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Sample records for atomistic fracture mechanics

  1. Atomistic simulations of fracture

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-12-31

    Embedded atom interaction potentials are used to simulate the atomistic aspects of the fracture process. Simulations are presented for the behavior of cracks in pure metals and intermetallics, near the Griffith condition. The materials considered include Fe, Cu, Ni as well as Fe, Ni, Co, and Ti aluminides. The work focuses on the comparative study of fracture behavior in the different materials. The role of the atomic relaxation at the crack tip and of lattice trapping phenomena is analyzed.

  2. Atomistic Simulations of Nanotube Fracture

    CERN Document Server

    Belytschko, T; Schatz, G; Ruoff, R S

    2002-01-01

    The fracture of carbon nanotubes is studied by atomistic simulations. The fracture behavior is found to be almost independent of the separation energy and to depend primarily on the inflection point in the interatomic potential. The rangle of fracture strians compares well with experimental results, but predicted range of fracture stresses is marketly higher than observed. Various plausible small-scale defects do not suffice to bring the failure stresses into agreement with available experimental results. As in the experiments, the fracture of carbon nanotubes is predicted to be brittle. The results show moderate dependence of fracture strength on chirality.

  3. A comparison of finite element and atomistic modelling of fracture

    International Nuclear Information System (INIS)

    Are the cohesive laws of interfaces sufficient for modelling fracture in polycrystals using the cohesive zone model? We examine this question by comparing a fully atomistic simulation of a silicon polycrystal with a finite element simulation with a similar overall geometry. The cohesive laws used in the finite element simulation are measured atomistically. We describe in detail how to convert the output of atomistic grain boundary fracture simulations into the piecewise linear form needed by a cohesive zone model. We discuss the effects of grain boundary microparameters (the choice of section of the interface, the translations of the grains relative to one another and the cutting plane of each lattice orientation) on the cohesive laws and polycrystal fracture. We find that the atomistic simulations fracture at lower levels of external stress, indicating that the initiation of fracture in the atomistic simulations is likely dominated by irregular atomic structures at external faces, internal edges, corners and junctions of grains. Thus, the cohesive properties of interfaces alone are not likely to be sufficient for modelling the fracture of polycrystals using continuum methods

  4. 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.

  5. 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...

  6. Atomistic Mechanisms of Fatigue in Nanocrystalline Metals

    Science.gov (United States)

    Farkas, D.; Willemann, M.; Hyde, B.

    2005-04-01

    We investigate the mechanisms of fatigue behavior in nanocrystalline metals at the atomic scale using empirical force laws and molecular level simulations. A combination of molecular statics and molecular dynamics was used to deal with the time scale limitations of molecular dynamics. We show that the main atomistic mechanism of fatigue crack propagation in these materials is the formation of nanovoids ahead of the main crack. The results obtained for crack advance as a function of stress intensity amplitude are consistent with experimental studies and a Paris law exponent of about 2.

  7. Atomistic modeling of BN nanofillers for mechanical and thermal properties: a review

    Science.gov (United States)

    Kumar, Rajesh; Parashar, Avinash

    2015-12-01

    Due to their exceptional mechanical properties, thermal conductivity and a wide band gap (5-6 eV), boron nitride nanotubes and nanosheets have promising applications in the field of engineering and biomedical science. Accurate modeling of failure or fracture in a nanomaterial inherently involves coupling of atomic domains of cracks and voids as well as a deformation mechanism originating from grain boundaries. This review highlights the recent progress made in the atomistic modeling of boron nitride nanofillers. Continuous improvements in computational power have made it possible to study the structural properties of these nanofillers at the atomistic scale.

  8. Atomistically derived cohesive zone model of intergranular fracture in polycrystalline graphene

    Science.gov (United States)

    Guin, Laurent; Raphanel, Jean L.; Kysar, Jeffrey W.

    2016-06-01

    Pristine single crystal graphene is the strongest known two-dimensional material, and its nonlinear anisotropic mechanical properties are well understood from the atomic length scale up to a continuum description. However, experiments indicate that grain boundaries in the polycrystalline form reduce the mechanical behavior of polycrystalline graphene. Herein, we perform atomistic-scale molecular dynamics simulations of the deformation and fracture of graphene grain boundaries and express the results as continuum cohesive zone models (CZMs) that embed notions of the grain boundary ultimate strength and fracture toughness. To facilitate energy balance, we employ a new methodology that simulates a quasi-static controlled crack propagation which renders the kinetic energy contribution to the total energy negligible. We verify good agreement between Griffith's critical energy release rate and the work of separation of the CZM, and we note that the energy of crack edges and fracture toughness differs by about 35%, which is attributed to the phenomenon of bond trapping. This justifies the implementation of the CZM within the context of the finite element method (FEM). To enhance computational efficiency in the FEM implementation, we discuss the use of scaled traction-separation laws (TSLs) for larger element sizes. As a final result, we have established that the failure characteristics of pristine graphene and high tilt angle bicrystals differ by less than 10%. This result suggests that one could use a unique or a few typical TSLs as a good approximation for the CZMs associated with the mechanical simulations of the polycrystalline graphene.

  9. Atomistic mechanisms of fatigue in nanotwinned metals

    International Nuclear Information System (INIS)

    We investigate the fatigue behavior of nanotwinned Cu using a combination of molecular statics and molecular dynamics simulations. The presence of nanoscale twins is found to enhance fatigue crack growth resistance. For the twin-free nanocrystalline samples, the fatigue crack propagates by linking the nanovoids that are formed ahead of the crack tip. In the case of the nanotwinned samples, however, it advances as the crack tip alternately blunts and re-sharpens due to dislocation emission and slip. Both detwinning and crack closure are observed in the path of the fatigue crack in nanotwinned samples with a high density of twin boundaries. As the twin number per grain (quantified by the ratio of the mean grain size to the twin boundary spacing d/λ) increases, detwinning increases the dissipated energy of fatigue cracking, leading to enhanced fatigue resistance. The atomistic simulations show that fatigue crack growth in nanotwinned Cu conforms to Paris’ law. In conjunction with the experimental results, we obtain a quantitative estimation of the Paris’ law exponent (∼4.0), which is in agreement with the theoretical predictions from the damage accumulation model

  10. Intergranular fracture in UO2: derivation of traction-separation law from atomistic simulations

    Energy Technology Data Exchange (ETDEWEB)

    Yongfeng Zhang; Paul C Millett; Michael R Tonks; Xian-Ming Bai; S Bulent Biner

    2013-10-01

    In this study, the intergranular fracture behavior of UO2 was studied by molecular dynamics simulations using the Basak potential. In addition, the constitutive traction-separation law was derived from atomistic data using the cohesive-zone model. In the simulations a bicrystal model with the (100) symmetric tilt E5 grain boundaries was utilized. Uniaxial tension along the grain boundary normal was applied to simulate Mode-I fracture. The fracture was observed to propagate along the grain boundary by micro-pore nucleation and coalescence, giving an overall intergranular fracture behavior. Phase transformations from the Fluorite to the Rutile and Scrutinyite phases were identified at the propagating crack tips. These new phases are metastable and they transformed back to the Fluorite phase at the wake of crack tips as the local stress concentration was relieved by complete cracking. Such transient behavior observed at atomistic scale was found to substantially increase the energy release rate for fracture. Insertion of Xe gas into the initial notch showed minor effect on the overall fracture behavior.

  11. 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.)

  12. Dislocation pinning effects on fracture behavior: Atomistic and dislocation dynamics simulations

    Science.gov (United States)

    Noronha, S. J.; Farkas, D.

    2002-10-01

    We introduce an approach in which results from atomistic simulations are combined with discrete dislocation dynamics simulations of crack-tip plasticity. The method is used to study the effects of dislocation pinning due to grain boundaries or secondary particles on the fracture behavior of aluminum. We find that the fracture resistance is reduced with decreasing pinning distance. The results show that the pinning of the dislocations causes a net decrease in the shear stress projected on the slip plane, preventing further dislocation emission. Semibrittle cleavage occurs after a certain number of dislocations is emitted.

  13. Probabilistic fracture mechanics

    International Nuclear Information System (INIS)

    It has been attempted to present the elements of probabilistic fracture mechanics in a self-contained way. First, for brittle fracture, damage theories are discussed which allow for the effects of both size and local strength of the structure on the probability of fracture. Second, combined crack and damage theories are presented. They provide insight into macro-crack formation and take into account the effects of crack orientation and multiaxial states of stress. For fatigue, both the two-phase theory of damage and crack extension as well as the cumulative theory (of damage or of crack extension) are presented. They give estimates for the lifetime of a structure under random load. The effect of random material properties may be included. Finally, an assessment of the probability of failure of reactor pressure vessels is discussed. There, brittle fracture and fatigue are taken into account and both fracture toughness and crack size are considered to be random quantities. (Auth.)

  14. Comparative study of embedded atom potentials for atomistic simulations of fracture in α-iron

    International Nuclear Information System (INIS)

    Atomistic simulations play a crucial role in advancing our understanding of the crack-tip processes that take place during fracture of semi-brittle materials like α-iron. As with all atomistic simulations, the results of such simulations however depend critically on the underlying atomic interaction model. Here, we present a systematic study of eight α-iron embedded atom method potentials used to model cracks subjected to plane strain mode-I loading conditions in six different crystal orientations. Molecular statics simulations are used to determine the fracture behavior (cleavage, dislocation emission, twinning) and the critical stress intensity factor KIc. The structural transformations in front of the crack tips, and in particular the occurrence of {1 1 0} planar faults, are analyzed in detail and related to the strain-dependent generalized stacking fault energy curve. The simulation results are discussed in terms of theoretical fracture criteria and compared to recent experimental data. The different potentials are ranked according to their capability to model the experimentally observed fracture behavior. (paper)

  15. Atomistic simulations of Mg-Cu metallic glasses: Mechanical properties

    DEFF Research Database (Denmark)

    Bailey, Nicholas; Schiøtz, Jakob; Jacobsen, Karsten Wedel

    2004-01-01

    The atomistic mechanisms of plastic deformation in amorphous metals are far from being understood. We have derived potential parameters for molecular dynamics simulations of Mg-Cu amorphous alloys using the Effective Medium Theory. We have simulated the formation of alloys by cooling from the melt......, and have used these glassy configurations to carry out simulations of plastic deformation. These involved different compositions, temperatures (including zero), and types of deformation (uniaxial strain/pure shear), and yielded stress-strain curves and values of flow stress. Separate simulations were...

  16. 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.

  17. 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.

  18. 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...... and the goveming equations are explicit and simple. These properties of the model make it a very powerful tool, which is applicable for the designing engineer. The method is also extended to reinforced concrete, where the results look very promising. The large experimental investigation on high-strength concrete...

  19. Atomistic simulations of mechanical properties of graphene nanoribbons

    International Nuclear Information System (INIS)

    The mechanical behavior of graphene nanoribbons (GNRs) was investigated by molecular dynamics (MD) simulations. The simulation results showed that GNRs behave nonlinear elastically under tensile loads. When the strain exceeds 18%, the stress stiffening causes an increase in the Young's modulus. The width of a GNR has slight effects on the Young modulus and fracture strength. The maximum strain at which fracture occurs can reach 30.26% with an intrinsic strength of about 0.175 TPa. The excellent flexibility is attributed to the elongation of the C-C bonds and the variations of the bond angles.

  20. Mechanical properties of fracture zones

    International Nuclear Information System (INIS)

    Available data on mechanical characteristics of fracture zones are compiled and discussed. The aim is to improve the basis for adequate representation of fracture zones in geomechanical models. The sources of data researched are primarily borehole investigations and case studies in rock engineering, involving observations of fracture zones subjected to artificial load change. Boreholes only yield local information about the components of fracture zones, i.e. intact rock, fractures and various low-strength materials. Difficulties are therefore encountered in evaluating morphological and mechanical properties of fracture zones from borehole data. Although often thought of as macroscopically planar features, available field data consistently show that fracture zones are characterized by geometrical irregularities such as thickness variations, surface undulation and jogs. These irregularities prevail on all scales. As a result, fracture zones are on all scales characterized by large, in-plane variation of strength- and deformational properties. This has important mechanical consequences in terms of non-uniform stress transfer and complex mechanisms of shear deformation. Field evidence for these findings, in particular results from the underground research laboratory in Canada and from studies of induced fault slip in deep mines, is summarized and discussed. 79 refs

  1. Real-Time Examination of Atomistic Mechanisms during Shock-Induced Structural Transformation in Silicon.

    Science.gov (United States)

    Turneaure, Stefan J; Sinclair, N; Gupta, Y M

    2016-07-22

    The experimental determination of atomistic mechanisms linking crystal structures during a compression-driven solid-solid phase transformation is a long-standing and challenging scientific objective. Using new capabilities at the Dynamic Compression Sector at the Advanced Photon Source, the structure of shocked Si at 19 GPa was identified as simple hexagonal, and the lattice orientations between ambient cubic diamond and simple hexagonal structures were related. The approach is general and provides a powerful new method for examining atomistic mechanisms during stress-induced structural changes. PMID:27494481

  2. Real-Time Examination of Atomistic Mechanisms during Shock-Induced Structural Transformation in Silicon

    Science.gov (United States)

    Turneaure, Stefan J.; Sinclair, N.; Gupta, Y. M.

    2016-07-01

    The experimental determination of atomistic mechanisms linking crystal structures during a compression-driven solid-solid phase transformation is a long-standing and challenging scientific objective. Using new capabilities at the Dynamic Compression Sector at the Advanced Photon Source, the structure of shocked Si at 19 GPa was identified as simple hexagonal, and the lattice orientations between ambient cubic diamond and simple hexagonal structures were related. The approach is general and provides a powerful new method for examining atomistic mechanisms during stress-induced structural changes.

  3. Room Temperature Deformation Mechanisms of Alumina Particles Observed from In Situ Micro-compression and Atomistic Simulations

    Science.gov (United States)

    Sarobol, Pylin; Chandross, Michael; Carroll, Jay D.; Mook, William M.; Bufford, Daniel C.; Boyce, Brad L.; Hattar, Khalid; Kotula, Paul G.; Hall, Aaron C.

    2016-01-01

    Aerosol deposition (AD) is a solid-state deposition technology that has been developed to fabricate ceramic coatings nominally at room temperature. Sub-micron ceramic particles accelerated by pressurized gas impact, deform, and consolidate on substrates under vacuum. Ceramic particle consolidation in AD coatings is highly dependent on particle deformation and bonding; these behaviors are not well understood. In this work, atomistic simulations and in situ micro-compressions in the scanning electron microscope, and the transmission electron microscope (TEM) were utilized to investigate fundamental mechanisms responsible for plastic deformation/fracture of particles under applied compression. Results showed that highly defective micron-sized alumina particles, initially containing numerous dislocations or a grain boundary, exhibited no observable shape change before fracture/fragmentation. Simulations and experimental results indicated that particles containing a grain boundary only accommodate low strain energy per unit volume before crack nucleation and propagation. In contrast, nearly defect-free, sub-micron, single crystal alumina particles exhibited plastic deformation and fracture without fragmentation. Dislocation nucleation/motion, significant plastic deformation, and shape change were observed. Simulation and TEM in situ micro-compression results indicated that nearly defect-free particles accommodate high strain energy per unit volume associated with dislocation plasticity before fracture. The identified deformation mechanisms provide insight into feedstock design for AD.

  4. Collaborative Simulation Grid: Multiscale Quantum-Mechanical/Classical Atomistic Simulations on Distributed PC Clusters in the US and Japan

    Science.gov (United States)

    Kikuchi, Hideaki; Kalia, Rajiv; Nakano, Aiichiro; Vashishta, Priya; Iyetomi, Hiroshi; Ogata, Shuji; Kouno, Takahisa; Shimojo, Fuyuki; Tsuruta, Kanji; Saini, Subhash; Biegel, Bryan (Technical Monitor)

    2002-01-01

    A multidisciplinary, collaborative simulation has been performed on a Grid of geographically distributed PC clusters. The multiscale simulation approach seamlessly combines i) atomistic simulation backed on the molecular dynamics (MD) method and ii) quantum mechanical (QM) calculation based on the density functional theory (DFT), so that accurate but less scalable computations are performed only where they are needed. The multiscale MD/QM simulation code has been Grid-enabled using i) a modular, additive hybridization scheme, ii) multiple QM clustering, and iii) computation/communication overlapping. The Gridified MD/QM simulation code has been used to study environmental effects of water molecules on fracture in silicon. A preliminary run of the code has achieved a parallel efficiency of 94% on 25 PCs distributed over 3 PC clusters in the US and Japan, and a larger test involving 154 processors on 5 distributed PC clusters is in progress.

  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. Atomistic Failure Mechanism of Single Wall Carbon Nanotubes with Small Diameters

    Institute of Scientific and Technical Information of China (English)

    JI Dong; GAO Xiang; KONG Xiang-Yang; LI Jia-Ming

    2007-01-01

    @@ Single wall carbon nanotubes with small diameters (< 5.0 (A)) subjected to bending deformation are simulated by orthogonal tight-binding molecular dynamics approach. Based on the calculations of C-C bond stretching and breaking in the bending nanotubes, we elucidate the atomistic failure mechanisms of nanotube with small diameters. In the folding zone of bending nanotube, a large elongation of C-C bonds occurs, accounting for the superelastic behaviour.

  7. Fatigue mechanisms in an austenitic steel under cyclic loading: Experiments and atomistic simulations

    International Nuclear Information System (INIS)

    Experimental investigations on the austenitic stainless steel X6CrNiNb18-10 (AISI – 347) and concomitant atomistic simulations of a FeNi nanocrystalline model system have been performed in order to understand the basic mechanisms of fatigue damage under cyclic loading. Using electron backscatter diffraction (EBSD) the influence of deformation induced martensitic transformation and NbC size distribution on the fatigue crack formation has been demonstrated. The martensite nucleates prevalently at grain boundaries, triple points and at the specimen free surface and forms small (∼1 µm sized) differently oriented grains. The atomistic simulations show the role of regions of a high density of stacking faults for the martensitic transformation

  8. Fatigue mechanisms in an austenitic steel under cyclic loading: Experiments and atomistic simulations

    Energy Technology Data Exchange (ETDEWEB)

    Soppa, E.A., E-mail: ewa.soppa@mpa.uni-stuttgart.de; Kohler, C., E-mail: christopher.kohler@mpa.uni-stuttgart.de; Roos, E., E-mail: eberhard.roos@mpa.uni-stuttgart.de

    2014-03-01

    Experimental investigations on the austenitic stainless steel X6CrNiNb18-10 (AISI – 347) and concomitant atomistic simulations of a FeNi nanocrystalline model system have been performed in order to understand the basic mechanisms of fatigue damage under cyclic loading. Using electron backscatter diffraction (EBSD) the influence of deformation induced martensitic transformation and NbC size distribution on the fatigue crack formation has been demonstrated. The martensite nucleates prevalently at grain boundaries, triple points and at the specimen free surface and forms small (∼1 µm sized) differently oriented grains. The atomistic simulations show the role of regions of a high density of stacking faults for the martensitic transformation.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1998-08-04

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

  10. Atomistic mechanisms governing structural stability change of zinc antimony thermoelectrics

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Xiaolong [Frontier Institute of Science and Technology, Xi' an Jiaotong University, Xi' an 710054 (China); Lin, Jianping, E-mail: jaredlin@163.com [School of Materials Science and Engineering, Xiamen University of Technology, Xiamen 361024 (China); Qiao, Guanjun [State Key Laboratory for Mechanical Behavior of Materials, Xi' an Jiaotong University, Xi' an 710049 (China); Wang, Zhao, E-mail: zwangzhao@gmail.com [Frontier Institute of Science and Technology, Xi' an Jiaotong University, Xi' an 710054 (China); State Key Laboratory for Mechanical Behavior of Materials, Xi' an Jiaotong University, Xi' an 710049 (China)

    2015-01-05

    The structural stability of thermoelectric materials is a subject of growing importance for their energy harvesting applications. Here, we study the microscopic mechanisms governing the structural stability change of zinc antimony at its working temperature, using molecular dynamics combined with experimental measurements of the electrical and thermal conductivity. Our results show that the temperature-dependence of the thermal and electrical transport coefficients is strongly correlated with a structural transition. This is found to be associated with a relaxation process, in which a group of Zn atoms migrates between interstitial sites. This atom migration gradually leads to a stabilizing structural transition of the entire crystal framework, and then results in a more stable crystal structure of β–Zn{sub 4}Sb{sub 3} at high temperature.

  11. Fracture mechanics of mollusc shells

    Energy Technology Data Exchange (ETDEWEB)

    Cortie, Michael B. [Institute for Nanoscale Technology, University of Technology, Sydney (Australia)]. E-mail: michael.cortie@uts.edu.au; McBean, Katie E. [Microstructural Analysis Unit, University of Technology, Sydney (Australia); Elcombe, Margaret M. [Bragg Institute, Australian Nuclear Science and Technology Organisation, PMB 1, NSW (Australia)

    2006-11-15

    The shape and structure of the shells of molluscs has attracted considerable attention. One aspect of interest is the comparatively high resistance to fracture of these shells. It is known that they are composite structures of aragonite, other calcereous materials, and up to 5% by volume of protein 'glue'. A large component of their toughening derives from crack tip blunting, deflection and closure, concepts well-known from the field of fracture mechanics. However, the possibility that they might also derive a measure of toughening from a residual stress distribution has been generally overlooked, although Illert first raised this over a decade ago. The optimum situation would be when the inner surface of the shell is maintained in a state of tensile stress, while the outer layers are in the necessarily counter-balancing compressive state. We have examined this hypothesis using a combination of neutron diffraction and scanning electron microscopy and find that it is certainly feasible. However, a definitive proof will require a diffraction study at higher resolution.

  12. 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.

  13. 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.

  14. Calculation and visualization of atomistic mechanical stresses in nanomaterials and biomolecules.

    Directory of Open Access Journals (Sweden)

    Andrew T Fenley

    Full Text Available Many biomolecules have machine-like functions, and accordingly are discussed in terms of mechanical properties like force and motion. However, the concept of stress, a mechanical property that is of fundamental importance in the study of macroscopic mechanics, is not commonly applied in the biomolecular context. We anticipate that microscopical stress analyses of biomolecules and nanomaterials will provide useful mechanistic insights and help guide molecular design. To enable such applications, we have developed Calculator of Atomistic Mechanical Stress (CAMS, an open-source software package for computing atomic resolution stresses from molecular dynamics (MD simulations. The software also enables decomposition of stress into contributions from bonded, nonbonded and Generalized Born potential terms. CAMS reads GROMACS topology and trajectory files, which are easily generated from AMBER files as well; and time-varying stresses may be animated and visualized in the VMD viewer. Here, we review relevant theory and present illustrative applications.

  15. Atomistic simulations of fracture in the B2 phase of the Nb-Ti-Al system

    Energy Technology Data Exchange (ETDEWEB)

    Farkas, D. [Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Computer Simulation Lab.

    1998-06-30

    Atomistic simulations of the crack tip configuration in the B2 phase of Nb-rich alloys in the Nb-Ti-Al are presented. The alloy compositions studied are Nb-16Al-16Ti and Nb-16Al-33Ti. The simulations were carried out using molecular statics and empirical embedded atom method (EAM) potentials for the ternary system developed in previous work. The behavior of a semi-infinite crack was studied under mode I loading for different crack tip geometries. The crack was embedded in a simulation cell with periodic boundary conditions along the direction parallel to the crack front and fixed boundary conditions along the periphery of the simulation cell. The quasi-static simulations were carried out using a molecular statics relaxation technique to obtain the minimum energy configuration of the atoms starting from their initial elastic positions, under increasingly higher stress intensities. The competition between dislocation emission and cleavage was studied in these alloys as a function of Ti content. Cracks along {l_brace}110{r_brace}-type planes with crack fronts oriented along different directions were studied. The alloys showed increased ductility with increased Ti content. The simulations show more ductile behavior than other intermetallics, due to easier dislocation emission processes at the crack tip. (orig.) 30 refs.

  16. Physical fracture properties (fracture surfaces as information sources; crackgrowth and fracture mechanisms; exemples of cracks)

    International Nuclear Information System (INIS)

    Fracture surfaces are considered as a useful source of informations: an introduction to fractography is presented; the fracture surface may be observed through X ray microanalysis, and other physical methods such as Auger electron spectroscopy or secundary ion emission. The mechanisms of macroscopic and microscopic crackgrowth and fracture are described, in the case of unstable fracture (cleavage, ductile with shear, intergranular brittleness) and of progressive crack propagation (creep, fatigue). Exemples of cracks are presented in the last chapter

  17. A hybrid atomistic electrodynamics-quantum mechanical approach for simulating surface-enhanced Raman scattering.

    Science.gov (United States)

    Payton, John L; Morton, Seth M; Moore, Justin E; Jensen, Lasse

    2014-01-21

    Surface-enhanced Raman scattering (SERS) is a technique that has broad implications for biological and chemical sensing applications by providing the ability to simultaneously detect and identify a single molecule. The Raman scattering of molecules adsorbed on metal nanoparticles can be enhanced by many orders of magnitude. These enhancements stem from a twofold mechanism: an electromagnetic mechanism (EM), which is due to the enhanced local field near the metal surface, and a chemical mechanism (CM), which is due to the adsorbate specific interactions between the metal surface and the molecules. The local field near the metal surface can be significantly enhanced due to the plasmon excitation, and therefore chemists generally accept that the EM provides the majority of the enhancements. While classical electrodynamics simulations can accurately simulate the local electric field around metal nanoparticles, they offer few insights into the spectral changes that occur in SERS. First-principles simulations can directly predict the Raman spectrum but are limited to small metal clusters and therefore are often used for understanding the CM. Thus, there is a need for developing new methods that bridge the electrodynamics simulations of the metal nanoparticle and the first-principles simulations of the molecule to facilitate direct simulations of SERS spectra. In this Account, we discuss our recent work on developing a hybrid atomistic electrodynamics-quantum mechanical approach to simulate SERS. This hybrid method is called the discrete interaction model/quantum mechanics (DIM/QM) method and consists of an atomistic electrodynamics model of the metal nanoparticle and a time-dependent density functional theory (TDDFT) description of the molecule. In contrast to most previous work, the DIM/QM method enables us to retain a detailed atomistic structure of the nanoparticle and provides a natural bridge between the electronic structure methods and the macroscopic

  18. Fully atomistic molecular-mechanical model of liquid alkane oils: Computational validation.

    Science.gov (United States)

    Zahariev, Tsvetan K; Slavchov, Radomir I; Tadjer, Alia V; Ivanova, Anela N

    2014-04-15

    Fully atomistic molecular dynamics simulations were performed on liquid n-pentane, n-hexane, and n-heptane to derive an atomistic model for middle-chain-length alkanes. All simulations were based on existing molecular-mechanical parameters for alkanes. The computational protocol was optimized, for example, in terms of thermo- and barostat, to reproduce properly the properties of the liquids. The model was validated by comparison of thermal, structural, and dynamic properties of the normal alkane liquids to experimental data. Two different combinations of temperature and pressure coupling algorithms were tested. A simple differential approach was applied to evaluate fluctuation-related properties with sufficient accuracy. Analysis of the data reveals a satisfactory representation of the hydrophobic systems behavior. Thermodynamic parameters are close to the experimental values and exhibit correct temperature dependence. The observed intramolecular geometry corresponds to extended conformations domination, whereas the intermolecular structure demonstrates all characteristics of liquid systems. Cavity size distribution function was calculated from coordinates analysis and was applied to study the solubility of gases in hexane and heptane oils. This study provides a platform for further in-depth research on hydrophobic solutions and multicomponent systems.

  19. 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.

  20. Atomistic study of lipid membranes containing chloroform: looking for a lipid-mediated mechanism of anesthesia.

    Directory of Open Access Journals (Sweden)

    Ramon Reigada

    Full Text Available The molecular mechanism of general anesthesia is still a controversial issue. Direct effect by linking of anesthetics to proteins and indirect action on the lipid membrane properties are the two hypotheses in conflict. Atomistic simulations of different lipid membranes subjected to the effect of small volatile organohalogen compounds are used to explore plausible lipid-mediated mechanisms. Simulations of homogeneous membranes reveal that electrostatic potential and lateral pressure transversal profiles are affected differently by chloroform (anesthetic and carbon tetrachloride (non-anesthetic. Simulations of structured membranes that combine ordered and disordered regions show that chloroform molecules accumulate preferentially in highly disordered lipid domains, suggesting that the combination of both lateral and transversal partitioning of chloroform in the cell membrane could be responsible of its anesthetic action.

  1. Mechanism of the Cassie-Wenzel transition via the atomistic and continuum string methods

    Energy Technology Data Exchange (ETDEWEB)

    Giacomello, Alberto, E-mail: alberto.giacomello@uniroma1.it; Casciola, Carlo Massimo [Dipartimento di Ingegneria Meccanica e Aerospaziale, Università di Roma “La Sapienza,” 00184 Rome (Italy); Meloni, Simone, E-mail: simone.meloni@epfl.ch [Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne (Switzerland); Müller, Marcus [Institut für Theoretische Physik, Georg-August-Universität Göttingen, 37077 Göttingen (Germany)

    2015-03-14

    The string method is a general and flexible strategy to compute the most probable transition path for an activated process (rare event). We apply here the atomistic string method in the density field to the Cassie-Wenzel transition, a central problem in the field of superhydrophobicity. We discuss in detail the mechanism of wetting of a submerged hydrophobic cavity of nanometer size and its dependence on the geometry of the cavity. Furthermore, we analyze the algorithmic analogies between the continuum “interface” string method and CREaM [Giacomello et al., Phys. Rev. Lett. 109, 226102 (2012)], a method inspired by the string that allows for a faster and simpler computation of the mechanism and of the free-energy profiles of the wetting process.

  2. Mechanical properties of various two-dimensional silicon carbide sheets: An atomistic study

    Science.gov (United States)

    Nguyen, Danh-Truong; Le, Minh-Quy

    2016-10-01

    We investigate through molecular dynamics finite element method with Tersoff potential the mechanical properties of 13 SimCn sheets under uniaxial tension in the armchair and zigzag directions. It is found that the presence and dispersion of silicon atoms in SimCn sheets affect strongly the mechanical properties and the anisotropy of these sheets. The Young's modulus and fracture stress of the SimCn sheet decrease in general when the silicon concentration increases from 0 to 0.2. In contrast, the mechanical properties (Young's modulus, fracture stress, and fracture strain) increase slightly when the silicon concentration increases from 0.3 to 0.5 due to an increase of the degree of dispersion of silicon atoms in the SimCn sheet. The mechanical properties of the sheet are relatively high when the silicon concentration is low or silicon atoms are well dispersed.

  3. Mechanisms of hydraulic fracturing in cohesive soil

    Directory of Open Access Journals (Sweden)

    Jun-jie WANG

    2009-12-01

    Full Text Available Hydraulic fracturing in the soil core of earth-rockfill dams is a common problem affecting the safety of the dams. Based on fracture tests, a new criterion for hydraulic fracturing in cohesive soil was suggested. Using this criterion, the mechanisms of hydraulic fracturing in cubic soil specimens were investigated. The results indicate that the propagation of the crack in a cubic specimen under water pressure occurs in a mixed mode I-II if the crack face is not perpendicular to any of the principal stresses, and the crack most likely to propagate is the one that is perpendicular to the minor principal stress and propagates in mode I.

  4. Mechanisms of hydraulic fracturing in cohesive soil

    OpenAIRE

    Wang, Jun-Jie; Zhang, Hui-ping; Ming-jie ZHAO; Lin, Xin

    2009-01-01

    Hydraulic fracturing in the soil core of earth-rockfill dams is a common problem affecting the safety of the dams. Based on fracture tests, a new criterion for hydraulic fracturing in cohesive soil was suggested. Using this criterion, the mechanisms of hydraulic fracturing in cubic soil specimens were investigated. The results indicate that the propagation of the crack in a cubic specimen under water pressure occurs in a mixed mode I-II if the crack face is not perpendicular to any of the pri...

  5. Atomistic mechanisms of amorphization during nanoindentation of SiC: A molecular dynamics study

    Science.gov (United States)

    Szlufarska, Izabela; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya

    2005-05-01

    Atomistic mechanisms underlying the nanoindentation-induced amorphization in SiC crystal has been studied by molecular dynamics simulations on parallel computers. The calculated load-displacement curve consists of a series of load drops, corresponding to plastic deformation, in addition to a shoulder at a smaller displacement, which is fully reversible upon unloading. The peaks in the load-displacement curve are shown to reflect the crystalline structure and dislocation activities under the surface. The evolution of indentation damage and defect accumulation are also discussed in terms of bond angles, local pressure, local shear stress, and spatial rearrangements of atoms. These structural analyses reveal that the defect-stimulated growth and coalescence of dislocation loops are responsible for the crystalline-to-amorphous transition. The shortest-path-ring analysis is effectively employed to characterize nanoindentation-induced structural transformations and dislocation activities.

  6. Unfolding proteins with mechanical forces: From toy models to atomistic simulations

    Science.gov (United States)

    Makarov, Dmitrii

    2011-03-01

    The remarkable combination of strength and toughness, displayed by certain biological materials (e.g. spider silk) and often unmatched by artificial materials, is believed to originate from the mechanical response of individual load-bearing protein domains. Single-molecule pulling experiments carried out during the last decade showed that those proteins, when loaded, respond in a non-equilibrium fashion and can dissipate large amounts of energy though the breaking of sacrificial bonds. In my talk, I will discuss what structural properties correlate with mechanical strength and toughness at the single-molecule level, how thermodynamic stability is related to the mechanical stability, and why both atomistic simulations and simple models seem to fail to reconcile the mechanical responses of the same proteins measured under varied loading regimes. I will further discuss whether it is easier to unfold a protein mechanically by pulling at its ends or by threading it through a narrow pore. The latter process is believed to commonly occur in living organisms as an intermediate step in protein degradation. Supported by the NSF and the Robert A. Welch Foundation.

  7. Atomistic insights into dislocation-based mechanisms of void growth and coalescence

    Science.gov (United States)

    Mi, Changwen; Buttry, Daniel A.; Sharma, Pradeep; Kouris, Demitris A.

