composites through the use of hardness and tensile tests. The fracture surfaces of composite specimens were also studied to identify the main fracture mechanisms of the composites. The results obtained indicated that all samples fractured due to the interdendritic cracking of the matrix alloy. Reinforcing the Al matrix alloy with ZrO2 particles increased the hardness and ultimate tensile strength of the alloy to the maximum values of 70 BHN and 232 MPa, respectively. The best mechanical properties were obtained for the specimens with 15 vol.% of ZrO2 produced at 75 0°C.

  20. Fractures and Rock Mechanics, Phase 1

    DEFF Research Database (Denmark)

    Havmøller, Ole; Krogsbøll, Anette

    1997-01-01

    The main objectives of the project are to combine geological description of fractures, chalk types and rock mechanical properties, and to investigate whether the chosen outcrops can be used as analogues to reservoir chalks. Five chalk types, representing two outcrop localities: Stevns and Hillers......The main objectives of the project are to combine geological description of fractures, chalk types and rock mechanical properties, and to investigate whether the chosen outcrops can be used as analogues to reservoir chalks. Five chalk types, representing two outcrop localities: Stevns...

  1. Fractures and Rock Mechanics, Phase 1

    DEFF Research Database (Denmark)

    Havmøller, Ole; Krogsbøll, Anette

    1997-01-01

    The main objectives of the project are to combine geological description of fractures, chalk types and rock mechanical properties, and to investigate whether the chosen outcrops can be used as analogues to reservoir chalks. Five chalk types, representing two outcrop localities: Stevns and Hillers......The main objectives of the project are to combine geological description of fractures, chalk types and rock mechanical properties, and to investigate whether the chosen outcrops can be used as analogues to reservoir chalks. Five chalk types, representing two outcrop localities: Stevns...... and Hillerslev, and three reservoir zones: Tyra Maastrictian, Valhall Tor and Valhall Hod are investigated. Different test types are applied in small and large scale in order to investigate the influence on stiffness and strength from natural and induced fractures, stylolites, bedding planes and healed fractures....... The main conclusions are: that Hillerslev and Stevns can be regarded as close analogues to the Valhall Tor formation, but neither to Valhall Hod nor to Tyra formations; and that compressive strength is reduced by initial fractures, whereas stifness seems to be unaffected; and that large test specimens have...

  2. Fracture mechanics of PGX graphite

    Energy Technology Data Exchange (ETDEWEB)

    Ho, F.H.; Vollman, R.E.; Cull, A.D.

    1981-03-01

    Fracture mechanics tests were performed on grade PGX graphite. A compact tension specimen configuration which yields consistent values of the opening mode critical stress intensity factor K/sub IC/, was designed. For the calculation of the fracture toughness and crack growth rate the concept of the effective crack length is used. It corresponds to the crack length of a machined notched specimen with the same compliance. Fracture toughness testing was performed in two environments, air and helium, both at room temperature. The critical stress intensity factor, K/sub IC/, is calculated based on the maximum load and the effective crack length. The fatigue crack growth test was performed in air only. A break-in period was observed for the machined notch to develop into a naturally occurring crack path. Half of the fatigue life was spent in this period.

  3. Fractures and Rock Mechanics, Phase 1

    DEFF Research Database (Denmark)

    Krogsbøll, Anette; Jakobsen, Finn; Madsen, Lena

    1997-01-01

    The main objective of the project is to combine geological descriptions of fractures, chalk types and rock mechanical properties in order to investigate whether the chosen outcrops can be used as analogues to reservoir chalks. This report deals with 1) geological descriptions of outcrop locality...

  4. Fractures and Rock Mechanics, Phase 1

    DEFF Research Database (Denmark)

    Krogsbøll, Anette; Jakobsen, Finn; Madsen, Lena

    1997-01-01

    The main objective of the project is to combine geological descriptions of fractures, chalk types and rock mechanical properties in order to investigate whether the chosen outcrops can be used as analogues to reservoir chalks. This report deals with 1) geological descriptions of outcrop locality...

  5. Continuum damage and fracture mechanics

    CERN Document Server

    Öchsner, Andreas

    2016-01-01

    This textbook offers readers an introduction to damage and fracture mechanics, equipping them to grasp the basic ideas of the presented approaches to modeling in applied mechanics. In the first part, the book reviews and expands on the classical theory of elastic and elasto-plastic material behavior. A solid understanding of these two topics is the essential prerequisite to advancing to damage and fracture mechanics. Thus, the second part of this course provides an introduction to the treatment of damage and fractures in the context of applied mechanics. Wherever possible, the one-dimensional case is first introduced and then generalized in a following step. This departs somewhat from the more classical approach, where first the most general case is derived and then simplified to special cases. In general, the required mathematics background is kept to a minimum.   Tutorials are included at the end of each chapter, presenting the major steps for the solution and offering valuable tips and tricks. The supplem...

  6. Fracture mechanics of protein materials

    Directory of Open Access Journals (Sweden)

    Markus J. Buehler

    2007-09-01

    Full Text Available Proteins are the fundamental building blocks of a vast array of biological materials involved in critical functions of life, many of which are based on highly characteristic nanostructured arrangements of protein components that include collagen, alpha helices, or beta sheets. Bone, providing structure to our body, or spider silk, used for prey procurement, are examples of materials that have incredible elasticity, strength, and robustness unmatched by many synthetic materials. This is mainly attributed to their structural formation with molecular precision. We review recent advances in using large-scale atomistic and molecular modeling to elucidate the deformation and fracture mechanics of vimentin intermediate filaments (IFs, which are hierarchical self-assembled protein networks that provide structure and stability to eukaryotic cells. We compare the fracture and failure mechanisms of biological protein materials (BPMs with those observed in brittle and ductile crystalline materials such as metals or ceramics. Our studies illustrate how atomistic-based multiscale modeling can be employed to provide a first principles based material description of deformation and fracture, linking nano- to macroscales.

  7. Fracture mechanics safety assessment based on mechanics of materials

    Energy Technology Data Exchange (ETDEWEB)

    Roos, E.; Demler, T.; Eisele, U.; Gillot, R. (Stuttgart Univ. (Germany, F.R.). Staatliche Materialpruefungsanstalt)

    1990-01-01

    In order to determine the influence of the test temperature on the fracture mechanics characteristics for static and dynamic initiation, crack growth, and arrest, investigations were carried out on pressure vessel and piping steels of different toughness and strength (22 NiMoCr 37; 15 NiCuMoNb 5; 20 MnMoNi 55; 15 MnNi 63). The selected temperature range allowed both linear-elastic and elastic-plastic material behaviour to be examined. In the regime of linear-elastic fracture mechanics (LEFM) the conservatism of the reference curves of American and German guidelines could be demonstrated. In the upper shelf, where elastic-plastic, fracture mechanics (EPFM) parameters have to be applied, toughness-dependent overestimations of the real material properties result from the application of the reference curves. (orig./MM).

  8. Numerical Modeling and Investigation of Fluid-Driven Fracture Propagation in Reservoirs Based on a Modified Fluid-Mechanically Coupled Model in Two-Dimensional Particle Flow Code

    Directory of Open Access Journals (Sweden)

    Jian Zhou

    2016-09-01

    Full Text Available Hydraulic fracturing is a useful tool for enhancing rock mass permeability for shale gas development, enhanced geothermal systems, and geological carbon sequestration by the high-pressure injection of a fracturing fluid into tight reservoir rocks. Although significant advances have been made in hydraulic fracturing theory, experiments, and numerical modeling, when it comes to the complexity of geological conditions knowledge is still limited. Mechanisms of fluid injection-induced fracture initiation and propagation should be better understood to take full advantage of hydraulic fracturing. This paper presents the development and application of discrete particle modeling based on two-dimensional particle flow code (PFC2D. Firstly, it is shown that the modeled value of the breakdown pressure for the hydraulic fracturing process is approximately equal to analytically calculated values under varied in situ stress conditions. Furthermore, a series of simulations for hydraulic fracturing in competent rock was performed to examine the influence of the in situ stress ratio, fluid injection rate, and fluid viscosity on the borehole pressure history, the geometry of hydraulic fractures, and the pore-pressure field, respectively. It was found that the hydraulic fractures in an isotropic medium always propagate parallel to the orientation of the maximum principal stress. When a high fluid injection rate is used, higher breakdown pressure is needed for fracture propagation and complex geometries of fractures can develop. When a low viscosity fluid is used, fluid can more easily penetrate from the borehole into the surrounding rock, which causes a reduction of the effective stress and leads to a lower breakdown pressure. Moreover, the geometry of the fractures is not particularly sensitive to the fluid viscosity in the approximate isotropic model.

  9. Experimental and finite element analysis of fracture criterion in general yielding fracture mechanics

    Indian Academy of Sciences (India)

    D M Kulkarni; Ravi Prakash; A N Kumar

    2002-12-01

    Efforts made over the last three decades to understand the fracture behaviour of structural materials in elastic and elasto-plastic fracture mechanics are numerous, whereas investigations related to fracture behaviour of materials in thin sheets or general yielding fracture regimes are limited in number. Engineering simulative tests are being used to characterize formability and drawability of sheet metals. However, these tests do not assure consistency in quality of sheet metal products. The prevention of failure in stressed structural components currently requires fracture mechanics based design parameters like critical load, critical crack-tip opening displacement or fracture toughness. The present attempt would aim to fulfill this gap and generate more information thereby increased understanding on fracture behaviour of sheet metals. In the present investigation, using a recently developed technique for determining fracture criteria in sheet metals, results are generated on critical CTOD and fracture toughness. Finite element analysis was performed to support the results on various fracture parameters. The differences are within 1 to 4%. At the end it is concluded that magnitude of critical CTOD and/or critical load can be used as a fracture criterion for thin sheets.

  10. Mechanisms of plastic instability and fracture of compressed and tensile tested Mg-Li alloys investigated using the acoustic emission method

    Directory of Open Access Journals (Sweden)

    A. Pawełek

    2016-01-01

    Full Text Available The results of the investigation of both mechanical and acoustic emission (AE behaviors of Mg4Li5Al alloy subjected to compression and tensile tests at room temperature are compared with the test results obtained using the same alloy and loading scheme but at elevated temperatures. The main aim of the paper is to investigate, to determine and to explain the possible influence of factors related with enhanced internal stresses such as: segregation of precipitates along grain boundaries or solute atoms along dislocations (Cottrell atmospheres or dislocation pile-ups at grain boundaries which create very high stress concentration leading to fracture. The results show that the plastic instabilities are related to the Portevin–Le Châtelier phenomenon (PL effect and they are correlated with the generation of AE peaks. The fractography of breaking samples was analyzed on the basis of light (optical, TEM and SEM images.

  11. Recent trends in fracture and damage mechanics

    CERN Document Server

    Zybell, Lutz

    2016-01-01

    This book covers a wide range of topics in fracture and damage mechanics. It presents historical perspectives as well as recent innovative developments, presented by peer reviewed contributions from internationally acknowledged authors.  The volume deals with the modeling of fracture and damage in smart materials, current industrial applications of fracture mechanics, and it explores advances in fracture testing methods. In addition, readers will discover trends in the field of local approach to fracture and approaches using analytical mechanics. Scholars in the fields of materials science, engineering and computational science will value this volume which is dedicated to Meinhard Kuna on the occasion of his 65th birthday in 2015. This book incorporates the proceedings of an international symposium that was organized to honor Meinhard Kuna’s contributions to the field of theoretical and applied fracture and damage mechanics.

  12. Crack propagation in fracture mechanical graded structures

    Directory of Open Access Journals (Sweden)

    B. Schramm

    2015-10-01

    Full Text Available The focus of manufacturing is more and more on innovative and application-oriented products considering lightweight construction. Hence, especially functional graded materials come to the fore. Due to the application-matched functional material gradation different local demands such as absorbability, abrasion and fatigue of structures are met. However, the material gradation can also have a remarkable influence on the crack propagation behavior. Therefore, this paper examines how the crack propagation behavior changes when a crack grows through regions which are characterized by different fracture mechanical material properties (e.g. different threshold values KI,th, different fracture toughness KIC. In particular, the emphasis of this paper is on the beginning of stable crack propagation, the crack velocity, the crack propagation direction as well as on the occurrence of unstable crack growth under static as well as cyclic loading. In this context, the developed TSSR-concept is presented which allows the prediction of crack propagation in fracture mechanical graded structures considering the loading situation (Mode I, Mode II and plane Mixed Mode and the material gradation. In addition, results of experimental investigations for a mode I loading situation and numerical simulations of crack growth in such graded structures confirm the theoretical findings and clarify the influence of the material gradation on the crack propagation behavior.

  13. Fracture mechanics of piezoelectric and ferroelectric solids

    CERN Document Server

    Fang, Daining

    2013-01-01

    Fracture Mechanics of Piezoelectric and Ferroelectric Solids presents a systematic and comprehensive coverage of the fracture mechanics of piezoelectric/ferroelectric materials, which includes the theoretical analysis, numerical computations and experimental observations. The main emphasis is placed on the mechanics description of various crack problems such static, dynamic and interface fractures as well as the physical explanations for the mechanism of electrically induced fracture. The book is intended for postgraduate students, researchers and engineers in the fields of solid mechanics, applied physics, material science and mechanical engineering. Dr. Daining Fang is a professor at the School of Aerospace, Tsinghua University, China; Dr. Jinxi Liu is a professor at the Department of Engineering Mechanics, Shijiazhuang Railway Institute, China.

  14. Fracture Mechanics Prediction of Fatigue Life of Aluminum Highway Bridges

    DEFF Research Database (Denmark)

    Rom, Søren; Agerskov, Henning

    2015-01-01

    Fracture mechanics prediction of the fatigue life of aluminum highway bridges under random loading is studied. The fatigue life of welded joints has been determined from fracture mechanics analyses and the results obtained have been compared with results from experimental investigations. The fati......Fracture mechanics prediction of the fatigue life of aluminum highway bridges under random loading is studied. The fatigue life of welded joints has been determined from fracture mechanics analyses and the results obtained have been compared with results from experimental investigations...... against fatigue in aluminum bridges, may give results which are unconservative. Furthermore, it was in both investigations found that the validity of the results obtained from Miner's rule will depend on the distribution of the load history in tension and compression....

  15. Numerical Investigation of Fracture Propagation in Geomaterials

    Science.gov (United States)

    Newell, P.; Borowski, E.; Major, J. R.; Eichhubl, P.

    2015-12-01

    Fracture in geomaterials is a critical behavior that affects the long-term structural response of geosystems. The processes involving fracture initiation and growth in rocks often span broad time scales and size scales, contributing to the complexity of these problems. To better understand fracture behavior, the authors propose an initial investigation comparing the fracture testing techniques of notched three-point bending (N3PB), short rod (SR), and double torsion (DT) on geomaterials using computational analysis. Linear softening cohesive fracture modeling (LCFM) was applied using ABAQUS to computationally simulate the three experimental set-ups. By applying material properties obtained experimentally, these simulations are intended to predict single-trace fracture growth. The advantages and limitations of the three testing techniques were considered for application to subcritical fracture propagation taking into account the accuracy of constraints, load applications, and modes of fracture. This work is supported as part of the Geomechanics of CO2 Reservoir Seals, a DOE-NETL funded under Award Number DE-FOA-0001037. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  16. Fracture mechanism of a thermal barrier coating

    Science.gov (United States)

    Samoilenko, V. M.; Ravilov, R. G.; Drevnyak, V. V.; Petrova, M. A.

    2016-06-01

    The fracture mechanism of the thermal barrier coating of gas turbine blades is studied. The causes of the fracture of the ceramic layer are discussed and the possible ways to increase the fatigue life of the thermal barrier coating are considered.

  17. Mechanical Behaviour of Materials Volume II Fracture Mechanics and Damage

    CERN Document Server

    François, Dominique; Zaoui, André

    2013-01-01

    Designing new structural materials, extending lifetimes and guarding against fracture in service are among the preoccupations of engineers, and to deal with these they need to have command of the mechanics of material behaviour. This ought to reflect in the training of students. In this respect, the first volume of this work deals with elastic, elastoplastic, elastoviscoplastic and viscoelastic behaviours; this second volume continues with fracture mechanics and damage, and with contact mechanics, friction and wear. As in Volume I, the treatment links the active mechanisms on the microscopic scale and the laws of macroscopic behaviour. Chapter I is an introduction to the various damage phenomena. Chapter II gives the essential of fracture mechanics. Chapter III is devoted to brittle fracture, chapter IV to ductile fracture and chapter V to the brittle-ductile transition. Chapter VI is a survey of fatigue damage. Chapter VII is devoted to hydogen embrittlement and to environment assisted cracking, chapter VIII...

  18. Fracture Mechanisms in Steel Castings

    Directory of Open Access Journals (Sweden)

    Z. Stradomski

    2013-07-01

    Full Text Available The investigations were inspired with the problem of cracking of steel castings during the production process. A single mechanism of decohesion - the intergranular one - occurs in the case of hot cracking, while a variety of structural factors is decisive for hot cracking initiation, depending on chemical composition of the cast steel. The low-carbon and low-alloyed steel castings crack due to the presence of the type II sulphides, the cause of cracking of the high-carbon tool cast steels is the net of secondary cementite and/or ledeburite precipitated along the boundaries of solidified grains. Also the brittle phosphor and carbide eutectics precipitated in the final stage solidification are responsible for cracking of castings made of Hadfield steel. The examination of mechanical properties at 1050°C revealed low or very low strength of high-carbon cast steels.

  19. The Shear Mechanisms of Natural Fractures during the Hydraulic Stimulation of Shale Gas Reservoirs

    Directory of Open Access Journals (Sweden)

    Zhaobin Zhang

    2016-08-01

    Full Text Available The shearing of natural fractures is important in the permeability enhancement of shale gas reservoirs during hydraulic fracturing treatment. In this work, the shearing mechanisms of natural fractures are analyzed using a newly proposed numerical model based on the displacement discontinuities method. The fluid-rock coupling system of the model is carefully designed to calculate the shearing of fractures. Both a single fracture and a complex fracture network are used to investigate the shear mechanisms. The investigation based on a single fracture shows that the non-ignorable shearing length of a natural fracture could be formed before the natural fracture is filled by pressurized fluid. Therefore, for the hydraulic fracturing treatment of the naturally fractured shale gas reservoirs, the shear strength of shale is generally more important than the tensile strength. The fluid-rock coupling propagation processes of a complex fracture network are simulated under different crustal stress conditions and the results agree well with those of the single fracture. The propagation processes of complex fracture network show that a smaller crustal stress difference is unfavorable to the shearing of natural fractures, but is favorable to the formation of complex fracture network.

  20. Numerical Investigation into the Effect of Natural Fracture Density on Hydraulic Fracture Network Propagation

    Directory of Open Access Journals (Sweden)

    Zhaohui Chong

    2017-07-01

    Full Text Available Hydraulic fracturing is an important method to enhance permeability in oil and gas exploitation projects and weaken hard roofs of coal seams to reduce dynamic disasters, for example, rock burst. It is necessary to fully understand the mechanism of the initiation, propagation, and coalescence of hydraulic fracture network (HFN caused by fluid flow in rock formations. In this study, a coupled hydro-mechanical model was built based on synthetic rock mass (SRM method to investigate the effects of natural fracture (NF density on HFN propagation. Firstly, the geometrical structures of NF obtained from borehole images at the field scale were applied to the model. Secondly, the micro-parameters of the proposed model were validated against the interaction between NF and hydraulic fracture (HF in physical experiments. Finally, a series of numerical simulations were performed to study the mechanism of HFN propagation. In addition, confining pressure ratio (CPR and injection rate were also taken into consideration. The results suggested that the increase of NF density drives the growth of stimulated reservoir volume (SRV, concentration area of injection pressure (CAIP, and the number of cracks caused by NF. The number of tensile cracks caused by rock matrix decrease gradually with the increase of NF density, and the number of shear cracks caused by rock matrix are almost immune to the change of NF density. The propagation orientation of HFN and the breakdown pressure in rock formations are mainly controlled by CPR. Different injection rates would result in a relatively big difference in the gradient of injection pressure, but this difference would be gradually narrowed with the increase of NF density. Natural fracture density is the key factor that influences the percentages of different crack types in HFN, regardless of the value of CPR and injection rate. The proposed model may help predict HFN propagation and optimize fracturing treatment designs in

  1. Validity of parental recall of children’s fracture: implications for investigation of childhood osteoporosis

    Science.gov (United States)

    Moon, Rebecca J; Lim, Adelynn; Farmer, Megan; Segaran, Avinash; Clarke, Nicholas MP; Harvey, Nicholas C; Cooper, Cyrus; Davies, Justin H

    2015-01-01

    Purpose The diagnosis of osteoporosis in children requires either a vertebral compression fracture, or a significant fracture history (defined as ≥2 long bone fractures <10 years or ≥3 long bone fractures <19 years, excluding high impact fractures) and low bone mineral density. As children with frequent fractures might benefit from further evaluation, we determined whether parental reports of lifetime fracture were accurate compared to radiological reports, and if they appropriately selected children for further consideration of osteoporosis. Methods Parents of children (<18 years) with a musculoskeletal injury completed a questionnaire on their child’s fracture history, including age, site and mechanism of previous fracture(s). Radiological reports were reviewed to confirm the fracture. Results 660 parents completed the questionnaire, and reported 276 previous fractures in 207 children. An injury treated at our hospital was recorded in 214 of the 276 parentally reported fractures. 34 of 214 (16%) had not resulted in a confirmed fracture. An injury was recorded for all parentally reported fractures in 150 children, but for 21% children there were inaccurate details (no evidence of fracture, incorrect site or forgotten fractures) on parent report. 18/150 children had a significant fracture history on parental report alone, but following review of radiology reports, 2 of 18 (11%) did not have clinically significant fracture histories. Conclusions Approximately 1 in 6 fractures reported by parents to have occurred in their child’s lifetime had not resulted in a fracture. 1 in 9 children with a significant fracture history could have been investigated unnecessarily. PMID:26286627

  2. Size Effects in Linear Elastic Fracture Mechanics

    Science.gov (United States)

    1988-01-01

    Recent Theoretical and Experimental Developments in Fracture Mechanics", Fracture 1977, 1 (1977) 695-723. 40 S. Mindess and J. S. Nadeau," Effect of Notch...0.4 1.42 b 2.0 0.80 b Mindess and Nadeau [40], 1.0 3.98 0.86 b Mortar, 3PB 8.03 0.80 b 12.0 0.82 b 16.0 0.84 b 20.0 0.83 b Concrete, 3PB 1.0 3.54 1.08

  3. Crack branching in carbon steel. Fracture mechanisms

    Science.gov (United States)

    Syromyatnikova, A. S.; Alekseev, A. A.; Levin, A. I.; Lyglaev, A. V.

    2010-04-01

    The fracture surfaces of pressure vessels made of carbon steel that form during crack branching propagation are examined by fractography. Crack branching is found to occur at a crack velocity higher than a certain critical value V > V c . In this case, the material volume that is involved in fracture and depends on the elastoplastic properties of the material and the sample width has no time to dissipate the energy released upon crack motion via the damage mechanisms intrinsic in the material under given deformation conditions (in our case, via cracking according to intragranular cleavage).

  4. Relating Cohesive Zone Model to Linear Elastic Fracture Mechanics

    Science.gov (United States)

    Wang, John T.

    2010-01-01

    The conditions required for a cohesive zone model (CZM) to predict a failure load of a cracked structure similar to that obtained by a linear elastic fracture mechanics (LEFM) analysis are investigated in this paper. This study clarifies why many different phenomenological cohesive laws can produce similar fracture predictions. Analytical results for five cohesive zone models are obtained, using five different cohesive laws that have the same cohesive work rate (CWR-area under the traction-separation curve) but different maximum tractions. The effect of the maximum traction on the predicted cohesive zone length and the remote applied load at fracture is presented. Similar to the small scale yielding condition for an LEFM analysis to be valid. the cohesive zone length also needs to be much smaller than the crack length. This is a necessary condition for a CZM to obtain a fracture prediction equivalent to an LEFM result.

  5. Fracture mechanics of collagen fibrils

    DEFF Research Database (Denmark)

    Svensson, Rene B; Mulder, Hindrik; Kovanen, Vuokko

    2013-01-01

    Tendons are important load-bearing structures, which are frequently injured in both sports and work. Type I collagen fibrils are the primary components of tendons and carry most of the mechanical loads experienced by the tissue, however, knowledge of how load is transmitted between and within...

  6. INVESTIGATION OF EFFICIENCY IMPROVEMENTS DURING CO2 INJECTION IN HYDRAULICALLY AND NATURALLY FRACTURED RESERVOIRS

    Energy Technology Data Exchange (ETDEWEB)

    David S. Schechter

    2005-04-27

    This report describes the work performed during the fourth year of the project, ''Investigating of Efficiency Improvements during CO{sub 2} Injection in Hydraulically and Naturally Fractured Reservoirs.'' The objective of this project is to perform unique laboratory experiments with artificially fractured cores (AFCs) and X-ray CT scanner to examine the physical mechanisms of bypassing in hydraulically fractured reservoirs (HFR) and naturally fractured reservoirs (NFR) that eventually result in more efficient CO{sub 2} flooding in heterogeneous or fracture-dominated reservoirs. In Chapter 1, we worked with DOE-RMOTC to investigate fracture properties in the Tensleep Formation at Teapot Dome Naval Reserve as part of their CO{sub 2} sequestration project. In Chapter 2, we continue our investigation to determine the primary oil recovery mechanism in a short vertically fractured core. Finally in Chapter 3, we report our numerical modeling efforts to develop compositional simulator with irregular grid blocks.

  7. Fracture mechanics safety assessment based on mechanics of materials. Werkstoffmechanische Grundlagen bruchmechanischer Sicherheitsanalysen

    Energy Technology Data Exchange (ETDEWEB)

    Roos, E.; Demler, T.; Eisele, U.; Gillot, R. (Stuttgart Univ. (Germany). Staatliche Materialpruefungsanstalt)

    1990-01-01

    Investigations are reported of pressure vessel and piping steels (22 NiMoCr 3 7) of various toughness and strength, for determining the influence of the testing temperature on fracture-mechanical characteristics with regard to static and dynamic crack initiation, crack growth and crack stop. The tests have been made in a temperature range where both linear-elastic and elastic-plastic materials behaviour is possible. Within the linear-elastic fracture-mechanical regime, the conservativity of the limiting curves given in American and German technical codes and standards have been confirmed. Within the regime of upper-shelf toughness, where characteristics of elastic-plastic fracture-mechanical behaviour are to be used for analysis, application of the limiting curves given in standards leads to an overassessment of real fracture-mechanical characteristics. (orig./DG).

  8. Investigation of possible wellbore cement failures during hydraulic fracturing operations

    Science.gov (United States)

    Researchers used the peer-reviewed TOUGH+ geomechanics computational software and simulation system to investigate the possibility of fractures and shear failure along vertical wells during hydraulic fracturing operations.

  9. CT for diagnosing fractures of the undersurface of the talus and mechanism of injury

    Energy Technology Data Exchange (ETDEWEB)

    Okamoto, Hideaki; Shibata, Yoshimori; Nishi, Genzaburo; Tago, Kyoji; Tsuchiya, Daiji; Chiba, Takehiro; Okumura, Hisashi [Aichiken Koseiren Kainan Hospital, Yatomi (Japan); Ikeda, Takeshi; Wada, Ikuo

    2000-02-01

    Talus fractures whose fracture lines extend to the subtalar joint, except fractures of the neck and the body of the talus, are defined as fractures of the lower portion of the talus. It is difficult to make a correctly diagnosis of inferior fractures of the talus by plain radiography or tomography alone. The author encountered 12 cases of inferior fractures of the talus between 1989 and 1997, and CT imaging in 2 directions, in the horizontal and frontal plane, was useful in making the diagnosis. The correct diagnosis rate was 100%, and differentiation of the site and extent of the fractures was possible. Based on the CT findings, the fractures were classified into 8 types (fractures of the lateral process of the talus, fractures of the medial tubercle, fractures of the posterior process, and combinations of the above, and comminuted fractures). The mechanism of the injuries was also investigated, and the fractures of the lateral process of the talus seemed to have been caused by excessive eversion force on the ankle joint, with the lateral process becoming trapped between the fibula and the calcaneus. Medial tubercle fractures also seemed to be caused by forcible inversion of the ankle, with the tip of the medial malleous impacting and the medial tubercle being trapped between it and the sustentaculum tali. The comminuted fractures seem to have been caused by axial compression added to various of external forces. (K.H.)

  10. Investigation of fatigue fracture of generator-rotor fan blades

    Energy Technology Data Exchange (ETDEWEB)

    Sameezadeh, Mahmood; Farhangi, Hassan [School of Metallurgy and Materials Engineering, Univ. of Tehran (Iran); Soltani, Nasser [School of Mechanical Engineering, Univ. of Tehran (Iran); Ataei, Peyman [Dept. of Metallurgy and Materials Engineering, South Tehran Branch of Azad Univ., Tehran (Iran)

    2009-11-15

    The failure of a rotating axial flow fan of a 123 MW electric power generator unit is analyzed. The fan was mounted on the generator-rotor at the turbine end. Initial investigations showed that three fan blades had fractured just about 11 h after resuming operation following the last overhaul, causing extensive damage to the unit. The failure of the blades was investigated using fractographic and microstructural characterization techniques as well as mechanical evaluations. Based on fractographic observations high cycle fatigue was identified as the failure mechanism. Formation of multiple primary cracks which coalesced during crack growth to form shallow and semi-elliptical crack geometry was indicative of the influence of additional bending stresses, probably resulting from excessive vibrations. Using fracture mechanics principles, the magnitude of the maximum stress at the time of final fracture of the first broken blade was estimated to be more than 3 times higher than the design operating stress. Furthermore, crack growth lifetime of the blades was evaluated using FRANC3D software. It was found that an operating period of just about one hour was required for small initial cracks to propagate to final failure under the action of excessive bending stresses. (orig.)

  11. Comparative analysis of deterministic and probabilistic fracture mechanical assessment tools

    Energy Technology Data Exchange (ETDEWEB)

    Heckmann, Klaus [Gesellschaft fuer Anlagen- und Reaktorsicherheit (GRS) gGmbH, Koeln (Germany); Saifi, Qais [VTT Technical Research Centre of Finland, Espoo (Finland)

    2016-11-15

    Uncertainties in material properties, manufacturing processes, loading conditions and damage mechanisms complicate the quantification of structural reliability. Probabilistic structure mechanical computing codes serve as tools for assessing leak- and break probabilities of nuclear piping components. Probabilistic fracture mechanical tools were compared in different benchmark activities, usually revealing minor, but systematic discrepancies between results of different codes. In this joint paper, probabilistic fracture mechanical codes are compared. Crack initiation, crack growth and the influence of in-service inspections are analyzed. Example cases for stress corrosion cracking and fatigue in LWR conditions are analyzed. The evolution of annual failure probabilities during simulated operation time is investigated, in order to identify the reasons for differences in the results of different codes. The comparison of the tools is used for further improvements of the codes applied by the partners.

  12. Effects of Silicon on Mechanical Properties and Fracture Toughness of Heavy-Section Ductile Cast Iron

    Directory of Open Access Journals (Sweden)

    Liang Song

    2015-01-01

    Full Text Available The effects of silicon (Si on the mechanical properties and fracture toughness of heavy-section ductile cast iron were investigated to develop material for spent-nuclear-fuel containers. Two castings with different Si contents of 1.78 wt.% and 2.74 wt.% were prepared. Four positions in the castings from the edge to the center, with different solidification cooling rates, were chosen for microstructure observation and mechanical properties’ testing. Results show that the tensile strength, elongation, impact toughness and fracture toughness at different positions of the two castings decrease with the decrease in cooling rate. With an increase in Si content, the graphite morphology and the mechanical properties at the same position deteriorate. Decreasing cooling rate changes the impact fracture morphology from a mixed ductile-brittle fracture to a brittle fracture. The fracture morphology of fracture toughness is changed from ductile to brittle fracture. When the Si content exceeds 1.78 wt.%, the impact and fracture toughness fracture morphology transforms from ductile to brittle fracture. The in-situ scanning electronic microscope (SEM tensile experiments were first used to observe the dynamic tensile process. The influence of the vermicular and temper graphite on fracture formation of heavy section ductile iron was investigated.

  13. Mechanic behavior of unloading fractured rock mass

    Institute of Scientific and Technical Information of China (English)

    YIN Ke; ZHANG Yongxing; WU Hanhui

    2003-01-01

    Under tension and shear conditions related to unloading of rock mass, a jointed rock mass model of linear elastic fracture mechanics is established. According to the model, the equations of stresses, strains and displacements of the region influenced by the crack but relatively faraway the crack (the distance between the research point and the center of the crack is longer than the length of crack) are derived. They are important for evaluating the deformation of cracked rock. It is demonstrated by the comparison between computational results of these theoretical equations and the observed data from unloading test that they are applicable for actual engineering.

  14. Thermal-mechanical coupled effect on fracture mechanism and plastic characteristics of sandstone

    Institute of Scientific and Technical Information of China (English)

    ZUO; JianPing; XIE; HePing; ZHOU; HongWei; PENG; SuPing

    2007-01-01

    Scanning electronic microscopy (SEM) was employed to investigate fractographs of sandstone in mine roof strata under thermal-mechanical coupled effect. Based on the evolution of sandstone surface morphology in the failure process and fractography, the fracture mechanism was studied and classified under meso and micro scales, respectively. The differences between fractographs under different temperatures were examined in detail. Under high temperature, fatigue fracture and plastic deformation occurred in the fracture surface. Therefore, the temperature was manifested by these phenomena to influence strongly on micro failure mechanism of sandstone. In addition, the failure mechanism would transit from brittle failure mechanism at low temperature to coupled brittle-ductile failure mechanism at high temperature. The variation of sandstone strength under different temperature can be attributed to the occurrence of plastic deformation, fatigue fracture, and microcracking. The fatigue striations in the fracture surfaces under high temperature may be interpreted as micro fold. And the coupled effect of temperature and tensile stress may be another formation mechanism of micro fold in geology.

  15. Analogy between fluid cavitation and fracture mechanics

    Science.gov (United States)

    Hendricks, R. C.; Mullen, R. L.; Braun, M. J.

    1983-01-01

    When the stresses imposed on a fluid are sufficiently large, rupture or cavitation can occur. Such conditions can exist in many two-phase flow applications, such as the choked flows, which can occur in seals and bearings. Nonspherical bubbles with large aspect ratios have been observed in fluids under rapid acceleration and high shear fields. These bubbles are geometrically similar to fracture surface patterns (Griffith crack model) existing in solids. Analogies between crack growth in solid and fluid cavitation are proposed and supported by analysis and observation (photographs). Healing phenomena (void condensation), well accepted in fluid mechanics, have been observed in some polymers and hypothesized in solid mechanics. By drawing on the strengths of the theories of solid mechanics and cavitation, a more complete unified theory can be developed.

  16. The effect of multiaxial stress state on creep behavior and fracture mechanism of P92 steel

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Yuan; Xu, Hong, E-mail: xuhong@ncepu.edu.cn; Ni, Yongzhong; Lan, Xiang; Li, Hongyuan

    2015-06-11

    The creep experiments on plain and double U-typed notched specimens were conducted on P92 steel at 650 °C. The notch strengthening effect was found in the notched specimens. Fracture appearance observed by scanning electron microscopy revealed that dimpled fracture for relatively blunt notched specimen, and dimpled fracture doubled with intergranular brittle fracture for relatively sharp notched specimen, which meant that fracture mechanism of P92 steel altered due to the presence of the notch. Meanwhile, based on Norton–Bailey and Kachanov–Robotnov constitutive models, a modified model was proposed. Finite element simulations were carried out to investigate the effect of multiaxial stress state on the creep behavior, fracture mechanism and damage evolvement of P92 steel. The simulation results agreed well with the fracture behaviors observed experimentally.

  17. Development of Numerical Analysis Techniques Based on Damage Mechanics and Fracture Mechanics

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Yoon Suk; Lee, Dock Jin; Choi, Shin Beom; Kim, Sun Hye; Cho, Doo Ho; Lee, Hyun Boo [Sungkyunkwan University, Seoul (Korea, Republic of)

    2010-04-15

    The scatter of measured fracture toughness data and transferability problems among different crack configurations as well as geometry and loading conditions are major obstacles for application of fracture mechanics. To address these issues, recently, concerns on the local approach employing reliable micro-mechanical damage models are being increased again in connection with a progress of computational technology. In the present research, as part of development of fracture mechanical evaluation model for material degradation of reactor pressure boundary, several investigations on fracture behaviors were carried out. Especially, a numerical scheme to determine key parameters consisting both cleavage and ductile fracture estimate models was changed efficiently by incorporating a genetic algorithm. Also, with regard to the well-known master curve, newly reported methods such as bimodal master curve, randomly inhomogeneous master curve and single point estimation were reviewed to deal with homogeneous and inhomogeneous material characteristics. A series of preliminary finite element analyses was conducted to examine the element size effect on micro-mechanical models. Then, a new thickness correction equation was derived from parametric three-dimensional numerical simulations, which was founded on the current test standard, ASTM E1921, but could lead to get more realistic fracture toughness values. As a result, promising modified master curves as well as fracture toughness diagrams to convert data between pre-cracked V-notched and compact tension specimens were generated. Moreover, a user-subroutine in relation to GTN(Gurson-Tvergaard-Needleman) model was made by adopting Hill's 48 yield potential theory. By applying GTN model combined with the subroutine to small punch specimens, the effect of inhomogeneous properties on fracture behaviors of miniature specimens was confirmed. Therefore, it is anticipated that the aforementioned enhanced research results can be

  18. Evaluation of Osteoporosis in Patients with Hip Fracture - Original Investigation

    Directory of Open Access Journals (Sweden)

    Firuzan Altın

    2007-03-01

    Full Text Available Aim: The aim of this study is to determine the state of osteoporosis and treatment in patients with osteoporotic hip fracture. Patients and Methods: 39 patients enrolled in this study that were above 50 years with an atraumatic hip fracture and operated in 1. and 2. Department of Orthopedics and Traumatology. Istanbul Training and Research Hospital, in our study (31 women, 8 men we investigate patients about risk factors of osteoporosis, before and after fracture severity of osteoporosis, treatment of osteoporosis. Patients who are younger than 50 years, and immobilized for long time, have pathological fracture, hip fracture is 2 cm distal than minor trochanter; are taken out from our study. Results: There is not significant difference between type of fracture, age, sex and risk factors. Before fractured 5 patients were diagnosed as osteoporosis and only 4 of them had been using antiresorptive, vitamin D, and calcium preparats. 36 patients that we studied never examined and treated for osteoporosis. All patients participating in study were informed about osteoporosis. Each patient was asked to apply for physical therapy and rehabilitation department with result of lumber and femoral bone mineral density measurement. Conclusion: Patients who had recent osteoporotic fractures must be treated to prevent new fracture. Orthopedic doctors should care osteoporosis and a new fracture risk as a serious important complication of osteoporotic hip fracture. (From the World of Osteoporosis 2007;13:11-4

  19. Mechanical stratigraphic controls on natural fracture spacing and penetration

    Science.gov (United States)

    McGinnis, Ronald N.; Ferrill, David A.; Morris, Alan P.; Smart, Kevin J.; Lehrmann, Daniel

    2017-02-01

    Fine-grained low permeability sedimentary rocks, such as shale and mudrock, have drawn attention as unconventional hydrocarbon reservoirs. Fracturing - both natural and induced - is extremely important for increasing permeability in otherwise low-permeability rock. We analyze natural extension fracture networks within a complete measured outcrop section of the Ernst Member of the Boquillas Formation in Big Bend National Park, west Texas. Results of bed-center, dip-parallel scanline surveys demonstrate nearly identical fracture strikes and slight variation in dip between mudrock, chalk, and limestone beds. Fracture spacing tends to increase proportional to bed thickness in limestone and chalk beds; however, dramatic differences in fracture spacing are observed in mudrock. A direct relationship is observed between fracture spacing/thickness ratio and rock competence. Vertical fracture penetrations measured from the middle of chalk and limestone beds generally extend to and often beyond bed boundaries into the vertically adjacent mudrock beds. In contrast, fractures in the mudrock beds rarely penetrate beyond the bed boundaries into the adjacent carbonate beds. Consequently, natural bed-perpendicular fracture connectivity through the mechanically layered sequence generally is poor. Fracture connectivity strongly influences permeability architecture, and fracture prediction should consider thin bed-scale control on fracture heights and the strong lithologic control on fracture spacing.

  20. Numerical modelling in non linear fracture mechanics

    Directory of Open Access Journals (Sweden)

    Viggo Tvergaard

    2007-07-01

    Full Text Available Some numerical studies of crack propagation are based on using constitutive models that accountfor damage evolution in the material. When a critical damage value has been reached in a materialpoint, it is natural to assume that this point has no more carrying capacity, as is done numerically in the elementvanish technique. In the present review this procedure is illustrated for micromechanically based materialmodels, such as a ductile failure model that accounts for the nucleation and growth of voids to coalescence, and a model for intergranular creep failure with diffusive growth of grain boundary cavities leading to micro-crack formation. The procedure is also illustrated for low cycle fatigue, based on continuum damage mechanics. In addition, the possibility of crack growth predictions for elastic-plastic solids using cohesive zone models to represent the fracture process is discussed.

  1. Mechanical Properties, Damage and Fracture Mechanisms of Bulk Metallic Glass Materials

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The deformation, damage, fracture, plasticity and melting phenomenon induced by shear fracture were investigated and summarized for Zr-, Cu-, Ti- and Mg-based bulk metallic glasses (BMGs) and their composites. The shear fracture angles of these BMG materials often display obvious differences under compression and tension,and follow either the Mohr-Coulomb criterion or the unified tensile fracture criterion. The compressive plasticity of the composites is always higher than the tensile plasticity, leading to a significant inconsistency. The enhanced plasticity of BMG composites containing ductile dendrites compared to monolithic glasses strongly depends on the details of the microstructure of the composites. A deformation and damage mechanism of pseudo-plasticity, related to local cracking, is proposed to explain the inconsistency of plastic deformation under tension and compression. Besides, significant melting on the shear fracture surfaces was observed. It is suggested that melting is a common phenomenon in these materials with high strength and high elastic energy, as it is typical for BMGs and their composites failing under shear fracture. The melting mechanism can be explained by a combined effect of a significant temperature rise in the shear bands and the instantaneous release of the large amount of elastic energy stored in the material.

  2. Water coning mechanism in Tarim fractured sandstone gas reservoirs

    Institute of Scientific and Technical Information of China (English)

    沈伟军; 刘晓华; 李熙喆; 陆家亮

    2015-01-01

    The problem of water coning into the Tarim fractured sandstone gas reservoirs becomes one of the major concerns in terms of productivity, increased operating costs and environmental effects. Water coning is a phenomenon caused by the imbalance between gravity and viscous forces around the completion interval. There are several controllable and uncontrollable parameters influencing this problem. In order to simulate the key parameters affecting the water coning phenomenon, a model was developed to represent a single well with an underlying aquifer using the fractured sandstone gas reservoir data of the A-Well in Dina gas fields. The parametric study was performed by varying six properties individually over a representative range. The results show that matrix permeability, well penetration (especially fracture permeability), vertical-to-horizontal permeability ratio, aquifer size and gas production rate have considerable effect on water coning in the fractured gas reservoirs. Thus, investigation of the effective parameters is necessary to understand the mechanism of water coning phenomenon. Simulation of the problem helps to optimize the conditions in which the breakthrough of water coning is delayed.

  3. Numerical investigation and optimization of multiple fractures in tight gas reservoirs

    Energy Technology Data Exchange (ETDEWEB)

    Hou, M.Z. [Technische Univ. Clausthal, Clausthal-Zellerfeld (Germany). ITE; Energie-Forschungszentrum Niedersachsen, Goslar (Germany); Zhou, L. [Energie-Forschungszentrum Niedersachsen, Goslar (Germany)

    2013-08-01

    The main objective of the project DGMK-680 in phase 2 was to investigate the influence of fractures on each other in a multi-fracture system including their space optimization by using the numerical program FLAC3D with our own developments, which treats all fractures in one 3D geometric model under 3D stress state with fully hydro-mechanical coupling effect. The case study was conducted on a horizontal wellbore at location A, which was stimulated hydraulically with a total of eight transverse fractures in summer 2009. Transverse multiple fractures were simulated using the modified continuum method. In the simulation all fractures were generated in one single model, comprising 22 different rock layers. Each layer was assumed to be homogeneous with regard to its rock and hydromechanical parameters. Thus the influence of the individual fractures on each other can be investigated. The simulation procedure applied, which is a consecutive execution ofa hydraulic and a mechanical computation, is the same for all fractures. The only differences are the primary in-situ stresses, the initial pore pressure, the injection parameters (location, rate, volume, duration), which lead to different patterns of fracture propagations. But there are still some common points, such as irregular patterns of the fracture front, which represents the heterogeneity of the model. All fractures (1 to 8) have their fracture average half-length between 70 m to 115 m, height between 93 m to 114 m and average width between 18 mm to 31 mm. The percentage difference of fracture height for individual fractures is obviously smaller than that of the fracture half-lengths, because the fracture barriers at bottom and top limit the fracture propagation in z-direction. Incomparison with the analytical simulator (FracPro) most results match well. Simulation of multiple fractures at location A, with the newly developed algorithms, shows that individual transverse multiple fractures at distances between 100

  4. Finnie's notes on fracture mechanics fundamental and practical lessons

    CERN Document Server

    Dharan, C K H; Finnie, Iain

    2016-01-01

    This textbook consists primarily of notes by Iain Finnie who taught a popular course on fracture mechanics at the University of California at Berkeley. It presents a comprehensive and detailed exposition of fracture, the fundamentals of fracture mechanics and procedures for the safe design of engineering components made from metal alloys, brittle materials like glasses and ceramics, and composites. Interesting and practical problems are listed at the end of most chapters to give the student practice in applying the theory. A solutions manual is provided to the instructor. The text presents a unified perspective of fracture with a strong fundamental foundation and practical applications. In addition to its role as a text, this reference would be invaluable for the practicing engineer who is involved in the design and evaluation of components that are fracture critical. This book also: Presents details of derivations of the basic equations of fracture mechanics and the historical context of the development of f...

  5. Fracture mechanics of concrete: Will applications start to emerge?

    NARCIS (Netherlands)

    Van Mier, J.G.M.

    1995-01-01

    Fracture mechanics of concrete has developed into an active field of research in the past decades. It promises a rational solution technique to structural problems in reinforced concrete in the limit state. Numerical tools have been developed on the basis of fracture mechanics theories. The question

  6. Polypropylene–rubber blends: 5. Deformation mechanism during fracture

    NARCIS (Netherlands)

    Wal, van der A.; Gaymans, R.J.

    1999-01-01

    The deformation mechanism of polypropylene–EPDM rubber blends during fracture was studied by post-mortem SEM fractography. The deformation mechanism was determined for various blend morphologies and test conditions. Brittle fracture merely gives rise to voids, which are caused by voiding of the rubb

  7. Effect of aging on the fracture mechanics of unsaturated polyester based on recycled PET polymer concrete

    Energy Technology Data Exchange (ETDEWEB)

    Reis, J.M.L., E-mail: jreis@mec.uff.br [Theoretical and Applied Mechanics Laboratory - LMTA, Mechanical Engineering Post Graduate Program - PGMEC, Universidade Federal Fluminense - UFF, Rua Passo da Patria, 156 Bl. E Sala 216, Niteroi, RJ (Brazil)

    2011-03-15

    This research investigates, the fracture mechanics (toughness and energy), at early ages, of polymer concrete made with unsaturated polyester resin as binder. The results indicate that the fracture parameters (toughness and energy) decrease and the brittleness increases with the age of the polymer concrete.

  8. Mechanical and fracture behavior of calcium phosphate cements

    Science.gov (United States)

    Jew, Victoria Chou

    Apatite-based calcium phosphate cements are currently employed to a limited extent in the biomedical and dental fields. They present significant potential for a much broader range of applications, particularly as a bone mineral substitute for fracture fixation. Specifically, hydroxyapatite (HA) is known for its biocompatibility and non-immunogenicity, attributed to its similarity to the mineral phase of natural bone. The advantages of a cement-based HA include injectability, greater resorbability and osteoconductivity compared to sintered HA, and an isothermal cement-forming reaction that avoids necrosis during cement setting. Although apatite cements demonstrate good compressive strength, tensile properties are very weak compared to natural bone. Applications involving normal weight-bearing require better structural integrity than apatite cements currently provide. A more thorough understanding of fracture behavior can elucidate failure mechanisms and is essential for the design of targeted strengthening methods. This study investigated a hydroxyapatite cement using a fracture mechanics approach, focusing on subcritical crack growth properties. Subcritical crack growth can lead to much lower load-bearing ability than critical strength values predict. Experiments show that HA cement is susceptible to crack growth under both cyclic fatigue-crack growth and stress corrosion cracking conditions, but only environmental, not mechanical, mechanisms contribute to crack extension. This appears to be the first evidence ever presented of stress corrosion crack growth behavior in calcium phosphate cements. Stress corrosion cracking was examined for a range of environmental conditions. Variations in pH have surprisingly little effect. Behavior in water at elevated temperature (50°C) is altered compared to water at ambient temperature (22°C), but only for crack-growth velocities below 10-7 m/s. However, fracture resistance of dried HA cement in air increases significantly

  9. Fluid driven fracture mechanics in highly anisotropic shale: a laboratory study with application to hydraulic fracturing

    Science.gov (United States)

    Gehne, Stephan; Benson, Philip; Koor, Nick; Enfield, Mark

    2017-04-01

    The finding of considerable volumes of hydrocarbon resources within tight sedimentary rock formations in the UK led to focused attention on the fundamental fracture properties of low permeability rock types and hydraulic fracturing. Despite much research in these fields, there remains a scarcity of available experimental data concerning the fracture mechanics of fluid driven fracturing and the fracture properties of anisotropic, low permeability rock types. In this study, hydraulic fracturing is simulated in a controlled laboratory environment to track fracture nucleation (location) and propagation (velocity) in space and time and assess how environmental factors and rock properties influence the fracture process and the developing fracture network. Here we report data on employing fluid overpressure to generate a permeable network of micro tensile fractures in a highly anisotropic shale ( 50% P-wave velocity anisotropy). Experiments are carried out in a triaxial deformation apparatus using cylindrical samples. The bedding planes are orientated either parallel or normal to the major principal stress direction (σ1). A newly developed technique, using a steel guide arrangement to direct pressurised fluid into a sealed section of an axially drilled conduit, allows the pore fluid to contact the rock directly and to initiate tensile fractures from the pre-defined zone inside the sample. Acoustic Emission location is used to record and map the nucleation and development of the micro-fracture network. Indirect tensile strength measurements at atmospheric pressure show a high tensile strength anisotropy ( 60%) of the shale. Depending on the relative bedding orientation within the stress field, we find that fluid induced fractures in the sample propagate in two of the three principal fracture orientations: Divider and Short-Transverse. The fracture progresses parallel to the bedding plane (Short-Transverse orientation) if the bedding plane is aligned (parallel) with the

  10. Complexity: a new paradigm for fracture mechanics

    Directory of Open Access Journals (Sweden)

    S. Puzzi

    2009-10-01

    Full Text Available The so-called Complexity Sciences are a topic of fast growing interest inside the scientific community. Actually, researchers did not come to a definition of complexity, since it manifests itself in so many different ways [1]. This field itself is not a single discipline, but rather a heterogeneous amalgam of different techniques of mathematics and science. In fact, under the label of Complexity Sciences we comprehend a large variety of approaches: nonlinear dynamics, deterministic chaos theory, nonequilibrium thermodynamics, fractal geometry, intermediate asymptotics, complete and incomplete similarity, renormalization group theory, catastrophe theory, self-organized criticality, neural networks, cellular automata, fuzzy logic, etc. Aim of this paper is at providing insight into the role of complexity in the field of Materials Science and Fracture Mechanics [2-3]. The presented examples will be concerned with the snap-back instabilities in the structural behaviour of composite structures (Carpinteri [4-6], the occurrence of fractal patterns and selfsimilarity in material damage and deformation of heterogeneous materials, and the apparent scaling on the nominal mechanical properties of disordered materials (Carpinteri [7,8]. Further examples will deal with criticality in the acoustic emissions of damaged structures and with scaling in the time-to-failure (Carpinteri et al. [9]. Eventually, results on the transition towards chaos in the dynamics of cracked beams will be reported (Carpinteri and Pugno [10,11].

  11. Fracture mechanics analyses of the slip-side joggle regions of wing-leading-edge panels

    Directory of Open Access Journals (Sweden)

    Kyongchan Song

    2011-01-01

    Full Text Available The Space Shuttle wing-leading edge consists of panels that are made of reinforced carbon-carbon. Coating spallation was observed near the slip-side region of the panels that experience extreme heating. To understand this phenomenon, a root-cause investigation was conducted. As part of that investigation, fracture mechanics analyses of the slip-side joggle regions of the hot panels were conducted. This paper presents an overview of the fracture mechanics analyses.

  12. Fracture Mechanics Analyses of the Slip-Side Joggle Regions of Wing-Leading-Edge Panels

    Science.gov (United States)

    Raju, Ivatury S.; Knight, Norman F., Jr.; Song, Kyongchan; Phillips, Dawn R.

    2011-01-01

    The Space Shuttle wing-leading edge consists of panels that are made of reinforced carbon-carbon. Coating spallation was observed near the slip-side region of the panels that experience extreme heating. To understand this phenomenon, a root-cause investigation was conducted. As part of that investigation, fracture mechanics analyses of the slip-side joggle regions of the hot panels were conducted. This paper presents an overview of the fracture mechanics analyses.

  13. INVESTIGATION OF EFFICIENCY IMPROVEMENTS DURING CO2 INJECTION IN HYDRAULICALLY AND NATURALLY FRACTURED RESERVOIRS

    Energy Technology Data Exchange (ETDEWEB)

    David S. Schechter

    2003-10-01

    This report describes the work performed during the second year of the project, ''Investigating of Efficiency Improvements during CO{sub 2} Injection in Hydraulically and Naturally Fractured Reservoirs.'' The objective of this project is to perform unique laboratory experiments with artificial fractured cores (AFCs) and X-ray CT to examine the physical mechanisms of bypassing in HFR and NFR that eventually result in less efficient CO{sub 2} flooding in heterogeneous or fracture-dominated reservoirs. To achieve this objective, in this period we concentrated our effort on modeling the fluid flow in fracture surface, examining the fluid transfer mechanisms and describing the fracture aperture distribution under different overburden pressure using X-ray CT scanner.

  14. INVESTIGATION OF EFFICIENCY IMPROVEMENTS DURING CO2 INJECTION IN HYDRAULICALLY AND NATURALLY FRACTURED RESERVOIRS

    Energy Technology Data Exchange (ETDEWEB)

    David S. Schechter

    2004-04-26

    This report describes the work performed during the second year of the project, ''Investigating of Efficiency Improvements during CO{sub 2} Injection in Hydraulically and Naturally Fractured Reservoirs.'' The objective of this project is to perform unique laboratory experiments with artificial fractured cores (AFCs) and X-ray CT to examine the physical mechanisms of bypassing in HFR and NFR that eventually result in less efficient CO{sub 2} flooding in heterogeneous or fracture-dominated reservoirs. To achieve this objective, in this period we concentrated our effort on investigating the effect of CO{sub 2} injection rates in homogeneous and fractured cores on oil recovery and a strategy to mitigate CO{sub 2} bypassing in a fractured core.

  15. Cell wall swelling, fracture mode, and the mechanical properties of cherry fruit skins are closely related.

    Science.gov (United States)

    Brüggenwirth, Martin; Knoche, Moritz

    2017-04-01

    Cell wall swelling, fracture mode (along the middle lamellae vs. across cell walls), stiffness, and pressure at fracture of the sweet cherry fruit skin are closely related. Skin cracking is a common phenomenon in many crops bearing fleshy fruit. The objectives were to investigate relationships between the mode of fracture, the extent of cell wall swelling, and the mechanical properties of the fruit skin using sweet cherry (Prunus avium) as a model. Cracking was induced by incubating whole fruit in deionised water or by fracturing exocarp segments (ESs) in biaxial tensile tests. The fracture mode of epidermal cells was investigated by light microscopy. In biaxial tensile tests, the anticlinal cell walls of the ES fractured predominantly across the cell walls (rather than along) and showed no cell wall swelling. In contrast, fruit incubated in water fractured predominantly along the anticlinal epidermal cell walls and the cell walls were swollen. Swelling of cell walls also occurred when ESs were incubated in malic acid, in hypertonic solutions of sucrose, or in water. Compared to the untreated controls, these treatments resulted in more frequent fractures along the cell walls, lower pressures at fracture (p fracture), and lower moduli of elasticity (E, i.e., less stiff). Conversely, compared to the untreated controls, incubating the ES in CaCl2 and in high concentrations of ethanol resulted in thinner cell walls, in less frequent fractures along the cell walls, higher E and p fracture. Our study demonstrates that fracture mode, stiffness, and pressure at fracture are closely related to cell wall swelling. A number of other factors, including cultivar, ripening stage, turgor, CaCl2, and malic acid, exert their effects only indirectly, i.e., by affecting cell wall swelling.

  16. Tribological Aspects of Cast Iron Investigated Via Fracture Toughness

    Directory of Open Access Journals (Sweden)

    C. Fragassa

    2016-03-01

    Full Text Available Linear-elastic plane-strain fracture toughness of metallic materials is a method which covers the determination of the strain fracture toughness (KIC of metallic materials by increasing-force test of fatigue precracked specimens. This method has been applied for investigating the fracture behaviour of cast iron. Two groups of cast alloys, Compacted Graphite Iron (CGI and Spheroidal Graphite Iron (SGI have been investigated. While SGI benefits of a wide scientific literature, CGI is a relatively unknown material despite of its large potentialities in industrial applications.

  17. Investigation of the plastic fracture of high strength steels

    Science.gov (United States)

    Cox, T. B.; Low, J. R., Jr.

    1972-01-01

    This investigation deals in detail with the three recognized stages of plastic fracture in high strength steels, namely, void initiation, void growth, and void coalescence. The particular steels under investigation include plates from both commercial purity and high purity heats of AISI 4340 and 18 Ni, 200 grade maraging steels. A scanning electron microscope equipped with an X-ray energy dispersive analyzer, together with observations made using light microscopy, revealed methods of improving the resistance of high strength steels to plastic fracture.

  18. Studies investigate effects of hydraulic fracturing

    Science.gov (United States)

    Balcerak, Ernie

    2012-11-01

    The use of hydraulic fracturing, also known as fracking, to enhance the retrieval of natural gas from shale has been increasing dramatically—the number of natural gas wells rose about 50% since 2000. Shale gas has been hailed as a relatively low-cost, abundant energy source that is cleaner than coal. However, fracking involves injecting large volumes of water, sand, and chemicals into deep shale gas reservoirs under high pressure to open fractures through which the gas can travel, and the process has generated much controversy. The popular press, advocacy organizations, and the documentary film Gasland by Josh Fox have helped bring this issue to a broad audience. Many have suggested that fracking has resulted in contaminated drinking water supplies, enhanced seismic activity, demands for large quantities of water that compete with other uses, and challenges in managing large volumes of resulting wastewater. As demand for expanded domestic energy production intensifies, there is potential for substantially increased use of fracking together with other recovery techniques for "unconventional gas resources," like extended horizontal drilling.

  19. Fracture mechanics solution of confined water progressive intrusion height of mining fracture floor

    Institute of Scientific and Technical Information of China (English)

    Lu Haifeng; Yao Duoxi; Shen Dan; Cao Jiyang

    2015-01-01

    In order to obtain the value of confined water progressive intrusion height of mining fracture floor, the analysis equation was deduced based on the fracture extension theory of the fracture mechanics. Further-more, the influence of some parameters (e.g., advancing distance of working face, water pressure, initial fracture length and its angle) on confined water progressive intrusion height were analyzed. The results indicate that tension-shearing fracture of floor is extended more easily than compression-shearing frac-ture under the same conditions. When floor fracture dip angle is less than 90?, tension-shearing extension occurs more easily on the left edge of the goaf. If fracture dip angle is larger than 90?, it occurs more easily on the right edge of the goaf. The longer the advancing distance of working face is, the greater initial frac-ture length goes; or the larger water pressure is, the greater possibility of tension-shearing extension occurs. The confined water progressive intrusion height reaches the maximum on the edge of the goaf. Field in situ test is consistent with the theoretical analysis result.

  20. Fracture mechanics and statistical mechanics of reinforced elastomeric blends

    CERN Document Server

    Heinrich, Gert; Kaliske, Michael; Klüppel, Manfred; Schneider, Konrad; Vilgis, Thomas

    2013-01-01

    Elastomers are found in many applications ranging from technology to daily life applications for example in tires, drive systems, sealings and print rollers. Dynamical operation conditions put extremely high demands on the performance and stability of these materials and their elastic and flow properties can be easily adjusted by simple manipulations on their elastic and viscous properties. However, the required service life suffers often from material damage as a result of wear processes such as abrasion and wear fatigue, mostly caused by crack formation and propagation. This book covers interdisciplinary research between physics, physical chemistry, material sciences and engineering of elastomers within the range from nanometres to millimetres and connects these aspects with the constitutive material properties. The different chapters describe reliable lifetime and durability predictions based on new fracture mechanical testing concepts and advanced material-theoretical methods which are finally implemented...

  1. Nonlinear Fracture Mechanics and Plasticity of the Split Cylinder Test

    DEFF Research Database (Denmark)

    Olesen, John Forbes; Østergaard, Lennart; Stang, Henrik

    2006-01-01

    demonstrates the influence of varying geometry or constitutive properties. For a split cylinder test in load control it is shown how the ultimate load is either plasticity dominated or fracture mechanics dominated. The transition between the two modes is related to changes in geometry or constitutive......The split cylinder testis subjected to an analysis combining nonlinear fracture mechanics and plasticity. The fictitious crack model is applied for the analysis of splitting tensile fracture, and the Mohr-Coulomb yield criterion is adopted for modelling the compressive crushing/sliding failure. Two...

  2. Morphology Evolution on the Fracture Surface and Fracture Mechanisms of Multiphase Nanostructured ZrCu-Base Alloys

    Directory of Open Access Journals (Sweden)

    Feng Qiu

    2017-03-01

    Full Text Available A multiphase nanostructured ZrCu-base bulk alloy which showed a unique microstructure consisting of sub-micrometer scale Zr2Cu solid solution, nano-sized twinned plate-like ZrCu martensite (ZrCu (M, and retained ZrCu (B2 austenite was fabricated by copper mold casting. The observation of periodic morphology evolution on the fracture surface of the multiphase nanostructured ZrCu-base alloys has been reported, which suggested a fluctuant local stress intensity along the crack propagation. It is necessary to investigate the compressive deformation behavior and the fracture mechanism of the multiphase alloy and the relation to the unique microstructures. The results obtained in this study provide a better understanding of the deformation and fracture mechanisms of multiphase hybrid nanostructured ZrCu-based alloys and give guidance on how to improve the ductility/toughness of bulk ZrCu-based alloys.

  3. Fracture mechanics parameters of multilayer pipes

    Directory of Open Access Journals (Sweden)

    Šestáková L.

    2007-10-01

    Full Text Available Multilayer pipes consisting of different materials are frequently used in praxis because of partial improvement of the properties of pipe systems. To estimate lifetime of these pipes the basic fracture parameters have to be determined. In this work finite element calculations are applied in order to estimate the stress intensity factor K and T-stress values for a new type of non-homogenous C-shape specimen. The application of calculated K and T values to laboratory estimation of fracture toughness and its transferability to real pipe system is discussed.

  4. Fracture mechanics of piezoelectric solids with interface cracks

    CERN Document Server

    Govorukha, Volodymyr; Loboda, Volodymyr; Lapusta, Yuri

    2017-01-01

    This book provides a comprehensive study of cracks situated at the interface of two piezoelectric materials. It discusses different electric boundary conditions along the crack faces, in particular the cases of electrically permeable, impermeable, partially permeable, and conducting cracks. The book also elaborates on a new technique for the determination of electromechanical fields at the tips of interface cracks in finite sized piezoceramic bodies of arbitrary shape under different load types. It solves scientific problems of solid mechanics in connection with the investigation of electromechanical fields in piezoceramic bodies with interface cracks, and develops calculation models and solution methods for plane fracture mechanical problems for piecewise homogeneous piezoceramic bodies with cracks at the interfaces. It discusses the “open” crack model, which leads to a physically unrealistic oscillating singularity at the crack tips, and the contact zone model for in-plane straight interface cracks betw...

  5. In Vitro Fracture of Human Cortical Bone: Local Fracture Criteria and Toughening Mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Nalla, R; Stolken, J; Kinney, J; Ritchie, R

    2004-08-18

    A micro-mechanistic understanding of bone fracture that encompasses how cracks interact with the underlying microstructure and defines their local failure mode is lacking, despite extensive research on the response of bone to a variety of factors like aging, loading, and/or disease. Micro-mechanical models for fracture incorporating such local failure criteria have been widely developed for metallic and ceramic materials systems; however, few such deliberations have been undertaken for the fracture of bone. In fact, although the fracture event in mineralized tissues such as bone is commonly believed to be locally strain controlled, until recently there has been little experimental evidence to support this widely held belief. In the present study, a series of in vitro experiments involving a double-notch bend test geometry are performed in order to shed further light on the nature of the local cracking events that precede catastrophic fracture in bone and to define their relationship to the microstructure. Specifically, crack-microstructure interactions are examined to determine the salient toughening mechanisms in human cortical bone and to characterize how these may affect the anisotropy in fracture properties. Based on preliminary micro-mechanical models of these processes, in particular crack deflection and uncracked ligament bridging, the relative importance of these toughening mechanisms is established.