    2011-09-01

    One of the low-temperature failure mechanisms in ductile metallic alloys is the growth of voids and their coalescence. In the present work we attempt to obtain atomistic insights into the mechanisms underpinning cavitation in a representative metal, namely Aluminum. Often the pre-existing voids in metallic alloys such as Al have complex shapes (e.g. corrosion pits) and the defromation/damage mechanisms exhibit a rich size-dependent behavior across various material length scales. We focus on these two issues in this paper through large-scale calculations on specimens of sizes ranging from 18 thousand to 1.08 million atoms. In addition to the elucidation of the dislocation propagation based void growth mechanism we highlight the observed length scale effect reflected in the effective stress-strain response, stress triaxiality and void fraction evolution. Furthermore, as expected, the conventionally used Gurson's model fails to capture the observed size-effects calling for a mechanistic modification that incorporates the mechanisms observed in our (and other researchers') simulation. Finally, in our multi-void simulations, we find that, the splitting of a big void into a distribution of small ones increases the load-carrying capacity of specimens. However, no obvious dependence of the void fraction evolution on void coalescence is observed.

  8. 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...

  9. Application of microstatistical fracture mechanics to dynamic fracture problems

    International Nuclear Information System (INIS)

    This chapter presents a microstatistical treatment of shear bands. Describes the microstatistical fracture mechanics (MSFM) approach by illustrating its use in the case of shock-induced ductile voids in steel. Shows that the microstatistical approach merges with the continuum approach. Computes the behavior of a macrocrack propagating in a DCB specimen by using MSFM and the data generated in the shock wave experiments. Discusses shockwave-induced ductile fractures; plate impact experiments; data analysis; progress in MSFM and required research efforts; and macrocrack propagation. Points out that although continuum treatments have the advantage of simplicity and low cost, the more complex and expensive MSFM treatment may be the only viable approach when detailed information is needed such as size, velocity, and trajectory distributions of fragments ejected from a plate of armor steel after impact

  10. Atomistic modeling of structure II gas hydrate mechanics: Compressibility and equations of state

    Directory of Open Access Journals (Sweden)

    Thomas M. Vlasic

    2016-08-01

    Full Text Available This work uses density functional theory (DFT to investigate the poorly characterized structure II gas hydrates, for various guests (empty, propane, butane, ethane-methane, propane-methane, at the atomistic scale to determine key structure and mechanical properties such as equilibrium lattice volume and bulk modulus. Several equations of state (EOS for solids (Murnaghan, Birch-Murnaghan, Vinet, Liu were fitted to energy-volume curves resulting from structure optimization simulations. These EOS, which can be used to characterize the compressional behaviour of gas hydrates, were evaluated in terms of their robustness. The three-parameter Vinet EOS was found to perform just as well if not better than the four-parameter Liu EOS, over the pressure range in this study. As expected, the Murnaghan EOS proved to be the least robust. Furthermore, the equilibrium lattice volumes were found to increase with guest size, with double-guest hydrates showing a larger increase than single-guest hydrates, which has significant implications for the widely used van der Waals and Platteeuw thermodynamic model for gas hydrates. Also, hydrogen bonds prove to be the most likely factor contributing to the resistance of gas hydrates to compression; bulk modulus was found to increase linearly with hydrogen bond density, resulting in a relationship that could be used predictively to determine the bulk modulus of various structure II gas hydrates. Taken together, these results fill a long existing gap in the material chemical physics of these important clathrates.

  11. Atomistic modeling of structure II gas hydrate mechanics: Compressibility and equations of state

    Science.gov (United States)

    Vlasic, Thomas M.; Servio, Phillip; Rey, Alejandro D.

    2016-08-01

    This work uses density functional theory (DFT) to investigate the poorly characterized structure II gas hydrates, for various guests (empty, propane, butane, ethane-methane, propane-methane), at the atomistic scale to determine key structure and mechanical properties such as equilibrium lattice volume and bulk modulus. Several equations of state (EOS) for solids (Murnaghan, Birch-Murnaghan, Vinet, Liu) were fitted to energy-volume curves resulting from structure optimization simulations. These EOS, which can be used to characterize the compressional behaviour of gas hydrates, were evaluated in terms of their robustness. The three-parameter Vinet EOS was found to perform just as well if not better than the four-parameter Liu EOS, over the pressure range in this study. As expected, the Murnaghan EOS proved to be the least robust. Furthermore, the equilibrium lattice volumes were found to increase with guest size, with double-guest hydrates showing a larger increase than single-guest hydrates, which has significant implications for the widely used van der Waals and Platteeuw thermodynamic model for gas hydrates. Also, hydrogen bonds prove to be the most likely factor contributing to the resistance of gas hydrates to compression; bulk modulus was found to increase linearly with hydrogen bond density, resulting in a relationship that could be used predictively to determine the bulk modulus of various structure II gas hydrates. Taken together, these results fill a long existing gap in the material chemical physics of these important clathrates.

  12. Atomistic tensile deformation mechanisms of Fe with gradient nano-grained structure

    Directory of Open Access Journals (Sweden)

    Wenbin Li

    2015-08-01

    Full Text Available Large-scale molecular dynamics (MD simulations have been performed to investigate the tensile properties and the related atomistic deformation mechanisms of the gradient nano-grained (GNG structure of bcc Fe (gradient grains with d from 25 nm to 105 nm, and comparisons were made with the uniform nano-grained (NG structure of bcc Fe (grains with d = 25 nm. The grain size gradient in the nano-scale converts the applied uniaxial stress to multi-axial stresses and promotes the dislocation behaviors in the GNG structure, which results in extra hardening and flow strength. Thus, the GNG structure shows slightly higher flow stress at the early plastic deformation stage when compared to the uniform NG structure (even with smaller grain size. In the GNG structure, the dominant deformation mechanisms are closely related to the grain sizes. For grains with d = 25 nm, the deformation mechanisms are dominated by GB migration, grain rotation and grain coalescence although a few dislocations are observed. For grains with d = 54 nm, dislocation nucleation, propagation and formation of dislocation wall near GBs are observed. Moreover, formation of dislocation wall and dislocation pile-up near GBs are observed for grains with d = 105 nm, which is the first observation by MD simulations to our best knowledge. The strain compatibility among different layers with various grain sizes in the GNG structure should promote the dislocation behaviors and the flow stress of the whole structure, and the present results should provide insights to design the microstructures for developing strong-and-ductile metals.

  13. Thermodynamic and mechanical properties of copper precipitates in α-iron from atomistic simulations

    Science.gov (United States)

    Erhart, Paul; Marian, Jaime; Sadigh, Babak

    2013-07-01

    Precipitate hardening is commonly used in materials science to control strength by acting on the number density, size distribution, and shape of solute precipitates in the hardened matrix. The Fe-Cu system has attracted much attention over the last several decades due to its technological importance as a model alloy for Cu steels. In spite of these efforts several aspects of its phase diagram remain unexplained. Here we use atomistic simulations to characterize the polymorphic phase diagram of Cu precipitates in body-centered cubic (BCC) Fe and establish a consistent link between their thermodynamic and mechanical properties in terms of thermal stability, shape, and strength. The size at which Cu precipitates transform from BCC to a close-packed 9R structure is found to be strongly temperature dependent, ranging from approximately 4 nm in diameter (˜2700atoms) at 200 K to about 8 nm (˜22800atoms) at 700 K. These numbers are in very good agreement with the interpretation of experimental data given Monzen [Philos. Mag. APMAADG0141-861010.1080/01418610008212077 80, 711 (2000)]. The strong temperature dependence originates from the entropic stabilization of BCC Cu, which is mechanically unstable as a bulk phase. While at high temperatures the transition exhibits first-order characteristics, the hysteresis, and thus the nucleation barrier, vanish at temperatures below approximately 300 K. This behavior is explained in terms of the mutual cancellation of the energy differences between core and shell (wetting layer) regions of BCC and 9R nanoprecipitates, respectively. The proposed mechanism is not specific for the Fe-Cu system but could generally be observed in immiscible systems, whenever the minority component is unstable in the lattice structure of the host matrix. Finally, we also study the interaction of precipitates with screw dislocations as a function of both structure and orientation. The results provide a coherent picture of precipitate strength that unifies

  14. Numerical methods in dynamic fracture mechanics

    International Nuclear Information System (INIS)

    A review of numerical methods for the solution of dynamic problems of fracture mechanics is presented. Finite difference, finite element and boundary element methods as applied to linear elastic or viscoelastic and non-linear elastoplastic or elastoviscoplastic dynamic fracture mechanics problems are described and critically evaluated. Both cases of stationary cracks and rapidly propagating cracks of simple I, II, III or mixed modes are considered. Harmonically varying with time or general transient dynamic disturbances in the form of external loading or incident waves are taken into account. Determination of the dynamic stress intensity factor for stationary cracks or moving cracks with known velocity history as well as determination of the crack-tip propagation history for given dynamic fracture toughness versus crack velocity relation are described and illustrated by means of certain representative examples. Finally, a brief assessment of the present state of knowledge is made and research needs are identified

  15. Geometry, mechanics and transmissivity of rock fractures

    International Nuclear Information System (INIS)

    This thesis work investigates methods and tools for characterising, testing and modelling the behaviour of rock fractures. Using a 3D-laser-scanning technique, the topography of the surfaces and their position with respect to one another are measured. From the fracture topography, fracture roughness, angularity and aperture are quantified; the major features used for characterisation. The standard deviations for the asperity heights, surface slopes and aperture are determined. These statistical parameters usually increase/decrease according to power laws of the sampling size, and sometimes reach a sill beyond which they become constant. Also the number of contact spots with a certain area decreases according to a power-law function of the area. These power-law relations reveal the self affine fractal nature of roughness and aperture. Roughness is 'persistent' while aperture varies between 'persistent' and 'anti-persistent' probably depending on the degree of match of the fracture walls. The fractal models for roughness, aperture and contact area are used to develop a constitutive model, based on contact mechanics, for describing the fracture normal and shear deformability. The experimental testing results of normal deformability are simulated well by the model whereas fracture shear deformability is not as well modelled. The model predicts well fracture dilation but is too stiff compared to rock samples. A mathematical description of the aperture pattern during shearing is also formulated. The mean value and covariance of the aperture in shearing is calculated and verifies reported observations. The aperture map of samples is inserted in a numerical program for flow calculation. The 'integral transform method' is used for solving the Reynolds' equation; it transforms the fracture transmissivity pattern into a frequency-based function. This closely resembles the power laws that describe fractals. This function can be described directly from the fractal properties of

  16. 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 ...

  17. 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...

  18. Fracture mechanics of collagen fibrils

    DEFF Research Database (Denmark)

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

    2013-01-01

    technique to measure the mechanical behavior of individual collagen fibrils loaded to failure. Fibrils from human patellar tendons, rat-tail tendons (RTTs), NaBH₄ reduced RTTs, and tail tendons of Zucker diabetic fat rats were tested. We found a characteristic three-phase stress-strain behavior in the human...... fibrils is limited. The presence of covalent enzymatic cross-links between collagen molecules is an important factor that has been shown to influence mechanical behavior of the tendons. To improve our understanding of how molecular bonds translate into tendon mechanics, we used an atomic force microscopy...... and the plateau continued until failure. The importance of cross-link lability was investigated by NaBH₄ reduction of the rat-tail fibrils, which did not alter their behavior. These findings shed light on the function of cross-links at the fibril level, but further studies will be required to establish...

  19. Computational simulation methods for composite fracture mechanics

    Science.gov (United States)

    Murthy, Pappu L. N.

    1988-01-01

    Structural integrity, durability, and damage tolerance of advanced composites are assessed by studying damage initiation at various scales (micro, macro, and global) and accumulation and growth leading to global failure, quantitatively and qualitatively. In addition, various fracture toughness parameters associated with a typical damage and its growth must be determined. Computational structural analysis codes to aid the composite design engineer in performing these tasks were developed. CODSTRAN (COmposite Durability STRuctural ANalysis) is used to qualitatively and quantitatively assess the progressive damage occurring in composite structures due to mechanical and environmental loads. Next, methods are covered that are currently being developed and used at Lewis to predict interlaminar fracture toughness and related parameters of fiber composites given a prescribed damage. The general purpose finite element code MSC/NASTRAN was used to simulate the interlaminar fracture and the associated individual as well as mixed-mode strain energy release rates in fiber composites.

  20. 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.

  1. Use of fracture mechanics parameters to characterize comminution

    OpenAIRE

    Hao, Bin

    1996-01-01

    This report is to investigate the use of fracture mechanics parameters (fracture toughness, specific work of fracture) to characterize comminution process. Comminution is a very important industrial process and is extremely low in efficiency. Establishment of a crushing index based on fracture mechanics principles is of great significance for improved machine design and enhanced efficiency. Single particle fracture study has been reviewed because it is considered the most eleme...

  2. Molecular and intermolecular effects in collagen fibril mechanics: a multiscale analytical model compared with atomistic and experimental studies.

    Science.gov (United States)

    Marino, Michele

    2016-02-01

    Both atomistic and experimental studies reveal the dependence of collagen fibril mechanics on biochemical and biophysical features such as, for instance, cross-link density, water content and protein sequence. In order to move toward a multiscale structural description of biological tissues, a novel analytical model for collagen fibril mechanics is herein presented. The model is based on a multiscale approach that incorporates and couples: thermal fluctuations in collagen molecules; the uncoiling of collagen triple helix; the stretching of molecular backbone; the straightening of the telopeptide in which covalent cross-links form; slip-pulse mechanisms due to the rupture of intermolecular weak bonds; molecular interstrand delamination due to the rupture of intramolecular weak bonds; the rupture of covalent bonds within molecular strands. The effectiveness of the proposed approach is verified by comparison with available atomistic results and experimental data, highlighting the importance of cross-link density in tuning collagen fibril mechanics. The typical three-region shape and hysteresis behavior of fibril constitutive response, as well as the transition from a yielding-like to a brittle-like behavior, are recovered with a special insight on the underlying nanoscale mechanisms. The model is based on parameters with a clear biophysical and biochemical meaning, resulting in a promising tool for analyzing the effect of pathological or pharmacological-induced histochemical alterations on the functional mechanical response of collagenous tissues.

  3. 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.

  4. Atomistic simulations of nanoindentation

    Directory of Open Access Journals (Sweden)

    Izabela Szlufarska

    2006-05-01

    Full Text Available Our understanding of mechanics is pushed to its limit when the functionality of devices is controlled at the nanometer scale. A fundamental understanding of nanomechanics is needed to design materials with optimum properties. Atomistic simulations can bring an important insight into nanostructure-property relations and, when combined with experiments, they become a powerful tool to move nanomechanics from basic science to the application area. Nanoindentation is a well-established technique for studying mechanical response. We review recent advances in modeling (atomistic and beyond of nanoindentation and discuss how they have contributed to our current state of knowledge.

  5. Investigations on the mechanical behavior of nanowires with twin boundaries by atomistic simulations

    Energy Technology Data Exchange (ETDEWEB)

    Tian, Xia, E-mail: tianxia@lsec.cc.ac.cn [College of Mechanics and Materials, HoHai University, Nanjing 210098 (China)

    2015-03-10

    Atomistic simulations are used to study the deformation behavior of twinned Cu nanowires with a <111> growth orientation under tension. Due to the existence of the twin boundaries, the strength of the twinned nanowires is higher than that of the twin-free nanowire and the yielding stress of twinned nanowires is inversely proportional to the spacings of the twin boundaries. Moreover, The ductility of the twin-free nanowire is the highest of all and it grows with the increasing spacings of the twin boundaries for twinned nanowires. Besides, we find that the twin boundaries can be served as dislocation sources as well as the free surfaces and grain boundaries.

  6. 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.

  7. Atomistic Conversion Reaction Mechanism of WO3 in Secondary Ion Batteries of Li, Na, and Ca

    Energy Technology Data Exchange (ETDEWEB)

    He, Yang; Gu, Meng; Xiao, Hai Yan; Luo, Langli; Shao, Yuyan; Gao, Fei; Du, Yingge; Mao, Scott X.; Wang, Chong M.

    2016-05-13

    Reversible insertion and extraction of ionic species into a host lattice governs the basic operating principle for both rechargeable battery (such as lithium batteries) and electrochromic devices (such as ANA Boeing 787-8 Dreamliner electrochromic window). Intercalation and/or conversion are two fundamental chemical processes for some materials in response to the ion insertion. The interplay between these two chemical processes has never been established. It is speculated that the conversion reaction is initiated by ion intercalation. However, experimental evidence of intercalation and subsequent conversion remains unexplored. Here, using in situ HRTEM and spectroscopy, we captured the atomistic conversion reaction processes during lithium, sodium and calcium ion insertion into tungsten trioxide (WO3) single crystal model electrodes. An intercalation step right prior to conversion is explicitly revealed at atomic scale for the first time for these three ion species. Combining nanoscale diffraction and ab initio molecular dynamics simulations, it is found that, beyond intercalation, the inserted ion-oxygen bonding formation destabilized the transition-metal framework which gradually shrunk, distorted and finally collapsed to a pseudo-amorphous structure. This study provides a full atomistic picture on the transition from intercalation to conversion, which is of essential for material applications in both secondary ion batteries and electrochromic devices.

  8. Patterns and perspectives in applied fracture mechanics

    Energy Technology Data Exchange (ETDEWEB)

    Merkle, J.G.

    1994-12-31

    This lecture begins with a overview of applied fracture mechanics pertinent to safety of pressure vessels. It then progresses to a chronological panorama of experimental and analytical results. To be useful and dependable in safety analysis of real structures, new analysis developments must be physically realistic, which means that they must accurately describe physical cause and effect. Consequently, before mathematical modeling can begin, cause and effect must be established from experimental data. This can be difficult and time consuming, but worth the effort. Accordingly, the theme of this paper is that the search for patterns is constant and vital. This theme is illustrated by the development of small, single-specimen, fracture toughness testing techniques. It is also illustrated by the development, based on two different published large-strain, elastic-plastic, three-dimensional finite-element analyses, of a hypothesis concerning three-dimensional loss of constraint. When a generalization of Irwin`s thickness-normalized plastic-zone parameter, reaches a value close to 2{pi}, the through-thickness contraction strain at the apex of the near-tip logarithmic-spiral slip-line region becomes the dominant negative strain accommodating crack opening. Because slip lines passing from the midplane to the stress-free side surfaces do not have to curve, once these slip lines are established, stresses near the crack tip are only elevated by strain hardening and constraint becomes significantly relaxed. This hypothesis, based on published three-dimensional elastic-plastic analyses, provides a potentially valuable means for gaining additional insight into constraint effects on fracture toughness by considering the roles played by the plastic strains as well as the stresses that develop near a crack tip.

  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. Atomistic simulations to micro-mechanisms of adhesion in automotive applications

    Science.gov (United States)

    Sen, Fatih Gurcag

    This study aimed at depicting atomistic and microstructural aspects of adhesion and friction that appear in different automotive applications and manufacturing processes using atomistic simulations coupled with tribological tests and surface characterization experiments. Thin films that form at the contact interfaces due to chemical reactions and coatings that are developed to mitigate or enhance adhesion were studied in detail. The adhesion and friction experiments conducted on diamond-like carbon (DLC) coatings against Al indicated that F incorporation into DLC decreased the coefficient of friction (COF) by 30% -with respect to H-DLC that is known to have low COF and anti-adhesion properties against Al- to 0.14 owing to formation of repulsive F-F interactions at the sliding interface as shown by density functional theory (DFT) calculations. F atoms transferred to the Al surface with an increase in the contact pressure, and this F transfer led to the formation of a stable AlF3 compound at the Al surface as confirmed by XPS and cross-sectional FIB-TEM. The incorporation of Si and O in a F-containing DLC resulted in humidity independent low COF of 0.08 due to the hydration effect of the Si-O-Si chains in the carbonaceous tribolayers that resulted in repulsive OH-OH interactions at the contact interface. At high temperatures, adhesion of Al was found to be enhanced as a result of superplastic oxide fibers on the Al surface. Molecular dynamics (MD) simulations of tensile deformation of Al nanowires in oxygen carried out with ReaxFF showed that native oxide of Al has an oxygen deficient, low density structure and in O2, the oxygen diffusion in amorphous oxide healed the broken Al-O bonds during applied strain and resulted in the superplasticity. The oxide shell also provided nucleation sites for dislocations in Al crystal. In fuel cell applications, where low Pt/carbon adhesion is causing durability problems, spin-polarized DFT showed that metals with unfilled d

  11. Solution-adaptive finite element method in computational fracture mechanics

    Science.gov (United States)

    Min, J. B.; Bass, J. M.; Spradley, L. W.

    1993-01-01

    Some recent results obtained using solution-adaptive finite element method in linear elastic two-dimensional fracture mechanics problems are presented. The focus is on the basic issue of adaptive finite element method for validating the applications of new methodology to fracture mechanics problems by computing demonstration problems and comparing the stress intensity factors to analytical results.

  12. 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

  13. 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

  14. 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...

  15. Fracture mechanics behaviour of neutron irradiated Alloy A-286

    International Nuclear Information System (INIS)

    The effect of fast-neutron irradiation on the fatigue-crack propagation and fracture toughness behaviour of Alloy A-286 was characterized using fracture mechanics techniques. The fracture toughness was found to decrease continuously with increasing irradiation damage at both 24 deg. C and 427 deg. C. In the unirradiated and low fluence conditions, specimens displayed appreciable plasticity prior to fracture, and equivalent Ksub(Ic) values were determined from Jsub(Ic) fracture toughness results. At high irradiation exposure levels, specimens exhibited a brittle Ksub(Ic) fracture mode. The 427 deg. C fracture toughness fell from 129 MPa√m in the unirradiated condition to 35 MPa√m at an exposure of 16.2 dpa (total fluence of 5.2x1022n/cm2). Room temperature fracture toughness values were consistently 40 to 60 percent higher than the 427 deg. C values. Electron fractography revealed that the reduction in fracture resistance was attributed to a fracture mechanism transition from ductile microvoid coalescence to channel fracture. Fatigue-crack propagation tests were conducted at 427 deg. C on specimens irradiated at 2.4 dpa and 16.2 dpa. Crack growth rates at the lower exposure level were comparable to those in unirradiated material, while those at the higher exposure were slightly higher than in unirradiated material. (author)

  16. 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].

  17. Atomistic mechanisms of strain relaxation due to ductile void growth in ultrathin films of face-centered-cubic metals

    International Nuclear Information System (INIS)

    A comprehensive computational analysis is reported of the atomistic mechanisms of strain relaxation and failure in free-standing Cu thin films under applied biaxial tensile strain for strain levels up to 6%. The analysis focuses on nanometer-scale-thick films with a preexisting void extending across the film thickness and the film plane oriented normal to the [111] crystallographic direction. Our computational study is based on isothermal-isostrain large-scale molecular-dynamics simulations within an embedded-atom-method parametrization for Cu. Our analysis has revealed various regimes in the film's mechanical response as the applied strain level increases. Within the considered strain range, after an elastic response at a low strain (<2%), void growth is the major strain relaxation mechanism mediated by the emission of perfect screw dislocation pairs from the void surface and subsequent dislocation propagation; as a result, a plastic zone forms around the void. Plastic deformation is accompanied by the glide motion of the dislocations emitted from the void surface, void surface morphological transitions, formation of a step pattern on the film's surfaces, dislocation jogging, vacancy generation due to gliding jogged dislocations, dislocation-vacancy interactions, vacancy pipe diffusion along dislocation cores, as well as dislocation-dislocation interactions. The increase in film surface roughness with increasing strain eventually leads to nucleation and propagation from the film surfaces of threading dislocation loops, which ultimately break up when they reach the opposite free surface of the thin film

  18. Integration of NDE Reliability and Fracture Mechanics

    Energy Technology Data Exchange (ETDEWEB)

    Becker, F. L.; Doctor, S. R.; Heas!er, P. G.; Morris, C. J.; Pitman, S. G.; Selby, G. P.; Simonen, F. A.

    1981-03-01

    The Pacific Northwest Laboratory is conducting a four-phase program for measuring and evaluating the effectiveness and reliability of in-service inspection (lSI} performed on the primary system piping welds of commercial light water reactors (LWRs). Phase I of the program is complete. A survey was made of the state of practice for ultrasonic rsr of LWR primary system piping welds. Fracture mechanics calculations were made to establish required nondestrutive testing sensitivities. In general, it was found that fatigue flaws less than 25% of wall thickness would not grow to failure within an inspection interval of 10 years. However, in some cases failure could occur considerably faster. Statistical methods for predicting and measuring the effectiveness and reliability of lSI were developed and will be applied in the "Round Robin Inspections" of Phase II. Methods were also developed for the production of flaws typical of those found in service. Samples fabricated by these methods wilI be used in Phase II to test inspection effectiveness and reliability. Measurements were made of the influence of flaw characteristics {i.e., roughness, tightness, and orientation) on inspection reliability. These measurernents, as well as the predictions of a statistical model for inspection reliability, indicate that current reporting and recording sensitivities are inadequate.

  19. Atomistic mechanisms of strain relaxation due to ductile void growth in ultrathin films of face-centered-cubic metals

    Science.gov (United States)

    Gungor, M. Rauf; Maroudas, Dimitrios

    2005-06-01

    A comprehensive computational analysis is reported of the atomistic mechanisms of strain relaxation and failure in free-standing Cu thin films under applied biaxial tensile strain for strain levels up to 6%. The analysis focuses on nanometer-scale-thick films with a preexisting void extending across the film thickness and the film plane oriented normal to the [111] crystallographic direction. Our computational study is based on isothermal-isostrain large-scale molecular-dynamics simulations within an embedded-atom-method parametrization for Cu. Our analysis has revealed various regimes in the film's mechanical response as the applied strain level increases. Within the considered strain range, after an elastic response at a low strain (pipe diffusion along dislocation cores, as well as dislocation-dislocation interactions. The increase in film surface roughness with increasing strain eventually leads to nucleation and propagation from the film surfaces of threading dislocation loops, which ultimately break up when they reach the opposite free surface of the thin film.

  20. Intergranular fracture in nanocrystalline metals

    Science.gov (United States)

    Farkas, D.; van Swygenhoven, H.; Derlet, P. M.

    2002-08-01

    Crack propagation studies in nanocrystalline Ni samples with mean grain sizes ranging from 5 to 12 nm are reported using atomistic simulations. For all grain sizes pure intergranular fracture is observed. Intergranular fracture is shown to proceed by the coalescence of microvoids formed at the grain boundaries ahead of the crack. The energy released during propagation is higher than the Griffith value, indicating an additional grain-boundary accommodation mechanism.

  1. 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.

  2. 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...

  3. Lipid exchange mechanism of the cholesteryl ester transfer protein clarified by atomistic and coarse-grained simulations.

    Directory of Open Access Journals (Sweden)

    Artturi Koivuniemi

    2012-01-01

    Full Text Available Cholesteryl ester transfer protein (CETP transports cholesteryl esters, triglycerides, and phospholipids between different lipoprotein fractions in blood plasma. The inhibition of CETP has been shown to be a sound strategy to prevent and treat the development of coronary heart disease. We employed molecular dynamics simulations to unravel the mechanisms associated with the CETP-mediated lipid exchange. To this end we used both atomistic and coarse-grained models whose results were consistent with each other. We found CETP to bind to the surface of high density lipoprotein (HDL -like lipid droplets through its charged and tryptophan residues. Upon binding, CETP rapidly (in about 10 ns induced the formation of a small hydrophobic patch to the phospholipid surface of the droplet, opening a route from the core of the lipid droplet to the binding pocket of CETP. This was followed by a conformational change of helix X of CETP to an open state, in which we found the accessibility of cholesteryl esters to the C-terminal tunnel opening of CETP to increase. Furthermore, in the absence of helix X, cholesteryl esters rapidly diffused into CETP through the C-terminal opening. The results provide compelling evidence that helix X acts as a lid which conducts lipid exchange by alternating the open and closed states. The findings have potential for the design of novel molecular agents to inhibit the activity of CETP.

  4. Fracture mechanical assessment of the quality of piping

    International Nuclear Information System (INIS)

    The function, goals and methods of fracture-mechanical analysis of pipeline systems are described as a function of their safety relevance and defect conditions. A distinction is made between postulated, production-induced and operation-induced defects, and the interdependence between fracture-mechanical and non-destructive testing is pointed out. To maintain the integrity of pipelines and exclude pipeline fracture, it is necessary to know about damage mechanisms so that defects can be excluded already during production. Here, fracture mechanical analysis is a supplementary method for proof of integrity. As there are no real findings, defect sizes must be postulated on the basis of the minimum defect size identified by non-destructive testing

  5. Void Coalescence Processes Quantified Through Atomistic and Multiscale Simulation

    Energy Technology Data Exchange (ETDEWEB)

    Rudd, R E; Seppala, E T; Dupuy, L M; Belak, J

    2007-01-12

    Simulation of ductile fracture at the atomic scale reveals many aspects of the fracture process including specific mechanisms associated with void nucleation and growth as a precursor to fracture and the plastic deformation of the material surrounding the voids and cracks. Recently we have studied void coalescence in ductile metals using large-scale atomistic and continuum simulations. Here we review that work and present some related investigations. The atomistic simulations involve three-dimensional strain-controlled multi-million atom molecular dynamics simulations of copper. The correlated growth of two voids during the coalescence process leading to fracture is investigated, both in terms of its onset and the ensuing dynamical interactions. Void interactions are quantified through the rate of reduction of the distance between the voids, through the correlated directional growth of the voids, and through correlated shape evolution of the voids. The critical inter-void ligament distance marking the onset of coalescence is shown to be approximately one void radius based on the quantification measurements used, independent of the initial separation distance between the voids and the strain-rate of the expansion of the system. No pronounced shear flow is found in the coalescence process. We also discuss a technique for optimizing the calculation of fine-scale information on the fly for use in a coarse-scale simulation, and discuss the specific case of a fine-scale model that calculates void growth explicitly feeding into a coarse-scale mechanics model to study damage localization.

  6. Mechanical Properties and Failure of Biopolymers: Atomistic Reactions to Macroscale Response.

    Science.gov (United States)

    Jung, GangSeob; Qin, Zhao; Buehler, Markus J

    2015-01-01

    The behavior of chemical bonding under various mechanical loadings is an intriguing mechanochemical property of biological materials, and the property plays a critical role in determining their deformation and failure mechanisms. Because of their astonishing mechanical properties and roles in constituting the basis of a variety of physiologically relevant materials, biological protein materials have been intensively studied. Understanding the relation between chemical bond networks (structures) and their mechanical properties offers great possibilities to enable new materials design in nanotechnology and new medical treatments for human diseases. Here we focus on how the chemical bonds in biological systems affect mechanical properties and how they change during mechanical deformation and failure. Three representative cases of biomaterials related to the human diseases are discussed in case studies, including: amyloids, intermediate filaments, and collagen, each describing mechanochemical features and how they relate to the pathological conditions at multiple scales.

  7. Effects of surface atomistic modification on mechanical properties of gold nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Xiao-Yu [AML and CNMM, Department of Engineering Mechanics, Tsinghua University, Beijing 100084 (China); Department of Engineering Mechanics, School of Civil Engineering, Wuhan University, Wuhan 430072 (China); Xu, Yuanjie [Department of Engineering Mechanics, School of Civil Engineering, Wuhan University, Wuhan 430072 (China); Wang, Gang-Feng [Department of Engineering Mechanics, Xi' an Jiaotong University, Xi' an 710049 (China); Gu, Yuantong [School of Chemistry, Physics, and Mechanical Engineering, Queensland University of Technology, Brisbane 4001 (Australia); Feng, Xi-Qiao, E-mail: fengxq@tsinghua.edu.cn [AML and CNMM, Department of Engineering Mechanics, Tsinghua University, Beijing 100084 (China)

    2015-09-18

    Highlights: • Molecular dynamics simulations of surface modification effect of Au nanowires. • Surface modification can greatly affect the mechanical properties of nanowires. • Core–shell model is used to elucidate the effect of residual surface stress. - Abstract: Modulation of the physical and mechanical properties of nanowires is a challenging issue for their technological applications. In this paper, we investigate the effects of surface modification on the mechanical properties of gold nanowires by performing molecular dynamics simulations. It is found that by modifying a small density of silver atoms to the surface of a gold nanowire, the residual surface stress state can be altered, rendering a great improvement of its plastic yield strength. This finding is in good agreement with experimental measurements. The underlying physical mechanisms are analyzed by a core–shell nanowire model. The results are helpful for the design and optimization of advanced nanomaterial with superior mechanical properties.

  8. 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.

  9. 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.

  10. Analysis of a Prototypical Multiscale Method Coupling Atomistic and Continuum Mechanics:the Convex Case

    Institute of Scientific and Technical Information of China (English)

    Xavier Blanc; Claude Le Bris; Prédéric Legol

    2007-01-01

    In order to describe a solid which deforms smoothly in some region,but non smoothly in some other region,many multiscale methods have been recently proposed that aim at coupling an atonfistic model (discrete mechanics)with a macroscopic model(continuum mechanics).We provide here a theoretical basis for such a coupling in a one-dimensional setting,in the case of convex energy.

  11. Ab initio atomistic thermodynamics study on the oxidation mechanism of binary and ternary alloy surfaces

    International Nuclear Information System (INIS)

    Utilizing a combination of ab initio density-functional theory and thermodynamics formalism, we have established the microscopic mechanisms for oxidation of the binary and ternary alloy surfaces and provided a clear explanation for the experimental results of the oxidation. We construct three-dimensional surface phase diagrams (SPDs) for oxygen adsorption on three different Nb-X(110) (X = Ti, Al or Si) binary alloy surfaces. On the basis of the obtained SPDs, we conclude a general microscopic mechanism for the thermodynamic oxidation, that is, under O-rich conditions, a uniform single-phase SPD (type I) and a nonuniform double-phase SPD (type II) correspond to the sustained complete selective oxidation and the non-sustained partial selective oxidation by adding the X element, respectively. Furthermore, by revealing the framework of thermodynamics for the oxidation mechanism of ternary alloys through the comparison of the surface energies of two separated binary alloys, we provide an understanding for the selective oxidation behavior of the Nb ternary alloy surfaces. Using these general microscopic mechanisms, one could predict the oxidation behavior of any binary and multi-component alloy surfaces based on thermodynamics considerations

  12. Ab initio atomistic thermodynamics study on the oxidation mechanism of binary and ternary alloy surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Shi-Yu, E-mail: buaasyliu@gmail.com [College of Physics and Electronic Information Science, Tianjin Normal University, Tianjin 300387 (China); Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Kowloon, Hong Kong (China); Liu, Shiyang [Institute of Information Optics, Zhejiang Normal University, Jinhua, Zhejiang 321004 (China); Li, De-Jun [College of Physics and Electronic Information Science, Tianjin Normal University, Tianjin 300387 (China); Wang, Sanwu, E-mail: sanwu-wang@utulsa.edu [Department of Physics and Engineering Physics, The University of Tulsa, Tulsa, Oklahoma 74104 (United States); Guo, Jing; Shen, Yaogen, E-mail: meshen@cityu.edu.hk [Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Kowloon, Hong Kong (China)

    2015-02-14

    Utilizing a combination of ab initio density-functional theory and thermodynamics formalism, we have established the microscopic mechanisms for oxidation of the binary and ternary alloy surfaces and provided a clear explanation for the experimental results of the oxidation. We construct three-dimensional surface phase diagrams (SPDs) for oxygen adsorption on three different Nb-X(110) (X = Ti, Al or Si) binary alloy surfaces. On the basis of the obtained SPDs, we conclude a general microscopic mechanism for the thermodynamic oxidation, that is, under O-rich conditions, a uniform single-phase SPD (type I) and a nonuniform double-phase SPD (type II) correspond to the sustained complete selective oxidation and the non-sustained partial selective oxidation by adding the X element, respectively. Furthermore, by revealing the framework of thermodynamics for the oxidation mechanism of ternary alloys through the comparison of the surface energies of two separated binary alloys, we provide an understanding for the selective oxidation behavior of the Nb ternary alloy surfaces. Using these general microscopic mechanisms, one could predict the oxidation behavior of any binary and multi-component alloy surfaces based on thermodynamics considerations.

  13. Void Coalescence Processes Quantified through Atomistic and Multiscale Simulation

    Energy Technology Data Exchange (ETDEWEB)

    Rudd, R E; Seppala, E T; Dupuy, L M; Belak, J

    2005-12-31

    Simulation of ductile fracture at the atomic scale reveals many aspects of the fracture process including specific mechanisms associated with void nucleation and growth as a precursor to fracture and the plastic deformation of the material surrounding the voids and cracks. Recently we have studied void coalescence in ductile metals using large-scale atomistic and continuum simulations. Here we review that work and present some related investigations. The atomistic simulations involve three-dimensional strain-controlled multi-million atom molecular dynamics simulations of copper. The correlated growth of two voids during the coalescence process leading to fracture is investigated, both in terms of its onset and the ensuing dynamical interactions. Void interactions are quantified through the rate of reduction of the distance between the voids, through the correlated directional growth of the voids, and through correlated shape evolution of the voids. The critical inter-void ligament distance marking the onset of coalescence is shown to be approximately one void radius based on the quantification measurements used, independent of the initial separation distance between the voids and the strain-rate of the expansion of the system. No pronounced shear flow is found in the coalescence process.

  14. Atomistic Modeling of Mechanical Characteristics of CNT-Polyethylene with Interfacial Covalent Interaction

    Directory of Open Access Journals (Sweden)

    Qi-lin Xiong

    2015-01-01

    Full Text Available The mechanical properties of carbon nanotube- (CNT- reinforced polyethylenes (PE with interfacial covalent bonded interaction are investigated using molecular dynamics simulations. A reactive force field for hydrocarbons (ReaxFF is used in the nanocomposite system. Through a series of the tensile and pullout tests of carbon nanotube-reinforced polyethylene, Young’s modulus and the interfacial shear stress of the nano-reinforced polyethylene are obtained. The comparisons between the MD results of this work and the relevant experimental data of the existing literature are made and the results show that the interfacial covalent bonded interaction between CNTs and the polymer matrix is indispensable. The bond interaction plays the main role in the load transfer of nanocomposites. In addition, the influences of carbon nanotube embedded length and diameter on the interfacial mechanical properties also are studied.

  15. Atomistic Modeling of Mechanical Characteristics of CNT-Polyethylene with Interfacial Covalent Interaction

    OpenAIRE

    2015-01-01

    The mechanical properties of carbon nanotube- (CNT-) reinforced polyethylenes (PE) with interfacial covalent bonded interaction are investigated using molecular dynamics simulations. A reactive force field for hydrocarbons (ReaxFF) is used in the nanocomposite system. Through a series of the tensile and pullout tests of carbon nanotube-reinforced polyethylene, Young’s modulus and the interfacial shear stress of the nano-reinforced polyethylene are obtained. The comparisons between the MD resu...

  16. Simulating surface-enhanced Raman optical activity using atomistic electrodynamics-quantum mechanical models.

    Science.gov (United States)

    Chulhai, Dhabih V; Jensen, Lasse

    2014-10-01

    Raman optical activity has proven to be a powerful tool for probing the geometry of small organic and biomolecules. It has therefore been expected that the same mechanisms responsible for surface-enhanced Raman scattering may allow for similar enhancements in surface-enhanced Raman optical activity (SEROA). However, SEROA has proved to be an experimental challenge and mirror-image SEROA spectra of enantiomers have so far not been measured. There exists a handful of theories to simulate SEROA, all of which treat the perturbed molecule as a point-dipole object. To go beyond these approximations, we present two new methods to simulate SEROA: the first is a dressed-tensors model that treats the molecule as a point-dipole and point-quadrupole object; the second method is the discrete interaction model/quantum mechanical (DIM/QM) model, which considers the entire charge density of the molecule. We show that although the first method is acceptable for small molecules, it fails for a medium-sized one such as 2-bromohexahelicene. We also show that the SEROA mode intensities and signs are highly sensitive to the nature of the local electric field and gradient, the orientation of the molecule, and the surface plasmon frequency width. Our findings give some insight into why experimental SEROA, and in particular observing mirror-image SEROA for enantiomers, has been difficult.

  17. Mechanical Behavior of Carbon Nanotubes Filled With Metal Nanowires By Atomistic Simulations

    Science.gov (United States)

    Danailov, Daniel; Keblinski, Pawel; Pulickel, Ajayan; Nayak, Saroj

    2002-03-01

    Using molecular dynamics simulations we studied mechanical behavior of (10,10) carbon nanotubes filled with a crystalline fcc metal wires. The interatomic interactions were described by a combination of Terfoff’s bond-order potential for carbon, embedded atom method (EAM) potential for metal and pair potential for carbon-metal interactions. The elastic properties, as well as failure mechanism were determined by simulating three point bending test, by pressing the center and the ends of relatively long tube in determined relatively small ring areas. We observed that following elastic response, at larger deformation, the metal wire yields well before the carbon bonding is affected. The behavior of filled tubes was compared with that of hollow tubes. Interesting is thet the hollow carbon (10,10) nanotube is more strong elastically than the same tube filled with Au-metal nanowire. We also simulated indentation of filled tubes residing on a hard flat surface. Similarly as in the bending test, metal wire yields first, is cut in between hard cylinder and hard plane and pushed away from under the indenter. Upon further increase of the indentation force, carbon tube is broken and forms two open ends that are rapidly zipped around the cut metal wire. Remarkably, the shape of the zipped tube ends strong depend of the speed of the punching of the tube. This result imply a possibility of designing tubes with various closed end shapes with applicationusing in the nanoscale manipulation procedures used for production.

  18. 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.

  19. 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

  20. Atomistic mechanism of charge separation upon photoexcitation at the dye-semiconductor interface for photovoltaic applications.

    Science.gov (United States)

    Jiao, Yang; Ding, Zijing; Meng, Sheng

    2011-08-01

    Charge separation in excited states upon visible light absorption is a central process in photovoltaic solar cell applications. Employing state-of-the-art first principles calculations based on time-dependent density functional theory (TDDFT), we simulate electron-hole dynamics in real time and illustrate the microscopic mechanism of charge separation at the interface between organic dye molecules and oxide semiconductor surfaces in dye-sensitized solar cells. We found that electron-hole separation proceeds non-adiabatically on an ultrafast timescale <100 fs at an anthocyanin/TiO(2) interface, and it is strongly mediated by the vibrations of interface Ti-O bonds, which anchor the dye onto the TiO(2) surface. The obtained absorption spectrum and electron injection timescale agree with experimental measurements.

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

    DEFF Research Database (Denmark)

    Jensen, Henrik Myhre

    2006-01-01

    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......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...... 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....

  2. 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.

    1994-09-01

    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.

  3. Mechanisms of radiation strengthening in Fe–Cr alloys as revealed by atomistic studies

    Energy Technology Data Exchange (ETDEWEB)

    Terentyev, D.; Bonny, G. [Structural Materials Modelling and Microstructure Unit, SMA/NMS, Studiecentrum voor Kernenergie, Centre d’Etudes de l’Energie Nucléaire (SCK-CEN), Boeretang 200, 2400 Mol (Belgium); Domain, C.; Monnet, G. [EDF-R and D, Département MMC, Les Renardières, 77818 Moret sur Loing Cedex (France); Malerba, L., E-mail: lmalerba@sckcen.be [Structural Materials Modelling and Microstructure Unit, SMA/NMS, Studiecentrum voor Kernenergie, Centre d’Etudes de l’Energie Nucléaire (SCK-CEN), Boeretang 200, 2400 Mol (Belgium)

    2013-11-15

    A review of experimental results shows that the dependence on Cr content of radiation-induced strengthening in Fe–Cr alloys and ferritic/martensitic steels is peculiar, exhibiting an increase as soon as Cr is added, followed by a local maximum and then a local minimum. This dependence is to date unexplained. In this paper we try to rationalise it, by reviewing recent (published and unpublished) molecular dynamics simulations work, devoted to the investigation of several possible mechanisms of radiation strengthening in Fe–Cr. In particular, the following questions are addressed quantitatively: (i) Does Cr influence the glide of dislocations? If so, how? (ii) Does Cr influence the interaction between dislocations and radiation-produced defects? If so, why? The latter question involves also a study of the interaction of moving dislocations with experimentally observed Cr-enriched loops. We find that the fact of shifting from a loop-absorption (pure Fe) to a loop-non-absorption (Fe–Cr) regime, because of the Cr–enrichment of loops, contributes to explaining why Fe–Cr alloys harden more under irradiation than Fe. If, in addition, the existence of a large density of invisible and Cr-enriched loops is postulated, the origin of the effect becomes even more clear. Moreover, the different strength of 〈1 1 1〉 and 〈1 0 0〉 loops as obstacles to dislocations movement, depending on whether or not loop absorption can occur, might explain why radiation strengthening decreases between 2% and 9%Cr. The formation of α′ precipitates, on the other hand, explains why radiation strengthening increases again above 9%Cr. Altogether, these effects might explain the origin of the minimum of radiation-induced embrittlement at 9%Cr, as correlated to strengthening.

  4. The hydro-mechanical modeling of the fractured media

    International Nuclear Information System (INIS)

    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

  5. Statistical fracture mechanics approach to the strength of brittle rock

    International Nuclear Information System (INIS)

    Statistical fracture mechanics concepts used in the past for rock are critically reviewed and modifications are proposed which are warranted by (1) increased understanding of fracture provided by modern fracture mechanics and (2) laboratory test data both from the literature and from this research. Over 600 direct and indirect tension tests have been performed on three different rock types; Stripa Granite, Sierra White Granite and Carrara Marble. In several instances assumptions which are common in the literature were found to be invalid. A three parameter statistical fracture mechanics model with Mode I critical strain energy release rate as the variant is presented. Methodologies for evaluating the parameters in this model as well as the more commonly employed two parameter models are discussed. The experimental results and analysis of this research indicate that surfacially distributed flaws, rather than volumetrically distributed flaws are responsible for rupture in many testing situations. For several of the rock types tested, anisotropy (both in apparent tensile strength and size effect) precludes the use of contemporary statistical fracture mechanics models

  6. 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 fatigue life of welded plate specimens has been investigated. Both the fracture mechanics analyses and the fatigue tests have been carried out using load histories, which correspond to one week's traffic loading, determined by means of strain gauge measurements on the deck structure of the Farø Bridges...... 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....

  7. Mechanical transport in two-dimensional networks of fractures

    International Nuclear Information System (INIS)

    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

  8. Computational aspects of nonlinear fracture mechanics

    International Nuclear Information System (INIS)

    The following contribution will essentially restrict to the application of the von Mises theory of incremental plasticity to cracked specimens and components. In particular, the classical parameters of EPFM, J and CTOD, as well as subsequently proposed parameters such as energy dissipation rate and crack-tip opening angle (CTOA) and the related computational aspects will be discussed. Some remarks follow on the 'local approach to fracture' which is based on continuum field quantities, namely stresses and strains, and the damage models of Gurson (1977) and Rousselier (1987), which have now found increasing application, will be briefly addressed in Section 3.03.4. The numerical modeling of decohesion and separation phenomena by 'cohesive elements' will be presented in Section 3.03.5. (orig.)

  9. Fracture mechanics based life assessment in petrochemical plants

    International Nuclear Information System (INIS)

    The increasing use of thick walled pressure vessels in petrochemical plants operating at high pressure under severe service conditions could lead to catastrophic failure. In the Malaysian Institute for Nuclear Technology Research (MINT), initial efforts are underway to apply fracture mechanics approach for assessment of significance of defects detected during periodic in service inspection (ISI) of industrial plants. This paper outlines the integrity management strategy based on fracture mechanics and proposes a new procedure for life assessment of petrochemical plants based on ASME Boiler and Pressure Vessel Code, Section XI, BSI PD 6493:1991, BSI 6539:1994, BSI Standard 7910:1999 and API 579:2000. Essential relevant data required for the assessment is listed. Several methods available for determination of fracture toughness are reviewed with limitations in their application to petrochemical plants. A new non destructive method for determination of fracture toughness based on hardness testing and normalized key roughness curve is given. Results of fracture mechanics based life assessment conducted for 100 mm thick ammonia converter of Ni r o steel and 70 mm thick plat forming reactor vessel of ASTM A 38 7 grade B steel in operational fertilizer and petroleum refining plants are presented. (Author)

  10. Fracture mechanics: proceedings of the 12th national symposium on fracture mechanics

    International Nuclear Information System (INIS)

    The conference proceedings contains 30 papers of which five are abstracted separately. The subjects covered include fatigue crack growth in aircraft materials, fractographic measurements, fatigue cracks in nylon 66 blends, cyclic inelastic deformation aspects, prestressing, tensile cracks in creeping solids, creep-crack-growth in 304 stainless steel, high-temperature fatigue, parallel impact loading, numerical fracture dynamic code, J-resistance curves, specimen geometry effects, reactor piping systems, temperature dependence of fracture toughness, small-scale yielding, compact specimens, power hardening materials, semi-empirical fracture analyses, pipeline girth welds, wrought steels, and A36 bridge steels

  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. Nonlinear Fracture Mechanics and Plasticity of the Split Cylinder Test

    DEFF Research Database (Denmark)

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

    2006-01-01

    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...... models are presented, a simple semi-analytical model based on analytical solutions for the crack propagation in a rectangular prismatic body, and a finite element model including plasticity in bulk material as well as crack propagation in interface elements. A numerical study applying these models...... 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...

  13. 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.

  14. 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....

  15. 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

  16. 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.

  17. Hierarchical Statistical 3D ' Atomistic' Simulation of Decanano MOSFETs: Drift-Diffusion, Hydrodynamic and Quantum Mechanical Approaches

    Science.gov (United States)

    Asenov, Asen; Brown, A. R.; Slavcheva, G.; Davies, J. H.

    2000-01-01

    When MOSFETs are scaled to deep submicron dimensions the discreteness and randomness of the dopant charges in the channel region introduces significant fluctuations in the device characteristics. This effect, predicted 20 year ago, has been confirmed experimentally and in simulation studies. The impact of the fluctuations on the functionality, yield, and reliability of the corresponding systems shifts the paradigm of the numerical device simulation. It becomes insufficient to simulate only one device representing one macroscopical design in a continuous charge approximation. An ensemble of macroscopically identical but microscopically different devices has to be characterized by simulation of statistically significant samples. The aims of the numerical simulations shift from predicting the characteristics of a single device with continuous doping towards estimating the mean values and the standard deviations of basic design parameters such as threshold voltage, subthreshold slope, transconductance, drive current, etc. for the whole ensemble of 'atomistically' different devices in the system. It has to be pointed out that even the mean values obtained from 'atomistic' simulations are not identical to the values obtained from continuous doping simulations. In this paper we present a hierarchical approach to the 'atomistic' simulation of aggressively scaled decanano MOSFETs. A full scale 3D drift-diffusion'atomostic' simulation approach is first described and used for verification of the more economical, but also more restricted, options. To reduce the processor time and memory requirements at high drain voltage we have developed a self-consistent option based on a thin slab solution of the current continuity equation only in the channel region. This is coupled to the Poisson's equation solution in the whole simulation domain in the Gummel iteration cycles. The accuracy of this approach is investigated in comparison with the full self-consistent solution. At low drain

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. Probability fracture mechanics analysis of plates with surface cracks

    International Nuclear Information System (INIS)

    Background: The uncertainties of input parameters in an deterministic structural integrity assessment of pressure vessels may affect the assessment results. This can be improved by performing probability fracture mechanics (PFM) analysis. Purpose: This work investigates the effect of uncertainties of load, defect size, fracture toughness and failure criteria on the failure probability of semi-elliptical surface cracks in plates under combined tension and bending. Methods: The correction factor method provided by EPRI is used to estimate the stress intensity factor (SIF). The J-integral values at the deepest point of the surface crack tip are evaluated using the reference stress method and the globe limit load solution developed by Goodall and Webster and Lei. PFM analysis is performed with considering the uncertainty of crack size, yield strength and fracture toughness and Monte-Carlo (MC) simulation is used to calculate the failure probability. Results: Failure probability increases with increase of load level, Lr, for all load ratio values considered in this work for a given failure criterion. However, the failure probability based on the elastic-plastic fracture criterion is higher than that based on the linear elastic fracture criterion for a given load lever, Lr. Conclusions: The load level and the failure criteria have significant effect on the failure probability. However, the load ratio makes a little contribution to the failure probability for a given failure criterion. (authors)

  4. Hydraulic Fracture Extending into Network in Shale: Reviewing Influence Factors and Their Mechanism

    Directory of Open Access Journals (Sweden)

    Lan Ren

    2014-01-01

    Full Text Available Hydraulic fracture in shale reservoir presents complex network propagation, which has essential difference with traditional plane biwing fracture at forming mechanism. Based on the research results of experiments, field fracturing practice, theory analysis, and numerical simulation, the influence factors and their mechanism of hydraulic fracture extending into network in shale have been systematically analyzed and discussed. Research results show that the fracture propagation in shale reservoir is influenced by the geological and the engineering factors, which includes rock mineral composition, rock mechanical properties, horizontal stress field, natural fractures, treating net pressure, fracturing fluid viscosity, and fracturing scale. This study has important theoretical value and practical significance to understand fracture network propagation mechanism in shale reservoir and contributes to improving the science and efficiency of shale reservoir fracturing design.

  5. 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.

  6. Hydraulic Fracture Extending into Network in Shale: Reviewing Influence Factors and Their Mechanism

    OpenAIRE

    Lan Ren; Jinzhou Zhao; Yongquan Hu

    2014-01-01

    Hydraulic fracture in shale reservoir presents complex network propagation, which has essential difference with traditional plane biwing fracture at forming mechanism. Based on the research results of experiments, field fracturing practice, theory analysis, and numerical simulation, the influence factors and their mechanism of hydraulic fracture extending into network in shale have been systematically analyzed and discussed. Research results show that the fracture propagation in shale reservo...

  7. 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.

  8. Atomistic Properties of Solids

    CERN Document Server

    Sirdeshmukh, Dinker B; Subhadra, K G

    2011-01-01

    The book deals with atomistic properties of solids which are determined by the crystal structure, interatomic forces and atomic displacements influenced by the effects of temperature, stress and electric fields. The book gives equal importance to experimental details and theory. There are full chapters dedicated to the tensor nature of physical properties, mechanical properties, lattice vibrations, crystal structure determination and ferroelectricity. The other crystalline states like nano-, poly-, liquid- and quasi crystals are discussed. Several new topics like nonlinear optics and the Rietveld method are presented in the book. The book lays emphasis on the role of symmetry in crystal properties. Comprehensiveness is the strength of the book; this allows users at different levels a choice of chapters according to their requirements.

  9. Fatigue and fracture mechanics analysis of threaded connections

    OpenAIRE

    Brennan, F. P.

    1992-01-01

    This thesis aims to develop a comprehensive usable engineering design approach to the fatigue analysis of threaded connections. Although primarily concerned with the fatigue-fracture mechanics behaviour of screw threads, a broad review of stress analysis investigations in such connections is reported. Connection types, their functions and standardisation authorities are presented with the purpose of familiarising the reader with the subject and the options available to th...

  10. 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.

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

    International Nuclear Information System (INIS)

    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

  12. 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.

  13. Atomistic Mechanisms of Chemical Mechanical Polishing of a Cu Surface in Aqueous H2O2: Tight-Binding Quantum Chemical Molecular Dynamics Simulations.

    Science.gov (United States)

    Kawaguchi, Kentaro; Ito, Hiroshi; Kuwahara, Takuya; Higuchi, Yuji; Ozawa, Nobuki; Kubo, Momoji

    2016-05-11

    We applied our original chemical mechanical polishing (CMP) simulator based on the tight-binding quantum chemical molecular dynamics (TB-QCMD) method to clarify the atomistic mechanism of CMP processes on a Cu(111) surface polished with a SiO2 abrasive grain in aqueous H2O2. We reveal that the oxidation of the Cu(111) surface mechanically induced at the friction interface is a key process in CMP. In aqueous H2O2, in the first step, OH groups and O atoms adsorbed on a nascent Cu surface are generated by the chemical reactions of H2O2 molecules. In the second step, at the friction interface between the Cu surface and the abrasive grain, the surface-adsorbed O atom intrudes into the Cu bulk and dissociates the Cu-Cu bonds. The dissociation of the Cu-Cu back-bonds raises a Cu atom from the surface that is mechanically sheared by the abrasive grain. In the third step, the raised Cu atom bound to the surface-adsorbed OH groups is removed from the surface by the generation and desorption of a Cu(OH)2 molecule. In contrast, in pure water, there are no geometrical changes in the Cu surface because the H2O molecules do not react with the Cu surface, and the abrasive grain slides smoothly on the planar Cu surface. The comparison between the CMP simulations in aqueous H2O2 and pure water indicates that the intrusion of a surface-adsorbed O atom into the Cu bulk is the most important process for the efficient polishing of the Cu surface because it induces the dissociation of the Cu-Cu bonds and generates raised Cu atoms that are sheared off by the abrasive grain. Furthermore, density functional theory calculations show that the intrusion of the surface-adsorbed O atoms into the Cu bulk has a high activation energy of 28.2 kcal/mol, which is difficult to overcome at 300 K. Thus, we suggest that the intrusion of surface-adsorbed O atoms into the Cu bulk induced by abrasive grains at the friction interface is a rate-determining step in the Cu CMP process. PMID:27092706

  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. [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.

  16. 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.

  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. Principles of fracture mechanics applications in nuclear power plants

    International Nuclear Information System (INIS)

    Fracture mechanics is widely used in nuclear plants safety assessment and remaining life evaluation. Methods of flow assessment in nuclear components are at an advanced stage of development and are suitable for general application in light water reactors and liquid metal cooled reactors. Following the first Saclay International Seminar on Structural Integrity (SISSI), hold in October 1991 and devoted to fracture in austenitic steels components, the second SISSI convened in April 1994 the European specialists to review the flaw assessment guides in application or in development in their countries, to discuss supporting research and development validation programs, application experience on the nuclear power plants and consequences on the components design. The seminar is sponsored by the CEA, Electricite de France, Framatome and the European Union D.G. XI. (J.S.)

  19. FRACTURAL PROCESS AND TOUGHENING MECHANISM OF LAMINATED CERAMIC COMPOSITES

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Based on the model of multi-layer beam and the assumption of micro-inhomogeneity of material, the 3D fractural characteristics of laminated ceramic composites have been studied with numerical simulation. Under three-point bending load, crack initiation, coalescence, propagation, tuning off in the weak interface and final rupture have been simulated. The spatial distribution and evolution process of acoustic emission are also presented in the paper. The simulation verifies the primary mechanism of the weak interface inducing the crack to expand along there and absorbing the fractural energy. The disciplinary significance of the effect of strength and properties of material on the toughness and strength of laminated ceramic composites is, therefore,discussed in this paper.

  20. OCA-P, PWR Vessel Probabilistic Fracture Mechanics

    International Nuclear Information System (INIS)

    1 - Description of program or function: OCA-P is a probabilistic fracture-mechanics code prepared specifically for evaluating the integrity of pressurized-water reactor vessels subjected to overcooling-accident loading conditions. Based on linear-elastic fracture mechanics, it has two- and limited three-dimensional flaw capability, and can treat cladding as a discrete region. Both deterministic and probabilistic analyses can be performed. For deterministic analysis, it is possible to conduct a search for critical values of the fluence and the nil-ductility reference temperature corresponding to incipient initiation of the initial flaw. The probabilistic portion of OCA-P is based on Monte Carlo techniques, and simulated parameters include fluence, flaw depth, fracture toughness, nil-ductility reference temperature, and concentrations of copper, nickel, and phosphorous. Plotting capabilities include the construction of critical-crack-depth diagrams (deterministic analysis) and a variety of histograms (probabilistic analysis). 2 - Method of solution: OAC-P accepts as input the reactor primary- system pressure and the reactor pressure-vessel downcomer coolant temperature, as functions of time in the specified transient. Then, the wall temperatures and stresses are calculated as a function of time and radial position in the wall, and the fracture-mechanics analysis is performed to obtain the stress intensity factors as a function of crack depth and time in the transient. In a deterministic analysis, values of the static crack initiation toughness and the crack arrest toughness are also calculated for all crack depths and times in the transient. A comparison of these values permits an evaluation of flaw behavior. For a probabilistic analysis, OCA-P generates a large number of reactor pressure vessels, each with a different combination of the various values of the parameters involved in the analysis of flaw behavior. For each of these vessels, a deterministic fracture

  1. Scalability of a Low-Cost Multi-Teraflop Linux Cluster for High-End Classical Atomistic and Quantum Mechanical Simulations

    Science.gov (United States)

    Kikuchi, Hideaki; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya; Shimojo, Fuyuki; Saini, Subhash

    2003-01-01

    Scalability of a low-cost, Intel Xeon-based, multi-Teraflop Linux cluster is tested for two high-end scientific applications: Classical atomistic simulation based on the molecular dynamics method and quantum mechanical calculation based on the density functional theory. These scalable parallel applications use space-time multiresolution algorithms and feature computational-space decomposition, wavelet-based adaptive load balancing, and spacefilling-curve-based data compression for scalable I/O. Comparative performance tests are performed on a 1,024-processor Linux cluster and a conventional higher-end parallel supercomputer, 1,184-processor IBM SP4. The results show that the performance of the Linux cluster is comparable to that of the SP4. We also study various effects, such as the sharing of memory and L2 cache among processors, on the performance.

  2. Probabilistic/Fracture-Mechanics Model For Service Life

    Science.gov (United States)

    Watkins, T., Jr.; Annis, C. G., Jr.

    1991-01-01

    Computer program makes probabilistic estimates of lifetime of engine and components thereof. Developed to fill need for more accurate life-assessment technique that avoids errors in estimated lives and provides for statistical assessment of levels of risk created by engineering decisions in designing system. Implements mathematical model combining techniques of statistics, fatigue, fracture mechanics, nondestructive analysis, life-cycle cost analysis, and management of engine parts. Used to investigate effects of such engine-component life-controlling parameters as return-to-service intervals, stresses, capabilities for nondestructive evaluation, and qualities of materials.

  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. Elastic, plastic, and fracture mechanisms in graphene materials

    International Nuclear Information System (INIS)

    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. (topical review)

  6. 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

    2015-09-01

    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.

  7. 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.)

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

    International Nuclear Information System (INIS)

    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.)

  9. Application of probabilistic fracture mechanics to the PTS issue

    International Nuclear Information System (INIS)

    As a part of the NRC effort to obtain a resolution to the PWR PTS issue, a probabilistic approach has been applied that includes a probabilistic fracture-mechanics (PFM) analysis. The PFM analysis is performed with OCA-P, a computer code that performs thermal, stress and fracture-mechanics analyses and estimates the conditional probability of vessel failure, P(F/E), using Monte Carlo techniques. The stress intensity factor (K/sub I/) is calculated for two- and three-dimensional surface flaws using superposition techniques and influence coefficients. Importance-sampling techniques are used, as necessary, to limit to a reasonable value the number of vessels actually calculated. Analyses of three PWR plants indicate that (1) the critical initial flaw depth is very small (5 to 15 mm), (2) the benefit of warm prestressing and the role of crack arrest are transient dependent, (3) crack arrest does not occur for the dominant transients, and (4) the single largest uncertainty in the overall probabilistic analysis is the number of surface flaws per vessel. 30 refs., 6 figs., 4 tabs

  10. A fracture mechanics analysis of the DCDC specimen

    International Nuclear Information System (INIS)

    The ''double cleavage drilled compression'' (DCDC) specimen is a rectangular bar with a circular hole in its centre that is loaded by compressive stresses. Due to the hole, positive stresses are generated in the vicinity that cause positive mode-I stress intensity factors. This specimen is used for the determination of crack growth under mode-I and in a modified version under mixed-mode loading conditions. A fracture mechanics analysis is presented on the basis of finite element computations. After compilation of literature results on mixed-mode stress intensity factors and T-stresses, weight functions for mode I and mode II are derived. The consequences of load misalignment and crack kinking are shown. Since stress intensity factor results from literature are available for long cracks compared with the hole radius only, also short-crack solutions are derived by use of the weight function technique. These results al-low to discuss the generation of the initial cracks necessary for fracture mechanics tests. In several papers, the side surface displacements were reported and discussed with respect to the occurrence of plasticity effects in glass. In order to decide whether deviations from the pure linear-elastic material behaviour are measured, it is necessary to know the elastic response. Therefore, a 3-dimensional finite element study is performed. It exhibits depression and uplifting of the free surface very similar to the re-sults found in literature

  11. Application of fracture mechanics to weldments; Bruchmechanische Bewertung von Schweissverbindungen

    Energy Technology Data Exchange (ETDEWEB)

    Zerbst, U.; Kocak, M. [GKSS-Forschungszentrum Geesthacht GmbH (Germany). Inst. fuer Werkstofforschung; Huebner, P. [Technische Univ. Bergakademie Freiberg (Germany)

    2002-07-01

    Weldments have been a major topic of engineering fracture mechanics research for many years as it shows up in the immense number of scientific papers published recently. Part of this generated knowledge has already been implemented in some industrial codes and standards. The focussing on weldments has its own reason in the utmost importance of this class of components in many industrial fields, but also in its susceptibility to the formation of defects during manufacturing and cracks in service, which promotes the danger of component failure. The present report is addressed to designers and material testers to provide updated information on the present state-of-the-art of fracture mechanics application to weldments. (orig.) [German] Schweissverbindungen bilden seit vielen Jahren einen Schwerpunkt der anwendungsnahen bruchmechanischen Forschung, was seinen Niederschlag in einer nahezu unuebersehbaren Fuelle an wissenschaftlichen Publikationen findet. Ein Teil der Ergebnisse hat bereits Eingang in industrienahe bruchmechanische Bewertungsvorschriften gefunden. Die Konzentration auf Schweissverbindungen hat ihre Ursache in der immensen Bedeutung dieser Bauteilklasse fuer viele Gebiete der Volkswirtschaft, aber auch in ihrer besonderen Anfaelligkeit zur Rissbildung in der Fertigung und im Betrieb und damit hinsichtlich der Gefahr von Bauteilversagen. Der vorliegende Beitrag wendet sich an Konstrukteure und Werkstoffpruefer, die einen Einblick in den gegenwaertigen Stand der Ingenieurbruchmechanik an Schweissverbindungen gewinnen wollen. (orig.)

  12. Numerical tools for atomistic simulations.

    Energy Technology Data Exchange (ETDEWEB)

    Fang, H. (Mississippi State University); Gullett, Philip Michael; Slepoy, Alexander (Sandia National Laboratories, Albuquerque, NM); Horstemeyer, Mark F. (Mississippi State University); Baskes, Michael I. (Los Alamos National Laboratory, Los Alamos, NM); Wagner, Gregory John; Li, Mo (Materials Science and Engineering, Atlanta, GA)

    2004-01-01

    The final report for a Laboratory Directed Research and Development project entitled 'Parallel Atomistic Computing for Failure Analysis of Micromachines' is presented. In this project, atomistic algorithms for parallel computers were developed to assist in quantification of microstructure-property relations related to weapon micro-components. With these and other serial computing tools, we are performing atomistic simulations of various sizes, geometries, materials, and boundary conditions. These tools provide the capability to handle the different size-scale effects required to predict failure. Nonlocal continuum models have been proposed to address this problem; however, they are phenomenological in nature and are difficult to validate for micro-scale components. Our goal is to separately quantify damage nucleation, growth, and coalescence mechanisms to provide a basis for macro-scale continuum models that will be used for micromachine design. Because micro-component experiments are difficult, a systematic computational study that employs Monte Carlo methods, molecular statics, and molecular dynamics (EAM and MEAM) simulations to compute continuum quantities will provide mechanism-property relations associated with the following parameters: specimen size, number of grains, crystal orientation, strain rates, temperature, defect nearest neighbor distance, void/crack size, chemical state, and stress state. This study will quantify sizescale effects from nanometers to microns in terms of damage progression and thus potentially allow for optimized micro-machine designs that are more reliable and have higher fidelity in terms of strength. In order to accomplish this task, several atomistic methods needed to be developed and evaluated to cover the range of defects, strain rates, temperatures, and sizes that a material may see in micro-machines. Therefore we are providing a complete set of tools for large scale atomistic simulations that include pre

  13. Mechanics, hydraulic and coupled hydromechanics of fractured rock mass investigated by numerical experiment

    International Nuclear Information System (INIS)

    The Discrete Fracture Network-Discrete Element Method (DFN-DEM) approach uses DFN as the geometry of fractured rock and DEM for the solution technique to simulate the hydraulic and mechanical behaviour of fractured rock. This overview paper intends to summarize the applications on fractured rock using the DFN-DEM approach with the focus upon the determination of mechanical and hydraulic properties of fractured rock and their stress dependencies. The establishment of methodologies and actual applications in a site considered for geological repository of nuclear waste are introduced. (author)

  14. 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.