  6. Novel perfused compression bioreactor system as an in vitro model to investigate fracture healing

    Directory of Open Access Journals (Sweden)

    Waldemar eHoffmann

    2015-02-01

    Full Text Available Secondary bone fracture healing is a physiological process that leads to functional tissue regeneration via endochondral bone formation. In vivo studies have demonstrated that early mobilization and the application of mechanical loads enhances the process of fracture healing. However, the influence of specific mechanical stimuli and particular effects during specific phases of fracture healing remain to be elucidated. In this work, we have developed and provided proof-of-concept of an in vitro human organotypic model of physiological loading of a cartilage callus, based on a novel perfused compression bioreactor system (PCB. We then used the fracture callus model to investigate the regulatory role of dynamic mechanical loading. Our findings provide a proof-of-principle that dynamic mechanical loading applied by the PCB can enhance the maturation process of mesenchymal stromal cells towards late hypertrophic chondrocytes and the mineralization of the deposited extracellular matrix. The PCB provides a promising tool to study fracture healing and for the in vitro assessment of alternative fracture treatments based on engineered tissue grafts or pharmaceutical compounds, allowing for the reduction of animal experiments.

  7. Colloid retention mechanisms in single, saturated, variable-aperture fractures.

    Science.gov (United States)

    Rodrigues, S N; Dickson, S E; Qu, J

    2013-01-01

    The characterization of fractured aquifers is commonly limited to the methodologies developed for unconsolidated porous media aquifers, which results in many uncertainties. Recent work indicates that fractured rocks remove more particulates than they are conventionally credited for. This research was designed to quantify the number of Escherichia coli RS2-GFP retained in single, saturated, variable-aperture fractures extracted from the natural environment. Conservative solute and E. coli RS2-GFP tracer experiments were used to elucidate the relationships between dominant retention mechanisms, aperture field characteristics, and flow rate. A non-destructive method of determining a surrogate measure of a coefficient of variation (COV(S)) for each fracture was used to better understand the transport behaviour of E. coli RS2-GFP. The results from this research all point to the importance of aperture field characterization in understanding the fate and transport of contaminants in fractured aquifers. The mean aperture was a very important characteristic in determining particulate recovery, so were matrix properties, COV(s), and flow rate. It was also determined that attachment is a much more significant retention mechanism than straining under the conditions employed in this research. Finally, it was demonstrated that the dominant retention mechanism in a fracture varies depending on the specific discharge. An improved understanding of the mechanisms that influence the fate and transport of contaminants through fractures will lead to the development of better tools and methodologies for the characterization of fractured aquifers, as well as the ability to manipulate the relevant mechanisms to increase or decrease retention, depending on the application.

  8. THE INVESTIGATION OF FRACTURE PROPERTIES OF SISAL TEXTILE REINFORCED POLYMERS

    Institute of Scientific and Technical Information of China (English)

    LiYan

    2004-01-01

    Sisal fibre is a kind of natural fibre which possesses high specific strength and modulus, low price, recycalability, easy availability in some countries. Using sisal fibre as reinforcement to make sisal fibre reinforced polymer composites has aroused great interest of materials scientists and engineers all over the world. Many researches have been done in recent years which include the study of mechanical properties of the composites, finding an efficient way to improve the interfacial bonding properties between sisal fibre and polymeric matrices and fibre surface treatment on the mechanical performance of the composites. Though many researches on sisal fibre reinforced composites have been done so far, none deals with the fracture properties of this novel composite which is crucial for the actual application of this material. In this research, Charpy impact test and compact tension test were employed to study the fracture toughness of sisal fibre reinforced vinyl ester and epoxy composites. The effect of fibre surface treatment on the fracture properties of these composites by permanganate and silane was evaluated. The initiation and propagation of the crack were observed with optical microscopy (OM). The fracture morphologies revealed by OM explains the fracture phenomenon of sisal fibre reinforced composites.

  9. Clastic patterned ground in Lomonosov crater, Mars: examining fracture controlled formation mechanisms

    Science.gov (United States)

    Barrett, Alexander M.; Balme, Matthew R.; Patel, Manish R.; Hagermann, Axel

    2017-10-01

    The area surrounding Lomonosov crater on Mars has a high density of seemingly organised boulder patterns. These form seemingly sorted polygons and stripes within kilometre scale blockfields, patches of boulder strewn ground which are common across the Martian high latitudes. Several hypotheses have been suggested to explain the formation of clastic patterned ground on Mars. It has been proposed that these structures could have formed through freeze-thaw sorting, or conversely by the interaction of boulders with underlying fracture polygons. In this investigation a series of sites were examined to evaluate whether boulder patterns appear to be controlled by the distribution of underlying fractures and test the fracture control hypotheses for their formation. It was decided to focus on this suite of mechanisms as they are characterised by a clear morphological relationship, namely the presence of an underlying fracture network which can easily be evaluated over a large area. It was found that in the majority of examples at these sites did not exhibit fracture control. Although fractures were present at many sites there were very few sites where the fracture network appeared to be controlling the boulder distribution. In general these were not the sites with the best examples of organization, suggesting that the fracture control mechanisms are not the dominant geomorphic process organising the boulders in this area.

  10. Interaction of hydraulic and buckling mechanisms in blowout fractures.

    Science.gov (United States)

    Nagasao, Tomohisa; Miyamoto, Junpei; Jiang, Hua; Tamaki, Tamotsu; Kaneko, Tsuyoshi

    2010-04-01

    The etiology of blowout fractures is generally attributed to 2 mechanisms--increase in the pressure of the orbital contents (the hydraulic mechanism) and direct transmission of impacts on the orbital walls (the buckling mechanism). The present study aims to elucidate whether or not an interaction exists between these 2 mechanisms. We performed a simulation experiment using 10 Computer-Aided-Design skull models. We applied destructive energy to the orbits of the 10 models in 3 different ways. First, to simulate pure hydraulic mechanism, energy was applied solely on the internal walls of the orbit. Second, to simulate pure buckling mechanism, energy was applied solely on the inferior rim of the orbit. Third, to simulate the combined effect of the hydraulic and buckling mechanisms, energy was applied both on the internal wall of the orbit and inferior rim of the orbit. After applying the energy, we calculated the areas of the regions where fracture occurred in the models. Thereafter, we compared the areas among the 3 energy application patterns. When the hydraulic and buckling mechanisms work simultaneously, fracture occurs on wider areas of the orbital walls than when each of these mechanisms works separately. The hydraulic and buckling mechanisms interact, enhancing each other's effect. This information should be taken into consideration when we examine patients in whom blowout fracture is suspected.

  11. Mode Ⅱ fracture mechanism of direct shearing specimen with guiding grooves of rock

    Institute of Scientific and Technical Information of China (English)

    饶秋华; 孙宗颀; 王桂尧; 徐纪成; 张静宜

    2001-01-01

    Fracture mechanism of direct shear specimen with guiding grooves of rock was investigated experimentally and numerically in order to explore a favorable stress condition for creating Mode Ⅱ fracture and guide design of specimen configuration for determining Mode Ⅱ fracture toughness of rock, KⅡC. The experimental and numerical results demonstrate that Mode Ⅱ fracture can be successfully achieved in the direct shearing specimen with guiding groove because the guiding grooves added in the notch plane can generate a favorable stress condition for Mode Ⅱ fracture, i.e. tensile stress at the notch tip is completely depressed and shear stress at the notch tip is very high in the notch plane. The optimum design of the specimen configuration for KⅡC testing should aim to reduce tensile stress to be compressive stress or be lower than tensile strength and greatly increase shear stress at crack tip.

  12. Modeling elastic tensile fractures in snow using nonlocal damage mechanics

    Science.gov (United States)

    Borstad, C. P.; McClung, D. M.

    2011-12-01

    The initiation and propagation of tensile fractures in snow and ice are fundamental to numerous important physical processes in the cryosphere, from iceberg calving to ice shelf rift propagation to slab avalanche release. The heterogeneous nature of snow and ice, their proximity to the melting temperature, and the varied governing timescales typically lead to nonlinear fracture behavior which does not follow the predictions of Linear Elastic Fracture Mechanics (LEFM). Furthermore, traditional fracture mechanics is formally inapplicable for predicting crack initiation in the absence of a pre-existing flaw or stress concentration. An alternative to fracture mechanics is continuum damage mechanics, which accounts for the material degradation associated with cracking in a numerically efficient framework. However, damage models which are formulated locally (e.g. stress and strain are defined as point properties) suffer from mesh-sensitive crack trajectories, spurious localization of damage and improper fracture energy dissipation with mesh refinement. Nonlocal formulations of damage, which smear the effects of the material heterogeneity over an intrinsic length scale related to the material microstructure, overcome these difficulties and lead to numerically efficient and mesh-objective simulations of the tensile failure of heterogeneous materials. We present the results of numerical simulations of tensile fracture initiation and propagation in cohesive snow using a nonlocal damage model. Seventeen beam bending experiments, both notched and unnotched, were conducted using blocks of cohesive dry snow extracted from an alpine snowpack. Material properties and fracture parameters were calculated from the experimental data using beam theory and quasi-brittle fracture mechanics. Using these parameters, a nonlocal isotropic damage model was applied to two-dimensional finite element meshes of the same scale as the experiments. The model was capable of simulating the propagation

  13. Toughness of carbon nanotubes conforms to classic fracture mechanics.

    Science.gov (United States)

    Yang, Lin; Greenfeld, Israel; Wagner, H Daniel

    2016-02-01

    Defects in crystalline structure are commonly believed to degrade the ideal strength of carbon nanotubes. However, the fracture mechanisms induced by such defects, as well as the validity of solid mechanics theories at the nanoscale, are still under debate. We show that the fracture toughness of single-walled nanotubes (SWNTs) conforms to the classic theory of fracture mechanics, even for the smallest possible vacancy defect (~2 Å). By simulating tension of SWNTs containing common types of defects, we demonstrate how stress concentration at the defect boundary leads to brittle (unstable) fracturing at a relatively low strain, degrading the ideal strength of SWNTs by up to 60%. We find that, owing to the SWNT's truss-like structure, defects at this scale are not sharp and stress concentrations are finite and low. Moreover, stress concentration, a geometric property at the macroscale, is interrelated with the SWNT fracture toughness, a material property. The resulting SWNT fracture toughness is 2.7 MPa m(0.5), typical of moderately brittle materials and applicable also to graphene.

  14. Theoretical Analysis of the Mechanism of Fracture Network Propagation with Stimulated Reservoir Volume (SRV Fracturing in Tight Oil Reservoirs.

    Directory of Open Access Journals (Sweden)

    Yuliang Su

    Full Text Available Stimulated reservoir volume (SRV fracturing in tight oil reservoirs often induces complex fracture-network growth, which has a fundamentally different formation mechanism from traditional planar bi-winged fracturing. To reveal the mechanism of fracture network propagation, this paper employs a modified displacement discontinuity method (DDM, mechanical mechanism analysis and initiation and propagation criteria for the theoretical model of fracture network propagation and its derivation. A reasonable solution of the theoretical model for a tight oil reservoir is obtained and verified by a numerical discrete method. Through theoretical calculation and computer programming, the variation rules of formation stress fields, hydraulic fracture propagation patterns (FPP and branch fracture propagation angles and pressures are analyzed. The results show that during the process of fracture propagation, the initial orientation of the principal stress deflects, and the stress fields at the fracture tips change dramatically in the region surrounding the fracture. Whether the ideal fracture network can be produced depends on the geological conditions and on the engineering treatments. This study has both theoretical significance and practical application value by contributing to a better understanding of fracture network propagation mechanisms in unconventional oil/gas reservoirs and to the improvement of the science and design efficiency of reservoir fracturing.

  15. Theoretical Analysis of the Mechanism of Fracture Network Propagation with Stimulated Reservoir Volume (SRV) Fracturing in Tight Oil Reservoirs.

    Science.gov (United States)

    Su, Yuliang; Ren, Long; Meng, Fankun; Xu, Chen; Wang, Wendong

    2015-01-01

    Stimulated reservoir volume (SRV) fracturing in tight oil reservoirs often induces complex fracture-network growth, which has a fundamentally different formation mechanism from traditional planar bi-winged fracturing. To reveal the mechanism of fracture network propagation, this paper employs a modified displacement discontinuity method (DDM), mechanical mechanism analysis and initiation and propagation criteria for the theoretical model of fracture network propagation and its derivation. A reasonable solution of the theoretical model for a tight oil reservoir is obtained and verified by a numerical discrete method. Through theoretical calculation and computer programming, the variation rules of formation stress fields, hydraulic fracture propagation patterns (FPP) and branch fracture propagation angles and pressures are analyzed. The results show that during the process of fracture propagation, the initial orientation of the principal stress deflects, and the stress fields at the fracture tips change dramatically in the region surrounding the fracture. Whether the ideal fracture network can be produced depends on the geological conditions and on the engineering treatments. This study has both theoretical significance and practical application value by contributing to a better understanding of fracture network propagation mechanisms in unconventional oil/gas reservoirs and to the improvement of the science and design efficiency of reservoir fracturing.

  16. The hydro-mechanical modeling of the fractured media; Modelisation hydromecanique des milieux fractures

    Energy Technology Data Exchange (ETDEWEB)

    Kadiri, I

    2002-10-15

    The hydro-mechanical modeling of the fractured media is quite complex. Simplifications are necessary for the modeling of such media, but, not always justified, Only permeable fractures are often considered. The rest of the network is approximated by an equivalent continuous medium. Even if we suppose that this approach is validated, the hydraulic and mechanical properties of the fractures and of the continuous medium are seldom known. Calibrations are necessary for the determination of these properties. Until now, one does not know very well the nature of measurements which must be carried out in order to carry on a modeling in discontinuous medium, nor elements of enough robust validation for this kind of modeling. For a better understanding of the hydro-mechanical phenomena in fractured media, two different sites have been selected for the work. The first is the site of Grimsel in Switzerland in which an underground laboratory is located at approximately 400 m of depth. The FEBEX experiment aims at the in-situ study of the consecutive phenomena due to the installation of a heat source representative of radioactive waste in the last 17 meters of the FEBEX tunnel in the laboratory of Grimsel. Only, the modeling of the hydro-mechanical of the excavation was model. The modeling of the Febex enabled us to establish a methodology of calibration of the hydraulic properties in the discontinuous media. However, this kind of study on such complex sites does not make possible to answer all the questions which arise on the hydro-mechanical behavior of the fractured media. We thus carried out modeling on an other site, smaller than the fist one and more accessible. The experimental site of Coaraze, in the Maritime Alps, is mainly constituted of limestone and fractures. Then the variation of water pressure along fractures is governed by the opening/closure sequence of a water gate. Normal displacement as well as the pore pressure along these fractures are recorded, and then

  17. Tensile Fracture Mechanism of Claviform Hybrid Composite Rebar

    Institute of Scientific and Technical Information of China (English)

    CAI Lurong; ZENG Qingdun; WANG Ronghui

    2012-01-01

    Based on the shear-lag theory,a hexagonal model of fiber bundles was established to study the tensile fracture mechanism of a claviform hybrid composite rebar.Firstly,the stress redistributions are investigated on two conditions:one condition is that interfacial damage is taken into accotmt and the other is not.Then,a micro-statistical analysis of the multiple tensile failures of the rebar was performed by using the random critical-core theory.The results indicate that the predictions of the tensile failure strains of the rebar,in which the interracial damage is taken into account,are in better agreement with the existing experimental results than those when only elastic case is considered.Through the comparison between the theoretical and experimental results,the shear-lag theory and the model are verified feasibly in studying the claviform hybrid composite rebar.

  18. Facial fractures with concomitant open globe injury: mechanisms and fracture patterns associated with blindness.

    Science.gov (United States)

    Vaca, Elbert E; Mundinger, Gerhard S; Kelamis, Joseph A; Dorafshar, Amir H; Christy, Michael R; Manson, Paul N; Rodriguez, Eduardo D

    2013-06-01

    Treatment of facial fractures in the setting of open-globe injuries poses a management dilemma because of the often disparate treatment priorities of multidisciplinary trauma teams and the lack of prognostic data regarding visual outcomes. Patients in the University of Maryland Shock Trauma Registry sustaining facial fractures with concomitant open-globe injuries from January of 1998 to August of 2010 were identified. Odds ratios were calculated to identify demographic and clinical variables associated with blindness, and multivariate regression analysis was performed. A total of 99 patients were identified with 105 open-globe injuries. Seventy-nine percent of injuries were blinding, whereas 4.8 percent of globes achieved a final visual acuity greater than or equal to 20/400. Blindness was associated with penetrating injury, increasing number of facial fractures, zygomaticomaxillary complex fracture, admission Glasgow Coma Scale score less than or equal to 8, and globe injury spanning all three eye zones. Fracture repair was performed more frequently (62.5 percent) and more quickly (average time to fracture repair, 4.5 days) in cases of primary globe enucleation/evisceration when compared with complete (21.2 percent; 8 days; p=0.35) or incomplete (42.9 percent; 11 days; p=0.058) primary globe repair. Penetrating injury mechanism and zone of eye injury appear to be better indicators of visual prognosis than facial fracture patterns. Given the high rates of blindness, secondary enucleation, and delay of fracture repair in patients that were not primarily enucleated, the authors recommend that orbital fracture repair not be delayed in the hopes of eventual visual recovery in cases of high-velocity projectile trauma. Risk, III.

  19. A Fracture Mechanical Model and a Cohesive Zone Model of Interface Fracture

    DEFF Research Database (Denmark)

    Jensen, Henrik Myhre

    2006-01-01

    A comparison between the prediction of crack propagation through an adhesive interface based on a fracture mechanics approach and a cohesive zone approach is presented. Attention is focussed on predicting the shape of the crack front and the critical stress required to propagate the crack under...... quasi-static conditions. The cohesive zone model has several advantages over the fracture mechanics based model. It is easier to generalise the cohesive zone model to take into account effects such as plastic deformation in the adherends, and to take into account effects of large local curvatures...... of the interface crack front. The comparison shows a convergence of the results based on the cohesive zone model towards the results based on a fracture mechanics approach in the limit where the size of the cohesive zone becomes smaller than other relevant geometrical lengths for the problem....

  20. Fracture mechanics life analytical methods verification testing

    Science.gov (United States)

    Favenesi, J. A.; Clemons, T. G.; Riddell, W. T.; Ingraffea, A. R.; Wawrzynek, P. A.

    1994-01-01

    The objective was to evaluate NASCRAC (trademark) version 2.0, a second generation fracture analysis code, for verification and validity. NASCRAC was evaluated using a combination of comparisons to the literature, closed-form solutions, numerical analyses, and tests. Several limitations and minor errors were detected. Additionally, a number of major flaws were discovered. These major flaws were generally due to application of a specific method or theory, not due to programming logic. Results are presented for the following program capabilities: K versus a, J versus a, crack opening area, life calculation due to fatigue crack growth, tolerable crack size, proof test logic, tearing instability, creep crack growth, crack transitioning, crack retardation due to overloads, and elastic-plastic stress redistribution. It is concluded that the code is an acceptable fracture tool for K solutions of simplified geometries, for a limited number of J and crack opening area solutions, and for fatigue crack propagation with the Paris equation and constant amplitude loads when the Paris equation is applicable.

  1. Fracture mechanisms in biopolymer films using coupling of mechanical analysis and high speed visualization technique

    NARCIS (Netherlands)

    Paes, S.S.; Yakimets, I.; Wellner, N.; Hill, S.E.; Wilson, R.H.; Mitchell, J.R.

    2010-01-01

    The aim of this study was to provide a detailed description of the fracture mechanisms in three different biopolymer thin materials: gelatin, hydroxypropyl cellulose (HPC) and cassava starch films. That was achieved by using a combination of fracture mechanics methodology and in situ visualization w

  2. Vertebral Fractures and Spondylosis in Men - Original Investigation

    Directory of Open Access Journals (Sweden)

    Selmin Gülbahar

    2008-04-01

    Full Text Available Aim: The aim of this study was to investigate the relationship between vertebral fractures and spondylosis and bone mineral density in men older than 60 years. Material and Method: Thirty-two men with back and low back pain aged over 60 years were included into the study. Thoracic and lumbar spine radiographs were taken and, anterior, central and posterior heights of each vertebral body from T4 to L5 was measured and than the number of vertebral fractures was assessed. Osteophyte and disc scores were used for evaluation of spondylosis. Bone mineral density was measured by dual-energy-X-ray absorptiometry. Measurements were obtained from lumbar vertebrae and proximal femoral region. Results: Significant positive correlations were found between vertebral fracture and osteophyte score and bone mineral density of total femoral region. When osteophyte score and total femoral bone mineral density were taken into consideration, there were no significant correlations between other parameters and vertebral fracture. Significant positive correlations were observed between osteophyte score and bone mineral density and t scores of L1-4. Also there were significant positive correlations between disc score and both bone mineral density and t scores of L1-4. Significant positive correlation was also found between femoral bone density and body weight. Conclusion: Finally, lumbar bone mineral density increases with spinal degenerative changes, but the increase in bone mineral density can not prevent sub clinic vertebral fractures. Especially, in the men who have intensive spinal degenerative changes, the measurement of lumbar bone mineral density is not enough for determining the fracture risk. Measurement of femoral bone mineral density and evaluation of clinic risk factors are more important for determining the fracture risk. (From the World of Osteoporosis 2008;14:1-6

  3. Effect laws and mechanisms of different temperatures on isothermal tensile fracture morphologies of high-strength boron steel

    Institute of Scientific and Technical Information of China (English)

    刘佳宁; 宋燕利; 路珏; 郭巍

    2015-01-01

    The fracture behaviour and morphologies of high-strength boron steel were investigated at different temperatures at a constant strain rate of 0.1 s−1 based on isothermal tensile tests. Fracture mechanisms were also analyzed based on the relationship between microstructure transformation and continuous cooling transformation (CCT) curves. It is found that 1) fractures of the investigated steel at high temperatures are dimple fractures; 2) the deformation of high-strength boron steel at high temperatures accelerates diffusion transformations;thus, to obtain full martensite, a higher cooling rate is needed;and 3) the investigated steel has the best plasticity when the deformation temperature is 750 °C.

  4. Investigation of Weibull statistics in fracture analysis of cast aluminum

    Science.gov (United States)

    Holland, F. A., Jr.; Zaretsky, E. V.

    1989-01-01

    The fracture strengths of two large batches of A357-T6 cast aluminum coupon specimens were compared by using two-parameter Weibull analysis. The minimum number of these specimens necessary to find the fracture strength of the material was determined. The applicability of three-parameter Weibull analysis was also investigated. A design methodolgy based on the combination of elementary stress analysis and Weibull statistical analysis is advanced and applied to the design of a spherical pressure vessel shell. The results from this design methodology are compared with results from the applicable ASME pressure vessel code.

  5. Investigation of Weibull statistics in fracture analysis of cast aluminum

    Science.gov (United States)

    Holland, F. A., Jr.; Zaretsky, E. V.

    1989-01-01

    The fracture strengths of two large batches of A357-T6 cast aluminum coupon specimens were compared by using two-parameter Weibull analysis. The minimum number of these specimens necessary to find the fracture strength of the material was determined. The applicability of three-parameter Weibull analysis was also investigated. A design methodolgy based on the combination of elementary stress analysis and Weibull statistical analysis is advanced and applied to the design of a spherical pressure vessel shell. The results from this design methodology are compared with results from the applicable ASME pressure vessel code.

  6. Mechanical transport in two-dimensional networks of fractures

    Energy Technology Data Exchange (ETDEWEB)

    Endo, H.K.

    1984-04-01

    The objectives of this research are to evaluate directional mechanical transport parameters for anisotropic fracture systems, and to determine if fracture systems behave like equivalent porous media. The tracer experiments used to measure directional tortuosity, longitudinal geometric dispersivity, and hydraulic effective porosity are conducted with a uniform flow field and measurements are made from the fluid flowing within a test section where linear length of travel is constant. Since fluid flow and mechanical transport are coupled processes, the directional variations of specific discharge and hydraulic effective porosity are measured in regions with constant hydraulic gradients to evaluate porous medium equivalence for the two processes, respectively. If the fracture region behaves like an equivalent porous medium, the system has the following stable properties: (1) specific discharge is uniform in any direction and can be predicted from a permeability tensor; and (2) hydraulic effective porosity is directionally stable. Fracture systems with two parallel sets of continuous fractures satisfy criterion 1. However, in these systems hydraulic effective porosity is directionally dependent, and thus, criterion 2 is violated. Thus, for some fracture systems, fluid flow can be predicted using porous media assumptions, but it may not be possible to predict transport using porous media assumptions. Two discontinuous fracture systems were studied which satisfied both criteria. Hydraulic effective porosity for both systems has a value between rock effective porosity and total porosity. A length-density analysis (LDS) of Canadian fracture data shows that porous media equivalence for fluid flow and transport is likely when systems have narrow aperture distributions. 54 references, 90 figures, 7 tables.

  7. Evolution of Stiffness and Permeability in Fractures Subject to - and Mechanically-Activated Dissolution

    Science.gov (United States)

    Faoro, I.; Elsworth, D.; Candela, T.

    2013-12-01

    Strong feedbacks link thermal gradients (T), hydrologic flow (H), chemical alteration (C) and mechanical deformation (M) in fractured rock. These processes are strongly interconnected since one process effects the initiation and progress of another. Dissolution and precipitation of minerals are affected by temperature and stress, and can result in significant changes in permeability and solute transport characteristics. Understanding these couplings is important for oil, gas, and geothermal reservoir engineering and for waste disposal in underground repositories and reservoirs. In order to experimentally investigate the interactions between THCM processes in a natural stressed fracture, we report on heated ( up to 150C) flow-through experiments on fractured core samples of Westerly granite. These experiments are performed to examine the influence of thermally and mechanically activated dissolution on the mechanical (stress/strain) and transport (permeability) characteristics of fractures. The evolutions of both the permeability and stiffness of the sample are recorded as the experimental thermal conditions change and chemical alteration progresses. Furthermore efflux of dissolved mineral mass is measured periodically to provide a record of the net mass removal, to correlate this with observed changes in fracture aperture, defined by the flow test. During the experiments the fracture shows high hydraulic sensitivity to the changing conditions of stress and temperature. Significant variation of the effluent fluid chemistry is observed. We argue that the formation of clay (Kaolinite) is the main mechanism responsible for the permanent change in permeability recorded at higher confining stresses (40 MPa).

  8. Mechanical strength and analysis of fracture of titanium joining submitted to laser and tig welding

    Directory of Open Access Journals (Sweden)

    Ana Cláudia Gabrielli Piveta

    2012-12-01

    Full Text Available This study compared the tensile strength and fracture mechanism of tungsten inert gas (TIG welds in cylindrical rods of commercially pure titanium (cp Ti with those of laser welds and intact samples. Thirty dumbbell-shaped samples were developed by using brass rods as patterns. The samples were invested in casings, subjected to thermal cycles, and positioned in a plasma arc welding machine under argon atmosphere and vacuum, and titanium was injected under vacuum/pressure. The samples were X-rayed to detect possible welding flaws and randomly assigned to three groups to test the tensile strength and the fracture mechanism: intact, laser welding, and TIG welding. The tensile test results were investigated using ANOVA, which indicated that the samples were statistically similar. The fracture analysis showed that the cpTi samples subjected to laser welding exhibited brittle fracture and those subjected to TIG welding exhibited mixed brittle/ductile fracture with a predominance of ductile fracture with the presence of microcavities and cleavage areas. Intact samples presented the characteristic straightening in the fracture areas, indicating the ductility of the material.

  9. Finite elements in fracture mechanics theory, numerics, applications

    CERN Document Server

    Kuna, Meinhard

    2013-01-01

    Fracture mechanics has established itself as an important discipline of growing interest to those working to assess the safety, reliability and service life of engineering structures and materials. In order to calculate the loading situation at cracks and defects, nowadays numerical techniques like finite element method (FEM) have become indispensable tools for a broad range of applications. The present monograph provides an introduction to the essential concepts of fracture mechanics, its main goal being to procure the special techniques for FEM analysis of crack problems, which have to date only been mastered by experts. All kinds of static, dynamic and fatigue fracture problems are treated in two- and three-dimensional elastic and plastic structural components. The usage of the various solution techniques is demonstrated by means of sample problems selected from practical engineering case studies. The primary target group includes graduate students, researchers in academia and engineers in practice.

  10. Comparative study of fracture mechanical test methods for concrete

    DEFF Research Database (Denmark)

    Østergaard, Lennart; Olesen, John Forbes

    2004-01-01

    and the interpretation, i.e. the analysis needed to extract the stress-crack opening relationship, the fracture energy etc. Experiments are carried out with each test configuration using mature, high performance concrete. The results show that the UTT is a highly complicated test, which only under very well controlled......This paper describes and compares three different fracture mechanical test methods; the uniaxial tension test (UTT), the three point bending test (TPBT) and the wedge splitting test (WST). Potentials and problems with the test methods will be described with regard to the experiment...... circumstances will yield the true fracture mechanical properties. It is also shown that both the three point bending test and the WST are well-suited substitutes for the uniaxial tension test....

  11. Fracture mechanics evaluation for at typical PWR primary coolant pipe

    Energy Technology Data Exchange (ETDEWEB)

    Tanaka, T. [Kansai Electric Power Company, Osaka (Japan); Shimizu, S.; Ogata, Y. [Mitsubishi Heavy Industries, Ltd., Kobe (Japan)

    1997-04-01

    For the primary coolant piping of PWRs in Japan, cast duplex stainless steel which is excellent in terms of strength, corrosion resistance, and weldability has conventionally been used. The cast duplex stainless steel contains the ferrite phase in the austenite matrix and thermal aging after long term service is known to change its material characteristics. It is considered appropriate to apply the methodology of elastic plastic fracture mechanics for an evaluation of the integrity of the primary coolant piping after thermal aging. Therefore we evaluated the integrity of the primary coolant piping for an initial PWR plant in Japan by means of elastic plastic fracture mechanics. The evaluation results show that the crack will not grow into an unstable fracture and the integrity of the piping will be secured, even when such through wall crack length is assumed to equal the fatigue crack growth length for a service period of up to 60 years.

  12. Measurements of residual stress in fracture mechanics coupons

    Energy Technology Data Exchange (ETDEWEB)

    Prime, Michael B [Los Alamos National Laboratory; Hill, Michael R [U.C. DAVIS; Nav Dalen, John E [HILL ENGINEERING

    2010-01-01

    This paper describes measurements of residual stress in coupons used for fracture mechanics testing. The primary objective of the measurements is to quantify the distribution of residual stress acting to open (and/or close) the crack across the crack plane. The slitting method and the contour method are two destructive residual stress measurement methods particularly capable of addressing that objective, and these were applied to measure residual stress in a set of identically prepared compact tension (C(T)) coupons. Comparison of the results of the two measurement methods provides some useful observations. Results from fracture mechanics tests of residual stress bearing coupons and fracture analysis, based on linear superposition of applied and residual stresses, show consistent behavior of coupons having various levels of residual stress.

  13. Rheology and Fracture Mechanics of Foods

    NARCIS (Netherlands)

    Vliet, van T.

    2013-01-01

    The mechanical properties of food play an important role during manufacturing, storage, handling, and last but not least, during consumption. For an adequate understanding of the mechanical properties of liquid, liquid-like, soft solid, and solid foods, a basic understanding of relevant aspects of r

  14. A Fracture Probability Competition Mechanism of Stress Corrosion Cracking

    Institute of Scientific and Technical Information of China (English)

    Yanliang HUANG

    2001-01-01

    The stress corrosion cracking (SCC) of austenitic stainless steel was studied via polarization,slow strain rate and scanning electron microscope (SEM) techniques. Many SCC mechanisms have been proposed in which hydrogen embrittlement and passive film rupture-repassivation theories are generally accepted, but they can hardly explain the SCC mechanism of austenitic stainless steel in acidic chloride solution adequately, because the steel is in active dissolution state and cathodic polarization can prevent it from occurring. Our experiment shows that the anodic current increases the creep rate and decreases the plastic strength of the material on single smooth specimen as well as at the SCC crack tip. The fractured surface was characterized as brittle cleavage, while the surface crack of smooth specimen was almost vertical to the tensile strength, which can confirm that the cracks were caused by tensile stresses. A fracture probability competition mechanism of SCC was proposed on the basis of the experimental results combined with the viewpoint of ductile-brittle fracture competition. When the anodic dissolution current is increased to a certain degree, the probability of fracture by tensile stress will exceed that by shear stress, and the brittle fracture will occur. The proposed SCC mechanism can not only explain the propagation of SCC cracks but can explain the crack initiation as well. The strain on the surface distributes unevenly when a smooth specimen is deformed, so does the anodic current distribution. The crack will initiate at a point where the anodic current density is large enough to cause the material at a specific point to fracture in brittle manner.

  15. [Investigate progress of intraoperative periprosthetic fracture of total hip arthroplasty].

    Science.gov (United States)

    Cong, Yu; Zhao, Jian-ning

    2011-02-01

    One of the complications of total hip arthroplasty is intraoperative periprosthetic fracture. Periprosthetic fracture is divided into acetabular fracture and femoral fracture. Risk factors for intraoperative periprosthetic fracture include use of minimally invasive techniques, press-fit cementless stems, revision operations and osteoporosis. It has been recognized that treatment of intraoperative periprosthetic fractures should be based on the classification of the Vancouver system for intraoperative fractures.

  16. Hydrogen Embrittlement - Loading Rate Effects in Fracture Mechanics Testing

    NARCIS (Netherlands)

    Koers, R.W.J.; Krom, A.H.M.; Bakker, A.

    2001-01-01

    The fitness for purpose methodology is more and more used in the oil and gas industry to evaluate the significance of pre-existing flaws and material deficiencies with regard to the suitability of continued operation of equipment. In this methodology, traditional fracture mechanics is integrated wit

  17. Fracture Mechanics of an Elastic Softening Material like Concrete

    NARCIS (Netherlands)

    Reinhardt, H.W.

    1984-01-01

    Concrete is modelled as a linear elastic softening material and introduced into fracture mechanics. A discrete crack is considered with softening zones at the crack tips. Following the approach of Dugdale/Barenblatt, closing stresses are applied to the crack faces in the softening zone. The stresses

  18. 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.

  19. Coupled phenomenological and fracture mechanics approach to assess the fracture behaviour of TWC piping component

    Energy Technology Data Exchange (ETDEWEB)

    Saxena, Sanjeev, E-mail: san_bpl@yahoo.co [Advanced Materials and Processes Research Institute (AMPRI), CSIR Concern, Hoshangabad Road, Bhopal 462026 (India); Ramakrishnan, N. [Advanced Materials and Processes Research Institute (AMPRI), CSIR Concern, Hoshangabad Road, Bhopal 462026 (India); Chouhan, J.S. [Civil Engineering Department, Samrat Ashok Technological Institute, Vidisha (India)

    2010-04-15

    The present study demonstrates the numerical prediction of experimental specimen J-R curve using Gurson-Tvergaard-Needleman phenomenologically based material model. The predicted specimen J-R curve is used to determine the geometric independent initiation fracture toughness (J{sub SZWc}) value that compares well with experimental result. Using the experimentally determined and numerically predicted J{sub SZWc} values and specimen J-R curves, the accuracy of predicting the fracture behaviour of the cracked component is judged. Thus the present study proposed a coupled phenomenological and fracture mechanics approach to predict the crack initiation and instability stages in cracked piping components using numerically predicted specimen J-R curve obtained from tensile specimens testing data.

  20. Draft fracture mechanics code case for American Society of Mechanical Engineers NUPACK rules

    Energy Technology Data Exchange (ETDEWEB)

    McConnell, P.; Sorenson, K. [Sandia National Labs., Albuquerque (United States); Nickell, R. [Applied Science and Technology, Poway (United States); Saegusa, T. [Central Research Inst. for Electric Power Industry, Abiko (Japan)

    2004-07-01

    The containment boundaries of most spent-fuel casks certified for use in the United States by the Nuclear Regulatory Commission are constructed with stainless steel, a material that is ductile in an engineering sense at all temperatures and for which, therefore, fracture mechanics principles are not relevant for the containment application. Ferritic materials may fail in a nonductile manner at sufficiently low temperatures, so fracture mechanics principles may be applied to preclude nonductile fracture. Because of the need to transport and store spent nuclear fuel safely in all types of climatic conditions, these vessels have regulatory lowest service temperatures that range down to -40 C (-40 F) for transport application. Such low service temperatures represent a severe challenge in terms of fracture toughness to many ferritic materials. Linear-elastic and elastic-plastic fracture mechanics principles provide a methodology for evaluating ferritic materials under such conditions.

  1. Application of fracture mechanics to materials and structures

    Energy Technology Data Exchange (ETDEWEB)

    Sih, G.C.; Sommer, E.; Dahl, W.

    1984-01-01

    The general theme is the interplay between material and design requirements, and this was underlined in many of the technical presentations. A panel discussion further clarified the objectives of fracture mechanics as a discipline and tool to guard structural and machine components against premature failure. Numerical and experimental techniques were shown to be essential in compiling laboratory data on fracture testing, and the need for the development of rational procedures to ensure safety and reliability in the design of modern structures was very strongly emphasized.

  2. Unique Mechanism of Chance Fracture in a Young Adult Male

    Directory of Open Access Journals (Sweden)

    Aaron Birch

    2013-03-01

    Full Text Available Since the first description of the Chance fracture in 1948, there have been few case reports ofunique mechanisms causing this classical flexion-extension injury to the spine in motor vehicleaccidents, sports injury, and falls. To our knowledge, this injury has not been reported from a fall withthe mechanistic forces acting laterally on the spine and with spinal support in place. We present a21-year-old male who slid down a flight of stairs onto his side wearing a heavy mountaineering stylebackpack, subsequently sustaining a Chance fracture of his first lumbar vertebrae.

  3. Unique mechanism of chance fracture in a young adult male.

    Science.gov (United States)

    Birch, Aaron; Walsh, Ryan; Devita, Diane

    2013-03-01

    Since the first description of the Chance fracture in 1948, there have been few case reports of unique mechanisms causing this classical flexion-extension injury to the spine in motor vehicle accidents, sports injury, and falls. To our knowledge, this injury has not been reported from a fall with the mechanistic forces acting laterally on the spine and with spinal support in place. We present a 21-year-old male who slid down a flight of stairs onto his side wearing a heavy mountaineering style backpack, subsequently sustaining a Chance fracture of his first lumbar vertebrae.

  4. Summary of fracture mechanics problems analysis method in ABAQUS

    Directory of Open Access Journals (Sweden)

    Duan Hongjun

    2015-07-01

    Full Text Available Fracture mechanics is the study of the strength of the materials or structures with crack and crack propagation regularity of a discipline. There are a lot of analysis function of ABAQUS, including fracture analysis. ABAQUS is very easy to use and easy to establish a model of the complicated problem. In order to effectively study of strong discontinuity problems such as crack, provides two methods of simulating the problem of cracks of ABAQUS. This paper describes the two methods respectively, and compare two methods.

  5. Fracture mechanics in fiber reinforced composite materials, taking as examples B/A1 and CRFP

    Science.gov (United States)

    Peters, P. W. M.

    1982-01-01

    The validity of linear elastic fracture mechanics and other fracture criteria was investigated with laminates of boron fiber reinforced aluminum (R/A1) and of carbon fiber reinforced epoxide (CFRP). Cracks are assessed by fracture strength Kc or Kmax (critical or maximum value of the stress intensity factor). The Whitney and Nuismer point stress criterion and average stress criterion often show that Kmax of fiber composite materials increases with increasing crack length; however, for R/A1 and CFRP the curve showing fracture strength as a function of crack length is only applicable in a small domain. For R/A1, the reason is clearly the extension of the plastic zone (or the damage zone n the case of CFRP) which cannot be described with a stress intensity factor.

  6. The WST method, a fracture mechanics test method for FRC

    DEFF Research Database (Denmark)

    Lofgren, I.; Stang, Henrik; Olesen, John Forbes

    2008-01-01

    FRC compositions. Furthermore, for the WST method, two different specimen sizes have been investigated. Results from this investigation demonstrate the applicability of the WST method and show that the scatter of the test results is lower than for the 3PBT. Through inverse analysis, stress......The applicability of the wedge-splitting test method (WST), for determining fracture properties of fibre-reinforced concrete, is discussed. Experimental results, using the WST method, are compared with results from uniaxial tension tests (UTT) and three-point bending tests (3PBT) for five different......-crack opening (sigma-w) relationships have been determined for each mix and test method. For the two WST specimen sizes, there is no apparent difference either in the number of fibres (per cm(2)) crossing the fracture plane or in the fracture properties. The major factor contributing to the scatter in the test...

  7. Life Prediction of Ball Grid Array Soldered Joints under Thermal Cycling Loading by Fracture Mechanics Method

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Fatigue crack propagation life of ball grid array (BGA) soldered joints during thermal cycling loading was investigated by fracture mechanics approach using finite element analysis. The relationships between the strain energy release rate (G) and crack size (α), thermal cycle numbers (N) can be derived. Based on the relationships, fatigue life of the soldered joints was determined. The results showed that crack propagation life was higher than crack initiation life. Therefore, it appears that it is more appropriate to predict the fatigue life of soldered joints using the fracture mechanics method.

  8. Effect of Temperature-Force Factors and Concentrator Shape on Impact Fracture Mechanisms of 17Mn1Si Steel

    Directory of Open Access Journals (Sweden)

    S. V. Panin

    2017-01-01

    Full Text Available The influence of the notch shape on the impact fracture of 17Mn1Si steel is investigated at different temperatures with the focus placed on the low-temperature behavior. An approach towards fracture characterization has been suggested based on the description of elastic-plastic deformation of impact loaded specimens on the stage of crack initiation and growth at ambient and lower temperatures. The analysis of the impact loading diagrams and fracture energy values for the pipe steel 17Mn1Si revealed the fracture mechanisms depending on the notch shape. It was found that the testing temperature reduction played a decisive role in plastic strain localization followed by dynamic fracture of the specimens with differently shaped notches. A classification of fracture macro- and microscopic mechanisms for differently notched specimens tested at different temperatures was proposed which enabled a self-consistent interpretation of impact test results.

  9. Delayed Fracture Resistance and Mechanical Properties of 30MnSi High Strength Steel

    Institute of Scientific and Technical Information of China (English)

    XIAO Gui-zhi; DI Hong-shuang

    2009-01-01

    To investigate the effect of heat treatment on mechanical properties and delayed fracture resistance of high strength steel,30MnSi prestressed concrete (PC) steel bars are quenched and tempered.Tensile results show that,after 950 ℃ quenching and about 430 ℃ tempering,30MnSi PC steel bars have superior mechanical properties and delayed fracture resistance.Microstructursl observation shows that 30MnSi steel bar is mainly composed of fine tempered sorbite (troostite) with carbide distributed along the lath martensite boundaries.It can be concluded that thermal refining is an effective way to improve mechanical properties and delayed fracture resistance of 30MnSi PC steel bar.

  10. Effect of the build orientation on the mechanical properties and fracture modes of SLM Ti–6Al–4V

    Energy Technology Data Exchange (ETDEWEB)

    Simonelli, M., E-mail: M.Simonelli@lboro.ac.uk [Department of Materials, Loughborough University, Loughborough LE11 3TU (United Kingdom); Tse, Y.Y. [Department of Materials, Loughborough University, Loughborough LE11 3TU (United Kingdom); Tuck, C. [Additive Manufacturing and 3D Printing Research Group, Faculty of Engineering, The University of Nottingham, Nottingham NG7 2RD (United Kingdom)

    2014-10-20

    Recent research on the additive manufacturing (AM) of Ti alloys has shown that the mechanical properties of the parts are affected by the characteristic microstructure that originates from the AM process. To understand the effect of the microstructure on the tensile properties, selective laser melted (SLM) Ti–6Al–4V samples built in three different orientations were tensile tested. The investigated samples were near fully dense, in two distinct conditions, as-built and stress relieved. It was found that the build orientation affects the tensile properties, and in particular the ductility of the samples. The mechanical anisotropy of the parts was discussed in relation to the crystallographic texture, phase composition and the predominant fracture mechanisms. Fractography and electron backscatter diffraction (EBSD) results indicate that the predominant fracture mechanism is intergranular fracture present along the grain boundaries and thus provide and explain the typical fracture surface features observed in fracture AM Ti–6Al–4V.

  11. INVESTIGATION OF EFFICIENCY IMPROVEMENTS DURING CO2 INJECTION IN HYDRAULICALLY AND NATURALLY FRACTURED RESERVOIRS

    Energy Technology Data Exchange (ETDEWEB)

    David S. Schechter

    2005-09-28

    The objective of this project is to perform unique laboratory experiments with artificial fractured cores (AFCs) and X-ray CT to examine the physical mechanisms of bypassing in HFR and NFR that eventually result in more efficient CO{sub 2} flooding in heterogeneous or fracture-dominated reservoirs. To achieve this objective, we divided the report into two chapters. The first chapter was to image and perform experimental investigation of transfer mechanisms during CO{sub 2} flooding in NFR and HFR using X-ray CT scanner. In this chapter, we emphasized our work on understanding the connection between fracture properties and fundamentals of transfer mechanism from matrix to fractures and fluid flow through fracture systems. We started our work by investigating the effect of different overburden pressures and stress-state conditions on rock properties and fluid flow. Since the fracture aperture is one of important parameter that governs the fluid flow through the fracture systems, the average fracture aperture from the fluid flow experiments and fracture aperture distribution derived from X-ray CT scan were estimated for our modeling purposes. The fracture properties and fluid flow have significant changes in response to different overburden pressures and stress-state conditions. The fracture aperture distribution follows lognormal distribution even at elevated stress conditions. Later, we also investigated the fluid transfers between matrix and fracture that control imbibition process. We evaluated dimensionless time for validating the scheme of upscaling laboratory experiments to field dimensions. In CO{sub 2} injection experiments, the use of X-ray CT has allowed us to understand the mechanisms of CO{sub 2} flooding process in fractured system and to take important steps in reducing oil bypassed. When CO{sub 2} flooding experiments were performed on a short core with a fracture at the center of the core, the gravity plays an important role in the recovery of oil

  12. Formative mechanism of intracanal fracture fragments in thoracolumbar burst fractures: a finite element study

    Institute of Scientific and Technical Information of China (English)

    ZENG Zhi-li; ZHU Rui; LI Shan-zhu; YU Yan; WANG Jian-jie; JIA Yong-wei; CHEN Bo

    2013-01-01

    Background Thoracolumbar burst fracture is a common clinical injury,and the fracture mechanism is still controversial.The aim of this research was to study the formation of intracanal fracture fragments in thoracolumbar burst fractures and to provide information for the prevention of thoracolumbar bursts fractures and reduction of damage to the nervous system.Methods A nonlinear three-dimensional finite element model of T11-L3 segments was established,and the injury processes of thoracolumbar bursts were simulated.The intact finite element model and the finite element model after the superior articular were impacted by 100 J of energy in different directions.The distribution and variation of stress in the superior posterior region of the L1 vertebral body were analyzed.Abaqus 6.9 explicit dynamic solver was used as finite element software in calculations.Results A three-dimensional nonlinear finite element model of the thoracolumbar spine was created.In the intact model,stress was concentrated in the superior posterior region of the L1 vertebral body.The stress peak was a maximum for the extension impact load and a minimum for the flexion impact load.The stress peak and contact force in the facet joint had close correlation with time.The stress peak disappeared after excision of the superior articular process.Conclusions The three-dimensional nonlinear finite element model was suitable for dynamic analysis.The contact force in the facet joint,which can be transferred to the superior posterior vertebral body,may explain the spinal canal fragment in thoracolumbar burst fractures.

  13. Investigation of post hydraulic fracturing well cleanup physics in the Cana Woodford Shale

    Science.gov (United States)

    Lu, Rong

    Hydraulic fracturing was first carried out in the 1940s and has gained popularity in current development of unconventional resources. Flowing back the fracturing fluids is critical to a frac job, and determining well cleanup characteristics using the flowback data can help improve frac design. It has become increasingly important as a result of the unique flowback profiles observed in some shale gas plays due to the unconventional formation characteristics. Computer simulation is an efficient and effective way to tackle the problem. History matching can help reveal some mechanisms existent in the cleanup process. The Fracturing, Acidizing, Stimulation Technology (FAST) Consortium at Colorado School of Mines previously developed a numerical model for investigating the hydraulic fracturing process, cleanup, and relevant physics. It is a three-dimensional, gas-water, coupled fracture propagation-fluid flow simulator, which has the capability to handle commonly present damage mechanisms. The overall goal of this research effort is to validate the model on real data and to investigate the dominant physics in well cleanup for the Cana Field, which produces from the Woodford Shale in Oklahoma. To achieve this goal, first the early time delayed gas production was explained and modeled, and a simulation framework was established that included all three relevant damage mechanisms for a slickwater fractured well. Next, a series of sensitivity analysis of well cleanup to major reservoir, fracture, and operational variables was conducted; five of the Cana wells' initial flowback data were history matched, specifically the first thirty days' gas and water producing rates. Reservoir matrix permeability, net pressure, Young's modulus, and formation pressure gradient were found to have an impact on the gas producing curve's shape, in different ways. Some moderately good matches were achieved, with the outcome of some unknown reservoir information being proposed using the

  14. Relationship between microstructure, material distribution, and mechanical properties of sheep tibia during fracture healing process.

    Science.gov (United States)

    Gao, Jiazi; Gong, He; Huang, Xing; Fang, Juan; Zhu, Dong; Fan, Yubo

    2013-01-01

    The aim of this study was to investigate the relationship between microstructural parameters, material distribution, and mechanical properties of sheep tibia at the apparent and tissue levels during the fracture healing process. Eighteen sheep underwent tibial osteotomy and were sacrificed at 4, 8, and 12 weeks. Radiographs and micro-computed tomography (micro-CT) scanning were taken for microstructural assessment, material distribution evaluation, and micro-finite element analysis. A displacement of 5% compressive strain on the longitudinal direction was applied to the micro-finite element model, and apparent and tissue-level mechanical properties were calculated. Principle component analysis and linear regression were used to establish the relationship between principle components (PCs) and mechanical parameters. Visible bony callus formation was observed throughout the healing process from radiographic assessment. Apparent mechanical property increased at 8 weeks, but tissue-level mechanical property did not increase significantly until 12 weeks. Three PCs were extracted from microstructural parameters and material distribution, which accounted for 87.592% of the total variation. The regression results showed a significant relationship between PCs and mechanical parameters (R>0.8, PCT imaging could efficiently predict bone strength and reflect the bone remodeling process during fracture healing, which provides a basis for exploring the fracture healing mechanism and may be used as an approach for fractured bone strength assessment.

  15. Natural hydraulic fractures and the mechanical stratigraphy of shale-dominated strata

    Science.gov (United States)

    Imber, Jonathan; Armstrong, Howard; Atar, Elizabeth; Clancy, Sarah; Daniels, Susan; Grattage, Joshua; Herringshaw, Liam; Trabucho-Alexandre, João; Warren, Cassandra; Wille, Jascha; Yahaya, Liyana

    2016-04-01

    .2-4.3 fractures per m, consistent with field observations that this formation is more highly fractured than the Cleveland Ironstone Formation. Semi-quantitative estimates of the mineralogical "brittleness index" suggest the highly fractured, clay-rich Mulgrave Shale Member of the Whitby Mudstone Formation has a low brittleness. Our results are therefore inconsistent with the widely held assumption that natural fracture density is greatest within units characterised by a high brittleness index. We propose that stratigraphic variations in fracture densities are more likely to result from the different distributions of crack driving stresses; formations containing decimetre-scale, and most likely stiff, carbonate layers (such as the Cleveland Ironstone Formation) will have differing crack driving stresses compared with silt- and mudstone dominated successions (such as the Whitby Mudstone Formation). The high fracture density observed within the Mulgrave Shale Member is also consistent with propagation of natural hydraulic fractures driven by fluid overpressure caused by maturation of organic matter concentrated within this unit. The next step is to investigate the relative importance of maturation-driven overpressure v. mechanical heterogeneity by analysing the stratigraphic variations in fracture density within the underlying, organic-matter lean Redcar Mudstone Formation.

  16. A clinical investigation of the mechanism of growing skull fractures in children%儿童颅骨生长性骨折的机制再探讨及早期手术

    Institute of Scientific and Technical Information of China (English)

    鲍南; 徐织; 杨波; 宋云海; 陈成

    2012-01-01

    Objective Many theories have been offered to explain growing skull fractures (GSFs),such as dural tears,arachnoid herniation,increased intracranial pressure,bone absorption due to the ischemia of the fracture line,and delayed or ceased bone growth.These theories,however,are limited by certain inadequacies.In this prospective study,we sought to uncover the mechanisms of GSFs,and their treatment method in children.Methods Ten patients with GSFs who received treatment at our hospital between November 2000 and June 2010 were retrospectively analyzed.The age at injury,duration from the time of injury to the appearance of the GSFs,fracture width,and imaging characteristics were analyzed.Cranioplasty was carried out,while duraplasty was not performed.Results The age at injury ranged from 2 to 21 months,and the age at surgery ranged from 3 to 5 years.The injuries included 7 fail injuries and 3 automobile collision injuries.All were linear skull fractures.The duration from the time of injury to the appearance of a GSFs was < 1 month in 4 cases and < 2 months in 6 cases.Six patients had frontal bone fractures,2 had parietal bone fractures,and 2 had occipital bone fractures.The fracture width ranged from 1.5 to 2.5 cm.The growing fractures became stationary just after the onset,without further progression.Computed tomography (CT) revealed 4 cases of encephalocele underneath the fracture and 6 cases of encephalomalacia due to brain contusion.Follow - up ranged from 1 to 7 years.Titanium plate fixation was stable,without loosening or displacement.There were no skull deformities in any patient.Conclusion GSFs usually occur in young children.The dural tear and the rapid growth of the brain in young children produce an outward expansion force,which plays a crucial role in GSFs development.It is possible that the current theories such as arachnoid herniation,increased intracranial pressure,bone absorption due to ischemia of the fracture line,and delayed or ceased bone growth

  17. A fracture mechanics study of nodular iron; Estudio de una fundicion nodular mediante mecanica de la fractura

    Energy Technology Data Exchange (ETDEWEB)

    Fernandez-Carrasquilla, J. [Universidad Publica de Navarra. Pamplona (Spain); Rios, R. [Centro PolitecnicoSuperior. Zaragoza (Spain)

    1999-07-01

    In the present investigation, nodular graphite cast iron fracture toughness with different matrices and eutectic cell sizes is studied. Properties of tensile strength , hardness and impact toughness are also studied. The experimental data are compared to the same determined parameters in silicon steel with a chemical composition similar to that of the case iron matrix. A subsequent study of the crack surfaces enables us to establish fracture mechanisms. The joint analysis of the mechanical results and of the fractographic studies allows us to establish the influence of graphite on the different mechanical properties of cast iron and on fracture micromechanisms as well. (Author) 7 refs.

  18. Cyclic Fracture Toughness of Railway Axle and Mechanisms of its Fatigue Fracture

    Directory of Open Access Journals (Sweden)

    Sorochak Andriy

    2015-06-01

    Full Text Available The main regularities in fatigue fracture of the railway axle material - the OSL steel - are found in this paper. Micromechanisms of fatigue crack propagation are described and systematized, and a physical-mechanical interpretation of the relief morphology at different stages of crack propagation is proposed for fatigue cracks in specimens cut out of the surface, internal and central layers of the axle.

  19. Laboratory experimental investigation of heat transport in fractured media

    Science.gov (United States)

    Cherubini, Claudia; Pastore, Nicola; Giasi, Concetta I.; Allegretti, Nicoletta Maria

    2017-01-01

    Low enthalpy geothermal energy is a renewable resource that is still underexploited nowadays in relation to its potential for development in society worldwide. Most of its applications have already been investigated, such as heating and cooling of private and public buildings, road defrosting, cooling of industrial processes, food drying systems or desalination. Geothermal power development is a long, risky and expensive process. It basically consists of successive development stages aimed at locating the resources (exploration), confirming the power generating capacity of the reservoir (confirmation) and building the power plant and associated structures (site development). Different factors intervene in influencing the length, difficulty and materials required for these phases, thereby affecting their cost. One of the major limitations related to the installation of low enthalpy geothermal power plants regards the initial development steps that are risky and the upfront capital costs that are huge. Most of the total cost of geothermal power is related to the reimbursement of invested capital and associated returns. In order to increase the optimal efficiency of installations which use groundwater as a geothermal resource, flow and heat transport dynamics in aquifers need to be well characterized. Especially in fractured rock aquifers these processes represent critical elements that are not well known. Therefore there is a tendency to oversize geothermal plants. In the literature there are very few studies on heat transport, especially on fractured media. This study is aimed at deepening the understanding of this topic through heat transport experiments in fractured networks and their interpretation. Heat transfer tests have been carried out on the experimental apparatus previously employed to perform flow and tracer transport experiments, which has been modified in order to analyze heat transport dynamics in a network of fractures. In order to model the obtained

  20. Molecular dynamics investigation of the elastic and fracture properties of the R-graphyne under uniaxial tension

    Energy Technology Data Exchange (ETDEWEB)

    Rouhi, Saeed, E-mail: s_rouhi@iaul.ac.ir

    2017-05-15

    In this paper, the mechanical properties of the R-graphynes are investigated by using molecular dynamics simulations. For this purpose, the uniaxial strain is applied on the nanosheets. The effects of R-graphyne chirality and dimension on their fracture and elastic properties are investigated. It is shown that the fracture properties of the armchair R-graphyne are approximately independent from the nanosheet sizes. However, a clear dependence is observed in the fracture properties of the zigzag R-graphyne on the nanosheet dimensions. Comparing the elastic modulus of the armchair and zigzag R-graphynes, it is shown that for the same sizes, the elastic modulus of armchair R-graphyne is approximately equal to 2.5 times of the elastic modulus of the zigzag ones. Pursuing the fracture process of R-graphynes with different chiralities, it is represented that the fracture propagates in the zigzag nanosheet with a higher velocity than the armchair ones.

  1. Therapeutic ultrasound in fracture healing: The mechanism of osteoinduction

    Directory of Open Access Journals (Sweden)

    John P

    2008-01-01

    Full Text Available Background: Ultrasound has been used therapeutically for accelerating fracture healing since many years. However, the controversy on the exact mechanism of osteoinduction still continues. In this study, we try to bring out the exact biomolecular mechanism by which ultrasound induces fracture healing. Materials and Methods: The study was conducted in two phases: animal experiments and clinical study. In the first phase, we induced fractures on the left tibia of Wistar strain rats under anaesthesia. They were divided into two groups. One of the groups was given low-intensity, pulsed ultrasound (30 MW/cm 2 20 min a day for 10 days. Tissue samples and radiographs were taken weekly for 3 weeks from both the groups. In the second phase of our study, ten patients with fractures of the distal end of the radius (ten fractures were included. Five of these were treated as cases, and five were treated as controls. Ultrasound was given 30 MW/cm 2 for 20 min every day for 2 weeks. The patients were assessed radiologically and sonologically before and after ultrasound therapy. Tissue samples were studied with thymidine incorporation test with and without adding various neurotransmitter combinations. Results: Radiological findings revealed that there was an increased callus formation in the ultrasound group. At the cellular level, there was an increased thymidine incorporation in the ultrasound group. When various neurotransmitters were added to the cells, there was an increased thymidine incorporation in the ultrasound group. In the second phase of the study, radiological and sonological assessments showed that there was an increased callus formation in the ultrasound group. In cytological study, thymidine incorporation was found to be increased in the ultrasound group. Conclusions: The results of animal and clinical studies demonstrated an early and increased callus formation in the ultrasound group. Cytological studies revealed increased thymidine

  2. Mechanics of materials: Top-down approaches to fracture

    Energy Technology Data Exchange (ETDEWEB)

    Hutchinson, J.W.; Evans, A.G.

    2000-01-01

    The utility and robustness of the mechanics of materials is illustrated through a review of several recent applications to fracture phenomena, including adhesive failures, the role of plasticity in enhancing toughness in films and multilayers, and crack growth resistance in ductile structural alloys. The commonalty among the approaches rests in a reliance on experiments to provide calibration of the failure process at the smallest scale.

  3. Quantitative NDI integration with probabilistic fracture mechanics for the assessment of fracture risk in pipelines

    Energy Technology Data Exchange (ETDEWEB)

    Kurz, Jochen H.; Cioclov, Dragos; Dobmann, Gerd; Boiler, Christian [Fraunhofer Inst. fuer Zerstoerungsfreie Pruefverfahren (IZFP), Saarbruecken (Germany)

    2009-07-01

    In the context of probabilistic paradigm of fracture risk assessment in structural components a computer simulation rationale is presented which has at the base the integration of Quantitative Non-destructive Inspection and Probabilistic Fracture Mechanics. In this study the static failure under static loading is assessed in the format known as Failure Assessment Diagram (FAD). The key concept in the analysis is the stress intensity factor (SIF) which accounts on the geometry of the component and the size of a pre-existent defect of a crack nature. FAD assessments can be made in deterministic sense, which yields the end result in dual terms of fail/not-fail. The fracture risk is evaluated in probabilistic terms. The superposed probabilistic pattern over the deterministic one (in mean sense) is implemented via Monte-Carlo sampling. The probabilistic fracture simulation yields a more informative analysis in terms of probability of failure. An important feature of the PVrisk software is the ability to simulate the influence of the quality and reliability of non-destructive inspection (NDI). It is achieved by integrating, algorithmically. probabilistic FAD analysis and the Probability of Detection (POD). The POD information can only be applied in a probabilistic analysis and leads to a refinement of the assessment. By this means, it can be ascertained the decrease of probability of failure (increase of reliability) when POD-characterized NDI is applied. Therefore, this procedure can be used as a tool for inspection based life time conceptions. In this paper results of sensitivity analyses of the fracture toughness are presented with the aim to outline, in terms of non-failure probabilities, the benefits of applying NDI, in various qualities, in comparison with the situation when NDI is lacking. (orig.)

  4. Results of fracture mechanics tests on PNC SUS 304 plate

    Energy Technology Data Exchange (ETDEWEB)

    Mills, W.J.; James, L.A.; Blackburn, L.D.

    1985-08-01

    PNC provided SUS 304 plate to be irradiated in FFTF at about 400/sup 0/C to a target fluence of 5 x 10/sup 21/ n/cm/sup 2/ (E > 0.1 MeV). The actual irradiation included two basically different exposure levels to assure that information would be available for the exposure of interest. After irradiation, tensile properties, fatigue-crack growth rates and J-integral fracture toughness response were determined. These same properties were also measured for the unirradiated material so radiation damage effects could be characterized. This report presents the results of this program. It is expected that these results would be applicable for detailed fracture analysis of reactor components. Recent advances in elastic-plastic fracture mechanics enable reasonably accurate predictions of failure conditions for flawed stainless steel components. Extensive research has focused on the development of J-integral-based engineering approach for assessing the load carrying capacity of low-strength, high-toughness structural materials. Furthermore, Kanninen, et al., have demonstrated that J-integral concepts can accurately predict the fracture response for full-scale cracked structures manufactured from Type 304 stainless steel.

  5. Wide-range displacement expressions for standard fracture mechanics specimens

    Science.gov (United States)

    Kapp, J. A.; Gross, B.; Leger, G. S.

    1985-01-01

    Wide-range algebraic expressions for the displacement of cracked fracture mechanics specimens are developed. For each specimen two equations are given: one for the displacement as a function of crack length, the other for crack length as a function of displacement. All the specimens that appear in ASTM Test for Plane-Strain Fracture Toughness of Metallic Materials (E 399) are represented in addition to the crack mouth displacement for a pure bending specimen. For the compact tension sample and the disk-shaped compact tension sample, the displacement at the crack mouth and at the load line are both considered. Only the crack mouth displacements for the arc-shaped tension samples are presented. The agreement between the displacements or crack lengths predicted by the various equations and the corresponding numerical data from which they were developed are nominally about 3 percent or better. These expressions should be useful in all types of fracture testing including fracture toughness, K-resistance, and fatigue crack growth.

  6. State-of-the-art report on piping fracture mechanics

    Energy Technology Data Exchange (ETDEWEB)

    Wilkowski, G.M.; Olson, R.J.; Scott, P.M. [Battelle, Columbus, OH (United States)

    1998-01-01

    This report is an in-depth summary of the state-of-the-art in nuclear piping fracture mechanics. It represents the culmination of 20 years of work done primarily in the US, but also attempts to include important aspects from other international efforts. Although the focus of this work was for the nuclear industry, the technology is also applicable in many cases to fossil plants, petrochemical/refinery plants, and the oil and gas industry. In compiling this detailed summary report, all of the equations and details of the analysis procedure or experimental results are not necessarily included. Rather, the report describes the important aspects and limitations, tells the reader where he can go for further information, and more importantly, describes the accuracy of the models. Nevertheless, the report still contains over 150 equations and over 400 references. The main sections of this report describe: (1) the evolution of piping fracture mechanics history relative to the developments of the nuclear industry, (2) technical developments in stress analyses, material property aspects, and fracture mechanics analyses, (3) unresolved issues and technically evolving areas, and (4) a summary of conclusions of major developments to date.

  7. Preparation and investigation of ultrafine-grained tungsten carbide with high hardness and fracture toughness

    Science.gov (United States)

    Chuvil'deev, V. N.; Blagoveshchenskii, Yu. V.; Sakharov, N. V.; Boldin, M. S.; Nokhrin, A. V.; Isaeva, N. V.; Shotin, S. V.; Lopatin, Yu. G.; Smirnova, E. S.

    2015-07-01

    High-density samples of ultrafine-grained tungsten carbide with high hardness (up to 31-34 GPa) and increased fracture toughness (up to 5.2-6.4 MPa m1/2) are obtained using the technology of electropulse plasma sintering. The influence of the initial size of nanoparticles of α-WC prepared by plasmachemical synthesis on the density, structural parameters, and mechanical properties of tungsten carbide is investigated.

  8. Biomechanical investigation of titanium elastic nail prebending for treating diaphyseal long bone fractures.

    Science.gov (United States)

    Chen, Yen-Nien; Lee, Pei-Yuan; Chang, Chih-Wei; Ho, Yi-Hung; Peng, Yao-Te; Chang, Chih-Han; Li, Chun-Ting

    2016-12-02

    This study numerically investigated the deformation of titanium elastic nails prebent at various degrees during implantation into the intramedullary canal of fractured bones and the mechanism by which this prebending influenced the stability of the fractured bone. Three degrees of prebending the implanted portions of the nails were used: equal to, two times, and three times the diameter of the intramedullary canal. Furthermore, a simulated diaphyseal fracture with a 5-mm gap was created in the middle shaft portion of the bone fixed with two elastic nails in a double C-type configuration. End caps were simulated using a constraint equation. To confirm that the simulation process is able to present the mechanical response of the nail inside the intramedullary, an experiment was conducted by using sawbone for validation. The results indicated that increasing the degrees of nail prebending facilitated straightening the nails against the inner aspect of canal after implantation, with increase in stability under torsion. Furthermore, reducing nail prebending caused a larger portion of the nails to move closer to the loading site and center of bone after implantation; the use of end caps prevented the nail tips from collapsing and increased axial stability. End cap use was critical for preventing the nail tips from collapsing and for increasing the stability of the nails prebent at a degree equal to the diameter of the canal with insufficient frictional force between the nail and canal. Therefore, titanium elastic nail prebending in a double C-type configuration with a degree three times the diameter of the canal represents a superior solution for treating transverse fractures without a gap, whereas that with a degree equal to the diameter of the intramedullary canal and combined with end cap use represents an advanced solution for treating comminuted fractures in a diaphyseal long bone fracture.