  15. Wear resistance and fracture mechanics of WC-Co composites

    International Nuclear Information System (INIS)

    Manufacturing of WC-Co composites using the electroless precipitation method at different sintering temperatures of 1 100, 1 250, 1 350 and 1 500 C was successfully achieved. The chemical composition of the investigated materials was 90 wt.% WC with 10 wt.% Co, and 80 wt.% WC with 20 wt.% Co. The specific density, densification, and Vickers microhardness measurements were found to increase with increased sintering temperature for both the WC-Co compositions. The composites of tungsten carbide with 10 wt.% Co had a higher specific density and Vickers microhardness measurements than those for the composites of tungsten carbide with 20 wt.% Co. Composites with WC-10 wt.% Co had better wear resistance. The stress-strain and transverse rupture strength increased monotonically with the increase in sintering temperatures, agreeing with the material hardness and wear resistance behavior. Fractographical scanning electron microscopy analysis of the fracture surface demonstrated a rough characteristic conical shape failure in the direction of the maximum shear stress. A proposed mechanism for the formation of the conical fracture surface under compression testing is presented. (orig.)

  16. Wear resistance and fracture mechanics of WC-Co composites

    Energy Technology Data Exchange (ETDEWEB)

    Kaytbay, Saleh [Benha Univ. (Egypt). Dept. of Mechanical Engineering; El-Hadek, Medhat [Port-Said Univ. (Egypt). Dept. of Production and Mechanical Design

    2014-06-15

    Manufacturing of WC-Co composites using the electroless precipitation method at different sintering temperatures of 1 100, 1 250, 1 350 and 1 500 C was successfully achieved. The chemical composition of the investigated materials was 90 wt.% WC with 10 wt.% Co, and 80 wt.% WC with 20 wt.% Co. The specific density, densification, and Vickers microhardness measurements were found to increase with increased sintering temperature for both the WC-Co compositions. The composites of tungsten carbide with 10 wt.% Co had a higher specific density and Vickers microhardness measurements than those for the composites of tungsten carbide with 20 wt.% Co. Composites with WC-10 wt.% Co had better wear resistance. The stress-strain and transverse rupture strength increased monotonically with the increase in sintering temperatures, agreeing with the material hardness and wear resistance behavior. Fractographical scanning electron microscopy analysis of the fracture surface demonstrated a rough characteristic conical shape failure in the direction of the maximum shear stress. A proposed mechanism for the formation of the conical fracture surface under compression testing is presented. (orig.)

  17. Hydro-thermo-mechanical response of a fractured rock block

    International Nuclear Information System (INIS)

    Hydro-thermo-mechanical effects in fractured rocks are important in many engineering applications and geophysical processes. Modeling these effects is made difficult by the fact that the governing equations are nonlinear and coupled, and the problems to be solved are three dimensional. In this paper we describe a numerical code developed for this purpose. The code is finite element based to allow for complicated geometries, and the time differencing is implicit, allowing for large time steps. The use of state-of-the-art equation solvers has resulted in a practical code. The code is capable of fully three dimensional simulations, however, in this paper we consider only the case of two dimensional heat and mass flow coupled to one dimensional deformation. Partial verification of the code is obtained by comparison with published semianalytical results. Several examples are presented to demonstrate the effects of matrix expansion, due to pore pressure and heating, on fracture opening due to fluid injection. 16 refs., 11 figs

  18. Mechanical and fracture mechanical properties of fine grained concrete for textile reinforced composites

    OpenAIRE

    Brockmann, Tanja

    2006-01-01

    The development of textile reinforced concrete (TRC), where multi-axial fabrics are used in combination with fine grained concrete, allows the design of very thin-structured concrete elements with a high strength in compression as well as tension. It is the main objective of this study to determine the mechanical and fracture mechanical characteristics of the newly developed fine grained binder systems as a main component of the composite to allow for a reliable dimensioning of TRC structures...

  19. The mechanical behaviour of hydraulic fractured, possibly saturated materials

    NARCIS (Netherlands)

    Visser, J.H.M.; Mier, J.G.M. van

    1998-01-01

    The influence of a fluid pressure load on the extensile fracturing of mortar and sandstone has been investigated. A fluid pressure in the (initiating) fracture stimulates both fracture initiation and propagation and may be as effective as a directly applied uniaxial tensile stress. The efficiency of

  20. 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.

  1. 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.

  2. Fracture propagation in sandstone and slate – Laboratory experiments, acoustic emissions and fracture mechanics

    Directory of Open Access Journals (Sweden)

    Ferdinand Stoeckhert

    2015-06-01

    Full Text Available Fracturing of highly anisotropic rocks is a problem often encountered in the stimulation of unconventional 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 magnitudes to stress-dominated fracture propagation at high loading magnitudes.

  3. Fracture of brittle solids

    CERN Document Server

    Lawn, Brian

    1993-01-01

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

  4. ORNL probabilistic fracture-mechanics code OCA-P

    International Nuclear Information System (INIS)

    The computer code OCA-P was developed at the request of the USNRC for the purpose of helping to evaluate the integrity of PWR pressure vessels during overcooling accidents (OCA's). The code can be used for both deterministic and probabilistic fracture-mechanics calculations, and consists essentially of OCA-II and a Monte Carlo routine similar to that developed by Strosnider et al. In the probabilistic mode OCA-P generates a large number of vessels (106 more or less), each with a different combination of the various values of the different parameters involved in the analysis of flaw behavior. For each of these vessels a deterministic fracture-mechanics analysis is performed (calculation of K/sub I/, K/sub Ic/, K/sub Ia/) to determine whether vessel failure takes place. The conditional probability of failure is simply the number of vessels that fail divided by the number of vessels generated. OCA-II is used for the deterministic analysis. Basic input to OCA-II includes, among other things, the primry-system pressure transient and the temperature transient for the coolant in the reactor-vessel downcomer. With this and additional information available OCA-II performs a one-dimensional thermal analysis to obtain the temperature distribution in the wall as a function of time and then a one-dimensional linear-elastic stress analysis. OCA-P has been checked against similar codes and is presently being used in the Integrated Pressurized Thermal Shock Program for specific PWR plants

  5. Fracture mechanics analysis on VVER1000 RPV with different methodologies

    International Nuclear Information System (INIS)

    The main component that limits the operational life of the (Nuclear Power Plant) NPP is the Reactor pressure Vessel (RPV) because of the property of carbon steel material change during the operational life due to the different causes: high neutron flux in the welding region, thermal aging etc. This results in an increase of RPV embrittlement level that decreases the safety margin for the crack propagation in case of transients with fast cooling rate due to the emergency systems injection, or increase of secondary side heat exchange. This problem is known as Pressurized Thermal Shock (PTS) and constitutes a relevant problem for the safety of the NPP that are in operation from several years. Nowadays, the scientific community is trying to change the approach to the PTS analysis toward a “Best Estimate” (BE) scheme with the aim to remove the excess of conservatism in each step of the analysis coming from the limited knowledge of the phenomena in the eighties when the problem has been considered in the safety analysis. This change has been pushed from the possibility to extend the operational life of some plants and this has been possible due to the availability of always more powerful computer and sophisticated computer codes that allows to the analyst to perform very detailed analysis with very high degree of precision of the mixing phenomena occurring at small scale in the down-comer and to calculate the stress intensity factor at crack tip with very refined mesh of millions of nodes. This paper describes the main steps of a PTS analysis: system thermal-hydraulic calculation, CFD analysis, stress analysis and the Fracture Mechanics analysis for the RPV of a generic VVER1000. In particular the paper shows the comparison of the results of the fracture mechanics analysis performed with different methodology for the calculation of the stress intensity factor at crack tip (KI). (author)

  6. 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

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

    International Nuclear Information System (INIS)

    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

  8. Mechanical rock properties, fracture propagation and permeability development in deep geothermal reservoirs

    Science.gov (United States)

    Leonie Philipp, Sonja; Reyer, Dorothea

    2010-05-01

    Deep geothermal reservoirs are rock units at depths greater than 400 m from which the internal heat can be extracted using water as a transport means in an economically efficient manner. In many geothermal reservoirs, fluid flow is largely, and may be almost entirely, controlled by the permeability of the fracture network. No flow, however, takes place along a particular fracture network unless the fractures are interconnected. For fluid flow to occur from one site to another there must be at least one interconnected cluster of fractures that links these sites, that is, the percolation threshold must be reached. In "hydrothermal systems", only the natural fracture system (extension and shear fractures) creates the rock or reservoir permeability that commonly exceeds the matrix permeability by far; in "petrothermal systems", by contrast, interconnected fracture systems are formed by creating hydraulic fractures and massive hydraulic stimulation of the existing fracture system in the host rock. Propagation (or termination, that is, arrest) of both natural extension and shear fractures as well as man-made hydraulic fractures is mainly controlled by the mechanical rock properties, particularly rock toughness, stiffness and strengths, of the host rock. Most reservoir rocks are heterogeneous and anisotropic, in particular they are layered. For many layered rocks, the mechanical properties, particularly their Young's moduli (stiffnesses), change between layers, that is, the rocks are mechanically layered. Mechanical layering may coincide with changes in grain size, mineral content, fracture frequencies, or facies. For example, in sedimentary rocks, stiff limestone or sandstone layers commonly alternate with soft shale layers. In geothermal reservoirs fracture termination is important because non-stratabound fractures, that is, fractures not affected by layering, are more likely to form an interconnected fracture network than stratabound fractures, confined to single rock

  9. Effective Hydro-Mechanical Properties of Fluid-Saturated Fracture Networks

    Science.gov (United States)

    Pollmann, N.; Vinci, C.; Renner, J.; Steeb, H.

    2015-12-01

    Consideration of hydro-mechanical processes is essential for the characterization of liquid-resources as well as for many engineering applications. Furthermore, the modeling of seismic waves in fractured porous media finds application not only in geophysical exploration but also reservoir management. Fractures exhibit high-aspect-ratio geometries, i.e. they constitute thin and long hydraulic conduits. Motivated by this peculiar geometry, the investigation of the hydro-mechanically coupled processes is performed by means of a hybrid-dimensional modeling approach. The effective material behavior of domains including complex fracture patterns in a porous rock is assessed by investigating the fluid pressure and the solid displacement of the skeleton saturated by compressible fluids. Classical balance equations are combined with a Poiseuille-type flow in the dimensionally reduced fracture. In the porous surrounding rock, the classical Biot-theory is applied. For simple geometries, our findings show that two main fluid-flow processes occur, leak-off from fractures to the surrounding rock and fracture flow within and between the connected fractures. The separation of critical frequencies of the two flow processes is not straightforward, in particular for systems containing a large number of fractures. Our aim is to model three dimensional hydro-mechanically coupled processes within complex fracture patterns and in particular determine the frequency-dependent attenuation characteristics. Furthermore, the effect of asperities of the fracture surfaces on the fracture stiffness and on the hydraulic conductivity will be added to the approach.

  10. 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

  11. Failure mechanisms in DP600 steel: Initiation, evolution and fracture

    Energy Technology Data Exchange (ETDEWEB)

    Ghadbeigi, H., E-mail: h.ghadbeigi@sheffield.ac.uk [The University of Sheffield, Department of Mechanical Engineering, Mappin Street, Sheffield S1 3JD (United Kingdom); Pinna, C. [The University of Sheffield, Department of Mechanical Engineering, Mappin Street, Sheffield S1 3JD (United Kingdom); Celotto, S. [Tata Steel R and D, IJmuiden, 1970 CA (Netherlands)

    2013-12-20

    Local deformation and damage mechanisms have been studied for a commercial DP600 steel using in-situ tensile testing inside a scanning electron microscope (SEM) in combination with Digital Image Correlation (DIC). Different gauge geometries have been used to study damage evolution processes during tensile testing up to final failure. Strain distributions have been measured within the ferrite and martensite phases, together with the corresponding strain values for identified damage initiation mechanisms. According to the strain maps, large plastic deformation with strain values as large as 4.5 have been measured within the ferrite phase. Severe deformation localization and slip band formation were observed within the ferrite grains. The DIC results show that martensite in the studied material is plastically deformable with a heterogeneous strain distribution within the islands with values of up to 0.9 close to the phase boundaries. Failure of the martensite islands occurs mostly due to micro-crack initiation at the boundaries with the ferrite followed by crack propagation towards the centre of the islands. As for the ferrite matrix, it is found that its interface with the martensite is strong and cohesive. Localized damage in the matrix occurs by sub-micron void formation within the ferrite adjacent to the interface as opposed to the separation along the phase boundary itself or in the central regions of the ferrite grains A mechanism has been proposed to explain the deformation and damage evolution in the microstructure of the studied DP600 steel up to the final fracture.

  12. 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.)

  13. Isolated posterior malleolus fracture: a rare injury mechanism

    OpenAIRE

    Serbest, Sancar; Tiftikçi, Uğur; Tosun, Haci Bayram; Kesgin, Engin; KARATAŞ, Metin

    2015-01-01

    Sprain of the ankle is undoubtedly a common injury during athletic activity, and the sprain can be also associated with fracture of the ankle. Isolated posterior malleolus fracture is a very rare condition, which is usually missed. Here, we are presenting a 37 years old female patient, who suffered injury secondary pressing on brake pedal during collision in a traffic accident. Clinical evaluation is based on Ottawa Ankle Rules and a fracture is diagnosed; patient is started on daily activiti...

  14. Isolated posterior malleolus fracture: a rare injury mechanism.

    Science.gov (United States)

    Serbest, Sancar; Tiftikçi, Uğur; Tosun, Haci Bayram; Kesgin, Engin; Karataş, Metin

    2015-01-01

    Sprain of the ankle is undoubtedly a common injury during athletic activity, and the sprain can be also associated with fracture of the ankle. Isolated posterior malleolus fracture is a very rare condition, which is usually missed. Here, we are presenting a 37 years old female patient, who suffered injury secondary pressing on brake pedal during collision in a traffic accident. Clinical evaluation is based on Ottawa Ankle Rules and a fracture is diagnosed; patient is started on daily activities at postoperative Week 8. This study aims to emphasize that Ottawa Ankle Rules are usually efficient for evaluating fractures of ankle, but clinicians should always make a detailed physical examination. PMID:26097627

  15. 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.

  16. Atomistic insights into milling mechanisms in an Fe-Y{sub 2}O{sub 3} model alloy

    Energy Technology Data Exchange (ETDEWEB)

    Ressel, G.; Holec, D.; Mendez-Martin, F.; Leitner, H. [Montanuniversitaet Leoben, Department of Physical Metallurgy and Materials Testing, Leoben (Austria); Fian, A. [Joanneum Research Forschungsgesellschaft GmbH, Institute for Surface Technologies and Photonics, Weiz (Austria)

    2014-06-15

    This experimental study combined with first principles modeling focuses on the distribution and behavior of yttria in pure iron powder particles prepared by mechanical alloying. A profound verification of the mechanism during milling is still missing in literature. Atom probe tomography and X-ray photoelectron spectroscopy measurements directly after mechanical alloying revealed yttria dissolved in the iron matrix, which later rearranged in clusters. These findings are corroborated by ab initio calculations demonstrating that the formation energy for Y substitutional defect in bcc-Fe is significantly lower in the close neighborhood of vacancies. X-ray diffraction measurements revealed that mechanical alloying for at least 12 hours caused a dramatic decrease in domain size and an extraordinary increase of defect density. (orig.)

  17. EFFECTS OF ALTERNATIVE RAW MATERIALS AND VARYING RESIN CONTENT ON MECHANICAL AND FRACTURE MECHANICAL PROPERTIES OF PARTICLE BOARD

    Directory of Open Access Journals (Sweden)

    Jörn Rathke,

    2012-05-01

    Full Text Available Particle boards were produced from different types of wood particles, i.e. spruce, recovered particles, willow, poplar, and locust. Effects of raw material, as well as varying resin content on mechanical and fracture mechanical properties were investigated. For the analysis of mechanical properties, specific fracture energy, stress intensity factors, and the industrial European standard methods internal bond strength according to EN 319 and bending strength according to EN 310 were used. The total fracture energy was measured, and the stress intensity factor was calculated by means of data achieved through finite element simulations. Results of the fracture energy analysis were compared to internal bond strength (IB and bending strength. While IB and the modulus of elasticity (MOE showed a high variability, data scattering for fracture energy tests and modulus of rupture (MOR were smaller, which are due to significant differences between the resin contents of the various board types.

  18. Fracture mechanics parameters for cracks on a slightly undulating interface

    Science.gov (United States)

    Yang, Lin; Qu, Jianmin

    1993-11-01

    Typical bimaterial interfaces are nonplanar due to surface facets or roughness. Crack-tip stress fields of an interface crack must be influenced by nonplanarity of the interface. Consequently, interface toughness is affected. The crack-tip fields of a finite crack on an elastic/rigid interface with periodic undulation are studied. Particular emphasis is given to the fracture mechanics parameters, such as the stress intensity factors, crack-tip energy release rate, and crack-tip mode mixity. When the amplitude of interface undulation is very small relative to the crack length (which is the case for rough interfaces), asymptotic analysis is used to convert the nonplanarity effects into distributed dislocations located on the planar interface. Then, the resulting stress fields near the crack tip are obtained by using the Fourier integral transform method. It is found that the stress fields at the crack tip are strongly influenced by nonplanarity of the interface. Generally speaking, nonplanarity of the interface tends to shield the crack tip by reducing the crack-tip stress concentration.

  19. 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.

  20. Effects of Strain Rates on Mechanical Properties and Fracture Mechanism of DP780 Dual Phase Steel

    Science.gov (United States)

    Li, Shengci; Kang, Yonglin; Zhu, Guoming; Kuang, Shuang

    2015-06-01

    The mechanical properties of DP780 dual phase steel were measured by quasi-static and high-speed tensile tests at strain rates between 0.001 and 1000 s-1 at room temperature. The deformation and fracture mechanisms were analyzed by observation of the tensile fracture and microstructure near the fracture. Dynamic factor and feret ratio quantitative methods were applied to study the effect of strain rate on the microstructure and properties of DP780 steel. The constitutive relation was described by a modified Johnson-Cook and Zerilli-Armstrong model. The results showed that the strain rate sensitivity of yield strength is bigger than that of ultimate tensile strength; as strain rate increased, the formation of microcracks and voids at the ferrite/martensite interface can be alleviated; the strain rate effect is unevenly distributed in the plastic deformation region. Moreover, both models can effectively describe the experimental results, while the modified Zerilli-Armstrong model is more accurate because the strain-hardening rate of this model is independent of strain rate.

  1. 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.

  2. Contribution to the study of mechanical properties of nuclear fuel: atomistic modelling of the deformation of uranium dioxide

    International Nuclear Information System (INIS)

    Mechanical properties of nuclear fuel are a complex problem, involving many coupled mechanisms occurring at different length scales. We used Molecular Dynamics models to bring some light on some of these mechanisms at the atomic scale. We devised a procedure to calculate transition pathways between some UO2 polymorphs, and then carried out dynamics simulations of these transitions. We confirmed the stability of the cotunnite structure at high pressure using various empirical potentials, the fluorite structure being the most stable at room pressure. Moreover, we showed a reconstructive phase transition between the fluorite and cotunnite structures. We also showed the importance of the major deformation axis on the kind of transition that occur under tensile conditions. Depending on the loading direction, a scrutinyite or rutile phase can appear. We then calculated the elastic behaviour of UO2 using different potentials. The relative agreement between them was used to produce a set of parameters to be used as input in mesoscale models. We also simulated crack propagation in UO2 single crystals. These simulations showed secondary phases nucleation at crack tips, and hinted at the importance thereof on crack propagation at higher length-scales. We then described some properties of edge dislocations in UO2. The core structures were compared for various glide planes. The critical resolved shear stress was calculated for temperatures up to 2000 K. These calculations showed a link between lattice disorder at the dislocations core and the dislocations mobility. (author)

  3. 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.

  4. The inhibitory mechanism of a fullerene derivative against amyloid-β peptide aggregation: an atomistic simulation study.

    Science.gov (United States)

    Sun, Yunxiang; Qian, Zhenyu; Wei, Guanghong

    2016-05-14

    Alzheimer's disease (AD) is associated with the pathological self-assembly of amyloid-β (Aβ) peptides into β-sheet enriched fibrillar aggregates. Aβ dimers formed in the initial step of Aβ aggregation were reported to be the smallest toxic species. Inhibiting the formation of β-sheet-rich oligomers and fibrils is considered as the primary therapeutic strategy for AD. Previous studies reported that fullerene derivatives strongly inhibit Aβ fibrillation. However, the underlying inhibitory mechanism remains elusive. As a first step to understand fullerene-modulated full-length Aβ aggregation, we investigated the conformational ensemble of the Aβ1-42 dimer with and without 1,2-(dimethoxymethano)fullerene (DMF) - a more water-soluble fullerene derivative - by performing a 340 ns explicit-solvent replica exchange molecular dynamics simulation. Our simulations show that although disordered states are the most abundant conformations of the Aβ1-42 dimer, conformations containing diverse extended β-hairpins are also populated. The first most-populated β-hairpins involving residues L17-D23 and A30-V36 strongly resemble the engineered β-hairpin which is a building block of toxic Aβ oligomers. We find that the interaction of DMFs with Aβ peptides greatly impedes the formation of such β-hairpins and inter-peptide β-sheets. Binding energy analyses demonstrate that DMF preferentially binds not only to the central hydrophobic motif LVFFA of the Aβ peptide as suggested experimentally, but also to the aromatic residues including F4 and Y10 and the C-terminal hydrophobic region I31-V40. This study reveals a complete picture of the inhibitory mechanism of full-length Aβ1-42 aggregation by fullerenes, providing theoretical insights into the development of drug candidates against AD. PMID:27091578

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

    International Nuclear Information System (INIS)

    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.

  6. 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.

  7. 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.

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

    DEFF Research Database (Denmark)

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

    2008-01-01

    -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......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...... results is believed to be related to the variation in the number of fibres across the fracture plane. Furthermore, the inverse analyses indicate no systematic differences in the determined parameters between two WST specimens or between the WST and the 3PBT....

  9. 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.

  10. Verification of a fracture mechanics concept for the cleavage fracture behaviour of RAFM steels using local fracture criteria. Final report for task TW2-TTMS-005/D3

    International Nuclear Information System (INIS)

    An effort is made within the European Fusion Technology Programme framework to obtain a fracture mechanics description of the material behaviour in the ductile to brittle transition-regime using local fracture criteria. In a companion report, the necessary procedural steps towards the development of an according design code scheme were described. The present report contains application examples and verification results of the different procedural steps and identifies limitations of the approach for the two reference RAFM steels F82Hmod and EUROFER97. (orig.)

  11. Phase field crystal modelling of the order-to-disordered atomistic structure transition of metallic glasses

    Science.gov (United States)

    Zhang, W.; Mi, J.

    2016-03-01

    Bulk metallic glass composites are a new class of metallic alloy systems that have very high tensile strength, ductility and fracture toughness. This unique combination of mechanical properties is largely determined by the presence of crystalline phases uniformly distributed within the glassy matrix. However, there have been very limited reports on how the crystalline phases are nucleated in the super-cooled liquid and their growth dynamics, especially lack of information on the order-to-disordered atomistic structure transition across the crystalline-amorphous interface. In this paper, we use phase field crystal (PFC) method to study the nucleation and growth of the crystalline phases and the glass formation of the super cooled liquid of a binary alloy. The study is focused on understanding the order-to-disordered transition of atomistic configuration across the interface between the crystalline phases and amorphous matrix of different chemical compositions at different thermal conditions. The capability of using PFC to simulate the order-to-disorder atomistic transition in the bulk material or across the interface is discussed in details.

  12. 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.

  13. Radiology of Fractures in Intoxicated Emergency Department Patients: Locations, Mechanisms, Presentation, and Initial Interpretation Accuracy.

    Science.gov (United States)

    Morita, Yuka; Nozaki, Taiki; Starkey, Jay; Okajima, Yuka; Ohde, Sachiko; Matsusako, Masaki; Yoshioka, Hiroshi; Saida, Yukihisa; Kurihara, Yasuyuki

    2015-06-01

    The purpose of this study was to investigate the relationship of alcohol intoxication to time-to-presentation following injury, fracture type, mechanism of injury leading to fracture, and initial diagnostic radiology interpretation performance of emergency physicians versus diagnostic radiologists in patients who present to the emergency department (ED) and are subsequently diagnosed with fracture. Medical records of 1286 patients who presented to the ED and were diagnosed with fracture who also underwent plain film or computed tomography (CT) imaging were retrospectively reviewed. The subjects were divided into intoxicated and sober groups. Patient characteristics, injury-to-presentation time, fracture location, and discrepancies between initial clinical and radiological evaluations were compared. Of 1286 subjects, 181 patients were included in the intoxicated group. Only intoxicated patients presented with head/neck fractures more than 24 hours after injury. The intoxicated group showed a higher rate of head/neck fractures (skull 23.2% vs 5.8%, face and orbit 30.4% vs 9.5%; P spinal fractures during this period. Alcohol-related injuries are more often associated with head/neck fractures but less extremity injuries. The rate of fractures missed by emergency physicians but later diagnosed by radiologists was the same in intoxicated and sober patients. PMID:26091471

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

    International Nuclear Information System (INIS)

    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)

  15. 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)

  16. Atomistic simulation of tantalum nanoindentation: Effects of indenter diameter, penetration velocity, and interatomic potentials on defect mechanisms and evolution

    Energy Technology Data Exchange (ETDEWEB)

    Ruestes, C.J., E-mail: cjruestes@hotmail.com [Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093 (United States); Facultad de Ciencias Exactas y Naturales, Univ. Nac. de Cuyo, Mendoza 5500 (Argentina); CONICET, Mendoza 5500 (Argentina); Stukowski, A. [Technische Universität Darmstadt, Darmstadt 64287 (Germany); Tang, Y. [Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University, Shanghai 200072 (China); Tramontina, D.R. [Facultad de Ciencias Exactas y Naturales, Univ. Nac. de Cuyo, Mendoza 5500 (Argentina); Erhart, P. [Chalmers University of Technology, Department of Applied Physics, Gothenburg 41296 (Sweden); Remington, B.A. [Lawrence Livermore National Lab, Livermore, CA 94550 (United States); Urbassek, H.M. [Physics Department and Research Center OPTIMAS, University of Kaiserslautern, Kaiserslautern 67663 (Germany); Meyers, M.A. [Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093 (United States); Bringa, E.M. [Facultad de Ciencias Exactas y Naturales, Univ. Nac. de Cuyo, Mendoza 5500 (Argentina); CONICET, Mendoza 5500 (Argentina)

    2014-09-08

    Nanoindentation simulations are a helpful complement to experiments. There is a dearth of nanoindentation simulations for bcc metals, partly due to the lack of computationally efficient and reliable interatomic potentials at large strains. We carry out indentation simulations for bcc tantalum using three different interatomic potentials and present the defect mechanisms responsible for the creation and expansion of the plastic deformation zone: twins are initially formed, giving rise to shear loop expansion and the formation of sequential prismatic loops. The calculated elastic constants as function of pressure as well as stacking fault energy surfaces explain the significant differences found in the defect structures generated for the three potentials investigated in this study. The simulations enable the quantification of total dislocation length and twinning fraction. The indenter velocity is varied and, as expected, the penetration depth for the first pop-in (defect emission) event shows a strain rate sensitivity m in the range of 0.037–0.055. The effect of indenter diameter on the first pop-in is discussed. A new intrinsic length-scale model is presented based on the profile of the residual indentation and geometrically necessary dislocation theory.

  17. Elements of a fracture mechanics concept for the cleavage fracture behaviour of RAFM steels using local fracture criteria. Final report for task TW1-TTMS-005/D3

    International Nuclear Information System (INIS)

    An effort is made within the European Fusion Technology Programme framework to obtain a fracture mechanics description of the material behaviour in the ductile to brittle transition-regime using local fracture criteria. This report summarizes the necessary procedural steps towards the development of an according design code scheme. It makes heavy use of available code schemes such as the British Energy R6-Code or the ESIS P6 procedure and specializes in application to the class of low activation materials that are envisaged for ITER. Through an integrated approach using a numerical stress analysis at experimentally observed fracture loads of notched tensile specimens, a statistical evaluation of cleavage fracture parameters can be performed. The report contains a description of the necessary steps for the experimental characterization and the numerical analysis as well as results for the two RAFM steel variants F82Hmod and EUROFER 97 which serve as basis for the verification of the method. Statistical inference methods are addressed as well as fractographic investigations that are essential for the verification of the approach via numerical prediction of the fracture origin distribution. Limits of the current methodology are given and topics of future research are indicated. (orig.)

  18. 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.

  19. Subcritical fracture propagation in rocks: An examination using the methods of fracture mechanics and non-destructive testing. Ph.D. Thesis

    Science.gov (United States)

    Swanson, P. L.

    1984-01-01

    An experimental investigation of tensile rock fracture is presented with an emphasis on characterizing time dependent crack growth using the methods of fracture mechanics. Subcritical fracture experiments were performed in moist air on glass and five different rock types at crack velocities using the double torsion technique. The experimental results suggest that subcritical fracture resistance in polycrystals is dominated by microstructural effects. Evidence for gross violations of the assumptions of linear elastic fracture mechanics and double torsion theory was found in the tests on rocks. In an effort to obtain a better understanding of the physical breakdown processes associated with rock fracture, a series of nondestructive evaluation tests were performed during subcritical fracture experiments on glass and granite. Comparison of the observed process zone shape with that expected on the basis of a critical normal principal tensile stress criterion shows that the zone is much more elongated in the crack propagation direction than predicted by the continuum based microcracking model alone.

  20. Thermo-hydro-mechanical processes in fractured rock formations during glacial advance

    Science.gov (United States)

    Selvadurai, A. P. S.; Suvorov, A. P.; Selvadurai, P. A.

    2014-11-01

    The paper examines the coupled thermo-hydro-mechanical (THM) processes that develop in a fractured rock region within a fluid-saturated rock mass due to loads imposed by an advancing glacier. This scenario needs to be examined in order to assess the suitability of potential sites for the location of deep geologic repositories for the storage of high-level nuclear waste. The THM processes are examined using a computational multiphysics approach that takes into account thermo-poroelasticity of the intact geological formation and the presence of a system of sessile but hydraulically interacting fractures (fracture zones). The modeling considers coupled thermo-hydro-mechanical effects in both the intact rock and the fracture zones due to contact normal stresses and fluid pressure at the base of the advancing glacier. Computational modelling provides an assessment of the role of fractures that can modify the pore pressure generation within the entire rock mass.

  1. Thermo-hydro-mechanical processes in fractured rock formations during a glacial advance

    Science.gov (United States)

    Selvadurai, A. P. S.; Suvorov, A. P.; Selvadurai, P. A.

    2015-07-01

    The paper examines the coupled thermo-hydro-mechanical (THM) processes that develop in a fractured rock region within a fluid-saturated rock mass due to loads imposed by an advancing glacier. This scenario needs to be examined in order to assess the suitability of potential sites for the location of deep geologic repositories for the storage of high-level nuclear waste. The THM processes are examined using a computational multiphysics approach that takes into account thermo-poroelasticity of the intact geological formation and the presence of a system of sessile but hydraulically interacting fractures (fracture zones). The modelling considers coupled thermo-hydro-mechanical effects in both the intact rock and the fracture zones due to contact normal stresses and fluid pressure at the base of the advancing glacier. Computational modelling provides an assessment of the role of fractures in modifying the pore pressure generation within the entire rock mass.

  2. Quantum corrections to the `atomistic' MOSFET simulation

    OpenAIRE

    Asenov, A.

    2000-01-01

    In this paper we study the influence of the quantum effects in the inversion layer on the parameter fluctuation in decanano MOSFETs. The quantum mechanical effects are incorporated in our previously published 3D 'atomistic' simulation approach using a full 3D implementation of the density gradient formalism. This results in a consistent, fully 3D, quantum mechanical picture which incorporates the vertical inversion layer quantization, lateral confinement effects associated with the current fi...

  3. 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.

  4. 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.

  5. Mechanical properties and fracture behavior of single-layer phosphorene at finite temperatures

    Science.gov (United States)

    Sha, Zhen-Dong; Pei, Qing-Xiang; Ding, Zhiwei; Jiang, Jin-Wu; Zhang, Yong-Wei

    2015-10-01

    Phosphorene, a new two-dimensional (2D) material beyond graphene, has attracted great attention in recent years due to its superior physical and electrical properties. However, compared to graphene and other 2D materials, phosphorene has a relatively low Young’s modulus and fracture strength, which may limit its applications due to possible structure failures. For the mechanical reliability of future phosphorene-based nanodevices, it is necessary to have a deep understanding of the mechanical properties and fracture behaviors of phosphorene. Previous studies on the mechanical properties of phosphorene were based on first principles calculations at 0 K. In this work, we employ molecular dynamics simulations to explore the mechanical properties and fracture behaviors of phosphorene at finite temperatures. It is found that temperature has a significant effect on the mechanical properties of phosphorene. The fracture strength and strain reduce by more than 65% when the temperature increases from 0 K to 450 K. Moreover, the fracture strength and strain in the zigzag direction is more sensitive to the temperature rise than that in the armchair direction. More interestingly, the failure crack propagates preferably along the groove in the puckered structure when uniaxial tension is applied in the armchair direction. In contrast, when the uniaxial tension is applied in the zigzag direction, multiple cracks are observed with rough fracture surfaces. Our present work provides useful information about the mechanical properties and failure behaviors of phosphorene at finite temperatures.

  6. 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...

  7. Simulation of crack propagation in fiber-reinforced concrete by fracture mechanics

    International Nuclear Information System (INIS)

    Mode I crack propagation in fiber-reinforced concrete (FRC) is simulated by a fracture mechanics approach. A superposition method is applied to calculate the crack tip stress intensity factor. The model relies on the fracture toughness of hardened cement paste (KIC) and the crack bridging law, so-called stress-crack width (σ-δ) relationship of the material, as the fundamental material parameters for model input. As two examples, experimental data from steel FRC beams under three-point bending load are analyzed with the present fracture mechanics model. A good agreement has been found between model predictions and experimental results in terms of flexural stress-crack mouth opening displacement (CMOD) diagrams. These analyses and comparisons confirm that the structural performance of concrete and FRC elements, such as beams in bending, can be predicted by the simple fracture mechanics model as long as the related material properties, KIC and (σ-δ) relationship, are known

  8. 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.