  9. Numerical Investigation of Influence of In-Situ Stress Ratio, Injection Rate and Fluid Viscosity on Hydraulic Fracture Propagation Using a Distinct Element Approach

    Directory of Open Access Journals (Sweden)

    Bo Zhang

    2016-02-01

    Full Text Available Numerical simulation is very useful for understanding the hydraulic fracturing mechanism. In this paper, we simulate the hydraulic fracturing using the distinct element approach, to investigate the effect of some critical parameters on hydraulic fracturing characteristics. The breakdown pressure obtained by the distinct element approach is consistent with the analytical solution. This indicates that the distinct element approach is feasible on modeling the hydraulic fracturing. We independently examine the influence of in-situ stress ratio, injection rate and fluid viscosity on hydraulic fracturing. We further emphasize the relationship between these three factors and their contributions to the hydraulic fracturing. With the increase of stress ratio, the fracture aperture increases almost linearly; with the increase of injection rate and fluid viscosity, the fracture aperture and breakdown pressure increase obviously. A low value of product of injection rate and fluid viscosity (i.e., Qμ will lead to narrow fracture aperture, low breakdown pressure, and complex or dispersional hydraulic fractures. A high value of Qμ would lead wide fracture aperture, high breakdown pressure, and simple hydraulic fractures (e.g., straight or wing shape. With low viscosity fluid, the hydraulic fracture geometry is not sensitive to stress ratio, and thus becomes a complex fracture network.

  10. 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.

  11. Measurement of residual stresses using fracture mechanics weight functions

    Energy Technology Data Exchange (ETDEWEB)

    Fan, Y. [Bettis Atomic Power Laboratory, West Mifflin, PA (United States)

    2001-07-01

    A residual stress measurement method has been developed to quantify through-the-thickness residual stresses. Accurate measurement of residual stresses is crucial for many engineering structures. Fabrication processes such as welding and machining generate residual stresses that are difficult to predict. Residual stresses affect the integrity of structures through promoting failures due to brittle fracture, fatigue, stress corrosion cracking, and wear. In this work, the weight function theory of fracture mechanics is used to measure residual stresses. The weight function theory is an important development in computational fracture mechanics. Stress intensity factors for arbitrary stress distribution on the crack faces can be accurately and efficiently computed for predicting crack growth. This paper demonstrates that the weight functions are equally useful in measuring residual stresses. In this method, an artificial crack is created by a thin cut in a structure containing residual stresses. The cut relieves the residual stresses normal to the crack-face and allows the relieved residual stresses to deform the structure. Strain gages placed adjacent to the cut measure the relieved strains corresponding to incrementally increasing depths of the cut. The weight functions of the cracked body relate the measured strains to the residual stresses normal to the cut within the structure. The procedure details, such as numerical integration of the singular functions in applying the weight function method, will be discussed. (author)

  12. [Bone fracture and the healing mechanisms. Fragility fracture and bone quality].

    Science.gov (United States)

    Mawatari, Taro; Iwamoto, Yukihide

    2009-05-01

    Fracture occurs in bone having less than normal elastic resistance without any violence. Numerous terms have been used to classify various types of fractures from low trauma events; "fragility fracture", "stress fracture", "insufficiency fracture", "fatigue fracture", "pathologic fracture", etc. The definitions of these terms and clinical characteristics of these fractures are discussed. Also state-of-the-art bone quality assessments; Finite element analysis of clinical CT scans, assessments of the Microdamage, and the Cross-links of Collagen are introduced in this review.

  13. Numerical Investigation on Stress Shadowing in Fluid Injection-Induced Fracture Propagation in Naturally Fractured Geothermal Reservoirs

    Science.gov (United States)

    Yoon, Jeoung Seok; Zimmermann, Günter; Zang, Arno

    2015-07-01

    In low permeability shale reservoirs, multi-stage hydraulic fracturing is largely used to increase the productivity by enlarging the stimulated rock volume. Hydraulic fracture created alters the stress field around it, and affects the subsequent fractures by the change of the stress field, in particular, mostly increased minimum principal stress at the area of subsequent fracturing. This is called stress shadow which accumulates as the fracturing stages advance from toe to heel. Hydraulic fractures generated in such altered stress field are shorter and compact with orientation deviating significantly from the far-field maximum horizontal stress orientation. This paper presents 2D discrete element-based numerical modeling of multi-stage hydraulic fracturing in a naturally fractured reservoir and investigates stress shadowing. The stress shadowing is tested with two different injection scenarios: constant and cyclic rate injections. The results show that cyclic injection tends to lower the effect of stress shadow as well as mitigates the magnitude of the induced seismicity. Another modeling case is presented to show how the stress shadow can be utilized to optimize a hydraulic fracture network in application to Groß Schönebeck geothermal reservoir, rather than being mitigated. The modeling demonstrated that the stress shadow is successfully utilized for optimizing the geothermal heat exchanger by altering the initial in situ stress field from highly anisotropic to less or even to isotropic.

  14. Discrete fracture modeling of hydro-mechanical damage processes in geological systems

    Science.gov (United States)

    Kim, K.; Rutqvist, J.; Houseworth, J. E.; Birkholzer, J. T.

    2014-12-01

    This study presents a modeling approach for investigating coupled thermal-hydrological-mechanical (THM) behavior, including fracture development, within geomaterials and structures. In the model, the coupling procedure consists of an effective linkage between two codes: TOUGH2, a simulator of subsurface multiphase flow and mass transport based on the finite volume approach; and an implementation of the rigid-body-spring network (RBSN) method, a discrete (lattice) modeling approach to represent geomechanical behavior. One main advantage of linking these two codes is that they share the same geometrical mesh structure based on the Voronoi discretization, so that a straightforward representation of discrete fracture networks (DFN) is available for fluid flow processes. The capabilities of the TOUGH-RBSN model are demonstrated through simulations of hydraulic fracturing, where fluid pressure-induced fracturing and damage-assisted flow are well represented. The TOUGH-RBSN modeling methodology has been extended to enable treatment of geomaterials exhibiting anisotropic characteristics. In the RBSN approach, elastic spring coefficients and strength parameters are systematically formulated based on the principal bedding direction, which facilitate a straightforward representation of anisotropy. Uniaxial compression tests are simulated for a transversely isotropic material to validate the new modeling scheme. The model is also used to simulate excavation fracture damage for the HG-A microtunnel in the Opalinus Clay rock, located at the Mont Terri underground research laboratory (URL) near Saint-Ursanne, Switzerland. The Opalinus Clay has transversely isotropic material properties caused by natural features such as bedding, foliation, and flow structures. Preferential fracturing and tunnel breakouts were observed following excavation, which are believed to be strongly influenced by the mechanical anisotropy of the rock material. The simulation results are qualitatively

  15. Mechanical design optimization of bioabsorbable fixation devices for bone fractures.

    Science.gov (United States)

    Lovald, Scott T; Khraishi, Tariq; Wagner, Jon; Baack, Bret

    2009-03-01

    Bioabsorbable bone plates can eliminate the necessity for a permanent implant when used to fixate fractures of the human mandible. They are currently not in widespread use because of the low strength of the materials and the requisite large volume of the resulting bone plate. The aim of the current study was to discover a minimally invasive bioabsorbable bone plate design that can provide the same mechanical stability as a standard titanium bone plate. A finite element model of a mandible with a fracture in the body region is subjected to bite loads that are common to patients postsurgery. The model is used first to determine benchmark stress and strain values for a titanium plate. These values are then set as the limits within which the bioabsorbable bone plate must comply. The model is then modified to consider a bone plate made of the polymer poly-L/DL-lactide 70/30. An optimization routine is run to determine the smallest volume of bioabsorbable bone plate that can perform and a titanium bone plate when fixating fractures of this considered type. Two design parameters are varied for the bone plate design during the optimization analysis. The analysis determined that a strut style poly-L-lactide-co-DL-lactide plate of 690 mm2 can provide as much mechanical stability as a similar titanium design structure of 172 mm2. The model has determined a bioabsorbable bone plate design that is as strong as a titanium plate when fixating fractures of the load-bearing mandible. This is an intriguing outcome, considering that the polymer material has only 6% of the stiffness of titanium.

  16. Inclusion size effect on the fatigue crack propagation mechanism and fracture mechanics of a superalloy

    Science.gov (United States)

    Denda, Takeshi; Bretz, Perter L.; Tien, John K.

    1992-02-01

    Low cycle fatigue life of nickel-base superalloys is enhanced as a consequence of inclusion reduction in the melt process; however, the functional dependencies between fatigue characteristics and inclusions have not been well investigated. In this study, the propagation mechanism of the fatigue crack initiated from inclusions is examined in fine-grained IN718, which is a representative turbine disc material for jet engines. There is a faceted-striated crack transition on the fracture surfaces. This faceted-striated transition also appears in the da/dN vs crack length curves. It is observed that the faceted crack propagation time can be more than 50 pct of total lifetime in the low cycle fatigue test. The significance of inclusion size effect is explained on the premise that the faceted fatigue crack propagation time scales with the inclusion size, which is taken as the initial crack length. A predictive protocol for determining inclusion size effect is given.

  17. Investigations on the fracture toughness of austempered ductile irons austenitized at different temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Rao, P. Prasad; Putatunda, Susil K

    2003-05-25

    Ductile cast iron was austenitized at four different temperatures and subsequently austempered at six different temperatures. Plane strain fracture toughness was evaluated under all the heat treatment conditions and correlated with the microstructural features such as the austenite content and the carbon content of the austenite. Fracture mechanism was studied by scanning electron microscopy. It was found that the optimum austempering temperature for maximum fracture toughness decreased with increasing austenitizing temperature. This could be interpreted in terms of the microstructural features. A study of the fracture mechanism revealed that good fracture toughness is unlikely to be obtained when austempering temperature is less than half of the austenitizing temperature on the absolute scale.

  18. The effect of hydrogen on strain hardening and fracture mechanism of high-nitrogen austenitic steel

    Science.gov (United States)

    Maier, G. G.; Astafurova, E. G.; Melnikov, E. V.; Moskvina, V. A.; Vojtsik, V. F.; Galchenko, N. K.; Zakharov, G. N.

    2016-07-01

    High-nitrogen austenitic steels are perspective materials for an electron-beam welding and for producing of wear-resistant coatings, which can be used for application in aggressive atmospheres. The tensile behavior and fracture mechanism of high-nitrogen austenitic steel Fe-20Cr-22Mn-1.5V-0.2C-0.6N (in wt.%) after electrochemical hydrogen charging for 2, 10 and 40 hours have been investigated. Hydrogenation of steel provides a loss of yield strength, uniform elongation and tensile strength. The degradation of tensile properties becomes stronger with increase in charging duration - it occurs more intensive in specimens hydrogenated for 40 hours as compared to ones charged for 2-10 hours. Fracture analysis reveals a hydrogen-induced formation of brittle surface layers up to 6 μm thick after 40 hours of saturation. Hydrogenation changes fracture mode of steel from mixed intergranular-transgranular to mainly transgranular one.

  19. Mechanical Properties and Fracture Behavior of Cu-Co-Be Alloy after Plastic Deformation and Heat Treatment

    Institute of Scientific and Technical Information of China (English)

    Yan-jun ZHOU; Ke-xing SONG; Jian-dong XING; Zhou LI; Xiu-hua GUO

    2016-01-01

    Mechanical properties and fracture behavior of Cu-0.84Co-0.23Be alloy after plastic deformation and heat treatment were comparatively investigated.Severe plastic deformation by hot extrusion and cold drawing was adopted to induce large plastic strain of Cu-0.84Co-0.23Be alloy.The tensile strength and elongation are up to 476.6 MPa and 1 8%,respectively.The fractured surface consists of deep dimples and micro-voids.Due to the formation of su-persaturated solid solution on the Cu matrix by solution treatment at 950 ℃ for 1 h,the tensile strength decreased to 271.9 MPa,while the elongation increased to 42%.The fracture morphology is parabolic dimple.Furthermore,the tensile strength increased significantly to 580.2 MPa after aging at 480 ℃ for 4 h.During the aging process,a large number of precipitates formed and distributed on the Cu matrix.The fracture feature of aged specimens with low elongation (4.6%)exhibits an obvious brittle intergranular fracture.It is confirmed that the mechanical properties and fracture behavior are dominated by the microstructure characteristics of Cu-0.84Co-0.23Be alloy after plastic de-formation and heat treatment.In addition,the fracture behavior at 450 ℃ of aged Cu-0.84Co-0.23Be alloy was also studied.The tensile strength and elongation are 383.6 MPa and 11.2%,respectively.The fractured morphologies are mainly candy-shaped with partial parabolic dimples and equiaxed dimples.The fracture mode is multi-mixed mechanism that brittle intergranular fracture plays a dominant role and ductile fracture is secondary.

  20. Survival Predictions of Ceramic Crowns Using Statistical Fracture Mechanics.

    Science.gov (United States)

    Nasrin, S; Katsube, N; Seghi, R R; Rokhlin, S I

    2017-01-01

    This work establishes a survival probability methodology for interface-initiated fatigue failures of monolithic ceramic crowns under simulated masticatory loading. A complete 3-dimensional (3D) finite element analysis model of a minimally reduced molar crown was developed using commercially available hardware and software. Estimates of material surface flaw distributions and fatigue parameters for 3 reinforced glass-ceramics (fluormica [FM], leucite [LR], and lithium disilicate [LD]) and a dense sintered yttrium-stabilized zirconia (YZ) were obtained from the literature and incorporated into the model. Utilizing the proposed fracture mechanics-based model, crown survival probability as a function of loading cycles was obtained from simulations performed on the 4 ceramic materials utilizing identical crown geometries and loading conditions. The weaker ceramic materials (FM and LR) resulted in lower survival rates than the more recently developed higher-strength ceramic materials (LD and YZ). The simulated 10-y survival rate of crowns fabricated from YZ was only slightly better than those fabricated from LD. In addition, 2 of the model crown systems (FM and LD) were expanded to determine regional-dependent failure probabilities. This analysis predicted that the LD-based crowns were more likely to fail from fractures initiating from margin areas, whereas the FM-based crowns showed a slightly higher probability of failure from fractures initiating from the occlusal table below the contact areas. These 2 predicted fracture initiation locations have some agreement with reported fractographic analyses of failed crowns. In this model, we considered the maximum tensile stress tangential to the interfacial surface, as opposed to the more universally reported maximum principal stress, because it more directly impacts crack propagation. While the accuracy of these predictions needs to be experimentally verified, the model can provide a fundamental understanding of the

  1. Investigation of Nasal Bone Fractures in the Framework of the Turkish Penal Code

    Directory of Open Access Journals (Sweden)

    Hüseyin Kafadar

    2014-06-01

    Becauseofalltraumaticnasalinjuries areconsidered judicial cases that whith the goal of determination types of nasal bone fracture, x-Ray wiew and computerized tomography should investigate. We have considered that if it is clearly writen type of nasal bone fracture in foresic reports, recurrent correspondence would not have and judiciary process would not extend. Key words: Forensic medicine, nasal fracture, trauma.

  2. Humeral fracture in non-ambulant infants - a possible accidental mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Somers, John M.; Halliday, Katharine E. [Nottingham University Hospitals, Radiology Department, Nottingham (United Kingdom); Chapman, Stephen [Birmingham Children' s Hospital, Birmingham (United Kingdom)

    2014-10-15

    Humeral fracture in a non-ambulant infant younger than 1 year is suspicious for a non-accidental injury unless there is a credible accidental explanation. A previously unrecognised accidental mechanism was described in 1996 whereby a 5-month-old infant was rolled by a 3-year-old sibling from a prone to a supine position. To investigate the widely accepted view that an infant with limited mobility cannot sustain a fracture of the humerus by his or her own actions in the absence of the intervention of an external party. We present seven cases of non-ambulant infants between 4 and 7 months of age in whom an isolated humeral fracture was the only injury present. In each case the caregiver described the fracture occurring when the child rolled over, trapping the dependent arm, without the intervention of another party. There is no proof for this mechanism in the form of an independent witness or video recording. However, we propose that this mechanism is worthy of further consideration as a rare and unusual cause for the injury. Further study is required. (orig.)

  3. (Environmental and geophysical modeling, fracture mechanics, and boundary element methods)

    Energy Technology Data Exchange (ETDEWEB)

    Gray, L.J.

    1990-11-09

    Technical discussions at the various sites visited centered on application of boundary integral methods for environmental modeling, seismic analysis, and computational fracture mechanics in composite and smart'' materials. The traveler also attended the International Association for Boundary Element Methods Conference at Rome, Italy. While many aspects of boundary element theory and applications were discussed in the papers, the dominant topic was the analysis and application of hypersingular equations. This has been the focus of recent work by the author, and thus the conference was highly relevant to research at ORNL.

  4. Elastic, plastic, and fracture mechanisms in graphene materials.

    Science.gov (United States)

    Daniels, Colin; Horning, Andrew; Phillips, Anthony; Massote, Daniel V P; Liang, Liangbo; Bullard, Zachary; Sumpter, Bobby G; Meunier, Vincent

    2015-09-23

    In both research and industry, materials will be exposed to stresses, be it during fabrication, normal use, or mechanical failure. The response to external stress will have an important impact on properties, especially when atomic details govern the functionalities of the materials. This review aims at summarizing current research involving the responses of graphene and graphene materials to applied stress at the nanoscale, and to categorize them by stress-strain behavior. In particular, we consider the reversible functionalization of graphene and graphene materials by way of elastic deformation and strain engineering, the plastic deformation of graphene oxide and the emergence of such in normally brittle graphene, the formation of defects as a response to stress under high temperature annealing or irradiation conditions, and the properties that affect how, and mechanisms by which, pristine, defective, and polycrystalline graphene fail catastrophically during fracture. Overall we find that there is significant potential for the use of existing knowledge, especially that of strain engineering, as well as potential for additional research into the fracture mechanics of polycrystalline graphene and device functionalization by way of controllable plastic deformation of graphene.

  5. Fracture mechanics of materials under compression along cracks (survey). Structural materials

    Science.gov (United States)

    Guz', A. N.; Nazarenko, V. M.

    1989-10-01

    The results elucidated in this paper and in [A. N. Guz' and V. M. Nazarenko, "Fracture mechanics of materials under compression along cracks (Survey). Highly-elastic material," Prikl. Mekh., 25, No. 9, 3-32 (1989)] of investigations on compression of materials along defects of crack type are exact since they are obtained within the framework of rigorous three-dimensional linearized formulations. Let us note that the fact that the mentioned result are standards for approximate approaches is of independent value. The investigations performed whose survey is represented above should be considered the beginning of a study of problems of material fracture under compression along cracks in a rigorous formulation (within the framework of the linearized mechanics of deformable bodies).

  6. The Impact of Cracked Microparticles on the Mechanical and the Fracture Behavior of Particulate Composite

    Directory of Open Access Journals (Sweden)

    Waleed K. Ahmed

    2015-10-01

    Full Text Available In this investigation a metallic composite with a cracked micro has been investigated using finite element method. Particulate reinforced composite is one of the most favorite composite due to it quit isotopic properties. While being in metallic status, the micro particles may be subjected to deterioration which lead to crack embedded initiation within the micro particle. This crack lead to degradation in the mechanical as well as the fracture behavior in the composite. Mechanical characteristics through estimating the stiffness of the composite has been studied for intact and cracked particles as well as for the fractured particles. It has been found that as long as the crack propagates in the micro particle, there is reduction in the composite stiffness and increases in the stress intensity factor (SIF.

  7. Fracturing and flow: Investigations on the formation of shallow water sills on Europa

    Science.gov (United States)

    Craft, Kathleen L.; Patterson, G. Wes; Lowell, Robert P.; Germanovich, Leonid

    2016-08-01

    Double ridge tectonic features appear prominently and ubiquitously across the surface of Jupiter's icy moon Europa. Previous studies have interpreted flanking fractures observed along some of the ridges as indicators of stress resulting from the ridge loading and flexing of the ice shell above a shallow water body. Here, we investigate a shallow water sill emplacement process at a time when the shell is cooling and thickening and explore the conditions that would make such a system feasible on timescales of ridge formation. Results show that fracture initiation and transport of ocean water to shallow depths can realistically occur, although horizontal fracturing and sill lifetimes prove challenging. Finite element models demonstrate that mechanical layering or a fractured shell do not provide enough stress change to promote horizontal fracturing, but tidal forcing does result in a small amount of turn. Assuming it is possible for a shallow sill to form, a sill would convect internally and conduct heat out quickly, resulting in a short lifetime in comparison to an estimated flexure timeframe of 100 kyr suggested required for double ridge formation. Consideration of heat transfer and residence in the overlying ice, however, extends the flexure timeframe and multiple sill intrusions or replenishment with warm ocean water could prolong the effective sill lifetime. Though challenges still remain for sill formation at Europa, these analyses constrain the potential mechanisms for emplacement and indicate sills can act as viable options for supplying the heat needed for surface flexure. Further analyses and future missions to Europa will help to increase our understanding of these enigmatic processes.

  8. Experimental investigation of heat transport through single synthetic fractures

    Science.gov (United States)

    Pastore, Nicola; Cherubini, Claudia; Giasi, Concetta I.; Redondo, Jose M.

    2017-04-01

    In fractured geothermal reservoirs, heat transport is highly influenced by the presence of the fractures, so appropriate knowledge of heat behaviour in fractured porous media is essential for accurate prediction of the energy extraction in geothermal reservoirs. The present study focuses on the study of heat transport within single synthetic fractures. In particular manner several tests have been carried out in order to explore the role of fracture roughness, aperture variability and the fracture-matrix ratio on the heat transport dynamics. The Synfrac program together with a 3d printer have been used to build several fracture planes having different geometrical characteristics that have been moulded to generate concrete porous fractured blocks. The tests regard the observation of the thermal breakthrough curves obtained through a continuous flow injection in correspondence of eight thermocouples located uniformly on the fractured blocks. The physical model developed permits to reproduce and understand adequately some features of heat transport dynamics in fractured media. The results give emphasis on the errors of the assumptions commonly used in heat transport modelling.

  9. An investigation on the fracture of linkage connecting wing flap of aircraft

    Science.gov (United States)

    Feng, Yanpeng; Tang, Haijun; Wang, Chun; Shu, Ping; Ma, Xiaoming; Li, Chunguang

    2017-01-01

    Linkage that connected wing flap and supports was found broken several times during from 2011 to 2014. Flights data was check, no heavy landing or exceed limiting speed warning were found. To investigate the root cause of the failure process, macroscopic and micrograph of the fracture surface were research with optical micrograph and scanning electron micrograph. Results show that the surface of fracture was dimples and shearing fracture structure which mean transient breaking features. Nearby the fracture, a lot of scratch and paint marks were found, that indicated that the rod may collapsed by impacted with some mechanical components. But the distance to the nearest component is within the tolerance, during ground inspection. Basing on stability analysis of column, the linkage will be bending deflection with elastic deformation, when compress exceed a critical value, which decrease the distance. But it will be recovered, during ground inspection for lower compress. Finite Element methods were used to demonstrate the bending deformation too. Basing on the reports and analysis, enhanced linkages were provided and substituted for older versions, and the relevant incidents were never found.

  10. Investigating Fracture Behaviors of Polymer and Polymeric Composite Materials Using Spiral Notch Torsion Test

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jy-An John [ORNL; Ren, Fei [ORNL; Tan, Ting [ORNL; Lara-Curzio, Edgar [ORNL; Agastra, Pancasatya [Montana State University; Mandell, John [Montana State University; Bertelsen, Williams D. [Gougeon Brothers, Inc.; LaFrance, Carl M. [Molded Fiber Glass Companies

    2011-01-01

    Wind turbine blades are usually fabricated from fiber reinforced polymeric (FRP) materials, which are subject to complex loading conditions during service. The reliability of the blades thus depends on the mechanical behaviors of the FRP under various loading conditions. Specifically, the fracture behavior of FRP is of great importance to both the scientific research community and the wind industry. In the current project, a new testing technique is proposed based on the spiral notch torsion test (SNTT) to study the fracture behavior of composite structures under mixed mode loading conditions, particularly under combined Mode I (flexural or normal tensile stress) and Mode III (torsional shear stress) loading. For the SNTT test method, round-rod specimens with V-grooved spiral lines are subjected to pure torsion. Depending on the pitch angle of the spiral lines, pure Mode I, pure Mode III, or mixed Mode I/Mode III loading conditions can be simulated. A three dimensional finite element analysis is then used to evaluate the fracture toughness and energy release rate of SNTT specimens. In the current study, both epoxy and fiberglass reinforced epoxy materials are investigated using the SNTT technique. This paper will discuss the fracture behaviors of mode I and mixed mode samples, with or without fatigue precrack. In addition, results from fractographic study and finite element analysis will be presented and discussed in detail.

  11. Correlation of fracture features with mechanical properties as a function of strain rate in zirconium alloys

    Energy Technology Data Exchange (ETDEWEB)

    Das, Arpan; Chakravartty, Jayanta Kumar [Bhabha Atomic Research Centre (Department of Atomic Energy), Trombay, Mumbai, Maharashtra (India). Mechanical Metallurgy Div.

    2016-02-15

    Two dimensional fracture features (i. e., dimple diameter, extent of tearing ridges etc.) quantified from the tensile fractographs are investigated to predict the nature of variation in mechanical properties with strain rates in zirconium alloys tested under ambient temperature where the initial inclusion or other second phase particle contents were kept unaltered. It has been possible to reasonably estimate the strength and ductility properties of an alloy from a systematic analysis of fractographic features.

  12. Analysis of propagation mechanisms of stimulation-induced fractures in rocks

    Science.gov (United States)

    Krause, Michael; Renner, Joerg

    2016-04-01

    Effectivity of geothermal energy production depends crucially on the heat exchange between the penetrated hot rock and the circulating water. Hydraulic stimulation of rocks at depth intends to create a network of fractures that constitutes a large area for exchange. Two endmembers of stimulation products are typically considered, tensile hydro-fractures that propagate in direction of the largest principal stress and pre-existing faults that are sheared when fluid pressure reduces the effective normal stress acting on them. The understanding of the propagation mechanisms of fractures under in-situ conditions is still incomplete despite intensive research over the last decades. Wing-cracking has been suggested as a mechanism of fracture extension from pre-existent faults with finite length that are induced to shear. The initiation and extension of the wings is believed to be in tensile mode. Open questions concern the variability of the nominal material property controlling tensile fracture initiation and extension, the mode I facture toughness KIC, with in-situ conditions, e.g., its mean-stress dependence. We investigated the fracture-propagation mechanism in different rocks (sandstones and granites) under varying conditions mimicking those representative for geothermal systems. To determine KIC-values we performed 3-point bending experiments. We varied the confining pressure, the piston velocity, and the position of the chevron notch relative to the loading configuration. Additional triaxial experiments at a range of confining pressures were performed to study wing crack propagation from artificial flaws whose geometrical characteristics, i.e., length, width, and orientation relative to the axial load are varied. We monitored acoustic emissions to constrain the spacio-temporal evolution of the fracturing. We found a significant effect of the length of the artificial flaw and the confining pressure on wing-crack initiation but did not observe a systematic dependence

  13. Early Age Fracture Mechanics and Cracking of Concrete

    DEFF Research Database (Denmark)

    Østergaard, Lennart

    2003-01-01

    Modern high performance concretes have low water cement ratios and do often include silica fume. Also early age high strength cements are often applied and when all these factors sum up, it turns out that the cracking sensibility is dramatically increased in com- parison with ordinary concrete...... if applied in early age. The results are only valid after 24 hours for fast and normal hardening cements and after 48 hours for slow hardening cements. This is con¯rmed in a finite element model. The fracture properties of early age concrete have been determined. The framework of the investigations has been...

  14. Mechanical Behavior and Fracture Toughness Evaluation of Multiphase Polymer Nanocomposites Using Impact and J-Integral via Locus Method

    Directory of Open Access Journals (Sweden)

    Bishnu P. Panda

    2013-01-01

    Full Text Available Fracture behaviors of fibrillar silicate clay (MMT filled thermoplastic polyolefin (TPO containing polypropylene (PP blended with ethylene-propylene-diene monomer (EPDM were systematically investigated using impact test method and J-integral by locus method. Drastic increase in impact strength is observed for all developed compositions and generally shows higher value for the selected phases containing dispersed nanoclay in PP matrix. A fracture mechanics approach has been adopted by mode I test, and the effects of specimen geometry have been investigated. Increase in interlaminar fracture energy value, Gc, and J-integral value, Jc, is marked as the crack propagated through the composite; that is, a rising “R-curve” is observed. Toughness measurements revealed that the fracture toughness increased with increasing clay content reaching maximum at 3 wt% of clay than pure PP. Moreover, enhancement of fracture toughness was more remarkable than that of stiffness. The fracture surfaces taken from different specimens were observed for exploring the fracture mechanisms using transmission electron microscopy (TEM revealed a strong particle-matrix adhesion.

  15. Mechanical Models of Bed-Perpendicular Fractures in Layered Rocks Subjected to Extensional Strain

    Science.gov (United States)

    Sanz, P.; Pollard, D. D.; Borja, R. I.

    2010-12-01

    Natural fractures (joints) enhance permeability and therefore are important for the economical production of low-permeability hydrocarbon reservoirs and aquifers. In this work we investigate the formation of bed-perpendicular joints during extension in a stiff brittle layer surrounded by thick softer layers. The quasi-static finite element models consist of three elasto-plastic layers with frictional bedding interfaces and the middle layer contains layer-perpendicular fractures that can accommodate opening at the bedding surface accompanied by interface sliding. The upper and lower boundaries are subject to normal tractions appropriate for the depth of burial. Lateral boundaries are displaced horizontally to represent the extensional tectonic regime. We use an interface model that captures the most important mechanical features during sliding of bedding interfaces and opening of joints: unilateral contact, elastic and plastic relative deformation, tensile strength, cohesion, frictional sliding, and non-associative plastic flow. The constitutive law extends the Coulomb slip criterion to the tensile regime to capture opening of fractures in a quasi-brittle manner. The finite element implementation employs a penalty scheme to impose the contact constraints along the interfaces. The numerical simulations show the effects of mechanical properties of layers and interfaces in the development and spacing of bed-perpendicular joints. We evaluate the concepts of fracture saturation and sequential infilling, and the relationship between joint spacing and layer thickness in the context of the new modeling capabilities.

  16. Tribological performance evaluation of tungsten carbide-based cermets and development of a fracture mechanics wear model

    Energy Technology Data Exchange (ETDEWEB)

    Bhagat, R.B. [Pennsylvania State Univ., State College, PA (United States). Applied Research Lab.; Conway, J.C. Jr. [Pennsylvania State Univ., State College, PA (United States). Applied Research Lab.; Amateau, M.F. [Pennsylvania State Univ., State College, PA (United States). Applied Research Lab.; Brezler, R.A. III [Pennsylvania State Univ., State College, PA (United States). Applied Research Lab.

    1996-12-15

    Tungsten carbide tools may exhibit sudden brittle fracture at high stresses such as are encountered in shear and slitter knives. This has limited the use of tungsten carbide tools to certain applications in spite of their high hardness and wear resistance. The objective of this investigation is to evaluate the tribological performance of selected cermets and develop a fracture mechanics wear model. Six compositions of WC-Co materials (Co ranging from 4 to 30% by weight) with or without TiC, NbC, TaC, or Mo{sub 2}C were selected for relating wear modes of these tool materials to pertinent mechanical properties such as fracture toughness and hardness. The influence of mechanical properties such as Young`s modulus, hardness, fracture toughness, modulus of rupture, and Weibull modulus on wear rates and wear modes of the selected materials is presented and discussed. The major mechanisms of wear in WC-Co materials are discussed as they apply to the development of suitable relationships between wear and mechanical properties. The wear process is by the transfer of steel from the ring to the cemented carbide block specimens, initiation of mode I cracks normal to the mating surface, propagation of mode II cracks parallel to the wear surfaces and the subsequent separation of platelets with adhered WC and Co particles through adhesive forces with the steel ring. The wear rates of the cermets do not show a consistent relationship with mode I or mode II fracture toughness, but a general trend of decreasing wear rate with hardness is seen. This suggests that the tribological performance of these cermets depends on certain specific functions of pertinent parameters including fracture toughness, hardness, applied load, coefficient of friction and microstructural characteristics. A fracture mechanics-based wear model has been developed to relate the steady state wear rate (W{sub ss}) to hardness, mode II fracture toughness, coefficient of friction, and applied load. (orig./MM)

  17. Probabilistic Fracture Mechanics and Optimum Fracture Control Analytical Procedures for a Reusable Solid Rocket Motor Case

    Science.gov (United States)

    Hanagud, S.; Uppaluri, B.

    1977-01-01

    A methodology for the reliability analysis of a reusable solid rocket motor case is discussed. The analysis is based on probabilistic fracture mechanics and probability distribution for initial flaw sizes. The developed reliability analysis is used to select the structural design variables of the solid rocket motor case on the basis of minimum expected cost and specified reliability bounds during the projected design life of the case. Effects of failure prevention plans such as nondestructive inspection and the material erosion between missions are also considered in the developed procedure for selection of design variables. The reliability-based procedure can be modified to consider other similar structures of reusable space vehicle systems with different failure prevention plans.

  18. The Schwickerath adhesion test: A fracture mechanics analysis.

    Science.gov (United States)

    Schneider, G A; Swain, M V

    2015-08-01

    The Schwickerath three point bending adhesion test is the basis of the International Standard ISO 9693:1999 procedure for assessing porcelain bonding to metals [1]. It has also been used to evaluate the adhesion of porcelain to zirconia. The purpose of this paper is a fracture mechanics analysis of this test, which allows determination of the crack-length load-displacement and toughness dependence of cracks extending along or near the interface. Linear elastic mechanics is used to develop expressions for the strain energy and compliance of Schwickerath geometry specimens as a function of crack extension along or near the interface. From the derivative of the compliance as a function of crack growth the strain energy release rate (G, N/m) is determined. The energy release rate for interface crack extension of Schwickerath geometry specimens is determined. It is found that a simple relationship between the minima of the force-displacement response and the strain energy release rate G exists. Further development enables the predicted force-displacement response as a function of crack length to be derived for different values of G. Experimental results of porcelain bonded to zirconia with and without notches of various lengths machined along the interface verify the expressions and analysis developed. With the fracture mechanics analysis developed in this paper it is possible to determine the quality of adhesion in Schwickerath specimens by the interface toughness in addition to the nominal interface shear bond strength. As the toughness of brittle materials has much less scatter than its strength, the interface toughness characterization of the adhesion should allow for a better distinction between the adhesion quality of bonding. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  19. Fracture mechanisms of glass particles under dynamic compression

    Energy Technology Data Exchange (ETDEWEB)

    Parab, Niranjan D.; Guo, Zherui; Hudspeth, M.; Claus, Benjamin; Fezzaa, Kamel; Sun, Tao; Chen, Weinong W.

    2017-08-01

    In this study, dynamic fracture mechanisms of single and contacting spherical glass particles were observed using high speed synchrotron X-ray phase contrast imaging. A modified Kolsky bar setup was used to apply controlled dynamic compressive loading on the soda-lime glass particles. Four different configurations of particle arrangements with one, two, three, and five particles were studied. In single particle experiments, cracking initiated near the contact area between the particle and the platen, subsequently fragmenting the particle in many small sub-particles. In multi-particle experiments, a crack was observed to initiate from the point just outside the contact area between two particles. The initiated crack propagated at an angle to the horizontal loading direction, resulting in separation of a fragment. However, this fragment separation did not affect the ability of the particle to withstand further contact loading. On further compression, large number of cracks initiated in the particle with the highest number of particle-particle contacts near one of the particle-particle contacts. The initiated cracks roughly followed the lines joining the contact points. Subsequently, the initiated cracks along with the newly developed sub-cracks bifurcated rapidly as they propagated through the particle and fractured the particle explosively into many small fragments, leaving the other particles nearly intact.

  20. Chemical and Mechanical Alteration of Fractures: Micro-Scale Simulations and Comparison to Experimental Results

    Science.gov (United States)

    Ameli, P.; Detwiler, R. L.; Elkhoury, J. E.; Morris, J. P.

    2012-12-01

    Fractures are often the main pathways for subsurface fluid flow especially in rocks with low matrix porosity. Therefore, the hydro-mechanical properties of fractures are of fundamental concern for subsurface CO2 sequestration, enhanced geothermal energy production, enhanced oil recovery, and nuclear waste disposal. Chemical and mechanical stresses induced during these applications may lead to significant alteration of the hydro-mechanical properties of fractures. Laboratory experiments aimed at understanding the chemo-hydro-mechanical response of fractures have shown a range of results that contradict simple conceptual models. For example, under conditions favoring mineral dissolution, where one would expect an overall increase in permeability and fracture aperture, permeability increases under some conditions and decreases under others. Recent experiments have attempted to link these core-scale observations to the relevant small-scale processes occurring within fractures. Results suggest that the loss of mechanical strength in asperities due to chemical alteration may cause non-uniform deformation and alteration of fracture apertures. However, it remains difficult to directly measure the coupled chemical and mechanical processes that lead to alteration of contacting fracture surfaces, which challenges our ability to predict the long-term evolution of the hydro-mechanical properties of fractures. Here, we present a computational model that uses micro-scale surface roughness and explicitly couples dissolution and elastic deformation to calculate local alterations in fracture aperture under chemical and mechanical stresses. Chemical alteration of the fracture surfaces is modeled using a depth-averaged algorithm of fracture flow and reactive transport. Then, we deform the resulting altered fracture-surfaces using an algorithm that calculates the elastic deformation. Nonuniform dissolution may cause the location of the resultant force between the two contacting

  1. Fracto-mechanoluminescence and mechanics of fracture of solids

    Energy Technology Data Exchange (ETDEWEB)

    Chandra, B.P., E-mail: bpchandra4@yahoo.co.in [Department of Applied Physics, Ashoka Institute of Technology and Management, Torankatta, G.E. Road, Rajnandgaon, 491441 (C.G.) (India); Chandra, V.K. [Department of Electrical and Electronics Engineering, Chhatrapati Shivaji Institute of Technology, Shivaji Nagar, Kolihapuri, Durg 491001 (C.G.) (India); Jha, P.; Patel, Rashmi; Shende, S.K. [Department of Postgraduate Studies and Research in Physics, Rani Durgavati, University, Jabalpur 482001 (India); Thaker, S. [Department of Physics and Computer Science, Government Model Science College, Raipur, 492010 (C.G.) (India); Baghel, R.N. [School of Studies in Physics and Astrophysics, Pt. Ravishankar Shukla University, Raipur, 492010 (C.G.) (India)

    2012-08-15

    investigation may be useful in designing of damage sensors, fracture sensors, ML-based safety management monitoring system, fuse-system for army warheads, milling machine, etc. The present study may be helpful in understanding the processes involved in earthquakes, earthquake lights and mine-failure as they basically involve fracture of solids. - Highlights: Black-Right-Pointing-Pointer The correlation between fracto-mechanoluminescence and fracture of solids is explored. Black-Right-Pointing-Pointer A clear understanding of the physics of fracto-mechanoluminescence is reported. Black-Right-Pointing-Pointer The study may be useful in designing the ML-based devices. Black-Right-Pointing-Pointer The study may be helpful in understanding earthquakes, and earthquake lights.

  2. Diameter of basalt columns derived from fracture mechanics bifurcation analysis.

    Science.gov (United States)

    Bahr, H-A; Hofmann, M; Weiss, H-J; Bahr, U; Fischer, G; Balke, H

    2009-05-01

    The diameter of columnar joints forming in cooling basalt and drying starch increases with decreasing growth rate. This observation can be reproduced with a linear-elastic three-dimensional fracture mechanics bifurcation analysis, which has been done for a periodic array of hexagonal columnar joints by considering a bifurcation mode compatible with observations on drying starch. In order to be applicable to basalt columns, the analysis has been carried out with simplified stationary temperature fields. The critical diameter differs from the one derived with a two-dimensional model by a mere factor of 1/2. By taking into account the latent heat released at the solidification front, the results agree fairly well with observed column diameters.

  3. A mechanism-based approach to modeling ductile fracture.

    Energy Technology Data Exchange (ETDEWEB)

    Bammann, Douglas J.; Hammi, Youssef; Antoun, Bonnie R.; Klein, Patrick A.; Foulk, James W., III; McFadden, Sam X.

    2004-01-01

    Ductile fracture in metals has been observed to result from the nucleation, growth, and coalescence of voids. The evolution of this damage is inherently history dependent, affected by how time-varying stresses drive the formation of defect structures in the material. At some critically damaged state, the softening response of the material leads to strain localization across a surface that, under continued loading, becomes the faces of a crack in the material. Modeling localization of strain requires introduction of a length scale to make the energy dissipated in the localized zone well-defined. In this work, a cohesive zone approach is used to describe the post-bifurcation evolution of material within the localized zone. The relations are developed within a thermodynamically consistent framework that incorporates temperature and rate-dependent evolution relationships motivated by dislocation mechanics. As such, we do not prescribe the evolution of tractions with opening displacements across the localized zone a priori. The evolution of tractions is itself an outcome of the solution of particular, initial boundary value problems. The stress and internal state of the material at the point of bifurcation provides the initial conditions for the subsequent evolution of the cohesive zone. The models we develop are motivated by in-situ scanning electron microscopy of three-point bending experiments using 6061-T6 aluminum and 304L stainless steel, The in situ observations of the initiation and evolution of fracture zones reveal the scale over which the failure mechanisms act. In addition, these observations are essential for motivating the micromechanically-based models of the decohesion process that incorporate the effects of loading mode mixity, temperature, and loading rate. The response of these new cohesive zone relations is demonstrated by modeling the three-point bending configuration used for the experiments. In addition, we survey other methods with the potential

  4. Fracture propagation in sandstone and slate e Laboratory experiments, acoustic emissions and fracture mechanics

    Institute of Scientific and Technical Information of China (English)

    Ferdinand Stoeckhert; Michael Molenda; Sebastian Brenne; Michael Alber

    2015-01-01

    abstract Fracturing of highly anisotropic rocks is a problem often encountered in the stimulation of unconven-tional hydrocarbon or geothermal reservoirs by hydraulic fracturing. Fracture propagation in isotropic material is well understood but strictly isotropic rocks are rarely found in nature. This study aims at the examination of fracture initiation and propagation processes in a highly anisotropic rock, specifically slate. We performed a series of tensile fracturing laboratory experiments under uniaxial as well as triaxial loading. Cubic specimens with edge lengths of 150 mm and a central borehole with a diameter of 13 mm were prepared from Fredeburg slate. An experiment using the rather isotropic Bebertal sandstone as a rather isotropic rock was also performed for comparison. Tensile fractures were generated using the sleeve fracturing technique, in which a polymer tube placed inside the borehole is pressurized to generate tensile fractures emanating from the borehole. In the uniaxial test series, the loading was varied in order to observe the transition from strength-dominated fracture propagation at low loading mag-nitudes to stress-dominated fracture propagation at high loading magnitudes.

  5. Thermal-Hydrologic-Mechanical Behavior of Single Fractures in EGS Reservoirs

    Science.gov (United States)

    Zyvoloski, G.; Kelkar, S.; Yoshioka, K.; Rapaka, S.

    2010-12-01

    Enhanced Geothermal Systems (EGS) rely on the creation a connected fracture system or the enhancement of existing (natural) fractures by hydraulic and chemical treatments. EGS studies at Fenton Hill (New Mexico, USA) and Hijiori (Japan) have revealed that only a limited number of fractures contribute to the effective heat transfer surface area. Thus, the economic viability of EGS depends strongly on the creation and spacing of single fractures in order to efficiently mine heat from given volume of rock. Though there are many similarities between EGS and natural geothermal reservoirs, a major difference between the reservoir types is the (typically) high pumping pressures and induced thermal stresses at the injection wells of an EGS reservoir. These factors can be responsible for fracture dilation/extension and thermal short circuiting and depend strongly on the surrounding state of stress in the reservoir and mechanical properties. We will present results from our study of the thermal-hydrologic-mechanical (THM) behavior of a single fracture in a realistic subsurface stress field. We will show that fracture orientation, the stress environment, fracture permeability structure, and the relationship between permeability changes in a fracture resulting from mechanical displacement are all important when designing and managing an EGS reservoir. Lastly, we present a sensitivity analysis of the important parameters that govern fracture behavior with respect to field measurements. Temperature in high permeability fracture in an EGS reservoir

  6. Atypical subtrochanteric femoral shaft fractures: role for mechanics and bone quality.

    Science.gov (United States)

    van der Meulen, Marjolein C H; Boskey, Adele L

    2012-08-29

    Bisphosphonates are highly effective agents for reducing osteoporotic fractures in women and men, decreasing fracture incidence at the hip and spine up to 50%. In a small subset of patients, however, these agents have recently been associated with 'atypical femoral fractures' (AFFs) in the subtrochanteric region or the diaphysis. These fractures have several atypical characteristics, including occurrence with minimal trauma; younger age than typical osteoporotic fractures; occurrence at cortical, rather than cancellous sites; early radiographic appearance similar to that of a stress fracture; transverse fracture pattern rather than the familiar spiral or transverse-oblique morphologies; initiation on the lateral cortex; and high risk of fracture on the contralateral side, at the same location as the initial fracture. Fracture is a mechanical phenomenon that occurs when the loads applied to a structure such as a long bone exceed its load-bearing capacity, either due to a single catastrophic overload (traumatic failure) or as a result of accumulated damage and crack propagation at sub-failure loads (fatigue failure). The association of AFFs with no or minimal trauma suggests a fatigue-based mechanism that depends on cortical cross-sectional geometry and tissue material properties. In the case of AFFs, bisphosphonate treatment may alter cortical tissue properties, as these agents are known to alter bone remodeling. This review discusses the use of bisphosphonates, their effects on bone remodeling, mechanics and tissue composition, their significance as an effective therapy for osteoporosis, and why these agents may increase fracture risk in a small population of patients.

  7. An investigation of radial tracer flow in naturally fractured reservoirs

    Energy Technology Data Exchange (ETDEWEB)

    Jetzabeth, Ramirez-Sabag; Fernando, Samaniego V.; Jesus, Rivera R.; Fernando Rodriguez

    1991-01-01

    This study presents a general solution for the radial flow of tracers in naturally fractured reservoirs. Continuous and finite step injection of chemical and radioactive tracers are considered. The reservoir is treated as being composed of two regions: a mobile region where longitudinal dispersion and convection take place and a stagnant region where only diffusion and adsorption are allowed. Radioactive decay is considered in both regions. The model of this study is thoroughly compared to those previously presented in literature by Moench and Ogata, Tang et al., Chen et al., and Hsieh et al. The solution is numerically inverted by means of the Crump algorithm. A detailed validation of the model with respect to solutions previously presented and/or simplified physical conditions solutions (i.e., homogeneous case) or limit solutions (i.e., for short times) was carried out. The influence of various dimensionless parameters that enter into the solution was investigated. A discussion of results obtained through the Crump and Stehfest algorithm is presented, concluding that the Crump method provides more reliable tracer concentrations.

  8. Mechanism of fracture in macro- and micro-scales in hollow centre cracked disc specimen

    Institute of Scientific and Technical Information of China (English)

    M. Eftekhari; A. Baghbanan; H. Hashemolhosseini; H. Amrollahi

    2015-01-01

    The hollow centre cracked disc (HCCD) specimen is one of the suggested alternative methods for determining the fracture toughness of rock. This work aims to investigate the fracture mechanism in HCCD in macro- and micro-scales using numerical methods, extended finite element method (X-FEM) and particle flow code (PFC) modeling, respectively. In the X-FEM, heaviside and near-tip enrichment functions are employed to consider the presence of the crack in the model. In PFC modeling the movement and interaction of stressed assemblies of rigid spherical particles are modeled using the distinct element method (DEM). A numerical code called MEX-FEM based on XFEM has been developed to simulate the problems involving crack. The models of pure modes I and II in macro-scale are simulated in micro-scale. The results show that dimensionless stress intensity factors (YI,YI) for pure modes I and II increase by increasing the crack length ratio. The angle at which the pure mode II occurs decreases by increasing the crack length ratio. In mixed mode I-II, The value ofYI decreases by increasing the crack angle, while the value ofYI increases to a given crack angle and then it decreases. Moreover, the fracture in micro-scale, unlike the macro-scale, includes a combination of different modes of fracturing.

  9. Mechanism of fracture in macro- and micro-scales in hollow centre cracked disc specimen

    Institute of Scientific and Technical Information of China (English)

    M.Eftekhari; A.Baghbanan; H.Hashemolhosseini; H.Amrollahi

    2015-01-01

    The hollow centre cracked disc(HCCD) specimen is one of the suggested alternative methods for determining the fracture toughness of rock. This work aims to investigate the fracture mechanism in HCCD in macro- and micro-scales using numerical methods, extended finite element method(X-FEM) and particle flow code(PFC) modeling, respectively. In the X-FEM, heaviside and near-tip enrichment functions are employed to consider the presence of the crack in the model. In PFC modeling the movement and interaction of stressed assemblies of rigid spherical particles are modeled using the distinct element method(DEM). A numerical code called MEX-FEM based on XFEM has been developed to simulate the problems involving crack. The models of pure modes I and Ⅱ in macro-scale are simulated in micro-scale. The results show that dimensionless stress intensity factors(YI, YⅡ) for pure modes I and Ⅱ increase by increasing the crack length ratio. The angle at which the pure mode Ⅱ occurs decreases by increasing the crack length ratio. In mixed mode I-Ⅱ, The value of YI decreases by increasing the crack angle, while the value of YⅡ increases to a given crack angle and then it decreases. Moreover, the fracture in micro-scale, unlike the macro-scale, includes a combination of different modes of fracturing.

  10. Mechanical and mathematical models of multi-stage horizontal fracturing strings and their application

    OpenAIRE

    Zhanghua Lian; Ying Zhang; Xu Zhao; Shidong Ding; Tiejun Lin

    2015-01-01

    Multi-stage SRV fracturing in horizontal wells is a new technology developed at home and abroad in recent years to effectively develop shale gas or low-permeability reservoirs, but on the other hand makes the mechanical environment of fracturing strings more complicated at the same time. In view of this, based on the loading features of tubing strings during the multi-stage fracturing of a horizontal well, mechanical models were established for three working cases of multiple packer setting, ...

  11. Molecular dynamics investigation of the fracture behavior of nanocrystalline α-Fe

    Science.gov (United States)

    Latapie, A.; Farkas, D.

    2004-04-01

    We carried out classical atomistic studies of crack propagation in fully three-dimensional nanocrystalline α-Fe (body-centered cubic structure) to examine the influence of temperature and average grain size on the fracture mechanisms and properties. Digital samples with grain sizes ranging from 6 to 12 nm are reported at temperatures ranging from 100 K to 600 K using atomistic simulations. For all grain sizes, a combination of intragranular and intergranular fracture is observed. Mechanisms such as grain boundary accommodation, grain boundary triple junction activity, grain nucleation and grain rotation are observed to dictate the plastic deformation energy release. Intergranular fracture is shown to proceed by the coalescence of nanovoids formed at the grain boundaries ahead of the crack. The simulations also show that at an atomistic scale the fracture resistance and plastic deformation energy release mechanisms increase with increasing temperature. The observed fracture toughness increases with decreasing grain size.

  12. Combined Isolated Laugier's Fracture and Distal Radial Fracture: Management and Literature Review on the Mechanism of Injury

    Science.gov (United States)

    Osman, Walid; Alaya, Zeineb; Naouar, Nader; Ben Ayeche, Mohamed

    2016-01-01

    Introduction. Isolated fracture of the trochlea is an uncommon condition requiring a particular mechanism of injury. Its association with a distal radial fracture is rare. We aimed through this case report to identify the injury mechanism and to assess surgical outcomes. Case Presentation. We report a 26-year-old female who was admitted to our department for elbow trauma following an accidental fall on her outstretched right hand with her elbow extended and supinated. On examination, the right elbow was swollen with tenderness over the anteromedial aspect of the distal humerus. The elbow range was restricted. Standard radiographs showed an intra-articular half-moon-shaped fragment lying proximal and anterior to the distal humerus. There was a comminuted articular fracture of the distal radius with an anterior displacement. A computed tomography revealed an isolated shear fracture of the trochlea without any associated lesion of the elbow. The patient was surgically managed. Anatomical reduction was achieved and the fracture was fixed with 2 Kirschner wires. The distal radial fracture was treated by open reduction and plate fixation. The postoperative course was uneventful with a good recovery. Conclusion. Knowledge of such entity would be useful to indicate the suitable surgical management and eventually to obtain good functional outcomes. PMID:28070435

  13. Combined Isolated Laugier’s Fracture and Distal Radial Fracture: Management and Literature Review on the Mechanism of Injury

    Directory of Open Access Journals (Sweden)

    Walid Osman

    2016-01-01

    Full Text Available Introduction. Isolated fracture of the trochlea is an uncommon condition requiring a particular mechanism of injury. Its association with a distal radial fracture is rare. We aimed through this case report to identify the injury mechanism and to assess surgical outcomes. Case Presentation. We report a 26-year-old female who was admitted to our department for elbow trauma following an accidental fall on her outstretched right hand with her elbow extended and supinated. On examination, the right elbow was swollen with tenderness over the anteromedial aspect of the distal humerus. The elbow range was restricted. Standard radiographs showed an intra-articular half-moon-shaped fragment lying proximal and anterior to the distal humerus. There was a comminuted articular fracture of the distal radius with an anterior displacement. A computed tomography revealed an isolated shear fracture of the trochlea without any associated lesion of the elbow. The patient was surgically managed. Anatomical reduction was achieved and the fracture was fixed with 2 Kirschner wires. The distal radial fracture was treated by open reduction and plate fixation. The postoperative course was uneventful with a good recovery. Conclusion. Knowledge of such entity would be useful to indicate the suitable surgical management and eventually to obtain good functional outcomes.

  14. Fracture mechanics of polymer mortar made with recycled raw materials

    Directory of Open Access Journals (Sweden)

    Marco Antonio Godoy Jurumenha

    2010-12-01

    Full Text Available The aim of this work is to show that industrial residues could be used in construction applications so that production costs as well as environmental protection can be improved. The fracture properties of polymer mortar manufactured with recycled materials are investigated to evaluate the materials behaviour to crack propagation. The residues used in this work were spent sand from foundry industry as aggregate, unsaturated polyester resin from polyethylene terephthalate (PET as matrix and polyester textile fibres from garment industry, producing an unique composite material fully from recycled components with low cost. The substitution of fresh by used foundry sand and the insertions of textile fibres contribute to a less brittle behaviour of polymer mortar.

  15. Investigation of mixed mode - I/II fracture problems - Part 1: computational and experimental analyses

    Directory of Open Access Journals (Sweden)

    O. Demir

    2016-01-01

    Full Text Available In this study, to investigate and understand the nature of fracture behavior properly under in-plane mixed mode (Mode-I/II loading, three-dimensional fracture analyses and experiments of compact tension shear (CTS specimen are performed under different mixed mode loading conditions. Al 7075-T651 aluminum machined from rolled plates in the L-T rolling direction (crack plane is perpendicular to the rolling direction is used in this study. Results from finite element analyses and fracture loads, crack deflection angles obtained from the experiments are presented. To simulate the real conditions in the experiments, contacts are defined between the contact surfaces of the loading devices, specimen and loading pins. Modeling, meshing and the solution of the problem involving the whole assembly, i.e., loading devices, pins and the specimen, with contact mechanics are performed using ANSYSTM. Then, CTS specimen is analyzed separately using a submodeling approach, in which three-dimensional enriched finite elements are used in FRAC3D solver to calculate the resulting stress intensity factors along the crack front. Having performed the detailed computational and experimental studies on the CTS specimen, a new specimen type together with its loading device is also proposed that has smaller dimensions compared to the regular CTS specimen. Experimental results for the new specimen are also presented.

  16. Numerical and experimental investigation of the fracture behavior of shock loaded alumina

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Plate impact expeiments are conducted to investigate the dynamic behavior of alumina by using one stage light gas gun. A ve-locity interferometer system for reflectors (VISAR) is used to obtain Hugoniot elastic limit and the free surface velocity profile,which consists of an elastic wave followed immediately by a dispersive inelastic wave. The stress histories under different impact velocities are measured by in-material manganin gauges. Based on the experimental data a Hugoniot curve is fitted,which shows the compressive characteristics that alumina changes typically from elastic to "plastic" ,and under higher pressure it will be transferred to similar-fluid state. The turning point of the Hugoniot curve from a high pressure region to a low pressure region is about 11.4 GPa. The fracture process of alumina is simulated by way of finite element code. After the analysis of the fracture mechanism,the numerical results show an important role played by the nucleation and the growth of the cracks in the macro-scopic fracture of the alumina target. The numerical predictions of stress histories are compared with the experimental results,which indicates consistency between them.

  17. Constraint corrected fracture mechanics in structural integrity assessment

    Energy Technology Data Exchange (ETDEWEB)

    Laukkanen, A.; Wallin, K. [VTT Industrial Systems, Espoo (Finland)

    2004-07-01

    Specimen size, crack depth and loading conditions may affect the materials fracture toughness. In order to safeguard against these geometry effects, fracture toughness testing standards prescribe the use of highly constrained deep cracked bend specimens having a sufficient size to guarantee conservative fracture toughness values. One of the more advanced testing standards, for brittle fracture, is the Master Curve standard ASTM E1921, which is based on technology developed at VTT Industrial Systems. When applied to a structure with low constraint geometry, the standard fracture toughness estimates may lead to strongly over-conservative estimate of structural performance. In some cases this may lead to unnecessary repairs or even to an early 'retirement' of the structure. In the case of brittle fracture, essentially three different methods to quantify constraint have been proposed, J-small scale yielding correction (SSYC), Q-parameter and the T{sub stress}. (orig.)

  18. Investigation of Possible Wellbore Cement Failures During Hydraulic Fracturing Operations

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Jihoon; Moridis, George

    2014-11-01

    We model and assess the possibility of shear failure, using the Mohr-Coulomb model ? along the vertical well by employing a rigorous coupled flow-geomechanic analysis. To this end, we vary the values of cohesion between the well casing and the surrounding cement to representing different quality levels of the cementing operation (low cohesion corresponds to low-quality cement and/or incomplete cementing). The simulation results show that there is very little fracturing when the cement is of high quality.. Conversely, incomplete cementing and/or weak cement can causes significant shear failure and the evolution of long fractures/cracks along the vertical well. Specifically, low cohesion between the well and cemented areas can cause significant shear failure along the well, but the same cohesion as the cemented zone does not cause shear failure. When the hydraulic fracturing pressure is high, low cohesion of the cement can causes fast propagation of shear failure and of the resulting fracture/crack, but a high-quality cement with no weak zones exhibits limited shear failure that is concentrated near the bottom of the vertical part of the well. Thus, high-quality cement and complete cementing along the vertical well appears to be the strongest protection against shear failure of the wellbore cement and, consequently, against contamination hazards to drinking water aquifers during hydraulic fracturing operations.

  19. Study on mechanical parameters of fractured rock masses

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    The equivalent strength parameters of fractured rock masses are prerequisite for stability analysis of geotechnical engineering projects constructed in fractured rock masses which are encountered frequently in western china.Based on generated mesh of fractured rock masses,combined with statistic damage constitutive model of intact rock and damage model of structural plane,progressive failure of fractured rock masses is studied using finite element method(FEM) .Furthermore,Scale effect and anisotropy of compressive strength of fractured rock masses are studied.Study results show that the strength decreases and tend towards stability rapidly from intact rock to fractured rock masses,and the anisotropy of strength of fractured rock masses is not significant.At last,based on numerical simulation conducted on 10 m scale rock masses under different confining pressures,the equivalent strength parameters of fractured rock masses are gained and the results are compared with Hoek-Brown criteria.The method developed is helpful for determination of strength parameters of fractured rock masses.

  20. A coupled thermo-poro-mechanical finite element analysis of fractured porous rocks using a cohesive interface element

    Science.gov (United States)

    Wang, W.; Regueiro, R. A.

    2014-12-01

    The coupling between multiphase flow, heat transfer, and poromechanics in fractured geomaterials has aroused great interest in the areas of geomechanics, geoenvironmental engineering, and petroleum engineering. Relevant applications include nuclear waste repositories, geological sequestration of CO2, geothermal systems, and exploitation of shale gas reservoirs. The paper presents a fully coupled thermo-poro-mechanical (TPM) cohesive interface element (CIE) model, which can represent fluid and heat flow along and across the fracture, and shear/normal deformation of the fracture surfaces. The proposed model is then applied to analyze two popular geological engineering problems using the finite element method (FEM) with a small strain formulation. The first application is the fracturing process in organic-rich shale due to heating. In the finite element analysis, multiple horizontal microcracks parallel to the bedding plane are assumed to preexist in the porous source rock, and are represented by coupled TPM cohesive interface elements. The porous bulk rock is assumed to be homogeneous, isotropic (for the time being, with transverse isotropy a natural extension), and linearly elastic. The excess pore fluid pressure, which mainly causes the development of the fractures, is actually induced by the rapid decomposition of organic matter during heating according to the literature. However, the involved complex chemical reaction process is beyond the scope of the paper, and is therefore substituted by a fluid injection process within the cracks under room temperature (25C) and high temperature (400C) in the paper. We investigate the fracture propagation due to pore fluid pressure increase and the development of fracture-induced permeability. The second application is a nuclear waste repository in a partially saturated fractured rock. Multiphase transport of moisture and heat, thermally-induced stress, as well as the change of fracture apertures are investigated due to short

  1. Numerical Investigation into the Influence of Bedding Plane on Hydraulic Fracture Network Propagation in Shale Formations

    Science.gov (United States)

    Yushi, Zou; Xinfang, Ma; Shicheng, Zhang; Tong, Zhou; Han, Li

    2016-09-01

    Shale formations are often characterized by low matrix permeability and contain numerous bedding planes (BPs) and natural fractures (NFs). Massive hydraulic fracturing is an important technology for the economic development of shale formations in which a large-scale hydraulic fracture network (HFN) is generated for hydrocarbon flow. In this study, HFN propagation is numerically investigated in a horizontally layered and naturally fractured shale formation by using a newly developed complex fracturing model based on the 3D discrete element method. In this model, a succession of continuous horizontal BP interfaces and vertical NFs is explicitly represented and a shale matrix block is considered impermeable, transversely isotropic, and linearly elastic. A series of simulations is performed to illustrate the influence of anisotropy, associated with the presence of BPs, on the HFN propagation geometry in shale formations. Modeling results reveal that the presence of BP interfaces increases the injection pressure during fracturing. HF deflection into a BP interface tends to occur under high strength and elastic anisotropy as well as in low vertical stress anisotropy conditions, which generate a T-shaped or horizontal fracture. Opened BP interfaces may limit the growth of the fracture upward and downward, resulting in a very low stimulated thickness. However, the opened BP interfaces favor fracture complexity because of the improved connection between HFs and NFs horizontally under moderate vertical stress anisotropy. This study may help predict the HF growth geometry and optimize the fracturing treatment designs in shale formations with complex depositional heterogeneity.

  2. Requirements for investigating the temperature-dependent fracture behavior of irradiated materials by indentation

    Energy Technology Data Exchange (ETDEWEB)

    Sacksteder, Irène, E-mail: irene.sacksteder@kit.edu [Karlsruhe Institute of Technology, Institute for Applied Materials, Eggenstein-Leopoldshafen (Germany); Hostettler, Simon [Synton-MDP Inc., Nidau (Switzerland); Charbonneau, Grégoire; Albinski, Bartlomiej; Schneider, Hans-Christian [Karlsruhe Institute of Technology, Institute for Applied Materials, Eggenstein-Leopoldshafen (Germany)

    2013-10-15

    Highlights: • A custom-made indenter is designed for indentations at high temperature. • The instrumented indentation technique at high temperature will be used to investigate temperature dependent fracture mechanisms in structural materials. • A finite-element based model has been validated with a view to predict crack initiation and propagation in Eurofer97 and tungsten-like materials. -- Abstract: The instrumented indentation technique is an interesting testing tool to examine temperature-dependent fracture mechanisms. It is planned to be used to generate cracks at defined temperatures in hard and brittle metallic materials. The present study describes the properties needed for the use of a new type of indenter operating at high temperature. The indenter was designed to meet mechanical and thermal requirements and other constraints relating to the operation of functional units of the indentation instrument. Additionally, a finite element model has been built with a view to predict indentation induced cracks in Eurofer97 and tungsten. The model has been validated both with the theory of Hertz and experimentally by comparison with indentation curves.

  3. Characterization of an injectable, degradable polymer for mechanical stabilization of mandibular fractures.

    Science.gov (United States)

    Henslee, Allan M; Yoon, Diana M; Lu, Benjamin Y; Yu, Joseph; Arango, Andrew A; Marruffo, Liann P; Seng, Luke; Anver, Tamir D; Ather, Hunaiza; Nair, Manitha B; Piper, Sean O; Demian, Nagi; Wong, Mark E K; Kasper, F Kurtis; Mikos, Antonios G

    2015-04-01

    This study investigated the use of injectable poly(propylene fumarate) (PPF) formulations for mandibular fracture stabilization applications. A full factorial design with main effects analysis was employed to evaluate the effects of the PPF:N-vinyl pyrrolidone (NVP, crosslinking agent) ratio and dimethyl toluidine (DMT, accelerator) concentration on key physicochemical properties including setting time, maximum temperature, mechanical properties, sol fraction, and swelling ratio. Additionally, the effects of formulation crosslinking time on the mechanical and swelling properties were investigated. The results showed that increasing the PPF:NVP ratio from 3:1 to 4:1 or decreasing the DMT concentration from 0.05 to 0.01 v/w % significantly decreased all mechanical properties as well as significantly increased the sol fraction and swelling ratio. Also, increasing the crosslinking time at 37°C from 1 to 7 days significantly increased all mechanical properties and decreased both the sol fraction and swelling ratio. This study further showed that the flexural stiffness of ex vivo stabilized rabbit mandibles increased from 1.7 ± 0.3 N/mm with a traditional mini-plate fixator to 14.5 ± 4.1 N/mm for the 4:1 (0.05 v/w % DMT) PPF formulation at day 1. Overall, the formulations tested in this study were found to have properties suitable for potential further consideration in mandibular fracture fixation applications. © 2014 Wiley Periodicals, Inc.

  4. ADDITIONAL STRESS AND FRACTURE MECHANICS ANALYSES OF PRESSURIZED WATER REACTOR PRESSURE VESSEL NOZZLES

    Energy Technology Data Exchange (ETDEWEB)

    Walter, Matthew [Structural Integrity Associates, Inc.; Yin, Shengjun [ORNL; Stevens, Gary [U.S. Nuclear Regulatory Commission; Sommerville, Daniel [Structural Integrity Associates, Inc.; Palm, Nathan [Westinghouse Electric Company, Cranberry Township, PA; Heinecke, Carol [Westinghouse Electric Company, Cranberry Township, PA

    2012-01-01

    In past years, the authors have undertaken various studies of nozzles in both boiling water reactors (BWRs) and pressurized water reactors (PWRs) located in the reactor pressure vessel (RPV) adjacent to the core beltline region. Those studies described stress and fracture mechanics analyses performed to assess various RPV nozzle geometries, which were selected based on their proximity to the core beltline region, i.e., those nozzle configurations that are located close enough to the core region such that they may receive sufficient fluence prior to end-of-life (EOL) to require evaluation of embrittlement as part of the RPV analyses associated with pressure-temperature (P-T) limits. In this paper, additional stress and fracture analyses are summarized that were performed for additional PWR nozzles with the following objectives: To expand the population of PWR nozzle configurations evaluated, which was limited in the previous work to just two nozzles (one inlet and one outlet nozzle). To model and understand differences in stress results obtained for an internal pressure load case using a two-dimensional (2-D) axi-symmetric finite element model (FEM) vs. a three-dimensional (3-D) FEM for these PWR nozzles. In particular, the ovalization (stress concentration) effect of two intersecting cylinders, which is typical of RPV nozzle configurations, was investigated. To investigate the applicability of previously recommended linear elastic fracture mechanics (LEFM) hand solutions for calculating the Mode I stress intensity factor for a postulated nozzle corner crack for pressure loading for these PWR nozzles. These analyses were performed to further expand earlier work completed to support potential revision and refinement of Title 10 to the U.S. Code of Federal Regulations (CFR), Part 50, Appendix G, Fracture Toughness Requirements, and are intended to supplement similar evaluation of nozzles presented at the 2008, 2009, and 2011 Pressure Vessels and Piping (PVP

  5. Investigation of fracture-matrix interaction: Preliminary experiments in a simple system

    Energy Technology Data Exchange (ETDEWEB)

    Foltz, S.D. [New Mexico Univ., Albuquerque, NM (United States). Dept. of Physics and Astronomy; Tidwell, V.C.; Glass, R.J.; Sobolik, S.R. [Sandia National Labs., Albuquerque, NM (United States)

    1992-12-31

    Paramount to the modeling of unsaturated flow and transport through fractured porous media is a clear understanding of the processes controlling fracture-matrix interaction. As a first step toward such an understanding, two preliminary experiments have been performed to investigate the influence of matrix imbibition on water percolation through unsaturated fractures in the plane normal to the fracture. Test systems consisted of thin slabs of either tuff or an analog material cut by a single vertical fracture into which a constant fluid flux was introduced. Transient moisture content and solute concentration fields were imaged by means of x-ray absorption. Flow fields associated with the two different media were significantly different owing to differences in material properties relative to the imposed flux. Richards` equation was found to be a valid means of modeling the imbibition of water into the tuff matrix from a saturated fracture for the current experiment.

  6. An investigation of the plastic fracture of high strength steels. Ph.D. Thesis

    Science.gov (United States)

    Cox, T. B.; Low, J. R., Jr.

    1973-01-01

    Three generally recognized stages of plastic fracture in high strength steels are considered in detail. These stages consist of void initiation, void growth, and void coalescence. A brief review of the existing literature on plastic fracture is included along with an outline of the experimental approach used in the investigation.

  7. Materials characterization and fracture mechanics of a space grade dielectric silicone insulation

    Science.gov (United States)

    Abdel-Latif, A. I.; Tweedie, A. T.

    1982-01-01

    The present investigation is concerned with the DC 93-500 high voltage silicone insulation material employed to pot the gun and the collector end of a traveling wave tube (TWT) used on the Landsat D Satellite. The fracture mechanics behavior of the silicone resin was evaluated by measuring the slow crack velocity as a function of the opening mode of the stress intensity factor at +25 and -10 C, taking into account various uniaxial discrete strain values. It was found that the silicone resins slow crack growth is faster than that for a high voltage insulation polyurethane material at the same stress intensity factor value and room temperature.

  8. Fracture mechanics analysis of damaged turbine rotor discs using finite element method

    Directory of Open Access Journals (Sweden)

    Vasović Ivana V.

    2014-01-01

    Full Text Available This paper presents evaluation fracture mechanics parameters in low pressure turbine components. Critical locations such as keyway and dovetail area are experiencing stress concentration leading to crack initiation. Stress intensity factors were evaluated using the J-Integral approach available within ANSYS software code. The finite element method allowed the prediction of the point of crack initiation and the crack propagation using the orientations of the maximum principal stresses. Special attention in this investigation is focused to develop analytic expressions for stress intensity factors at critical location of low pres-sure steam turbine disc. [Projekat Ministarstva nauke Republike Srbije, br. I-174001 i br. TR-35045

  9. Chemically- and mechanically-mediated influences on the transport and mechanical characteristics of rock fractures

    Energy Technology Data Exchange (ETDEWEB)

    Min, K.-B.; Rutqvist, J.; Elsworth, D.

    2009-02-01

    A model is presented to represent changes in the mechanical and transport characteristics of fractured rock that result from coupled mechanical and chemical effects. The specific influence is the elevation of dissolution rates on contacting asperities, which results in a stress- and temperature-dependent permanent closure. A model representing this pressure-dissolution-like behavior is adapted to define the threshold and resulting response in terms of fundamental thermodynamic properties of a contacting fracture. These relations are incorporated in a stress-stiffening model of fracture closure to define the stress- and temperature-dependency of aperture loss and behavior during stress and temperature cycling. These models compare well with laboratory and field experiments, representing both decoupled isobaric and isothermal responses. The model was applied to explore the impact of these responses on heated structures in rock. The result showed a reduction in ultimate induced stresses over the case where chemical effects were not incorporated, with permanent reduction in final stresses after cooling to ambient conditions. Similarly, permeabilities may be lower than they were in the case where chemical effects were not considered, with a net reduction apparent even after cooling to ambient temperature. These heretofore-neglected effects may have a correspondingly significant impact on the performance of heated structures in rock, such as repositories for the containment of radioactive wastes.

  10. Comparison of GTN Model and XFEM for Fracture Mechanics Analysis

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Sung Jun; Chang, Yoon Suk [Kyung Hee University, Youngin (Korea, Republic of)

    2014-10-15

    The simulation of discontinuities such as stationary and growing cracks by conventional finite element(FE) method is limited for bulk materials due to the necessity of computationally expensive remeshing process and high mesh densities. Accordingly, several advanced finite element techniques have been introduced to model crack propagation without remeshing. However, there are still many modeling uncertainties relating to arbitrary discontinuities in respect of accuracy and efficiency. In order to overcome this problem, eXtended Finite Element Method(XFEM) which allows the presence of discontinuities in elements by enriching degrees of freedom(DOF) with special displacement function was developed by Belytschko and Black. In this paper, the XFEM was applied to tensile tests for API X65 steel to implement crack simulation based on fracture mechanics analyses and verify through the comparison with the preceding study using Gurson-Tvergaard-Needleman (GTN) model. In this paper, a comprehensive numerical analyses were carried out to verify an adequacy of the XFEM by comparing its results with those obtained from experiments and GTN model. The XFEM has an efficiency due to the accessibility to the corresponding parameters such as cohesive strength, cohesive energy and critical separation. Also, visualization of crack simulation has an advantage compared to the GTN model. In these respects, the XFEM can be widely used in industrial fields and further analyses for bulk materials are needed.

  11. Fracture Mechanics Analyses for Interface Crack Problems - A Review

    Science.gov (United States)

    Krueger, Ronald; Shivakumar, Kunigal; Raju, Ivatury S.

    2013-01-01

    Recent developments in fracture mechanics analyses of the interfacial crack problem are reviewed. The intent of the review is to renew the awareness of the oscillatory singularity at the crack tip of a bimaterial interface and the problems that occur when calculating mode mixity using numerical methods such as the finite element method in conjunction with the virtual crack closure technique. Established approaches to overcome the nonconvergence issue of the individual mode strain energy release rates are reviewed. In the recent literature many attempts to overcome the nonconvergence issue have been developed. Among the many approaches found only a few methods hold the promise of providing practical solutions. These are the resin interlayer method, the method that chooses the crack tip element size greater than the oscillation zone, the crack tip element method that is based on plate theory and the crack surface displacement extrapolation method. Each of the methods is validated on a very limited set of simple interface crack problems. However, their utility for a wide range of interfacial crack problems is yet to be established.

  12. Probabilistic prediction of fatigue damage based on linear fracture mechanics

    Directory of Open Access Journals (Sweden)

    M. Krejsa

    2017-01-01

    Full Text Available Paper describes in detail and gives example of the probabilistic assessment of a steel structural element subject to fatigue load, particular attention being paid to cracks from the edge and those from surface. Fatigue crack damage depends on a number of stress range cycles. Three sizes are important for the characteristics of the propagation of fatigue cracks - the initial size, detectable size and acceptable size. The theoretical model of fatigue crack progression in paper is based on a linear fracture mechanics. When determining the required degree of reliability, it is possible to specify the time of the first inspection of the construction which will focus on the fatigue damage. Using a conditional probability, times for subsequent inspections can be determined. For probabilistic calculation of fatigue crack progression was used the original and new probabilistic methods - the Direct Optimized Probabilistic Calculation (“DOProC”, which is based on optimized numerical integration. The algorithm of the probabilistic calculation was applied in the FCProbCalc code (“Fatigue Crack Probabilistic Calculation”, using which is possible to carry out the probabilistic modelling of propagation of fatigue cracks in a user friendly environment very effectively.

  13. Experimental and theoretical investigation of mechanical disturbances in epoxy-impregnated superconducting coils. 2. Shear-stress-induced epoxy fracture as the principal source of premature quenches and training theoretical analysis

    Science.gov (United States)

    Bobrov, E. S.; Williams, J. E. C.; Iwasa, Y.

    An epoxy-impregnated superconducting winding may be considered structurally as a unidirectional composite consisting of superconducting wires embedded in a matrix of epoxy resin. The epoxy, because of its low strength and brittleness at low temperatures, is susceptible to brittle fracture which occurs under stresses induced initially during the cooldown (by differential thermal contractions of epoxy and metal) and subsequently during the magnet charge-up (by the Lorentz forces). Various modes of matrix failure are discussed and analysed. For the composite winding represented by four principal characteristics - geometry; constituent material properties; winding boundary conditions; and microcracks which become stress concentration sites for the initiation of further cracking. It is demonstrated that the transverse shear stresses induced by Lorentz forces in windings with cylindrical symmetry are principally responsible for premature magnet quenches. It is further demonstrated that to minimize shear stresses and thus prevent epoxy fracture in the winding, the whole winding body must not be restrained by the coil form and must be free to take its natural shape as the magnet is energized. This unrestrained winding support design is called the floating coil concept. The conclusions of the analysis agree both qualitatively and quantitatively with experimental results reported in the next two parts of this work.

  14. Fracture mechanisms in dual phase steels based on the acicular ferrite + martensite/austenite microstructure

    Science.gov (United States)

    Poruks, Peter

    The fracture mechanisms of low carbon microalloyed plate steels based on the acicular ferrite + marten site/austenite microstructure (AF + M/A) are investigated. The final microstructure consists of a dispersed phase of submicron equi-axed martensite particles with a bainitic ferrite matrix. A series of plates with M/A volume fractions of 0.076--0.179 are studied. Brittle fracture is investigated by Instrumented Charpy impact testing of samples at -196°C and subsequent metallography. The M/A particles are identified as the crack nucleation sites and the cleavage fracture stress calculated to be 2400 MPa in a complete AF microstrucuture. This value is significantly larger than in steels that contain significant proportions of conventional bainite. Standard Charpy and Instrumented Charpy impact testing is conducted through a temperature range from -80 to + 22°C to study ductile fracture behaviour. The total absorbed energy is separated into energies of crack nucleation and of crack propagation. It is found that the energy of crack nucleation is weakly dependent on the volume fraction of M/A and completely independent of temperature over the range studied. The crack propagation energy varies significantly with both variables, decreasing with increased volume fraction of M/A and with decreasing temperature. The peak load in the instrumented Charpy data is used to calculate the dynamic fracture toughness, KId, which is found to be 105--120 MPa-m1/2. The void nucleation and void growth stages of ductile fracture are studied by metallographic examination of tensile bars. The sites of void nucleation are identified as inclusions and M/A particles. Voids nucleate at the M/A particles by decohesion of the particle-matrix interface. A constant void nucleation strain of epsilon = 0.90 +/- 0.05 is measured for all of the samples independent of the volume fraction of M/A. A stress-based criterion is used to predict void nucleation and the interface strength is determined to be

  15. Research advances in fracturing mechanism of amorphous materials

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    @@ The fracture behavior of brittle materials is a timehonored problem. Archeologists discover that prehistoric people created their primitive tools using this behavior. During the Stone Age, for example, they made simple wooden butchery implements by taking advantage of a sharp edge caused by the brittle fracture on flint. According to archeologists, the application of brittle fracture to the tool-making was one of monumental inventions to mark the very beginning of human civilization.Afterwards, ancient potters succeeded in decorating their works by having the surface of pottery inlaid with cracks and fissures.

  16. Dyke propagation and tensile fracturing at high temperature and pressure, insights from experimental rock mechanics.

    Science.gov (United States)

    Bakker, Richard; Benson, Philip; Vinciguerra, Sergio

    2014-05-01

    It is well known that magma ascends trough the crust by the process of dyking. To enable dyke emplacement, basement rocks typically fail in a mode 1 fracture, which acts as conduits for magma transport. An overpressure of the ascending magma will further open/widen the fracture and permit the fracture to propagate. In order to further understand the emplacement and arrest of dykes in the subsurface, analogue and numerical studies have been conducted. However, a number of assumptions regarding rock mechanical behaviour frequently has to be made as such data are very hard to directly measure at the pressure/temperature conditions of interest: high temperatures at relatively shallow depths. Such data are key to simulating the magma intrusion dynamics through the lithologies that underlie the volcanic edifice. Here we present a new laboratory setup, which allows us to investigate the tensile fracturing properties under both temperature and confining pressure, and the emplacement of molten material within the newly formed fracture. We have modified a traditional tri-axial test assembly setup to be able to use a Paterson type High Pressure, High Temperature deformation apparatus. Sample setup consists of cylindrical rock samples with a 22 mm diameter and a 8 mm bore at their centre, filled with a material chosen as such that it's in a liquid state at the experimental temperature and solid at room temperature to enable post-experiment analysis. The top and lower parts of the rock sample are fitted with plugs, sealing in the melt. The assembly is then placed between ceramic pistons to ensure there are no thermal gradients across the sample. The assembly is jacketed to ensure the confining medium (Ar) cannot enter the assembly. A piston is driven into the sample such that the inner conduit materials pressure is slowly increased. At some point a sufficient pressure difference between the inner and outer surfaces causes the sample to deform and fail in the tensile regime

  17. Analysis of interlaminar fracture toughness and damage mechanisms in composite laminates reinforced with sprayed multi-walled carbon nanotubes

    KAUST Repository

    Almuhammadi, Khaled

    2014-01-01

    The present work is focused on the nanoreinforcement of prepreg based carbon fiber composite laminates to improve delamination resistance. Functionalized multi-walled carbon nanotubes (MWCNTs) were dispersed over the interface between prepreg layers through solvent spraying and the resulting mode I interlaminar fracture toughness was determined. For comparison, baseline samples with neat prepregs were also prepared. Results indicate that the introduction of functionalized MWCNTs can favorably affect the interlaminar fracture toughness, and the associated mechanisms of failure have been investigated. The manufacturing procedures and the interfacial reinforcing mechanism were explored by analyzing (i) the wettability between CNTs-solvent solution and prepreg surface, (ii) CNTs dispersion and (iii) the fractured surfaces through high resolution scanning electron microscopy and Raman mapping. © 2013 Elsevier Ltd.

  18. Research progress in mechanism of traumatic brain injury affecting speed of fracture healing

    Institute of Scientific and Technical Information of China (English)

    ZHAO Xiao-gang; ZHAO Guang-feng; MA Yue-feng; JIANG Guan-yu

    2007-01-01

    @@ In patients who have sustained traumatic brain injury with associated extremity fracture, there is often a clinical perception that the rate of new bone formation around the fracture site increases. 1 An overgrowth of callus is observed and ectopic ossification even occurs in the muscle,2 but the mechanism remains unclear.

  19. Influence of ageing, inclusions and voids on ductile fracture mechanism in commercial Al-alloys

    Indian Academy of Sciences (India)

    A Chennakesava Reddy; S Sundar Rajan

    2005-02-01

    The objective of the paper is to study the effect of ageing, inclusions and voids on the mechanism of fracture and resultant toughness. It has been found that the voids are initiated at only a fraction of the larger inclusions present. The initiation of voids at small particles in the ductile fracture process appears to have little effect on fracture toughness. The strain hardening capacity has a marked effect on void size, and is an indicator of fracture toughness in the commercial Al alloy.

  20. Friction Stir-Welded Titanium Alloy Ti-6Al-4V: Microstructure, Mechanical and Fracture Properties

    Science.gov (United States)

    Sanders, D. G.; Edwards, P.; Cantrell, A. M.; Gangwar, K.; Ramulu, M.

    2015-05-01

    Friction stir welding (FSW) has been refined to create butt welds from two sheets of Ti-6Al-4V alloy to have an ultra-fine grain size. Weld specimen testing was completed for three different FSW process conditions: As welded, stress relieved, stress relieved and machined, and for the un-welded base material. The investigation includes macrostructure, microstructure, microhardness, tensile property testing, notched bar impact testing, and fracture toughness evaluations. All experiments were conducted in accordance with industry standard testing specifications. The microstructure in the weld nugget was found to consist of refined and distorted grains of alpha in a matrix of transformed beta containing acicular alpha. The enhanced fracture toughness of the welds is a result of increased hardness, which is attributed to an increase in alpha phase, increase in transformed beta in acicular alpha, and grain refinement during the weld process. The noted general trend in mechanical properties from as welded, to stress relieved, to stress relieved and machined conditions exhibited a decrease in ultimate tensile strength, and yield strength with a small increase in ductility and a significant increase in fracture toughness.

  1. A numerical model of hydro-thermo-mechanical coupling in a fractured rock mass

    Energy Technology Data Exchange (ETDEWEB)

    Bower, K.M.

    1996-06-01

    Coupled hydro-thermo-mechanical codes with the ability to model fractured materials are used for predicting groundwater flow behavior in fractured aquifers containing thermal sources. The potential applications of such a code include the analysis of groundwater behavior within a geothermal reservoir. The capability of modeling hydro-thermo systems with a dual porosity, fracture flow model has been previously developed in the finite element code, FEHM. FEHM has been modified to include stress coupling with the dual porosity feature. FEHM has been further developed to implicitly couple the dependence of fracture hydraulic conductivity on effective stress within two dimensional, saturated aquifers containing fracture systems. The cubic law for flow between parallel plates was used to model fracture permeability. The Bartin-Bandis relationship was used to determine the fracture aperture within the cubic law. The code used a Newton Raphson iteration to implicitly solve for six unknowns at each node. Results from a model of heat flow from a reservoir to the moving fluid in a single fracture compared well with analytic results. Results of a model showing the increase in fracture flow due to a single fracture opening under fluid pressure compared well with analytic results. A hot dry rock, geothermal reservoir was modeled with realistic time steps indicating that the modified FEHM code does successfully model coupled flow problems with no convergence problems.

  2. Analysis of seismic sources for different mechanisms of fracture growth for microseismic monitoring applications

    Energy Technology Data Exchange (ETDEWEB)

    Duchkov, A. A., E-mail: DuchkovAA@ipgg.sbras.ru [Trofimuk Institute of Petroleum Geology and Geophysics SB RAS, Novosibirsk, 630090 (Russian Federation); Novosibirsk State University, Novosibirsk, 630090 (Russian Federation); Stefanov, Yu. P., E-mail: stefanov@ispms.tsc.ru [Trofimuk Institute of Petroleum Geology and Geophysics SB RAS, Novosibirsk, 630090 (Russian Federation)

    2015-10-27

    We have developed and illustrated an approach for geomechanic modeling of elastic wave generation (microsiesmic event occurrence) during incremental fracture growth. We then derived properties of effective point seismic sources (radiation patterns) approximating obtained wavefields. These results establish connection between geomechanic models of hydraulic fracturing and microseismic monitoring. Thus, the results of the moment tensor inversion of microseismic data can be related to different geomechanic scenarios of hydraulic fracture growth. In future, the results can be used for calibrating hydrofrac models. We carried out a series of numerical simulations and made some observations about wave generation during fracture growth. In particular when the growing fracture hits pre-existing crack then it generates much stronger microseismic event compared to fracture growth in homogeneous medium (radiation pattern is very close to the theoretical dipole-type source mechanism)

  3. Fracture-Based Mesh Size Requirements for Matrix Cracks in Continuum Damage Mechanics Models

    Science.gov (United States)

    Leone, Frank A.; Davila, Carlos G.; Mabson, Gerald E.; Ramnath, Madhavadas; Hyder, Imran

    2017-01-01

    This paper evaluates the ability of progressive damage analysis (PDA) finite element (FE) models to predict transverse matrix cracks in unidirectional composites. The results of the analyses are compared to closed-form linear elastic fracture mechanics (LEFM) solutions. Matrix cracks in fiber-reinforced composite materials subjected to mode I and mode II loading are studied using continuum damage mechanics and zero-thickness cohesive zone modeling approaches. The FE models used in this study are built parametrically so as to investigate several model input variables and the limits associated with matching the upper-bound LEFM solutions. Specifically, the sensitivity of the PDA FE model results to changes in strength and element size are investigated.

  4. Lithium Ion Storage Characteristics of Mechanically Fractured Titanate Nanotubes

    Directory of Open Access Journals (Sweden)

    Jeongeun Kim

    2012-01-01

    Full Text Available The effect of mechanical milling on the formation of short titanate nanotube and structural change induced is investigated. Mechanical milling produces the short nanotubes with the length of 30–160 nm. The lithium ion intercalation characteristics of the obtained short titanate nanotube were studied to verify the effect of the newly formed cross-sections of nanotubes. It was found that the protonated titanate nanotubes maintained long shapes until 30 min of mechanical milling and were transformed into agglomerated nanosheets and finally anatase granules depending on the treatment duration. Through galvanostatic investigation, the nanotubes with milling of 15 min exhibited the highest discharge capacity of 336 mAh·g−1 in first cycle, 12.4% larger than pristine.

  5. Numerical investigation of the hydro-mechanical contribution to seismic attenuation in damaged rocks

    Science.gov (United States)

    Pollmann, Nele; Jänicke, Ralf; Renner, Jörg; Steeb, Holger

    2016-04-01

    The investigation of hydro-mechanical processes, in particular the modeling of seismic waves in fractured porous media, is essential for the physical interpretation of data obtained from seismic exploration. Here, we specifically investigate attenuation processes in fluid-saturated porous rock containing fracture networks to identify effective hydro-mechanical properties by numerical simulation. The main purpose of this work is the characterization of the overall hydro-mechanical properties by computational homogenization. We determine an effective Skempton coefficient by investigating the fluid pressure and the solid displacement of the skeleton saturated by compressible fluids. Fracture networks are stochastically generated to mimic geological in-situ situations. The fractures are approximated as ellipses with aspect ratios up to 1/100, i.e. they constitute thin and long hydraulic conduits with high permeabilities. Simulations are designed on the material scale with and without conservation of fluid mass in the control volume. Using computational homogenization approaches, we define an effective Skempton coefficient. A range of fracture networks with different characteristic properties is studied for different varieties of fractures. On the material scale we find strongly heterogeneous pressure propagation in the fracture network and the surrounding rock, respectively. The pressure diffusion is much faster in the fracture network than in the matrix, rendering the macroscopic hydro-mechanical behavior strongly time dependent. The effective Skempton coefficient converges to an ensemble-specific instantaneous value and to 1 for long-time studies. The ultimate objective of our study is to evaluate whether constraints on the structure of fracture networks can be deduced from observations of attenuation and its frequency dependence.

  6. Teardrop fracture following head-first impact in an ice hockey player: Case report and analysis of injury mechanisms.

    Science.gov (United States)

    Yue, James J; Ivancic, Paul C; Scott, David L

    2016-01-01

    We report a case of a young male athlete who sustained a three column displaced teardrop fracture of the C5 vertebra due to a head-first impact in hockey, suffered neurapraxia, yet made full neurological recovery. This full recovery was in sharp contrast to multiple case series which reported permanent quadriplegia in the vast majority of teardrop fracture patients. We investigate the etiology and biomechanical mechanisms of injury. Admission imaging revealed the teardrop fracture which consisted of: a frontal plane fracture which separated an anterior quadrilateral-shaped fragment from the posterior vertebral body; a vertical fracture of the posterior vertebral body in the sagittal plane; and incomplete fractures of the neural arch that initiated superiorly at the anterior aspect of the spinous process and left lamina adjacent to the superior facet. Epidural hematoma in the region of the C5 vertebra was observed in addition to disc and ligamentous disruptions at C4-5 and C5-6. Our patient was ultimately treated surgically with anterior fusion from C4 through C6 and subsequently with bilateral posterior fusion at C5-6. The injuries were caused by high-energy axial compression with the neck in a pre-flexed posture. The first fracture event consisted of the anterior vertebral body fragment being sheared off of the posterior fragment under the compression load due in part to the sagittal plane concavity of the C5 inferior endplate. The etiology of the vertical fracture of the posterior vertebral body fragment in the sagittal plane was consistent with a previously described hypothesis of the mechanistic injury events. First, the C4-5 disc height decreased under load which increased its hoop stress. Next, this increased hoop stress transferred lateral forces to the C5 uncinate processes which caused their outward expansion. Finally, the outward expansion of the uncinate processes caused the left and right sides of the vertebral body to split and spread. Evidence in

  7. The radiation swelling effect on fracture properties and fracture mechanisms of irradiated austenitic steels. Part II. Fatigue crack growth rate

    Science.gov (United States)

    Margolin, B.; Minkin, A.; Smirnov, V.; Sorokin, A.; Shvetsova, V.; Potapova, V.

    2016-11-01

    The experimental data on the fatigue crack growth rate (FCGR) have been obtained for austenitic steel of 18Cr-10Ni-Ti grade (Russian analog of AISI 321 steel) irradiated up to neutron dose of 150 dpa with various radiation swelling. The performed study of the fracture mechanisms for cracked specimens under cyclic loading has explained why radiation swelling affects weakly FCGR unlike its effect on fracture toughness. Mechanical modeling of fatigue crack growth has been carried out and the dependencies for prediction of FCGR in irradiated austenitic steel with and with no swelling are proposed and verified with the obtained experimental results. As input data for these dependencies, FCGR for unirradiated steel and the tensile mechanical properties for unirradiated and irradiated steels are used.

  8. ORIGINAL ARTICLE Investigation of Nonholonomic Mechanics ...

    African Journals Online (AJOL)

    In this article, methods of modeling dynamic systems namely, Nonholonomic mechanics, Vakonomic mechanics and Chetaev methods for constrained dynamic system are investigated. The fact ..... Chaotic Dyn. 7(1).43–47. [6] Cortés J. (2002).

  9. Investigations on the fracture toughness of austempered ductile iron alloyed with chromium

    Energy Technology Data Exchange (ETDEWEB)

    Rao, P. Prasad; Putatunda, Susil K

    2003-04-15

    An investigation was carried out to examine the influence of chromium content on the plane strain fracture toughness of austempered ductile iron (ADI). ADIs containing 0, 0.3 and 0.5 wt.% chromium were austempered over a range of temperatures to produce different microstructures. The microstructures were characterized by optical microscopy and X-ray diffraction. Plane strain fracture toughness of all these materials was determined and correlated with microstructure and chromium content. The chromium content was found to influence the fracture toughness through its influence on the processing window. Since the chromium addition shifts the processing window to shorter durations, the higher chromium alloys at higher austempering temperatures tend to fall outside of the processing window, resulting in less than optimum microstructure and inferior fracture toughness. A small chromium addition of 0.3 wt.% was found to be beneficial for the fracture toughness of ADI.

  10. Mechanics and mechano-biology of fracture healing in normal and osteoporotic bone.

    Science.gov (United States)

    Augat, Peter; Simon, Ulrich; Liedert, Astrid; Claes, Lutz

    2005-03-01

    Fracture repair, which aims at regaining the functional competence of a bone, is a complex and multifactorial process. For the success of fracture repair biology and mechanics are of immense importance. The biological and mechanical environments must be compatible with the processes of cell and tissue proliferation and differentiation. The biological environment is characterized by the vascular supply and by many biochemical components, the biochemical milieu. A good vascular supply is a prerequisite for the initiation of the fracture repair process. The biochemical milieu involves complex interactions among local and systemic regulatory factors such as growth factors or cytokines. The mechanical environment is determined by the local stress and strain within the fracture. However, the local stress and strain is not accessible, and the mechanical environment, therefore, is described by global mechanical factors, e.g., gap size or interfragmentary movement. The relationship between local stress and strain and the global mechanical factors can be obtained by numerical models (Finite Element Model). Moreover, there is considerable interaction between biological factors and mechanical factors, creating a biomechanical environment for the fracture healing process. The biomechanical environment is characterized by osteoblasts and osteocytes that sense the mechanical signal and express biological markers, which effect the repair process. This review will focus on the effects of biomechanical factors on fracture repair as well as the effects of age and osteoporosis.

  11. Refinement and fracture mechanisms of as-cast QT700-6 alloy by alloying method

    Directory of Open Access Journals (Sweden)

    Min-qiang Gao

    2017-01-01

    Full Text Available The as-cast QT700-6 alloy was synthesized with addition of a certain amount of copper, nickel, niobium and stannum elements by alloying method in a medium frequency induction furnace, aiming at improving its strength and toughness. Microstructures of the as-cast QT700-6 alloy were observed using a scanning-electron microscope (SEM and the mechanical properties were investigated using a universal tensile test machine. Results indicate that the ratio of pearlite/ferrite is about 9:1 and the graphite size is less than 40 μm in diameter in the as-cast QT700-6 alloy. The predominant refinement mechanism is attributed to the formation of niobium carbides, which increases the heterogeneous nucleus and hinders the growth of graphite. Meanwhile, niobium carbides also exist around the grain boundaries, which improve the strength of the ductile iron. The tensile strength and elongation of the as-cast QT700-6 alloy reach over 700 MPa and 6%, respectively, when the addition amount of niobium is 0.8%. The addition of copper and nickel elements contributed to the decrease of eutectoid transformation temperature, resulting in the decrease of pearlite lamellar spacing (about 248 nm, which is also beneficial to enhancing the tensile strength. The main fracture mechanism is cleavage fracture with the appearance of a small amount of dimples.

  12. Applicability of Fracture Mechanics Methodology to Cracking and Fracture of Concrete.

    Science.gov (United States)

    1986-02-01

    cracking and fracture. The publicized, annotated bibliography was the one by S. Mindess entitled "The Cracking and Fracture of Concrete: An Annotated...7 --- 109 157.0 Mindess , S.. J. S. Nadeau and J. M. Hay, Effects of Different Curing Conditions on Slow Crack Growth in Cement Paste, Cement and...Concrete Research. Vol. 4, 1974, pp. 953-965 158.0 Nadeau, J3. S.. S. Mindess and J3. MI. Hay, Slow Crack Growth in Cement Paste, Journal of the

  13. THERMO-HYDRO-MECHANICAL MODELING OF WORKING FLUID INJECTION AND THERMAL ENERGY EXTRACTION IN EGS FRACTURES AND ROCK MATRIX

    Energy Technology Data Exchange (ETDEWEB)

    Robert Podgorney; Chuan Lu; Hai Huang

    2012-01-01

    Development of enhanced geothermal systems (EGS) will require creation of a reservoir of sufficient volume to enable commercial-scale heat transfer from the reservoir rocks to the working fluid. A key assumption associated with reservoir creation/stimulation is that sufficient rock volumes can be hydraulically fractured via both tensile and shear failure, and more importantly by reactivation of naturally existing fractures (by shearing), to create the reservoir. The advancement of EGS greatly depends on our understanding of the dynamics of the intimately coupled rock-fracture-fluid-heat system and our ability to reliably predict how reservoirs behave under stimulation and production. Reliable performance predictions of EGS reservoirs require accurate and robust modeling for strongly coupled thermal-hydrological-mechanical (THM) processes. Conventionally, these types of problems have been solved using operator-splitting methods, usually by coupling a subsurface flow and heat transport simulators with a solid mechanics simulator via input files. An alternative approach is to solve the system of nonlinear partial differential equations that govern multiphase fluid flow, heat transport, and rock mechanics simultaneously, using a fully coupled, fully implicit solution procedure, in which all solution variables (pressure, enthalpy, and rock displacement fields) are solved simultaneously. This paper describes numerical simulations used to investigate the poro- and thermal- elastic effects of working fluid injection and thermal energy extraction on the properties of the fractures and rock matrix of a hypothetical EGS reservoir, using a novel simulation software FALCON (Podgorney et al., 2011), a finite element based simulator solving fully coupled multiphase fluid flow, heat transport, rock deformation, and fracturing using a global implicit approach. Investigations are also conducted on how these poro- and thermal-elastic effects are related to fracture permeability

  14. Site investigations: Strategy for rock mechanics site descriptive model

    Energy Technology Data Exchange (ETDEWEB)

    Andersson, Johan [JA Streamflow AB, Aelvsjoe (Sweden); Christiansson, Rolf [Swedish Nuclear Fuel and Waste Management Co., Stockholm (Sweden); Hudson, John [Rock Engineering Consultants, Welwyn Garden City (United Kingdom)

    2002-05-01

    As a part of the planning work for the Site Investigations, SKB has developed a Rock Mechanics Site Descriptive Modelling Strategy. Similar strategies are being developed for other disciplines. The objective of the strategy is that it should guide the practical implementation of evaluating site specific data during the Site Investigations. It is also understood that further development may be needed. This methodology enables the crystalline rock mass to be characterised in terms of the quality at different sites, for considering rock engineering constructability, and for providing the input to numerical models and performance assessment calculations. The model describes the initial stresses and the distribution of deformation and strength properties of the intact rock, of fractures and fracture zones, and of the rock mass. The rock mass mechanical properties are estimated by empirical relations and by numerical simulations. The methodology is based on estimation of mechanical properties using both empirical and heroretical/numerical approaches; and estimation of in situ rock stress using judgement and numerical modelling, including the influence of fracture zones. These approaches are initially used separately, and then combined to produce the required characterisation estimates. The methodology was evaluated with a Test Case at the Aespoe Hard Rock Laboratory in Sweden. The quality control aspects are an important feature of the methodology: these include Protocols to ensure the structure and coherence of the procedures used, regular meetings to enhance communication, feedback from internal and external reviewing, plus the recording of an audit trail of the development steps and decisions made. The strategy will be reviewed and, if required, updated as appropriate.

  15. Microstructure-Sensitive Investigation of Fracture Using Acoustic Emission Coupled With Electron Microscopy

    Science.gov (United States)

    Wisner, Brian; Cabal, Mike; Vanniamparambiland, Prashanth A.; Leser, William; Hochhalter, Jacob; Kontsos, Antonios

    2015-01-01

    A novel technique using Scanning Electron Microscopy (SEM) in conjunction with Acoustic Emission (AE) monitoring is proposed to investigate microstructure-sensitive fatigue and fracture of metals. The coupling between quasi in situ microscopy with actual in situ nondestructive evaluation falls into the ICME framework and the idea of quantitative data-driven characterization of material behavior. To validate the use of AE monitoring inside the SEM chamber, Aluminum 2024-B sharp notch specimen were tested both inside and outside the microscope using a small scale mechanical testing device. Subsequently, the same type of specimen was tested inside the SEM chamber. Load data were correlated with both AE information and observations of microcracks around grain boundaries as well as secondary cracks, voids, and slip bands. The preliminary results are in excellent agreement with similar findings at the mesoscale. Extensions of the application of this novel technique are discussed.

  16. Strontium Is Incorporated into the Fracture Callus but Does Not Influence the Mechanical Strength of Healing Rat Fractures

    DEFF Research Database (Denmark)

    Brüel, Annemarie; Olsen, Jakob; Birkedal, Henrik

    2011-01-01

    to study fracture healing in rats after 3 and 8 weeks of healing. Two groups of rats were treated with SrR (900 mg/kg/day) mixed into the food, while two groups served as control animals. The healing fractures were investigated by three-point bending, dual energy X-ray absorptiometry, energy-dispersive X......Strontium ranelate (SrR) is a new agent used in the treatment of osteoporosis and is suggested to reduce bone resorption and increase bone formation. We investigated whether SrR influences the macro- and nanomechnical properties of healing fractures in rats. A closed tibia fracture model was used......-ray spectroscopy (EDX), and nanoindentation. There was a 100-fold increase (P\\0.001) in serum Sr after 3 and 8 weeks of SrR treatment. The callus volume was significantly higher in the SrR-treated group than in control animals (P\\0.01) after 3 weeks of healing. This was accompanied by a significant increase...

  17. Numerical investigation of fracture behavior of tunnel by excavation loading

    Institute of Scientific and Technical Information of China (English)

    ZHANG Zhe; TANG Chun-an; MA Tian-hui; DUAN Dong

    2007-01-01

    A rock failure process analysis model, RFPA2D code, a two-dimensional numerical code, were proposed. The code not only satisfied the global equilibrium, strain consistent and nonlinear constitutive relationship of rock and soil materials but also took into account the heterogeneous characteristics of rock materials at macroscopic and microscopically level. The failure behavior of tunnel could be simulated by this numerical model. The model could realistically simulate the fracture behavior of tunnel by excavation loading, strength limits, and post peak response for both tension and compression. As the proposed method was used to conduct the stability analysis of tunnel, the safety factor of tunnel was defined as the ratio of actual shear strength parameter to critical failure shear strength parameter. Not only the safety factor of tunnel with specific physics meaning can be obtained, but also the overall failure process and the location of failure surface may also be determined at the same time.

  18. On the Role of Dimensionless Elastic Fracture Mechanics.

    Science.gov (United States)

    1985-07-03

    S. Mindess and J.S. Nadeau, Effect of notch width on K c for mortar and concrete. Cem. Concr. Res. 6, 529-534 (1976). * T. Nakazawa, S. Suzuki, T...Plastic Fracture, ASTM STP 668, 358-377 (1979). S. Mindess and J.S. Nadeau, Effect of notch width on K c for mortar and concrete. Cem. Concr. Res. 6

  19. Development of Fracture Mechanics Maps for Composite Materials. Volume 4.

    Science.gov (United States)

    1985-12-01

    Garber. "Tensile Stress-Strain Behavior oi Graphite/Epoxy Laminates", NASA CR 3592, 1982. 42. G. Caprino , J.C. Halpin and L. Nicolais, "Fracture...2336. 84. C. Caprino , "On the Prediction of Residual Strength for Notched Laminate". Journal Materials Science, Vol. 18, 1983, pp. 2269-2273. 8j. D.L

  20. Fracture Mechanics Analysis of a Modified TSD Specimen

    DEFF Research Database (Denmark)

    Berggreen, Christian; Carlsson, Leif A.

    2008-01-01

    The Tilted Sandwich Debond (TSD) specimen has been recognized as a viable candidate for characterization of the face/core fracture resistance. Analysis, however, shows that the range of phase angles that can be realized by altering the tilt angle is quite limited. A parametric study however shows...

  1. Correlating laboratory observations of fracture mechanical properties to hydraulically-induced microseismicity in geothermal reservoirs.

    Energy Technology Data Exchange (ETDEWEB)

    Stephen L. Karner, Ph.D

    2006-02-01

    To date, microseismicity has provided an invaluable tool for delineating the fracture network produced by hydraulic stimulation of geothermal reservoirs. While the locations of microseismic events are of fundamental importance, there is a wealth of information that can be gleaned from the induced seismicity (e.g. fault plane solutions, seismic moment tensors, source characteristics). Closer scrutiny of the spatial and temporal evolution of seismic moment tensors can shed light on systematic characteristics of fractures in the geothermal reservoir. When related to observations from laboratory experiments, these systematic trends can be interpreted in terms of mechanical processes that most likely operate in the fracture network. This paper reports on mechanical properties that can be inferred from observations of microseismicity in geothermal systems. These properties lead to interpretations about fracture initiation, seismicity induced after hydraulic shut-in, spatial evolution of linked fractures, and temporal evolution of fracture strength. The correlations highlight the fact that a combination of temperature, stressing rate, time, and fluid-rock interactions can alter the mechanical and fluid transport properties of fractures in geothermal systems.

  2. Correlating laboratory observations of fracture mechanical properties to hydraulically-induced microseismicity in geothermal reservoirs.

    Energy Technology Data Exchange (ETDEWEB)

    Stephen L. Karner, Ph.D

    2006-02-01

    To date, microseismicity has provided an invaluable tool for delineating the fracture network produced by hydraulic stimulation of geothermal reservoirs. While the locations of microseismic events are of fundamental importance, there is a wealth of information that can be gleaned from the induced seismicity (e.g. fault plane solutions, seismic moment tensors, source characteristics). Closer scrutiny of the spatial and temporal evolution of seismic moment tensors can shed light on systematic characteristics of fractures in the geothermal reservoir. When related to observations from laboratory experiments, these systematic trends can be interpreted in terms of mechanical processes that most likely operate in the fracture network. This paper reports on mechanical properties that can be inferred from observations of microseismicity in geothermal systems. These properties lead to interpretations about fracture initiation, seismicity induced after hydraulic shut-in, spatial evolution of linked fractures, and temporal evolution of fracture strength. The correlations highlight the fact that a combination of temperature, stressing rate, time, and fluid-rock interactions can alter the mechanical and fluid transport properties of fractures in geothermal systems.

  3. Metallographic investigation of fracture behavior in ITER-style Nb$_{3}$Sn superconducting strands

    CERN Document Server

    Jewell, M C; Larbalestier, D C; Nijhuis, A

    2009-01-01

    In this work we specify the extent to which fracture in two ITER-style Nb3Sn composite strands occurs in a collective or individual manner, under mechanical tension and bending from the TARSIS apparatus at the University of Twente. A bronze-route strand from European Advanced Superconductors (EAS), which has very uniform, well-spaced filaments, has a widely distributed (200 μm) fracture field and exhibits a composite of individual and collective cracks. An internal tin strand from Oxford Instruments – Superconducting Technology (OST) demonstrates much more localized, collective fracture behavior. The filaments in this strand are about four times larger (in area) than the filaments in the EAS strand, and also agglomerate significantly during heat treatment upon conversion of the Nb to Nb3Sn. These results demonstrate that the architecture of the strand can play a significant role in determining the mechanical toughness of the composite, and that strand design should incorporate mechanical considerations in ...

  4. Potential impact of enhanced fracture-toughness data on fracture mechanics assessment of PWR vessel integrity for pressurized thermal shock

    Energy Technology Data Exchange (ETDEWEB)

    Dickson, T.L.; Theiss, T.J.

    1991-01-01

    The Heavy Section Steel Technology (HSST) Program is involved with the generation of enhanced fracture-initiation toughness and fracture-arrest toughness data of prototypic nuclear reactor vessel steels. These two sets of data are enhanced because they have distinguishing characteristics that could potentially impact PWR pressure vessel integrity assessments for the pressurized-thermal shock (PTS) loading condition which is a major plant-life extension issue to be confronted in the 1990's. A series of large-scale fracture-mechanics experiments have produced crack-arrest (K{sub Ia}) data with the distinguishing characteristic that the values are considerably above 220 MPA {center dot} {radical}m. The implicit limit of the ASME Code and the limit used in the Integrated Pressurized Thermal Shock (IPTS) studies. Currently, the HSST Program is planning experiments to verify and quantify for A533B steel the distinguishing characteristic of elevated the distinguishing characteristic of elevated initiation-fracture toughness for shallow flaws which has been observed for other steels. The results of the analyses indicated that application of the enhanced K{sub Ia} data does reduce the conditional probability of failure P(F{vert bar}E); however, it does not appear to have the potential to significantly impact the results of PTS analyses. The application of enhanced fracture-initiation-toughness data for shallow flaws also reduces P(F{vert bar}E), and does appear to have a potential for significantly affecting the results of PTS analyses. 19 refs., 11 figs., 1 tab.

  5. Effects of Eutectic Si Particles on Mechanical Properties and Fracture Toughness of Cast A356 Aluminum Alloys

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Kyu Hong; Lee, Sung Hak [Pohang Univ. of Institute of Science and Technology, Pohang (Korea, Republic of); Kwon, Yong Nam [Korea Institute of Machinery and Materials, Daejeon (Korea, Republic of)

    2007-01-15

    The present study aims at investigating the effects of eutectic Si particles on mechanical properties and fracture toughness of three A356 aluminum alloys. These A356 alloys were fabricated by casting processes such as rheo-casting, squeeze-casting, and casting-forging, and their mechanical properties and fracture toughness were analyzed in relation with microfracture mechanism study. All the cast A356 alloys contained eutectic Si particles mainly segregated along solidification cells, and the distribution of Si particles was modified by squeeze-casting and casting-forging processes. Microfracture observation results showed that eutectic Si particles segregated along cells were cracked first, but that aluminum matrix played a role in blocking crack propagation. Tensile properties and fracture toughness of the squeeze cast and cast-forged alloys having homogeneous distribution of eutectic Si particles were superior to those of the rheo-cast alloy. In particular, the cast-forged alloy had excellent hardness, strength, ductility, and fracture toughness because of the matrix strengthening and homogeneous distribution of eutectic Si particles due to forging process.

  6. An Experimental Investigation of Hydraulic Jet Fracturing Technology with Coiled Tubing

    Institute of Scientific and Technical Information of China (English)

    2012-01-01

    To solve the increasingly serious problem of "many wells, but low productivity" in China, the hydraulic jetting fracturing technology with coiled tubing, as a new measure for effectively improving the production rate of individual well and enhancing oil and gas recovery, merits much attention nowa- days. On the basis of study of the hydraulic jetting fracturing mechanism with coiled tubing and numerical simulation of pressure distribution inside the pores, the mechanism of pressure rise inside the pores caused by the pressure boost action within the jetting pore and the hydraulic isolation action is examined, and the influence of main parameters on the pressure distribution inside the pores is analyzed. 3 kinds of operating methods of hydraulic jetting fracturing with coiled tubing are raised with the tubular diameter of coiled tub- ing as an important feature parameter. According to the experimental study, the fracturing mechanism and computational resuks of numerical simulation are both examined. It is considered that under the same pres- sure drop of jet nozzle, the pressure inside the pores increases with the confining pressure nearly at a line- ar state. When the vertical depth of the borehole is rather big and the rupture pressure of the formation is higher, it is recommended to use higher pressure drop of jet nozzle for achieving better pressure boost and hydraulic isolation effect. For the hydraulic jetting fracturing with coiled tubing, the coiled tubing with tu- bular diameter not less than 50. 8 mm (2 in. ) is usually used.

  7. Mechanical Properties and Fracture Behaviour of Multilayer Alumina Composites

    Institute of Scientific and Technical Information of China (English)

    ZHENG Xinguo; ZHAO Fei; ZHANG Jinyong

    2015-01-01

    Adopting a ceramic/polymer multilayer structure design to simulate the structure of nacre is usually believed to be an effective way to increase the toughness of ceramic composites at the expense of the material's bending strength. However, in this study, we found that both the bending strength and the toughness could be improved simultaneously when using a certain Al2O3/Kevlar multilayer composite design compared to pure alumina samples with the same dimensions. The fracture behaviour of the Al2O3/Kevlar multilayer composite was studied to ifnd a reason for this improvement. The results showed that the complex and asymmetrical stresses occurring in the Kevlar-reinforced layers were the main reason for the differences in fracture behaviour. We expect our results to open up new ways for the design of future high performance ceramic composites.

  8. Pseudoarthrosis following proximal humeral fractures: A possible mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Rooney, P.J.; Cockshott, W.P.

    1986-01-01

    A small series of four patients with pseudarthrosis of the proximal humeral shaft is reported. These patients all had restricted movement of the shoulder joint prior to the trauma, three as a result of rheumatoid arthritis and one due a surgical fusion of the glenohumeral joint. It is suggested that pseudarthrosis is more likely under these circumstances and that pursuit of union of the fracture in such patients may not always be necessary.

  9. Nanoindentation and micro-mechanical fracture toughness of electrodeposited nanocrystalline Ni-W alloy films

    Energy Technology Data Exchange (ETDEWEB)

    Armstrong, D.E.J., E-mail: david.armstrong@materials.ox.ac.uk [Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH (United Kingdom); Haseeb, A.S.M.A. [Department of Mechanical Engineering, University of Malaya, 50603 Kuala Lumpur (Malaysia); Roberts, S.G.; Wilkinson, A.J. [Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH (United Kingdom); Bade, K. [Institut fuer Mikrostrukturtechnik (IMT), Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany)

    2012-04-30

    Nanocrystalline nickel-tungsten alloys have great potential in the fabrication of components for microelectromechanical systems. Here the fracture toughness of Ni-12.7 at.%W alloy micro-cantilever beams was investigated. Micro-cantilevers were fabricated by UV lithography and electrodeposition and notched by focused ion beam machining. Load was applied using a nanoindenter and fracture toughness was calculated from the fracture load. Fracture toughness of the Ni-12.7 at.%W was in the range of 1.49-5.14 MPa {radical}m. This is higher than the fracture toughness of Si (another important microelectromechanical systems material), but considerably lower than that of electrodeposited nickel and other nickel based alloys. - Highlights: Black-Right-Pointing-Pointer Micro-scale cantilevers manufactured by electro-deposition and focused ion beam machining. Black-Right-Pointing-Pointer Nanoindenter used to perform micro-scale fracture test on Ni-13at%W micro-cantilevers. Black-Right-Pointing-Pointer Calculation of fracture toughness of electrodeposited Ni-13at%W thin films. Black-Right-Pointing-Pointer Fracture toughness values lower than that of nanocrystalline nickel.

  10. Fracture mechanical analysis of strengthened concrete tension members with one crack

    DEFF Research Database (Denmark)

    Hansen, Christian Skodborg; Stang, Henrik

    2012-01-01

    A concrete tension member strengthened 2 with fiber reinforced polymer plates on two sides 3 is analyzed with non-linear fracture mechanics. The 4 analysis of the strengthened tension member incorpo5 rates cohesive properties for both concrete and inter6 face between concrete and strengthening...... the structural classification parameters, is inves13 tigated in a non-dimensional analysis, and found to 14 depend strongly on the ratio between interfacial and 15 concrete fracture energies....

  11. Fracture Mechanisms of Layer-By-Layer Polyurethane/Poly(Acrylic Acid) Nanocomposite

    Science.gov (United States)

    Kheng, Eugene R.

    A layer-by-layer(LBL) manufactured material is examined in detail in this thesis. Improvements are made to the method of its manufacture. Efforts are made to understand its fracture mechanisms and take advantage of these fracture mechanisms in the absorption of impact energy. A novel series of experiments has been performed on LBL manufactured thin films to demonstrate their unique fracture mechanisms. Polyurethane/Poly(Acrylic Acid) (PU/PAA) and PU/PAA/(PU/Clay)5 nanocomposite films readily undergo Interlaminar mode II fracture, because of the relatively weak elctrostatic bonds between monolayers. Tensile tests performed while under observation by a scanning electron microscope demonstrate the tendency of these nanocomposite films to undergo interlaminar mode II fracture even when loads are applied in the plane of nanocomposite film. It is concluded that these mechanisms of energy dissipation are responsible for the enhanced toughness of these films when used as layers between glass blocks in the prevention of impact damage to the glass. A novel automated manufacturing facility has been designed and built to deposit large sheets of Layer-by-Layer nanocomposite film. These large sheets are incorporated into a borosillicate glass composite in order to compare the ballistic characteristics of LBL PU based nanocomposite films to a single cast layer of polyurethane. It is demonstrated that shear fracture is the mode of failure in the blocks containing the nanocomposite film. The shear fracture surface in the nanocomposite after it has undergone a ballistic impact is characterized. Additional experiments are performed to characterize the interlaminar fracture stresses and toughnesses of the nanocomposite LBL layers, to assist in the implementation of a numerical crack band model that describes the nanocomposite film. The computational model predicts the failure of the ballistic nanocomposite samples, and the predicted V50 velocity is found to be in good agreement with

  12. Fracture Resistance Measurement Method for in situ Observation of Crack Mechanisms

    DEFF Research Database (Denmark)

    Sørensen, Bent F.; Horsewell, A.; Jørgensen, O.

    1998-01-01

    observation and acoustic emission, As an example, crack growth in a cubic-phase yttria-stabilized zirconia is detected easily by in situ observation of the crack-tip region, Many fracture toughness measurements are obtained for each specimen, giving high confidence in the measured fracture toughness value......, In situ observation is useful for the study of toughening mechanisms and subcritical crack-growth behavior and to sort out erroneous measurements (e.g., due to crack branching)....

  13. Finite element analysis of surface cracks in the Wilkins Ice Shelf using fracture mechanics

    Science.gov (United States)

    Plate, Carolin; Müller, Ralf; Gross, Dietmar; Humbert, Angelika; Braun, Matthias

    2010-05-01

    Ice shelves, located between the warming atmosphere and the ocean, are sensitive elements of the climate system. The Wilkins Ice Shelf is situated in the south-western part of the Antarctic Peninsula, a well known hot spot of global warming. Recent break-up events exemplified the potential of disintegration of the ice shelf. A multi interdisciplinary project consisting of remote sensing, modeling of the ice dynamics and fracture mechanics intends to improve the understanding of the impacts of temperature increase on ice shelf stability. As a part of this project the aim of this presentation is to demonstrate the fracture mechanical approach using finite elements and configurational forces. For fracture mechanical purposes the material behavior of ice is treated as a brittle solid, and linear fracture mechanics is used. Crucial to all methods in linear fracture mechanics is the evaluation of the stress intensity factor K which is a measure for the load concentration at the crack tip and which depends on the geometry of the body and on the applied loading. The computed value of K can be compared to the critical stress intensity factor Kc, a material property obtained from experimental examinations, to judge whether a crack will propagate. One very effective procedure to obtain the stress intensity factor takes advantage of configurational forces, which can be easily obtained in the finite element analysis. An initial investigation is based on a 2-dimensional analysis of a single crack with a mode-I load type using a static plane strain model in the finite element analysis software COMSOL and additional routines to compute and evaluate the configurational forces. Analytical solutions of simple geometry and load cases are called on in comparison. The application to the Wilkins Ice Shelf follows by using material parameters, geometries and loading situations, which are obtained from literature values, remote sensing data analysis and modeling of the ice dynamics

  14. Mechanical and mathematical models of multi-stage horizontal fracturing strings and their application

    Directory of Open Access Journals (Sweden)

    Zhanghua Lian

    2015-03-01

    Full Text Available Multi-stage SRV fracturing in horizontal wells is a new technology developed at home and abroad in recent years to effectively develop shale gas or low-permeability reservoirs, but on the other hand makes the mechanical environment of fracturing strings more complicated at the same time. In view of this, based on the loading features of tubing strings during the multi-stage fracturing of a horizontal well, mechanical models were established for three working cases of multiple packer setting, open differential-pressure sliding sleeve, and open ball-injection sliding sleeve under a hold-down packer. Moreover, mathematical models were respectively built for the above three cases. According to the Lame formula and Von Mises stress calculation formula for the thick-walled cylinder in the theory of elastic mechanics, a mathematical model was also established to calculate the equivalent stress for tubing string safety evaluation when the fracturing string was under the combined action of inner pressure, external squeezing force and axial stress, and another mathematical model was built for the mechanical strength and safety evaluation of multi-stage fracturing strings. In addition, a practical software was developed for the mechanical safety evaluation of horizontal well multi-stage fracturing strings according to the mathematical model developed for the mechanical calculation of the multi-packer string in horizontal wells. The research results were applied and verified in a gas well of Tahe Oilfield in the Tarim Basin with excellent effects, providing a theoretical basis and a simple and reliable technical means for optimal design and safety evaluation of safe operational parameters of multi-stage fracturing strings in horizontal wells.

  15. Numerical investigations of rib fracture failure models in different dynamic loading conditions.

    Science.gov (United States)

    Wang, Fang; Yang, Jikuang; Miller, Karol; Li, Guibing; Joldes, Grand R; Doyle, Barry; Wittek, Adam

    2016-01-01

    Rib fracture is one of the most common thoracic injuries in vehicle traffic accidents that can result in fatalities associated with seriously injured internal organs. A failure model is critical when modelling rib fracture to predict such injuries. Different rib failure models have been proposed in prediction of thorax injuries. However, the biofidelity of the fracture failure models when varying the loading conditions and the effects of a rib fracture failure model on prediction of thoracic injuries have been studied only to a limited extent. Therefore, this study aimed to investigate the effects of three rib failure models on prediction of thoracic injuries using a previously validated finite element model of the human thorax. The performance and biofidelity of each rib failure model were first evaluated by modelling rib responses to different loading conditions in two experimental configurations: (1) the three-point bending on the specimen taken from rib and (2) the anterior-posterior dynamic loading to an entire bony part of the rib. Furthermore, the simulation of the rib failure behaviour in the frontal impact to an entire thorax was conducted at varying velocities and the effects of the failure models were analysed with respect to the severity of rib cage damages. Simulation results demonstrated that the responses of the thorax model are similar to the general trends of the rib fracture responses reported in the experimental literature. However, they also indicated that the accuracy of the rib fracture prediction using a given failure model varies for different loading conditions.

  16. A review on the applications of the nuclear magnetic resonance (NMR) technology for investigating fractures

    Science.gov (United States)

    Golsanami, Naser; Sun, Jianmeng; Zhang, Zhiying

    2016-10-01

    This review focuses on the recent applications of nuclear magnetic resonance (NMR) technology for characterizing fractures. The paper aims to help researchers in extending the existing reservoir characterization methods (which are commonly used in conventional hydrocarbon reservoirs) for appropriate usage in unconventional resources. This is because some techniques for quantifying and qualifying fractures have been investigated in conventional sandstone and carbonate reservoirs, but the reality for unconventional resources is that such techniques are still poorly developed. Fractures are necessary for economical production of petroleum from many low-permeability reservoirs. The characterization of fractures by well logging technology is of great interest in the petroleum industry. The main purpose of this study is to review the characterization techniques that are developed either for identifying fractures or distinguishing fracture porosity from matrix porosity. This concept plays a leading role in providing availability of an optimized well completion program. The results of this study indicated that in terms of both sandstone and carbonate tight reservoirs, there have not been many steps taken toward the aforementioned goal up to now. Nevertheless, these steps are valuable enough to be counted on and could serve a meaningful function in treating hydrocarbon reservoirs. Because of the ongoing changes in today's petroleum industry, development of a comprehensive methodology will create greater economic benefits in unconventional reservoirs than in the conventional ones.

  17. Three- to nine-year survival estimates and fracture mechanisms of zirconia- and alumina-based restorations using standardized criteria to distinguish the severity of ceramic fractures

    OpenAIRE

    Moraguez, Osvaldo; Wiskott, Anselm; Scherrer, Susanne

    2015-01-01

    The aims of this study were set as follows: 1. To provide verifiable criteria to categorize the ceramic fractures into non-critical (i.e., amenable to polishing) or critical (i.e., in need of replacement) 2. To establish the corresponding survival rates for alumina and zirconia restorations 3. To establish the mechanism of fracture using fractography

  18. Development of a new code to solve hydro-mechanical coupling, shear failure and tensile failure due to hydraulic fracturing operations.

    Science.gov (United States)

    María Gómez Castro, Berta; De Simone, Silvia; Carrera, Jesús

    2016-04-01

    Nowadays, there are still some unsolved relevant questions which must be faced if we want to proceed to the hydraulic fracturing in a safe way. How much will the fracture propagate? This is one of the most important questions that have to be solved in order to avoid the formation of pathways leading to aquifer targets and atmospheric release. Will the fracture failure provoke a microseismic event? Probably this is the biggest fear that people have in fracking. The aim of this work (developed as a part of the EU - FracRisk project) is to understand the hydro-mechanical coupling that controls the shear of existing fractures and their propagation during a hydraulic fracturing operation, in order to identify the key parameters that dominate these processes and answer the mentioned questions. This investigation focuses on the development of a new C++ code which simulates hydro-mechanical coupling, shear movement and propagation of a fracture. The framework employed, called Kratos, uses the Finite Element Method and the fractures are represented with an interface element which is zero thickness. This means that both sides of the element lie together in the initial configuration (it seems a 1D element in a 2D domain, and a 2D element in a 3D domain) and separate as the adjacent matrix elements deform. Since we are working in hard, fragile rocks, we can assume an elastic matrix and impose irreversible displacements in fractures when rock failure occurs. The formulation used to simulate shear and tensile failures is based on the analytical solution proposed by Okada, 1992 and it is part of an iterative process. In conclusion, the objective of this work is to employ the new code developed to analyze the main uncertainties related with the hydro-mechanical behavior of fractures derived from the hydraulic fracturing operations.

  19. Computational and Experimental Investigation into Fracture of Brittle Fiber - Brittle Matrix Composite Systems

    Science.gov (United States)

    1992-12-01

    solutions to fracture mechanics problems through integration of fundamental singular solutions across the crack boundary*. Crack-tip displacements...not volumes, need be discretized. The numerical elasticity solution is determined through superposition of a finite distribution of analytical singular ... solutions (to known influence or Green’s functions [181) which exactly satisfy the governing partial differential equations in 91, the region of

  20. Thermo-hydro-mechanical simulation of a 3D fractured porous rock: preliminary study of coupled matrix-fracture hydraulics

    Energy Technology Data Exchange (ETDEWEB)

    Canamon, I.; Javier Elorza, F. [Universidad Politecnica de Madrid, Dept. de Matematica Aplicada y Metodos Informaticas, ETSI Minas (UPM) (Spain); Ababou, R. [Institut de Mecanique des Fluides de Toulouse (IMFT), 31 (France)

    2007-07-01

    We present a problem involving the modeling of coupled flow and elastic strain in a 3D fractured porous rock, which requires prior homogenization (up-scaling) of the fractured medium into an equivalent Darcian anisotropic continuum. The governing equations form a system of PDE's (Partial Differential Equations) and, depending on the case being considered, this system may involve two different types of 'couplings' (in a real system, both couplings (1) and (2) generally take place): 1) Hydraulic coupling in a single (no exchange) or in a dual matrix-fracture continuum (exchange); 2) Thermo-Hydro-Mechanical interactions between fluid flow, pressure, elastic stress, strain, and temperature. We present here a preliminary model and simulation results with FEMLAB{sup R}, for the hydraulic problem with anisotropic heterogeneous coefficients. The model is based on data collected at an instrumented granitic site (FEBEX project) for studying a hypothetical nuclear waste repository at the Grimsel Test Site in the Swiss Alps. (authors)

  1. Relative permeability of fractured wellbore cement: an experimental investigation using electrical resistivity monitoring for moisture content

    Science.gov (United States)

    Um, W.; Rod, K. A.; Strickland, C. E.