  9. 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.

  10. 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.

  11. Fracto-mechanoluminescence and mechanics of fracture of solids

    International Nuclear Information System (INIS)

    The present paper explores the correlation between fracto-mechanoluminescence and fracture of solids and thereby provides a clear understanding of the physics of fracto-mechanoluminescence. When a fluorescent or non-photoluminescent crystal is fractured impulsively by dropping a load on it, then initially the mechanoluminescence (ML) intensity increases linearly with time, attains a maximum value Im at a particular time tm and later on it decreases exponentially with time. However, when a phosphorescent crystal is fractured impulsively by dropping a load on it, then initially the ML intensity increases linearly with time, attains a maximum value Im at a particular time tm and later on it decreases initially at a fast rate and then at a slow rate. For low impact velocity the value of tm is constant, however, for higher impact velocity tm decreases logarithmally with the increasing impact velocity. Whereas the peak ML intensity Im increases linearly with the impact velocity, the total ML intensity IT, initially increases linearly with the impact velocity and then it tends to attain a saturation value for higher values of the impact velocity. The value of tm increases logarithmally with the thickness of crystals, Im increases linearly with the area of cross-section of crystals and IT increases linearly with the volume of crystals. Generally, the ML of non-irradiated crystals decreases with increasing temperature of crystals. Depending on the prevailing conditions the ML spectra consist of either gas discharge spectra or solid state luminescence spectra or combination of the both. On the basis of the rate of generation of cracks and the rate of creation of new surface area of crystals, expressions are derived for the ML intensity and they are found to explain satisfactorily the temporal, spectral, thermal, crystal-size, impact velocity, surface area, and other characteristics of ML. The present investigation may be useful in designing of damage sensors, fracture

  12. Mechanical properties and fracture toughness of rail steels and thermite welds at low temperature

    Science.gov (United States)

    Wang, Yuan-qing; Zhou, Hui; Shi, Yong-jiu; Feng, Bao-rui

    2012-05-01

    Brittle fracture occurs frequently in rails and thermite welded joints, which intimidates the security and reliability of railway service. Railways in cold regions, such as Qinghai-Tibet Railway, make the problem of brittle fracture in rails even worse. A series of tests such as uniaxial tensile tests, Charpy impact tests, and three-point bending tests were carried out at low temperature to investigate the mechanical properties and fracture toughness of U71Mn and U75V rail steels and their thermite welds. Fracture micromechanisms were analyzed by scanning electron microscopy (SEM) on the fracture surfaces of the tested specimens. The ductility indices (percentage elongation after fracture and percentage reduction of area) and the toughness indices (Charpy impact energy A k and plane-strain fracture toughness K IC) of the two kinds of rail steels and the corresponding thermite welds all decrease as the temperature decreases. The thermite welds are more critical to fracture than the rail steel base metals, as indicated by a higher yield-to-ultimate ratio and a much lower Charpy impact energy. U71Mn rail steel is relatively higher in toughness than U75V, as demonstrated by larger A k and K IC values. Therefore, U71Mn rail steel and the corresponding thermite weld are recommended in railway construction and maintenance in cold regions.

  13. 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.

  14. Fracture Mechanical Trouser Taer Testing of thin polymer films

    OpenAIRE

    Mehmood, Nasir; Mao, Tan; Bhupati, Gaurav

    2012-01-01

    Tensile and Trouser tear tests of thin packaging polymer films have been done successfully in this research thesis. Two different polymers (PP and LDPE) are used. Mode I and Mode III fracture tests have been used for crack propagation analysis. Several experiments are performed to calculate the material parameters. The research study includes the experimental test along with virtual tests using the FEM software Abaqus 6.12-1. ASTM standard 1938-08 is followed for specimen size and experiments...

  15. Fracture Mechanics Characterization of an AnisotropicGeomaterial

    OpenAIRE

    Cravero, Masantonio; Iabichino, Giorgio; Valente, Silvio; Fidelibus, Corrado; Barpi, Fabrizio

    2012-01-01

    Argillites are considered worldwide as potential host rock for high level radioactive waste given the low permeability and strong adsorption potential. However, the excavation of the galleries of a repository would produce a disturbed zone around the boundaries rich of new fractures which may enhance the conductivity of the rock along the gallery axis. Several mine-by experiments have been performed in underground rock labs to investi- gate the features of the disturbed zone. In Mont Terri UR...

  16. State of the Art Report on Fracture Mechanics (Fracture in the Creep Range). Volume 3: Appendices H - M

    International Nuclear Information System (INIS)

    A CEC State of the Art Report on Fracture Mechanics for Fast Breeder Reactors (Fracture below the Creep Range) has recently been published by Bhandari and coworkers (1984). There has also been a compilation of Creep Crack Growth Data from Germany, France and the U.K. for 304 and 316 stainles steel by Lloyd et al (1984). The present Report provides considerably more data and analytical techniques taken from Worldwide sources on creep crack initiation and propagation. Since the subject is moving quickly there is an emphasis on the most recent work; indeed research studies as yet unpublished are also included. The total Report is in 3 volumes. Volume 3 contains the most important and up-to-date information in some detail in Appendices H to M; this provides a sound base for the Report and for future workers

  17. State of the Art Report on Fracture Mechanics (Fracture in the Creep Range). Volume 2: Appendices A - G

    International Nuclear Information System (INIS)

    A CEC State of the Art Report on Fracture Mechanics for Fast Breeder Reactors (Fracture below the Creep Range) has recently been published by Bhandari and coworkers (1984). There has also been a compilation of Creep Crack Growth Data from Germany, France and the U.K. for 304 and 316 stainles steel by Lloyd et al (1984). The present Report provides considerably more data and analytical techniques taken from Worldwide sources on creep crack initiation and propagation. Since the subject is moving quickly there is an emphasis on the most recent work; indeed research studies as yet unpublished are also included. The total Report is in 3 volumes. Volume 2 contains the most important and up-to-date information in some detail in Appendices A to G; this provides a sound base for the Report and for future workers

  18. 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.

  19. A Rock Mechanics and Coupled Hydro mechanical Analysis of Geological Repository of High Level Nuclear Waste in Fractured Rocks

    International Nuclear Information System (INIS)

    This paper introduces a few case studies on fractured hard rock based on geological data from Sweden, Korea is one of a few countries where crystalline rock is the most promising rock formation as a candidate site of geological repository of high level nuclear waste. Despite the progress made in the area of rock mechanics and coupled hydro mechanics, extensive site specific study on multiple candidate sites is essential in order to choose the optimal site. For many countries concerned about the safe isolation of nuclear wastes from the biosphere, disposal in a deep geological formation is considered an attractive option. In geological repository, thermal loading continuously disturbs the repository system in addition to disturbances a recent development in rock mechanics and coupled hydro mechanical study using DFN(Discrete Fracture Network) - DEM(Discrete Element Method) approach mainly applied in hard, crystalline rock containing numerous fracture which are main sources of deformation and groundwater flow

  20. A Modified TSD Specimen for Fracture Toughness Characterization – Fracture Mechanics Analysis and Design

    DEFF Research Database (Denmark)

    Berggreen, Christian; Carlsson, Leif A.

    2010-01-01

    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 and other parameters of the test is quite limited....... A method to extend the range of mode-mixities of the TSD specimen is to introduce a larger amount of transverse shear by reinforcing the loaded upper face with a stiff metal plate. Analysis shows that this method extends the range of phase angles to a practically useful range. Guidelines on selection...

  1. 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)....

  2. Mechanical Properties of Brittle Materials and Their Single Fracture under Dynamic Loading

    OpenAIRE

    YASHIMA, Saburo; Kanda, Yoshiteru; Saito, Fumio; Sasaki, Toru; Iijima, Masayoshi; HASHIMOTO, Hitoshi

    1983-01-01

    The meaning of study on single particle crushing is recognized at which it is regarded the accumulation of single particle crushing as the comminution performed in practical operations stochastic phenomena. Especially, experimental data concerning the mechanical properties of brittle solids measured under dynamic loading are so far very few. Further, the experimental data concerning compressive strength, sphere compressive strength, fracture energy, new surface produced and fracture surface e...

  3. 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

  4. 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.

  5. Fatigue crack growth and fracture mechanics analysis of a working roll surface layer material

    Directory of Open Access Journals (Sweden)

    M. Drobne

    2014-10-01

    Full Text Available Fatigue crack growth and fracture mechanics analysis of a working roll surface layer material is presented in this paper. The research is done on a hot strip mill working roll where High Chromium Steel is used for roll’s shell material. To obtain corresponding parameters, a rectangular single edge notched bend specimens – SENB, according to standard BS 7448, were used. The fatigue crack growth analysis was done on a resonant testing machine with use of special crack gauges, while for fracture mechanics parameters the electro–mechanical testing machine was used.

  6. Results of fracture mechanics analyses of the ederer cranes in the device assembly facility using reduced static fracture-toughness values

    Energy Technology Data Exchange (ETDEWEB)

    Dalder, E. N. C.

    1996-11-01

    The effects of a decreased static fracture-toughness value from that used in the previous fracture-mechanics analyses of the Ederer cranes in the Device Assembly Facility were examined to see what effects, if any, would be exerted on the fatigue crack growth and fracture behavior of the cranes. In particular, the behavior of the same 3 critical locations on the lower flanges of the load beams of the Ederer 5 ton and 4 ton cranes, were examined, with the reduced static fracture-toughness value.

  7. 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.

  8. In situ atomic scale mechanical microscopy discovering the atomistic mechanisms of plasticity in nano-single crystals and grain rotation in polycrystalline metals

    Energy Technology Data Exchange (ETDEWEB)

    Han, Xiaodong, E-mail: xdhan@bjut.edu.cn [Institute of Microstructure and Property of Advanced Materials, Beijing University of Technology (China); Wang, Lihua; Yue, Yonghai [Institute of Microstructure and Property of Advanced Materials, Beijing University of Technology (China); Zhang, Ze, E-mail: zezhang@zju.edu.cn [Institute of Microstructure and Property of Advanced Materials, Beijing University of Technology (China); Department of Materials Science, National Key Lab of Silicon Materials, Zhejiang University (China)

    2015-04-15

    In this review, we briefly introduce our in situ atomic-scale mechanical experimental technique (ASMET) for transmission electron microscopy (TEM), which can observe the atomic-scale deformation dynamics of materials. This in situ mechanical testing technique allows the deformation of TEM samples through a simultaneous double-tilt function, making atomic-scale mechanical microscopy feasible. This methodology is generally applicable to thin films, nanowires (NWs), tubes and regular TEM samples to allow investigation of the dynamics of mechanically stressed samples at the atomic scale. We show several examples of this technique applied to Pt and Cu single/polycrystalline specimens. The in situ atomic-scale observation revealed that when the feature size of these materials approaches the nano-scale, they often exhibit “unusual” deformation behaviours compared to their bulk counterparts. For example, in Cu single-crystalline NWs, the elastic–plastic transition is size-dependent. An ultra-large elastic strain of 7.2%, which approaches the theoretical elasticity limit, can be achieved as the diameter of the NWs decreases to ∼6 nm. The crossover plasticity transition from full dislocations to partial dislocations and twins was also discovered as the diameter of the single-crystalline Cu NWs decreased. For Pt nanocrystals (NC), the long-standing uncertainties of atomic-scale plastic deformation mechanisms in NC materials (grain size G less than 15 nm) were clarified. For larger grains with G<∼10 nm, we frequently observed movements and interactions of cross-grain full dislocations. For G between 6 and 10 nm, stacking faults resulting from partial dislocations become more frequent. For G<∼6 nm, the plasticity mechanism transforms from a mode of cross-grain dislocation to a collective grain rotation mechanism. This grain rotation process is mediated by grain boundary (GB) dislocations with the assistance of GB diffusion and shuffling. These in situ atomic

  9. Calculation research of fracture mechanics parameters KJ of cracks in elbows

    International Nuclear Information System (INIS)

    Background: Elbows are important constituent parts of piping systems in nuclear power plant. The pressure boundary integrity of elbows direct influences reliability of nuclear power plant operation. Purpose: Therefore, it is necessary to carry out analysis of the cracked elbows to evaluate whether the safety requirement is satisfied. Methods: The principal fracture mechanics parameters required in analysis and evaluation are stress intensity factor K and J integral. The most important procedure for calculating fracture parameters K/J is to build up correct and reasonable mesh using finite element method. Results: In this paper, a fast programmed and partitioned three dimensional modeling procedure was proposed, which is useful to model the complex finite element model in fracture mechanics calculation, and calculation case of KJ of cracked elbows which subjected to inner pressure and in-plan moment was given based on the modeling method. Conclusions: The results prove that the programmed and partitioned modeling method developed in this paper could solve the complex modeling issue in fracture mechanics calculation of cracked elbow, as well as offer experiences for modeling other cracked components and calculating fracture mechanics parameters KJ. (authors)

  10. Hydraulic and mechanical properties of natural fractures in low-permeability rock

    International Nuclear Information System (INIS)

    The results of a comprehensive laboratory study of the mechanical displacement, permeability, and void geometry of single rock fractures in a quartz monzonite are summarized and analyzed. A metal-injection technique was developed that provided quantitative data on the precise geometry of the void spaces between the fracture surfaces and the areas of contact at different stresses. At effective stresses of less than 20 MPa fluid flow was proportional to the mean fracture aperture raised to a power greater than 3. As stress was increased, contact area was increased and void spaces become interconnected by small tortuous channels that constitute the principal impediment to fluid flow. At effective stresses higher than 20 MPa, the mean fracture aperture continued to diminish with increasing stress, but this had little effect on flow because the small tortuous flow channels deformed little with increasing stress

  11. 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.

  12. 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.

  13. 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.)

  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. Prediction of retained residual stresses in laboratory fracture mechanics specimens extracted from welded components

    International Nuclear Information System (INIS)

    The measurement of weld material fracture toughness properties is important for the structural integrity assessment of engineering components. However, welds can contain high levels of residual stress and these can be retained in fracture mechanics specimens, particularly when machined from non-stress relieved welds. Retained residual stresses can make the measurement of valid fracture toughness properties difficult. This paper describes the results of analytical work undertaken to investigate factors that can influence the magnitude and distribution of residual stresses retained in fracture mechanics specimen blanks extracted from as-welded ferritic and austenitic stainless steel plates. The results indicate that significant levels of residual stress can be retained in specimen blanks prior to notching, and that the magnitude and distribution of stress is dependent upon material properties, specimen geometry and size, and extraction location through the thickness of the weld. Finite element modelling is shown to provide a useful approach for estimating the level and distributions of retained residual stresses. A new stress partitioning approach has been developed to estimate retained stress levels and results compare favourably with FE analysis and available experimental data. The approach can help guide the selection of specimen geometry and machining strategies to minimise the level of residual stresses retained in fracture mechanics specimen blanks extracted from non stress-relieved welds and thus improve the measurement of weld fracture toughness properties. - Highlights: • A simplified method for generating realistic weld residual stresses has been developed. • It has been shown that significant levels of residual stress can be retained within laboratory fracture mechanics specimens. • The level and distribution is dependant upon material, specimen type, specimen size and extraction location. • A method has been developed to allow estimates of the

  16. Non-double-couple mechanisms of microearthquakes induced by hydraulic fracturing

    Science.gov (United States)

    Sileny, J.; Hill, D.P.; Eisner, L.; Cornet, F.H.

    2009-01-01

    We have inverted polarity and amplitude information of representative microearthquakes to investigate source mechanisms of seismicity induced by hydraulic fracturing in the Carthage Cotton Valley, east Texas, gas field. With vertical arrays of four and eight three-component geophones in two monitoring wells, respectively, we were able to reliably determine source mechanisms of the strongest events with the best signal-to-noise ratio. Our analysis indicates predominantly non-double-couple source mechanisms with positive volumetric component consistent with opening cracks oriented close to expected hydraulic fracture orientation. Our observations suggest the induced events are directly the result of opening cracks by fluid injection, in contrast to many previous studies where the seismicity is interpreted to be primarily shearing caused by pore pressure diffusion into the surrounding rock or associated with shear stresses created at the hydraulic fracture tip. Copyright 2009 by the American Geophysical Union.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. 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.

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

    International Nuclear Information System (INIS)

    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

  4. 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.

  5. Cationic Au Nanoparticle Binding with Plasma Membrane-like Lipid Bilayers: Potential Mechanism for Spontaneous Permeation to Cells Revealed by Atomistic Simulations

    DEFF Research Database (Denmark)

    Heikkila, E.; Martinez-Seara, H.; Gurtovenko, A. A.;

    2014-01-01

    Despite being chemically inert as a bulk material, nanoscale gold can pose harmful side effects to living organisms. In particular, cationic Au nanoparticles (AuNP+) of 2 nm diameter or less permeate readily through plasma membranes and induce cell death. We report atomistic simulations of cationic...... Au nanoparticles interacting with realistic membranes and explicit solvent using a model system that comprises two cellular compartments, extracellular and cytosolic, divided by two asymmetric lipid bilayers. The membrane-AuNP+ binding and membrane reorganization processes are discovered...... of the zwitterionic lipids and nanoparticle side groups in the contact area, giving rise to the initial stage of pore formation on the membrane surface. Such behavior is not seen on the cytosolic side, where AuNP+ is spontaneously captured by the negatively charged phosphatidylserine lipids that diffuse to enrich...

  6. OCA-P, a deterministic and probabilistic fracture-mechanics code for application to pressure vessels

    International Nuclear Information System (INIS)

    The OCA-P code is a probabilistic fracture-mechanics code that was prepared specifically for evaluating the integrity of pressurized-water reactor vessels when subjected to overcooling-accident loading conditions. The code has two-dimensional- and some three-dimensional-flaw capability; it is based on linear-elastic fracture mechanics; and it can treat cladding as a discrete region. Both deterministic and probabilistic analyses can be performed. For the former analysis, it is possible to conduct a search for critical values of the fluence and the nil-ductility reference temperature corresponding to incipient initiation of the initial flaw. The probabilistic portion of OCA-P is based on Monte Carlo techniques, and simulated parameters include fluence, flaw depth, fracture toughness, nil-ductility reference temperature, and concentrations of copper, nickel, and phosphorous. Plotting capabilities include the construction of critical-crack-depth diagrams (deterministic analysis) and various histograms (probabilistic analysis)

  7. Effect of root canal preparation, type of endodontic post and mechanical cycling on root fracture strength

    Directory of Open Access Journals (Sweden)

    Marília Pivetta RIPPE

    2014-06-01

    Full Text Available Objective: To evaluate the impact of the type of root canal preparation, intraradicular post and mechanical cycling on the fracture strength of roots. Material and Methods: eighty human single rooted teeth were divided into 8 groups according to the instruments used for root canal preparation (manual or rotary instruments, the type of intraradicular post (fiber posts- FRC and cast post and core- CPC and the use of mechanical cycling (MC as follows: Manual and FRC; Manual, FRC and MC; Manual and CPC; Manual, CPC and MC; Rotary and FRC; Rotary, FRC and MC; Rotary and CPC; Rotary, CPC and MC. The filling was performed by lateral compactation. All root canals were prepared for a post with a 10 mm length, using the custom #2 bur of the glass fiber post system. For mechanical cycling, the protocol was applied as follows: an angle of incidence of 45°, 37°C, 88 N, 4 Hz, 2 million pulses. All groups were submitted to fracture strength test in a 45° device with 1 mm/ min cross-head speed until failure occurred. Results: The 3-way ANOVA showed that the root canal preparation strategy (p<0.03 and post type (p<0.0001 affected the fracture strength results, while mechanical cycling (p=0.29 did not. Conclusion: The root canal preparation strategy only influenced the root fracture strength when restoring with a fiber post and mechanical cycling, so it does not seem to be an important factor in this scenario.

  8. Constraints on bed scale fracture chronology with a FEM mechanical model of folding: The case of Split Mountain (Utah, USA)

    Science.gov (United States)

    Sassi, W.; Guiton, M. L. E.; Leroy, Y. M.; Daniel, J.-M.; Callot, J.-P.

    2012-11-01

    A technique is presented for improving the structural analysis of natural fractures development in large scale fold structures. A 3D restoration of a fold provides the external displacement loading conditions to solve, by the finite element method, the forward mechanical problem of an idealized rock material with a stress-strain relationship based on the activation of pervasive fracture sets. In this elasto-plasticity constitutive law, any activated fracture set contributes to the total plastic strain by either an opening or a sliding mode of rock failure. Inherited versus syn-folding fracture sets development can be studied using this mechanical model. The workflow of this methodology was applied to the Weber sandstone formation deformed by forced folding at Split Mountain Anticline, Utah for which the different fracture sets were created and developed successively during the Sevier and the syn-folding Laramide orogenic phases. The field observations at the top stratigraphic surface of the Weber sandstone lead to classify the fracture sets into a pre-fold WNW-ESE fracture set, and a NE-SW fracture set post-dating the former. The development and relative chronology of the fracture sets are discussed based on the geomechanical modeling results. Starting with a 3D restoration of the Split Mountain Anticline, three fold-fracture development models were generated, alternately assuming that the WNW-ESE fracture set is either present or absent prior to folding process. Depending on the initial fracture configuration, the calculated fracture patterns are markedly different, showing that assuming a WNW-ESE joint set to predate the fold best correlates with field observations. This study is a first step addressing the complex problem of identification of fold-related fracturing events using an elementary concept of rock mechanics. When tight to complementary field observations, including petrography, diagenesis and burial history, the approach can be used to better

  9. Data Resolution and Scale-dependent Fracture Clustering: Implications for Deformation Mechanisms

    Science.gov (United States)

    Roy, A.; Aydin, A.; Mukerji, T.; Cilona, A.

    2015-12-01

    zones that have relatively uniform spacing while higher resolution data capture both thin and short splay joints and shear joints that form fracture clusters. Therefore, it may be concluded that data resolution is critical for identifying deformation mechanisms and their products.

  10. Fatigue and fracture mechanics analysis of high pressure vessels

    International Nuclear Information System (INIS)

    A companion document to the ASME Boiler and Pressure Code, section VIII, Division 3 Alternative rules for Construction of High Pressure Vessels, emphasizes that Division 3 is 'intended for vessels in the design pressure range of about 10,000 to 165,000 psi: but no upper or lower limits are given nor are any upper limits implied for Divisions 1 and 2'. Although Division 3 includes much information on welded vessels, attention herein will be focused on the design of vessels that operate above 10,000 psi and are of monobloc or compound construction, using two or more cylindrical shells, that are forged from low- alloy high strength steel ingots. Threaded, pinned, or clamped closures are often used at one or both ends of such vessels; in some cases one end may be forged integrally with the cylindrical body, so-called 'blind end' closure. High pressure piping is connected to such vessels at holes in the end closures or at holes through the cylindrical part of the vessel, usually referred to as cross-bores. These vessels or components thereof may be overstrained (autofrettaged) to enhance static and/or fatigue performance. Division 3 was first published in 1997. In the interim there have been advances in the static, fatigue, and fracture analysis of such vessels and their closures and connections. The aim of this paper is to review some of these advances. (author)

  11. Effects of chemical alteration on fracture mechanical properties in hydrothermal systems

    Science.gov (United States)

    Callahan, O. A.; Eichhubl, P.; Olson, J. E.

    2015-12-01

    Fault and fracture networks often control the distribution of fluids and heat in hydrothermal and epithermal systems, and in related geothermal and mineral resources. Additional chemical influences on conduit evolution are well documented, with dissolution and precipitation of mineral species potentially changing the permeability of fault-facture networks. Less well understood are the impacts of chemical alteration on the mechanical properties governing fracture growth and fracture network geometry. We use double-torsion (DT) load relaxation tests under ambient air conditions to measure the mode-I fracture toughness (KIC) and subcritical fracture growth index (SCI) of variably altered rock samples obtained from outcrop in Dixie Valley, NV. Samples from southern Dixie Valley include 1) weakly altered granite, characterized by minor sericite in plagioclase, albitization and vacuolization of feldspars, and incomplete replacement of biotite with chlorite, and 2) granite from an area of locally intense propylitic alteration with chlorite-calcite-hematite-epidote assemblages. We also evaluated samples of completely silicified gabbro obtained from the Dixie Comstock epithermal gold deposit. In the weakly altered granite KIC and SCI are 1.3 ±0.2 MPam1/2 (n=8) and 59 ±25 (n=29), respectively. In the propylitic assemblage KIC is reduced to 0.6 ±0.1 MPam1/2 (n=11), and the SCI increased to 75 ±36 (n = 33). In both cases, the altered materials have lower fracture toughness and higher SCI than is reported for common geomechanical standards such as Westerly Granite (KIC ~1.7 MPam1/2; SCI ~48). Preliminary analysis of the silicified gabbro shows a significant increase in fracture toughness, 3.6 ±0.4 MPam1/2 (n=2), and SCI, 102 ±45 (n=19), compared to published values for gabbro (2.9 MPam1/2 and SCI = 32). These results suggest that mineralogical and textural changes associated with different alteration assemblages may result in spatially variable rates of fracture

  12. 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

  13. Forming limit and fracture mechanism of ferritic stainless steel sheets

    International Nuclear Information System (INIS)

    Research highlights: → Forming limit curves of two ferritic stainless steel sheets were well predicted. → Failure occurs by necking in uniaxial and plane strain tension for both materials. → Failure occurs by shearing in balanced biaxial tension for both materials. → Strain rate sensitivity does not affect the limit strains a lot for both materials. → Strain rate sensitivity likely influences the failure mode for both materials. - Abstract: In this work, the forming limit curves (FLCs) of two ferritic stainless steel sheets, AISI409L and AISI430, were predicted with the Marciniak-Kuczynski (MK) and Bressan-William-Hill (BWH) models, combined with the Yld2000-2d yield function and the Swift hardening law. Uniaxial tension, disk compression and hydraulic bulge tests were performed to determine the yield loci and hardening curves of both materials. Meanwhile, the strain rate sensitivity (SRS) coefficient was measured through uniaxial tension tests carried out at different strain rates. Out-of-plane stretching tests were conducted in sheet specimens to obtain the surface limit strains under different linear strain paths. Micrographs of the specimens fractured in different stress states were obtained by optical and scanning electron microscopy. The overall results show that the BWH model can predict the FLC better than the MK model, and that the SRS does not have much effect on the limit strains for both materials. The predicted FLCs and micrograph analysis both indicate that failure occurs by surface localized necking in uniaxial and plane strain tension states, whereas it occurs by localized shearing in the through thickness direction in balanced biaxial tension state.

  14. 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.

  15. DETERMINATION OF FRACTURE MECHANICS PARAMETERS FOR BODIES GYRATION IN UNSTEADY DYNAMIC PROBLEMS

    Directory of Open Access Journals (Sweden)

    V. A. Bazhenov

    2011-05-01

    Full Text Available On the basis of semi-analytical final elements method data validity research and research of effective determination of fracture mechanics parameters for bodies of revolution in non-stationary dynamics problems were conducted. New method of J-integral calculation and crack approximation under dynamic impact are presented.

  16. Determination of fracture mechanics parameters for bodies gyration in unsteady dynamic problems

    Directory of Open Access Journals (Sweden)

    V. A. Bazhenov

    2011-05-01

    Full Text Available On the basis of semi-analytical final elements method data validity research and research of effective determination of fracture mechanics parameters for bodies of revolution in non-stationary dynamics problems were conducted. New method of J-integral calculation and crack approximation under dynamic impact are presented.

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

    NARCIS (Netherlands)

    Wolterbeek, Timotheus K.T.; Hangx, Suzanne J.T.; Spiers, Christopher 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. Adaptive finite element methods for two-dimensional problems in computational fracture mechanics

    Science.gov (United States)

    Min, J. B.; Bass, J. M.; Spradley, L. W.

    1994-01-01

    Some recent results obtained using solution-adaptive finite element methods in two-dimensional problems in linear elastic fracture mechanics are presented. The focus is on the basic issue of adaptive finite element methods for validating the new methodology by computing demonstration problems and comparing the stress intensity factors to analytical results.

  19. 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.

  20. Study on the mechanism of seepage flow in the grouting for multiple fractured model

    International Nuclear Information System (INIS)

    The purpose of study is to improve the grouting method for fractured rock masses. In this paper, the results on the fundamental phenomenon for grasping the properties of grouting injection and seepage flow are discussed. The case of grouting stage is studied about the multiple hydraulic fractured apertures in the injected borehole. So the theory on the mechanism is constructed, and experiment is executed in order to verify the availability of the theory. From the results, it is shown that Bernoulli's law is able to prove the behavior of the grouting. And the theoretical evaluation is executed on the experiential procedure of the grouting. (author)

  1. The use of the J* integral for non-linear fracture mechanics

    International Nuclear Information System (INIS)

    The Griffith energy balance criterion, first postulated over 50 years ago, is still the basis of linear elastic fracture mechanics. From this, accurate numerical methods for establishing stress intensity factors and energy release rates have been developed. One such method involves path independent contour integrals about the crack tip. An improved contour integral, designated J* is discussed, and shown to have distinct advantages over others in non-linear strain situations. A number of examples are shown including fractures in thermo-plastic and creep situations. (author)

  2. The assessment of neutron radiation effect on reactor steels using fracture mechanics parameters

    International Nuclear Information System (INIS)

    The radiation stability is discussed of reactor material 15KH2MFA manufactured by Vitkovice Steel and by the SKODA works and of ASTM A543 manufactured by Vitkovice Steel, applying the parameters of fracture mechanics using the Ksub(IC), COD and Jsub(IC) techniques, the notch toughness and the plastic appearance of fractures of Charpy V (RV) samples. The shifts in transient temperatures are given effected in the individual tests by irradiation with fast neutrons (E>1MeV, 1023 n/m2). (author)

  3. Kinetics and fracture resistance of lithiated silicon nanostructure pairs controlled by their mechanical interaction

    Science.gov (United States)

    Lee, Seok Woo; Lee, Hyun-Wook; Ryu, Ill; Nix, William D.; Gao, Huajian; Cui, Yi

    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. Here, we demonstrate physical and 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 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.

  4. A novel diagnostic sign of hip fracture mechanism in ground level falls: two case reports and review of the literature

    Directory of Open Access Journals (Sweden)

    Kelly Douglas W

    2012-05-01

    Full Text Available Abstract Introduction Most elderly hip fractures are the result of a ground level fall. Defining high risk falls and fracture mechanisms are important to develop successful hip fracture prevention programs. This case series presents a previously unreported diagnostic sign and for the first time documents a hip fracture mechanism for a knee impact injury from a ground level fall in two elderly patients. Case presentation Case 1 was a 65-year-old Caucasian woman who fell forward with initial contact to her left knee, sustaining an impacted femoral neck fracture of her ipsilateral left hip. Case 2 was a 92-year-old Caucasian woman who fell bending forward, impacting her left knee and sustaining a comminuted intertrochanteric fracture of her ipsilateral left hip. The fractures occurred as a result of unprotected ground level falls in a forward direction with initial impact to the knee. The knee contusions were located near Gerdy’s tubercle and appear characteristic of a direct impact injury. Conclusion The physical finding of a small localized site of impact and/or contusion in the anterior aspect of the knee in both of these patients with radiographic evidence of an ipsilateral hip fracture would strongly suggest that a knee impact injury can transmit enough energy to the proximal femur by axial loading to result in the hip fracture. The physical finding described is a reliable indicator of this hip fracture mechanism.

  5. Rock mechanics issues and research needs in the disposal of wastes in hydraulic fractures

    Energy Technology Data Exchange (ETDEWEB)

    Doe, T.W.; McClain, W.C.

    1984-07-01

    The proposed rock mechanics studies outlined in this document are designed to answer the basic questions concerning hydraulic fracturing for waste disposal. These questions are: (1) how can containment be assured for Oak Ridge or other sites; and (2) what is the capacity of a site. The suggested rock mechanics program consists of four major tasks: (1) numerical modeling, (2) laboratory testing, (3) field testing, and (4) monitoring. These tasks are described.

  6. 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.)

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

    Science.gov (United States)

    Wolterbeek, Timotheus; Hangx, Suzanne; Spiers, Christopher

    2016-04-01

    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 ongoing changes in wellbore temperature and stress-state. To evaluate the potential for such effects, we performed triaxial compression tests on Class G Portland cement, conducted at down-hole temperature (80 ° C) and effective confining pressures ranging from 1 to 25 MPa. After deformation, samples displaying failure on localised shear fractures were reacted with CO2-H2O, and then subjected to a second triaxial test to assess changes in mechanical properties. Using results from the first phase of deformation, baseline yield and failure criteria were constructed for virgin cement. These delineate stress conditions where unreacted cement is most prone to dilatational (permeability-enhancing) failure. Once shear-fractures formed, later reaction with CO2 did not produce further geomechanical weakening. Instead, after six weeks of reaction, we observed up to 83% recovery of peak-strength and increased frictional strength (15-40%) in the post-failure regime, due to calcium carbonate precipitation in the fractures. As such, our results suggest more or less complete mechanical healing on timescales of the order of months.

  8. 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.

  9. 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.

  10. 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.

  11. 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)

  12. Mechanical Properties and Fracture Behavior of Directionally Solidified NiAl-V Eutectic Composites

    Science.gov (United States)

    Milenkovic, Srdjan; Caram, Rubens

    2015-02-01

    Directional solidification of eutectic alloys has been recognized as promising technique for producing in situ composite materials exhibiting balance of properties. Therefore, an in situ NiAl-V eutectic composite has been successfully directionally solidified using Bridgman technique. The mechanical behavior of the composite including fracture resistance, microhardness, and compressive properties at room and elevated temperatures was investigated. Damage evolution and fracture characteristics were also discussed. The obtained results indicate that the NiAl-V eutectic retains high yield strength up to 1073 K (800 °C), above which there is a rapid decrease in strength. Its yield strength is higher than that of binary NiAl and most of the NiAl-based eutectics. The exhibited fracture toughness of 28.5 MPa√m is the highest of all other NiAl-based systems investigated so far. The material exhibited brittle fracture behavior of transgranular type and all observations pointed out that the main fracture micromechanism was cleavage.