    2016-12-01

    Permeability is a critical parameter needed to understand flow in subsurface environments; it is particularly important in deep subsurface reservoirs where multiphase fluid flow is common, such as carbon sequestration and geothermal reservoirs. Cement is used in the annulus of wellbores due to its low permeable properties to seal aquifers, reducing leaks to adjacent strata. Extreme subsurface environments of CO2 storage and geothermal production conditions will eventually reduce the cement integrity, propagating fracture networks and increasing the permeability for air and/or water. To date, there have been no reproducible experimental investigations of relative permeability in fractured wellbore cement published. To address this gap, we conducted a series of experiments using fractured Portland cement monoliths with increasing fracture networks. The monolith cylinder sides were jacketed with heavy-duty moisture-seal heat-shrink tubing, then fractured using shear force applied via a hydraulic press. Fractures were generated with different severity for each of three monoliths. Stainless steel endcaps were fixed to the monoliths using the same shrink-wrapped jacket. Fracture characteristics were determined using X-ray microtomography and image analysis. Flow controllers were used to control flow of water and air to supply continuous water or water plus air, both of which were delivered through the influent end cap. Effluent air flow was monitored using a flow meter, and water flow was measured gravimetrically. To monitor the effective saturation of the fractures, a RCON2 concrete bulk electrical resistivity test device was attached across both endcaps and a 0.1M NaNO3 brine was used as the transport fluid to improve resistivity measurements. Water content correlated to resistivity measurements with a r2 > 0.96. Data from the experiments was evaluated using two relative permeability models, the Corey-curve, often used for modeling relative permeability in porous media

  2. Pilot case-control investigation of risk factors for hip fractures in the urban Indian population

    Directory of Open Access Journals (Sweden)

    Malhotra Nidhi

    2010-03-01

    Full Text Available Abstract Background Despite the reported high prevalence of osteoporosis in India, there have been no previous studies examining the risk factors for hip fracture in the Indian population. Methods We carried out a case control investigation comprising 100 case subjects (57 women and 43 men admitted with a first hip fracture into one of three hospitals across New Delhi. The 100 controls were age and sex matched subjects who were either healthy visitors not related to the case patients or hospital staff. Information from all subjects was obtained through a questionnaire based interview. Results There was a significant increase in the number of cases of hip fracture with increasing age. There were significantly more women (57% than men (43%. Univariate analysis identified protective effects for increased activity, exercise, calcium and vitamin supplements, almonds, fish, paneer (cottage cheese, curd (plain yogurt, and milk. However, tea and other caffeinated beverages were significant risk factors. In women, hormone/estrogen therapy appeared to have a marginal protective effect. For all cases, decreased agility, visual impairment, long term medications, chronic illnesses increased the risk of hip fracture. The multivariate analysis confirmed a protective effect of increased activity and also showed a decrease in hip fracture risk with increasing body mass index (odds ratio (OR 0.024, 95% confidence interval (CI 0.006-0.10 & OR 0.81, 95% CI 0.68-0.97 respectively. Individuals who take calcium supplements have a decreased risk of hip fracture (OR 0.076; CI 0.017-0.340, as do individuals who eat fish (OR 0.094; CI 0.020-0.431, and those who eat paneer (OR 0.152; 0.031-0.741. Tea drinkers have a higher risk of hip fracture (OR 22.8; 95% CI 3.73-139.43. Difficulty in getting up from a chair also appears to be an important risk factor for hip fractures (OR 14.53; 95% CI 3.86-54.23. Conclusions In the urban Indian population, dietary calcium, vitamin D

  3. Numerical Analysis and Experimental Study of Hard Roofs in Fully Mechanized Mining Faces under Sleeve Fracturing

    Directory of Open Access Journals (Sweden)

    Zhitao Zheng

    2015-11-01

    Full Text Available Sudden falls of large-area hard roofs in a mined area release a large amount of elastic energy, generate dynamic loads, and cause disasters such as impact ground pressure and gas outbursts. To address these problems, in this study, the sleeve fracturing method (SFM was applied to weaken a hard roof. The numerical simulation software FLAC3D was used to develop three models based on an analysis of the SFM working mechanism. These models were applied to an analysis of the fracturing effects of various factors such as the borehole diameter, hole spacing, and sleeve pressure. Finally, the results of a simulation were validated using experiments with similar models. Our research indicated the following: (1 The crack propagation directions in the models were affected by the maximum principal stress and hole spacing. When the borehole diameter was fixed, the fracturing pressure increased with increasing hole spacing. In contrast, when the fracturing pressure was fixed, the fracturing range increased with increasing borehole diameter; (2 The most ideal fracturing effect was found at a fracturing pressure of 17.6 MPa in the model with a borehole diameter of 40 mm and hole spacing of 400 mm. The results showed that it is possible to regulate the falls of hard roofs using the SFM. This research may provide a theoretical basis for controlling hard roofs in mining.

  4. Modelling of Debond and Crack Propagation in Sandwich Structures Using Fracture and Damage Mechanics

    DEFF Research Database (Denmark)

    Berggreen, C.; Simonsen, Bo Cerup; Toernqvist, Rikard

    2003-01-01

    Skin-core de-bonding or core crack propagation will often be dominating mechanisms in the collapse modes of sandwich structures. This paper presents two different methods for prediction of crack propagation in a sandwich structure: a fracture mechanics approach, where a new mode-mix method...

  5. Experimental Investigation of Moisture Driven Fracture in Solid Wood

    DEFF Research Database (Denmark)

    Larsen, Finn; Ormarsson, Sigurdur; Olesen, John Forbes

    2010-01-01

    Solid timber products, containing both heartwood and sapwood, often have a high tendency to crack during the drying process. This can cause severe loss of material for the saw-mills, especially for products with large cross sectional dimensions. The cracks (e.g. end-cracks) arise, in some cases, ...... of a finite element model to evaluate the various couplings in the hygro-mechanical problem that govern moisture driven cracking in wood....

  6. Vertebroplasty and Kyphoplasty Can Restore Normal Spine Mechanics following Osteoporotic Vertebral Fracture

    Directory of Open Access Journals (Sweden)

    Jin Luo

    2010-01-01

    Full Text Available Osteoporotic vertebral fractures often lead to pain and disability. They can be successfully treated, and possibly prevented, by injecting cement into the vertebral body, a procedure known as vertebroplasty. Kyphoplasty is similar, except that an inflatable balloon is used to restore vertebral body height before cement is injected. These techniques are growing rapidly in popularity, and a great deal of recent research, reviewed in this paper, has examined their ability to restore normal mechanical function to fractured vertebrae. Fracture reduces the height and stiffness of a vertebral body, causing the spine to assume a kyphotic deformity, and transferring load bearing to the neural arch. Vertebroplasty and kyphoplasty are equally able to restore vertebral stiffness, and restore load sharing towards normal values, although kyphoplasty is better at restoring vertebral body height. Future research should optimise these techniques to individual patients in order to maximise their beneficial effects, while minimising the problems of cement leakage and adjacent level fracture.

  7. Mechanical interactions between proppants and rock and their effect on hydraulic fracture performance

    Energy Technology Data Exchange (ETDEWEB)

    Legarth, B.A.; Raab, S.; Huenges, E. [GeoForschungsZentrum Potsdam (Germany)

    2005-07-01

    Proppants interact mechanically with the rock matrix. This causes damage to the fracture face and influences propped fracture performance. Therefore, proppant embedment and proppant crushing phenomena were analysed in laboratory under simulated in situ conditions. The embedment tests were performed in a conductivity cell using reassembled core halves. Embedment features in the rock matrix were optically analyzed. In a separate unit single grain strength tests were performed on a wide range of ceramic proppant types (AI203-based, coated/uncoated) and sizes (diameter 0,2-1,6 mm). The experiment showed that areas in the fracture with low proppant concentration revealed severe proppant crushing and embedment that occurred already at low effective stress. Punctual loading was identified as reason for premature proppant failure. Grain strength testing showed that compressive fracture force increases with grain diameter, is influenced by the presence of a coating and might be additionally controlled by grain surface structure. Compressive fracture strength is largely independent from size for same proppant types. A contact model introduced by Hertz was applied to retrieve the stress magnitudes at grain failure. Proppant crushing leads to generation of fines in the matrix and the proppant pack. These fines can be transported and plug pore-throats and flow channels. Dependent on completion type and expected fracture widths proppant grain size should be maximized for higher fracture conductivity. Proppant crushing and embedment processes are enforced by decreasing proppant concentration. Considering natural conditions in a fracture - rough surfaces, tortuous-twisted paths that hinder even proppant distribution - low proppant concentrations appear to be very real, maybe even the normal case in nature. Thus, high proppant concentration is the key issue to mitigate fracture impairment. (orig.)

  8. The mechanical benefit of medial support screws in locking plating of proximal humerus fractures.

    Directory of Open Access Journals (Sweden)

    Wen Zhang

    Full Text Available BACKGROUND: The purpose of this study was to evaluate the biomechanical advantages of medial support screws (MSSs in the locking proximal humeral plate for treating proximal humerus fractures. METHODS: Thirty synthetic left humeri were randomly divided into 3 subgroups to establish two-part surgical neck fracture models of proximal humerus. All fractures were fixed with a locking proximal humerus plate. Group A was fixed with medial cortical support and no MSSs; Group B was fixed with 3 MSSs but without medial cortical support; Group C was fixed with neither medial cortical support nor MSSs. Axial compression, torsional stiffness, shear stiffness, and failure tests were performed. RESULTS: Constructs with medial support from cortical bone showed statistically higher axial and shear stiffness than other subgroups examined (P<0.0001. When the proximal humerus was not supported by medial cortical bone, locking plating with medial support screws exhibited higher axial and torsional stiffness than locking plating without medial support screws (P ≤ 0.0207. Specimens with medial cortical bone failed primarily by fracture of the humeral shaft or humeral head. Specimens without medial cortical bone support failed primarily by significant plate bending at the fracture site followed by humeral head collapse or humeral head fracture. CONCLUSIONS: Anatomic reduction with medial cortical support was the stiffest construct after a simulated two-part fracture. Significant biomechanical benefits of MSSs in locking plating of proximal humerus fractures were identified. The reconstruction of the medial column support for proximal humerus fractures helps to enhance mechanical stability of the humeral head and prevent implant failure.

  9. Experimental investigation of effect of specimen thickness on fracture toughness of Al-TiC composites

    Directory of Open Access Journals (Sweden)

    M. S. Raviraj

    2016-07-01

    Full Text Available In this paper, the macro and micro-mechanical fracture behavior was studied for aluminum (Al6061 alloy matrix, reinforced with various proportions of TiC particles such as 3wt%, 5wt% and 7wt%. The Al6061-TiC metal matrix composites were produced by stir casting method to ensure uniform distribution of the TiC particulates in the Al matrix. The compact tension (CT specimens were machined according to ASTM E399 specifications to evaluate the fracture toughness for Al6061-TiC metal matrix composites. The CT specimens were machined for crack to width (a/W ratio of 0.5 and thickness to width (B/W ratios of 0.2 to 0.7 with an increment of 0.1. Load versus crack mouth opening displacement (CMOD data was plotted to estimate stress intensity factor KQ for various thicknesses of the specimen. The fracture toughness KIC was obtained by plotting stress intensity factor versus thickness to width ratios of specimen data. The fracture toughness of these composites varied between 16.4-19.2 MPa√m. Scanning Electron Microscope (SEM studies was made on the fractured surface of the specimens to understand the micro-mechanisms of failure involved in these composites. Void initiation is more significant in the matrix near the interface. The micro-cracks grow from these micro-voids and crack propagates by linking these micro cracks locating the crack path preferentially in the matrix adjacent to the interface indicating ductile fracture.

  10. Investigation of hydrogen assisted cracking in acicular ferrite using site-specific micro-fracture tests

    Energy Technology Data Exchange (ETDEWEB)

    Costin, Walter L. [School of Mechanical Engineering, The University of Adelaide, SA 5005 (Australia); Lavigne, Olivier, E-mail: Olivier.lavigne@adelaide.edu.au [School of Mechanical Engineering, The University of Adelaide, SA 5005 (Australia); Kotousov, Andrei; Ghomashchi, Reza [School of Mechanical Engineering, The University of Adelaide, SA 5005 (Australia); Linton, Valerie [Energy Pipelines Cooperative Research Centre, Faculty of Engineering, University of Wollongong, NSW 2522 (Australia)

    2016-01-10

    Hydrogen assisted cracking (HAC) is a common type of failure mechanism that can affect a wide range of metals and alloys. Experimental studies of HAC are cumbersome due to various intrinsic and extrinsic parameters and factors (associated with stress, hydrogen and the materials microstructure) contributing to the hydrogen crack kinetics. The microstructure of many materials consists of diverse constituents with characteristic features and mechanical properties which only occur in very small material volumes. The only way to differentiate the effect of these individual constituents on the hydrogen crack kinetics is to miniaturise the testing procedures. In this paper we present a new experimental approach to investigate hydrogen assisted crack growth in a microstructural constituent, i.e. acicular ferrite. For this purpose, sharply notched micro-cantilevers were fabricated with a Focus Ion Beam within this selected microscopic region. Acicular ferrite can be found in many ferrous alloys including ferritic weld metal and has specific features that control its intrinsic susceptibility to HAC. These features were characterised via Electron Backscatter Diffraction and the specimens were subsequently loaded under uncharged and hydrogen charged conditions with a nano-indenter. The outcomes of the testing, demonstrated that the threshold stress intensity factor, K{sub th}, to initiate crack propagation in acicular ferrite ranges between 1.56 MPa m{sup 1/2} and 4.36 MPa m{sup 1/2}. This range is significantly below the values of K{sub th} reported for various ferrous alloys in standard macro-tests. This finding indicates that the mechanisms and resistance to HAC at micro-scale could be very different than at the macro-scale as not all fracture toughening mechanisms may be activated at this scale level.

  11. Effects of investigations into vibrating disc use for rock fracturing

    Energy Technology Data Exchange (ETDEWEB)

    Krauze, K.; Pawlik, J.; Pawlik, K.

    1987-06-01

    Evaluates results of laboratory investigations into feasibility of mine drivage by heading machines with vibrating discs for rock cutting. Each cutting head was equipped with 2 discs. Discs with a diameter of 200 mm, 50 mm thick and with a wedge angle of 90 degrees were used for cutting three types of rocks (2 types of sandstones with a compression strength exceeding 80 MPa). Amplitude of disc vibrations ranged from 4 to 8 mm, frequency from 12 to 20 Hz. Investigations showed vibrating discs to be an efficient tool for cutting rocks with a high compression strength. Cutting disc wear was extremely low in contrast to wear of conventional picks of the NK-4 type (which after cutting a 0.3 m long rock section were removed due to wear). Cutting energy depended on vibration frequency and amplitude. 5 refs.

  12. Elastic-plastic fracture mechanics of strength-mismatching

    Energy Technology Data Exchange (ETDEWEB)

    Parks, D.M.; Ganti, S.; McClintock, F.A. [Massachusetts Institute of Technology, Cambridge, MA (United States)

    1996-12-31

    Approximate solutions to stress-fields are provided for a strength-mismatched interface crack in small-scale yielding (SSY) for non-hardening and low hardening materials. Variations of local deformation intensities, characterized by a J-type contour integral, are proposed. The softer material experiences a higher deformation intensity level, J{sub S}, while the harder material sees a much lower deformation intensity level, J{sub H}, compared to that obtained from the applied J near the respective homogeneous crack-tips. For a low hardening material, the stress fields are obtained by scaling from an elastic/perfectly-plastic problem, based on an effective mismatch, M{sub eff}, which is a function of mismatch, M, and the hardening exponent, n. Triaxial stress build-up is discussed quantitatively in terms of M. The influence of strength-mismatch on cleavage fracture is discussed using Weibull statistics.

  13. Deformation Mechanisms and Fracture of Ni-Based Metallic Glasses

    Directory of Open Access Journals (Sweden)

    Lesz S.

    2016-06-01

    Full Text Available The cracking of materials and fracture surface is of great practical and academic importance. Over the last few years the development of the fractography of crystalline alloys resulted in a useful tool for the prediction or failure analysis. Many attempts have been made to observe cracks using optical microscopy, X-ray topography and transmission electron microscopy (TEM. Of these techniques, the resolution of optical microscopy and X-ray topography is too poor. By contrast, the resolution of TEM is high enough for detailed information to be obtained. However, in order to apply TEM observations, a thin foil specimen must be prepared, and it is usually extremely difficult to prepare such a specimen from a pre-selected region containing a crack.

  14. Computational investigations of mechanical failures of internal plate fixation.

    Science.gov (United States)

    Chen, G; Schmutz, B; Wullschleger, M; Pearcy, M J; Schuetz, M A

    2010-01-01

    This paper investigated the biomechanics of two clinical cases of bone fracture treatments. Both fractures were treated with the same locking compression plate but with different numbers of screws as well as different plate materials. The fracture treated with 12 screws (rigid fixation) failed at 7 weeks with the plate breaking; the fracture with six screws (flexible fixation) endured the entire healing process. It was hypothesized that the plate failure in the unsuccessful case was due to the material fatigue induced by stress concentration in the plate. As the two clinical cases had different fracture locations and different plate materials, finite element simulations were undertaken for each fractured bone fixed by both a rigid and a flexible method. This enabled comparisons to be made between the rigid and flexible fixation methods. The fatigue life was assessed for each fixation method. The results showed that the stress in the rigid fixation methods could be significantly higher than that in flexible fixation methods. The fatigue analyses showed that, with the stress level in flexible fixation (i.e. with fewer screws), the plate was able to endure 2000 days, and that the plate in rigid fixation could fail by fatigue fracture in 20 days. The paper concludes that the rigid fixation method resulted in serious stress concentrations in the plate, which induced fatigue failure. The flexible fixation gave sufficient stability and was better for fracture healing.

  15. A numerical manifold method model for analyzing fully coupled hydro-mechanical processes in porous rock masses with discrete fractures

    Science.gov (United States)

    Hu, Mengsu; Rutqvist, Jonny; Wang, Yuan

    2017-04-01

    In this study, a numerical manifold method (NMM) model was developed for fully coupled analysis of hydro-mechanical (HM) processes in porous rock masses with discrete fractures. Using an NMM two-cover-mesh system of mathematical and physical covers, fractures are conveniently discretized by dividing the mathematical cover along fracture traces to physical cover, resulting in a discontinuous model on a non-conforming mesh. In this model, discrete fracture deformation (e.g. open and slip) and fracture fluid flow within a permeable and deformable porous rock matrix are rigorously considered. For porous rock, direct pore-volume coupling was modeled based on an energy-work scheme. For mechanical analysis of fractures, a fracture constitutive model for mechanically open states was introduced. For fluid flow in fractures, both along-fracture and normal-to-fracture fluid flow are modeled without introducing additional degrees of freedom. When the mechanical aperture of a fracture is changing, its hydraulic aperture and hydraulic conductivity is updated. At the same time, under the effect of coupled deformation and fluid flow, the contact state may dynamically change, and the corresponding contact constraint is updated each time step. Therefore, indirect coupling is realized under stringent considerations of coupled HM effects and fracture constitutive behavior transfer dynamically. To verify the new model, examples involving deformable porous media containing a single and two sets of fractures were designed, showing good accuracy. Last, the model was applied to analyze coupled HM behavior of fractured porous rock domains with complex fracture networks under effects of loading and injection.

  16. An Overview of Innovative Strategies for Fracture Mechanics at NASA Langley Research Center

    Science.gov (United States)

    Ransom, Jonathan B.; Glaessgen, Edward H.; Ratcliffe, James G.

    2010-01-01

    Engineering fracture mechanics has played a vital role in the development and certification of virtually every aerospace vehicle that has been developed since the mid-20th century. NASA Langley Research Center s Durability, Damage Tolerance and Reliability Branch has contributed to the development and implementation of many fracture mechanics methods aimed at predicting and characterizing damage in both metallic and composite materials. This paper presents a selection of computational, analytical and experimental strategies that have been developed by the branch for assessing damage growth under monotonic and cyclic loading and for characterizing the damage tolerance of aerospace structures

  17. Fatigue Performance of Microalloyed High-strength Rebar and Analysis of Fracture Mechanism

    Institute of Scientific and Technical Information of China (English)

    Peng-yan LU; Yu LIU; Hua-jie WU; Gang LIU; Xiang MENG; Yang XU

    2015-01-01

    Fatigue performance of hot-rolled ribbed-steel bar with the yield strength of 500 MPa (HRB500)was stud-ied with bend-rotating fatigue test at a stress ratio of R=-1 .It is determined by staircase method that its fatigue strength for 107 cycles is 451 MPa,which is higher than that of common carbon structural steel.This should be at-tributed to the fine-grain strengthening resulting from the high content of alloy element V and Thermo-Mechanical Control Process (TMCP).The S-N curve function is also obtained by nonlinear regression with three parameters power function.The fatigue fractures of the specimen were further analyzed with Scanning Electron Microscopy (SEM)and Energy Disperse Spectroscopy (EDS)to study the fracture mechanism.Taking into account microstruc-ture,hardness and cleanliness of the material,it implies that the fatigue fractures of HRB500 rebar all arise from surface substrates in which many brittle inclusions are contained,and that the fatigue crack propagation is principally based on the mechanism of quasi-cleavage fracture,because of the intracrystalline hard spots leading to stress con-centration and thus to the cracks.Moreover,the transient breaking area exhibits microvoid coalescence of ductile fracture due to the existing abundant inclusions.

  18. Experimental investigation of fundamental processes in mining induced fracturing and rock instability.

    CSIR Research Space (South Africa)

    Napier, JAL

    2002-03-01

    Full Text Available Final Report Experimental investigation of fundamental processes in mining induced fracturing and rock instability J.A.L. Napier, K. Drescher, M.W. Hildyard, M.O. Kataka, D.F. Malan, E.J. Sellers Research Agency : CSIR Miningtek Project No : GAP...

  19. Three- to nine-year survival estimates and fracture mechanisms of zirconia- and alumina-based restorations using standardized criteria to distinguish the severity of ceramic fractures.

    Science.gov (United States)

    Moráguez, Osvaldo D; Wiskott, H W Anselm; Scherrer, Susanne S

    2015-12-01

    The aims of this study were set as follows: 1. To provide verifiable criteria to categorize the ceramic fractures into non-critical (i.e., amenable to polishing) or critical (i.e., in need of replacement) 2. To establish the corresponding survival rates for alumina and zirconia restorations 3. To establish the mechanism of fracture using fractography Fifty-eight patients restored with 115 alumina-/zirconia-based crowns and 26 zirconia-based fixed dental prostheses (FDPs) were included. Ceramic fractures were classified into four types and further subclassified into "critical" or "non-critical." Kaplan-Meier survival estimates were calculated for "critical fractures only" and "all fractures." Intra-oral replicas were taken for fractographic analyses. Kaplan-Meier survival estimates for "critical fractures only" and "all fractures" were respectively: Alumina single crowns: 90.9 and 68.3 % after 9.5 years (mean 5.71 ± 2.6 years). Zirconia single crowns: 89.4 and 80.9 % after 6.3 years (mean 3.88 ± 1.2 years). Zirconia FDPs: 68.6 % (critical fractures) and 24.6 % (all fractures) after 7.2 and 4.6 years respectively (FDP mean observation time 3.02 ± 1.4 years). No core/framework fractures were detected. Survival estimates varied significantly depending on whether "all" fractures were considered as failures or only those deemed as "critical". For all restorations, fractographic analyses of failed veneering ceramics systematically demonstrated heavy occlusal wear at the failure origin. Therefore, the relief of local contact pressures on unsupported ceramic is recommended. Occlusal contacts on mesial or distal ridges should systematically be eliminated. A classification standard for ceramic fractures into four categories with subtypes "critical" and "non-critical" provides a differentiated view of the survival of ceramic restorations.

  20. Deformation mechanism under essential work of fracture process in polycyclo-olefin materials

    Directory of Open Access Journals (Sweden)

    2008-06-01

    Full Text Available The fracture toughness of a glassy polycyclo-olefin (PCO was investigated by the essential work of fracture (EWF method using a double-edge notched specimens. It was shown that the PCO follows the EWF concept in the temperature range between room temperature and glass transition temperature Tg where the ligament yielding appear at a maximum point on the stress-displacement curves and subsequently the necking and tearing processes take place in the post yielding region. The essential work of fracture required for the ligament yielding drops as the temperature approaches Tg. The non-essential work of fracture attributed to tearing process after yielding is consumed to expand the plastic region and causes molecular chains to orient to the stretching direction.

  1. A Novel Computer-Aided Approach for Parametric Investigation of Custom Design of Fracture Fixation Plates.

    Science.gov (United States)

    Chen, Xiaozhong; He, Kunjin; Chen, Zhengming

    2017-01-01

    The present study proposes an integrated computer-aided approach combining femur surface modeling, fracture evidence recover plate creation, and plate modification in order to conduct a parametric investigation of the design of custom plate for a specific patient. The study allows for improving the design efficiency of specific plates on the patients' femur parameters and the fracture information. Furthermore, the present approach will lead to exploration of plate modification and optimization. The three-dimensional (3D) surface model of a detailed femur and the corresponding fixation plate were represented with high-level feature parameters, and the shape of the specific plate was recursively modified in order to obtain the optimal plate for a specific patient. The proposed approach was tested and verified on a case study, and it could be helpful for orthopedic surgeons to design and modify the plate in order to fit the specific femur anatomy and the fracture information.

  2. A Novel Computer-Aided Approach for Parametric Investigation of Custom Design of Fracture Fixation Plates

    Science.gov (United States)

    2017-01-01

    The present study proposes an integrated computer-aided approach combining femur surface modeling, fracture evidence recover plate creation, and plate modification in order to conduct a parametric investigation of the design of custom plate for a specific patient. The study allows for improving the design efficiency of specific plates on the patients' femur parameters and the fracture information. Furthermore, the present approach will lead to exploration of plate modification and optimization. The three-dimensional (3D) surface model of a detailed femur and the corresponding fixation plate were represented with high-level feature parameters, and the shape of the specific plate was recursively modified in order to obtain the optimal plate for a specific patient. The proposed approach was tested and verified on a case study, and it could be helpful for orthopedic surgeons to design and modify the plate in order to fit the specific femur anatomy and the fracture information. PMID:28203270

  3. Mechanical and Structural Investigation of Porous Bulk Metallic Glasses

    Directory of Open Access Journals (Sweden)

    Baran Sarac

    2015-06-01

    Full Text Available The intrinsic properties of advanced alloy systems can be altered by changing their microstructural features. Here, we present a highly efficient method to produce and characterize structures with systematically-designed pores embedded inside. The fabrication stage involves a combination of photolithography and deep reactive ion etching of a Si template replicated using the concept of thermoplastic forming. Pt- and Zr-based bulk metallic glasses (BMGs were evaluated through uniaxial tensile test, followed by scanning electron microscope (SEM fractographic and shear band analysis. Compositional investigation of the fracture surface performed via energy dispersive X-ray spectroscopy (EDX, as well as Auger spectroscopy (AES shows a moderate amount of interdiffusion (5 at.% maximum of the constituent elements between the deformed and undeformed regions. Furthermore, length-scale effects on the mechanical behavior of porous BMGs were explored through molecular dynamics (MD simulations, where shear band formation is observed for a material width of 18 nm.

  4. Disadvantages of interfragmentary shear on fracture healing--mechanical insights through numerical simulation.

    Science.gov (United States)

    Steiner, Malte; Claes, Lutz; Ignatius, Anita; Simon, Ulrich; Wehner, Tim

    2014-07-01

    The outcome of secondary fracture healing processes is strongly influenced by interfragmentary motion. Shear movement is assumed to be more disadvantageous than axial movement, however, experimental results are contradictory. Numerical fracture healing models allow simulation of the fracture healing process with variation of single input parameters and under comparable, normalized mechanical conditions. Thus, a comparison of the influence of different loading directions on the healing process is possible. In this study we simulated fracture healing under several axial compressive, and translational and torsional shear movement scenarios, and compared their respective healing times. Therefore, we used a calibrated numerical model for fracture healing in sheep. Numerous variations of movement amplitudes and musculoskeletal loads were simulated for the three loading directions. Our results show that isolated axial compression was more beneficial for the fracture healing success than both isolated shearing conditions for load and displacement magnitudes which were identical as well as physiological different, and even for strain-based normalized comparable conditions. Additionally, torsional shear movements had less impeding effects than translational shear movements. Therefore, our findings suggest that osteosynthesis implants can be optimized, in particular, to limit translational interfragmentary shear under musculoskeletal loading. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

  5. Probabilistic fracture mechanics analysis of thermally aged nuclear piping in a pressurized water reactor

    Energy Technology Data Exchange (ETDEWEB)

    Li, Shuxiao; Zhang, Hailong; Li, Shilei; Wang, Yanli [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Xue, Fei [Suzhou Nuclear Power Research Institute, Suzhou 215004 (China); Wang, Xitao, E-mail: xtwang@ustb.edu.cn [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China)

    2013-12-15

    Highlights: • Thermal aging embrittlement was considered in the PFM analysis of nuclear pipe. • Predicting program for pipe failure probability was developed based on thermal aging. • Cumulative failure probability is significantly affected by fracture toughness. • Cumulative failure probability is slightly affected by fatigue crack growth rate. • Tensile strength increase due to thermal aging slightly reduces pipe failure risk. - Abstract: A predicting program for pipe break probability based on thermal aging embrittlement was developed. In order for life prediction, evolutions of fracture toughness and tensile strength were estimated for a Z3CN20-09M piping steel using the Argonne National Laboratory (ANL) procedure. To understand the influence of thermal aging on failure probability, different evolutions of fracture toughness, tensile strength and fatigue crack growth rate were employed in the prediction of cumulative failure probability. The results show that the cumulative failure probability for 40-year thermal aging increases by almost four times compared to without consideration of fracture toughness degradation. The cumulative failure probability is slightly affected by fatigue crack growth rate. The increase of tensile strength due to thermal aging reduces the risk of pipe failure. This work demonstrates that the degradation of fracture toughness due to thermal aging should be fully considered in the probabilistic fracture mechanics analysis of nuclear pressure pipes.

  6. Hygrothermal effects on dynamic mechanical snalysis and fracture behavior of polymeric composites

    Directory of Open Access Journals (Sweden)

    Michelle Leali Costa

    2005-09-01

    Full Text Available Polymer composites used above their glass transition temperatures Tg present a substantial degradation of physical properties; therefore a material's glass transition temperature and its change with moisture absorption are of practical importance. Little attention has been paid to the role of the adhesive bonding between the reinforcing fiber and matrix, particularly for BMI matrix. In this work the effect of moisture on the dynamic mechanical behavior and the fiber/matrix interface was investigated. Two systems were evaluated: carbon fabric/epoxy and carbon fabric/bismaleimide laminates. The results demonstrated that the moisture absorbed by the laminates causes either reversible or irreversible plasticization of the matrix. The humidity combined with the temperature effects may cause significant changes in the Tg matrix and toughness affecting the laminate strength. Moisture absorption was correlated to the fracture mode of the laminate demonstrating the deleterious effect of moisture on the interface. This leads to debonding between fiber and matrix. This behavior was investigated by scanning electron microscopy and dynamic mechanical analysis.

  7. A comparison of electromigration failure of metal lines with fracture mechanics

    Institute of Scientific and Technical Information of China (English)

    Hiroyuki Abé; Mikio Muraoka; Kazuhiko Sasagawa; Masumi Saka

    2012-01-01

    Atoms constructing an interconnecting metal line in a semiconductor device are transported by electron flow in high density.This phenomenon is called electromigration,which may cause the line failure.In order to characterize the electromigration failure,a comparison study is carried out with some typical phenomena treated by fracture mechanics for thin and large structures.An example of thin structures,which have been treated by fracture mechanics,is silica optical fibers for communication systems.The damage growth in a metal line by electromigration is characterized in comparison with the crack growth in a silica optical fiber subjected to static fatigue.Also a brief comparison is made between the electromigration failure and some fracture phenomena in large structures.

  8. Spectroscopic Investigation of the Mechanism of Photocatalysis

    Directory of Open Access Journals (Sweden)

    Yoshio Nosaka

    2014-11-01

    Full Text Available Reaction mechanisms of various kinds of photocatalysts have been reviewed based on the recent reports, in which various spectroscopic techniques including luminol chemiluminescence photometry, fluorescence probe method, electron spin resonance (ESR, and nuclear magnetic resonance (NMR spectroscopy were applied. The reaction mechanisms elucidated for bare and modified TiO2 were described individually. The modified visible light responsive TiO2 photocatalysts, i.e., Fe(III-deposited metal-doped TiO2 and platinum complex-deposited TiO2, were studied by detecting paramagnetic species with ESR, •O2− (or H2O2 with chemiluminescence photometry, and OH radicals with a fluorescence probe method. For bare TiO2, the difference in the oxidation mechanism for the different crystalline form was investigated by the fluorescence probe method, while the adsorption and decomposition behaviors of several amino acids and peptides were investigated by 1H-NMR spectroscopy.

  9. Microfluidic Investigation of Oil Mobilization in Shale Fracture Networks at Reservoir Conditions

    Science.gov (United States)

    Porter, M. L.; Jimenez-Martinez, J.; Carey, J. W.; Viswanathan, H. S.

    2015-12-01

    Investigations of pore-scale fluid flow and transport phenomena using engineered micromodels has steadily increased in recent years. In these investigations fluid flow is restricted to two-dimensions allowing for real time visualization and quantification of complex flow and reactive transport behavior, which is difficult to obtain in other experimental systems. One drawback to these studies is the use of engineered materials that do not faithfully represent the rock properties (e.g., porosity, wettability, roughness, etc.) encountered in subsurface formations. In this work, we describe a unique high pressure (up to 1500 psi) and temperature (up to 80 °C) microfluidics experimental system in which we investigate fluid flow and transport in geo-material (e.g., shale, Portland cement, etc.) micromodels. The use of geo-material micromodels allows us to better represent fluid-rock interactions including wettability, chemical reactivity, and nano-scale porosity at conditions representative of natural subsurface environments. Here, we present experimental results in fracture systems with applications to hydrocarbon mobility in hydraulically fractured shale. Complex fracture network patterns are derived from 3D x-ray tomography images of actual fractures created in shale rock cores. We use both shale and glass micromodels, allowing for a detailed comparison between flow phenomena in the different materials. We discuss results from two-phase huff-and-puff experiments involving N2 and n-Decane, as well as three-phase displacement experiments involving supercritical CO2, brine, and n-Decane.

  10. Probabilistic fracture mechanics analysis for the life extension estimate of the high flux isotope reactor vessel

    Energy Technology Data Exchange (ETDEWEB)

    Chang, S.J.

    1997-05-01

    The state of the vessel steel embrittlement as a result of neutron irradiation can be measured by its increase in the nil ductility temperature (NDT). This temperature is sometimes referred to as the brittle-ductile transition temperature (DBT) for fracture. The life extension of the High Flux Isotope Reactor (HFIR) vessel is calculated by using the method of fracture mechanics. A new method of fracture probability calculation is presented in this paper. The fracture probability as a result of the hydrostatic pressure test (hydrotest) is used to determine the life of the vessel. The hydrotest is performed in order to determine a safe vessel static pressure. It is then followed by using fracture mechanics to project the safe reactor operation time from the time of the satisfactory hydrostatic test. The life extension calculation provides the following information on the remaining life of the reactor as a function of the NDT increase: (1) the life of the vessel is determined by the probability of vessel fracture as a result of hydrotest at several hydrotest pressures and vessel embrittlement conditions, (2) the hydrotest time interval vs the NDT increase rate, and (3) the hydrotest pressure vs the NDT increase rate. It is understood that the use of a complete range of uncertainties of the NDT increase is equivalent to the entire range of radiation damage that can be experienced by the vessel steel. From the numerical values for the probabilities of the vessel fracture as a result of hydrotest, it is estimated that the reactor vessel life can be extended up to 50 EFPY (100 MW) with the minimum vessel operating temperature equal to 85{degrees}F.

  11. Fractures in anisotropic media

    Science.gov (United States)

    Shao, Siyi

    Rocks may be composed of layers and contain fracture sets that cause the hydraulic, mechanical and seismic properties of a rock to be anisotropic. Coexisting fractures and layers in rock give rise to competing mechanisms of anisotropy. For example: (1) at low fracture stiffness, apparent shear-wave anisotropy induced by matrix layering can be masked or enhanced by the presence of a fracture, depending on the fracture orientation with respect to layering, and (2) compressional-wave guided modes generated by parallel fractures can also mask the presence of matrix layerings for particular fracture orientations and fracture specific stiffness. This report focuses on two anisotropic sources that are widely encountered in rock engineering: fractures (mechanical discontinuity) and matrix layering (impedance discontinuity), by investigating: (1) matrix property characterization, i.e., to determine elastic constants in anisotropic solids, (2) interface wave behavior in single-fractured anisotropic media, (3) compressional wave guided modes in parallel-fractured anisotropic media (single fracture orientation) and (4) the elastic response of orthogonal fracture networks. Elastic constants of a medium are required to understand and quantify wave propagation in anisotropic media but are affected by fractures and matrix properties. Experimental observations and analytical analysis demonstrate that behaviors of both fracture interface waves and compressional-wave guided modes for fractures in anisotropic media, are affected by fracture specific stiffness (controlled by external stresses), signal frequency and relative orientation between layerings in the matrix and fractures. A fractured layered medium exhibits: (1) fracture-dominated anisotropy when the fractures are weakly coupled; (2) isotropic behavior when fractures delay waves that are usually fast in a layered medium; and (3) matrix-dominated anisotropy when the fractures are closed and no longer delay the signal. The

  12. Influence of ion nitriding regime on mechanical properties and fracture mechanism of austenitic steel subjected to different thermomechanical treatments

    Science.gov (United States)

    Moskvina, Valentina; Astafurova, Elena; Ramazanov, Kamil; Melnikov, Eugene; Maier, Galina; Budilov, Vladimir

    2016-11-01

    The effect of thermomechanical treatments and low-temperature ion nitriding on mechanical properties and a fracture mechanism of stable austenitic stainless steel Fe-17Cr-13Ni-1.7Mn-2.7Mo-0.5Si-0.01C (in wt %, 316L-type) was investigated. Irrespective of initial heat treatments of steel and the regime of nitrogen saturation, traditional ion nitriding and nitriding with hollow cathode effect do not influence the stages of plastic flow and strain hardening; instead, they contribute to surface hardening of steel samples and reduce their plastic properties due to formation of a brittle surface layer. Ion nitriding leads to formation of a hardened surface layer with the microhardness of 12 GPa. Formation of a high-defective grain/subgrain structure with high dislocation density contributes to strengthening of steel samples under ion nitriding and formation of a thicker strengthened layer in comparison with fine-crystalline and coarse-crystalline samples.

  13. Mineralogical and microstructural investigations of fractures in Permian z2 potash seam and surrounding salt rocks

    Science.gov (United States)

    Mertineit, Michael; Grewe, Wiebke; Schramm, Michael; Hammer, Jörg; Blanke, Hartmut; Patzschke, Mario

    2017-04-01

    Fractures occur locally in the z2 potash seam (Kaliflöz Staßfurt). Most of them extend several centimeter to meter into the surrounding salt rocks. The fractures are distributed on all levels in an extremely deformed area of the Morsleben salt mine, Northern Germany. The sampling site is located within a NW-SE trending synclinal structure, which was reverse folded (Behlau & Mingerzahn 2001). The samples were taken between the -195 m and - 305 m level at the field of Marie shaft. In this area, more than 200 healed fractures were mapped. Most of them show opening widths of only a few millimeters to rarely 10 cm. The fractures in rock salt are filled with basically polyhalite, halite and carnallite. In the potash seam, the fractures are filled with kainite, halite and minor amounts of carnallite and polyhalite. In some cases the fracture infill changes depending on the type of surrounding rocks. There are two dominant orientations of the fractures, which can be interpreted as a conjugated system. The main orientation is NE-SW trending, the dip angles are steep (ca. 70°, dip direction NW and SE, respectively). Subsequent deformation of the filled fractures is documented by a strong grain shape fabric of kainite, undulatory extinction and subgrain formation in kainite, and several mineral transformations. Subgrain formation in halite occurred in both, the fracture infill and the surrounding salt rocks. The results correlate in parts with investigations which were carried out at the close-by rock salt mine Braunschweig-Lüneburg (Horn et al. 2016). The development of the fractures occurred during compression of clayey salt rocks. However, the results are only partly comparable due to different properties (composition, impurities) of the investigated stratigraphic units. Further investigations will focus on detailed microstructural and geochemical analyses of the fracture infill and surrounding salt rocks. Age dating of suitable minerals, e.g. polyhalite (Leitner et al

  14. Intrinsic mechanical behavior of femoral cortical bone in young, osteoporotic and bisphosphonate-treated individuals in low- and high energy fracture conditions

    Science.gov (United States)

    Zimmermann, Elizabeth A.; Schaible, Eric; Gludovatz, Bernd; Schmidt, Felix N.; Riedel, Christoph; Krause, Matthias; Vettorazzi, Eik; Acevedo, Claire; Hahn, Michael; Püschel, Klaus; Tang, Simon; Amling, Michael; Ritchie, Robert O.; Busse, Björn

    2016-02-01

    Bisphosphonates are a common treatment to reduce osteoporotic fractures. This treatment induces osseous structural and compositional changes accompanied by positive effects on osteoblasts and osteocytes. Here, we test the hypothesis that restored osseous cell behavior, which resembles characteristics of younger, healthy cortical bone, leads to improved bone quality. Microarchitecture and mechanical properties of young, treatment-naïve osteoporosis, and bisphosphonate-treated cases were investigated in femoral cortices. Tissue strength was measured using three-point bending. Collagen fibril-level deformation was assessed in non-traumatic and traumatic fracture states using synchrotron small-angle x-ray scattering (SAXS) at low and high strain rates. The lower modulus, strength and fibril deformation measured at low strain rates reflects susceptibility for osteoporotic low-energy fragility fractures. Independent of age, disease and treatment status, SAXS revealed reduced fibril plasticity at high strain rates, characteristic of traumatic fracture. The significantly reduced mechanical integrity in osteoporosis may originate from porosity and alterations to the intra/extrafibrillar structure, while the fibril deformation under treatment indicates improved nano-scale characteristics. In conclusion, losses in strength and fibril deformation at low strain rates correlate with the occurrence of fragility fractures in osteoporosis, while improvements in structural and mechanical properties following bisphosphonate treatment may foster resistance to fracture during physiological strain rates.

  15. Experimental study on the mechanism of hydraulic fracture growth in a glutenite reservoir

    Science.gov (United States)

    Ma, Xinfang; Zou, Yushi; Li, Ning; Chen, Ming; Zhang, Yinuo; Liu, Zizhong

    2017-04-01

    Glutenite reservoirs are frequently significantly heterogeneous because of their unique depositional environment. The presence of gravel in this type of formation complicates the growth path of hydraulic fracture (HF). In this study, laboratory fracturing experiments were conducted on six large natural glutenite specimens (300 mm × 300 mm × 300 mm) using a true triaxial hydraulic fracturing system to investigate the growth law of HF in glutenite reservoirs. Before the experiments were performed, the rock properties of the gravel particles and matrix in the glutenite specimens were determined using various apparatuses. The effects of gravel size, horizontal differential stress, fracturing fluid type (or viscosity), and flow rate on the HF growth pattern, fracture width, and injection pressure were examined in detail. Similar to previous studies, four types of HF intersections with gravel particles, namely, termination, penetration, deflection, and attraction, were observed. The HF growth path in the glutenite specimens with large gravel (40 mm-100 mm) is likely branched and tortuous even under high horizontal differential stress. The HF growth path in the glutenite specimens with small gravel (less than 20 mm) is simple, but a process zone with multiple thin fractures may be created. Breakdown pressure may increase significantly when HF initiates from high-strength gravel particles, which are mainly composed of quartz. HF propagation is likely limited within high-strength gravel particles, thereby resulting in narrow fractures and even termination. The use of low-viscosity fluids, such as slickwater, and the low injection rate can further limit HF growth, particularly its width. As a response, high extension pressure builds up during fracturing.

  16. Three-Dimensional Problems in the Dynamic Fracture Mechanics of Materials with Interface Cracks (Review)

    Science.gov (United States)

    Guz, A. N.; Guz, I. A.; Men'shikov, A. V.; Men'shikov, V. A.

    2013-01-01

    Three-dimensional problems in the dynamic fracture mechanics of materials with interface cracks are considered as nonclassical problems of fracture mechanics. Physically correct results in fracture mechanics in the case where the interaction of the crack edges must be taken into account are analyzed. The linear (classical) and nonlinear (nonclassical) problems of dynamic fracture mechanics for materials with interface cracks are formulated using the above approaches. A method for solving three-dimensional linear dynamic problems based on boundary integral equations for piecewise-homogeneous materials and the boundary-element method is outlined. This method can be used for incremental solution of nonlinear problems. The method involves the regularization of hypersingular integrals. New classes of three-dimensional linear dynamic problems for circular and elliptic interface cracks are solved. Numerical values of stress intensity factors obtained with the linear problem formulation are the first step toward calculating them in the nonlinear formulation. The first results obtained in solving nonlinear dynamic problems for interface cracks with interacting faces are briefly analyzed

  17. Effect of CO2-induced reactions on the mechanical behaviour of fractured wellbore cement

    NARCIS (Netherlands)

    Wolterbeek, T.K.T.; Hangx, S.J.T.; Spiers, C.J.

    2016-01-01

    Geomechanical damage, such as fracturing of wellbore cement, can severely impact well integrity in CO2 storage fields. Chemical reactions between the cement and CO2-bearing fluids may subsequently alter the cement’s mechanical properties, either enhancing or inhibiting damage accumulation during ong

  18. Structural Reliability of Ceramics at High Temperature: Mechanisms of Fracture and Fatigue Crack Growth

    Energy Technology Data Exchange (ETDEWEB)

    Reinhold H. Dauskardt

    2005-08-01

    Final report of our DOE funded research program. Aim of the research program was to provide a fundamental basis from which the mechanical reliability of layered structures may be understood, and to provide guidelines for the development of technologically relevant layered material structures with optimum resistance to fracture and subcritical debonding. Progress in the program to achieve these goals is described.

  19. Experimental investigation on rainfall infiltration and solute transport in layered porous and fractured media

    Institute of Scientific and Technical Information of China (English)

    WANG Hui-fang; WANG Ming-yu

    2012-01-01

    Layered structures with upper porous and lower fractured media are widely distributed in the world.An experimental investigation on rainfall infiltration and solute transport in such layered structures can provide the necessary foundation for effectively preventing and forecasting water bursting in mines,controlling contamination of mine water,and accomplishing ecological restoration of mining areas.A typical physical model of the layered structures with porous and fractured media was created in this study.Then rainfall infiltration experiments were conducted after salt solution was sprayed on the surface of the layered structure.The volumetric water content and concentration of chlorine ions at different specified positions along the profile of the experiment system were measured in real-time.The experimental results showed that the lower fractured media,with a considerably higher permeability than that of the upper porous media,had significant effects on preventing water infiltration.Moreover,although the porous media were homogeneous statistically in the whole domain,spatial variations in the features of effluent concentrations with regards to time,or so called breakthrough curves,at various sampling points located at the horizontal plane in the porous media near the porous-fractured interface were observed,indicating the diversity of solute transport at small scales.Furthermore,the breakthrough curves of the outflow at the bottom,located beneath the underlying fractured rock,were able to capture and integrate features of the breakthrough curves of both the upper porous and fractured media,which exhibited multiple peaks,while the peak values were reduced one by one with time.

  20. A potential-of-mean-force approach for fracture mechanics of heterogeneous materials using the lattice element method

    Science.gov (United States)

    Laubie, Hadrien; Radjaï, Farhang; Pellenq, Roland; Ulm, Franz-Josef

    2017-08-01

    Fracture of heterogeneous materials has emerged as a critical issue in many engineering applications, ranging from subsurface energy to biomedical applications, and requires a rational framework that allows linking local fracture processes with global fracture descriptors such as the energy release rate, fracture energy and fracture toughness. This is achieved here by means of a local and a global potential-of-mean-force (PMF) inspired Lattice Element Method (LEM) approach. In the local approach, fracture-strength criteria derived from the effective interaction potentials between mass points are shown to exhibit a scaling commensurable with the energy dissipation of fracture processes. In the global PMF-approach, fracture is considered as a sequence of equilibrium states associated with minimum potential energy states analogous to Griffith's approach. It is found that this global approach has much in common with a Grand Canonical Monte Carlo (GCMC) approach, in which mass points are randomly removed following a maximum dissipation criterion until the energy release rate reaches the fracture energy. The duality of the two approaches is illustrated through the application of the PMF-inspired LEM for fracture propagation in a homogeneous linear elastic solid using different means of evaluating the energy release rate. Finally, by application of the method to a textbook example of fracture propagation in a heterogeneous material, it is shown that the proposed PMF-inspired LEM approach captures some well-known toughening mechanisms related to fracture energy contrast, elasticity contrast and crack deflection in the considered two-phase layered composite material.

  1. Mode I fracture toughness of coal

    Energy Technology Data Exchange (ETDEWEB)

    Bhagat, R.B.

    1985-10-01

    This investigation was undertaken to determine the fracture toughness and tensile strength of coal and to correlate these with the grindability of the coals in order to understand the fracture mechanics behaviour of coal. Results showed statistical relationships for the dependence of fracture toughness on the tensile strength of coal and between the fracture toughness and the Hardgrove Grindability Index. Softer coals have a lower fracture toughness value as coal is a brittle material. 16 references.

  2. MECHANISM ANALYSIS OF THICKNESS EFFECT ON MIXED MODE Ⅰ/Ⅱ FRACTURE OF LC4-CS ALUMINUM ALLOY

    Institute of Scientific and Technical Information of China (English)

    H.R. Dong; W.L. Guo

    2004-01-01

    Mixed mode Ⅰ/Ⅱ fracture experiments of LC4-CS aluminum alloy were conducted by using tension-shear specimens with thicknesses of 2, 4, 8 and 14mm. Fracture mechanisms of thickness effect on mixed mode Ⅰ/Ⅱ fracture were first examined from fracture surface morphology to correlate with the macroscopic fracture behavior and stress state. It is found that specimen thickness has a strong influence on mixed mode fracture. As thickness varies from thin to thick the macroscopic fracture surfaces appear the characteristics of plane stress state (2mm, 4mm-thick specimen), threedimensional stress state (8mm-thick specimens), and plane strain state (14mm-thick specimens), respectively. The specimens of all kinds of thicknesses are typical of tensile type failure under mode I loading condition and shear type failure under mode Ⅱloading condition. Two distinct features coexist on the fracture surfaces under mixed mode loading conditions, and the corresponding proportion varies with loading mixity. Void-growth processes are the failure mechanism in both predominately tensileand shear-type fractures. The size and depth of dimples on the fracture surface vary greatly with thickness. Therefore, it is extraordinary necessary to take into account the thickness effect when a mixed mode fracture criterion is being established.

  3. Mechanism and patterns of cervical spine fractures-dislocations in vertebral artery injury

    Directory of Open Access Journals (Sweden)

    Pankaj Gupta

    2012-01-01

    Full Text Available Purpose: To identify the fracture patterns and mechanism of injury, based on subaxial cervical spine injury classification system (SLIC, on non-contrast computed tomography (NCCT of cervical spine predictive of vertebral artery injury (VAI. Patients and Methods: We retrospectively analyzed cervical spine magnetic resonance imaging (MRI of 320 patients who were admitted with cervical spine injury in our level I regional trauma center over a period of two years (April 2010 to April 2012. Diagnosis of VAI was based on hyperintensity replacing the flow void on a T2-weighted axial image. NCCT images of the selected 43 patients with MRI diagnosis of VAI were then assessed for the pattern of injury. The cervical spinal injuries were classified into those involving the C1 and C2 and subaxial spine. For the latter, SLIC was used. Results: A total of 47 VAI were analyzed in 43 patients. Only one patient with VAI on MRI had no detectable abnormality on NCCT. C1 and C2 injuries were found in one and six patients respectively. In subaxial injuries, the most common mechanism of injury was distraction (37.5% with facet dislocation with or without fracture representing the most common pattern of injury (55%. C5 was the single most common affected vertebral level. Extension to foramen transversarium was present in 20 (42.5% cases. Conclusion: CT represents a robust screening tool for patients with VAI. VAI should be suspected in patients with facet dislocation with or without fractures, foramina transversarium fractures and C1-C3 fractures, especially type III odontoid fractures and distraction mechanism of injury.

  4. Assessment of strength-limiting flaws in ceramic heat exchanger components INEL support: Fracture mechanics and nondestructive evaluation technology. Final report, June 1, 1986--May 31, 1993

    Energy Technology Data Exchange (ETDEWEB)

    Lloyd, W.R.; Reuter, W.G.

    1993-06-01

    An examination of a siliconized SiC material, CS101K, has been performed to determine if linear fracture mechanics concepts can be used to characterize and predict the behavior of this material. Phase II of this project showed that a value that appeared to represent the true fracture toughness could be measured using small specimens with a machined notch, if the notch root radius was less than 75 {mu}m. Methods to produce sharply cracked specimens were then investigated to verify this hypothesis. A new technique, called the {open_quotes}beam support{close_quotes} precracking method, was subsequently developed and used to make sharply cracked SE(B) specimens. Tests of these specimens showed a slightly rising R-curve-type of behavior, with elevated values of plane strain fracture toughness. Interference of the crack surfaces in the precrack wake was hypothesized as the most likely cause of these phenomena. Subsequent testing with various precrack lengths provided preliminary verification of the hypothesis. Test results show that, for fracture mechanics-based design and assessment, adequate values of fracture toughness can be obtained from EDM-notched specimens, instead of the more costly precracked specimens. These results imply that, for the Si-SiC material tested, caution is warranted when using any of the methods of assessing fracture toughness that use a sharp precrack. It is also reasoned that these results may generally be more applicable to the coarser-grained structural ceramics that exhibit a rougher fracture surface. Based on results of testing EDM-notched bend specimens in 1250{degrees}C air, no degradation of material properties were observed for exposures, under applied stress, up to 900 h. Instead, some increase in fracture toughness was measured for these conditions. These same tests indicated that the threshold stress intensity factor for stress corrosion cracking (static fatigue) in the hot air environment was the same as the fracture toughness.

  5. Mechanical and fracture properties of a self-compacting version of CARDIFRC Mix II

    Indian Academy of Sciences (India)

    B S AL-AZZAWI; B L KARIHALOO

    2017-05-01

    CARDIFRC is the trade name of two main groups of ultra-high performance fibre-reinforced concrete mixes – Mixes I and II – differing primarily in the maximum size of quartz sand used (0.6 mm in Mix I,and 2 mm in Mix II). In this paper, the conversion of CARDIFRC Mix II to a self-compacting and industrially competitive ultra-high performance fibre-reinforced concrete (UHPFRC) is described. A full mechanical and fracture characterisation (i.e. size-independent fracture energy and the corresponding bi-linear stress-crack opening relationship) of this UHPFRC is provided.

  6. Probabilistic Fracture Mechanics of Reactor Pressure Vessels with Populations of Flaws

    Energy Technology Data Exchange (ETDEWEB)

    Spencer, Benjamin [Idaho National Lab. (INL), Idaho Falls, ID (United States); Backman, Marie [Univ. of Tennessee, Knoxville, TN (United States); Williams, Paul [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Hoffman, William [Idaho National Lab. (INL), Idaho Falls, ID (United States); Alfonsi, Andrea [Idaho National Lab. (INL), Idaho Falls, ID (United States); Dickson, Terry [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Bass, B. Richard [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Klasky, Hilda [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2016-09-01

    This report documents recent progress in developing a tool that uses the Grizzly and RAVEN codes to perform probabilistic fracture mechanics analyses of reactor pressure vessels in light water reactor nuclear power plants. The Grizzly code is being developed with the goal of creating a general tool that can be applied to study a variety of degradation mechanisms in nuclear power plant components. Because of the central role of the reactor pressure vessel (RPV) in a nuclear power plant, particular emphasis is being placed on developing capabilities to model fracture in embrittled RPVs to aid in the process surrounding decision making relating to life extension of existing plants. A typical RPV contains a large population of pre-existing flaws introduced during the manufacturing process. The use of probabilistic techniques is necessary to assess the likelihood of crack initiation at one or more of these flaws during a transient event. This report documents development and initial testing of a capability to perform probabilistic fracture mechanics of large populations of flaws in RPVs using reduced order models to compute fracture parameters. The work documented here builds on prior efforts to perform probabilistic analyses of a single flaw with uncertain parameters, as well as earlier work to develop deterministic capabilities to model the thermo-mechanical response of the RPV under transient events, and compute fracture mechanics parameters at locations of pre-defined flaws. The capabilities developed as part of this work provide a foundation for future work, which will develop a platform that provides the flexibility needed to consider scenarios that cannot be addressed with the tools used in current practice.

  7. Investigation of degradation mechanisms in composite matrices

    Science.gov (United States)

    Giori, C.; Yamauchi, T.

    1982-01-01

    Degradation mechanisms were investigated for graphite/polysulfone and graphite/epoxy laminates exposed to ultraviolet and high-energy electron radiations in vacuum up to 960 equivalent sun hours and 10 to the ninth power rads respectively. Based on GC and combined GC/MS analysis of volatile by-products evolved during irradiation, several free radical mechanisms of composite degradation were identified. The radiation resistance of different matrices was compared in terms of G values and quantum yields for gas formation. All the composite materials evaluated show high electron radiation stability and relatively low ultraviolet stability as indicated by low G values and high quantum for gas formation. Mechanical property measurements of irradiated samples did not reveal significant changes, with the possible exception of UV exposed polysulfone laminates. Hydrogen and methane were identified as the main by-products of irradiation, along with unexpectedly high levels of CO and CO2.

  8. Fracture mechanics characterisation of the WWER-440 reactor pressure vessel beltline welding seam of Greifswald unit 8

    Energy Technology Data Exchange (ETDEWEB)

    Viehrig, Hans-Werner; Schuhknecht, Jan [Forschungszentrum Dresden-Rossendorf (Germany)

    2008-07-01

    WWER-440 second generation (V-213) reactor pressure vessels (RPV) were produced by IZHORA in Russia and by SKODA in the former Czechoslovakia. The surveillance Charpy-V and fracture mechanics SE(B) specimens of both producers have different orientations. The main difference is the crack extension direction which is through the RPV thickness and circumferential for ISHORA and SKODA RPV, respectively. In particular for the investigation of weld metal from multilayer submerged welding seams the crack extension direction is of importance. Depending on the crack extension direction in the specimen there are different welding beads or a uniform structure along the crack front. The specimen orientation becomes more important when the fracture toughness of the weld metal is directly determined on surveillance specimens according to the Master Curve (MC) approach as standardised in the ASTM Standard Test Method E1921. This approach was applied on weld metal of the RPV beltline welding seam of Greifswald Unit 8 RPV. Charpy size SE(B) specimens from 13 locations equally spaced over the thickness of the welding seam were tested. The specimens are in TL and TS orientation. The fracture toughness values measured on the SE(B) specimens with both orientations follow the course of the MC. Nearly all values lie within the fracture toughness curves for 5% and 95% fracture probability. There is a strong variation of the reference temperature T{sub 0} though the thickness of the welding seam, which can be explained with structural differences. The scatter is more pronounced for the TS SE(B) specimens. It can be shown that specimens with TS and TL orientation in the welding seam have a differentiating and integrating behaviour, respectively. The statistical assumptions behind the MC approach are valid for both specimen orientations even if the structure is not uniform along the crack front. By comparison crack extension, JR, curves measured on SE(B) specimens with TL and TS orientation

  9. Flexible parallel implicit modelling of coupled thermal-hydraulic-mechanical processes in fractured rocks

    Science.gov (United States)

    Cacace, Mauro; Jacquey, Antoine B.

    2017-09-01

    Theory and numerical implementation describing groundwater flow and the transport of heat and solute mass in fully saturated fractured rocks with elasto-plastic mechanical feedbacks are developed. In our formulation, fractures are considered as being of lower dimension than the hosting deformable porous rock and we consider their hydraulic and mechanical apertures as scaling parameters to ensure continuous exchange of fluid mass and energy within the fracture-solid matrix system. The coupled system of equations is implemented in a new simulator code that makes use of a Galerkin finite-element technique. The code builds on a flexible, object-oriented numerical framework (MOOSE, Multiphysics Object Oriented Simulation Environment) which provides an extensive scalable parallel and implicit coupling to solve for the multiphysics problem. The governing equations of groundwater flow, heat and mass transport, and rock deformation are solved in a weak sense (either by classical Newton-Raphson or by free Jacobian inexact Newton-Krylow schemes) on an underlying unstructured mesh. Nonlinear feedbacks among the active processes are enforced by considering evolving fluid and rock properties depending on the thermo-hydro-mechanical state of the system and the local structure, i.e. degree of connectivity, of the fracture system. A suite of applications is presented to illustrate the flexibility and capability of the new simulator to address problems of increasing complexity and occurring at different spatial (from centimetres to tens of kilometres) and temporal scales (from minutes to hundreds of years).

  10. Focal mechanism caused by fracture or burst of a coal pillar

    Institute of Scientific and Technical Information of China (English)

    CAO An-ye; DOU Lin-ming; CHEN Guo-xiang; GONG Si-yuan; WANG Yu-gang; LI Zhi-hua

    2008-01-01

    As a regional, real-time and dynamic method, microseismic monitoring technology is quite an appropriate technology for forecasting geological hazards, such as rock bursts, mine tremors, coal and gas outbursts and can even be used to prevent or at least reduce these disasters. The study of the focal mechanisms of different seismic sources is the prerequisite and basis for forecasting rock burst by microseismic monitoring technology. Based on the analysis on the mechanism and fracture course of coal pillars where rock bursts occur mostly, the equivalent point source model of the seismicity caused by a coal pillar was created. Given the model, the seismic displacement equation of a coal pillar was analyzed and the seismic mechanism was pointed out by seismic wave theory. The course of the fracture of the coal pillar was simulated closely in the laboratory and the equivalent microseismic signals of the fractures of the coal pillar were acquired using a TDS-6 experimental system. The results show that, by the pressure and friction of a medium near the seismic source, both a compression wave and a shear wave will be emitted and shear fracture will be induced at the moment of breakage. The results can be used to provide an academic basis to forecast and prevent rock bursts or tremors in a coal pillar.

  11. Critical Chemical-Mechanical Couplings that Define Permeability Modifications in Pressure-Sensitive Rock Fractures

    Energy Technology Data Exchange (ETDEWEB)

    Derek Elsworth; Abraham Grader; Susan Brantley

    2007-04-25

    This work examined and quantified processes controlling changes in the transport characteristics of natural fractures, subjected to coupled thermal-mechanical-chemical (TMC) effects. Specifically, it examined the effects of mineral dissolution and precipitation mediated by mechanical effects, using laboratory through-flow experiments concurrently imaged by X-ray CT. These were conducted on natural and artificial fractures in cores using water as the permeant. Fluid and mineral mass balances are recorded and are correlated with in-sample saturation, porosity and fracture aperture maps, acquired in real-time by X-ray CT-imaging at a maximum spatial resolution of 15-50 microns per pixel. Post-test, the samples were resin-impregnated, thin-sectioned, and examined by microscopy to define the characteristics of dissolution and precipitation. The test-concurrent X-ray imaging, mass balances, and measurements of permeability, together with the post-test microscopy, were used to define dissolution/precipitation processes, and to constrain process-based models. These models define and quantify key processes of pressure solution, free-face dissolution, and shear-dilation, and the influence of temperature, stress level, and chemistry on the rate of dissolution, its distribution in space and time, and its influence on the mechanical and transport properties of the fracture.

  12. Combined loading effects on the fracture mechanics behavior of line pipes

    Energy Technology Data Exchange (ETDEWEB)

    Bravo, R.E.; Cravero, S.; Ernst, H.A. [Tenaris Group, Campana (Argentina). SIDERCA R and D Center

    2009-12-19

    For certain applications, pipelines may be submitted to biaxial loading situations. In these cases, it is not clear the influence of the biaxial loading on the fracture mechanics behavior of cracked pipelines. For further understanding of biaxial loading effects, this work presents a numerical simulation of ductile tearing in a circumferentially surface cracked pipe under biaxial loading using the computational cell methodology. The model was adjusted with experimental results obtained in laboratory using single edge cracked under tension (SENT) specimens. These specimens appear as the better alternative to conventional fracture specimens to characterize fracture toughness of cracked pipes. The negligible effect of biaxial loadings on resistance curves was demonstrated. To guarantee the similarities of stress and strains fields between SENT specimens and cracked pipes subjected to biaxial loading, a constraint study using the J-Q methodology and the h parameter was used. The constraint study gives information about the characteristics of the crack-tip conditions. (author)

  13. Experimental and computational investigation of the effect of phase transformation on fracture parameters of an SMA

    Science.gov (United States)

    Haghgouyan, Behrouz; Shafaghi, Nima; Aydıner, C. Can; Anlas, Gunay

    2016-07-01

    A comprehensive, multi-method experimental characterization of fracture is conducted on shape memory alloy NiTi that exhibits superelasticity due to austenite-to-martensite stress induced phase transformation. This characterization includes (i) load-based measurement of critical stress intensity factor (K max) using ASTM standard E399, (ii) measurement of crack tip opening displacement (CTOD) per ASTM standard E1290, (iii) the digital image correlation (DIC) characterization of the transformation zone as well as the displacement-field based measurement of K max from the DIC data. Samples have also been tested at T = 100 °C to suppress the martensitic transformation to investigate transformation toughening. The experimental investigation is complemented with finite element (FE) analysis that uses Auricchio-Taylor-Lubliner constitutive model. A direct observation with DIC revealed a small scale transformation (K-dominance). K max of the transforming material is higher than that of the transformation-suppressed material tested at 100 °C, suggesting transformation toughening. At 100 °C, the material becomes quite brittle with a very small crack-tip plastic zone when the transformation mechanism is blocked. By measures of critical CTOD, the gap widens even more between the superelastic and transformation-suppressed cases, particularly because of the side effect that, in this very interesting material, material modulus increases with temperature. Evaluating the transformation zone from the DIC strains with reference to the uniaxial stress-strain curve, an equivalent strain form is proposed in conjunction with the plane stress FE prediction.

  14. Erythropoietin (EPO): EPO-receptor signaling improves early endochondral ossification and mechanical strength in fracture healing.

    Science.gov (United States)

    Holstein, Joerg H; Menger, Michael D; Scheuer, Claudia; Meier, Christoph; Culemann, Ulf; Wirbel, Rainer J; Garcia, Patric; Pohlemann, Tim

    2007-02-13

    Beyond its role in the regulation of red blood cell proliferation, the glycoprotein erythropoietin (EPO) has been shown to promote cell regeneration and angiogenesis in a variety of different tissues. In addition, EPO has been indicated to share significant functional and structural homologies with the vascular endothelial growth factor (VEGF), a cytokine essential in the process of fracture healing. However, there is complete lack of information on the action of EPO in bone repair and fracture healing. Therefore, we investigated the effect of EPO treatment on bone healing in a murine closed femur fracture model using radiological, histomorphometric, immunohistochemical, biomechanical and protein biochemical analysis. Thirty-six SKH1-hr mice were treated with daily i.p. injections of 5000 U/kg EPO from day 1 before fracture until day 4 after fracture. Controls received equivalent amounts of the vehicle. After 2 weeks of fracture healing, we could demonstrate expression of the EPO-receptor (EPOR) in terminally differentiating chondrocytes within the callus. At this time point EPO-treated animals showed a higher torsional stiffness (biomechanical analysis: 39.6+/-19.4% of the contralateral unfractured femur) and an increased callus density (X-ray analysis (callus density/spongiosa density): 110.5+/-7.1%) when compared to vehicle-treated controls (14.3+/-8.2% and 105.9+/-6.6%; pEPO treatment had vanished at 5 weeks after fracture. We conclude that EPO-EPOR signaling is involved in the process of early endochondral ossification, enhancing the transition of soft callus to hard callus.

  15. Experimental investigation on fracture toughness of Al6061–graphite by using Circumferential Notched Tensile Specimens

    Directory of Open Access Journals (Sweden)

    Saleemsab Doddamani

    2017-01-01

    Full Text Available This paper presents the experimental work carried out on the fracture behavior of aluminium 6061 (Al6061 and graphite particulate composites. The required specimens are prepared using stir casting method with graphite proportions ranging from 3 to 12 % by weight. The fracture behavior of Al6061-graphite particulate composites produced using stir casting method, was investigated by conducting experiments on Universal Testing Machine (UTM. Circumferential Notched Tensile (CNT specimens were utilized to evaluate the fracture toughness of the composites. From the experiment the fracture toughness KIC= 15.85MPa m1/2 is obtained for Al6061-9% Graphite. Further, the experimental results revealed that, except 12% graphite, the fracture toughness of Al6061-graphite was observed to increases with an increase in weight percentage of graphite. The experimental results reinforce that Al6061-graphite particulate MMCs are suitable for automotive and aerospace applications requiring high fracture toughness apart from good wear resistance.

  16. Fracture Mechanics Analyses of Subsurface Defects in Reinforced Carbon-Carbon Joggles Subjected to Thermo-Mechanical Loads

    Science.gov (United States)

    Knight, Norman F., Jr.; Raju, Ivatury S.; Song, Kyongchan

    2011-01-01

    Coating spallation events have been observed along the slip-side joggle region of the Space Shuttle Orbiter wing-leading-edge panels. One potential contributor to the spallation event is a pressure build up within subsurface voids or defects due to volatiles or water vapor entrapped during fabrication, refurbishment, or normal operational use. The influence of entrapped pressure on the thermo-mechanical fracture-mechanics response of reinforced carbon-carbon with subsurface defects is studied. Plane-strain simulations with embedded subsurface defects are performed to characterize the fracture mechanics response for a given defect length when subjected to combined elevated-temperature and subsurface-defect pressure loadings to simulate the unvented defect condition. Various subsurface defect locations of a fixed-length substrate defect are examined for elevated temperature conditions. Fracture mechanics results suggest that entrapped pressure combined with local elevated temperatures have the potential to cause subsurface defect growth and possibly contribute to further material separation or even spallation. For this anomaly to occur, several unusual circumstances would be required making such an outcome unlikely but plausible.

  17. Understanding Irreversible Degradation of Nb3Sn Wires with Fundamental Fracture Mechanics

    Energy Technology Data Exchange (ETDEWEB)

    Zhai, Yuhu [PPPL; Calzolaio, Ciro [Univ of Geneva; Senatore, Carmine [Univ of Geneva

    2014-08-01

    Irreversible performance degradation of advanced Nb3Sn superconducting wires subjected to transverse or axial mechanical loading is a critical issue for the design of large-scale fusion and accelerator magnets such as ITER and LHC. Recent SULTAN tests indicate that most cable-in-conduit conductors for ITER coils made of Nb3Sn wires processed by various fabrication techniques show similar performance degradation under cyclic loading. The irreversible degradation due to filament fracture and local strain accumulation in Nb3Sn wires cannot be described by the existing strand scaling law. Fracture mechanic modeling combined with X-ray diffraction imaging of filament micro-crack formation inside the wires under mechanical loading may reveal exciting insights to the wire degradation mechanisms. We apply fundamental fracture mechanics with a singularity approach to study influence of wire filament microstructure of initial void size and distribution to local stress concentration and potential crack propagation. We report impact of the scale and density of the void structure on stress concentration in the composite wire materials for crack initiation. These initial defects result in an irreversible degradation of the critical current beyond certain applied stress. We also discuss options to minimize stress concentration in the design of the material microstructure for enhanced wire performance for future applications.

  18. Investigating Mechanisms of Marginal Settlement Life Improvement

    Directory of Open Access Journals (Sweden)

    Hamid M. Mohammadi

    2008-01-01

    Full Text Available The main purpose of this research was to investigate mechanisms to improve marginal settlement life in Koohdasht County in Lorestan province. This research was a sort of the survey studies and a questionnaire was compiled for collection of data. Statistical population of this study was included 1560 households; also sampling method was a sort of random sampling. Number of sample size was estimated 85 households. Questionnaire's reliability was confirmed through computing Cronbach's alpha coefficient which was 0.85. Face validity of questionnaire was confirmed by some Tehran university agricultural extension and education department scientific board members. Also data analyzed by WINspss 11.5. The results of research revealed that marginal area residents had not good financial situation but they undertook great supporting burden and in point of view access to services and life conditions had not good situation. Therefore improvement of life conditions of marginal settlement life such as fundamental infrastructure include communication systems and sanitation offloading system recognized as the most important mechanisms of marginal settlement improvement according to results of priority setting of marginal settlement situation mechanisms. Also the results of factor analysis showed that 7 main mechanisms were be effective in term of marginal settlement life improvement that in order to importance were included servicing and life condition improvement, credit-economic, civil and legal, control and prevention, population and migration control, infrastructures improvement and hygiene situation.

  19. First-order Description of the Mechanical Fracture Behavior of Fine-Grained Surficial Marine Sediments During Gas Bubble Growth

    Science.gov (United States)

    2010-01-01

    10 F04O29 BARRY ET AL.: BUBBLE GROWTH BY FRACTURE P04029 Figure 3. Map of field site. Canard, Nova Scotia, Canada. appears to approximate the...Bottinger. and T. Dahm (2005), Buoyancy-driven fracture ascent: Experiments in layered gelatine. J. Volcano!. Geotherm . Res., 144. 273-285. doi...Journal Article 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE First-order description of the mechanical fracture behavior of fine-grained

  20. Ipsilateral simultaneous fracture of the trochlea involving the lateral end clavicle and distal end radius: a rare combination and a unique mechanism of injury

    Directory of Open Access Journals (Sweden)

    Gupta RK

    2014-07-01

    Full Text Available 【Abstract】Isolated trochlea fracture in adults is a rare surgical entity as compared to its capitellar counterpart. It has been only mentioned sporadically in the literature as case reports. Fracture of the trochlea is accompanied by other elbow injuries like elbow dislocation, capitellum fracture, ulnar fracture and extraarticular condylar fracture. Here we report a unique case of isolated displaced trochlea fracture associated with fractures of the lateral end clavicle and the distal end radius. We propose a unique mechanism for this rare combination of injuries: typical triad of injury, i.e. fracture of the distal end radius with trochlea and fracture of the lateral end of the clavicle. Nonoperative treatment is recommended for undisplaced humeral trochlea fractures; but for displaced ones, anatomical reduction and internal fixation are essential to maintain the congruous trochleacoronoid articulation and hence to maintain the intrinsic stability of the elbow. Key words: Isolated trochlea fracture; Clavicle; Radius fractures

  1. Exploring particulate retention mechanisms through visualization of E. coli transport through a single, saturated fracture

    Science.gov (United States)

    Burke, M. G.; Dickson, S. E.; Schutten, M.

    2011-12-01

    Groundwater is an extremely valuable resource; a large body of work has been conducted towards remediating, tracking and reducing its contamination. Even so, there are large gaps within the current understanding of groundwater flow and contaminant transport, particularly within fractured media. Fractured media has the ability transport contaminants over longer distances in less time relative to porous media. Furthermore, colloids display unique transport characteristics in comparison to dissolved constituents, including the fact that they typically exhibit earlier initial arrival times. Of particular concern to human health are pathogenic microorganisms, which often originate from fecal contamination. Escherichia coli is a common indicator for fecal contamination; some strains are pathogenic, causing acute illness and sometimes death, in humans. A comprehensive understanding of the transport and retention of E. coli in fractured media will improve our ability to accurately assess whether a site is at risk of becoming contaminated by pathogenic microorganisms. Therefore, the goal of this work is to expand our mechanistic understanding particulate retention, specifically E. coli, in fractures, and the influence of flow rate on these mechanisms. In order to achieve this goal, clear epoxy casts were fabricated of two dolomitic limestone fractures retrieved from a quarry in Guelph, Ontario. Each aperture field was characterized through hydraulic and tracer tests, and measured directly using the light transmission technique. E. coli RS2-GFP, which is a non-pathogenic strain of E. coli that has been tagged with a green fluorescent protein, was injected into the cast under three separate specific discharges ranging from 5 - 30 m/d. These experiments were conducted on an ultraviolet light source, and a high resolution charged-couple device (CCD) camera was employed to take photos at regular intervals in order to capture the dominant flow paths and the areas of retention

  2. Fracture mechanics behaviour of ductile cast iron and martensitic steel at elevated temperature

    Energy Technology Data Exchange (ETDEWEB)

    Udoh, A.; Klenk, A.; Roos, E. [Stuttgart Univ. (Germany). MPA; Sasikala, G. [Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam (India)

    2010-07-01

    Ductile cast iron is employed increasingly due to the advantages regarding foundry practice, design as well as economic advantages in the thermal machinery and power plant construction. It is employed preferably where higher toughness is required, e.g. in valves or thickwalled components of thermal or nuclear power plants. For this reason the safety and availability criteria for fracture mechanics assessment of components are necessary in addition to the conventional strength design. Alloys with silicon and molybdenum are developed for the application at higher temperatures. The increase in the thermal efficiency of fossil fired steam power plant that can be achieved by increasing the steam temperature and pressure has provided the incentive for development of the 9% chromium steels towards improved creep rupture strength. During the last twenty years, three such steels, P91 (9Cr-1Mo-VNb), E911 (9Cr-1Mo-1W-V-Nb) and P92 (9Cr-0,5Mo-1,8W-V-Nb), have been developed for commercial production. For application in piping systems and boiler construction sufficient reliable information concerning the long-term behaviour are necessary as well as knowledge about fracture mechanical behaviour in order to ensure integrity of components. Different methods to characterize fracture behaviour of ductile cast iron and martensitic steel at elevated temperature have been employed. The RBR method is a novel and simple method developed at IGCAR for characterizing the ductile fracture behaviour of materials from tensile tests of cylindrical specimens. Using the data evaluated at both institutes, a fracture mechanics characterisation by determining crack initiation and crack resistance by J{sub R}-curves and RBR parameters is presented. (orig.)

  3. Deep Fracturing of the Hard Rock Surrounding a Large Underground Cavern Subjected to High Geostress: In Situ Observation and Mechanism Analysis

    Science.gov (United States)

    Feng, Xia-Ting; Pei, Shu-Feng; Jiang, Quan; Zhou, Yang-Yi; Li, Shao-Jun; Yao, Zhi-Bin

    2017-08-01

    Rocks that are far removed from caverns or tunnels peripheries and subjected to high geostress may undergo `deep fracturing'. Deep fracturing of hard rock can cause serious hazards that cause delays and increase the cost of construction of underground caverns with high sidewalls and large spans (especially when subjected to high geostress). To extensively investigate the mechanism responsible for deep fracturing, and the relationship between fracturing and the excavation & support of caverns, this paper presents a basic procedure for making in situ observations on the deep fracturing process in hard rock. The basic procedure involves predicting the stress concentration zones in the surrounding rocks of caverns induced by excavation using geomechanical techniques. Boreholes are then drilled through these stress concentration zones from pre-existing tunnels (such as auxiliary galleries) toward the caverns before its excavation. Continuous observations of the fracturing of the surrounding rocks are performed during excavation using a borehole camera in the boreholes in order to analyze the evolution of the fracturing process. The deep fracturing observed in a large underground cavern (high sidewalls and large span) in southwest China excavated in basalt under high geostress is also discussed. By continuously observing the hard rock surrounding the arch on the upstream side of the cavern during the excavation of the first three layers, it was observed that the fracturing developed into the surrounding rocks with downward excavation of the cavern. Fracturing was found at distances up to 8-9 m from the cavern periphery during the excavation of Layer III. Also, the cracks propagated along pre-existing joints or at the interfaces between quartz porphyry and the rock matrix. The relationship between deep fracturing of the surrounding rocks and the advance of the cavern working faces was analyzed during excavation of Layer Ib. The results indicate that the extent of the

  4. A damage-mechanics model for fracture nucleation and propagation

    CERN Document Server

    Yakovlev, G; Turcotte, D L; Rundle, J B; Klein, W; 10.1016/j.tafmec.2010.06.002.

    2010-01-01

    In this paper a composite model for earthquake rupture initiation and propagation is proposed. The model includes aspects of damage mechanics, fiber-bundle models, and slider-block models. An array of elements is introduced in analogy to the fibers of a fiber bundle. Time to failure for each element is specified from a Poisson distribution. The hazard rate is assumed to have a power-law dependence on stress. When an element fails it is removed, the stress on a failed element is redistributed uniformly to a specified number of neighboring elements in a given range of interaction. Damage is defined to be the fraction of elements that have failed. Time to failure and modes of rupture propagation are determined as a function of the hazard-rate exponent and the range of interaction.

  5. A microfluidic investigation of gas exsolution in glass and shale fracture networks

    Science.gov (United States)

    Porter, M. L.; Jimenez-Martinez, J.; Harrison, A.; Currier, R.; Viswanathan, H. S.

    2016-12-01

    Microfluidic investigations of pore-scale fluid flow and transport phenomena has steadily increased in recent years. In these investigations fluid flow is restricted to two-dimensions allowing for real-time visualization and quantification of complex flow and reactive transport behavior, which is difficult to obtain in other experimental systems. In this work, we describe a unique high pressure (up to 10.3 MPa) and temperature (up to 80 °C) microfluidics experimental system that allows us to investigate fluid flow and transport in geo-material (e.g., shale, Portland cement, etc.) micromodels. The use of geo-material micromodels allows us to better represent fluid-rock interactions including wettability, chemical reactivity, and nano-scale porosity at conditions representative of natural subsurface environments. Here, we present experimental results in fracture systems with applications to hydrocarbon mobility in fractured rocks. Complex fracture network patterns are derived from 3D x-ray tomography images of actual fractures created in shale rock cores. We use both shale and glass micromodels, allowing for a detailed comparison between flow phenomena in the different materials. We discuss results from two-phase gas (CO2 and N2) injection experiments designed to enhance oil recovery. In these experiments gas was injected into micromodels saturated with oil and allowed to soak for approximately 12 hours at elevated pressures. The pressure in the system was then decreased to atmospheric, causing the gas to expand and/or dissolve out of solution, subsequently mobilizing the oil. In addition to the experimental results, we present a relatively simple model designed to quantify the amount of oil mobilized as a function of decreasing system pressure. We will show comparisons between the experiments and model, and discuss the potential use of the model in field-scale reservoir simulations.

  6. A mechanical model for predicting the probability of osteoporotic hip fractures based in DXA measurements and finite element simulation

    Directory of Open Access Journals (Sweden)

    López Enrique

    2012-11-01

    Full Text Available Abstract Background Osteoporotic hip fractures represent major cause of disability, loss of quality of life and even mortality among the elderly population. Decisions on drug therapy are based on the assessment of risk factors for fracture, from BMD measurements. The combination of biomechanical models with clinical studies could better estimate bone strength and supporting the specialists in their decision. Methods A model to assess the probability of fracture, based on the Damage and Fracture Mechanics has been developed, evaluating the mechanical magnitudes involved in the fracture process from clinical BMD measurements. The model is intended for simulating the degenerative process in the skeleton, with the consequent lost of bone mass and hence the decrease of its mechanical resistance which enables the fracture due to different traumatisms. Clinical studies were chosen, both in non-treatment conditions and receiving drug therapy, and fitted to specific patients according their actual BMD measures. The predictive model is applied in a FE simulation of the proximal femur. The fracture zone would be determined according loading scenario (sideway fall, impact, accidental loads, etc., using the mechanical properties of bone obtained from the evolutionary model corresponding to the considered time. Results BMD evolution in untreated patients and in those under different treatments was analyzed. Evolutionary curves of fracture probability were obtained from the evolution of mechanical damage. The evolutionary curve of the untreated group of patients presented a marked increase of the fracture probability, while the curves of patients under drug treatment showed variable decreased risks, depending on the therapy type. Conclusion The FE model allowed to obtain detailed maps of damage and fracture probability, identifying high-risk local zones at femoral neck and intertrochanteric and subtrochanteric areas, which are the typical locations of

  7. Certain Discrete Element Methods in Problems of Fracture Mechanics

    Directory of Open Access Journals (Sweden)

    P. P. Procházka

    2002-01-01

    Full Text Available In this paper two discrete element methods (DEM are discussed. The free hexagon element method is considered a powerful discrete element method, which is broadly used in mechanics of granular media. It substitutes the methods for solving continuum problems. The great disadvantage of classical DEM, such as the particle flow code (material properties are characterized by spring stiffness, is that they have to be fed with material properties provided from laboratory tests (Young's modulus, Poisson's ratio, etc.. The problem consists in the fact that the material properties of continuum methods (FEM, BEM are not mutually consistent with DEM. This is why we utilize the principal idea of DEM, but cover the continuum by hexagonal elastic, or elastic-plastic, elements. In order to complete the study, another one DEM is discussed. The second method starts with the classical particle flow code (PFC - which uses dynamic equilibrium, but applies static equilibrium. The second method is called the static particle flow code (SPFC. The numerical experience and comparison numerical with experimental results from scaled models are discussed in forthcoming paper by both authors.

  8. Fracture Mechanics Analyses of Reinforced Carbon-Carbon Wing-Leading-Edge Panels

    Science.gov (United States)

    Raju, Ivatury S.; Phillips, Dawn R.; Knight, Norman F., Jr.; Song, Kyongchan

    2010-01-01

    Fracture mechanics analyses of subsurface defects within the joggle regions of the Space Shuttle wing-leading-edge RCC panels are performed. A 2D plane strain idealized joggle finite element model is developed to study the fracture behavior of the panels for three distinct loading conditions - lift-off and ascent, on-orbit, and entry. For lift-off and ascent, an estimated bounding aerodynamic pressure load is used for the analyses, while for on-orbit and entry, thermo-mechanical analyses are performed using the extreme cold and hot temperatures experienced by the panels. In addition, a best estimate for the material stress-free temperature is used in the thermo-mechanical analyses. In the finite element models, the substrate and coating are modeled separately as two distinct materials. Subsurface defects are introduced at the coating-substrate interface and within the substrate. The objective of the fracture mechanics analyses is to evaluate the defect driving forces, which are characterized by the strain energy release rates, and determine if defects can become unstable for each of the loading conditions.

  9. Development of fracture mechanics data for two hydrazine APU turbine wheel materials

    Science.gov (United States)

    Curbishley, G.

    1975-01-01

    The effects of high temperature, high pressure ammonia were measured on the fracture mechanics and fatigue properties of Astroloy and Rene' 41 turbine wheel materials. Also, the influence of protective coatings on these properties was investigated. Specimens of forged bar stock were subjected to LCF and HCF tests at 950 K (1250 F) and 3.4 MN/sq m (500 psig) pressure, in ammonia containing about 1.5 percent H2O. Aluminized samples (Chromizing Company's Al-870) and gold plated test bars were compared with uncoated specimens. Comparison tests were also run in air at 950 K (1250 F), but at ambient pressures. K sub IE and K sub TH were determined on surface flawed specimens in both the air and ammonia in both uncoated and gold plated conditions. Gold plated specimens exhibited better properties than uncoated samples, and aluminized test bars generally had lower properties. The fatigue properties of specimens tested in ammonia were higher than those tested in air, yet the K sub TH values of ammonia tested samples were lower than those tested in air. However, insufficient specimens were tested to develop significant design data.

  10. Fracture Mechanics Analyses of the Slip-Side Joggle Regions of Wing-Leading Edge Panels

    Science.gov (United States)

    Raju, Ivatury S.; Knight, Norman F., Jr.; Song, Kyongchan; Phillips, Dawn R.

    2010-01-01

    The Space Shuttle Orbiter wing comprises of 22 leading edge panels on each side of the wing. These panels are part of the thermal protection system that protects the Orbiter wings from extreme heating that take place on the reentry in to the earth atmosphere. On some panels that experience extreme heating, liberation of silicon carbon (SiC) coating was observed on the slip side regions of the panels. Global structural and local fracture mechanics analyses were performed on these panels as a part of the root cause investigation of this coating liberation anomaly. The wing-leading-edge reinforced carbon-carbon (RCC) panels, Panel 9, T-seal 10, and Panel 10, are shown in Figure 1 and the progression of the stress analysis models is presented in Figure 2. The global structural analyses showed minimal interaction between adjacent panels and the T-seal that bridges the gap between the panels. A bounding uniform temperature is applied to a representative panel and the resulting stress distribution is examined. For this loading condition, the interlaminar normal stresses showed negligible variation in the chord direction and increased values in the vicinity of the slip-side joggle shoulder. As such, a representative span wise slice on the panel can be taken and the cross section can be analyzed using plane strain analysis.

  11. Fatigue properties and fracture mechanism of load carrying type fillet joints with one-sided welding

    Directory of Open Access Journals (Sweden)

    Takamasa Abe

    2016-02-01

    Full Text Available The structures of the hydraulic excavator and the crane have numerous one-sided welded joints. However, attachments with box like structures are difficult to weld at both sides. Therefore, high accurate evaluation method is needed. In this study, the fatigue properties and the fracture mechanism of the load carrying type fillet joints with one-sided welding were investigated experimentally to evaluate its fatigue damage with high accuracy based on the experimental results. As the results, fatigue cracks in the test piece initiated from the tip of the unwelded portion and propagated into the welding materials. Multiple welding defects were observed in the unwelded portion, but did not appear to be crack origins. Although these welding defects affected the direction of crack propagation they exerted minimal influence. The three-dimensional observations revealed that fatigue cracks initiate at an early stage of the fatigue development. We infer that the fatigue lifetime is chiefly governed by the crack propagation lifetime. Cracks were initiated at multiple sites in the test piece. As the number of cycles increased, these cracks propagated and combined. So considering the combination of cracks from multiple crack origins is important for a precise evaluation of fatigue damage.

  12. Fatigue properties and fracture mechanism of load carrying type fillet joints with one-sided welding

    Directory of Open Access Journals (Sweden)

    Takamasa Abe

    2016-01-01

    Full Text Available The structures of the hydraulic excavator and the crane have numerous one-sided welded joints. However, attachments with box like structures are difficult to weld at both sides. Therefore, high accurate evaluation method is needed. In this study, the fatigue properties and the fracture mechanism of the load carrying type fillet joints with one-sided welding were investigated experimentally to evaluate its fatigue damage with high accuracy based on the experimental results. As the results, fatigue cracks in the test piece initiated from the tip of the unwelded portion and propagated into the welding materials. Multiple welding defects were observed in the unwelded portion, but did not appear to be crack origins. Although these welding defects affected the direction of crack propagation they exerted minimal influence. The three-dimensional observations revealed that fatigue cracks initiate at an early stage of the fatigue development. We infer that the fatigue lifetime is chiefly governed by the crack propagation lifetime. Cracks were initiated at multiple sites in the test piece. As the number of cycles increased, these cracks propagated and combined. So considering the combination of cracks from multiple crack origins is important for a precise evaluation of fatigue damage.

  13. Modelling of Debond and Crack Propagation in Sandwich Structures Using Fracture and Damage Mechanics

    DEFF Research Database (Denmark)

    Berggreen, C.; Simonsen, Bo Cerup; Toernqvist, Rikard

    2003-01-01

    Skin-core de-bonding or core crack propagation will often be dominating mechanisms in the collapse modes of sandwich structures. This paper presents two different methods for prediction of crack propagation in a sandwich structure: a fracture mechanics approach, where a new mode-mix method...... is presented, and a local damage mechanics approach. The paper presents a real-life application example, where the superstructure in a vessel pulls the skin off the sandwich deck. The calculations show almost unstable crack growth initially followed by a stabilization, and a nearly linear relation between...

  14. A qualitative engineering analysis of occlusion effects on mandibular fracture repair mechanics.

    Science.gov (United States)

    Katona, Thomas R

    2011-01-01

    Objectives. The purpose of this analytical study was to examine and critique the engineering foundations of commonly accepted biomechanical principles of mandible fracture repair. Materials and Methods. Basic principles of static equilibrium were applied to intact and plated mandibles, but instead of the traditional lever forces, the mandibles were subjected to more realistic occlusal forces. Results. These loading conditions produced stress distributions within the intact mandible that were very different and more complex than the customary lever-based gradient. The analyses also demonstrated the entirely different mechanical environments within intact and plated mandibles. Conclusions. Because the loading and geometry of the lever-idealized mandible is incomplete, the associated widely accepted bone stress distribution (tension on top and compression on the bottom) should not be assumed. Furthermore, the stress gradients within the bone of an intact mandible should not be extrapolated to the mechanical environment within the plated regions of a fractured mandible.

  15. An Analytical Model for Fatigue Life Prediction Based on Fracture Mechanics and Crack Closure

    DEFF Research Database (Denmark)

    Ibsø, Jan Behrend; Agerskov, Henning

    1996-01-01

    Fatigue in steel structures subjected to stochastic loading is studied. Of special interest is the problem of fatigue damage accumulation and in this connection, a comparison between experimental results and results obtained using fracture mechanics. Fatigue test results obtained for welded plate...... test specimens are compared with fatigue life predictions using a fracture mechanics approach. In the calculation of the fatigue life, the influence of the welding residual stresses and crack closure on the fatigue crack growth is considered. A description of the crack closure model for analytical...... determination of the fatigue life is included. Furthermore, the results obtained in studies of the various parameters that have an influence on the fatigue life, are given. A very good agreement between experimental and analytical results is obtained, when the crack closure model is used in determination...

  16. An Analytical Model for Fatigue Life Prediction Based on Fracture Mechanics and Crack Closure

    DEFF Research Database (Denmark)

    Ibsø, Jan Behrend; Agerskov, Henning

    1996-01-01

    Fatigue in steel structures subjected to stochastic loading is studied. Of special interest is the problem of fatigue damage accumulation and in this connection, a comparison between experimental results and results obtained using fracture mechanics. Fatigue test results obtained for welded plate...... test specimens are compared with fatigue life predictions using a fracture mechanics approach. In the calculation of the fatigue life, the influence of the welding residual stresses and crack closure on the fatigue crack growth is considered. A description of the crack closure model for analytical...... of the analytical fatigue lives. Both the analytical and experimental results obtained show that the Miner rule may give quite unconservative predictions of the fatigue life for the types of stochastic loading studied....

  17. Micromechanics, fracture mechanics and gas permeability of composite laminates for cryogenic storage systems

    Science.gov (United States)

    Choi, Sukjoo

    A micromechanics method is developed to investigate microcrack propagation in a liquid hydrogen composite tank at cryogenic temperature. The unit cell is modeled using square and hexagonal shapes depends on fiber and matrix layout from microscopic images of composite laminates. Periodic boundary conditions are applied to the unit cell. The temperature dependent properties are taken into account in the analysis. The laminate properties estimated by the micromechanics method are compared with empirical solutions using constituent properties. The micro stresses in the fiber and matrix phases based on boundary conditions in laminate level are calculated to predict the formation of microcracks in the matrix. The method is applied to an actual liquid hydrogen storage system. The analysis predicts micro stresses in the matrix phase are large enough to cause microcracks in the composite. Stress singularity of a transverse crack normal to a ply-interface is investigated to predict the fracture behavior at cryogenic conditions using analytical and finite element analysis. When a transverse crack touches a ply-interface of a composite layer with same fiber orientation, the stress singularity is equal to ½. When the transverse crack propagates to a stiffer layer normal to a ply-direction, the singularity becomes less than ½ and vice versa. Finite element analysis is performed to evaluate fracture toughness of a laminated beam subjected to the fracture load measured by the fracture experiment at room and cryogenic temperatures. As results, the fracture load at cryogenic temperature is significantly lower than that at room temperature. However, when thermal stresses are taken into consideration, for both cases of room and cryogenic temperatures, the variation of fracture toughness becomes insignificant. The result indicates fracture toughness is a characteristic property which is independent to temperature changes. The experimental analysis is performed to investigate the

  18. Fracture mechanics of pseudoelastic NiTi alloys: review of the research activities carried out at University of Calabria

    Directory of Open Access Journals (Sweden)

    E. Sgambitterra

    2013-01-01

    Full Text Available This paper reports a brief review of the research activities on fracture mechanics of nickel-titanium based shape memory alloys carried out at University of Calabria. In fact, this class of metallic alloys show a unusual fracture response due to the reversible stress-induced and thermally phase transition mechanisms occurring in the crack tip region as a consequence of the highly localized stresses. The paper illustrates the main results concerning numerical, analytical and experimental research activities carried out by using commercial NiTi based pseudoelastic alloys. Furthermore, the effect of several thermo-mechanical loading conditions on the fracture properties of NiTi alloys are illustrated.

  19. MWCNTs/Resin Nanocomposites: Structural, Thermal, Mechanical and Dielectric Investigation

    Directory of Open Access Journals (Sweden)

    N. D. Alexopoulos

    2015-11-01

    Full Text Available Multi-wall carbon nanotubes (MWCNTs were manufactured, characterized and added to a typical aeronautical resin matrix at different concentrations as nano-reinforcement. The carbon content of produced MWCNTs was determined to be around 98.5% while they consisted of 13-20 wall-layers and their external diameter had an average size in between 20 and 50 nm. MWCNTs were dispersed in an epoxy resin system and tensile specimens for different MWCNTs concentrations were prepared in an open mould. Electrical wiring was attached to the specimens’ surface and surface electrical resistance change was in-situ monitored during monotonic tension till fracture. Performed tensile tests showed that the MWCNTs addition increased both modulus of elasticity and ultimate tensile strength on the nano-composites with a simultaneously dramatic ductility decrease. The MWCNTs addition enhanced the investigated resin matrix with monitoring ability; electrical resistance change of the investigated tensile tests was correlated in the elastic regime with axial nominal strain and the gauge factor of the different MWCNTs concentration specimens were calculated. It was found that lowest MWCNTs concentration gave the best results in terms of piezo-resistivity and simultaneously the least enhancement in the mechanical properties.

  20. Multiscale Stochastic Fracture Mechanics of Composites Informed by In-situ XCT Tests

    Science.gov (United States)

    2016-02-02

    connecting the CFRP ribs and metal claddings of wings. Therefore, there is still an urgent need to get better understanding of the mechanical behaviour of...structural integrity can be assured. This project aims to characterise the microstructures, the damage and fracture behaviour of CFRP using the state...load-displacement curves in excellent agreement with those from a full micro-scale simulation, but consuming considerably less computation time of the

  1. Hip fracture presenting as mechanical low back pain subsequent to a fall: a case study

    OpenAIRE

    Gleberzon, Brian; Hyde, David

    2006-01-01

    This case chronicles the assessment and clinical management of a 54 year old female patient who presented with post traumatic lower back, hip and lower extremity pain, initially attributed to mechanical low back pain but ultimately diagnosed as a hip fracture. This case study illustrates a number of important issues germane to chiropractic care. These are; the importance of using different assessment procedures, combined with clinical experience, in order to differentiate between those patien...

  2. Applications of FEM and BEM in two-dimensional fracture mechanics problems

    Science.gov (United States)

    Min, J. B.; Steeve, B. E.; Swanson, G. R.

    1992-08-01

    A comparison of the finite element method (FEM) and boundary element method (BEM) for the solution of two-dimensional plane strain problems in fracture mechanics is presented in this paper. Stress intensity factors (SIF's) were calculated using both methods for elastic plates with either a single-edge crack or an inclined-edge crack. In particular, two currently available programs, ANSYS for finite element analysis and BEASY for boundary element analysis, were used.

  3. The Fracture Mechanical Markov Chain Fatigue Model Compared with Empirical Data

    DEFF Research Database (Denmark)

    Gansted, L.; Brincker, Rune; Hansen, Lars Pilegaard

    The applicability of the FMF-model (Fracture Mechanical Markov Chain Fatigue Model) introduced in Gansted, L., R. Brincker and L. Pilegaard Hansen (1991) is tested by simulations and compared with empirical data. Two sets of data have been used, the Virkler data (aluminium alloy) and data...... that the FMF-model gives adequate description of the empirical data using model parameters characteristic of the material....

  4. SEMI-ANALYTICAL FINITE ELEMENT METHOD FOR FICTITIOUS CRACK MODEL IN FRACTURE MECHANICS OF CONCRETE

    Institute of Scientific and Technical Information of China (English)

    王承强; 郑长良

    2004-01-01

    Based on the Hamiltonian governing equations of plane elasticity for sectorial domain, the variable separation and eigenfunction expansion techniques were employed to develop a novel analytical finite element for the fictitious crack model in fracture mechanics of concrete. The new analytical element can be implemented into FEM program systems to solve fictitious crack propagation problems for concrete cracked plates with arbitrary shapes and loads. Numerical results indicate that the method is more efficient and accurate than ordinary finite element method.

  5. Evaluation of dynamic fracture mechanics in the AISI 316 stainless steel using instrumented Charpy impact testing

    Energy Technology Data Exchange (ETDEWEB)

    Carvalho, Juliano Daniel de [Empresa Brasileira de Aeronautica S.A. (EMBRAER), Sao Jose dos Campos, SP (Brazil)]. E-mail: juliano.daniel@embraer.com.br; Rodrigues, Bruno Jardim Franca [Novo Nordisk, Montes Claros, MG (Brazil)]. E-mail: brro@novonordisk.com; Vilela, Jefferson Jose; Martins, Geraldo de Paula [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil)]. E-mail: gpm@cdtn.br; Carneiro, Jose Rubens Goncalves [Pontificia Universidade Catolica de Minas Gerais (PUC Minas), Belo Horizonte, MG (Brazil)]. E-mail: joserub@pucminas.br

    2007-07-01

    The nuclear power plant's surveillance program is based in Charpy test. But, this test could be used to evaluate integrity's secondary circuit. The steel similar to AISI 316 stainless steel could be used in this circuit. Some secondary circuit's components could be failed in dynamic condition. The dynamic fracture mechanics behavior of the AISI 316 was studied by using instrumented Charpy impact testing. The dynamic fracture toughness (J{sub ld}) could be evaluated by four different methods: compliance changing rate, stretching zone, energy revised and maximum load energy. The tests were made in temperature -196 deg C, room and 200 deg C. At each temperature two specimens were tested. The impact energy was 300 J and the impact velocity was 5.12 m/s. The Charpy specimens 10 x 10 x 50 mm were pre-cracked until 5 mm according to ASTM E-23. Stretching zone size was measured and analyzed by observing the fracture surfaces that were obtained in a scanning electron microscope. The dynamic fracture toughness calculated among four different methods showed a large difference. All studied methods did not agree ASTM E1820 (2001) standard that indicated to plane strain did not occurred in the tip crack. (author)

  6. Decoupling damage mechanisms in acid-fractured gas/condensate reservoirs

    Energy Technology Data Exchange (ETDEWEB)

    Bachman, R.C.; Walters, D.A. [Taurus Reservoir Solutions Ltd., Calgary, AB (Canada); Settari, A. [Calgary Univ., AB (Canada); Rahim, Z.; Ahmed, M.S. [Saudi Aramco, Dhahran (Saudi Arabia)

    2006-07-01

    The Khuff is a gas condensate field located 11,500 feet beneath the producing Ghawar oil field in Saudi Arabia. Wells are mainly acid fracture stimulated following drilling with excellent fracture conductivity and length properties. The wells experience a quick production loss however, after tie-in which eventually stabilizes after two to five months. In order to identify the source of productivity loss, such as near well liquid dropout, fracture conductivity loss, reservoir permeability loss due to increased effective stress, a study of a well in the Khuff field was conducted. The study reviewed basic geomechanical and reservoir properties and identified the mechanisms of production loss. The paper presented the methodology, data and preliminary analysis, relative permeability and results of the history matching. It was concluded that traditional production type curves in cases with changing skin may indicate that transient flow is occurring when boundary effects are felt. In addition, stress dependent fracture conductivity and reservoir permeability can be modeled with simpler pressure dependent functions for relatively low overall loss in reservoir pressure. 30 refs., 25 figs., 1 appendix.

  7. Investigating Knowledge Transfer Mechanisms for Oil Rigs

    DEFF Research Database (Denmark)

    Vianello, Giovanna; Ahmed, Saeema

    2009-01-01

    It is widely recognized, both in industry and academia, that clear strategies in knowledge transfer positively influence the success of a firm. A firm should support the transfer of knowledge by standardizing communication channels within and across departments, based upon personalization......, codification or a combination of these two strategies. The characteristics of the business influence the choice of communication channels used for knowledge transfer. This paper presents a case study exploring the transfer of knowledge within and across projects, specifically the transfer of service knowledge...... in the case of complex machinery. The strategies used for knowledge transfer were analysed and compared with the expected transfer mechanisms, similarities and differences were investigated and are described. A family of four identical rigs for offshore drilling was the selected case. The transfer...

  8. Automotive radar - investigation of mutual interference mechanisms

    Science.gov (United States)

    Goppelt, M.; Blöcher, H.-L.; Menzel, W.

    2010-09-01

    In the past mutual interference between automotive radar sensors has not been regarded as a major problem. With an increasing number of such systems, however, this topic is receiving more and more attention. The investigation of mutual interference and countermeasures is therefore one topic of the joint project "Radar on Chip for Cars" (RoCC) funded by the German Federal Ministry of Education and Research (BMBF). RoCC's goal is to pave the way for the development of high-performance, low-cost 79 GHz radar sensors based on Silicon-Germanium (SiGe) Monolithic Microwave Integrated Circuits (MMICs). This paper will present some generic interference scenarios and report on the current status of the analysis of interference mechanisms.

  9. Topological impact of constrained fracture growth

    Directory of Open Access Journals (Sweden)

    Sigmund Mongstad Hope

    2015-09-01

    Full Text Available The topology of two discrete fracture network models is compared to investigate the impact of constrained fracture growth. In the Poissonian discrete fracture network model the fractures are assigned length, position and orientation independent of all other fractures, while in the mechanical discrete fracture network model the fractures grow and the growth can be limited by the presence of other fractures. The topology is found to be impacted by both the choice of model, as well as the choice of rules for the mechanical model. A significant difference is the degree mixing. In two dimensions the Poissonian model results in assortative networks, while the mechanical model results in disassortative networks. In three dimensions both models produce disassortative networks, but the disassortative mixing is strongest for the mechanical model.

  10. Investigation of Adhesion and Fracture Toughness of Thermally Grown Oxide Scales by Interface Indentation Test

    Institute of Scientific and Technical Information of China (English)

    QI Yu-hong; p. Bruckel; P. Lours; ZHANG Zhan-ping

    2004-01-01

    The adhesion and the fracture toughness of thermally grown oxide scales for pure nickel were investigated using Vickers indentation technique. The nickel samples were oxidised at 1200℃ for 100h-600h. The crack length induced by Vickers indentation test at NiO/Ni interface increases linearly with the incresing of the applied load in a logarithmic scale for each oxide thickness. There is a critical load Pc, when the applied load P>Pc, the crack is produced at the oxide/metal interface. The critical load Pc decreases with the increasing of the oxide thickness. Therefore, the relation between the critical load Pc and the oxide thickness ho may be used as describing the adhesion of of thermally grown oxide scales. For pure nickel, the Pc-ho relation can be represented by the equation Pc = 761439e-0.0695h. The fracture toughness in oxide and at the interface decrease with the increasing of the oxide thickness in equation Ko = -1.0214Ln(ho) + 7.3382 (in oxide) and Ki = 529.71ho-0.9424 (at the interface). And there is a higher fracture toughness at the NiO/Ni interface. Therefore,for pure nickel, the oxide/metal interface is stronger than the oxide.

  11. Investigation of Adhesion and Fracture Toughness of Thermally Grown Oxide Scales by Interface Indentation Test

    Institute of Scientific and Technical Information of China (English)

    QIYu-hong; P.Bruckel; P.Lours; ZHANGZhan-ping

    2004-01-01

    The adhesion and the fracture toughness of thermally grown oxide scales for pure nickel were investigated using Vickers indentation technique. The nickel samples were oxidised at 1200℃ for 100h-600h. The crack length induced by Vickers indentation test at NiO/Ni interface increases linearly with the incresing of the applied load in a logarithmic scale for each oxide thickness. There is a critical load Pc, when the applied load P>Pc, the crack is produced at the oxide/metal interface. The critical load Pc decreases with the increasing of the oxide thickness. Therefore, the relation between the critical load Pc and the oxide thickness ho may be used as describing the adhesion of of thermally grown oxide scales. For pure nickel, the Pc-ho relation can be represented by the equatiun Pc=761439e-0.0695k, The fracture toughness in oxide and at the interlace decrease with the increasing of the oxide thickness in equation Ko=-1.0214Ln(h0)+7.3382 (in oxide) and Ki=529.71h-0.5424 (at the interface). And there is a higher fracture toughness at the NiO/Ni interlace. Theretore, for pure nickel, the oxide/metal interface is stronger than the oxide.

  12. Variable amplitude corrosion fatigue and fracture mechanics of weldable high strength jack-up steels

    Science.gov (United States)

    Etube, Linus Sone

    The tubular welded joints used in the construction of Offshore structures can experience millions of variable amplitude wave induced stress cycles during their operational life. Fatigue has been identified as the main cause of degradation of structural integrity in these structures. As a result, fatigue is an important consideration in their design. Jack-up legs are made from a range of high strength steels with yield strengths up to TOOMPa. These steels are thought to exhibit fatigue resistance properties which are different when compared with conventional fixed platform steels such as BS 4360 50D and BS 7191 355D. The difference in their behaviour was heightened by the discovery, in the late 80s and early 90s, of extensive cracking around the spud can regions of several Jack-ups operating in the North Sea. It was thought that these steels may be more susceptible to hydrogen cracking and embrittlement. There was the additional requirement to study their behaviour under realistic loading conditions typical of the North Sea environment. This thesis contains results of an investigation undertaken to assess the performance of a typical high strength weldable Jack-up steel under realistic loading and environmental conditions. Details of the methodology employed to develop a typical Jack-up Offshore Standard load History (JOSH) are presented. The factors which influence fatigue resistance of structural steels used in the construction of Jack-up structures are highlighted. The methods used to model the relevant factors for inclusion in JOSH are presented with particular emphasis on loading and structural response interaction. Results and details of experimental variable amplitude corrosion fatigue (VACF) tests conducted using JOSH are reported and discussed with respect to crack growth mechanisms in high strength weldable Jack-up steels. Different fracture mechanics models for VACF crack growth prediction are compared and an improved generalised methodology for fast

  13. Investigation of fracture conductivity under in situ conditions as a function of frac- and formation parameters

    Energy Technology Data Exchange (ETDEWEB)

    Meyn, V.; Lajcsak, I.

    1998-10-01

    Because of their low permeability, deep-lying gas fields are often developed by the fracturing technique. Essential for the economy of this measure is a high fracture conductivity which persists over a long period. The objective of the project was the investigation of the various factors influencing the fracture conductivity under reservoir conditions. Besides the breaking strength of proppants, which is decisive for the conductivity attainable at high confining pressure, the long-term stability, the embedment and the transport of fragments, which results in plugging, were examined. With the proppants Superprop and Carboprop HC, fracture conductivity exhibits only a slight dependence on the closure pressure. Transport of fragments and embedment play no important role. With resin-coated proppants, conductivity is not improved appreciably. The resin-coating doesn`t resist reservoir conditions. After only one week, aquathermolytic products were detected. (orig.) [Deutsch] Tiefliegende Erdgasfelder werden aufgrund ihrer niedrigen Permeabilitaet haeufig durch eine Frac-Behandlung erschlossen. Eine wesentliche Voraussetzung fuer die Wirtschaftlichkeit einer solchen Massnahme ist eine hohe Rissleitfaehigkeit, die ueber einen langen Zeitraum bestehen bleibt. Ziel des Projektes war die Untersuchung der verschiedenen Faktoren, die die Rissleitfaehigkeit unter Lagerstaettenbedingungen beeinflussen. Neben der Bruchfestigkeit des Stuetzmittels, die fuer die bei hohen Schliessdrucken erreichbaren Rissleitfaehigkeiten entscheidend ist, wurde die Langzeitstabilitaet, das Embedment und der zu Verstopfung fuehrende Transport von Bruchstuecken untersucht. Die Stuetzmittel Superprop und Carboprop HC weisen nur eine geringe Abhaengigkeit der Rissleitfaehigkeit vom Schliessdruck auf. Der Bruchstuecktransport sowie das Embedment spielen nur eine untergeordnete Rolle. Durch die Verwendung von beschichtetem Stuetzmittel wird die Rissleitfaehigkeit nicht wesentlich erhoeht. Die Beschichtung

  14. Effects of fracture distribution and length scale on the equivalent continuum elastic compliance of fractured rock masses

    Institute of Scientific and Technical Information of China (English)

    Marte Gutierrez; Dong-Joon Youn

    2015-01-01

    Fracture systems have strong influence on the overall mechanical behavior of fractured rock masses due to their relatively lower stiffness and shear strength than those of the rock matrix. Understanding the effects of fracture geometrical distribution, such as length, spacing, persistence and orientation, is important for quantifying the mechanical behavior of fractured rock masses. The relation between fracture geometry and the mechanical characteristics of the fractured rock mass is complicated due to the fact that the fracture geometry and mechanical behaviors of fractured rock mass are strongly dependent on the length scale. In this paper, a comprehensive study was conducted to determine the effects of fracture distribution on the equivalent continuum elastic compliance of fractured rock masses over a wide range of fracture lengths. To account for the stochastic nature of fracture distributions, three different simulation techniques involving Oda’s elastic compliance tensor, Monte Carlo simulation (MCS), and suitable probability density functions (PDFs) were employed to represent the elastic compliance of fractured rock masses. To yield geologically realistic results, parameters for defining fracture distribu-tions were obtained from different geological fields. The influence of the key fracture parameters and their relations to the overall elastic behavior of the fractured rock mass were studied and discussed. A detailed study was also carried out to investigate the validity of the use of a representative element volume (REV) in the equivalent continuum representation of fractured rock masses. A criterion was also proposed to determine the appropriate REV given the fracture distribution of the rock mass.

  15. Effects of fracture distribution and length scale on the equivalent continuum elastic compliance of fractured rock masses

    Directory of Open Access Journals (Sweden)

    Marte Gutierrez

    2015-12-01

    Full Text Available Fracture systems have strong influence on the overall mechanical behavior of fractured rock masses due to their relatively lower stiffness and shear strength than those of the rock matrix. Understanding the effects of fracture geometrical distribution, such as length, spacing, persistence and orientation, is important for quantifying the mechanical behavior of fractured rock masses. The relation between fracture geometry and the mechanical characteristics of the fractured rock mass is complicated due to the fact that the fracture geometry and mechanical behaviors of fractured rock mass are strongly dependent on the length scale. In this paper, a comprehensive study was conducted to determine the effects of fracture distribution on the equivalent continuum elastic compliance of fractured rock masses over a wide range of fracture lengths. To account for the stochastic nature of fracture distributions, three different simulation techniques involving Oda's elastic compliance tensor, Monte Carlo simulation (MCS, and suitable probability density functions (PDFs were employed to represent the elastic compliance of fractured rock masses. To yield geologically realistic results, parameters for defining fracture distributions were obtained from different geological fields. The influence of the key fracture parameters and their relations to the overall elastic behavior of the fractured rock mass were studied and discussed. A detailed study was also carried out to investigate the validity of the use of a representative element volume (REV in the equivalent continuum representation of fractured rock masses. A criterion was also proposed to determine the appropriate REV given the fracture distribution of the rock mass.

  16. Damage and fracture mechanism of 6063 aluminum alloy under three kinds of stress states

    Institute of Scientific and Technical Information of China (English)

    ZHU Hao; ZHU Liang; CHEN Jianhong

    2008-01-01

    To study the damage and fracture mechanism of 6063 aluminum alloy under different stress states,three kinds of representative triaxial stress states have been adopted,namely smooth tensile,notch tensile,and pure shear.The results of the study indicate the following.During the notch tensile test,a relatively higher stress triaxiality appears in the root of the notch.With the applied loading increasing,the volume fraction of microvoids in the root of the notch increases continuously.When it reaches the critical volume fraction of microvoids,the specimen fractures.During the pure shear test,the stress triaxiality almost equals to zero,and there is almost no microvoids but a shear band at the center of the butterfly specimen.The shear band results from nonuniform deformation constantly under the shear stress.With stress concentration,cracks are produced within the shear band and are later coalesced.When the equivalent plastic strain reaches the critical value (equivalent plastic fracture strain),the butterfly specimen fractures.During the smooth tensile test,the stress triaxiality in the gauge of the specimen remains constant at 0.33.Thus,the volume of microvoids of the smooth tensile test is less than that of the notch tensile test and the smooth specimen fractures due to shearing between microvoids.The G-T-N damage model and Johnson-Cook model are used to simulate the notch tensile and shear test,respectively.The simulated engineering stress-strain curves fit the measured engineering stress-strain curves very well.In addition,the empirical damage evolution equation for the notch specimen is obtained from the experimental data and FEM simulations.

  17. Control effect of fracture on hard coal cracking in a fully mechanized longwall top coal caving face

    Institute of Scientific and Technical Information of China (English)

    WEI Jin-ping; LI Zhong-hua; SANG Pei-miao; CHEN Shang-qiang

    2009-01-01

    Through theoretical analysis,simulation test and practice,the law of a fracture's influence on hard top coal press cracking was studied.The study focused on the relation between fracture and coal strength,top coal caving ability and work face layout.Based on the investigation of the fracture system,the control of press cracking was achieved by matching working face to fracture orientation to improve top-coal caving ability and recov-ery.The matching principle was pointed out: The top-coal caving working face should be perpendicular to or obliquely cross the primary fracture at a large angle,and cross the secondary fracture at a small angle.The rational match can increase the recovery ratio of top-coal and avoid rib spalling.The application of control technology on hard top coal press cracking was introduced at the Iongwall top-coal caving face.

  18. Dependence of the mechanical fracture energy of the polymeric composite material from the mixture of filler fractions

    National Research Council Canada - National Science Library

    E M Nurullaev; A S Ermilov

    2015-01-01

    ...) with regard to the basic formulation parameters. By means of the developed computer program the authors calculated the mechanical fracture energy of the polymer binder of the 3D cross-linked plasticized elastomer filled with multifractional silica...

  19. Computational implementation of the multi-mechanism deformation coupled fracture model for salt

    Energy Technology Data Exchange (ETDEWEB)

    Koteras, J.R.; Munson, D.E.

    1996-05-01

    The Multi-Mechanism Deformation (M-D) model for creep in rock salt has been used in three-dimensional computations for the Waste Isolation Pilot Plant (WIPP), a potential waste, repository. These computational studies are relied upon to make key predictions about long-term behavior of the repository. Recently, the M-D model was extended to include creep-induced damage. The extended model, the Multi-Mechanism Deformation Coupled Fracture (MDCF) model, is considerably more complicated than the M-D model and required a different technology from that of the M-D model for a computational implementation.

  20. Development of probabilistic fracture mechanics code PASCAL and user's manual

    Energy Technology Data Exchange (ETDEWEB)

    Shibata, Katsuyuki; Onizawa, Kunio [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment; Li, Yinsheng; Kato, Daisuke [Fuji Research Institute Corporation, Tokyo (Japan)

    2001-03-01

    As a part of the aging and structural integrity research for LWR components, a new PFM (Probabilistic Fracture Mechanics) code PASCAL (PFM Analysis of Structural Components in Aging LWR) has been developed since FY1996. This code evaluates the failure probability of an aged reactor pressure vessel subjected to transient loading such as PTS (Pressurized Thermal Shock). The development of the code has been aimed to improve the accuracy and reliability of analysis by introducing new analysis methodologies and algorithms considering the recent development in the fracture mechanics methodologies and computer performance. The code has some new functions in optimized sampling and cell dividing procedure in stratified Monte Carlo simulation, elastic-plastic fracture criterion of R6 method, extension analysis models in semi-elliptical crack, evaluation of effect of thermal annealing and etc. In addition, an input data generator of temperature and stress distribution time histories was also prepared in the code. Functions and performance of the code have been confirmed based on the verification analyses and some case studies on the influence parameters. The present phase of the development will be completed in FY2000. Thus this report provides the user's manual and theoretical background of the code. (author)

  1. Laser Engineered Net Shaping of Nickel-Based Superalloy Inconel 718 Powders onto AISI 4140 Alloy Steel Substrates: Interface Bond and Fracture Failure Mechanism.

    Science.gov (United States)

    Kim, Hoyeol; Cong, Weilong; Zhang, Hong-Chao; Liu, Zhichao

    2017-03-25

    As a prospective candidate material for surface coating and repair applications, nickel-based superalloy Inconel 718 (IN718) was deposited on American Iron and Steel Institute (AISI) 4140 alloy steel substrate by laser engineered net shaping (LENS) to investigate the compatibility between two dissimilar materials with a focus on interface bonding and fracture behavior of the hybrid specimens. The results show that the interface between the two dissimilar materials exhibits good metallurgical bonding. Through the tensile test, all the fractures occurred in the as-deposited IN718 section rather than the interface or the substrate, implying that the as-deposited interlayer bond strength is weaker than the interfacial bond strength. From the fractography using scanning electron microscopy (SEM) and energy disperse X-ray spectrometry (EDS), three major factors affecting the tensile fracture failure of the as-deposited part are (i) metallurgical defects such as incompletely melted powder particles, lack-of-fusion porosity, and micropores; (ii) elemental segregation and Laves phase, and (iii) oxide formation. The fracture failure mechanism is a combination of all these factors which are detrimental to the mechanical properties and structural integrity by causing premature fracture failure of the as-deposited IN718.

  2. The Relationship Between DP, Fracture Degree and Mechanical Strength of Cellulose Iβ in Insulation Paper by Molecular Dynamic Simulations

    Science.gov (United States)

    Wang, You-Yuan; Yang, Tao; Tian, Miao; Liao, Rui-Jin

    2013-09-01

    The degree of polymerization (DP) has been regarded as an important symbol of mechanical strength, reflecting the aging condition of transformer insulation paper. In this article, a new concept called fracture degree is proposed on the basis of DP. First, nine cellulose Iβ crystal models with different fracture degrees were built. Then relevant mechanical parameters and hydrogen bond numbers were calculated by molecular dynamics (MD) simulation. Results showed that during the aging process of insulation paper with fracture of cellulose chain, the elastic constant C33 produces appreciable impact on the Young's modulus (E). With the decrease of DP and increase of fracture degree, the Young's modulus step decreases. To the 50% and 100% fracture degree models respectively, the relationship between their different degrees of polymerization and Young's modulus is subjected to similar exponential distributions. With the increase of the fracture degree, the average hydrogen bond number drops, and the change rules apply to the Young's modulus. Since hydrogen bond is the main factor of mechanical strength, it can be inferred that the fracture degree influences mechanical strength seriously.

  3. Experimental investigations of mechanical and electrical characteristics of a nanomodified epoxy resin DER-330

    Science.gov (United States)

    Brusentseva, T. A.

    2016-11-01

    Technique preparation of a composite material based on epoxy resin DER-330 and 5 different nanopowders has been developed. The modifiers exert a positive effect on the elastic modulus, flexural strength, and dielectric permittivity of the epoxy-anhydride polymers. Weight content of nanoadditives in the matrix ranged from 0% to 4%. Dependences between mechanical properties of epoxy composites and concentration and nature of the filler were investigated in a three-point bending. Morphology of the fracture surface was studied. The complex analysis of nanofillers allowed us optimum fillers and concentrations when a significant increase of elastic and strength characteristics is achieved. It was showed that addition of silica fume nanoparticles A-380 to the matrix increases fracture stress on 30%. Composites with nanoparticles of aluminum nitride showed the best mechanical values in case of jointly investigated parameters. Growth of the elastic modulus is 12% and increase of the fracture stress is 7%. Adding alumina nanoparticles and nanofibers in the range of investigated concentration does not lead to significant changes in the mechanical characteristics of the composite

  4. STUDY OF DEFECT ADMISSIBILITY IN GAS PIPELINES BASED ON FRACTURE MECHANICS

    Directory of Open Access Journals (Sweden)

    N. ABDELBAKI

    2009-03-01

    Full Text Available Bearing in mind the considerable distances between natural gas fields and consumers’ appliances, transport by gas pipelines remains the most competitive means. These gas pipelines which are generally made of steel pipes may contain however several types of defects of various origins and which are susceptible to initiate cracks which may grow under some circumstances to such extent as to lead to fracture. Failures of gas pipelines may have serious consequences and may lead to catastrophes from ecological and financial viewpoints. It is therefore interesting to study the defect admissibility so as to maximize safety and minimize exploitation costs through a simplified method based on the Failure Assessment Diagram (FAD. The latter is used in conjunction with Finite Element Analysis (FEM applied to fracture mechanics to help decision making as to whether a given defect present in a pipe is acceptable or not.

  5. A novel Lagrangian approach for the stable numerical simulation of fault and fracture mechanics

    Science.gov (United States)

    Franceschini, Andrea; Ferronato, Massimiliano; Janna, Carlo; Teatini, Pietro

    2016-06-01

    The simulation of the mechanics of geological faults and fractures is of paramount importance in several applications, such as ensuring the safety of the underground storage of wastes and hydrocarbons or predicting the possible seismicity triggered by the production and injection of subsurface fluids. However, the stable numerical modeling of ground ruptures is still an open issue. The present work introduces a novel formulation based on the use of the Lagrange multipliers to prescribe the constraints on the contact surfaces. The variational formulation is modified in order to take into account the frictional work along the activated fault portion according to the principle of maximum plastic dissipation. The numerical model, developed in the framework of the Finite Element method, provides stable solutions with a fast convergence of the non-linear problem. The stabilizing properties of the proposed model are emphasized with the aid of a realistic numerical example dealing with the generation of ground fractures due to groundwater withdrawal in arid regions.

  6. Probabilistic Fatigue Life Prediction of Bridge Cables Based on Multiscaling and Mesoscopic Fracture Mechanics

    Directory of Open Access Journals (Sweden)

    Zhongxiang Liu

    2016-04-01

    Full Text Available Fatigue fracture of bridge stay-cables is usually a multiscale process as the crack grows from micro-scale to macro-scale. Such a process, however, is highly uncertain. In order to make a rational prediction of the residual life of bridge cables, a probabilistic fatigue approach is proposed, based on a comprehensive vehicle load model, finite element analysis and multiscaling and mesoscopic fracture mechanics. Uncertainties in both material properties and external loads are considered. The proposed method is demonstrated through the fatigue life prediction of cables of the Runyang Cable-Stayed Bridge in China, and it is found that cables along the bridge spans may have significantly different fatigue lives, and due to the variability, some of them may have shorter lives than those as expected from the design.

  7. Investigation of the cold process pipe rupture mechanism

    CERN Document Server

    CERN. Geneva

    2016-01-01

    Cryogenic process pipelines are part of the basic subsystem used in installations for fundamental research in physics, as well as in industrial plants which use LNG or liquid nitrogen. The significant increase in importance of cryogenics entails the need to explore phenomena which have direct impact in the design process of cryogenic systems and their safety systems. These aspects are of high priority due to high investment costs, mainly because of safety issues and reliability. One of the issues which requires thorough investigation is the fracture mechanics of gas pipelines in cryogenic conditions. For this subject, importance is placed not only in when the cracks begin to appear, but also in how they form and how quickly they propagate. Currently, there is a lack of reliable research in the available literature in this area. This is often raised as a significant problem for designers, because knowledge in this topic should be reflected e.g., in the sizing calculations of safety valves for the vacuum syste...

  8. A review of the effect of a/W ratio on fracture toughness (Ⅰ)-experimental investigation in EPFM

    Institute of Scientific and Technical Information of China (English)

    LI Qing-fen; JIN Guo; WANG Yan-bo

    2005-01-01

    Many experimental investigations have previously been performed and recently done on different shipbuilding structural steels where the specimens size and crack depth/specimen width (a/W) were varied. A series of interesting results have been gained. It is worthwhile to have a review on the effect of a/W ratio on fracture toughness, and further theoretical analysis is necessary. In this paper, experimental work in elastic-plastic fracture mechanics(EPFM) was discussed. Tests had been carried out on 10 kinds of strength steels. Results showed that Ji and δi values increased with decreasing a/W when a/W<0.3 for three-point bend specimens and that shallow crack specimens which have less constrained flow field give markedly higher values of toughness than deeply notched specimens. However, for a/W>0.3, the toughness was found to be independent of a/W. Slip line field analysis shows that for shallow cracks, the hydrostatic stress is lower than that from standard deeply cracked bend specimen which develops a high level of crack tip constraint, provides a lower bound estimate of toughness, and will ensure an unduly conservative approach when applied to structure defects especially if initiation values of COD / J-integral are used.

  9. Numerical investigation of 3-D constraint effects on brittle fracture in SE(B) and C(T) specimens

    Energy Technology Data Exchange (ETDEWEB)

    Nevalainen, M. [Valtion Teknillinen Tutkimuskeskus, Espoo (Finland); Dodds, R.H. Jr. [Illinois Univ., Urbana, IL (United States). Dept. of Civil Engineering

    1996-07-01

    This investigation employs 3-D nonlinear finite element analyses to conduct an extensive parametric evaluation of crack front stress triaxiality for deep notch SE(B) and C(T) specimens and shallow notch SE(B) specimens, with and without side grooves. Crack front conditions are characterized in terms of J-Q trajectories and the constraint scaling model for cleavage fracture toughness proposed previously by Dodds and Anderson. The 3-D computational results imply that a significantly less strict size/deformation limit, relative to the limits indicated by previous plane-strain computations, is needed to maintain small-scale yielding conditions at fracture by a stress- controlled, cleavage mechanism in deep notch SE(B) and C(T) specimens. Additional new results made available from the 3-D analyses also include revised {eta}-plastic factors for use in experimental studies to convert measured work quantities to thickness average and maximum (local) J-values over the crack front.

  10. Water-soluble gases as partitioning tracers to investigate the pore volume?transmissivity correlation in a fracture

    Science.gov (United States)

    Lunati, Ivan; Kinzelbach, Wolfgang

    2004-11-01

    Hydraulically equivalent fractures may show striking differences when a gas-migration experiment is performed because of the different correlations between transmissivity, pore volume and entry pressure. We numerically simulate gas migration between injection and extraction boreholes in a parallel plate fracture with a heterogeneous fault gouge, in a rough-walled fracture filled with homogeneous material, and in a rough-walled empty fracture. The parallel plate model and the empty model clearly show the existence of preferential paths; for high variance of the transmissivity field, gas flow takes place only in few discrete channels separated by water-saturated regions. In contrast, in the fracture filled with homogeneous fault gouge, the gas saturation is continuous and more uniformly distributed. It appears a fundamental issue to be able to discriminate in situ among conceptual models that can yield such a different gas-saturation distribution. As in practice, the saturation distribution cannot be directly observed, tracer experiments are performed to characterize a fracture. For these reasons, we simulate the transport of tracers, which are added to the gas phase as soon as quasi-steady saturation distribution and extraction rate are achieved, and we compare the breakthrough curves obtained assuming different models. Our numerical simulations suggest that discrimination among the models on the basis of single-tracer tests is unlikely. A better tool to investigate fracture properties is provided by a gas-tracer test, in which a cocktail of gases with different water solubility is employed. These gases behave as partitioning tracers and allow us to estimate the gas saturation in the fracture. Indeed, by comparison of the residence-time distributions of different gases, we are able to compute a streamline effective saturation, which is an excellent estimate of fracture saturation. In addition, the streamline effective saturation curve contains information that is

  11. Application of microdynamics and lattice mechanics to problems in plastic flow and fracture. Final report, 1 April 1973--31 March 1978

    Energy Technology Data Exchange (ETDEWEB)

    Bilello, J C; Liu, J M

    1978-06-21

    Progress in an investigation of the application of microdynamics and lattice mechanics to the problems in plastic flow and fracture is described. The research program consisted of both theoretical formulations and experimental measurements of a number of intrinsic material parameters in bcc metals and alloys including surface energy, phonon-dispersion curves for dislocated solids, dislocation-point defect interaction energy, slip initiation and microplastic flow behavior. The study has resulted in an improved understanding in the relationship among the experimentally determined fracture surface energy, the intrinsic cohesive energy between atomic planes, and the plastic deformation associated with the initial stages of crack propagation. The values of intrinsic surface energy of tungsten, molybdenum, niobium and niobium-molybdenum alloys, deduced from the measurements, serve as a starting point from which fracture toughness of these materials in engineering service may be intelligently discussed.

  12. THE STRESS IMPACT ON MECHANICAL PROPERTIES OF ROCKS IN HYDRO FRACTURING TECHNIQUE

    Directory of Open Access Journals (Sweden)

    B. GURUPRASAD

    2012-02-01

    Full Text Available Ground water is considered to be the best safe protected drinking water source and bore wells are drilled in hard crystalline rock terrains for drinking water, irrigation and industrial purposes. Even after scientific location, some bore wells yield inadequate quantity of water or fail to yield. The success of bore wells depend largely onnumber, length, dilation and interconnectivity of fractures encountered on drilling. Considering the cost factor involved in drilling a new bore well, rejuvenation of failed bore well through some technique is thought off. The innovative technology of ‘hydro fracturing’ is a new interdisciplinary approach of Hydro mechanical tostimulate the bore well to improve the yield by applying water pressure into bore well by using a heavy duty mechanical compressor. The hydro fracturing technique was first used in oil well to increase oil and gas production. In this research paper, the hydraulic pressure applied increases with depth reflecting the rigidness,toughness of rock. The fracture development, propagation of fracture and stress behavior depends on the physical and mechanical properties of rocks. The hydro fracturing process has been conducted in three depth zones ranging from 8 m to 45 m below ground level in Annavasal union of Pudukottai district, Tamil Nadu, India. The Pressure application varies depending on the geological formations. This study pertains to a part of research work. The minimum and maximum pressures applied are 1 and 10 N/mm2 respectively. The maximumpressure of 10 N/mm2 has been recorded in the third zone, where the country rock is charnockite which is generally massive, compact and dense rock. Generally for the igneous rock in the third zone in the depth range of 40 to 50 m, more than 7 N/mm2 of pressure has been applied indicating extremely strong nature with uniaxial compressive strength 100 – 300 N/mm2, tensile strength 7- 25 N/mm2. Out of 37 bore wells 32.4% of bore wells have shown

  13. Posterior periosteal disruption in Salter-Harris Type II fractures of the distal femur: evidence for a hyperextension mechanism.

    Science.gov (United States)

    Kritsaneepaiboon, Supika; Shah, Rajvee; Murray, Martha M; Kleinman, Paul K

    2009-12-01

    Patterns of periosteal disruption are important factors in assessing the mechanism of injury of radiologically evident Salter-Harris (SH) fractures. The purpose of this study is to assess the frequency of posterior periosteal disruption on MRI in radiographically occult or subtle SH type II fractures of the distal femur and to evaluate associated soft-tissue findings that support a hyperextension mechanism of injury. We found that all children in our experience with occult or subtle SH type II fractures of the distal femur have posterior periosteal disruption and other MRI findings to indicate a hyperextension mechanism of injury. Direct indicators of fracture may be inconspicuous, and the presence of posterior periosteal disruption is a clue that should prompt a search for other features of this serious pediatric injury, which may be followed by limb shortening or angular deformity.