  13. Mechanical response and fracture dynamics of polymeric foams

    Science.gov (United States)

    Deschanel, S.; Vanel, L.; Godin, N.; Maire, E.; Vigier, G.; Ciliberto, S.

    2009-11-01

    Heterogeneous materials usually break through a process of microcracking that eventually leads to final rupture after accumulation and coalescence of many microcracks. The statistical properties of microcracking rupture have been known to resemble critical point statistics, with many of the physical quantities obeying power law distributions. However, there is no clear understanding of the origin of these distributions and of the specific values observed for the power law exponents. In this paper, we review the special case of polymeric foams that have the advantage of containing a single material component, the polymer, as opposed to usual heterogeneous materials such as composites. First, we briefly review the typical features of the polymeric foam mechanical response up to rupture that have been widely studied previously. Then, we focus on a less well-known aspect: the rupture dynamics of polymeric foams. We not only show that polymeric foams behave like other heterogeneous materials, i.e. they display power law statistics, but we are also able to test the effect on the power laws of the following properties: the foam heterogeneity by changing its density, the foam mechanical response by changing its temperature and the mechanical history by comparing creep tests and tensile tests.

  14. 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

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

    International Nuclear Information System (INIS)

    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

  16. 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.

  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. 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....... The reasons are the increased autogenous deformation, the high rate of heat evolution and a higher brittleness of these concretes. Due to these adverse mechanisms the interest in the full description of the behavior of early age concrete has increased dramatically in the last two or three decades. Almost all...... the governing material parameters have undergone intensive research and the body of knowledge provides today a basis for calculation of the stress evolution and thus, repre- sents a tool for prediction of whether cracking will occur or not. However, the experimental investigation and the modelling of the early...

  19. 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.

  20. 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.

  1. 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

  2. Tobacco extract but not nicotine impairs the mechanical strength of fracture healing in rats.

    Science.gov (United States)

    Skott, Martin; Andreassen, Troels T; Ulrich-Vinther, Michael; Chen, X; Keyler, Dan E; LeSage, Mark G; Pentel, Paul R; Bechtold, Joan E; Soballe, Kjeld

    2006-07-01

    The influence of nicotine and tobacco extract (without nicotine) alone and in combination on and mechanical strength of closed femoral fractures in rats was investigated. One hundred four male Sprague-Dawley rats were divided into four groups receiving: nicotine, tobacco extract, tobacco extract plus nicotine, and saline. One week prior to fracture, osmotic pumps were implanted subcutaneously in all animals to administer nicotine equivalent to the serum level of nicotine observed in a smoker consuming one to two packs of cigarettes daily. An equivalent volume of saline was administered to the control animals. Tobacco extract was administered orally. A closed transverse femoral diaphysial fracture was performed, and stabilized with an intramedullary pin. The fractures were mechanically tested after 21 days of healing. Tobacco extract alone decreased the mechanical strength. Ultimate torque and torque at yield point of the tobacco extract group were decreased by 21% (p=0.010) and 23% (p=0.056), respectively, compared with the vehicle (saline) group, and by 20% (p=0.023) and 26% (p=0.004), respectively, compared with the nicotine group. No difference was found between the tobacco extract and tobacco extract plus nicotine groups. An 18% (p=0.013) reduction in torque at yield point was observed in the tobacco extract plus nicotine group compared with the nicotine group. No differences in ultimate stiffness, energy absorption, and callus bone mineral content at the fracture line were found between any of the groups. Serum levels of nicotine were between 40-50 ng/mL in the group given nicotine alone and the group given tobacco extract plus nicotine (equivalent to serum levels observed in persons smoking one to two packs of cigarettes per day). PMID:16705735

  3. 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.)

  4. A robust, coupled approach for atomistic-continuum simulation.

    Energy Technology Data Exchange (ETDEWEB)

    Aubry, Sylvie; Webb, Edmund Blackburn, III (Sandia National Laboratories, Albuquerque, NM); Wagner, Gregory John; Klein, Patrick A.; Jones, Reese E.; Zimmerman, Jonathan A.; Bammann, Douglas J.; Hoyt, Jeffrey John (Sandia National Laboratories, Albuquerque, NM); Kimmer, Christopher J.

    2004-09-01

    This report is a collection of documents written by the group members of the Engineering Sciences Research Foundation (ESRF), Laboratory Directed Research and Development (LDRD) project titled 'A Robust, Coupled Approach to Atomistic-Continuum Simulation'. Presented in this document is the development of a formulation for performing quasistatic, coupled, atomistic-continuum simulation that includes cross terms in the equilibrium equations that arise due to kinematic coupling and corrections used for the calculation of system potential energy to account for continuum elements that overlap regions containing atomic bonds, evaluations of thermo-mechanical continuum quantities calculated within atomistic simulations including measures of stress, temperature and heat flux, calculation used to determine the appropriate spatial and time averaging necessary to enable these atomistically-defined expressions to have the same physical meaning as their continuum counterparts, and a formulation to quantify a continuum 'temperature field', the first step towards constructing a coupled atomistic-continuum approach capable of finite temperature and dynamic analyses.

  5. 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.

  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. Atomistic aspects of crack propagation along high angle grain boundaries

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-12-31

    The author presents atomistic simulations of the crack tip configuration near a high angle {Sigma} = 5 [001](210) symmetrical tilt grain boundary in NiAl. The simulations were carried out using molecular statics and embedded atom (EAM) potentials. The cracks are stabilized near a Griffith condition involving the cohesive energy of the grain boundary. The atomistic configurations of the tip region are different in the presence of the high angle grain boundary than in the bulk. Three different configurations of the grain boundary were studied corresponding to different local compositions. It was found that in ordered NiAl, cracks along symmetrical tilt boundaries show a more brittle behavior for Al rich boundaries than for Ni-rich boundaries. Lattice trapping effects in grain boundary fracture were found to be more significant than in the bulk.

  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. The COD concept and its application to fracture mechanical evaluation of cracked components

    International Nuclear Information System (INIS)

    Based on a comprehensive literature study, this report critically evaluates the current state of experiences with the COD concept in fracture mechanics. First the concept is explained and the procedure of materials testing with a view to fracture mechanics is discussed in detail with emphasis on: The definition of crack shape modification; the procedure to detect crack modification, with subsequent comparison; the determination of material characteristics; the impact on the characteristics of the crack tip opening and the dispersion of results. The correlation between crack tip opening characteristics and notch impact strength is explained, and the methods applied for analysis of the streses affecting the structural components are shown. The design-based and failure threshold curves and the treatment of real crack geometries are also discussed. Problems still to be solved are shown. (orig./HP)

  10. Mechanical Behavior and Fracture Properties of NiAl Intermetallic Alloy with Different Copper Contents

    Directory of Open Access Journals (Sweden)

    Tao-Hsing Chen

    2016-03-01

    Full Text Available The deformation behavior and fracture characteristics of NiAl intermetallic alloy containing 5~7 at% Cu are investigated at room temperature under strain rates ranging from 1 × 10−3 to 5 × 103 s−1. It is shown that the copper contents and strain rate both have a significant effect on the mechanical behavior of the NiAl alloy. Specifically, the flow stress increases with an increasing copper content and strain rate. Moreover, the ductility also improves as the copper content increases. The change in the mechanical response and fracture behavior of the NiAl alloy given a higher copper content is thought to be the result of the precipitation of β-phase (Ni,CuAl and γ'-phase (Ni,Cu3Al in the NiAl matrix.

  11. Fracture mechanical evaluation of high temperature structure and creep-fatigue defect assessment

    Energy Technology Data Exchange (ETDEWEB)

    Park, Chang Gyu; Kim, Jong Bum; Lee, Jae Han

    2004-02-01

    This study proposed the evaluation procedure of high temperature structures from the viewpoint of fracture mechanics on the cylindrical structure applicable to the KALIMER, which is developed by KAERI. For the evaluation of structural integrity, linear and non-linear fracture mechanics parameters were analyzed. Parameters used in creep defect growth applicable to high temperature structure of liquid metal reactor and the evaluation codes with these parameters were analyzed. The evaluation methods of defect initiation and defect growth which were established in R5/R6 code(UK), JNC method (Japan) and RCC-MR A16(France) code were analyzed respectively. The evaluation procedure of leak before break applicable to KALIMER was preliminarily developed and proposed. As an application example of defect growth, the creep-fatigue defect growth on circumferential throughwall defect in high temperature cylindrical structure was evaluated by RCC-MR A16 and this application technology was established.

  12. 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.

  13. Cracking analysis of fracture mechanics by the finite element method of lines (FEMOL)

    Institute of Scientific and Technical Information of China (English)

    Shaowei Hu; Brian Moran; Yunming Chen

    2005-01-01

    The Finite Element Method of Lines (FEMOL) is a semi-analytic approach and takes a position between FEM and analytic methods. First, FEMOL in Fracture Mechanics is presented in detail. Then, the method is applied to a set of examples such as edge-crack plate, the central-crack plate, the plate with cracks emanating from a hole under tensile or under combination loads of tensile and bending. Their dimensionless stress distribution, the stress intensify factor (SIF) and crack opening displacement (COD) are obtained,and comparison with known solutions by other methods are reported. It is found that a good accuracy is achieved by FEMOL. The method is successfully modified to remarkably increase the accuracy and reduce convergence difficulties. So it is a very useful and new tool in studying fracture mechanics problems.

  14. 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.

  15. 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.

  16. Considerations to the possibilities and limits of the application of fracture mechanics

    International Nuclear Information System (INIS)

    The present report gives a review on the principal possibilities and problems of the application of fracture mechanics. In principle, a loading parameter - the crack field parameter P - is compared with a material property R. It is demonstrated that failure loads, critical crack lengths, and residual lifetimes can be determined by procedures which are based on simple principles. Furthermore, the problems which may set limits to the application of these simple procedures are discussed in detail. (orig.)

  17. Thermo-hydro-mechanical processes in fractured rock formations during a glacial advance

    OpenAIRE

    Selvadurai, A. P. S.; Suvorov, A. P.; Selvadurai, P. A.

    2015-01-01

    The paper examines the coupled thermo-hydro-mechanical (THM) processes that develop in a fractured rock region within a fluid-saturated rock mass due to loads imposed by an advancing glacier. This scenario needs to be examined in order to assess the suitability of potential sites for the location of deep geologic repositories for the storage of high-level nuclear waste. The THM processes are examined using a computational multiphysics approach that takes into account thermo-...

  18. Fracture risk assessment of trunk oil pipeline by corrosion fatigue mechanism of service defects development

    OpenAIRE

    Vasyl Luzhetskyy

    2013-01-01

    Engineering estimations of the corrosion fracture velocity of oil pipelines have been given, which include both mechanical and physical-chemical interaction operation factors of strained material with workspace. Characteristics of cyclic corrosion crack resistance of a pipe metal of the exploited oil-trunk pipeline with the regard for operating production factors have been defined. New data about corrosive and fatigue failure of pipes in dependence on the initial sizes and forms of their dete...

  19. The effect of adhesive layer elasticity on the fracture mechanics of a blister test specimen

    Science.gov (United States)

    Updike, D. P.

    1975-01-01

    An analytical model of a blister type specimen for evaluating adhesive bond strength was developed. Plate theory with shear deformation was used to model the deformation of the plate, and elastic deformation of the adhesive layer is taken into account. It is shown that the inclusion of the elastic deformation of the adhesive layer can have a significant influence in the energy balance calculations of fracture mechanics.

  20. Fracture mechanics approaches for assessment of HTGR steam generator tube weld integrity

    International Nuclear Information System (INIS)

    HTGR steam generator tube welds with circumferential cracks in their highest stress region were assessed by linear elastic fracture mechanics methods. The computed stress intensity factors were below the threshold level for propagation and crack propagation will not occur for the pipe geometry (radius and thickness of tube wall) and the stress levels considered. In addition crack arrest may be expected if the predominant stress field is a thermally induced bending stress field

  1. 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.

  2. Development of classical boundary element analysis of fracture mechanics in gradient materials

    OpenAIRE

    Xiao, HT; Yue, QZQ

    2013-01-01

    Over the last decade, the authors have extended the classical boundary element methods (BEM) for analysis of the fracture mechanics in functionally gradient materials. This paper introduces the dual boundary element method associated with the generalized Kelvin fundamental solutions of multilayered elastic solids (or Yue’s solution). This dual BEM uses a pair of the displacement and traction boundary integral equations. The former is collocated exclusively on the uncracked boundary, and the l...

  3. Fracture mechanics analysis of a high-pressure hydrogen facility compressor

    Science.gov (United States)

    Vroman, G. A.

    1974-01-01

    The investigation and analysis of a high-pressure hydrogen facility compressor is chronicled, and a life prediction based on fracture mechanics is presented. Crack growth rates in SA 105 Gr II steel are developed for the condition of sustained loading, using a hypothesis of hydrogen embrittlement associated with plastic zone reverse yielding. The resultant formula is compared with test data obtained from laboratory specimens.

  4. 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.

  5. A fracture mechanics study of tungsten failure under high heat flux loads

    International Nuclear Information System (INIS)

    The performance of fusion devices is highly dependent on plasma-facing components. Tungsten is the most promising candidate material for armors in plasma-facing components in ITER and DEMO. However, the brittleness of tungsten below the ductile-to-brittle transition temperature is very critical to the reliability of plasma-facing components. In this work, thermo-mechanical and fracture behaviors of tungsten are predicted numerically under fusion relevant thermal loadings.

  6. Atomistic Determination of Cross-Slip Pathway and Energetics

    DEFF Research Database (Denmark)

    Rasmussen, Torben; Jacobsen, Karsten Wedel; Leffers, Torben;

    1997-01-01

    The mechanism for cross slip of a screw dislocation in Cu is determined by atomistic simulations that only presume the initial and final states of the process. The dissociated dislocation constricts in the primary plane and redissociates into the cross-slip plane while still partly in the primary...

  7. Investigation of the Thermal, Mechanical, and Fracture Properties of Alumina-Epoxy Composites

    Energy Technology Data Exchange (ETDEWEB)

    McGrath,L.; Parnas, R.; King, S.; Schroeder, J.; Fischer, D.; Lenhart, J.

    2008-01-01

    A combination of dynamic shear rheology, thermomechanical analysis (TMA), scanning electron microscopy (SEM), Near-Edge X-ray Absorption Fine Structure (NEXAFS), and fracture toughness testing was utilized to characterize the thermal, mechanical, chemical, and fracture properties of alumina (a-Al2O3)-filled epoxy resins as a function of average filler size, size distribution, particle shape, loading, and epoxy crosslink density. In general the cured properties of the filled composites were robust. Small changes in particle size, shape, and size distribution had little impact on the final properties. Resin crosslink density and filler loading were the most critical variables, causing changes in all properties. However, most applications could likely tolerate small changes in these variables also. SEM and NEXAFS characterization of the fracture surfaces revealed that the fracture occurs at the filler interface and the interfacial epoxy composition is similar to the bulk resin, indicating a weak epoxy-alumina interaction. These results are critical for implementation of particulate-filled polymer composites in practical applications because relaxed material specifications and handling procedures can be incorporated in production environments to improve efficiency.

  8. Study of Mechanical Properties and Fracture Mode of Alumina-Silicon Carbide Nanocomposites

    Science.gov (United States)

    Rahimnezhad Yazdi, A.; Baharvandi, H. R.; Abdizadeh, H.; Ehsani, N.

    In this study Al2O3-SiC nanocomposites have been fabricated by mixing of alumina and silicon carbide nano powders, followed by hot pressing at 1700°C. The mechanical properties and fracture mode of Al2O3-SiC nanocomposites containing different volume fractions (5, 10 and 15%) of nano scale SiC particles were investigated and compared with those of alumina. Al2O3-SiC powders were prepared by planetary milling in isopropanol. Fracture mode of specimens was investigated by means of scanning electron microscopy. Nanocomposites were tougher than alumina when they were hot pressed at the same temperature, and the values of nanocomposite's flexural strength and hardness were higher than those of alumina. Flexural strength, hardness and fracture toughness of the nanocomposites increase by increasing the volume percent of SiC up to 10% and then decrease slightly. The Scanning electron microscopy observations showed that fracture mode changes from intergranular for alumina to transgranular for nanocomposites. Finally X-ray diffraction analysis couldn't detect any chemical reactions between Al2O3 and SiC particles.

  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. 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.

  11. The microstructural, mechanical, and fracture properties of austenitic stainless steel alloyed with gallium

    Science.gov (United States)

    Kolman, D. G.; Bingert, J. F.; Field, R. D.

    2004-11-01

    The mechanical and fracture properties of austenitic stainless steels (SSs) alloyed with gallium require assessment in order to determine the likelihood of premature storage-container failure following Ga uptake. AISI 304 L SS was cast with 1, 3, 6, 9, and 12 wt pct Ga. Increased Ga concentration promoted duplex microstructure formation with the ferritic phase having a nearly identical composition to the austenitic phase. Room-temperature tests indicated that small additions of Ga (less than 3 wt pct) were beneficial to the mechanical behavior of 304 L SS but that 12 wt pct Ga resulted in a 95 pct loss in ductility. Small additions of Ga are beneficial to the cracking resistance of stainless steel. Elastic-plastic fracture mechanics analysis indicated that 3 wt pct Ga alloys showed the greatest resistance to crack initiation and propagation as measured by fatigue crack growth rate, fracture toughness, and tearing modulus. The 12 wt pct Ga alloys were least resistant to crack initiation and propagation and these alloys primarily failed by transgranular cleavage. It is hypothesized that Ga metal embrittlement is partially responsible for increased embrittlement.

  12. 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.

  13. 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.

  14. Martensitic stainless steel AISI 420—mechanical properties, creep and fracture toughness

    Science.gov (United States)

    Brnic, J.; Turkalj, G.; Canadija, M.; Lanc, D.; Krscanski, S.

    2011-11-01

    In this paper some experimental results and analyses regarding the behavior of AISI 420 martensitic stainless steel under different environmental conditions are presented. That way, mechanical properties like ultimate tensile strength and 0.2 percent offset yield strength at lowered and elevated temperatures as well as short-time creep behavior for selected stress levels at selected elevated temperatures of mentioned material are shown. The temperature effect on mentioned mechanical properties is also presented. Fracture toughness was calculated on the basis of Charpy impact energy. Experimentally obtained results can be of importance for structure designers.

  15. MECHANICAL FAILURE OF THE LONG GAMMA NAIL IN TWO PROXIMAL FEMUR FRACTURES

    OpenAIRE

    Najibi, Soheil; Mark, Lemos; Fehnel, David

    2010-01-01

    Mechanical failure of the long gamma nail was encountered in two elderly patients with proximal femur fractures over a 6-month period. One of the patients had a known history of lymphoma. The other patient had a history of rheumatoid arthritis but no history of cancer or other metabolic bone disease. Both nails failed at the junction of the compression screw and the nail. The angle of failure of the nail was the same in both cases. The index of suspicion for imminent mechanical failure of the...

  16. 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)

  17. Characterization of the Microstructure, Fracture, and Mechanical Properties of Aluminum Alloys 7085-O and 7175-T7452 Hollow Cylinder Extrusions

    Science.gov (United States)

    Benoit, Samuel G.; Chalivendra, Vijaya B.; Rice, Matthew A.; Doleski, Robert F.

    2016-06-01

    Microstructural, tensile, and fracture characterizations of cylindrically forged forms of aluminum alloys AA7085-O and AA7175-T7452 were performed. Mechanical and fracture properties were investigated along radial, circumferential, and longitudinal directions to determine directional dependency. American Society for Testing and Materials (ASTM) test methods (ASTM E8-04 and ASTM E1820) were employed for both the tensile and fracture characterizations, respectively. The tensile and fracture properties were related to microstructure in each direction. The strength, elongation at break, and ultimate tensile strength of AA7085-O were higher than those of AA7175-T7452. AA7175-T7452 alloy failed in a brittle manner during fracture studies. AA7085-O outperformed AA7175-T7452 on fracture energy in all of the orientations studied. Smaller grain sizes on the planes normal to circumferential and longitudinal directions showed improvement in both elongation at break and fracture energy values compared to those of radial direction. Scanning electron microscopy images demonstrated cleavage fracture in AA7175-T7452 and transgranular fracture in AA7085-O.

  18. 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.

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

    International Nuclear Information System (INIS)

    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 KI 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.)

  20. 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.)

  1. Fatigue behaviour and fracture mechanism of cryogenically treated En 353 steel

    International Nuclear Information System (INIS)

    An experimental investigation was conducted for a better understanding of fatigue and fracture behaviour of carburized steel used in the manufacture of vehicle transmission elements such as crown wheel and pinion. An attempt was made to study the fatigue strength of En 353 based on failure at 107 cycles after subjecting to three different treatments namely conventional heat treatment, shallow cryogenic treatment and deep cryogenic treatment. Rotating bending fatigue test was performed in air at room temperature for all specimens. Fractured specimen surfaces were examined by scanning electron microscope to identify the mechanism involved during fatigue. The study concludes that shallow and deep cryogenically treated samples show an improvement with an overall fatigue life of 71% and a reduction of 26% over conventionally heat treated samples respectively. The combined presence of retained austenite and fine carbides has resulted in enhanced fatigue strength of shallow cryogenically treated specimens over the conventionally heat treated and deep cryogenically treated specimens.

  2. 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...... medium, and 7 results in closed formsolutions for the load-crack open8 ing relationship. To distinguish between single and 9 multiple cracking in a design process, structural clas10 sification parameters are derived. The minimum rein11 forcement ratio for obtainingmultiple cracking derived 12 from...... 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....

  3. 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

  4. 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

  5. Ballistic Fracturing of Carbon Nanotubes.

    Science.gov (United States)

    Ozden, Sehmus; Machado, Leonardo D; Tiwary, ChandraSekhar; Autreto, Pedro A S; Vajtai, Robert; Barrera, Enrique V; Galvao, Douglas S; Ajayan, Pulickel M

    2016-09-21

    Advanced materials with multifunctional capabilities and high resistance to hypervelocity impact are of great interest to the designers of aerospace structures. Carbon nanotubes (CNTs) with their lightweight and high strength properties are alternative to metals and/or metallic alloys conventionally used in aerospace applications. Here we report a detailed study on the ballistic fracturing of CNTs for different velocity ranges. Our results show that the highly energetic impacts cause bond breakage and carbon atom rehybridizations, and sometimes extensive structural reconstructions were also observed. Experimental observations show the formation of nanoribbons, nanodiamonds, and covalently interconnected nanostructures, depending on impact conditions. Fully atomistic reactive molecular dynamics simulations were also carried out in order to gain further insights into the mechanism behind the transformation of CNTs. The simulations show that the velocity and relative orientation of the multiple colliding nanotubes are critical to determine the impact outcome.

  6. Fracture mechanics of human cortical bone: The relationship of geometry, microstructure and composition with the fracture of the tibia, femoral shaft and the femoral neck

    Science.gov (United States)

    Yeni, Yener Nail

    Bone fracture is a major health problem in old population with its complications leading to mortality and morbidity. Therapies mostly involve preventing bone mass loss. Individuals with high bone mass, however, may still suffer fractures suggesting that additional components such as bone microstructure and composition may be responsible for increased fracture risk in the elderly. The relationship of bone constituents with bone fragility, however, is not well-understood. A better understanding of these relationships will help improving therapies by controlling the relevant biological processes. Bone is a composite material with many constituents such as osteons embedded with vascular channels, collagen fibers, mineral crystals, etc. The nature of interfacing between these constituents makes bone a more complex material. Bone also has a structure that adapts itself, both internally and externally, to better fit its needs. This suggested that, unlike man-made materials, a relationship between material properties and structural properties may exist. Because bone has some similarities with engineering composite materials and also experiences microcracks, a fracture mechanics approach would be more appropriate for investigating its fragility. Choosing mode I and mode II fracture toughness (Gsb{Ic} and Gnsb{IIc}, respectively) as indicators of bone fragility, their relationship with bone microstructure (porosity, osteon morphology, mineral crystal imperfection and microdamage), composition (density, mineral, organic, water and collagen content) and macrostructure (thickness, diameter and moment of inertia of the shaft and angle between the femoral neck and femoral shaft from different views) was investigated. Use of x-ray radiogrammetry for detecting the latter was tested. Differences among the femoral shaft, femoral neck and the tibia were investigated for an age range of 22-94 years. In general, fracture toughness increased with increasing bone quantity. However, the

  7. 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

  8. Atomistic Processes of Catalyst Degradation

    Energy Technology Data Exchange (ETDEWEB)

    None

    2004-11-27

    The purpose of this cooperative research and development agreement (CRADA) between Sasol North America, Inc., and the oak Ridge National Laboratory (ORNL) was to improve the stability of alumina-based industrial catalysts through the combination of aberration-corrected scanning transmission electron microscopy (STEM) at ORNL and innovative sample preparation techniques at Sasol. Outstanding progress has been made in task 1, 'Atomistic processes of La stabilization'. STEM investigations provided structural information with single-atom precision, showing the lattice location of La dopant atoms, thus enabling first-principles calculations of binding energies, which were performed in collaboration with Vanderbilt University. The stabilization mechanism turns out to be entirely due to a particularly strong binding energy of the La tom to the {gamma}-alumina surface. The large size of the La atom precludes incorporation of La into the bulk alumina and also strains the surface, thus preventing any clustering of La atoms. Thus highly disperse distribution is achieved and confirmed by STEM images. la also affects relative stability of the exposed surfaces of {gamma}-alumina, making the 100 surface more stable for the doped case, unlike the 110 surface for pure {gamma}-alumina. From the first-principles calculations, they can estimate the increase in transition temperature for the 3% loading of La used commercially, and it is in excellent agreement with experiment. This task was further pursued aiming to generate useable recommendations for the optimization of the preparation techniques for La-doped aluminas. The effort was primarily concentrated on the connection between the boehmitre-{gamma}-Al{sub 2}O{sub 3} phase transition (i.e. catalyst preparation) and the resulting dispersion of La on the {gamma}-Al{sub 2}O{sub 3} surface. It was determined that the La distribution on boehmite was non-uniform and different from that on the {gamma}-Al{sub 2}O{sub 3} and thus

  9. 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. PMID:24934595

  10. 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.

  11. 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.

  12. A rock mechanics study of fracture zone 2 at the Finnsjoen site

    International Nuclear Information System (INIS)

    Comprehensive field investigations at the Finnsjoen study site have revealed a subhorizontal zone, termed Zone 2, that exhibits anomalous characteristics in terms of high hydraulic conductivity, governing the groundwater transport pattern on a regional scale. The present study provides an assessment of the characteristics of Zone 2. Thus, estimates of the deformational characteristics of the zone, based on available borehole information, show that the zone forms a diffuse and rather moderate mechanical contrast to the surrounding bedrock. As also verified by stress measurement results, major stress anomalies attributable to the zone are therefore not to be expected. Bound estimates of stress conditions during periods of glaciation and deglaciation are also derived, and possible impacts of these loadings on the fracture zone are discussed. It is concluded that glaciation represents stable conditions, whilst the complex loading mechanisms encountered during deglaciation may trigger reactivation of structures at shallow depth. Taking the above results as an example, implications of a feature like Zone 2 on the integrity of a hypothetical repository are discussed in more general terms. Considering the likely spatial extension of the mechanical disturbances related to the repository excavations and the fracture zone respectively, it is suggested that a mutual distance of the order of one hundred metres is sufficient to avoid mechanical interaction. (au)

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

    Institute of Scientific and Technical Information of China (English)

    RK Gupta; Raj Singh; Vinit Verma; Amit Batra; Nishant Setia; Paritosh Gogna; Jeetesh Gawande

    2014-01-01

    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.

  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. 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.

  16. 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.

  17. Simultaneous hydraulic fracturing of ultra-low permeability sandstone reservoirs in China:Mechanism and its field test

    Institute of Scientific and Technical Information of China (English)

    任岚; 林然; 赵金洲; 杨克文; 胡永全; 王秀娟

    2015-01-01

    Based on the impact of the stress perturbation effect created by simultaneous propagation of multiple fractures in the process of simultaneous hydraulic fracturing, a thorough research on the mechanism and adaptation of simultaneous fracturing of double horizontal wells in ultra-low permeability sandstone reservoirs was conducted by taking two adjacent horizontal wells (well Yangping-1 and well Yangping-2 located in Longdong area of China Changqing Oilfield) as field test wells. And simultaneous fracturing optimal design of two adjacent horizontal wells was finished and employed in field test. Micro-seismic monitoring analysis of fracture propagation during the stimulation treatment shows that hydraulic fractures present a pattern of complicated network expansion, and the well test data after fracturing show that the daily production of well Yangping-1 and well Yangping-2 reach 105.8 t/d and 87.6 t/d, which are approximately 9.4 times and 7.8 times the daily production of a fractured vertical well in the same area, respectively. Field test reflects that simultaneous hydraulic fracturing of two adjacent horizontal wells can enlarge the expansion area of hydraulic fractures to obtain a lager drainage area and realize the full stimulation of ultra-low permeability sandstone reservoirs in China Changqing oilfield. Therefore, simultaneous fracturing of two adjacent horizontal wells provides a good opportunity in stimulation techniques for the efficient development of ultra-low permeability reservoirs in China Changqing oilfield, and it has great popularization value and can provide a new avenue for the application of stimulation techniques in ultra-low permeability reservoirs in China.

  18. 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

    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...... 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...... in callus bone mineral content (P\\0.05). However, after 8 weeks of healing, no difference was found in either callus volume or bone mineral content. SrR did not influence maximum load or stiffness of the fractures after either 3 or 8 weeks of healing. EDX showed that Sr was incorporated into the callus...

  19. Adaptation of OCA-P, a probabilistic fracture-mechanics code, to a personal computer

    International Nuclear Information System (INIS)

    The OCA-P probabilistic fracture-mechanics code can now be executed on a personal computer with 512 kilobytes of memory, a math coprocessor, and a hard disk. A user's guide for the particular adaptation has been prepared, and additional importance sampling techniques for OCA-P have been developed that allow the sampling of only the tails of selected distributions. Features have also been added to OCA-P that permit RTNDT to be used as an ''independent'' variable in the calculation of P

  20. 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.

  1. Dynamic Response and Fracture Mechanism of a Novel Structural Radar Absorbing Material

    Institute of Scientific and Technical Information of China (English)

    CAO Mao-Sheng; ZHOU Wei; QU Gui-Min; RONG Ji-Li

    2008-01-01

    @@ A novel structural radar absorbing material (SRAM), which gives the normal resin-base composites new function, is prepared. The dynamic compressive tests of SRAM are carried out in both in-plane and normal directions of composites by means of the split Hopkinson pressure bar (SHPB). In the compressive test along in-plane direction, failure occurs at the interface between a fibre and the matrix. A fracture mode and mechanism was proposed to explain these results. The addition of absorbing particles results in the deterioration of the compressive properties. However, there is no obvious decrease on compressive strength of SRAM with the radar absorbing properties.

  2. A fracture- mechanics calculation of crack growth rate for a gas turbine blade

    International Nuclear Information System (INIS)

    The existence of thermo-mechanical stresses, due to the frequent start-ups and shutdowns of gas turbines. Combined with high working temperatures may cause creep and fatigue failure of the blades. This paper describes a fracture-mechanics life assessment of a gas turbine blade. Initially, the distributions of thermal and mechanical stresses were obtained by using the finite element method. Accordingly; the crack modeling was performed in a high stress region at the suction side surface of the blade. Several crack growth increments were observed and the related crack tip parameters were calculated. Finally; the creep-fatigue crack growth in each cycle was calculated and the total number of start-stop cycles was determined

  3. 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.

  4. Analysis and modeling of coupled thermo-hydro-mechanical phenomena in 3D fractured media

    International Nuclear Information System (INIS)

    This doctoral research was conducted as part of a joint France-Spain co-tutelage PhD thesis in the framework of a bilateral agreement between two universities, the Institut National Polytechnique de Toulouse (INPT) and the Universidad Politecnica de Madrid (UPM). It concerns a problem of common interest at the national and international levels, namely, the disposal of radioactive waste in deep geological repositories. The present work is devoted, more precisely, to near-field hydrogeological aspects involving mass and heat transport phenomena. The first part of the work is devoted to a specific data interpretation problem (pressures, relative humidities, temperatures) in a multi-barrier experimental system at the scale of a few meters - the 'Mock-Up Test' of the FEBEX project, conducted in Spain. Over 500 time series are characterized in terms of spatial, temporal, and/or frequency/scale-based statistical analysis techniques. The time evolution and coupling of physical phenomena during the experiment are analyzed, and conclusions are drawn concerning the behavior and reliability of the sensors. The second part of the thesis develops in more detail the 3-Dimensional (3D) modeling of coupled Thermo-Hydro-Mechanical phenomena in a fractured porous rock, this time at the scale of a hundred meters, based on the data of the 'In-Situ Test' of the FEBEX project conducted at the Grimsel Test Site in the Swiss Alps. As a first step, a reconstruction of the 3D fracture network is obtained by Monte Carlo simulation, taking into account through optimization the geomorphological data collected around the FEBEX gallery. The heterogeneous distribution of traces observed on the cylindrical wall of the tunnel is fairly well reproduced in the simulated network. In a second step, we develop a method to estimate the equivalent permeability of a many-fractured block by extending the superposition method of Ababou et al. [1994] to the case where the permeability of the rock matrix is not

  5. Improved Mechanical Performance Fracture Properties and Reliability of Radical-Cured Thermosets.

    Energy Technology Data Exchange (ETDEWEB)

    Redline, Erica Marie; Bolintineanu, Dan; Lane, J. Matthew; Stevens, Mark J.; Alam, Todd M.; Celina, Mathias C.