  14. High-Temperature Mechanical Behavior and Fracture Analysis of a Low-Carbon Steel Related to Cracking

    Science.gov (United States)

    Santillana, Begoña; Boom, Rob; Eskin, Dmitry; Mizukami, Hideo; Hanao, Masahito; Kawamoto, Masayuki

    2012-12-01

    Cracking in continuously cast steel slabs has been one of the main problems in casting for decades. In recent years, the use of computational models has led to a significant improvement in caster performance and product quality. However, these models require accurate thermomechanical properties as input data, which are either unreliable or nonexistent for many alloys of commercial interest. A major reason for this lack of reliable data is that high-temperature mechanical properties are difficult to measure. Several methods have been developed to assess the material strength during solidification, especially for light alloys. The tensile strength during solidification of a low carbon aluminum-killed (LCAK; obtained from Tata Steel Mainland Europe cast at the DSP plant in IJmuiden, the Netherlands) has been studied by a technique for high-temperature tensile testing, which was developed at Sumitomo Metal Industries in Japan. The experimental technique enables a sample to melt and solidify without a crucible, making possible the accurate measurement of load over a small solidification temperature range. In the current study, the tensile test results are analyzed and the characteristic zero-ductility and zero-strength temperatures are determined for this particular LCAK steel grade. The fracture surfaces are investigated following tensile testing, which provides an invaluable insight into the fracture mechanism and a better understanding with respect to the behavior of the steel during solidification. The role of minor alloying elements, like sulfur, in hot cracking susceptibility is also discussed.

  15. Atomistic study on mixed-mode fracture mechanisms of ferrite iron interacting with coherent copper and nickel nanoclusters

    Science.gov (United States)

    Al-Motasem, Ahmed Tamer; Mai, Nghia Trong; Choi, Seung Tae; Posselt, Matthias

    2016-04-01

    The effect of copper and/or nickel nanoclusters, generally formed by neutron irradiation, on fracture mechanisms of ferrite iron was investigated by using molecular statics simulation. The equilibrium configuration of nanoclusters was obtained by using a combination of an on-lattice annealing based on Metropolis Monte Carlo method and an off-lattice relaxation by molecular dynamics simulation. Residual stress distributions near the nanoclusters were also calculated, since compressive or tensile residual stresses may retard or accelerate, respectively, the propagation of a crack running into a nanocluster. One of the nanoclusters was located in front of a straight crack in ferrite iron with a body-centered cubic crystal structure. Two crystallographic directions, of which the crack plane and crack front direction are (010)[001] and (111) [ 1 bar 10 ] , were considered, representing cleavage and non-cleavage orientations in ferrite iron, respectively. Displacements corresponding to pure opening-mode and mixed-mode loadings were imposed on the boundary region and the energy minimization was performed. It was observed that the fracture mechanisms of ferrite iron under the pure opening-mode loading are strongly influenced by the presence of nanoclusters, while under the mixed-mode loading the nanoclusters have no significant effect on the crack propagation behavior of ferrite iron.

  16. Fracture mechanics analysis on Smart-Cut(R) technology. Part 1: Effects of stiffening wafer and defect interaction

    Institute of Scientific and Technical Information of China (English)

    Bin Gu; Hongyuan Liu; YiuWing Mai; Xi Qiao Feng; Shou Wen Yu

    2009-01-01

    In the present paper, continuum fracture mecha-nics is used to analyze the Smart-Cut process, a recently established ion cut technology which enables highly efficient fabrication of various silicon-on-insulator (SO1) wafers of high uniformity in thickness. Using integral transform and Cauchy singular integral equation methods, the mode-Ⅰ and mode-II stress intensity factors, energy release rate, and crack opening displacements are derived in order to examine seve-ral important fracture mechanisms involved in the Smart-Cut process. The effects of defect interaction and stiffening wafer on defect growth are investigated. The numerical results indi-cate that a stiffener/handle wafer can effectively prevent the donor wafer from blistering and exfoliation, but it slows down the defect growth by decreasing the magnitudes of SIF's. Defect interaction also plays an important role in the splitting process of SOI wafers, but its contribution depends strongly on the size, interval and internal pressure of defects. Finally, an analytical formula is derived to estimate the implantation dose required for splitting a SOI wafer.

  17. Kinetics and fracture resistance of lithiated silicon nanostructure pairs controlled by their mechanical interaction

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Seok Woo; /Stanford U., Geballe Lab.; Lee, Hyun-Wook; /Stanford U., Materials Sci. Dept.; Ryu, Ill; /Brown U.; Nix, William D.; /Stanford U., Materials Sci. Dept.; Gao, Huajian; /Brown U.; Cui, Yi; /Stanford U., Materials Sci. Dept. /SLAC

    2015-06-01

    Following an explosion of studies of silicon as a negative electrode for Li-ion batteries, the anomalous volumetric changes and fracture of lithiated single Si particles have attracted significant attention in various fields, including mechanics. However, in real batteries, lithiation occurs simultaneously in clusters of Si in a confined medium. Hence, understanding how the individual Si structures interact during lithiation in a closed space is necessary. Herein, we demonstrate physical/mechanical interactions of swelling Si structures during lithiation using well-defined Si nanopillar pairs. Ex situ SEM and in situ TEM studies reveal that compressive stresses change the reaction kinetics so that preferential lithiation occurs at free surfaces when the pillars are mechanically clamped. Such mechanical interactions enhance the fracture resistance of This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Contract No. DE-AC02-76SF00515. SLAC-PUB-16300 2 lithiated Si by lessening the tensile stress concentrations in Si structures. This study will contribute to improved design of Si structures at the electrode level for high performance Li-ion batteries.

  18. A rare case of bicondylar Hoffa fracture associated with ipsilateral tibial spine avulsion and extensor mechanism disruption

    Institute of Scientific and Technical Information of China (English)

    Kamal Bali; Aditya Krishna Mootha; Vibhu Krishnan; Vishal Kumar; Saurabh Rawall

    2011-01-01

    Intra-articular coronal fractures (Hoffas fractures) of distal femur are rare. Although bicondylar involvement in these fractures has been reported in the literature in association with high velocity traumata, the occurrence of these fractures involving extensor mechanism rupture and avulsion of ipsilateral tibial spine is extremely rare. To our acquaintance, such a fracture pattern has not yet been reported in the literature so far. In this article, we report one such case and discuss the importance of early diagnosis and prompt internal fixation in the management of such cases. We believe that these rare combinations of injuries should be treated aggressively by early open reduction and anatomic rigid internal fixation in order toachieve good recovery of function.

  19. Mechanical Properties and Fracture Behaviors of GTA-Additive Manufactured 2219-Al After an Especial Heat Treatment

    Science.gov (United States)

    Bai, J. Y.; Fan, C. L.; Lin, S. B.; Yang, C. L.; Dong, B. L.

    2017-03-01

    2219-Al parts were produced by gas tungsten arc-additive manufacturing and sequentially processed by an especial heat treatment. In order to investigate the effects of heat treatment on its mechanical properties, multiple tests were conducted. Hardness tests were carried out on part scale and layer scale along with tensile tests which were performed on welding and building directions. Results show that compared to conventional casting + T6 2219-Al, the current deposit + T6 2219-Al exhibits satisfying properties with regard to strength but unsatisfying results in plasticity. Additionally, anisotropy is significant. Fractures were observed and the cracks' propagating paths in both directional specimens are described. The effects of heat treatment on the cracks' initiation and propagation were also investigated. Ultimately, a revised formula was developed to calculate the strength of the deposit + T6 2219-Al. The aforementioned formula, which takes into consideration the belt-like porosities-distributing feature, can scientifically describe the anisotropic properties in the material.

  20. Low-temperature embrittlement and fracture of metals with different crystal lattices – Dislocation mechanisms

    Directory of Open Access Journals (Sweden)

    V.M. Chernov

    2016-12-01

    Full Text Available The state of a low-temperature embrittlement (cold brittleness and dislocation mechanisms for formation of the temperature of a ductile-brittle transition and brittle fracture of metals (mono- and polycrystals with various crystal lattices (BCC, FCC, HCP are considered. The conditions for their formation connected with a stress-deformed state and strength (low temperature yield strength as well as the fracture breaking stress and mobility of dislocations in the top of a crack of the fractured metal are determined. These conditions can be met for BCC and some HCP metals in the initial state (without irradiation and after a low-temperature damaging (neutron irradiation. These conditions are not met for FCC and many HCP metals. In the process of the damaging (neutron irradiation such conditions are not met also and the state of low-temperature embrittlement of metals is absent (suppressed due to arising various radiation dynamic processes, which increase the mobility of dislocations and worsen the strength characteristics.

  1. Salter-Harris I and II fractures of the distal tibia: does mechanism of injury relate to premature physeal closure?

    Science.gov (United States)

    Rohmiller, Michael T; Gaynor, Tracey P; Pawelek, Jeff; Mubarak, Scott J

    2006-01-01

    The distal tibial physis is the second most commonly injured physis in long bones. Recent reports demonstrate a high rate of premature physeal closure (PPC) in Salter-Harris (SH) type I or II fractures of the distal tibia. At our institution, 137 distal tibial SH type I or II fractures were treated from 1994 to 2002. Reviews were performed on all patients and 91 fractures met inclusion criteria. Patients were categorized according to treatment. We report a PPC rate of 39.6% in SH type I or II fractures of the distal tibial physis. We found a difference in PPC based on injury mechanism. The rate of PPC in patients with a supination-external-rotation-type injury was 35%, whereas patients with pronation-abduction-type injuries developed PPC in 54% of cases. Type of treatment may prevent PPC in some fractures. The most important determinant of PPC is the fracture displacement following reduction. PPC is a common problem following SH type I or II fractures of the distal tibia. Operative treatment may decrease the frequency of PPC in some fractures. Regardless of treatment method, we recommend anatomic reduction to decrease the risk of PPC.

  2. The effects of Mg microaddition on the mechanical behavior and fracture mechanism of MAR-M247 superalloy at elevated temperatures

    Science.gov (United States)

    Bor, H. Y.; Chao, C. G.; Ma, C. Y.

    1999-03-01

    The effects of microadditions of Mg on the mechanical behavior and fracture mechanism of MAR-M247 superalloy were investigated in this study. The microstructural observations and image analysis showed that a Mg microaddition ranging from 30 to 80 ppm significantly changed the primary MC carbide characteristics and inhibited the scriptlike carbide formation. After a 80 ppm Mg addition, the elongation measured at 1172 K increased over 3 times found that for the Mg-free MAR-M247 superalloy. The creep life and rupture elongation of the MAR-M247 superalloy with 80 ppm Mg was also improved up to 3 to 5 times that of the alloy without Mg during a 1033 K/724 MPa creep test. The fracture analyses demonstrated that cracks were mainly initiated and propagated at the interface of scriptlike MC carbides in the Mg-free MAR-M247 superalloy at elevated temperatures. The Mg microaddition effectively refined and spheroidized these coarse carbides so that a change in the crack initiation occurred from the carbide/matrix interface to that along the γ-γ' eutectic. Interfacial analysis using Auger electron spectroscopy illustrated that Mg segregated to the interface of the MC carbide/matrix, causing a change in the morphology and interfacial behavior of the carbides. This improvement contributed to a prolonged rupture life and upgraded the moderate temperature ductility of the MAR-M247 superalloy.

  3. A comparison of the stress corrosion cracking susceptibility of commercially pure titanium grade 4 in Ringer's solution and in distilled water: a fracture mechanics approach.

    Science.gov (United States)

    Roach, Michael D; Williamson, R Scott; Thomas, Joseph A; Griggs, Jason A; Zardiackas, Lyle D

    2014-01-01

    From the results of laboratory investigations reported in the literature, it has been suggested that stress corrosion cracking (SCC) mechanisms may contribute to early failures in titanium alloys that have elevated oxygen concentrations. However, the susceptibility of titanium alloys to SCC in physiological environments remains unclear. In this study, a fracture mechanics approach was used to examine the SCC susceptibility of CP titanium grade 4 in Ringer's solution and distilled de-ionized (DI) water, at 37°C. The study duration was 26 weeks, simulating the non-union declaration of a plated fracture. Four wedge loads were used corresponding to 86-95% of the alloy's ligament yield load. The longest cracks were measured to be 0.18 mm and 0.10 mm in Ringer's solution and DI water, respectively. SEM analysis revealed no evidence of extensive fluting and quasi-cleavage fracture features which, in literature reports, were attributed to SCC. We thus postulate that the Ringer's solution accelerated the wedge-loaded crack growth without producing the critical stresses needed to change the fracture mechanism. Regression analysis of the crack length results led to a significant best-fit relationship between crack growth velocity (independent variable) and test electrolyte, initial wedge load, and time of immersion of specimen in electrolyte (dependent variables).

  4. Modeling and additive manufacturing of bio-inspired composites with tunable fracture mechanical properties.

    Science.gov (United States)

    Dimas, Leon S; Buehler, Markus J

    2014-07-07

    Flaws, imperfections and cracks are ubiquitous in material systems and are commonly the catalysts of catastrophic material failure. As stresses and strains tend to concentrate around cracks and imperfections, structures tend to fail far before large regions of material have ever been subjected to significant loading. Therefore, a major challenge in material design is to engineer systems that perform on par with pristine structures despite the presence of imperfections. In this work we integrate knowledge of biological systems with computational modeling and state of the art additive manufacturing to synthesize advanced composites with tunable fracture mechanical properties. Supported by extensive mesoscale computer simulations, we demonstrate the design and manufacturing of composites that exhibit deformation mechanisms characteristic of pristine systems, featuring flaw-tolerant properties. We analyze the results by directly comparing strain fields for the synthesized composites, obtained through digital image correlation (DIC), and the computationally tested composites. Moreover, we plot Ashby diagrams for the range of simulated and experimental composites. Our findings show good agreement between simulation and experiment, confirming that the proposed mechanisms have a significant potential for vastly improving the fracture response of composite materials. We elucidate the role of stiffness ratio variations of composite constituents as an important feature in determining the composite properties. Moreover, our work validates the predictive ability of our models, presenting them as useful tools for guiding further material design. This work enables the tailored design and manufacturing of composites assembled from inferior building blocks, that obtain optimal combinations of stiffness and toughness.

  5. Field investigation into directional hydraulic fracturing for hard roof in Tashan Coal Mine

    Institute of Scientific and Technical Information of China (English)

    Bing-Xiang HUANG; Bin YU; Feng FENG; Zhao LI; You-Zhuang WANG; Jin-Rong LIU

    2013-01-01

    Research and development of safe and effective control technology of hard roof is an inevitable trend at present.Directional hydraulic fracturing technology is expected to become a safe and effective way to control and manage hard roof.In order to make hard roof fracture in a directional way,a hydraulic fracture field test has been conducted in the third panel district of Tashan Coal Mine in Datong.First,two hydraulic fracturing drilling holes and four observing drilling holes were arranged in the roof,followed by a wedge-shaped ring slot in each hydraulic fracturing drilling hole.The hydraulic fracturing holes were then sealed and,hydraulic fracturing was conducted.The results show that the hard roof is fractured directionally by the hydraulic fracturing function of the two fracturing drilling holes; the sudden drop,or the overall downward trend of hydraulic pressure from hydraulic monitoring is the proof that the rock in the hard roof has been fractured.The required hydraulic pressure to fracture the hard roof in Tashan coal mine,consisting of carboniferous sandstone layer,is 50.09 MPa,and the fracturing radius of a single drilling hole is not less than 10.5 m.The wedge-shaped ring slot made in the bottom of the hydraulic fracturing drilling hole plays a guiding role for crack propagation.After the hydraulic fracturing drill hole is cracked,the propagation of the resulting hydraulic crack,affected mainly by the regional stress field,will turn to other directions.

  6. Review of the mechanical and fracture behavior of perovskite lead-free ferroelectrics for actuator applications

    Science.gov (United States)

    Webber, Kyle G.; Vögler, Malte; Khansur, Neamul H.; Kaeswurm, Barbara; Daniels, John E.; Schader, Florian H.

    2017-06-01

    There has been considerable progress in the development of large strain lead-free perovskite ferroelectrics over the past decade. Under certain conditions, the electromechanical properties of some compositions now match or even surpass commercially available lead-containing materials over a wide temperature range, making them potentially attractive for non-resonant displacement applications. However, the phenomena responsible for the large unipolar strains and piezoelectric responses can be markedly different to classical ferroelectrics such as Pb(Zr,Ti)O3 and BaTiO3. Despite the promising electromechanical properties, there is little understanding of the mechanical properties and fracture behavior, which is crucial for their implementation into applications where they will be exposed to large electrical, mechanical, and thermal fields. This work discusses and reviews the current understanding of the mechanical behavior of large-strain perovskite lead-free ferroelectrics for use in actuators and provides recommendations for further work in this important field.

  7. Alteration of Fractured Rocks Due to Coupled Chemical and Mechanical Processes: High-Resolution Simulations and Experimental Observations

    Science.gov (United States)

    Ameli, Pasha

    Engineering activities such as enhanced geothermal energy production and improved oil recovery techniques are heavily dependent on the permeability of the subsurface, while others such as CO2 sequestration and nuclear waste disposal rely on the efficiency of rock formations as transport barriers. In either case fractures provide the main pathways for fluid flow and transport, especially in rocks with lower matrix porosity. Laboratory experiments aimed at quantifying the chemo-mechanical responses of fractures have shown a range of results, some of which contradict simple conceptual models. For example, under conditions favoring mineral dissolution, where one would expect an overall increase in permeability, experiments show that permeability increases under some conditions and decreases under others. Recent experiments have attempted to link these core-scale observations to the relevant small-scale processes occurring within fractures. Results suggest that the loss of mechanical strength in asperities due to chemical alteration may cause non-uniform deformation and alteration of fracture apertures. However, due to the lack of direct micro-scale measurements of the coupled chemical and mechanical processes that lead to alteration of contacting fracture surfaces, our ability to predict the long-term evolution of fractures is still limited. To explore the processes that control permeability evolution, I developed a computational model that uses micro-scale surface roughness and explicitly couples dissolution and elastic deformation to calculate local alterations in fracture aperture under chemical and mechanical stresses. A depth-averaged algorithm of fracture flow is used to model reactive transport and chemical alteration of the fracture surfaces. Then, I deform the resulting altered fracture-surfaces using an algorithm that calculates the elastic deformation. The results of the model are compared with flow-through experiments conducted on fractured limestone. The

  8. INVESTIGATION OF FRACTURE DESIGN FOR MEDIUM CARBON STEEL UNDER EXTRA-LOW CYCLIC FATIGUE IN AXIAL LOADING

    Institute of Scientific and Technical Information of China (English)

    Youtang Li; Shuai Tan; Hongyan Duan

    2008-01-01

    The extra-low cyclic fracture problem of medium carbon steel under axial fatigue loading was investigated.Several problems,such as the relations of the cycle times to the depth and tip radius of the notch,loading frequency,loading range and the parameters of fracture design for medium carbon steel on condition of extra-low axial fatigue loading were discussed based on the experiments.Experimental results indicated that the tension-pressure fatigue loading mode was suitable for extra-low cyclic fatigue fracture design of medium carbon steel and it resulted in low energy consumption,fracture surface with high quality,low cycle times,and high efficiency.The appropriate parameters were as follows:loading frequency 3-5 Hz,notch tip radius r=(0.2-0.3)mm,opening angle α=60°,and notch depth t=(0.14-0.17)D.

  9. 可降解聚合物压裂球的降解行为及机理%Degradation Behavior and Mechanism of Degradable Fracturing Polymer Ball

    Institute of Scientific and Technical Information of China (English)

    邹鹏; 王林; 张建华; 樊玉生; 赵世华

    2016-01-01

    To reveal the performance characteristics of homemade degradable fracturing polymer ball,the degradation behavior of fracturing ball at various degradable time and temperature was investigated by using water,fracturing fluid and flow-back fluid acting as a degradable media of fracturing ball.Furthermore,the degradation mechanism of fracturing ball was discussed via infrared spectroscopy and XRD technology.The results showed that the mass and diameter of fracturing ball,immersing in water at 100℃,decreased gradually when degradable time increased.The mass of fracturing ball,immersing in flow-back fluid,decreased gradually when degradable time increased,and the degradation rate of fracturing ball increased when environment temperature increased.When they were immersed in fracturing fluid,the mass and diameter of fracturing ball kept instant with increasing degradable time.The degradation mechanism of fracturing ball was analyzed from molecular structure and aggregation of polymers.Fracturing polymer ball with stable compressive property was carried out in a conventional pitching manner in fracturing process.After fracturing,polymer ball was self-degraded without recycling.Degradable polymer ball had a wider application compared with degradable alloy ball.%为揭示所研制的可降解性聚合物压裂球的性能特征,分别采用自来水、压裂液与返排液作为聚合物压裂球的降解液,研究了降解时间与温度对压裂球降解行为的影响,并用红外光谱与X-射线衍射方法分析了压裂球的降解机理.结果表明:在100℃自来水中,随降解时间延长,压裂球的质量与直径减小.在返排液中,随降解时间延长,压裂球质量逐渐减小;随环境温度的升高,压裂球降解速率增大.在压裂液中,压裂球的质量与直径不随浸泡时间的延长而变化.从聚合物聚集态和分子层面分析了聚合物压裂球的降解机理.聚合物压裂球抗压差性能稳定,压裂施工过程中按

  10. Mechanisms of defect complex formation and environmental-assisted fracture behavior of iron aluminides

    Energy Technology Data Exchange (ETDEWEB)

    Cooper, B.R.; Muratov, L.S.; Kang, B.S.J.; Li, K.Z. [West Virginia Univ., Morgantown, WV (United States)

    1997-12-01

    Iron aluminide has excellent corrosion resistance in high-temperature oxidizing-sulfidizing environments; however, there are problems at room and medium temperature with hydrogen embrittlement as related to exposure to moisture. In this research, a coordinated computational modeling/experimental study of mechanisms related to environmental-assisted fracture behavior of selected iron aluminides is being undertaken. The modeling and the experimental work will connect at the level of coordinated understanding of the mechanisms for hydrogen penetration and for loss of strength and susceptibility to fracture. The focus of the modeling component at this point is on the challenging question of accurately predicting the iron vacancy formation energy in Fe{sub 3}A{ell} and the subsequent tendency, if present, for vacancy clustering. The authors have successfully performed, on an ab initio basis, the first calculation of the vacancy formation energy in Fe{sub 3}A{ell}. These calculations include lattice relaxation effects which are quite large. This has significant implications for vacancy clustering effects with consequences to be explored for hydrogen diffusion. The experimental work at this stage has focused on the relationship of the choice and concentration of additives to the improvement of resistance to hydrogen embrittlement and hence to the fracture behavior. For this reason, comparative crack growth tests of FA-186, FA-187, and FA-189 iron aluminides (all with basic composition of Fe-28A{ell}-5Cr, at % with micro-alloying additives of Zr, C or B) under, air, oxygen, or water environment have been performed. These tests showed that the alloys are susceptible to room temperature hydrogen embrittlement in both B2 and DO{sub 3} conditions. Test results indicated that FA-187, and FA-189 are intrinsically more brittle than FA-186.

  11. Strain rate effects on the mechanical properties and fracture mode of skeletal muscle

    Energy Technology Data Exchange (ETDEWEB)

    Shapiro, Michael; Tovar, Nick; Yoo, Daniel [Biomaterials and Biomimetics, New York University College of Dentistry (United States); Sobieraj, Micheal [Orthopedic Surgery, Hospital for Joint Diseases (United States); Gupta, Nikhil [Mechanical and Aerospace Engineering, NYU-Poly (United States); Branski, Ryan C. [Dept of Otolaryngology, New York University School of Medicine (United States); Coelho, Paulo G., E-mail: pc92@nyu.edu [Biomaterials and Biomimetics, New York University College of Dentistry (United States)

    2014-06-01

    The present study aimed to characterize the mechanical response of beagle sartorius muscle fibers under strain rates that increase logarithmically (0.1 mm/min, 1 mm/min and 10 mm/min), and provide an analysis of the fracture patterns of these tissues via scanning electron microscopy (SEM). Muscle tissue from dogs' sartorius was excised and test specimens were sectioned with a lancet into sections with nominal length, width, and thickness of 7, 2.5 and 0.6 mm, respectively. Trimming of the tissue was done so that the loading would be parallel to the direction of the muscle fiber. Samples were immediately tested following excision and failures were observed under the SEM. No statistically significant difference was observed in strength between the 0.1 mm/min (2.560 ± 0.37 MPa) and the 1 mm/min (2.702 ± 0.55 MPa) groups. However, the 10 mm/min group (1.545 ± 0.50 MPa) had a statistically significant lower strength than both the 1 mm/min group and the 0.1 mm/min group with p < 0.01 in both cases. At the 0.1 mm/min rate the primary fracture mechanism was that of a shear mode failure of the endomysium with a significant relative motion between fibers. At 1 mm/min this continues to be the predominant failure mode. At the 10 mm/min strain rate there is a significant change in the fracture pattern relative to other strain rates, where little to no evidence of endomysial shear failure nor of significant motion between fibers was detected.

  12. The application of fracture mechanics to the safety assessment of transport casks for radioactive materials

    Energy Technology Data Exchange (ETDEWEB)

    Zencker, U.; Mueller, K.; Droste, B.; Roedel, R.; Voelzke, H. [Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin (Germany)

    2004-07-01

    BAM is the German responsible authority for the mechanical and thermal design safety assessment of packages for the transport of radioactive materials. The assessment has to cover the brittle fracture safety proof of package components made of potentially brittle materials. This paper gives a survey of the regulatory and technical requirements for such an assessment according to BAM's new ''Guidelines for the Application of Ductile Cast Iron for Transport and Storage Casks for Radioactive Materials''. Based on these guidelines higher stresses than before can become permissible, but it is necessary to put more effort into the safety assessment procedure. The fundamentals of such a proof with the help of the methods of fracture mechanics are presented. The recommended procedure takes into account the guidelines of the IAEA Advisory Material which are based on the prevention of crack initiation. Examples of BAM's research and safety assessment practices are given. Recommendations for further developments towards package designs with higher acceptable stress levels will be concluded.

  13. Fracture mechanics based design for radioactive material transport packagings -- Historical review

    Energy Technology Data Exchange (ETDEWEB)

    Smith, J.A.; Salzbrenner, D.; Sorenson, K.; McConnell, P.

    1998-04-01

    The use of a fracture mechanics based design for the radioactive material transport (RAM) packagings has been the subject of extensive research for more than a decade. Sandia National Laboratories (SNL) has played an important role in the research and development of the application of this technology. Ductile iron has been internationally accepted as an exemplary material for the demonstration of a fracture mechanics based method of RAM packaging design and therefore is the subject of a large portion of the research discussed in this report. SNL`s extensive research and development program, funded primarily by the U. S. Department of Energy`s Office of Transportation, Energy Management and Analytical Services (EM-76) and in an auxiliary capacity, the office of Civilian Radioactive Waste Management, is summarized in this document along with a summary of the research conducted at other institutions throughout the world. In addition to the research and development work, code and standards development and regulatory positions are also discussed.

  14. Fracture mechanics models developed for piping reliability assessment in light water reactors: piping reliability project

    Energy Technology Data Exchange (ETDEWEB)

    Harris, D.O.; Lim, E.Y.; Dedhia, D.D.; Woo, H.H.; Chou, C.K.

    1982-06-01

    The efforts concentrated on modifications of the stratified Monte Carlo code called PRAISE (Piping Reliability Analysis Including Seismic Events) to make it more widely applicable to probabilistic fracture mechanics analysis of nuclear reactor piping. Pipe failures are considered to occur as the result of crack-like defects introduced during fabrication, that escape detection during inspections. The code modifications allow the following factors in addition to those considered in earlier work to be treated: other materials, failure criteria and subcritical crack growth characteristic; welding residual and vibratory stresses; and longitudinal welds (the original version considered only circumferential welds). The fracture mechanics background for the code modifications is included, and details of the modifications themselves provided. Additionally, an updated version of the PRAISE user's manual is included. The revised code, known as PRAISE-B was then applied to a variety of piping problems, including various size lines subject to stress corrosion cracking and vibratory stresses. Analyses including residual stresses and longitudinal welds were also performed.

  15. Structure, thermal and fracture mechanical properties of benzoxazine-modified amine-cured DGEBA epoxy resins

    Directory of Open Access Journals (Sweden)

    2011-03-01

    Full Text Available First, traditional diamine hardeners of epoxy resins (EP were checked as potential accelerators for the benzoxazine (BOX homopolymerization. It was established that the acceleration effect depends on both the type and amount of the diamine compounds. In the follow-up work amine-curable diglycidyl ether bisphenol A (DGEBA type EP was modified with BOX keeping the EP/BOX ratio constant (75/25 wt.%. The amine hardeners, added in the EP in stoichiometric amounts, were of aliphatic and aromatic nature, viz. diethylenetriamine (DETA, 4,4'-diaminodiphenyl methane (DDM, and their 1/1 mixture. The thermal, viscoelastic, flexural and fracture mechanical properties of the EP/BOX hybrids were determined and compared to those of the reference EPs. Based on dynamic-mechanical thermal analysis and atomic force microscopy the formation of co-network between EP and BOX was concluded. Homopolymerized BOX was built in the network in nanoscaled inclusions and it was associated with internal antiplasticization. Incorporation of BOX improved the charring, enhanced the flexural modulus and strength, and reduced the glass transition of the parent EP. The fracture toughness and energy were not improved by hybridization with BOX.

  16. Mechanisms of fracture of the free surface of shock-compressed metals

    Energy Technology Data Exchange (ETDEWEB)

    Mokhova, V. V., E-mail: vvmokhova@yandex.ru; Mikhailov, A. L.; Til’kunov, A. V. [Russian Federal Nuclear Center–All-Russia Research Institute of Experimental Physics (Russian Federation); Orlov, N. I. [National Nuclear Research University MEPhI, Sarov State Physicotechnical Institute (Russian Federation); Kanunova, L. I.; Bragunets, V. A.; Tkachenko, M. I.; Simakov, V. G.; Sokolov, S. S.; Podurets, A. M. [Russian Federal Nuclear Center–All-Russia Research Institute of Experimental Physics (Russian Federation)

    2015-12-15

    The mechanisms of the ejection of aluminum and copper microparticles from the free surfaces of these metals have been studied under conditions of the escape of a moderate-intensity shock wave from a sample. The free surfaces of samples contained 0.7–0.9 mm deep artificial wells and protrusions simulating (on a greater scale of 10: 1) the natural surface roughness retained upon mechanical processing. The pressure in a shock-wave pulse at the base of a protrusion was controlled within P = 5–20 GPa (i.e., below the melting region), and the variable duration of pressure pulses was 0.02, 0.2, and 1 μs. Analysis of the free surfaces of postloaded samples showed that, for certain loading and roughness parameters, the ejection of metal from vertices of protruding ridges or pyramids (as a result of the longitudinal fracture) was about ten times greater than the amount of metal ejected in the form of cumulative jets from wells. The amount of ejected metal and the size distribution of metal microparticles were quantitatively characterized using “soft collecting targets” and by measuring mass losses of samples upon fracture.

  17. Standard guide for evaluating data acquisition systems used in cyclic fatigue and fracture mechanics testing

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    1998-01-01

    1.1 This guide covers how to understand and minimize the errors associated with data acquisition in fatigue and fracture mechanics testing equipment. This guide is not intended to be used instead of certified traceable calibration or verification of data acquisition systems when such certification is required. It does not cover static load verification, for which the user is referred to the current revision of Practices E 4, or static extensometer verification, for which the user is referred to the current revision of Practice E 83. The user is also referred to Practice E 467. 1.2 The output of the fatigue and fracture mechanics data acquisition systems described in this guide is essentially a stream of digital data. Such digital data may be considered to be divided into two types- Basic Data, which are a sequence of digital samples of an equivalent analog waveform representing the output of transducers connected to the specimen under test, and Derived Data, which are digital values obtained from the Basic D...

  18. A mechanism for the production of ultrafine particles from concrete fracture.

    Science.gov (United States)

    Jabbour, Nassib; Rohan Jayaratne, E; Johnson, Graham R; Alroe, Joel; Uhde, Erik; Salthammer, Tunga; Cravigan, Luke; Faghihi, Ehsan Majd; Kumar, Prashant; Morawska, Lidia

    2017-03-01

    While the crushing of concrete gives rise to large quantities of coarse dust, it is not widely recognized that this process also emits significant quantities of ultrafine particles. These particles impact not just the environments within construction activities but those in entire urban areas. The origin of these ultrafine particles is uncertain, as existing theories do not support their production by mechanical processes. We propose a hypothesis for this observation based on the volatilisation of materials at the concrete fracture interface. The results from this study confirm that mechanical methods can produce ultrafine particles (UFP) from concrete, and that the particles are volatile. The ultrafine mode was only observed during concrete fracture, producing particle size distributions with average count median diameters of 27, 39 and 49 nm for the three tested concrete samples. Further volatility measurements found that the particles were highly volatile, showing between 60 and 95% reduction in the volume fraction remaining by 125 °C. An analysis of the volatile fraction remaining found that different volatile material is responsible for the production of particles between the samples. Copyright © 2016 Elsevier Ltd. All rights reserved.

  19. Investigating the fracture non-linear dynamics through multi-spectral time series analysis of fracture-induced electromagnetic emissions

    Science.gov (United States)

    Kalimeris, Anastasios; Potirakis, Stelios M.; Eftaxias, Konstantinos; Antonopoulos, George; Kopanas, John; Nomicos, Constantinos

    2013-04-01

    Electromagnetic (EM) emissions (EME) in a wide frequency spectrum ranging from kHz to MHz are produced by cracks' opening, considered as fracture precursors. Thus, their study constitutes a nondestructive method for the monitoring of the evolution of damage process at the laboratory scale. Earthquakes (EQs) are large-scale fracture phenomena in the Earth's heterogeneous crust. Accordingly, it has been suggested that fracture induced MHz-kHz EME, emerging from a few days up to a few hours before the main seismic shock permit a monitoring of the damage process during the last stages of EQ preparation. The use of spectral decomposition techniques, namely Singular Spectral Analysis (SSA), Wavelets Analysis (WA) and their Monte Carlo counterparts (MC SSA and MC WA), as well as the revised Multi-Taper Method (MTM) for a reliable discrimination of fracto-EM emissions from the natural geo-EM field is proposed here; the well documented fracture-induced kHz EME time-series associated with the Athens' EQ (M=5.9, 7 September 1999) is employed as a test case. An adequately long time period (> month) prior to the occurrence of the EQ is considered in order to include all different phases of a large-scale fracture, from the "quite" period where only the geo-EM field and its modulation by the ionospheric variations is observed, to the final stages of the EQ preparation process where fracto-EM emissions occur. The examined time series, recorded at the 10 kHz band and at a high temporal resolution (sampling frequency 1 Hz), is first split into three characteristic excerpts (a) the quiet period well (35 to 25 days) before the event, (b) the first epoch of the candidate pre-seismically active time period (8 to 4 days before the event), and (c) the final epoch of the candidate pre-seismically active time period (~3 days before the event until short after the event). The Maximum Entropy and Blackman-Tukey FFT methods are initially used for the preliminary evaluation of the time

  20. Evaluation of an injectable hydrogel and polymethyl methacrylate in restoring mechanics to compressively fractured spine motion segments.

    Science.gov (United States)

    Balkovec, Christian; Vernengo, Andrea J; Stevenson, Peter; McGill, Stuart M

    2016-11-01

    Compressive fracture can produce profound changes to the mechanical profile of a spine segment. Minimally invasive repair has the potential to restore both function and structural integrity to an injured spine. Use of both hydrogels to address changes to the disc, combined with polymethyl methacrylate (PMMA) to address changes to the vertebral body, has the potential to facilitate repair. The purpose of this investigation was to determine if the combined use of hydrogel injection and PMMA could restore the mechanical profile of an axially injured spinal motion segment. This is a basic science study evaluating a combination of hydrogel injection and vertebroplasty on restoring mechanics to compressively injured porcine spine motion segments. Fourteen porcine spine motion segments were subject to axial compression until fracture using a dynamic servohydraulic testing apparatus. Rotational and compressive stiffness was measured for each specimen under the following conditions: initial undamaged, fractured, fatigue loading under compression, hydrogel injection, PMMA injection, and fatigue loading under compression. Group 1 received hydrogel injection followed by PMMA injection, whereas Group 2 received PMMA injection followed by hydrogel injection. This study was funded under a Natural Sciences and Engineering Research Council of Canada discovery grant. PMMA injection was found to alter the compressive stiffness properties of axially injured spine motion segments, restoring values from Groups 1 and 2 to 89.3%±29.3% and 81%±27.9% of initial values respectively. Hydrogel injection was found to alter the rotational stiffness properties, restoring specimens in Groups 1 and 2 to 151.5%±81% and 177.2%±54.9% of initial values respectively. Prolonged restoration of function was not possible, however, after further fatigue loading. Using this repair technique, replication of the mechanism of injury appears to cause a rapid deterioration in function of the motion segments

  1. Continuum Damage Mechanics A Continuum Mechanics Approach to the Analysis of Damage and Fracture

    CERN Document Server

    Murakami, Sumio

    2012-01-01

    Recent developments in engineering and technology have brought about serious and enlarged demands for reliability, safety and economy in wide range of fields such as aeronautics, nuclear engineering, civil and structural engineering, automotive and production industry.  This, in turn, has caused more interest in continuum damage mechanics and its engineering applications.   This book aims to give a concise overview of the current state of damage mechanics, and then to show the fascinating possibility of this promising branch of mechanics, and to provide researchers, engineers and graduate students with an intelligible and self-contained textbook.   The book consists of two parts and an appendix.  Part I  is concerned with the foundation of continuum damage mechanics.  Basic concepts of material damage and the mechanical representation of damage state of various kinds are described in Chapters 1 and 2.  In Chapters 3-5, irreversible thermodynamics, thermodynamic constitutive theory and its application ...

  2. Hydrologic Mechanisms Governing Fluid Flow in a Partially Saturated, Fractured, Porous Medium

    Science.gov (United States)

    Wang, J. S. Y.; Narasimhan, T. N.

    1985-12-01

    In contrast to the saturated zone within which fluid moves rapidly along fractures, the fractures (with apertures large relative to the size of matrix pores) will desaturate first during the drainage process, and the bulk of fluid flow would be through interconnected pores in the matrix. Within a partially drained fracture, the presence of a relatively continuous air phase will produce practically an infinite resistance to liquid flow in the direction parallel to the fracture. The residual liquid will be held by capillary force, in regions around fracture contact areas where the apertures are small. Normal to the fracture surfaces, the drained portion of the fractures will reduce the effective area for liquid flow from one matrix block to another matrix block. A general statistical theory is constructed for flow along the fracture and for flow between the matrix blocks to the fractures under partially saturated conditions. Results are obtained from an aperture distribution model for fracture saturation, hydraulic conductivity, and effective matrix-fracture flow areas as functions of pressure. The effects of distortion of flow paths by the air pockets are taken into account by a phase-separation constriction factor in a generalized cubic law for fracture flow under a partially saturated condition. The reduction of matrix-fracture flow area is taken into account by summing the aperture distribution function to a saturation cutoff aperture, which is inversely proportional to the suction head. Drainage from a column of fractured tuff is simulated using available parameters for the densely welded tuff of the Topopah Spring Member at Yucca Mountain, southern Nevada. The column is bounded by discrete vertical fractures and dissected by horizontal fractures with the fracture spacings determined by the frequencies and orientations of fractured cores. The fraction of fracture surfaces with coatings is assumed to correspond to the fraction of in situ fracture contact area

  3. A predictive mechanical model for evaluating vertebral fracture probability in lumbar spine under different osteoporotic drug therapies.

    Science.gov (United States)

    López, E; Ibarz, E; Herrera, A; Puértolas, S; Gabarre, S; Más, Y; Mateo, J; Gil-Albarova, J; Gracia, L

    2016-07-01

    Osteoporotic vertebral fractures represent a major cause of disability, loss of quality of life and even mortality among the elderly population. Decisions on drug therapy are based on the assessment of risk factors for fracture from bone mineral density (BMD) measurements. A previously developed model, based on the Damage and Fracture Mechanics, was applied for the evaluation of the mechanical magnitudes involved in the fracture process from clinical BMD measurements. BMD evolution in untreated patients and in patients with seven different treatments was analyzed from clinical studies in order to compare the variation in the risk of fracture. The predictive model was applied in a finite element simulation of the whole lumbar spine, obtaining detailed maps of damage and fracture probability, identifying high-risk local zones at vertebral body. For every vertebra, strontium ranelate exhibits the highest decrease, whereas minimum decrease is achieved with oral ibandronate. All the treatments manifest similar trends for every vertebra. Conversely, for the natural BMD evolution, as bone stiffness decreases, the mechanical damage and fracture probability show a significant increase (as it occurs in the natural history of BMD). Vertebral walls and external areas of vertebral end plates are the zones at greatest risk, in coincidence with the typical locations of osteoporotic fractures, characterized by a vertebral crushing due to the collapse of vertebral walls. This methodology could be applied for an individual patient, in order to obtain the trends corresponding to different treatments, in identifying at-risk individuals in early stages of osteoporosis and might be helpful for treatment decisions.

  4. Investigations on mechanical behaviour of dental composites.

    Science.gov (United States)

    Ilie, Nicoleta; Hickel, Reinhard

    2009-12-01

    Since a direct comparison of composites efficacy in clinical studies is very difficult, our study aimed to analyse in laboratory tests under standardised and simulated clinical conditions a large variety of commercial composite materials belonging to eight different materials categories. Thus, 72 hybrid, nano-hybrid, micro-filled, packable, ormocer-based and flowable composites, compomers and flowable compomers were compared in terms of their mechanical behaviour. Flexural strength (FS), flexural modulus (FM), diametric tensile (DTS) and compressive strength (CS) were measured after the samples had been stored in water for 24 h at 37 degrees C. Results were statistically analysed using one-way ANOVA with Tukey HSD post hoc test (alpha = 0.05) as well as partial eta2 statistics. Large varieties between the tested materials within the same material category were found. The hybrid, nano-hybrid, packable and ormocer-based composites do not differ significantly among each other as a material type, reaching the highest FS values. Nano-hybrid composites are characterised by a good FS, the best DTS but a low FM. The lowest mechanical properties achieved the micro-filled hybrids. The flowable composites and compomers showed for all properties comparable result. Both flowable material categories do not differ significantly from the micro-filled composites for the most mechanical properties, showing only a higher DTS. The filler volume was shown to have the highest influence on the measured properties, inducing a maximum FS and FM at a level of 60%, whereas such dependence was not measured for DTS or CS. The influence of the type of material on the mechanical properties was significant but very low, showing the strongest influence on the CS.

  5. Preliminary rock mechanics laboratory: Investigation plan

    Energy Technology Data Exchange (ETDEWEB)

    Oschman, K.P.; Hummeldorf, R.G.; Hume, H.R.; Karakouzian, M.; Vakili, J.E.

    1987-01-01

    This document presents the rationale for rock mechanics laboratory testing (including the supporting analysis and numerical modeling) planned for the site characterization of a nuclear waste repository in salt. This plan first identifies what information is required for regulatory and design purposes, and then presents the rationale for the testing that satisfies the required information needs. A preliminary estimate of the minimum sampling requirements for rock laboratory testing during site characterization is also presented. Periodic revision of this document is planned.

  6. A multiphase mesostructure mechanics approach to the study of the fracture-damage behavior of concrete

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    A multiphase mesostructure mechanical model is proposed to study the deformation and failure process of concrete considering its heterogeneity at the meso scopic level.Herein,concrete is taken as a type of three-component composite material composed of mortar matrix,aggregates and interfaces on the meso-scale.First,an efficient approach to the disposition of aggregates of concrete and a state matrix method to generate mesh coordinates for aggregates are proposed.Secondly,based on the nonlinear continuum damage mechanics,a meso-scale finite element model is presented with damage softening stress-strain relationship for describing the mechanical behavior of different components of concrete.In this method,heterogeneities of each component in the concrete are considered by assuming the material properties of three components conform to the Weibull distribution law.Finally,based on this multiphase meso-mechanics model,a simulation analysis of fracture behavior of a rock-fill concrete(RFC) beam is accomplished.The study includes experimental tests for determining basic mechanical parameters of three components of RFC and four-point flexural beam tests for verification of the model.It is preliminarily shown that the numerical model is applicable to studying failure mechanisms and process of concrete type material.

  7. Investigation of temperature dependence of fracture toughness in high-dose HT9 steel using small-specimen reuse technique

    Energy Technology Data Exchange (ETDEWEB)

    Baek, Jong-Hyuk [KAERI; Byun, Thak Sang [ORNL; Maloy, S [Los Alamos National Laboratory (LANL); Toloczko, M [Pacific Northwest National Laboratory (PNNL)

    2014-01-01

    The temperature dependence of fracture toughness in HT9 steel irradiated to 3 145 dpa at 380 503 C was investigated using miniature three-point bend (TPB) fracture specimens. A miniature-specimen reuse technique has been established: the tested halves of subsize Charpy impact specimens with dimensions of 27 mm 3mm 4 mm were reused for this fracture test campaign by cutting a notch with a diamond-saw in the middle of each half, and by fatigue-precracking to generate a sharp crack tip. It was confirmed that the fracture toughness of HT9 steel in the dose range depends more strongly on the irradiation temperature than the irradiation dose. At an irradiation temperature <430 C, the fracture toughness of irradiated HT9 increased with the test temperature, reached an upper shelf of 180 200 MPa ffiffiffiffiffi m p at 350 450 C, and then decreased with the test temperature. At an irradiation temperatureP430 C, the fracture toughness was nearly unchanged up to about 450 C and decreased slowly with test temperatures in a higher temperature range. Such a rather monotonic test temperature dependence after high-temperature irradiation is similar to that observed for an archive material generally showing a higher degree of toughness. A brittle fracture without stable crack growth occurred in only a few specimens with relatively lower irradiation and test temperatures. In this discussion, these TPB fracture toughness data are compared with previously published data from 12.7 mm diameter disc compact tension (DCT) specimens.

  8. Investigation of temperature dependence of fracture toughness in high-dose HT9 steel using small-specimen reuse technique

    Energy Technology Data Exchange (ETDEWEB)

    Baek, Jong-Hyuk, E-mail: jhbaek@kaeri.re.kr [Korea Atomic Energy Research Institute, Daejeon 305-353 (Korea, Republic of); Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Byun, Thak Sang [Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Maloy, Start A. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Toloczko, Mychailo B. [Pacific Northwest National Laboratory, Richland, WA 99352 (United States)

    2014-01-15

    The temperature dependence of fracture toughness in HT9 steel irradiated to 3–145 dpa at 380–503 °C was investigated using miniature three-point bend (TPB) fracture specimens. A miniature-specimen reuse technique has been established: the tested halves of subsize Charpy impact specimens with dimensions of 27 mm × 3 mm × 4 mm were reused for this fracture test campaign by cutting a notch with a diamond-saw in the middle of each half, and by fatigue-precracking to generate a sharp crack tip. It was confirmed that the fracture toughness of HT9 steel in the dose range depends more strongly on the irradiation temperature than the irradiation dose. At an irradiation temperature <430 °C, the fracture toughness of irradiated HT9 increased with the test temperature, reached an upper shelf of 180–200MPa√(m) at 350–450 °C, and then decreased with the test temperature. At an irradiation temperature ⩾430 °C, the fracture toughness was nearly unchanged up to about 450 °C and decreased slowly with test temperatures in a higher temperature range. Such a rather monotonic test temperature dependence after high-temperature irradiation is similar to that observed for an archive material generally showing a higher degree of toughness. A brittle fracture without stable crack growth occurred in only a few specimens with relatively lower irradiation and test temperatures. In this discussion, these TPB fracture toughness data are compared with previously published data from 12.7 mm diameter disc compact tension (DCT) specimens.

  9. Investigation of temperature dependence of fracture toughness in high-dose HT9 steel using small-specimen reuse technique

    Energy Technology Data Exchange (ETDEWEB)

    Baek, Jong-Hyuk; Byun, Thak Sang; Maloy, Stuart A.; Toloczko, Mychailo B.

    2014-01-01

    The temperature dependence of fracture toughness in HT9 steel irradiated to 3–145 dpa at 380–503 degrees*C was investigated using miniature three-point bend (TPB) fracture specimens. A miniature-specimen reuse technique has been established: the tested halves of subsize Charpy impact specimens with dimensions of 27 mm *3mm* 4 mm were reused for this fracture test campaign by cutting a notch with a diamond-saw in the middle of each half, and by fatigue-precracking to generate a sharp crack tip. It was confirmed that the fracture toughness of HT9 steel in the dose range depends more strongly on the irradiation temperature than the irradiation dose. At an irradiation temperature <430 *degreesC, the fracture toughness of irradiated HT9 increased with the test temperature, reached an upper shelf of 180—200 MPa*m^.5 at 350–450 degrees*C, and then decreased with the test temperature. At an irradiation temperature >430 degrees*C, the fracture toughness was nearly unchanged up to about 450 *degreesC and decreased slowly with test temperatures in a higher temperature range. Such a rather monotonic test temperature dependence after high-temperature irradiation is similar to that observed for an archive material generally showing a higher degree of toughness. A brittle fracture without stable crack growth occurred in only a few specimens with relatively lower irradiation and test temperatures. In this discussion, these TPB fracture toughness data are compared with previously published data from 12.7 mm diameter disc compact tension (DCT) specimens.

  10. INVESTIGATION ON THE FRACTURE PROPERTIES[1mm] OF POLYURETHANE RIGID FOAM PLASTICS%聚氨酯泡沫塑料的强度与断裂韧性

    Institute of Scientific and Technical Information of China (English)

    卢子兴; 高镇同; 朱汪鲲; 寇长河

    2000-01-01

    As one kind of structural material, it is indispensable to undergotensile loadingin use for high-density foam plastics. So, it is an important work toinvestigate its tensile fracture properties and to determine its tensilefracture strength as well as the fracture toughness for engineeringapplications. In this paper,the tensile experiments have been done for the polyurethane rigid foam plastics of threedifferent densities. Their tensile fracture strength and fracturetoughness were determined byspecimens without and with a notch, respectively. In order to investigate thetensile fracture mechanism, the SEM analyses have been conducted forthe broken specimens. In addition, the theoretical prediction for fracturetoughness of polyurethane rigid foam plastics is also discussed in this paper. Finally,the following conclusions can be drawn:   1) The Young's modulus and tensile fracture strength of polyurethane rigid foamplastics increase with its density.   2) The fracture toughness of polyurethane rigid foam plastics alsoincreases with itsdensity.   3) It is shown by SEM analyses that the cell failure of foam plasticsgenerally originates from the edge of penetrating holes on the cell walland its breaking basically belongs to one kind of britle fracture.   4) The fracture toughness of polyurethane rigid foam plastics has a direct bearing onthe cell size of it.   5) The micro-defects (or voids) exert a larger effect on the practicalstrength of foam plastics, but they hardly affect its fracturetoughness.%针对3种密度的聚氨酯泡沫塑料进行了拉伸实验.通过无缺口试件确定了3种密度泡沫塑料的拉伸断裂强度, 而利用有缺口试件确定了这些材料的拉伸断裂韧性.为了研究高密度泡沫塑料的拉伸断裂机制, 还对破坏后试件进行了扫描电镜分析.此外,还简要讨论了泡沫塑料拉伸断裂力学性能的理论预测问题.

  11. Lithostratigraphic contact – a significant site for hydrogeological investigation in crystalline fractured-rock terrains

    Indian Academy of Sciences (India)

    Tapas Acharya; Rajesh Prasad

    2017-02-01

    Estimating the hydrogeologic control of fractured aquifers in hard crystalline and metamorphosed rocks is challenging due to complexity in the development of secondary porosity. The present study in the Precambrian metamorphic terrain in and around the Balarampur of Purulia district, West Bengal, India, aims to estimate the hydrogeologic significance of lithostratigraphic contacts using fracture characteristics obtained from surface bedrock exposures supported by hydrological data from the existing dugwells. This study involves the domain-wise analysis of the frequencies of fractures that control the fractureporosity.The domain-wise study reveals higher fracture-frequencies adjacent to the lithostratigraphic contacts. The concurrence of lithostratigraphic contacts with the occurrences of high-discharging wells and also with the deep weathered zone in low-lying areas is clearly established, thus assigning the lithostratigraphic contact as hydrogeologically significant. An increase in frequencies of the fractures within the ‘influence zone’ of the lithocontact, is clearly visible. Among those fractures, particularly, which make the angle greater than the ‘limiting angle’ with the lithocontact are characterised by increased frequencies. However, brittle rocks like quartz biotite granite gneisses, phyllite and epidiorite show high porosity of fracture, within the ‘influence zone’ of the lithostratigraphic contact. Enhanced deepening of the weathered-zone at lower topographic region may perhaps be a plausible explanation for this increased fracture-porosity at lithocontact to assign it as a hydrogeologically significant transmissive zone within fractured rocks.

  12. Investigation on Mechanical Property of Seamless Pipe

    Institute of Scientific and Technical Information of China (English)

    ZHAO Li-ming; YANG Xiao-yong; LIU Ye

    2004-01-01

    The mechanical properties of the steel pipe rolled with continuously casting round billet after determining the chemical composition in steel were studied. The results show that the total reduction ratio should be higher than 5.2 when the line pipes of grade B, grade 20 and other general seamless pipe were rolled with continuously casting round billet. And the total reduction ratio should be higher than 10.2 and the grain size should be controlled more than grade 7 for casing of oil countryside tubular goods (OCTG).

  13. Investigations on Sugarcane De-Trashing Mechanisms

    Directory of Open Access Journals (Sweden)

    Joby Bastian, B. Shridar

    2014-07-01

    Full Text Available Sugarcane is the second most important industrial crop in India grown in 4.4 million hectares with an average productivity of about 68 tonnes per hectare (Anon.2013. To mitigate the labour scarcity and ensure timely operations mechanization is a must. Mechanisation will also improve the overall energy use efficiency of sugarcane based farming (Duttamajumder et al. 2011. About 45-48% of the total cost of cultivation is accountable to harvesting operation in manual harvesting. Mechanisation of harvesting operations is imperative in increasing the cost effectiveness of sugarcane production system.

  14. Investigation into the mechanism regulating MRP localization.

    Science.gov (United States)

    van den Bout, Iman; van Rheenen, Jacco; van Angelen, Annelies A; de Rooij, Johan; Wilhelmsen, Kevin; Jalink, Kees; Divecha, Nullin; Sonnenberg, Arnoud

    2008-01-15

    The major PKC substrates MARCKS and MacMARCKS (MRP) are membrane-binding proteins implicated in cell spreading, integrin activation and exocytosis. According to the myristoyl-electrostatic switch model the co-operation between the myristoyl moiety and the positively charged effector domain (ED) is an essential mechanism by which proteins bind to membranes. Loss of the electrostatic interaction between the ED and phospholipids, such as Ptdins(4,5)P2, results in the translocation of such proteins to the cytoplasm. While this model has been extensively tested for the binding of MARCKS far less is known about the mechanisms regulating MRP localization. We demonstrate that after phosphorylation, MRP is relocated to the intracellular membranes of late endosomes and lysosomes. MRP binds to all membranes via its myristoyl moiety, but for its localization at the plasma membrane the ED is also required. Although the ED of MRP can bind to Ptdins(4,5)P2 in vitro, this binding is not essential for its retention at or targeting to the plasma membrane. We conclude that the co-operation between the myristoyl moiety and the ED is not required for the binding to membranes in general but that it is essential for the targeting of MRP to the plasma membrane in a Ptdins(4,5)P2-independent manner.

  15. How vein sealing boosts fracture widening rates - The buckling-enhanced aperture growth mechanism for syn-tectonic veins

    Science.gov (United States)

    Nüchter, Jens-Alexander

    2017-01-01

    The paper introduces the mechanism of buckling-enhanced aperture growth for syn-tectonic veins that formed in simple-shear dominated kinematic frameworks in the middle or lower crust. Apart from the well understood concepts of fracture widening driven by effective tensile stresses, buckling-enhanced fracture aperture growth relates widening to active outward buckling of more viscous incipient cement layers precipitated as hydrothermal minerals for the pore fluid on the walls of juvenile syn-tectonic veins, driven by fracture-parallel compressive creep strain in the host rocks. Thus, the mechanism proposed here follows similar principles as tectonic folding, although important differences exist. Inspired by the structural record of low-aspect ratio veins exposed in HP/LT metamorphic rocks cropping out on south Evia island, Greece, generic numerical models are calculated to study development of buckling instabilities in such incompletely cemented veins and their impact on aperture growth rates. The models indicate (1) that aperture growth rates increase with increasing viscosity contrast between the host rocks and the cement layers, (2) an increase in the thickness of the cement layers cause acceleration of aperture growth, (3) that support of restraining forces at the vein tips offered by the host rocks against buckling of the cement layers cause fully compressive states of stress ahead the fracture tips, and (4) that fracture aperture growth is possible against fully compressive fracture-normal stresses. The buckling-enhanced vein aperture growth mechanism yields important implications for the maintenance and decay of fracture-bound permeability and for the mechanical state of the middle and lower crust in seismically active regions.

  16. Length-scale and strain rate-dependent mechanism of defect formation and fracture in carbon nanotubes under tensile loading

    Science.gov (United States)

    Javvaji, Brahmanandam; Raha, S.; Mahapatra, D. Roy

    2017-02-01

    Electromagnetic and thermo-mechanical forces play a major role in nanotube-based materials and devices. Under high-energy electron transport or high current densities, carbon nanotubes fail via sequential fracture. The failure sequence is governed by certain length scale and flow of current. We report a unified phenomenological model derived from molecular dynamic simulation data, which successfully captures the important physics of the complex failure process. Length-scale and strain rate-dependent defect nucleation, growth, and fracture in single-walled carbon nanotubes with diameters in the range of 0.47 to 2.03 nm and length which is about 6.17 to 26.45 nm are simulated. Nanotubes with long length and small diameter show brittle fracture, while those with short length and large diameter show transition from ductile to brittle fracture. In short nanotubes with small diameters, we observe several structural transitions like Stone-Wales defect initiation, its propagation to larger void nucleation, formation of multiple chains of atoms, conversion to monatomic chain of atoms, and finally complete fracture of the carbon nanotube. Hybridization state of carbon-carbon bonds near the end cap evolves, leading to the formation of monatomic chain in short nanotubes with small diameter. Transition from ductile to brittle fracture is also observed when strain rate exceeds a critical value. A generalized analytical model of failure is established, which correlates the defect energy during the formation of atomic chain with aspect ratio of the nanotube and strain rate. Variation in the mechanical properties such as elastic modulus, tensile strength, and fracture strain with the size and strain rate shows important implications in mitigating force fields and ways to enhance the life of electronic devices and nanomaterial conversion via fracture in manufacturing.

  17. Fracture mechanics in new designed power module under thermo-mechanical loads

    Directory of Open Access Journals (Sweden)

    Durand Camille

    2014-06-01

    Full Text Available Thermo-mechanically induced failure is a major reliability issue in the microelectronic industry. On this account, a new type of Assembly Interconnected Technology used to connect MOSFETs in power modules has been developed. The reliability is increased by using a copper clip soldered on the top side of the chip, avoiding the use of aluminium wire bonds, often responsible for the failure of the device. Thus the new designed MOSFET package does not follow the same failure mechanisms as standard modules. Thermal and power cycling tests were performed on these new packages and resulting failures were analyzed. Thermo-mechanical simulations including cracks in the aluminium metallization and intermetallics (IMC were performed using Finite Element Analysis in order to better understand crack propagation and module behaviour.

  18. Investigating learners' epistemological framings of quantum mechanics

    Science.gov (United States)

    Dini, Vesal

    Classical mechanics challenges students to use their intuitions and experiences as a basis for understanding, in effect to approach learning as "a refinement of everyday thinking'' (Einstein, 1936). Moving on to quantum mechanics (QM), students, like physicists, need to adjust this approach, in particular with respect to the roles that intuitive knowledge and mathematics play in the pursuit of coherent understanding (these are adjustments to aspects of their epistemologies). In this dissertation, I explore how some students manage the epistemological transition. I began this work by recruiting both graduate and undergraduate students, interviewing each subject several times as they moved through coursework in QM. The interviews featured, among other things, how students tried to fit ideas together in mutually consistent ways, including with respect to intuitive knowledge, mathematics and experiment, if at all. I modeled these dynamic cognitive processes as different epistemological framings (i.e., tacit, in-the-moment responses to the question "How should I approach knowledge?''). Through detailed qualitative analyses of students' reasoning and a systematic coding of their interviews, I explored how these coherence seeking related framings impacted their learning. The dissertation supports three main findings: (1) students' patterns of epistemological framing are mostly stable within a given course; (2) students who profess epistemologies aligned with the coordination of coherence seeking framings tend to be more stable in demonstrating them; and (3) students aware that their understanding of QM ultimately anchors in its mathematics tend to produce more coherent explanations and perform better in their courses. These findings are consistent with existing research on student epistemologies in QM and imply that epistemologies, in particular whether and how students seek coherence, require greater attention and emphasis in instruction.

  19. Growth Kinematics of Opening-Mode Fractures

    Science.gov (United States)

    Eichhubl, P.; Alzayer, Y.; Laubach, S.; Fall, A.

    2014-12-01

    Fracture aperture is a primary control on flow in fractured reservoirs of low matrix permeability including unconventional oil and gas reservoirs and most geothermal systems. Guided by principles of linear elastic fracture mechanics, fracture aperture is generally assumed to be a linear function of fracture length and elastic material properties. Natural opening-mode fractures with significant preserved aperture are observed in core and outcrop indicative of fracture opening strain accommodated by permanent solution-precipitation creep. Fracture opening may thus be decoupled from length growth if the material effectively weakens after initial elastic fracture growth by either non-elastic deformation processes or changes in elastic properties. To investigate the kinematics of fracture length and aperture growth, we reconstructed the opening history of three opening-mode fractures that are bridged by crack-seal quartz cement in Travis Peak Sandstone of the SFOT-1 well, East Texas. Similar crack-seal cement bridges had been interpreted to form by repeated incremental fracture opening and subsequent precipitation of quartz cement. We imaged crack-seal cement textures for bridges sampled at varying distance from the tips using scanning electron microscope cathodoluminescence, and determined the number and thickness of crack-seal cement increments as a function of position along the fracture length and height. Observed trends in increment number and thickness are consistent with an initial stage of fast fracture propagation relative to aperture growth, followed by a stage of slow propagation and pronounced aperture growth. Consistent with fluid inclusion observations indicative of fracture opening and propagation occurring over 30-40 m.y., we interpret the second phase of pronounced aperture growth to result from fracture opening strain accommodated by solution-precipitation creep and concurrent slow, possibly subcritical, fracture propagation. Similar deformation

  20. The effect of deformation on two-phase flow through proppant-packed fractured shale samples: A micro-scale experimental investigation

    Science.gov (United States)

    Arshadi, Maziar; Zolfaghari, Arsalan; Piri, Mohammad; Al-Muntasheri, Ghaithan A.; Sayed, Mohammed

    2017-07-01

    We present the results of an extensive micro-scale experimental investigation of two-phase flow through miniature, fractured reservoir shale samples that contained different packings of proppant grains. We investigated permeability reduction in the samples by conducting experiments under a wide range of net confining pressures. Three different proppant grain distributions in three individual fractured shale samples were studied: i) multi-layer, ii) uniform mono-layer, and iii) non-uniform mono-layer. We performed oil-displacing-brine (drainage) and brine-displacing-oil (imbibition) flow experiments in the proppant packs under net confining pressures ranging from 200 to 6000 psi. The flow experiments were performed using a state-of-the-art miniature core-flooding apparatus integrated with a high-resolution, X-ray microtomography system. We visualized fluid occupancies, proppant embedment, and shale deformation under different flow and stress conditions. We examined deformation of pore space within the proppant packs and its impact on permeability and residual trapping, proppant embedment due to changes in net confining stress, shale surface deformation, and disintegration of proppant grains at high stress conditions. In particular, geometrical deformation and two-phase flow effects within the proppant pack impacting hydraulic conductivity of the medium were probed. A significant reduction in effective oil permeability at irreducible water saturation was observed due to increase in confining pressure. We propose different mechanisms responsible for the observed permeability reduction in different fracture packings. Samples with dissimilar proppant grain distributions showed significantly different proppant embedment behavior. Thinner proppant layer increased embedment significantly and lowered the onset confining pressure of embedment. As confining stress was increased, small embedments caused the surface of the shale to fracture. The produced shale fragments were

  1. Investigation of the DC vacuum breakdown mechanism

    CERN Document Server

    Descoeudres, A; Calatroni, S; Taborelli, M; Wuensch, W

    2009-01-01

    Breakdowns occurring in rf accelerating structures will limit the ultimate performance of future linear colliders such as the Compact Linear Collider (CLIC). Because of the similarity of many aspects of dc and rf breakdown, a dc breakdown study is underway at CERN to better understand the vacuum breakdown mechanism in a simple setup. Measurements of the field enhancement factor β show that the local breakdown field is constant and depends only on the electrode material. With copper electrodes, the local breakdown field is around 10:8 GV/m, independent of the gap distance. The β value characterizes the electrode surface state, and the next macroscopic breakdown field can be well predicted. In breakdown rate experiments, where a constant field is applied to the electrodes, clusters of consecutive breakdowns alternate with quiet periods. The occurrence and lengths of these clusters and quiet periods depend on the evolution of β. The application of a high field can even modify the electrode surface in the abse...

  2. Mechanical assessment of local bone quality to predict failure of locked plating in a proximal humerus fracture model.

    Science.gov (United States)

    Röderer, Götz; Brianza, Stefano; Schiuma, Damiano; Schwyn, Ronald; Scola, Alexander; Gueorguiev, Boyko; Gebhard, Florian; Tami, Andrea

    2013-09-01

    The importance of osteoporosis in proximal humerus fractures is well recognized. However, the local distribution of bone quality in the humeral head may also have a significant effect because it remains unclear in what quality of bone screws of standard implants purchase. The goal of this study was to investigate whether the failure of proximal humerus locked plating can be predicted by the DensiProbe (ARI, Davos, Switzerland). A 2-part fracture with metaphyseal impaction was simulated in 12 fresh-frozen human cadaveric humeri. Using the DensiProbe, local bone quality was determined in the humeral head in the course of 6 proximal screws of a standard locking plate (Philos; Synthes GmbH, Solothurn, Switzerland). Cyclic mechanical testing with increasing axial loading until failure was performed. Bone mineral density (BMD) significantly correlated with cycles until failure. Head migration significantly increased between 1000 and 2000 loading cycles and significantly correlated with BMD after 3000 cycles. DensiProbe peak torque in all screw positions and their respective mean torque correlated significantly with the BMD values. In 3 positions, the peak torque significantly correlated with cycles to failure; here BMD significantly influenced mechanical stability. The validity of the DensiProbe was proven by the correlation between its peak torque measurements and BMD. The correlation between the peak torque and cycles to failure revealed the potential of the DensiProbe to predict the failure of locked plating in vitro. This method provides information about local bone quality, potentially making it suitable for intraoperative use by allowing the surgeon to take measures to improve stability.

  3. A fracture mechanics analysis of bonded repaired skin/stiffener structures with inclined central crack

    Energy Technology Data Exchange (ETDEWEB)

    Chung, Ki Hyun; Yang, Won Ho; Kim, Cheol; Heo, Sung Pil [Sungkyunkwan Univ., Seoul (Korea, Republic of); Ko, Myung Hoon [Daelim College, Anyang (Korea, Republic of)

    2001-07-01

    Composite patch repair of cracked aircraft structures has been accepted as one of improving fatigue life and attaining better structural integrity. Analysis for the stress intensity factor at the skin/stiffener structure with inclined central crack repaired by composite stiffened panels are developed. A numerical investigation was conducted to characterize the fracture behavior and crack growth behavior. In order to investigate the crack growth direction, Maximum Tangential Stress(MTS) criteria is used. The main objective of this research is the validation of the inclined crack patching design. In this paper, the reduction of stresses intensity factors at the crack-tip and prediction of crack growth direction are determined to evaluate the effects of various non-dimensional design parameter including; composite patch thickness and stiffener distance. The research on cracked structure subjected to mixed mode loading is accomplished and it is evident that more work using different approaches is necessary.

  4. Mechanics of tungsten blistering II: Analytical treatment and fracture mechanical assessment

    Energy Technology Data Exchange (ETDEWEB)

    Li, Muyuan; You, Jeong-Ha, E-mail: you@ipp.mpg.de

    2015-10-15

    Since a decade the blistering of pure tungsten under hydrogen implantation has been one of the major research topics in relation to the plasma–wall interaction of tungsten-armored first wall. Overall blistering may reduce the erosion lifetime of the wall. Mature blisters grown by high internal pressure are likely to burst leading to exfoliation of the surface. Therefore, the control and suppression of blistering is an important concern for sustainable operation of the tungsten-armored plasma-facing components. In this context, a quantitative assessment of the mechanical conditions for blister bulging and growth is an important concern. In this article a theoretical framework is presented to describe the bulging deformation of tungsten blisters and to estimate the mechanical driving force of blister growth. The validity of the analytical formulations based on the theory of elastic plates is evaluated with the help of finite element analysis. Plastic strains and J-integral values at the blister boundary edge are assessed by means of numerical simulation. Extensive parametric studies were performed for a range of blister geometry (cap aspect ratio), gas pressure, yield stress and hardening rate. The characteristic features of the blistering mechanics are discussed and the cracking energy is quantitatively estimated for the various combinations of parameters.

  5. Mechanics of tungsten blistering II: Analytical treatment and fracture mechanical assessment

    Science.gov (United States)

    Li, Muyuan; You, Jeong-Ha

    2015-10-01

    Since a decade the blistering of pure tungsten under hydrogen implantation has been one of the major research topics in relation to the plasma-wall interaction of tungsten-armored first wall. Overall blistering may reduce the erosion lifetime of the wall. Mature blisters grown by high internal pressure are likely to burst leading to exfoliation of the surface. Therefore, the control and suppression of blistering is an important concern for sustainable operation of the tungsten-armored plasma-facing components. In this context, a quantitative assessment of the mechanical conditions for blister bulging and growth is an important concern. In this article a theoretical framework is presented to describe the bulging deformation of tungsten blisters and to estimate the mechanical driving force of blister growth. The validity of the analytical formulations based on the theory of elastic plates is evaluated with the help of finite element analysis. Plastic strains and J-integral values at the blister boundary edge are assessed by means of numerical simulation. Extensive parametric studies were performed for a range of blister geometry (cap aspect ratio), gas pressure, yield stress and hardening rate. The characteristic features of the blistering mechanics are discussed and the cracking energy is quantitatively estimated for the various combinations of parameters.

  6. Complementary hydro-mechanical coupled finite/discrete element and microseismic modelling to predict hydraulic fracture propagation in tight shale reservoirs

    Science.gov (United States)

    Profit, Matthew; Dutko, Martin; Yu, Jianguo; Cole, Sarah; Angus, Doug; Baird, Alan

    2016-04-01

    This paper presents a novel approach to predict the propagation of hydraulic fractures in tight shale reservoirs. Many hydraulic fracture modelling schemes assume that the fracture direction is pre-seeded in the problem domain discretisation. This is a severe limitation as the reservoir often contains large numbers of pre-existing fractures that strongly influence the direction of the propagating fracture. To circumvent these shortcomings, a new fracture modelling treatment is proposed where the introduction of discrete fracture surfaces is based on new and dynamically updated geometrical entities rather than the topology of the underlying spatial discretisation. Hydraulic fracturing is an inherently coupled engineering problem with interactions between fluid flow and fracturing when the stress state of the reservoir rock attains a failure criterion. This work follows a staggered hydro-mechanical coupled finite/discrete element approach to capture the key interplay between fluid pressure and fracture growth. In field practice, the fracture growth is hidden from the design engineer and microseismicity is often used to infer hydraulic fracture lengths and directions. Microseismic output can also be computed from changes of the effective stress in the geomechanical model and compared against field microseismicity. A number of hydraulic fracture numerical examples are presented to illustrate the new technology.

  7. A probabilistic fracture mechanics approach for structural reliability assessment of space flight systems

    Science.gov (United States)

    Sutharshana, S.; Creager, M.; Ebbeler, D.; Moore, N.

    1992-01-01

    A probabilistic fracture mechanics approach for predicting the failure life distribution due to subcritical crack growth is presented. A state-of-the-art crack propagation method is used in a Monte Carlo simulation to generate a distribution of failure lives. The crack growth failure model expresses failure life as a function of stochastic parameters including environment, loads, material properties, geometry, and model specification errors. A stochastic crack growth rate model that considers the uncertainties due to scatter in the data and mode misspecification is proposed. The rationale for choosing a particular type of probability distribution for each stochastic input parameter and for specifying the distribution parameters is presented. The approach is demonstrated through a probabilistic crack growth failure analysis of a welded tube in the Space Shuttle Main Engine. A discussion of the results from this application of the methodology is given.

  8. Biosilicification mechanisms: An investigation using computational modeling and experimentation

    NARCIS (Netherlands)

    Javaheri, N.

    2016-01-01

    Biomineralization is the deposition of minerals by living organisms. The question of how and by which mechanisms nature has developed biominerals can be addressed via several complementary approaches. This dissertation investigates these mechanisms from several perspectives using both computational

  9. Multiple bilateral lower limb fractures in a 2-year-old child: previously unreported injury with a unique mechanism

    Directory of Open Access Journals (Sweden)

    Anuj Jain

    2014-10-01

    Full Text Available 【Abstract】Fall from height is a common cause of unintentional injuries in children and accounts for 6% of all trauma-related childhood deaths, usually from head injury. We report a case of a 2-year-old child with multiple fractures of the bilateral lower limbs due to this reason. A child fell from a height of around 15 feet after toppling from a alcony. He developed multiple fractures involving the right femoral shaft, right distal femoral epiphysis (Salter Harris type 2, right distal metaphysis of the tibia and fi bula, and undisplaced Salter Harris type 2 epiphyseal injury of the left distal tibia. There were no head, abdominal or spinal injuries. The patient was taken into emergency operation theatre after initial management which consisted of intravenous fl uids, blood transfusion, and splintage of both lower limbs. Fracture of the femoral shaft was treated by closed reduction and fixation using two titanium elastic nails. Distal femoral physeal injury required open eduction and fixation with K wires. Distal tibia fractures were closely reduced and managed nonoperatively in both the lower limbs. All the fractures united in four weeks. At the last follow-up, the child had no disability and was able to perform daily ctivities comfortably. We also proposed the unique mechanism of injury in this report. Key words: Multiple bilateral lower limb fractures; Fall; Child

  10. Training and Research on Probabilistic Hydro-Thermo-Mechanical Modeling of Carbon Dioxide Geological Sequestration in Fractured Porous Rocks

    Energy Technology Data Exchange (ETDEWEB)

    Gutierrez, Marte

    2013-05-31

    Colorado School of Mines conducted research and training in the development and validation of an advanced CO{sub 2} GS (Geological Sequestration) probabilistic simulation and risk assessment model. CO{sub 2} GS simulation and risk assessment is used to develop advanced numerical simulation models of the subsurface to forecast CO2 behavior and transport; optimize site operational practices; ensure site safety; and refine site monitoring, verification, and accounting efforts. As simulation models are refined with new data, the uncertainty surrounding the identified risks decrease, thereby providing more accurate risk assessment. The models considered the full coupling of multiple physical processes (geomechanical and fluid flow) and describe the effects of stochastic hydro-mechanical (H-M) parameters on the modeling of CO{sub 2} flow and transport in fractured porous rocks. Graduate students were involved in the development and validation of the model that can be used to predict the fate, movement, and storage of CO{sub 2} in subsurface formations, and to evaluate the risk of potential leakage to the atmosphere and underground aquifers. The main major contributions from the project include the development of: 1) an improved procedure to rigorously couple the simulations of hydro-thermomechanical (H-M) processes involved in CO{sub 2} GS; 2) models for the hydro-mechanical behavior of fractured porous rocks with random fracture patterns; and 3) probabilistic methods to account for the effects of stochastic fluid flow and geomechanical properties on flow, transport, storage and leakage associated with CO{sub 2} GS. The research project provided the means to educate and train graduate students in the science and technology of CO{sub 2} GS, with a focus on geologic storage. Specifically, the training included the investigation of an advanced CO{sub 2} GS simulation and risk assessment model that can be used to predict the fate, movement, and storage of CO{sub 2} in

  11. Orthopedic surgeons' attitudes to osteoporosis investigation and management after minimal trauma fracture (MTF).

    Science.gov (United States)

    Anderson-Wurf, Jane; McGirr, Joe; Seal, Alexa; Harding, Catherine

    2017-12-01

    A study of orthopedic surgeons in rural and regional Southeast Australia to determine attitudes to investigation and management of osteoporosis found they believe follow-up in regard to osteoporosis after MTF is important; responsibility for follow-up diagnosis and management lies with primary health care and current communication systems are poor. The investigation and treatment of osteoporosis after minimal trauma fracture (MTF) is regarded as sub-optimal. There is strong evidence of the benefit of identifying and treating osteoporosis after MTF, and there has been discussion of the possible role that orthopedic surgeons might play in the management of osteoporosis after MTF. The study surveyed orthopedic surgeons in rural and regional Southeast Australia to determine their attitudes to investigation and management of osteoporosis, the role health professionals should play, and the communication and co-ordination of follow-up care. A survey was developed and piloted prior to being posted to 69 orthopedic surgeons asking for their opinions about the general management of osteoporosis, and the roles and responsibilities of health professionals in dealing with osteoporosis following an MTF. Responses were received from 42 participants (60.8%) with the majority of respondents agreeing that it is important to treat osteoporosis following MTF. Less than 15% of respondents felt that it was their responsibility to initiate discussion or treatment or investigation after MTF. No respondent felt that the coordination of osteoporosis care was good and 45% stated it was poor. Communication after discharge is mostly left to the hospital (30%), while 20% stated they did not follow up at all. This study shows that many rural orthopedic surgeons believe that follow-up in regard to osteoporosis after MTF is important, that responsibility for follow-up diagnosis and management of osteoporosis lies with primary health care and the current communication systems are poor.

  12. The effect of friction stir processing on the microstructure, mechanical properties and fracture behavior of investment cast titanium aluminum vanadium

    Science.gov (United States)

    Pilchak, Adam L.

    . Thus, the mechanical properties were investigated using micropillar compression and microtensile specimens. The effect of friction stir processing on crack initiation resistance was assessed using high cycle fatigue tests conducted in four-point bend which put only the stir zone in maximum tension. The results indicated that at constant stress amplitude, there was greater than an order of magnitude increase in fatigue life after friction stir processing. In addition, the fatigue strength of the investment cast material was improved between 20 pct. and 60 pct. by friction stir processing. These improvements have been verified with a statistically significant number of tests. Finally, the wide range of microstructures created by friction stir processing provided an opportunity to study the effect of underlying microstructure on the fracture behavior of alpha + beta titanium alloys. For this purpose, high resolution fractography coupled with quantitative tilt fractography and electron backscatter diffraction was used to provide a direct link between microstructure, crystallography and fracture topography. These techniques have been used extensively to study the early stages of post-initiation crack growth in Ti-6Al-4V, especially at low stress intensity ranges (DeltaK) in the as-cast material. A limited number of experiments were also performed on Ti-6Al-4V specimens in other microstructural conditions to assess the generality of the detailed results obtained for the fully lamellar material. The results show that fracture topography depends strongly on DeltaK and microstructural length scale. In addition, many of the features observed on the fracture surface were directly related to the underlying crystallographic orientation.

  13. Numerical Investigation of Dynamic Rock Fracture Toughness Determination Using a Semi-Circular Bend Specimen in Split Hopkinson Pressure Bar Testing

    Science.gov (United States)

    Xu, Y.; Dai, F.; Xu, N. W.; Zhao, T.

    2016-03-01

    The International Society for Rock Mechanics (ISRM) has suggested a notched semi-circular bend technique in split Hopkinson pressure bar (SHPB) testing to determine the dynamic mode I fracture toughness of rock. Due to the transient nature of dynamic loading and limited experimental techniques, the dynamic fracture process associated with energy partitions remains far from being fully understood. In this study, the dynamic fracturing of the notched semi-circular bend rock specimen in SHPB testing is numerically simulated for the first time by the discrete element method (DEM) and evaluated in both microlevel and energy points of view. The results confirm the validity of this DEM model to reproduce the dynamic fracturing and the feasibility to simultaneously measure key dynamic rock fracture parameters, including initiation fracture toughness, fracture energy, and propagation fracture toughness. In particular, the force equilibrium of the specimen can be effectively achieved by virtue of a ramped incident pulse, and the fracture onset in the vicinity of the crack tip is found to synchronize with the peak force, both of which guarantee the quasistatic data reduction method employed to determine the dynamic fracture toughness. Moreover, the energy partition analysis indicates that simplifications, including friction energy neglect, can cause an overestimation of the propagation fracture toughness, especially under a higher loading rate.

  14. Femoral Geometry in Male Patients with Atraumatic Hip Fracture - Original Investigation

    Directory of Open Access Journals (Sweden)

    Gülten Tan

    2007-03-01

    Full Text Available Aims: Hip fracture is the most serious complication of osteoporosis and the most disabling type of fracture. In this study, we aimed to compare femoral geometry in hip fractured male patients aged more than 65 years old with age matched controls. Patients and Methods: 20 male patients with a history of nontraumatic hip fracture and 19 age-matched healthy controls were included in this study. Bone mineral density of neck and trochanter of hip were measured by DEXA. In addition to BMD, an experienced radiologist measured proximal femur geometric parameters potentially involved in bone strength. Results: Mean BMDs of trochanteric region were not significantly different between groups, but mean BMDs of neck region were statistically significantly lower in the hip fractured group. Neck shaft angle and femur shaft width were the geometric parameters found to be significantly higher in the hip fractured group. The correlation between femur geometric and the anthropometric measurements was present only in the kontrol group. Conclusion: We concluded that besides femur geometric measurements, correlation between these measurements might be an important factors for the fracture risk. (From the World of Osteoporosis 2007;13:15-8

  15. AN ULTRASTRUCTURE INVESTIGATION OF OSTEOPORO-SIS FRACTURE HEALING IN OVARIECTOMIZED RAT

    Institute of Scientific and Technical Information of China (English)

    楼国祥; 张先龙

    2003-01-01

    Objective To elucidate the influence of osteoporosis on the fracture healing in ovariectomized rat. Methods 24 females 8-month-old SD rats were divided randomly into two groups.12 were sham-operated(Sham)and 12 were bilaterally ovariectomized(OVX) 3 months later.The femoral fracture model were made in both groups,the healing process was observed by transmission electron microscopy(TEM) on d3,d7,d14,d21,d28,and d42 after making fracture in control groups(Sham) and the osteoporosis group(OVX).Results According to the TEM findings,the types of fracture healing cells,their ultrastructure changes and functional states were almost identical in both groups till d21 after making fracture.In OVX group,the calcified cartilage was not resorbed and replaced by new woven bone,a lot of necrosis chondrocytes were found being embedded in a calcified chondroid matrix on d28;after this period,osteoclastic bone resorption become severe gra-dually accompanied by osteocytic osteolysis during d28 to d42 of fracture healing. Conclusion Osteoporosis greatly affect the fracture healing in the later period of healing proess.It demonstrated as endochondral bone formation delayed and increased osteoclastic bone resorption which was made even more severed by osteocytic osteolysis during the period of bone callus remodelling.

  16. A vast increase in the use of CT scans for investigating occult hip fractures

    Energy Technology Data Exchange (ETDEWEB)

    Jordan, Robert, E-mail: Robert.jordan@doctors.org.uk; Dickenson, Edward, E-mail: edwarddickenson@doctors.org.uk; Westacott, Daniel, E-mail: dan_westacott@hotmail.com; Baraza, Njalalle, E-mail: njaleb@Doctors.Org.Uk; Srinivasan, Kuntrapka, E-mail: bijusri@Yahoo.Co.Uk

    2013-08-15

    Background: Early diagnosis in neck of femur fractures has been shown to improve outcome. The National Institute for Clinical Excellence recommends if an occult hip fracture is suspected then an MRI should be performed and if not available within 24 h a CT should be considered. At our centre, emergency MRI is rarely available and so CT is commonly used. Objectives: Our study aims to analyse the trends in CT use over a five year period for the diagnosis of neck of femur fractures. Methods: Both the number of patients with a hip fracture and those undergoing a CT hip to diagnose an occult injury were identified across two district general hospitals between 2006–2007 and 2010–2011. The time from initial radiograph to CT and initial radiograph to operation were calculated. Results: In 2006–2007, of 547 hip fractures, 20 CT hips were performed and 6 reported as a fractured neck of femur (30%). In 2010–2011, of 499 hip fractures, 239 CT hips were performed and 65 fractures were recognised (27%). The mean time from radiograph until CT scan was 2.0 days in 2007 and 3.2 days in 2011, which was a statistically significant difference (p < 0.001). For those diagnosed using a CT scan the mean time from admission X-ray to surgery was 1.2 days in 2007 and 3.6 days in 2011. Conclusion: Clinicians are becoming increasingly reliant on CT for the diagnosis of hip fractures with our data suggesting further imaging is one factor that can delay time to diagnosis and theatre.

  17. The effect of particle size on fracture properties and size effect of concrete

    NARCIS (Netherlands)

    Schlangen, E.; Lim, H.S.; Weerheijm, J.

    2005-01-01

    In the study the effect of scaling the material structure on the fracture behaviour of concrete is investigated. Next to this the size effect of concrete fracture strength and fracture energy is studied. The fracture mechanism of concrete made with different size aggregates are tested numerically. A

  18. Investigation of fatigue and mechanical properties of the pipe grade poly(vinyl chloride using recycled scraps

    Directory of Open Access Journals (Sweden)

    J-M. Lee

    2015-04-01

    Full Text Available In this paper, the effect of using pre-consumer PVC scraps on static and long-term mechanical properties is studied. The degradation characteristics of mixing virgin PVC with crushed pre-consumer and PVC pipe scraps are analyzed using various tools including Gel Permeation Chromatography (GPC, Thermogravimetric Analysis (TGA, X-ray fluorescence (XRF and Fourier Transform Infrared (FTIR spectroscopy. The variation of static mechanical properties as a function of adding pre-consumer PVC pipe scraps is investigated using the degradation analyses of recycled PVC scraps. In addition, fatigue tests are executed to evaluate the long-term durability of blending virgin PVC and recycled PVC scraps, and the fracture surface is investigated in detail to reveal the variation of the fracture mechanisms.

  19. Upscaling Cement Paste Microstructure to Obtain the Fracture, Shear, and Elastic Concrete Mechanical LDPM Parameters.

    Science.gov (United States)

    Sherzer, Gili; Gao, Peng; Schlangen, Erik; Ye, Guang; Gal, Erez

    2017-02-28

    Modeling the complex behavior of concrete for a specific mixture is a challenging task, as it requires bridging the cement scale and the concrete scale. We describe a multiscale analysis procedure for the modeling of concrete structures, in which material properties at the macro scale are evaluated based on lower scales. Concrete may be viewed over a range of scale sizes, from the atomic scale (10(-10) m), which is characterized by the behavior of crystalline particles of hydrated Portland cement, to the macroscopic scale (10 m). The proposed multiscale framework is based on several models, including chemical analysis at the cement paste scale, a mechanical lattice model at the cement and mortar scales, geometrical aggregate distribution models at the mortar scale, and the Lattice Discrete Particle Model (LDPM) at the concrete scale. The analysis procedure starts from a known chemical and mechanical set of parameters of the cement paste, which are then used to evaluate the mechanical properties of the LDPM concrete parameters for the fracture, shear, and elastic responses of the concrete. Although a macroscopic validation study of this procedure is presented, future research should include a comparison to additional experiments in each scale.

  20. Importance of fracture mechanics for materials development. Safety analysis of steel structures using fracture mechanics methods. Bedeutung der Bruchmechanik fuer die Werkstoffentwicklung. Sicherheitsanalyse von Bauwerken aus Stahl mit Hilfe bruchmechanischer Methoden

    Energy Technology Data Exchange (ETDEWEB)

    Dahl, W. (Technische Hochschule Aachen (Germany, F.R.). Lehrstuhl und Inst. fuer Eisenhuettenkunde)

    1991-01-01

    Following a brief description of the safety analysis procedure, the article deals with the fracture mechanics behaviour of cracked components and material test pieces. A component is assessed by comparing the loads (stress applied, maximum stress intensity, etc.) and the material characteristics (proof stress, fracture toughness, critical J-integral, etc.). Quantifying the toughness of materials is a particularly important aspect. It can be further improved by material development (increased purity, less segregation, finer grain). Generally valid equations cannot be expected but reliable estimates of the relationships are possible. (orig.).

  1. Hydraulic fracture propagation modeling and data-based fracture identification

    Science.gov (United States)

    Zhou, Jing

    Successful shale gas and tight oil production is enabled by the engineering innovation of horizontal drilling and hydraulic fracturing. Hydraulically induced fractures will most likely deviate from the bi-wing planar pattern and generate complex fracture networks due to mechanical interactions and reservoir heterogeneity, both of which render the conventional fracture simulators insufficient to characterize the fractured reservoir. Moreover, in reservoirs with ultra-low permeability, the natural fractures are widely distributed, which will result in hydraulic fractures branching and merging at the interface and consequently lead to the creation of more complex fracture networks. Thus, developing a reliable hydraulic fracturing simulator, including both mechanical interaction and fluid flow, is critical in maximizing hydrocarbon recovery and optimizing fracture/well design and completion strategy in multistage horizontal wells. A novel fully coupled reservoir flow and geomechanics model based on the dual-lattice system is developed to simulate multiple nonplanar fractures' propagation in both homogeneous and heterogeneous reservoirs with or without pre-existing natural fractures. Initiation, growth, and coalescence of the microcracks will lead to the generation of macroscopic fractures, which is explicitly mimicked by failure and removal of bonds between particles from the discrete element network. This physics-based modeling approach leads to realistic fracture patterns without using the empirical rock failure and fracture propagation criteria required in conventional continuum methods. Based on this model, a sensitivity study is performed to investigate the effects of perforation spacing, in-situ stress anisotropy, rock properties (Young's modulus, Poisson's ratio, and compressive strength), fluid properties, and natural fracture properties on hydraulic fracture propagation. In addition, since reservoirs are buried thousands of feet below the surface, the

  2. Traffic Accident Investigation: A Suitable Theme for Teaching Mechanics.

    Science.gov (United States)

    Tao, P. K.

    1987-01-01

    Suggests the development of curriculum materials on the applications of physics to traffic accident investigations as a theme for teaching mechanics. Describes several standard investigation techniques and the physics principles involved, along with some sample exercises. (TW)

  3. Mechanical properties and failure characteristics of fractured sandstone with grouting and anchorage

    Institute of Scientific and Technical Information of China (English)

    Zong Yijiang; Han Lijun; Qu Tao; Yang Shengqi

    2014-01-01

    Based on uniaxial compression experimental results on fractured sandstone with grouting and anchorage, we studied the strength and deformation properties, the failure model, crack formation and evolution laws of fractured sandstone under different conditions of anchorage. The experimental results show that the strength and elastic modulus of fractured sandstone with different fracture angles are sig-nificantly lower than those of intact sandstone. Compared with the fractured samples without anchorage, the peak strength, residual strength, peak and ultimate axial strain of fractured sandstone under different anchorage increase by 64.5-320.0%, 62.8-493.0%, and 31.6-181.4%, respectively. The number of bolts and degree of pre-stress has certain effects on the peak strength and failure model of fractured sandstone. The peak strength of fractured sandstone under different anchorage increases to some extent, and the failure model of fractured sandstone also transforms from tensile failure to tensile-shear mixed failure with the number of bolts. The pre-stress can restrain the formation and evolution process of tensile cracks, delay the failure process of fractured sandstone under anchorage and impel the transformation of failure model from brittle failure to plastic failure.

  4. Theoretical and experimental investigation of thermohydrologic processes in a partially saturated, fractured porous medium

    Energy Technology Data Exchange (ETDEWEB)

    Green, R.T.; Manteufel, R.D. [Nuclear Regulatory Commission, Washington, DC (United States). Div. of Regulatory Applications; Dodge, F.T.; Svedeman, S.J. [Southwest Research Inst., San Antonio, TX (United States). Center for Nuclear Waste Regulatory Analyses

    1993-07-01

    The performance of a geologic repository for high-level nuclear waste will be influenced to a large degree by thermohydrologic phenomena created by the emplacement of heat-generating radioactive waste. The importance of these phenomena is manifest in that they can greatly affect the movement of moisture and the resulting transport of radionuclides from the repository. Thus, these phenomena must be well understood prior to a definitive assessment of a potential repository site. An investigation has been undertaken along three separate avenues of analysis: (i) laboratory experiments, (ii) mathematical models, and (iii) similitude analysis. A summary of accomplishments to date is as follows. (1) A review of the literature on the theory of heat and mass transfer in partially saturated porous medium. (2) A development of the governing conservation and constitutive equations. (3) A development of a dimensionless form of the governing equations. (4) A numerical study of the importance and sensitivity of flow to a set of dimensionless groups. (5) A survey and evaluation of experimental measurement techniques. (6) Execution of laboratory experiments of nonisothermal flow in a porous medium with a simulated fracture.

  5. A general mixed mode fracture mechanics test specimen: The DCB-specimen loaded with uneven bending moments

    DEFF Research Database (Denmark)

    Sørensen, Bent F.; Jørgensen, K.; Jacobsen, T.K.;

    2004-01-01

    A mixed mode specimen is proposed for fracture mechanics characterisation of adhesive joints, laminates and multilayers. The specimen is a double cantilever beam specimen loaded with uneven bending moments at the two free beams. By varying the ratiobetween the two applied moments, the full mode...

  6. Experimentation, numerical simulation and the role of engineering judgement in the fracture mechanics of concrete and concrete structures

    NARCIS (Netherlands)

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

    1999-01-01

    Fracture mechanics plays a role in both structural engineering and materials engineering. The aim here is to improve understanding of the behaviour of structures and materials in the limit state. The use of numerical models can help improve the accuracy of our designs, but only if the certainty

  7. Investigating the microstructural effect on elastic and fracture behavior of polycrystals using a nonlocal lattice particle model

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Hailong; Jiao, Yang; Liu, Yongming, E-mail: Yongming.Liu@asu.edu

    2015-04-17

    A novel nonlocal lattice particle framework is proposed to investigate the microstructural effects, such as the crystallographic orientation distribution and grain boundary properties, on the mechanical performance of 2D polycrystalline materials. The classical approach of treating material anisotropy in other numerical methods, such as finite element method, is by transforming the material stiffness matrix for each crystallite. In the proposed method, the polycrystalline microstructures are constructed by rotating the underlying topological lattice structure consistently with the material crystallographic orientation while keeping the material stiffness matrix intact. By rotating the underlying lattice structure, the grain boundaries between different grains are naturally generated at locations where two crystallites meet. Thus, the grain boundary effect on the performance of the crystalline aggregates can be naturally incorporated. Parametric studies on the effects of crystallographic orientation distribution on both elastic and fracture behavior of polycrystalline materials are performed. The simulation results are compared with both analytical solutions and experimental observations in the open literature. Conclusions and discussions are drawn based on the current study.

  8. Experimental Investigation on the Basic Law of Hydraulic Fracturing After Water Pressure Control Blasting

    Science.gov (United States)

    Huang, Bingxiang; Li, Pengfeng; Ma, Jian; Chen, Shuliang

    2014-07-01

    Because of the advantages of integrating water pressure blasting and hydraulic fracturing, the use of hydraulic fracturing after water pressure control blasting is a method that is used to fully transform the structure of a coal-rock mass by increasing the number and range of hydraulic cracks. An experiment to study hydraulic fracturing after water pressure blasting on cement mortar samples (300 × 300 × 300 mm3) was conducted using a large-sized true triaxial hydraulic fracturing experimental system. A traditional hydraulic fracturing experiment was also performed for comparison. The experimental results show that water pressure blasting produces many blasting cracks, and follow-up hydraulic fracturing forces blasting cracks to propagate further and to form numerous multidirectional hydraulic cracks. Four macroscopic main hydraulic cracks in total were noted along the borehole axial and radial directions on the sample surfaces. Axial and radial main failure planes induced by macroscopic main hydraulic cracks split the sample into three big parts. Meanwhile, numerous local hydraulic cracks were formed on the main failure planes, in different directions and of different types. Local hydraulic cracks are mainly of three types: local hydraulic crack bands, local branched hydraulic cracks, and axial layered cracks. Because local hydraulic cracks produce multiple local layered failure planes and lamellar ruptures inside the sample, the integrity of the sample decreases greatly. The formation and propagation process of many multidirectional hydraulic cracks is affected by a combination of water pressure blasting, water pressure of fracturing, and the stress field of the surrounding rock. To a certain degree, the stress field of surrounding rock guides the formation and propagation process of the blasting crack and the follow-up hydraulic crack. Following hydraulic fracturing that has been conducted after water pressure blasting, the integrity of the sample is found to

  9. [Acetabular fractures].

    Science.gov (United States)

    Gänsslen, A; Oestern, H J

    2011-12-01

    Treatment of acetabular fractures requires extensive knowledge of the bony anatomy, the amount of possible exposure of the bone with the selected approaches and fracture type-dependent indications of operative treatment. Classification of the fracture with detailed analysis of the fracture morphology is the basis for decision making and planning. The primary treatment aim is the anatomic reconstruction of the acetabulum which results in optimal long-term results.The basis of this overview is the presentation of standard treatment concepts in acetabular fracture surgery. Beside characteristics of the acetabular bony anatomy, biomechanical and pathomechanical principles and the relevant radiological anatomy, the treatment options, both conservative and operative and basic principles of the indications for standard surgical approaches will be discussed.The special fracture type is discussed in detail regarding incidence, injury mechanism, concomitant injuries, options for conservative and operative treatment, quality of operative reduction and long-term results.Furthermore, epidemiological data on typical postoperative complications are evaluated.

  10. Experimental and Numerical Investigation of Preferential Flow in Fractured Network with Clogging Process

    Directory of Open Access Journals (Sweden)

    Xiaobing Chen

    2014-01-01

    Full Text Available In this study, physical experiments and numerical simulations are combined to provide a detailed understanding of flow dynamics in fracture network. Hydraulic parameters such as pressure head, velocity field, Reynolds number on certain monitoring cross points, and total flux rate are examined under various clogging conditions. Applying the COMSOL Multiphysics code to solve the Navier-Stokes equation instead of Reynolds equation and using the measured data to validate the model, the fluid flow in the horizontal 2D cross-sections of the fracture network was simulated. Results show that local clogging leads to a significant reshaping of the flow velocity field and a reduction of the transport capacity of the entire system. The flow rate distribution is highly influenced by the fractures connected to the dominant flow channels, although local disturbances in velocity field are unlikely to spread over the whole network. Also, modeling results indicate that water flow in a fracture network, compared with that in a single fracture, is likely to transit into turbulence earlier under the same hydraulic gradient due to the influence of fracture intersections.

  11. The Effect of Fracture on Quality of Life in Postmenopausal Osteoporotic Women - Original Investigation

    Directory of Open Access Journals (Sweden)

    Belgin Erhan

    2006-06-01

    Full Text Available Prolonged human life span and amelioration of the current health conditions brings up the risk of fracture related to osteoporosis as an important medical problem. In this study, we aim to study the effect of fracture on quality of life with 29 postmenopopausal women with fracture and 33 without osteoporotic fracture. Demographic data, height, maximum height, body weight, body weight at age 25, localization of fracture of the patients were recorded. All of the patients' bone mineral densities (BMD were evaluated with Dual energy X ray absorbtiometri (DXA. For evaluating quality of life Short Form 36 (SF 36 survey was used. In this study there were no statistical differences between the 2 groups when their age, menarc age, menopause age, number of pregnancies, height, body weight, maximum height and body weight at age 25 were compared. There was statistical difference between the groups in their shortening of height. When BMD levels were compared with DXA it was noted that the T scores at femur neck area and lowest area of BMD were statistically lower in the group with fractures; however there was no statistical difference in T scores of L2-L4. When we compared the quality of life of the 2 groups using SF 36 there was no statistical difference. (Osteoporoz Dünyasından 2006; 12 (2: 31-34

  12. Stiffness and strength of fracture callus. Relative rates of mechanical maturation as evaluated by a uniaxial tensile test.

    Science.gov (United States)

    Black, J; Perdigon, P; Brown, N; Pollack, S R

    1984-01-01

    Mechanical evaluation of healing fractures in rabbits suggests that tensile testing both minimizes artifacts and permits direct intrinsic determinations of tissue quality. In healing osteotomies in the rabbit fibula, there is a rapid return of stiffness at 16 days, correlating with callus maturation. The failure mode proved to be a "delamination" fracture. Values for the strength of bone (3.3 N/m2) and fibrocartilage (0.2 N/m2) correlate well with the results of other studies but are probably values of maximum tissue adhesion strength.

  13. Fracture Mechanics, Crack Propagation and Microhardness Studies on Flux Grown ErAlO3 Single Crystals

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Results on fracture mechanics and crack propagation have been obtained, making use of Vickers microhardness studies on two different crystallographic planes [(110) and (001)] of flux grown erbium aluminate crystals in the load ranging from 10~100 g. The variation of microhardness with load which is best explained by Hays and Kendall's law leads to the load independent values of hardness. Classification of cracks is dealt with and it is reported that the transition from Palmqvist to median types of cracks occurs at higher loads. The values of fracture toughness (Kc), and brittleness index (Bi) are calculated using median types of cracks.

  14. Cleavage Fracture Modeling of Pressure Vessels under Transient Thermo-Mechanical Loading

    Energy Technology Data Exchange (ETDEWEB)

    Qian, Xudong [National University of Singapore; Dodds, Robert [University of Illinois; Yin, Shengjun [ORNL; Bass, Bennett Richard [ORNL

    2008-02-01

    The next generation of fracture assessment procedures for nuclear reactor pressure vessels (RPVs) will combine nonlinear analyses of crack-front response with stochastic treatments of crack size, shape, orientation, location, material properties and thermal-pressure transients. The projected computational demands needed to support stochastic approaches with detailed 3-D, nonlinear stress analyses of vessels containing defects appear well beyond current and near-term capabilities. In the interim, 2-D models become appealing to approximate certain classes of critical flaws in RPVs, and have computational demands within reach for stochastic frameworks. The present work focuses on the capability of 2-D models to provide values for the Weibull stress fracture parameter with accuracy comparable to those from very detailed 3-D models. Weibull stress approaches provide one route to connect nonlinear vessel response with fracture toughness values measured using small laboratory specimens. The embedded axial flaw located in the RPV wall near the cladding-vessel interface emerges from current linear-elastic, stochastic investigations as a critical contributor to the conditional probability of initiation. Three different types of 2-D models reflecting this configuration are subjected to a thermal-pressure transient characteristic of a critical pressurized thermal shock event. The plane-strain, 2-D models include: the modified boundary layer (MBL) model, the middle tension (M(T)) model, and the 2-D RPV model. The 2-D MBL model provides a high quality estimate for the Weibull stress but only in crack-front regions with a positive T-stress. For crack-front locations with low constraint (T-stress < 0), the M(T) specimen provides very accurate Weibull stress values but only for pressure load acting alone on the RPV. For RPVs under a combined thermal-pressure transient, Weibull stresses computed from the 2-D RPV model demonstrate close agreement with those computed from the

  15. Cleavage Fracture Modeling of Pressure Vessels Under Transient Thermo-Mechanical Loading

    Energy Technology Data Exchange (ETDEWEB)

    Qian, Xudong [National University of Singapore; Dodds, Robert [University of Illinois; Yin, Shengjun [ORNL; Bass, Bennett Richard [ORNL

    2008-01-01

    Abstract The next generation of fracture assessment procedures for nuclear reactor pressure vessels (RPVs) will combine nonlinear analyses of crack-front response with stochastic treatments of crack size, shape, orientation, location, material properties and thermal-pressure transients. The projected computational demands needed to support stochastic approaches with detailed 3-D, nonlinear stress analyses of vessels containing defects appear well beyond current and near-term capabilities. In the interim, 2-D models be-come appealing to approximate certain classes of critical flaws in RPVs, and have computational demands within reach for stochastic frameworks. The present work focuses on the capability of 2-D models to provide values for the Weibull stress fracture parameter with accuracy comparable to those from very detailed 3-D models. Weibull stress approaches provide one route to connect nonlinear vessel response with fracture toughness values measured using small laboratory specimens. The embedded axial flaw located in the RPV wall near the cladding-vessel interface emerges from current linear-elastic, stochastic investigations as a critical contributor to the conditional probability of initiation. Three different types of 2-D models reflecting this configuration are subjected to a thermal-pressure transient characteristic of a critical pressurized thermal shock event. The plane-strain, 2-D models include: the modified boundary layer (MBL) model, the middle tension (M(T)) model, and the 2-D RPV model. The 2-D MBL model provides a high quality estimate for the Weibull stress but only in crack-front regions with a positive T-stress. For crack-front locations with low constraint (T-stress < 0), the M(T) specimen provides very accurate Weibull stress values but only for pressure load acting alone on the RPV. For RPVs under a combined thermal-pressure transient, Weibull stresses computed from the 2-D RPV model demonstrate close agreement with those computed from

  16. Fracture mechanics analysis on Smart-Cut technology. Part 2: Effect of bonding flaws

    Institute of Scientific and Technical Information of China (English)

    Bin Gu; Hongyuan Liu; Yiu-Wing Mai; Xi Qiao Feng; Shou Wen Yu

    2009-01-01

    In Part 2 of the paper on the Smart-Cut process,the effects of bonding flaws characterized by the size and internal pressure before and after splitting are studied by using fracture mechanics models. It is found that the bonding flaws with large size are prone to cause severe deviation of defect growth, leading to a non-transferred area of thin layer when splitting. In a practical Smart-Cut process where the internal pressure of bonding flaws is very small,large interfacial defects always promote defect growth in the splitting process. Meanwhile, increasing the internal pressure of the bonding flaws decreases the defect growth and its deviation before splitting. The mechanism of relaxation of stiffener constraint is proposed to clarify the effect of bonding flaws. Moreover, the progress of the splitting process is analyzed when bonding flaws are present. After splitting,those bonding flaws with large size and high internal pressure are vulnerable for the blistering of the thin film during high-temperature annealing.

  17. Fracture mechanics by three-dimensional crack-tip synchrotron X-ray microscopy.

    Science.gov (United States)

    Withers, P J

    2015-03-06

    To better understand the relationship between the nucleation and growth of defects and the local stresses and phase changes that cause them, we need both imaging and stress mapping. Here, we explore how this can be achieved by bringing together synchrotron X-ray diffraction and tomographic imaging. Conventionally, these are undertaken on separate synchrotron beamlines; however, instruments capable of both imaging and diffraction are beginning to emerge, such as ID15 at the European Synchrotron Radiation Facility and JEEP at the Diamond Light Source. This review explores the concept of three-dimensional crack-tip X-ray microscopy, bringing them together to probe the crack-tip behaviour under realistic environmental and loading conditions and to extract quantitative fracture mechanics information about the local crack-tip environment. X-ray diffraction provides information about the crack-tip stress field, phase transformations, plastic zone and crack-face tractions and forces. Time-lapse CT, besides providing information about the three-dimensional nature of the crack and its local growth rate, can also provide information as to the activation of extrinsic toughening mechanisms such as crack deflection, crack-tip zone shielding, crack bridging and crack closure. It is shown how crack-tip microscopy allows a quantitative measure of the crack-tip driving force via the stress intensity factor or the crack-tip opening displacement. Finally, further opportunities for synchrotron X-ray microscopy are explored.

  18. Thermomechanical Modeling of Sintered Silver - A Fracture Mechanics-based Approach: Extended Abstract: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Paret, Paul P [National Renewable Energy Laboratory (NREL), Golden, CO (United States); DeVoto, Douglas J [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Narumanchi, Sreekant V [National Renewable Energy Laboratory (NREL), Golden, CO (United States)

    2017-09-01

    Sintered silver has proven to be a promising candidate for use as a die-attach and substrate-attach material in automotive power electronics components. It holds promise of greater reliability than lead-based and lead-free solders, especially at higher temperatures (less than 200 degrees Celcius). Accurate predictive lifetime models of sintered silver need to be developed and its failure mechanisms thoroughly characterized before it can be deployed as a die-attach or substrate-attach material in wide-bandgap device-based packages. We present a finite element method (FEM) modeling methodology that can offer greater accuracy in predicting the failure of sintered silver under accelerated thermal cycling. A fracture mechanics-based approach is adopted in the FEM model, and J-integral/thermal cycle values are computed. In this paper, we outline the procedures for obtaining the J-integral/thermal cycle values in a computational model and report on the possible advantage of using these values as modeling parameters in a predictive lifetime model.

  19. Fracture Mechanics Method for Word Embedding Generation of Neural Probabilistic Linguistic Model

    Directory of Open Access Journals (Sweden)

    Size Bi

    2016-01-01

    Full Text Available Word embedding, a lexical vector representation generated via the neural linguistic model (NLM, is empirically demonstrated to be appropriate for improvement of the performance of traditional language model. However, the supreme dimensionality that is inherent in NLM contributes to the problems of hyperparameters and long-time training in modeling. Here, we propose a force-directed method to improve such problems for simplifying the generation of word embedding. In this framework, each word is assumed as a point in the real world; thus it can approximately simulate the physical movement following certain mechanics. To simulate the variation of meaning in phrases, we use the fracture mechanics to do the formation and breakdown of meaning combined by a 2-gram word group. With the experiments on the natural linguistic tasks of part-of-speech tagging, named entity recognition and semantic role labeling, the result demonstrated that the 2-dimensional word embedding can rival the word embeddings generated by classic NLMs, in terms of accuracy, recall, and text visualization.

  20. A witnessed case of a classic metaphyseal fracture caused during IV line placement in a child: Insight into mechanism of injury.

    Science.gov (United States)

    Burrell, Tanya; Opfer, Erin; Berglund, Lisa; Lowe, Lisa H; Anderst, James

    2015-10-01

    Recent publications argue that classic metaphyseal fractures are caused by rickets as opposed to trauma. Previous case reports of accidental traumatic classic metaphyseal fractures have been discounted due to lack of identification of the fracture at the time of the traumatic event, and lack of an evaluation for boney metabolic disorders. We report a case of a 20 day old male with a diagnosis of congenital vertical talus who sustained a classic metaphyseal fracture of the distal tibia during manipulation in preparation for intravenous line placement. The mechanics of the event causing the classic metaphyseal fracture were witnessed and accompanied by an audible "pop". Prior x-rays of the tibia demonstrate normal osseous morphology, and an evaluation for boney metabolic disorders was normal. This case identifies a traumatic classic metaphyseal fracture and provides insight into the types of forces necessary to cause such a fracture.

  1. Effectiveness of surgical rib fixation on prolonged mechanical ventilation in patients with traumatic rib fractures: A propensity score-matched analysis.

    Science.gov (United States)

    Wada, Tomoki; Yasunaga, Hideo; Inokuchi, Ryota; Matsui, Hiroki; Matsubara, Takehiro; Ueda, Yoshihiro; Gunshin, Masataka; Ishii, Takeshi; Doi, Kent; Kitsuta, Yoichi; Nakajima, Susumu; Fushimi, Kiyohide; Yahagi, Naoki

    2015-12-01

    We investigated whether surgical rib fixation improved outcomes in patients with traumatic rib fractures. This was a retrospective study using a Japanese administrative claim and discharge database. We included patients with traumatic rib fractures admitted to hospitals where surgical rib fixation was available from July 1 2010, to March 31, 2013. We detected patients who underwent surgical rib fixation within 10 days of hospital admission (surgical group) and those who did not (control group). The main outcome was prolonged mechanical ventilation, defined as that performed for 5 or more days, or death within 28 days. One-to-four propensity score matching was performed between the 2 groups with adjustment for possible confounders. Among 4577 eligible patients, 90 (2.0%) underwent the surgical rib fixation. After the matching, we obtained 84 and 336 patients in the surgical and control groups, respectively. Logistic regression analyses showed that the surgical group was significantly less likely to receive prolonged mechanical ventilation or die within 28 days than the control group (22.6% vs 33.3%; odds ratio, 0.59; 95% confidence interval, 0.36-0.96; P=.034). Surgical rib fixation within 10 days of hospital admission may improve outcomes in patients with traumatic rib fractures. Copyright © 2015 Elsevier Inc. All rights reserved.

  2. Rib stress fractures among rowers: definition, epidemiology, mechanisms, risk factors and effectiveness of injury prevention strategies.

    Science.gov (United States)

    McDonnell, Lisa K; Hume, Patria A; Nolte, Volker

    2011-11-01

    Rib stress fractures (RSFs) can have serious effects on rowing training and performance and accordingly represent an important topic for sports medicine practitioners. Therefore, the aim of this review is to outline the definition, epidemiology, mechanisms, intrinsic and extrinsic risk factors, injury management and injury prevention strategies for RSF in rowers. To this end, nine relevant books, 140 journal articles, the proceedings of five conferences and two unpublished presentations were reviewed after searches of electronic databases using the keywords 'rowing', 'rib', 'stress fracture', 'injury', 'mechanics' and 'kinetics'. The review showed that RSF is an incomplete fracture occurring from an imbalance between the rate of bone resorption and the rate of bone formation. RSF occurs in 8.1-16.4% of elite rowers, 2% of university rowers and 1% of junior elite rowers. Approximately 86% of rowing RSF cases with known locations occur in ribs four to eight, mostly along the anterolateral/lateral rib cage. Elite rowers are more likely to experience RSF than nonelite rowers. Injury occurrence is equal among sweep rowers and scullers, but the regional location of the injury differs. The mechanism of injury is multifactorial with numerous intrinsic and extrinsic risk factors contributing. Posterior-directed resultant forces arising from the forward directed force vector through the arms to the oar handle in combination with the force vector induced by the scapula retractors during mid-drive, or repetitive stress from the external obliques and rectus abdominis in the 'finish' position, may be responsible for RSF. Joint hypomobility, vertebral malalignment or low bone mineral density may be associated with RSF. Case studies have shown increased risk associated with amenorrhoea, low bone density or poor technique, in combination with increases in training volume. Training volume alone may have less effect on injury than other factors. Large differences in seat and handle

  3. Research on the Fracture Properties and Modification Mechanism of Polyester Fiber and SBR Latex Modified Cement Concrete

    Directory of Open Access Journals (Sweden)

    Mingkai Zhou

    2016-01-01

    Full Text Available Polyester fiber and SBR latex cement concrete is prepared as pavement surface material; its fracture properties including fracture toughness, fracture energy, CMOD, and flexural strength are studied comparing with those of normal concrete (NC, polyester fiber modified concrete (FMC, SBR polymer modified concrete (SMC, and the combination of polyester fiber and SBR polymer modified concrete (FSMC. The modification mechanism of the latex and fiber on the concrete was also studied by the methods including X-ray test, chemically combined water, heat of hydration, water loss, and scanning electron microscope. Results indicated that the concrete modified by latex and polyester fiber has flexural strength, fracture toughness, and fracture energy of 44.4%, 397.0%, and 462.8% higher than the reference normal concrete, the polymer retarded the hydration process and reduced the hydration degree of cement at early age, while the hydration degree is promoted by the polymer film for its excellent water resistance after 28 d, and the bond between the fiber and cement paste is improved by the latex.

  4. Multiple bilateral lower limb fractures in a 2-year-old child: previously unreported injury with a unique mechanism

    Institute of Scientific and Technical Information of China (English)

    Basant Repswal; Anuj Jain; Sunil Gupta; Aditya Aggarwal; Tushar Kohli; Devendra Pathrot

    2014-01-01

    Fall from height is a common cause of unintentional injuries in children and accounts for 6% of all trauma-related childhood deaths,usually from head injury.We report a case of a 2-year-old child with multiple fractures of the bilateral lower limbs due to this reason.A child fell from a height of around 15 feet after toppling from a balcony.He developed multiple fractures involving the right femoral shaft,right distal femoral epiphysis (Salter Harris type 2),right distal metaphysis of the tibia and fibula,and undisplaced Salter Harris type 2 epiphyseal injury of the left distal tibia.There were no head,abdominal or spinal injuries.The patient was taken into emergency operation theatre after initial management which consisted of intravenous fluids,blood transfusion,and splintage of both lower limbs.Fracture of the femoral shaft was treated by closed reduction and fixation using two titanium elastic nails.Distal femoral physeal injury required open reduction and fixation with K wires.Distal tibia fractures were closely reduced and managed nonoperatively in both the lower limbs.All the fractures united in four weeks.At the last follow-up,the child had no disability and was able to perform daily activities comfortably.We also proposed the unique mechanism of injury in this report.

  5. Probabilistic fracture mechanics applied for DHC assessment in the cool-down transients for CANDU pressure tubes

    Energy Technology Data Exchange (ETDEWEB)

    Radu, Vasile, E-mail: vasile.radu@nuclear.ro [Institute for Nuclear Research Pitesti, 1st Campului Street, 115400 Mioveni, Arges, P.O. Box 78, Mioveni (Romania); Roth, Maria [Institute for Nuclear Research Pitesti, 1st Campului Street, 115400 Mioveni, Arges, P.O. Box 78, Mioveni (Romania)

    2012-12-15

    For CANDU pressure tubes made from Zr-2.5%Nb alloy, the mechanism called delayed hydride cracking (DHC) is widely recognized as main mechanism responsible for crack initiation and propagation in the pipe wall. Generation of some blunt flaws at the inner pressure tube surface during refueling by fuel bundle bearing pad or by debris fretting, combined with hydrogen/deuterium up-take (20-40 ppm) from normal corrosion process with coolant, may lead to crack initiation and growth. The process is governed by hydrogen hysteresis of terminal solid solubility limits in Zirconium and the diffusion of hydrogen atoms in the stress gradient near to a stress spot (flaw). Creep and irradiation growth under normal operating conditions promote the specific mechanisms for Zirconium alloys, which result in circumferential expansion, accompanied by wall thinning and length increasing. These complicate damage mechanisms in the case of CANDU pressure tubes that are also are affected by irradiation environment in the reactor core. The structural integrity assessment of CANDU fuel channels is based on the technical requirements and methodology stated in the Canadian Standard N285.8. Usually it works with fracture mechanics principles in a deterministic manner. However, there are inherent uncertainties from the in-service inspection, which are associated with those from material properties determination; therefore a necessary conservatism in deterministic evaluation should be used. Probabilistic approach, based on fracture mechanics principle and appropriate limit state functions defined as fracture criteria, appears as a promising complementary way to evaluate structural integrity of CANDU pressure tubes. To perform this, one has to account for the uncertainties that are associated with the main parameters for pressure tube assessment, such as: flaws distribution and sizing, initial hydrogen concentration, fracture toughness, DHC rate and dimensional changes induced by long term

  6. Investigation of microstructure and mechanical properties of Cu/ZnO nano composite produced by ARB process

    Science.gov (United States)

    Shahhoseyni, M.; Qods, F.

    2014-08-01

    In this study, ARB process was used to produce Cu/Nano ZnO composite and samples were subjected up to six ARB cycles. Microstructural and mechanical properties of the composite within different ARB cycles were investigated by scanning electron microscopy (SEM) and tensile and micro hardness tests. The results showed that increasing the number of cycles, not only helped the distribution of reinforcing Nano-reinforcement in the matrix, but also improved the initial bonding strength, so that at final cycles, structural integration was achieved. Mechanical experiments also showed that increasing the number of ARB cycles, increased yield and ultimate strengths as well as micro hardness. However, elongation decreased up to second cycle and then increased by later final cycles. SEM studies of the fracture surfaces after the tensile test showed that the fracture mechanism of the composite was shear ductile rupture.

  7. Model of mechanical representation of the formation of natural fractures inside a petroleum reservoir; Modele de representation mecanique de la formation des fractures naturelles d'un reservoir petrolier

    Energy Technology Data Exchange (ETDEWEB)

    Picard, D.

    2005-09-15

    The optimisation of the oil production requires a better characterisation of naturally fractured reservoirs. We consider and analyse two spatial distributions. One with systematic joints is arranged in an homogeneous way; joint spacing is linked to individual bedding thickness with propagation frequently interrupted by stratigraphic interfaces (single layer jointing). The second, so-called fracture swarms, consists in fractures clustering, where stratigraphic interfaces seem to play a minor role. The analysis is based on the singularity theory and matched asymptotic expansions method with a fine scale for local perturbations and a global one for general trends. We examine the conditions of fracture propagation that are determined herein using simultaneously two fracture criteria an energy and a stress condition. We consider two modes of loading. Usually, the joint (crack opening mode) and fracture swarm growths are explained by a first order phenomenon involving effective traction orthogonal to fracture plane. Although commonly used, this hypothesis seems unrealistic in many circumstances and may conflict with geological observations. Then, we try to describe fracture growth as a second order phenomena resulting from crack parallel compression. As far as propagation across layer interfaces is concerned, the effect of loading and geometry has been summarised in maps of fracture mechanisms, describing areas of 'step-over', 'straight through propagation' and 'crack arrest'. Fracture criteria, relative size of heterogeneities, contrast of mechanical properties between bed and layer are parameters of the problem. For fracture swarms, we present a discussion bringing out what is reasonable as a loading to justify their morphology. In particular, horizontal effective tension is unable to explain neighbouring joints. Simultaneous propagation of parallel near cracks is explained by finite width cracks growing under the influence of vertical

  8. Combined finite element and multibody musculoskeletal investigation of a fractured clavicle with reconstruction plate

    DEFF Research Database (Denmark)

    Cronskar, Marie; Rasmussen, John; Tinnsten, Mats

    2015-01-01

    This paper addresses the various treatment options for clavicle fractures by means of computational models, more precisely cases with a need for internal fixation: non-unions and certain complex fractures. The motivation for the work is that treatment can be enhanced by a better understanding...... of the loading of the clavicle and fixation device. This study aimed to develop a method for realistic simulation of stresses in the bone and fixation device in the case of a fractured clavicle. A finite element (FE) mesh of the clavicle geometry was created from computer tomography (CT) data and imported...... into the FE solver where the model was subjected to muscle forces and other boundary conditions from a multibody musculoskeletal model performing a typical activity of daily life. A reconstruction plate and screws were also imported into the model. The combination models returned stresses and displacements...

  9. An investigation of fracture and fatigue crack growth behavior of cast niobium aluminide intermetallics

    Energy Technology Data Exchange (ETDEWEB)

    Ye, F.; Soboyejo, W.O. [Ohio State Univ., Columbus, OH (United States). Dept. of Materials Science and Engineering; Farkas, D. [Department of Materials Science and Engineering, Virginia Polytechnic Institute and State University, 213 Holden Hall, Blacksburg, VA 24061-0237 (United States)

    1999-05-31

    This paper presents the results of a combined experimental and theoretical study of fracture toughness and fatigue crack growth in cast Nb-15Al-xTi (x=10, 25 and 40 at%) niobium aluminide-based intermetallics. Fracture toughness and fatigue crack growth resistance are shown to improve significantly in the cast alloy containing 40 at% Ti. The improvements in the fracture toughness of the 40Ti alloy are shown to be due to the combined effects of ligament toughening, crack-tip plasticity and crack-tip blunting. The atomistic simulations show that the increased plasticity in these alloys is associated with their higher Ti content. The micromechanisms of fatigue crack growth are also elucidated. The implications of the results are discussed for potential structural application of niobium aluminide intermetallics. (orig.) 19 refs.

  10. Experimental Investigation of Seepage Properties of Fractured Rocks Under Different Confining Pressures

    Science.gov (United States)

    Ma, D.; Miao, X. X.; Chen, Z. Q.; Mao, X. B.

    2013-09-01

    The effectiveness of transmitting underground water in rock fractures is strongly influenced by the widths of the fractures and their interconnections. However, the geometries needed for water flow in fractured rock are also heavily controlled by the confining pressure conditions. This paper is intended to study the seepage properties of fractured rocks under different confining pressures. In order to do this, we designed and manufactured a water flow apparatus that can be connected to the electro-hydraulic servo-controlled test system MTS815.02, which provides loading and exhibits external pressures in the test. Using this apparatus, we tested fractured mudstone, limestone and sandstone specimens and obtained the relationship between seepage properties and variations in confining pressure. The calculation of the seepage properties based on the collection of water flow and confining pressure differences is specifically influenced by non-Darcy flow. The results show that: (1) The seepage properties of fractured rocks are related to confining pressure, i.e. with the increase of confining pressure, the permeability decreases and the absolute value of non-Darcy flow coefficient increases. (2) The sandstone coefficients and range from to m2 and to m-1, respectively, and exhibit a greater change compared to coefficients of mudstone and limestone. (3) From the regression analysis of experimental data, it is concluded that the polynomial function is a better fit than the power and logarithmic functions. The results obtained can provide an important reference for understanding the stability of rock surrounding roadways toward prevention of underground water gushing-out, and for developing underground resources (e.g. coal).

  11. Influence of mechanical rock properties and fracture healing rate on crustal fluid flow dynamics

    Science.gov (United States)

    Sachau, Till; Bons, Paul; Gomez-Rivas, Enrique; Koehn, Daniel; de Riese, Tamara

    2016-04-01

    Fluid flow in the Earth's crust is very slow over extended periods of time, during which it occurs within the connected pore space of rocks. If the fluid production rate exceeds a certain threshold, matrix permeability alone is insufficient to drain the fluid volume and fluid pressure builds up, thereby reducing the effective stress supported by the rock matrix. Hydraulic fractures form once the effective pressure exceeds the tensile strength of the rock matrix and act subsequently as highly effective fluid conduits. Once local fluid pressure is sufficiently low again, flow ceases and fractures begin to heal. Since fluid flow is controlled by the alternation of fracture permeability and matrix permeability, the flow rate in the system is strongly discontinuous and occurs in intermittent pulses. Resulting hydraulic fracture networks are largely self-organized: opening and subsequent healing of hydraulic fractures depends on the local fluid pressure and on the time-span between fluid pulses. We simulate this process with a computer model and describe the resulting dynamics statistically. Special interest is given to a) the spatially and temporally discontinuous formation and closure of fractures and fracture networks and b) the total flow rate over time. The computer model consists of a crustal-scale dual-porosity setup. Control parameters are the pressure- and time-dependent fracture healing rate, and the strength and the permeability of the intact rock. Statistical analysis involves determination of the multifractal properties and of the power spectral density of the temporal development of the total drainage rate and hydraulic fractures. References Bons, P. D. (2001). The formation of large quartz veins by rapid ascent of fluids in mobile hydrofractures. Tectonophysics, 336, 1-17. Miller, S. a., & Nur, A. (2000). Permeability as a toggle switch in fluid-controlled crustal processes. Earth and Planetary Science Letters, 183(1-2), 133-146. Sachau, T., Bons, P. D

  12. Comparative investigation of micro-flaw models for the simulation of brittle fracture in rock

    CSIR Research Space (South Africa)

    Sellers, E

    1997-07-01

    Full Text Available on each potential fracture site. The properties are given in Table 1. The ?aws and intergran- ular sites have a nonzero residual cohesion to simulate ductile ?ow and the intragranular sites have a higher ini- tial cohesion which is reduced to zero.... T. (1996): Quanti?cation of stope fracture zone behaviour in deep level gold mines. J. SAIMM (in prep.) Marder, M.; Gross, S. (1995): Origin of crack tip instabilities. J. Mech. Phys. Solids 43, 1?48 Sellers, E. J. (1994): An anisotropic damage model...

  13. Simulation of complex fracture networks influenced by natural fractures in shale gas reservoir

    Directory of Open Access Journals (Sweden)

    Zhao Jinzhou

    2014-10-01

    Full Text Available When hydraulic fractures intersect with natural fractures, the geometry and complexity of a fracture network are determined by the initiation and propagation pattern which is affected by a number of factors. Based on the fracture mechanics, the criterion for initiation and propagation of a fracture was introduced to analyze the tendency of a propagating angle and factors affecting propagating pressure. On this basis, a mathematic model with a complex fracture network was established to investigate how the fracture network form changes with different parameters, including rock mechanics, in-situ stress distribution, fracture properties, and frac treatment parameters. The solving process of this model was accelerated by classifying the calculation nodes on the extending direction of the fracture by equal pressure gradients, and solving the geometrical parameters prior to the iteration fitting flow distribution. With the initiation and propagation criterion as the bases for the propagation of branch fractures, this method decreased the iteration times through eliminating the fitting of the fracture length in conventional 3D fracture simulation. The simulation results indicated that the formation with abundant natural fractures and smaller in-situ stress difference is sufficient conditions for fracture network development. If the pressure in the hydraulic fractures can be kept at a high level by temporary sealing or diversion, the branch fractures will propagate further with minor curvature radius, thus enlarging the reservoir stimulation area. The simulated shape of fracture network can be well matched with the field microseismic mapping in data point range and distribution density, validating the accuracy of this model.

  14. A New Approach to the Modeling and Analysis of Fracture through Extension of Continuum Mechanics to the Nanoscale

    KAUST Repository

    Sendova, T.

    2010-02-15

    In this paper we focus on the analysis of the partial differential equations arising from a new approach to modeling brittle fracture based on an extension of continuum mechanics to the nanoscale. It is shown that ascribing constant surface tension to the fracture surfaces and using the appropriate crack surface boundary condition given by the jump momentum balance leads to a sharp crack opening profile at the crack tip but predicts logarithmically singular crack tip stress. However, a modified model, where the surface excess property is responsive to the curvature of the fracture surfaces, yields bounded stresses and a cusp-like opening profile at the crack tip. Further, two possible fracture criteria in the context of the new theory are discussed. The first is an energy-based crack growth condition, while the second employs the finite crack tip stress the model predicts. The classical notion of energy release rate is based upon the singular solution, whereas for the modeling approach adopted here, a notion analogous to the energy release rate arises through a different mechanism associated with the rate of working of the surface excess properties at the crack tip. © The Author(s), 2010.

  15. Mechanical Properties and Fracture Behaviour of LMD Produced 2.4682 and Wrought 2.4630 Dissimilar Welds

    Science.gov (United States)

    Dahmen, Martin; Göbel, Marco

    A bearing made of Stellite 31 (2.4682) has to be welded onto a housing of Nimonic 75 (2.4630) by autogenous laser beam welding. The bearing part is produced by laser metal deposition (LMD), the housing consists of wrought sheet metal. An investigation is undertaken in order to study the effect of the anisotropy of the LMD part on the weld quality. Tensile specimens were produced and tested under varying load directions and test temperatures, and application of different weld heat treatments. The fractured specimens were analysed by metallography and fractography. Tensile tests at room temperature show a dependency of the fracture location and the mode of failure on the load direction with respect to the layer direction in conjunction with the heat treatment. At elevated temperature of 750° all specimens broke in the base material of 2.4630 in ductile fracture mode. Strength measured supersedes the values of either of the base materials.

  16. Fracture mechanism of TiAl intermetallics caused by hydride and atomic hydrogen

    Institute of Scientific and Technical Information of China (English)

    高克玮; 王燕斌; 林志; 乔利杰; 褚武扬

    1999-01-01

    Hydrogen embrittlement (HE) of TiAl intermetallics was studied at room temperature. The results showed that there were two forms of HE in TiAl intermetallics, i.e. hydride HE and atomic HE. Most of hydrogen in TiAl intermetallics was transformed into hydrides at room temperature. The hydride exists as (TiAl)Hx for a low hydrogen concentration while it exists in several forms for a higher hydrogen concentration. Stress intensity factor KIC decreased with increase in hydride concentration. KIC decreased further when TiAl intermetallics were charged cathodically with hydrogen in 1 mol/L H2SO4 solution. Stress intensity factor during hydrogen charging KIH was about 50% KIC. 20% of the decrease was caused by hydrides while 30% was caused by atomic hydrogen. Mechanism of HE caused hydrides was the same as any other second phase in nature. Delayed fracture caused by atomic hydrogen resulted from hydrogen induced local plastic deformation.

  17. NASCRAC - A computer code for fracture mechanics analysis of crack growth

    Science.gov (United States)

    Harris, D. O.; Eason, E. D.; Thomas, J. M.; Bianca, C. J.; Salter, L. D.

    1987-01-01

    NASCRAC - a computer code for fracture