    2016-10-01

    The aim of this study was to alter polymerization chemistry to improve network homogeneity in free-radical crosslinked systems. It was hypothesized that a reduction in heterogeneity of the network would lead to improved mechanical performance. Experiments and simulations were carried out to investigate the connection between polymerization chemistry, network structure and mechanical properties. Experiments were conducted on two different monomer systems - the first is a single monomer system, urethane dimethacrylate (UDMA), and the second is a two-monomer system consisting of bisphenol A glycidyl dimethacrylate (BisGMA) and triethylene glycol dimethacrylate (TEGDMA) in a ratio of 70/30 BisGMA/TEGDMA by weight. The methacrylate systems were crosslinked using traditional radical polymeriza- tion (TRP) with azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO) as an initiator; TRP systems were used as the control. The monomers were also cross-linked using activator regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) as a type of controlled radical polymerization (CRP). FTIR and DSC were used to monitor reac- tion kinetics of the systems. The networks were analyzed using NMR, DSC, X-ray diffraction (XRD), atomic force microscopy (AFM), and small angle X-ray scattering (SAXS). These techniques were employed in an attempt to quantify differences between the traditional and controlled radical polymerizations. While a quantitative methodology for characterizing net- work morphology was not established, SAXS and AFM have shown some promising initial results. Additionally, differences in mechanical behavior were observed between traditional and controlled radical polymerized thermosets in the BisGMA/TEGDMA system but not in the UDMA materials; this finding may be the result of network ductility variations between the two materials. Coarse-grained molecular dynamics simulations employing a novel model of the CRP reaction were carried out for

  6. 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.

  7. 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.

  8. Scalable Atomistic Simulation Algorithms for Materials Research

    Directory of Open Access Journals (Sweden)

    Aiichiro Nakano

    2002-01-01

    Full Text Available A suite of scalable atomistic simulation programs has been developed for materials research based on space-time multiresolution algorithms. Design and analysis of parallel algorithms are presented for molecular dynamics (MD simulations and quantum-mechanical (QM calculations based on the density functional theory. Performance tests have been carried out on 1,088-processor Cray T3E and 1,280-processor IBM SP3 computers. The linear-scaling algorithms have enabled 6.44-billion-atom MD and 111,000-atom QM calculations on 1,024 SP3 processors with parallel efficiency well over 90%. production-quality programs also feature wavelet-based computational-space decomposition for adaptive load balancing, spacefilling-curve-based adaptive data compression with user-defined error bound for scalable I/O, and octree-based fast visibility culling for immersive and interactive visualization of massive simulation data.

  9. Study of mechanical properties and fracture mechanisms of synthetic fibers nylon-and-polyester type, used in engineering products

    International Nuclear Information System (INIS)

    Fibers are groups formed by molecular-chain-oriented filaments. Fibers play a fundamental role in human being's daily life and they can be found in several forms and geometries, such as filaments, yarns, beams, rope, fabric, composite, coatings, others. They are used in various segments such as civil, mechanical, electrical, electronics, military, naval, nautical, aviation, health, medicine, environment, communications, safety, space, others. Fibers are divided into two distinct classes: natural and chemical ones, which cover synthetic and man-made sub-classes. They can be produced from several materials, such as wool, cotton, rayon, flax, silk, rock, nylon, polyester, polyethylene, poly-propylene, aramid, glass, carbon, steel, ceramic, others. Globally, the participation of chemical fibers corresponds to approximately 59,9%, and the synthetic fiber polyester, the most used one, represents approximately 63% of the world market. Vital needs have led to the development of multi-function fibers and the focus has changed in the last 10 years with the use of nano technology for environmental responsibility and smart fibers. The study of mechanical properties and fracture mechanisms of fibers is of great relevance for characterization and understanding of causes as consequence of failures. For such reason, it was selected technical fabrics made of high performance synthetic fiber nylon-and-polyester type, used in engineered products such as tires, belts, hoses and pneumatic springs, which have been analyzed in each processing phase. Fiber samples were extracted after each processing phase to be analyzed, by traction destructive tests and scanning electron microscopy. The results of analysis of mechanical properties showed loss of resistance to temperature and multi axial stress during fiber processing phase. Through microscopy tests, it was possible to find contamination, surface stains, plastic deformations, scaling, variations in the fracture faces of the filaments and

  10. 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.

  11. Fracture mechanics models developed for piping reliability assessment in light water reactors: piping reliability project

    International Nuclear Information System (INIS)

    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

  12. Advances in fracture mechanics analyses of primary system performance under operating and accident conditions

    International Nuclear Information System (INIS)

    Safety research sponsored by the Nuclear Regulatory Commission, Division of Reactor Safety Research, has resulted in notable advances in several areas of importance in the safety evaluation of reactor primary systems under normal operations and accident situations. First, the methods of linear elastic fracture mechanics and of elastic plastic fracture mechanics have been validated for prediction of pressure vessel performance by the Intermediate Vessel Test program results at the Oak Ridge National Laboratory. The ability confidently to predict vessel performance under realistic service conditions has permitted development of the computer program OCTAVIA which computes failure curves for a range of flaw sizes in terms of pressure and temperature for specified presure vessel material at specific neutron fluence levels. It then considers the probability of occurrence of flaw sizes and magnitude of pressure during an operational, overpressurization transient and determines the probability of failure, for both individual flaw sizes and for the full spectrum. This advance has been verified by the confirmatory results of testing small thick-walled cylinders under thermal shock conditions in the Heavy Section Steel Technology program, and of warm prestressing tests at the US Navel Research Laboratory. Thirdly, the technology of crack arrest has reached a level wherein standardization of test specimens and testing methods is now possible and, indeed, is underway. (Auth.)

  13. On the estimation of the steam generator maintenance efficiency by the means of probabilistic fracture mechanics

    International Nuclear Information System (INIS)

    In this report, an original probabilistic model aimed to assess the efficiency of particular maintenance strategy in terms of tube failure probability is proposed. The model concentrates on axial through wall cracks in the residual stress dominated tube expansion transition zone. It is based on the recent developments in probabilistic fracture mechanics and accounts for scatter in material, geometry and crack propagation data. Special attention has been paid to model the uncertainties connected to non-destructive examination technique (e.g., measurement errors, non-detection probability). First and second order reliability methods (FORM and SORM) have been implemented to calculate the failure probabilities. This is the first time that those methods are applied to the reliability analysis of components containing stress-corrosion cracks. In order to predict the time development of the tube failure probabilities, an original linear elastic fracture mechanics based crack propagation model has been developed. It accounts for the residual and operating stresses together. Also, the model accounts for scatter in residual and operational stresses due to the random variations in tube geometry and material data. Due to the lack of reliable crack velocity vs load data, the non-destructive examination records of the crack propagation have been employed to estimate the velocities at the crack tips. (orig./GL)

  14. 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.

  15. 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...

  16. 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.

  17. Fracture mechanics environmental degradation assessment of nuclear pressure vessel and piping materials

    International Nuclear Information System (INIS)

    A new set of fracture mechanics stress corrosion crack growth data is presented for transgranular cracking of low alloy steels used in various nuclear components as well as intergranular cracking of stabilized austenitic stainless steels used primarily for nuclear piping. The essential observations are as follows: In low alloy steels, fast stress corrosion crack growth rates between 10-9 and 10-8 m/s may be observed down to 400 ppb dissolved oxygen at water conductivities of 0.5 μS/cm in refreshed autoclaves. However, there is an indication, substantiated by only few data, that at lower conductivities and/or lower oxygen concentrations the crack growth rates in ferritic steels come down to about 3 x 10-11 m/s. This crack velocity has also been found to be typical for stabilized austenitic stainless steels exposed to faulted simulated BWR water. Crack growth at this rate is observed in mill annealed (fine grained) as well as in sensitized or coarse grained or cold worked stabilized austenitic stainless steels. On average, the crack growth rates measured in the laboratory by using fracture mechanics methods correlate well with stress corrosion service experience of the steels discussed here

  18. 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.

  19. 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 ...

  20. Proceedings of the Joint IAEA/CSNI Specialists' Meeting on Fracture Mechanics Verification by Large-Scale Testing

    International Nuclear Information System (INIS)

    This report provides the proceedings of a Specialists' Meeting on Fracture Mechanics Verification by Large-Scale Testing that was held in Oak Ridge, Tennessee, on October 23-25, 1992. The meeting was jointly sponsored by the International Atomic Energy Agency (IAEA) and the Nuclear Energy Agency (NEA) of the Organization for Economic Cooperation and Development. In particular, the International Working Group (IWG) on Life Management of Nuclear Power Plants (LMNPP) was the IAEA sponsor, and the Principal Working Group 3 (PWG-3) (Primary System Component Integrity) of the Committee for the Safety of Nuclear Installations (CSNI) was the NEA's sponsor. This meeting was preceded by two prior international activities that were designed to examine the state-of-the-art in fracture analysis capabilities and emphasized applications to the safety evaluation of nuclear power facilities. The first of those two activities was an IAEA Specialists' Meeting on Fracture Mechanics Verification by Large-Scale Testing that was held at the Staatliche Materialprufungsanstalt (MPA) in Stuttgart, Germany, on May 25-27, 1988; the proceedings of that meeting were published 1991.1 The second activity was the CSNI/PWG-3's Fracture Assessment Group's Project FALSIRE (Fracture Analyses of Large-Scale International Reference Experiments). The proceedings of the FALSIRE workshop that was held in Boston, Massachusetts, U.S.A., on May 8-10, 1990, was recently published by the Oak Ridge National Laboratory (ORNL). Those previous activities identified capabilities and shortcomings of various fracture analysis methods based on analyses of six available large-scale experiments. Different modes of fracture behavior, which ranged from brittle to ductile, were considered. In addition, geometry, size, constraint and multiaxial effects were considered. While generally good predictive capabilities were demonstrated for brittle fracture, issues were identified relative to predicting fracture behavior at higher

  1. 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.

  2. Atomistic study of crack propagation and dislocation emission in Cu-Ni multilayers

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-09-01

    The authors present atomistic simulations of the crack tip configuration in multilayered Cu-Ni materials. The simulations were carried out using molecular statics and EAM potentials. The atomistic structure of the interface was studied first for a totally coherent structure. Cracks were simulated near a Griffith condition in different possible configurations of the crack plane and front with respect to the axis of the layers. Results show that interface effects predominantly control the mechanical behavior of the system studied.

  3. Material fields in atomistics as pull-backs of spatial distributions

    Science.gov (United States)

    Chandra Admal, Nikhil; Tadmor, Ellad B.

    2016-04-01

    The various fields defined in continuum mechanics have both a material and a spatial description that are related through the deformation mapping. In contrast, continuum fields defined for atomistic systems using the Irving-Kirkwood or Murdoch-Hardy procedures correspond to a spatial description. It is uncommon to define atomistic fields in the reference configuration due to the lack of a unique definition for the deformation mapping in atomistic systems. In this paper, we construct referential atomistic distributions as pull-backs of the spatial distributions obtained in the Murdoch-Hardy procedure with respect to a postulated deformation mapping that tracks particles. We then show that some of these referential distributions are independent of the choice of the deformation mapping and only depend on the reference and current configuration of particles. Therefore, the fields obtained from these distributions can be calculated without explicitly constructing a deformation map, and by construction they satisfy the balance equations. In particular, we obtain definitions for the first and second atomistic Piola-Kirchhoff stress tensors. We demonstrate the validity of these definitions through a numerical example involving finite deformation of a slab containing a notch under tension. An interesting feature of the atomistic first Piola-Kirchhoff stress tensor is the absence of a kinetic part, which in the atomistic Cauchy stress tensor accounts for thermal fluctuations. We show that this effect is implicitly included in the atomistic first Piola-Kirchhoff stress tensor through the motion of the particles. An open source program to compute the atomistic Cauchy and first Piola-Kirchhoff stress fields called MDStressLab is available online at

  4. Study of the competition between ductile tearing and brittle fracture : Application to the mechanical strength of C-Mn pipes and their welded joints.

    OpenAIRE

    Le Corre, Vincent

    2006-01-01

    This study deals with the fracture behaviour of welded thin structures in the ductile to brittle transition range. It aims to propose a criterion to define the conditions for which the risk of fracture per cleavage does not exist on a cracked structure.The literature review shows that the difficulties of prediction of the fracture behaviour of a structure are related to the dependence of the fracture probability to the mechanical fields at the crack tip. The ductile to brittle transition rang...

  5. Mechanisms Predisposing Penile Fracture and Long-Term Outcomes on Erectile and Voiding Functions

    Directory of Open Access Journals (Sweden)

    Leonardo O. Reis

    2014-01-01

    Full Text Available Purpose. To determine the mechanisms predisposing penile fracture as well as the rate of long-term penile deformity and erectile and voiding functions. Methods. All fractures were repaired on an emergency basis via subcoronal incision and absorbable suture with simultaneous repair of eventual urethral lesion. Patients’ status before fracture and voiding and erectile functions at long term were assessed by periodic follow-up and phone call. Detailed history included cause, symptoms, and single-question self-report of erectile and voiding functions. Results. Among the 44 suspicious cases, 42 (95.4% were confirmed, mean age was 34.5 years (range: 18–60, mean follow-up 59.3 months (range 9–155. Half presented the classical triad of audible crack, detumescence, and pain. Heterosexual intercourse was the most common cause (28 patients, 66.7%, followed by penile manipulation (6 patients, 14.3%, and homosexual intercourse (4 patients, 9.5%. “Woman on top” was the most common heterosexual position (n=14, 50%, followed by “doggy style” (n=8, 28.6%. Four patients (9.5% maintained the cause unclear. Six (14.3% patients had urethral injury and two (4.8% had erectile dysfunction, treated by penile prosthesis and PDE-5i. No patient showed urethral fistula, voiding deterioration, penile nodule/curve or pain. Conclusions. “Woman on top” was the potentially riskiest sexual position (50%. Immediate surgical treatment warrants long-term very low morbidity.

  6. 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

  7. Interstitial helium diffusion mechanisms in 〈1 1 0〉 tilt grain boundaries in BCC FeCr alloys: A atomistic study

    Energy Technology Data Exchange (ETDEWEB)

    He, X., E-mail: hexinfu@ciae.ac.cn [China Institute of Atomic Energy, Beijing (China); Terentyev, D. [SCK-CEN, Structural Materials Group, Nuclear Materials Science Institute, B-2400 Mol (Belgium); Lin, Y.; Yang, W. [China Institute of Atomic Energy, Beijing (China)

    2013-11-15

    In this work, we studied the migration of He in different 〈1 1 0〉 tilt grain boundaries (GBs) (Σ19{3 3 1}, Σ9{2 2 1}, Σ3{1 1 1}, Σ3{1 1 2}, Σ11{1 1 3}, Σ9{1 1 4}) in Fe–(5,10,14)Cr random alloys, with the misorientation angle varying in the range 26°–141°. We performed systematic molecular statics and molecular dynamics simulations to characterize the interaction of He with the core of the GBs and to estimate the diffusion coefficient, migration mechanism, and effective core migration energy. The simulations were performed in the 600–1400 K temperature range, applying a set of interatomic potentials for Fe–Cr–He system recently proposed by Juslin et al., specially fitted to the properties of He in bulk Fe. We found that the migration of an interstitial He near the core of the Σ3{1 1 2} GB is essentially three-dimensional (3D) within the investigated temperature range. The transition of diffusion mode from one-dimensional (1D) to 3D was observed in other GBs in the studied alloys. The results clearly demonstrate, that the accommodation, migration mechanism, and diffusivity of He is extremely sensitive to variations in atomic structure of a particular GB. Alloying with Cr was found to enhance the mobility of a He interstitial in the GB region.

  8. Mechanical properties and microstructure of an α+β titanium alloy with high strength and fracture toughness

    Institute of Scientific and Technical Information of China (English)

    YU Yang; HUI Songxiao; YE Wenjun; XIONG Baiqing

    2009-01-01

    The Ti-Al-Sn-Zr-Cr-Mo-V-Si (Ti-62A) alloy, an alpha-beta alloy with high strength and fracture toughness, is currently used as an advanced structural material in aerospace and non-aerospace applications. Thermo-mechanical processes can be used to optimize the relationship be-twcen its strength and fracture toughness. A Ti-62A alloy bar can be machined through a transus β-forged plus α+β solution treated and aged specimen with a lamellar alpha microstructure. The effects of heat treatment on the mechanical properties were discussed. Heat treatment provided a practical balance of strength, fracture toughness, and fatigue crack growth resistance. A comparison of the Ti-62A alloy with the Ti-62222S alloy under the same thermo-mechanical processing conditions showed that their properties are at the same level.

  9. Atomistic modelling of radiation effects: Towards dynamics of exciton relaxation

    OpenAIRE

    Shluger, A. L.; Gavartin, J. L.; Szymanski, M. A.; Stoneham, A. M.

    2000-01-01

    This brief review is focused on recent results of atomistic modelling and simulation of exciton related processes in ionic materials. We present an analysis of thermal fluctuations of the electrostatic potential in cubic ionic crystals and their relation to formation of a tail in the electron density of states and localisation of electronic states. Then the possible 'fast' mechanism of formation of F-H pairs in KBr as a result of decomposition of relaxing excitons is discussed. We briefly des...

  10. Atomistic Simulations of Pore Formation and Closure in Lipid Bilayers

    OpenAIRE

    Bennett, W. F. Drew; Sapay, Nicolas; Tieleman, D. Peter

    2014-01-01

    Cellular membranes separate distinct aqueous compartments, but can be breached by transient hydrophilic pores. A large energetic cost prevents pore formation, which is largely dependent on the composition and structure of the lipid bilayer. The softness of bilayers and the disordered structure of pores make their characterization difficult. We use molecular-dynamics simulations with atomistic detail to study the thermodynamics, kinetics, and mechanism of pore formation and closure in DLPC, DM...

  11. FAVOR: A new fracture mechanics code for reactor pressure vessels subjected to pressurized thermal shock

    International Nuclear Information System (INIS)

    This report discusses probabilistic fracture mechanics (PFM) analysis which is a major element of the comprehensive probabilistic methodology endorsed by the NRC for evaluation of the integrity of Pressurized Water Reactor (PWR) pressure vessels subjected to pressurized-thermal-shock (PTS) transients. It is anticipated that there will be an increasing need for an improved and validated PTS PFM code which is accepted by the NRC and utilities, as more plants approach the PTS screening criteria and are required to perform plant-specific analyses. The NRC funded Heavy Section Steel Technology (HSST) Program at Oak Ridge National Laboratories is currently developing the FAVOR (Fracture Analysis of Vessels: Oak Ridge) PTS PFM code, which is intended to meet this need. The FAVOR code incorporates the most important features of both OCA-P and VISA-II and contains some new capabilities such as PFM global modeling methodology, the capability to approximate the effects of thermal streaming on circumferential flaws located inside a plume region created by fluid and thermal stratification, a library of stress intensity factor influence coefficients, generated by the NQA-1 certified ABAQUS computer code, for an adequate range of two and three dimensional inside surface flaws, the flexibility to generate a variety of output reports, and user friendliness

  12. Fatigue Properties and Fracture Mechanism of Steel Coated with Diamond-Like Carbon Films

    Science.gov (United States)

    Akebono, Hiroyuki; Kato, Masahiko; Sugeta, Atsushi

    Diamond-like carbon (DLC) films have attracted much attention in many industrial fields because of their excellent tribological properties, high hardness, chemical inertness and biocompatibility. In order to examine the fatigue properties and to clear the fracture mechanism of DLC coated materials, AISI4140 steel coated with DLC films by using unbalanced magnetron sputtering method was prepared and two types of fatigue test were carried out by using a tension and compression testing machine with stress ratio -1 and a bending testing machine with stress ratio -1 with a focused on the fatigue crack behavior in detail. The fracture origin changed from the slip deformation to micro defects at surface whose size didn't affect the fatigue crack initiation behavior in the case of Virgin series because the hard coating like DLC films make the defect sensitivity of coated material higher. However, DLC series indicated higher fatigue strengths in finite life region and fatigue limit compared with Virgin series. From the continuously observation by using a plastic replicas technique, it is clear that there are no noticeable differences on fatigue crack propagation rate between the Virgin and DLC series, however the fatigue crack initiation of DLC series was delayed significantly by existence of DLC films compared with Virgin series.

  13. Elastic-plastic fracture mechanics analyses of cracked steam generator tubes under internal pressure

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hyeong Keun; Ahn, Min Yong; Moon, Seong In; Chang, Yoon Suk; Kim, Young Jin [Sungkyunkwan Univ., Suwon (Korea, Republic of); Hwang, Seong Sik; Kim, Joung Soo [KAERI, Taejon (Korea, Republic of)

    2005-07-01

    The structural and leakage integrity of steam generator tube should be maintained during operation even though a crack is existed on it. During the past three decades, several limit load solutions have been proposed to resolve the integrity issue. However, for exact load carrying capacity estimation of specific components under different conditions, these solutions have to be modified by using lots of experimental data. The purpose of this paper is to introduce a new burst pressure estimation scheme based on fracture mechanics analyses for steam generator tube with an axial or circumferential through-wall crack. To do this, closed-form engineering equations were derived to get relevant parameters from three dimensional elastic-plastic finite element analyses combined with reference stress method. Also, a series of structural integrity analyses were carried out using the calculated J-integral from engineering equations and fracture toughness data. Thereby, in comparison with the experimental data as well as corresponding estimation results from limit load solutions, it was proven that the proposed estimation scheme can be used as an efficient tool for integrity evaluation of cracked steam generator tubes.

  14. Pressurized thermal shock probabilistic fracture mechanics sensitivity analysis for Yankee Rowe reactor pressure vessel

    International Nuclear Information System (INIS)

    The Nuclear Regulatory Commission (NRC) requested Oak Ridge National Laboratory (ORNL) to perform a pressurized-thermal-shock (PTS) probabilistic fracture mechanics (PFM) sensitivity analysis for the Yankee Rowe reactor pressure vessel, for the fluences corresponding to the end of operating cycle 22, using a specific small-break-loss- of-coolant transient as the loading condition. Regions of the vessel with distinguishing features were to be treated individually -- upper axial weld, lower axial weld, circumferential weld, upper plate spot welds, upper plate regions between the spot welds, lower plate spot welds, and the lower plate regions between the spot welds. The fracture analysis methods used in the analysis of through-clad surface flaws were those contained in the established OCA-P computer code, which was developed during the Integrated Pressurized Thermal Shock (IPTS) Program. The NRC request specified that the OCA-P code be enhanced for this study to also calculate the conditional probabilities of failure for subclad flaws and embedded flaws. The results of this sensitivity analysis provide the NRC with (1) data that could be used to assess the relative influence of a number of key input parameters in the Yankee Rowe PTS analysis and (2) data that can be used for readily determining the probability of vessel failure once a more accurate indication of vessel embrittlement becomes available. This report is designated as HSST report No. 117

  15. Modeling the Progressive Failure of Jointed Rock Slope Using Fracture Mechanics and the Strength Reduction Method

    Science.gov (United States)

    Zhang, Ke; Cao, Ping; Meng, Jingjing; Li, Kaihui; Fan, Wenchen

    2015-03-01

    The fracturing process during the progressive failure of a jointed rock slope is numerically investigated by using fracture mechanics and the strength reduction method (SRM). A displacement discontinuity method containing frictional elements is developed for the calculation of the stress intensity factor (SIF). The failure initiation of the jointed rock slope is analyzed by evaluating the SIF. A new joint model is proposed by combining solid elements with interface elements in the commercial software FLAC3D. These represent the discontinuous planes in a rock mass on which sliding or separation can occur. The progressive failure process is simulated by reducing the shear strength of the rock mass, which includes the process of stress concentration, crack initiation, crack propagation, slip weakening, and coalescence of failure surfaces. The factor of safety (FS) and location of the critical failure surface are determined by the SRM. The influence of the joint inclination is investigated using the FS and the SIF. Laboratory experiments on specimens containing an inclined flaw under compression-shear stress are also conducted to investigate the effect of the angle between the shear direction and the flaw inclination, which provides an experimental explanation for the shear behavior of jointed rock. The results show that the joint inclination dominates the failure behavior of jointed rock slope, and two failure patterns have been classified.

  16. Solute transport in fractured media - The important mechanisms for performance assessment

    International Nuclear Information System (INIS)

    The most important mechanisms that control the release of contaminants from a repository for nuclear or chemical waste have been studied. For the time scale of interest for the disposal of nuclear or even chemical waste, diffusion into the rock matrix is an important factor which retards and dilutes the contaminants. It is found that the water flow-rate distribution and the flow-wetted surface are the entities that primarily determine the solute transport. If the diffusion in the rock matrix is negligible, the solute transport is determined by the water flow-rate and the flow porosity. This is shown by simulations using analytical solutions obtained for simple geometries, such as the flow in a fracture or a channel. Similar results are obtained for more complex systems, such as flow in a fracture with variable aperture and through a network of channels. It is also found that the use of a retardation factor relating the travel times of interacting and noninteracting solutes is inappropriate and may be misleading. 11 refs, 9 figs, 1 tab

  17. Fracture of ECAP-deformed iron and the role of extrinsic toughening mechanisms

    OpenAIRE

    Hohenwarter, A.; Pippan, R.

    2013-01-01

    The fracture behaviour of pure iron deformed by equal-channel angular pressing via route A was examined. The fracture toughness was determined for different specimen orientations and measured in terms of the critical plane strain fracture toughness, KIC , the critical J integral, JIC , and the crack opening displacement for crack initiation, CODi . The results demonstrate that the crack plane orientation has a pronounced effect on the fracture toughness. Different crack plane orientations lea...

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

    Science.gov (United States)

    An, Qi; Goddard, William A.

    2015-09-01

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

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

    Science.gov (United States)

    An, Qi; Goddard, William A

    2015-09-01

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

  20. User's manual and analysis methodology of probabilistic fracture mechanics analysis code PASCAL3 for reactor pressure vessel (Contract research)

    International Nuclear Information System (INIS)

    As a part of the structural integrity research for aging LWR (Light Water Reactor) components, the probabilistic fracture mechanics (PFM) analysis code PASCAL (PFM Analysis of Structural Components in Aging LWR) has been developed in JAEA. The PASCAL code evaluates the conditional probabilities of crack initiation and fracture of a reactor pressure vessel (RPV) under transient conditions such as pressurized thermal shock (PTS). The continuous development of the code has been aimed to improve the accuracy and reliability of analysis by introducing new analysis methodologies and algorithms considering recent developments in the fracture mechanics and computer performance. Previous version of PASCAL (PASCAL Ver.2) that was released in 2007 has many functions including the evaluation method for an embedded crack and conditional probabilities of crack initiation and fracture of a RPV, PTS transient database, inspection crack detection probability model and others. Since 2007, the PASCAL Ver. 2 has been improved mainly considering the effects of weld-overlay cladding on the inner surface of RPV. A generalized analysis method is available on the basis of the development of PASCAL Ver.3 and sensitivity analysis results. Graphical user interface (GUI) including a generalized method and some functions of probabilistic fracture mechanics have been also updated for PASCAL3. This report provides the user's manual, examples of analysis and theoretical background of PASCAL Ver.3. (author)

  1. 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.

  2. FFTF irradiation of fracture mechanics specimens for out-of-core structures

    International Nuclear Information System (INIS)

    The National Program Plan has established data requirements for out-of-core structures for FBRs. Significant FFTF irradiation space with moderate gamma heating levels is required to irradiate relatively large fracture mechanics specimens to total neutron fluences ranging between 5 x 1021 and 5 x 1022 n/cm2 and temperatures which range between 4000C (7500F) and 6500C (12000F). Priority 1 data on stainless steel welds requires a test volume of 7443 cm3 (454 in3). Priority 2 data on 304 and 316 SS and Inconel 718 materials and Inconel 718 welds requires 2760 cm3 (168 in3). Priority 3 data on stainless steels, other nickel-base alloys, and ferritics requires 33,118 cm3 (2021 in3). Priority 4 data at elevated temperatures on stainless steels, other nickel-base alloys and ferritics requires 69,182 cm3

  3. 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.

  4. Fracture mechanical analysis of tungsten armor failure of a water-cooled divertor target

    International Nuclear Information System (INIS)

    Highlights: • The FEM-based VCE method and XFEM were employed for computing KI (or J-integral) and predicting progressive cracking, respectively. • The most probable pattern of crack formation is radial cracking in the tungsten armor block. • The most probable site of cracking is the upper interfacial region of the tungsten armor block adjacent to the top position of the copper interlayer. • The initiation of a major crack becomes likely, only when the strength of tungsten armor block is significantly reduced from its original strength. - Abstract: The inherent brittleness of tungsten at low temperature and the embrittlement by neutron irradiation are its most critical weaknesses for fusion applications. In the current design of the ITER and DEMO divertor, the high heat flux loads during the operation impose a strong constraint on the structure–mechanical performance of the divertor. Thus, the combination of brittleness and the thermally induced stress fields due to the high heat flux loads raises a serious reliability issue in terms of the structural integrity of tungsten armor. In this study, quantitative estimates of the vulnerability of the tungsten monoblock armor cracking under stationary high heat flux loads are presented. A comparative fracture mechanical investigation has been carried out by means of two different types of computational approaches, namely, the extended finite element method (XFEM) and the finite element method (FEM)-based virtual crack tip extension (VCE) method. The fracture analysis indicates that the most probable pattern of crack formation is radial cracking in the tungsten armor starting from the interface to tube and the most probable site of cracking is the upper interfacial region of the tungsten armor adjacent to the top position of the copper interlayer. The strength threshold for crack initiation and the high heat flux load threshold for crack propagation are evaluated based on XFEM simulations and computations of

  5. 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

  6. 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.

  7. PASCAL, Probabilistic Fracture Mechanics Analysis of Structural Components in Aging LWR

    International Nuclear Information System (INIS)

    A - Description of program or function: PASCAL (PFM analysis of Structural Components in Aging LWR) is a PFM (Probabilistic Fracture Mechanics) code for evaluating the failure probability of aged pressure components. PASCAL has been developed as a part of the JAERI's research program on aging and structural integrity of LWR components, in order to respond to the increasing need of the probabilistic methodology in the regulation and inspection of nuclear components with the objective to provide a rational tool for the evaluation of the reliability and integrity of structural components. In order to improve the accuracy and reliability of the analysis code, some new fracture mechanics models or computational techniques are introduced considering the recent progress in the state of the art and performance of PC. Thus some new analysis models and original methodologies were introduced in PASCAL such as the elastic-plastic fracture criterion based on R6 method, a new crack extension model of semi-elliptical crack evaluation and so on. Moreover a function to evaluate the effect of embrittlement recovery by annealing of irradiated RPV is also introduced in the code based on the USNRC R.G. 1.162(1996). The code has been verified through various failure analysis results and international PTS round robin analysis ICAS which had been organized by the Principal Working Group 3 of OECD/NEA/CSNI. In order to attain a high usability, PASCAL Ver.1 with GUI provides an exclusive FEM pre-processor Pre-PASCAL for generating the input load transient data, a GUI system for generating the input data for PASCAL main processor of main solver and post-processor for output data. - Pre-PASCAL: Pre-PASCAL is an exclusive 3-D FEM pre-processor for generating the input transient data provided with 3 RPV mesh models and two simple specimen mesh models, i.e. CT and CCP. Almost the same input data format with that of PASCAL main processor is used. Output data of temperature and stress distribution

  8. Fracture mechanics-based life management of structural materials operating at elevated temperatures

    International Nuclear Information System (INIS)

    Full text: All aspects of plant safety are paramount in the nuclear industry and therefore advanced methodologies have to be developed to cater for high levels of conservatism and extreme caution in design and plant life extension. Fracture mechanics based design and remaining life prediction methods coupled with multi-disciplinary materials modelling are the likely candidates for this task. Since the likelihood of failure is increased when cracks or defects are present in the structure and in particular in regions of weldments it becomes imperative to further develop predictive techniques. Fracture mechanics is routinely applied at British Energy Plc. [United Kingdom] codes of Practice R5/R6 to predict failure behaviour in equipment operating in the creep and creep/fatigue range by assessing crack initiation and growth from existing defects. This paper considers the relevant structural integrity aspects of a high temperature fracture-based methodology by considering the background to the present codes and standards that are used, role of residual stresses and the theory which deals with cracked structures at elevated temperatures for components. An international collaborative effort under the auspices of the Versailles Agreement on Materials and Standards (VAMAS) is now underway to deal with these aspects and develop recommendations for standard bodies. Aging structures and components which are at the end of their operation design life need to prove safety levels in order to get approval for life extension. Even more stringent criteria for both clean and safe nuclear energy production are needed to improve public perception of the long term safety and societal compatibility with nuclear energy. Also the trends towards higher operating temperatures extend the life of existing nuclear power plant, mean that new and more accurate and reliable experimental data and fracture mechanics models on newer steels will be needed. Another important aspect of improving lifting

  9. Tensile and fracture behavior of AA6061-T6 aluminum alloys: micro-mechanical approach

    International Nuclear Information System (INIS)

    The AA6061-T6 aluminum alloy was chosen as the material for the core vessel of the future Jules Horowitz testing reactor (JHR). The objective of this thesis is to understand and model the tensile and fracture behavior of the material, as well as the origin of damage anisotropy. A micro-mechanical approach was used to link the microstructure and mechanical behavior. The microstructure of the alloy was characterized on the surface via Scanning Electron Microscopy and in the 3D volume via synchrotron X-ray tomography and laminography. The damage mechanism was identified by in-situ SEM tensile testing, ex-situ X-ray tomography and in-situ laminography on different levels of triaxiality. The observations have shown that damage nucleated at lower strains on Mg2Si coarse precipitates than on iron rich intermetallics. The identified scenario and the in-situ measurements were then used to develop a coupled GTN damage model incorporating nucleation, growth and coalescence of cavities formed by coarse precipitates. The relationship between the damage and the microstructure anisotropies was explained and simulated. (author)

  10. User's manual and analysis methodology of probabilistic fracture mechanics analysis code PASCAL Ver.2 for reactor pressure vessel (Contract research)

    International Nuclear Information System (INIS)

    As a part of the aging structural integrity research for LWR components, the probabilistic fracture mechanics (PFM) analysis code PASCAL (PFM Analysis of Structural Components in Aging LWR) has been developed in JAEA. This code evaluates the conditional probabilities of crack initiation and fracture of a reactor pressure vessel (RPV) under transient conditions such as pressurized thermal shock (PTS). 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 and computer performance. PASCAL Ver.1 has functions of optimized sampling in the stratified Monte Carlo simulation, elastic-plastic fracture criterion of the R6 method, crack growth analysis models for a semi-elliptical crack, recovery of fracture toughness due to thermal annealing and so on. Since then, under the contract between the Ministry of Economy, Trading and Industry of Japan and JAEA, we have continued to develop and introduce new functions into PASCAL Ver.2 such as the evaluation method for an embedded crack, KI database for a semi-elliptical crack considering stress discontinuity at the base/cladding interface, PTS transient database, and others. A generalized analysis method is proposed on the basis of the development of PASCAL Ver.2 and results of sensitivity analyses. Graphical user interface (GUI) including a generalized method as default values has been also developed for PASCAL Ver.2. This report provides the user's manual and theoretical background of PASCAL Ver.2. (author)

  11. Structure-Property-Fracture Mechanism Correlation in Heat-Affected Zone of X100 Ferrite-Bainite Pipeline Steel

    Science.gov (United States)

    Li, Xueda; Ma, Xiaoping; Subramanian, S. V.; Misra, R. D. K.; Shang, Chengjia

    2015-03-01

    Structural performance of a weld joint primarily depends on the microstructural characteristics of heat-affected zone (HAZ). In this regard, the HAZ in X100 ferrite-bainite pipeline steel was studied by separating the HAZ into intercritically reheated coarse-grained (ICCG) HAZ containing and non-containing regions. These two regions were individually evaluated for Charpy impact toughness and characterized by electron back-scattered diffraction (EBSD). Low toughness of ~50 J was obtained when the notch of impact specimen encountered ICCGHAZ and high toughness of ~180 J when the notch did not contain ICCGHAZ. Fracture surface was ~60 pct brittle in the absence of ICCGHAZ, and 95 pct brittle (excluding shear lip) in the presence of ICCGHAZ in the impact tested samples. The underlying reason is the microstructure of ICCGHAZ consisted of granular bainite and upper bainite with necklace-type martensite-austenite (M-A) constituent along grain boundaries. The presence of necklace-type M-A constituent notably increases the susceptibility of cleavage microcrack nucleation. ICCGHAZ was found to be both the initiation site of the whole fracture and cleavage facet initiation site during brittle fracture propagation stage. Furthermore, the study of secondary microcracks beneath CGHAZ and ICCGHAZ through EBSD suggested that the fracture mechanism changes from nucleation-controlled in CGHAZ to propagation-controlled in ICCGHAZ because of the presence of necklace-type M-A constituent in ICCGHAZ. Both fracture mechanisms contribute to the poor toughness of the sample contained ICCGHAZ.

  12. Peridynamics as a rigorous coarse-graining of atomistics for multiscale materials design.

    Energy Technology Data Exchange (ETDEWEB)

    Lehoucq, Richard B.; Aidun, John Bahram; Silling, Stewart Andrew; Sears, Mark P.; Kamm, James R.; Parks, Michael L.

    2010-09-01

    This report summarizes activities undertaken during FY08-FY10 for the LDRD Peridynamics as a Rigorous Coarse-Graining of Atomistics for Multiscale Materials Design. The goal of our project was to develop a coarse-graining of finite temperature molecular dynamics (MD) that successfully transitions from statistical mechanics to continuum mechanics. The goal of our project is to develop a coarse-graining of finite temperature molecular dynamics (MD) that successfully transitions from statistical mechanics to continuum mechanics. Our coarse-graining overcomes the intrinsic limitation of coupling atomistics with classical continuum mechanics via the FEM (finite element method), SPH (smoothed particle hydrodynamics), or MPM (material point method); namely, that classical continuum mechanics assumes a local force interaction that is incompatible with the nonlocal force model of atomistic methods. Therefore FEM, SPH, and MPM inherit this limitation. This seemingly innocuous dichotomy has far reaching consequences; for example, classical continuum mechanics cannot resolve the short wavelength behavior associated with atomistics. Other consequences include spurious forces, invalid phonon dispersion relationships, and irreconcilable descriptions/treatments of temperature. We propose a statistically based coarse-graining of atomistics via peridynamics and so develop a first of a kind mesoscopic capability to enable consistent, thermodynamically sound, atomistic-to-continuum (AtC) multiscale material simulation. Peridynamics (PD) is a microcontinuum theory that assumes nonlocal forces for describing long-range material interaction. The force interactions occurring at finite distances are naturally accounted for in PD. Moreover, PDs nonlocal force model is entirely consistent with those used by atomistics methods, in stark contrast to classical continuum mechanics. Hence, PD can be employed for mesoscopic phenomena that are beyond the realms of classical continuum mechanics and

  13. 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.

  14. 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...

  15. Nano sculpt: A methodology for generating complex realistic configurations for atomistic simulations.

    Science.gov (United States)

    Prakash, A; Hummel, M; Schmauder, S; Bitzek, E

    2016-01-01

    Atomistic simulations have now become commonplace in the study of the deformation and failure of materials. Increase in computing power in recent years has made large-scale simulations with billions, or even trillions, of atoms a possibility. Most simulations to-date, however, are still performed with quasi-2D geometries or rather simplistic 3D setups. Although controlled studies on such well-defined structures are often required to obtain quantitative information from atomistic simulations, for qualitative studies focusing on e.g. the identification of mechanisms, researchers would greatly benefit from a methodology that helps realize more realistic configurations. The ideal scenario would be a one-on-one reconstruction of experimentally observed structures. To this end, we propose a new method and software tool called nano sculpt with the following features:•The method allows for easy sample generation for atomistic simulations from any arbitrarily shaped 3D enclosed volume.•The tool can be used to build atomistic samples from artificial geometries, including CAD geometries and structures obtained from simulation methods other than atomistic simulations.•The tool enables the generation of experimentally informed atomistic samples, by e.g. digitization of micrographs or usage of tomography data.

  16. Nano sculpt: A methodology for generating complex realistic configurations for atomistic simulations.

    Science.gov (United States)

    Prakash, A; Hummel, M; Schmauder, S; Bitzek, E

    2016-01-01

    Atomistic simulations have now become commonplace in the study of the deformation and failure of materials. Increase in computing power in recent years has made large-scale simulations with billions, or even trillions, of atoms a possibility. Most simulations to-date, however, are still performed with quasi-2D geometries or rather simplistic 3D setups. Although controlled studies on such well-defined structures are often required to obtain quantitative information from atomistic simulations, for qualitative studies focusing on e.g. the identification of mechanisms, researchers would greatly benefit from a methodology that helps realize more realistic configurations. The ideal scenario would be a one-on-one reconstruction of experimentally observed structures. To this end, we propose a new method and software tool called nano sculpt with the following features:•The method allows for easy sample generation for atomistic simulations from any arbitrarily shaped 3D enclosed volume.•The tool can be used to build atomistic samples from artificial geometries, including CAD geometries and structures obtained from simulation methods other than atomistic simulations.•The tool enables the generation of experimentally informed atomistic samples, by e.g. digitization of micrographs or usage of tomography data. PMID:27054098

  17. FAVOR: A new fracture mechanics code for reactor pressure vessels subjected to pressurized thermal shock

    International Nuclear Information System (INIS)

    Probabilistic fracture mechanics (PFM) analysis is a major element of the comprehensive probabilistic methodology endorsed by the Nuclear Regulatory Commission (NRC) for evaluation of the integrity of pressurized water reactor pressure vessels subjected to pressurized-thermal-shock (PTS) transients. OCA-P and VISA-II are PTS PFM computer codes that are currently referenced in Regulatory Guide 1.154 as acceptable codes for performing plant-specific analyses. These codes perform PFM analyses to estimate the increase in vessel failure probability as the vessel accumulates radiation damage over the operating life of the vessel. Experience with the application of these codes in the last few years has provided insights into areas where they could be improved. As more plants approach the PTS screening criteria and are required to perform plant-specific analyses, there will be an increasing need for an improved and validated PTS PFM code that is accepted by the NRC and utilities. The NRC funded Heavy Section Steel Technology Program (HSST) at the Oak Ridge National Laboratory is currently developing the FAVOR (Fracture Analysis of Vessels: Oak Ridge) code, which is expected to meet this need. The FAVOR code incorporates the most important features of both OCA-P and VISA-II and contains some new capabilities such as (1) a PFM global modeling methodology; (2) the calculation of the axial stress component associated with coolant streaming beneath an inlet nozzle; (3) a library of stress intensity factor influence coefficients, generated by the NQA-1 certified ABAQUS computer code, for an appropriate range of two and three dimensional inner-surface flaws; (4) the flexibility to generate a variety of output reports; and (5) enhanced user friendliness

  18. Fracture of ECAP-deformed iron and the role of extrinsic toughening mechanisms.

    Science.gov (United States)

    Hohenwarter, A; Pippan, R

    2013-05-01

    The fracture behaviour of pure iron deformed by equal-channel angular pressing via route A was examined. The fracture toughness was determined for different specimen orientations and measured in terms of the critical plane strain fracture toughness, KIC , the critical J integral, JIC , and the crack opening displacement for crack initiation, CODi . The results demonstrate that the crack plane orientation has a pronounced effect on the fracture toughness. Different crack plane orientations lead to either crack deflection or delamination, resulting in increased fracture resistance in comparison to one remarkably weak specimen orientation. The relation between the microstructure typical for the applied deformation route and the enormous differences in the fracture toughness depending on the crack plane orientation will be analyzed in this paper. PMID:23645995

  19. Research on the Fracture Mechanism of Scored Liner Under Explosive Loading

    Institute of Scientific and Technical Information of China (English)

    尹建平; 王志军; 张云逸; 周栋

    2011-01-01

    The notch tip fracture criterion of cored liner is proposed based on a dislocation, model. The analysis reveals that the ductile shear fracture is a dominant fracture mode in the scored liner, and the fracture path is along the maximum shear stress tracing line. The numerical simulation of fracture process of scored liner under explosive loading is performed using the nonlinear finite element analysis program ANSYS-LS/DYNA, and then the experiments are made to verify the simulation. The experimental results are demonstrated to be in line with the numerical simulation results. The liner can form a focused jet of metal fragments with certain amount and mass that travels at very high speed in the cone-angle direction, which indicates that the dislocation model can be used to analyze the crack fracture of notch tip.

  20. The fracture mechanisms in duplex stainless steels at sub-zero temperatures

    OpenAIRE

    Pilhagen, Johan

    2013-01-01

    The aim of the thesis was to study the susceptibility for brittle failures and the fracture process of duplex stainless steels at sub-zero temperatures (°C). In the first part of the thesis plates of hot-rolled duplex stainless steel with various thicknesses were used to study the influence of delamination (also known as splits) on the fracture toughness. The methods used were impact and fracture toughness testing. Light optical microscopy and scanning electron microscopy were used to investi...

  1. Comparison between Visa-II and OCA-P for probabilistic fracture mechanics analysis focusing on analysis method

    International Nuclear Information System (INIS)

    Probabilistic fracture mechanics (PFM) analyses have been widely applied to evaluate the failure probabilities of PWR reactor pressure vessels subjected to pressurized thermal shock. In this study, a comparison between the VISA-II and OCA-P codes for PFM analyses was performed to clarify the differences in the numerical processes. For this purpose, the benchmark problems proposed by the U.S. Nuclear Regulatory Commission and the Electric Power Research Institute were applied. It is also discussed the algorithm to evaluate the deviations from the means of RTNDT and fracture toughness, and the numerical treatment of initial flaw depth as the major differences in these codes. 4 refs., 9 figs

  2. Modeling of the fracture behavior of spot welds using advanced micro-mechanical damage models

    Science.gov (United States)

    Sommer, Silke

    2010-06-01

    This paper presents the modeling of deformation and fracture behavior of resistance spot welded joints in DP600 steel sheets. Spot welding is still the most commonly used joining technique in automotive engineering. In overloading situations like crash joints are often the weakest link in a structure. For those reasons, crash simulations need reliable and applicable tools to predict the load bearing capacity of spot welded components. Two series of component tests with different spot weld diameters have shown that the diameter of the weld nugget is the main influencing factor affecting fracture mode (interfacial or pull-out fracture), load bearing capacity and energy absorption. In order to find a correlation between nugget diameter, load bearing capacity and fracture mode, the spot welds are simulated with detailed finite element models containing base metal, heat affected zone and weld metal in lap-shear loading conditions. The change in fracture mode from interfacial to pull-out or peel-out fracture with growing nugget diameter under lap-shear loading was successfully modeled using the Gologanu-Leblond model in combination with the fracture criteria of Thomason and Embury. A small nugget diameter is identified to be the main cause for interfacial fracture. In good agreement with experimental observations, the calculated pull-out fracture initiates in the base metal at the boundary to the heat affected zone.

  3. A computational linear elastic fracture mechanics-based model for alkali-silica reaction

    International Nuclear Information System (INIS)

    This article presents a fracture mechanics model for Alkali-Silica Reaction (ASR). The model deals with the case of a concrete made up of dense aggregates submitted to chemical attack. The chemistry and diffusion (of ions and gel) are not modelled. The focus is put on the mechanical consequences of the progressive replacement of the outer layer of the aggregate by a less dense gel. A schematic cracking pattern is assumed: a ring-shaped crack appears in the cement paste surrounding the spherical aggregate depending on the pressure build-up. The onset of cracking is determined using an incremental energy criterion. The stored elastic energy and deformation of a given configuration are determined assuming that each aggregate behaves as if it was embedded in an infinite cement paste matrix. The calculations are performed by Finite Element Analysis. We note a very different behaviour of aggregates of different sizes. Adding the contributions of different aggregate sizes leads to an estimation of the global free expansion of a concrete of given aggregate size distribution. A rate of attack is identified that leads to recover the usual sigmoid ASR expansion curve. (authors)

  4. Environment enhanced fatigue crack propagation in metals: Inputs to fracture mechanics life prediction models

    Science.gov (United States)

    Gangloff, Richard P.; Kim, Sang-Shik

    1993-01-01

    This report is a critical review of both environment-enhanced fatigue crack propagation data and the predictive capabilities of crack growth rate models. This information provides the necessary foundation for incorporating environmental effects in NASA FLAGRO and will better enable predictions of aerospace component fatigue lives. The review presents extensive literature data on 'stress corrosion cracking and corrosion fatigue.' The linear elastic fracture mechanics approach, based on stress intensity range (Delta(K)) similitude with microscopic crack propagation threshold and growth rates, provides a basis for these data. Results are presented showing enhanced growth rates for gases (viz., H2 and H2O) and electrolytes (e.g. NaCl and H2O) in aerospace alloys including: C-Mn and heat treated alloy steels, aluminum alloys, nickel-based superalloys, and titanium alloys. Environment causes purely time-dependent accelerated fatigue crack growth above the monotonic load cracking threshold (KIEAC) and promotes cycle-time dependent cracking below (KIEAC). These phenomenon are discussed in terms of hydrogen embrittlement, dissolution, and film rupture crack tip damage mechanisms.

  5. 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.

  6. Atomistic simulations of dislocation processes in copper

    DEFF Research Database (Denmark)

    Vegge, T.; Jacobsen, K.W.

    2002-01-01

    We discuss atomistic simulations of dislocation processes in copper based on effective medium theory interatomic potentials. Results on screw dislocation structures and processes are reviewed with particular focus on point defect mobilities and processes involving cross slip. For example, the sta......We discuss atomistic simulations of dislocation processes in copper based on effective medium theory interatomic potentials. Results on screw dislocation structures and processes are reviewed with particular focus on point defect mobilities and processes involving cross slip. For example...

  7. Multiple bilateral lower limb fractures in a 2-year-old child: previously unreported injury with a unique mechanism.

    Science.gov (United States)

    Repswal, Basant; Jain, Anuj; Gupta, Sunil; Aggarwal, Aditya; Kohli, Tushar; Pathrot, Devendra

    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. PMID:25293902

  8. Mechanism of evolution on winter-time natural convection cooling effect of fractured-rock embankment in permafrost regions

    Institute of Scientific and Technical Information of China (English)

    SUN Binxiang; XU Xuezu; LAI Yuanming; WANG Shuangjie; ZHANG Jinzhao

    2005-01-01

    Mechanism and evolution of the pore-air natural convection cooling effect in fractured-rock embankments in permafrost regions are studied using a numerical representation of the non-dimensional governing equations in variable permeability porous media. The analyses show that winter-time natural convection in fractured-rock embankments begins to occur in the side slope portions and gradually develops from the left and right side slope portions to the middle portion of embankment. The more significant distortion of isotherms from their initial orientations due to heat conduction alone is that the cooling effect of winter-time natural convection on the fractured-rock embankment is stronger. The minimum critical Rayleigh numbers triggering natural convection of the pore-air in the side slope portions and the middle portion of embankment were obtained. The factors of influence on triggering winter-time convection cooling effect in fractured-rock embankments were analyzed.Finally, the assertion that the techniques of the fractured-rock revetment and berm are the effective measures to maintain the heat stability of the roadbed in permafrost regions is theoretically demonstrated.

  9. 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.

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

    International Nuclear Information System (INIS)

    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 √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: ► Micro-scale cantilevers manufactured by electro-deposition and focused ion beam machining. ► Nanoindenter used to perform micro-scale fracture test on Ni-13at%W micro-cantilevers. ► Calculation of fracture toughness of electrodeposited Ni-13at%W thin films. ► Fracture toughness values lower than that of nanocrystalline nickel.

  11. 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.

  12. Effect of roughness and material strength on the mechanical properties of fracture replicas

    International Nuclear Information System (INIS)

    This report presents the results of 11 rotary shear tests conducted on replicas of three hollow cylinders of natural fractures with JRC values of 7.7, 9.4 and 12.0. The JRC values were determined from the results of laser profilometer measurements. The replicas were created from gypsum cement. By varying the water-to-gypsum cement ratio from 30 to 45%, fracture replicas with different values of compressive strength (JCS) were created. The rotary shear experiments were performed under constant normal (nominal) stresses ranging between 0.2 and 1.6 MPa. In this report, the shear test results are compared with predictions using Barton's empirical peak shear strength equation. observations during the experiments indicate that only certain parts of the fracture profiles influence fracture shear strength and dilatancy. Under relatively low applied normal stresses, the JCS does not seem to have a significant effect on shear behavior. As an alternative, a new procedure for predicting the shear behavior of fractures was developed. The approach is based on basic fracture properties such as fracture surface profile data and the compressive strength, modulus of elasticity, and Poisson's ratio of the fracture walls. Comparison between predictions and actual shear test results shows that the alternative procedure is a reliable method

  13. 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

    The aim of this study is to investigate stratigraphic variations in the spatial distribution and density of natural hydraulic and other fractures within oil mature, shale-dominated strata from the Cleveland Basin, northeast England. The studied interval includes the Pliensbachian Cleveland Ironstone and Toarcian Whitby Mudstone Formations. The Cleveland Ironstone Formation (ca. 25m thick) consists of silt- and mudstone units with discrete ironstone layers (seams). Ironstones account for 20% of the thickness of the formation. The Whitby Mudstone Formation is up to ca. 100 m thick; up to 2% of its total thickness consists of discrete calcium carbonate horizons, such as the Top Jet Dogger. Natural hydraulic fractures, characterised by plumose marks and concentric arrest lines on fracture surfaces are ubiquitous throughout both formations; shear fractures with mm- to cm-scale displacements occur locally, particularly within silt- and mudstones. Natural hydraulic fractures locally contain thin, sometimes fibrous, calcite fills and are commonly observed to terminate at bedding plane interfaces between silt- or mudstone and carbonate beds. We have recorded fracture locations and apertures along 139 transects in both shale (i.e. silt- and mudstone intervals) and carbonate strata. Natural hydraulic and shear fractures, measured along transects up to 50m long within all lithologies in both formations, typically display uniform distributions. There is no correlation between spacing distribution and bulk extension in any lithology. Median fracture densities recorded within the Cleveland Ironstone Formation are higher in intervening ironstone beds (lean Redcar Mudstone Formation.

  14. 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

  15. Strengths and Fracture Mechanisms of Al2O3 Short Fiber Reinforced Al-Mg Alloy Matrix Composite at Elevated Temperatures

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Using the experimental and theoretical methods, the tensile strengths and fracture mechanisms of Al2O3 short fiber reinforced Al-Mg alloy matrix composite at elevated temperatures were researched. The interfacial microstructural characteristics and the fracture surfaces of the composite at different temperatures were observed by transmission electron microscope (TEM) and by scanning electron microscope (SEM), respectively. Then, from the results of microscopic observation, the fracture mechanisms of the composite at different temperatures are discussed. Finally,the tensile strengths of the composite at elevated temperatures were predicted by statistical integration average (SIA) method with the consideration of various fracture mechanisms. It was shown that the strengths and fracture mechanisms of the composite at elevated temperature (300 C) were significantly different from those at room temperature due to the variations of interfacial bonding states. The tensile strengths predicted by the SIA method at elevated temperatures agreed well with the experimental results.

  16. Influence of two different heat treatment procedures on mechanical and fracture properties of 65 Si 7 steel

    International Nuclear Information System (INIS)

    This paper deals with the results of investigations of two different heat treatment procedures and their influence on some mechanical properties as well as on the magnitude of some fracture mechanics parameters for a particular type of steel. The experimental investigations were performed on the specimens made of 65Si7 steel. The processes occurring by tempering of two different microstructures of the steel, i. e. martensite and lower bainite were investigated. An advantage of austempering over hardening and tempering is in obtaining the bainite microstructure. Steel of bainite microstructure has a greater toughness, ductility, contraction, fatigue strength and a better fracture toughness than a tempered martensite of the same type of steel. A bainite microstructure also gives a better resistance to thermal fatigue in comparison with martensite microstructure. The above mentioned improved values of mechanical properties refer to the untempered state of bainite. (author)

  17. 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

  18. Evaluation of fracture toughness in C/C composite under four-point bending. Difference in fabrication method and fracture mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Kawada, Hiroyuki; Hayashi, Ikuhiko [Waseda Univ., Tokyo (Japan). School of Science and Engineering; Matsumori, Makoto; Omata, Hideo; Uruno, Tomoyuki; Hiramoto, Jiro

    1994-04-01

    To evaluate fracture toughness of C/C composites, four-point bending tests (SEN) are performed. The C/C composites are carbonized from the CFRPs, which are fabricated by means of two different methods (a hot-press method and a vacuum-bagging one). It is found that each fabrication method leads to a different distribution of bending strength. The vacuum-bagging method is preferable to obtain uniform bending strength properties. Crack growth resistance curves are obtained based on the compliance matching method. These curves have an inclination of convergence at a nearly equal constant value regardless of fabrication method. Existence of the stress shielding mechanism in the C/C composites is suggested by the R curves. From a fractographic observation, crack propagates three-dimensionally, and then pullouts of the fiber bundle occur at a large scale in the fiber-bridging mechanism. (author).

  19. Tissue level microstructure and mechanical properties of the femoral head in the proximal femur of fracture patients

    Science.gov (United States)

    Lü, Linwei; Meng, Guangwei; Gong, He; Zhu, Dong; Gao, Jiazi; Fan, Yubo

    2015-04-01

    This study aims to investigate the regional variations of trabecular morphological parameters and mechanical parameters of the femoral head, as well as to determine the relationship between trabecular morphological and mechanical parameters. Seven femoral heads from patients with fractured proximal femur were scanned using a micro-CT system. Each femoral head was divided into 12 sub-regions according to the trabecular orientation. One trabecular cubic model was reconstructed from each sub-region. A total of 81 trabecular models were reconstructed, except three destroyed sub-regions from two femoral heads during the surgery. Trabecular morphological parameters, i.e. trabecular separation (Tb.Sp), trabecular thickness (Tb.Th), specific bone surface (BS/BV), bone volume fraction (BV/TV), structural model index (SMI), and degree of anisotropy (DA) were measured. Micro-finite element analyses were performed for each cube to obtain the apparent Young's modulus and tissue level von Mises stress distribution under 1 % compressive strain along three orthogonal directions, respectively. Results revealed significant regional variations in the morphological parameters (). Young's moduli along the trabecular orientation were significantly higher than those along the other two directions. In general, trabecular mechanical properties in the medial region were lower than those in the lateral region. Trabecular mechanical parameters along the trabecular orientation were significantly correlated with BS/BV, BV/TV, Tb.Th, and DA. In this study, regional variations of microstructural features and mechanical properties in the femoral head of patients with proximal femur fracture were thoroughly investigated at the tissue level. The results of this study will help to elucidate the mechanism of femoral head fracture for reducing fracture risk and developing treatment strategies for the elderly.

  20. 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.

  1. Fracture mechanical studies on high temperature alloys between room temperature and 9000C

    International Nuclear Information System (INIS)

    As a contribution to the fracture mechanics characterization of the three solid-solution hardened alloys X10NiCrAlTi 32 20, NiCr 22 Co 12 Mo and NiCr 22 W 12 Si, (material No. 1.4876, No. 2.4663 and No. 2.4972) investigations of the J-integral concept in room temperature tests, of creep crack growth at 800 and 8500C and of fatigue crack growth at 700-9000C were carried out. Standard compact tension test pieces (1/2 inch and 1 inch) were used. In order to assess the transferability of crack growth relationships determined on standardized specimens to component geometries, fatigue crack growth tests were carried out on thick-walled tubes with external circumferential notches. The measurement of crack length was accomplished using the d. c. potential drop method which was further developed and optimized for these particular experimental conditions. The creep crack growth was described using the stress intensity (KI), the energy rate integral (C*) and the net stress (σnet) concepts. For description (ΔKI) could be applied. Because no dependence of fatigue crack growth on either specimen size or on specimen geometry (CT specimen, tube specimen) was found, fatigue crack growth data determined on CT specimens are transferable to tubes with circumferential notches. (orig./IHOE)

  2. Integrated evaluation of maintenance optimization for pipes in nuclear power plants based on probabilistic fracture mechanics

    International Nuclear Information System (INIS)

    As an application of probabilistic fracture mechanics (PFM) and a financial method, risk-benefit analyses were performed for the purpose of optimizing maintenance activities of steam generator (SG) tubes used in pressurized water reactors (PWRs). Parameters such as inspection accuracy, inspection interval, sampling inspection, replacement of SGs and maintenance criteria (operation with verified cracks) were selected for sensitivity analyses. In the analysis of the operation introducing maintenance criteria, the effect of quantitative accuracy of the inspection (sizing performance) was also taken into account. Although the analyses were mainly conducted for SG tubes made of Inconel 600 mill anneal (MA) materials, the analyses were also performed for Inconel 690 thermal treatment (TT) materials with making assumptions on their crack initiation probabilities and crack propagation laws. To justify whether or not it is worth while implementing the selected maintenance strategies in terms of an economic point of view, net present value (NPV) was calculated as an index which is one of the most fundamental financial indices for decision-making based on the discounted cash flow (DCF) method. (authors)

  3. A fracture mechanical study for determining the fatique behaviour of disc-like components

    International Nuclear Information System (INIS)

    A reliable determination of the fatigue life of a structural component is one of the important aspects of its safety analysis. The most common flaws in such components are part-through surface and internal cracks of more or less elliptical shape. The theoretical-experimental procedure as presented allows evaluation of the double amplitude ΔK of the stress intensity factor K for such surface cracks in tensile plates and determination of parameters reproducing the same value of ΔK as a function of crack length in an appropriate (e.g. compact type) specimen. Comparisons of cycle numbers obtained with equivalent crack growth in tensile plates and corresponding CT specimens indicate that, in using the proposed procedure, results on the safe side are most probable. One of the problems encountered lies in the fact that the propagation of surface cracks in the direction of depth cannot be measured directly. A new crack measuring system, the 'Crack Micro-Gauge', based on AC potential technique, was applied. The error thus obtained was generally less than +- 0.5 mm. On-line strain gauge measurements helped to reduce undesirable bending effects in the loaded plates. The main topic of this report is the transfer of test results to engineering components (structures) by the use of readily available fracture mechanics concepts. (Auth.)

  4. 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.

  5. 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.

  6. 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.

  7. Low Magnitude Mechanical Signals Reduce Risk-Factors for Fracture during 90-Day Bed Rest

    Science.gov (United States)

    Muir, J. W.; Xia, Y.; Holquin, N.; Judex, S.; Qin, Y.; Evans, H.; Lang, T.; Rubin, C.

    2007-01-01

    Long duration spaceflight leads to multiple deleterious changes to the musculoskeletal system, where loss of bone density, an order of magnitude more severe than that which follows the menopause, combined with increased instability, conspire to elevate the risk of bone fracture due to falls on return to gravitational fields. Here, a ground-based analog for spaceflight is used to evaluate the efficacy of a low-magnitude mechanical intervention, VIBE (Vibrational Inhibition of Bone Erosion), as a potential countermeasure to preserve musculoskeletal integrity in the face of disuse. Twenty-six subjects consented to ninety days of six-degree head-down tilt bed-rest. 18 completed the 90d protocol, 8 of which received daily 10-minute exposure to 30 Hz, 0.3g VIBE, applied in the supine position using a vest elastically coupled to the vibrating platform. The shoulder harness induced a load of 60% of the subjects body weight. At baseline and 90d, Qualitative Ultrasound Scans (QUS) of the calcaneus and CT-scans of the hip and spine were performed to measure changes in bone density. Postural control (PC) was assessed through center of pressure (COP) recordings while subjects stood on a force platform for 4 minutes of quiet stance with eyes closed, and again with eyes opened. As compared to control bedrest subjects,

  8. 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.

  9. 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.

  10. Atomistic k ⋅ p theory

    Energy Technology Data Exchange (ETDEWEB)

    Pryor, Craig E., E-mail: craig-pryor@uiowa.edu [Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242 (United States); Pistol, M.-E., E-mail: mats-erik.pistol@ftf.lth.se [NanoLund and Solid State Physics, Lund University, P.O. Box 118, 221 00 Lund (Sweden)

    2015-12-14

    Pseudopotentials, tight-binding models, and k ⋅ p theory have stood for many years as the standard techniques for computing electronic states in crystalline solids. Here, we present the first new method in decades, which we call atomistic k ⋅ p theory. In its usual formulation, k ⋅ p theory has the advantage of depending on parameters that are directly related to experimentally measured quantities, however, it is insensitive to the locations of individual atoms. We construct an atomistic k ⋅ p theory by defining envelope functions on a grid matching the crystal lattice. The model parameters are matrix elements which are obtained from experimental results or ab initio wave functions in a simple way. This is in contrast to the other atomistic approaches in which parameters are fit to reproduce a desired dispersion and are not expressible in terms of fundamental quantities. This fitting is often very difficult. We illustrate our method by constructing a four-band atomistic model for a diamond/zincblende crystal and show that it is equivalent to the sp{sup 3} tight-binding model. We can thus directly derive the parameters in the sp{sup 3} tight-binding model from experimental data. We then take the atomistic limit of the widely used eight-band Kane model and compute the band structures for all III–V semiconductors not containing nitrogen or boron using parameters fit to experimental data. Our new approach extends k ⋅ p theory to problems in which atomistic precision is required, such as impurities, alloys, polytypes, and interfaces. It also provides a new approach to multiscale modeling by allowing continuum and atomistic k ⋅ p models to be combined in the same system.

  11. Atomistic k ⋅ p theory

    International Nuclear Information System (INIS)

    Pseudopotentials, tight-binding models, and k ⋅ p theory have stood for many years as the standard techniques for computing electronic states in crystalline solids. Here, we present the first new method in decades, which we call atomistic k ⋅ p theory. In its usual formulation, k ⋅ p theory has the advantage of depending on parameters that are directly related to experimentally measured quantities, however, it is insensitive to the locations of individual atoms. We construct an atomistic k ⋅ p theory by defining envelope functions on a grid matching the crystal lattice. The model parameters are matrix elements which are obtained from experimental results or ab initio wave functions in a simple way. This is in contrast to the other atomistic approaches in which parameters are fit to reproduce a desired dispersion and are not expressible in terms of fundamental quantities. This fitting is often very difficult. We illustrate our method by constructing a four-band atomistic model for a diamond/zincblende crystal and show that it is equivalent to the sp3 tight-binding model. We can thus directly derive the parameters in the sp3 tight-binding model from experimental data. We then take the atomistic limit of the widely used eight-band Kane model and compute the band structures for all III–V semiconductors not containing nitrogen or boron using parameters fit to experimental data. Our new approach extends k ⋅ p theory to problems in which atomistic precision is required, such as impurities, alloys, polytypes, and interfaces. It also provides a new approach to multiscale modeling by allowing continuum and atomistic k ⋅ p models to be combined in the same system

  12. Engineering geological characteristics and the hydraulic fracture propagation mechanism of the sand-shale interbedded formation in the Xu5 reservoir

    Science.gov (United States)

    Lu, Cong; Li, Mei; Guo, Jian-Chun; Tang, Xu-Hai; Zhu, Hai-Yan; Yong-Hui, Wang; Liang, Hao

    2015-06-01

    In the Xu5 formation the sandstone reservoir and the shale reservoir are interbedded with each other. The average thickness of each formation is about 8 m, which increases the difficulty of the hydraulic fracturing treatment. The shale thickness ratio (the ratio of shale thickness to formation thickness) is 55-62.5%. The reservoir is characterized by ultra-low porosity and permeability. The brittleness index of sandstone is 0.5-0.8, and the brittleness index of shale is 0.3-0.8. Natural fractures are poorly developed and are mainly horizontal and at a low angle. The formation strength is medium and the reservoir is of the hybrid strike-slip fault and reverse fault stress regime. The difference between the minimum principal stress and the vertical stress is small, and the maximum horizontal principal stress is 20 MPa higher than the minimum horizontal principal stress and vertical stress. A mechanical model of a hydraulic fracture encountering natural fractures is built according to geological characteristics. Fracture mechanics theory is then used to establish a hydraulic fracturing model coupling the seepage-stress-damage model to simulate the initiation and propagation of a fracture. The hydraulic fracture geometry is mainly I-shaped and T-shaped, horizontal propagation dominates the extension, and vertical propagation is limited. There is a two to three meter stress diversion area around a single hydraulic fracture. The stress diversion between a hydraulic fracture and a natural fracture is advantageous in forming a complex fracture. The research results can provide theoretical guidance for tight reservoir fracturing design.

  13. Nanotwin-governed toughening mechanism in hierarchically structured biological materials

    Science.gov (United States)

    Shin, Yoon Ah; Yin, Sheng; Li, Xiaoyan; Lee, Subin; Moon, Sungmin; Jeong, Jiwon; Kwon, Minhyug; Yoo, Seung Jo; Kim, Young-Min; Zhang, Teng; Gao, Huajian; Oh, Sang Ho

    2016-02-01

    As a natural biocomposite, Strombus gigas, commonly known as the giant pink queen conch shell, exhibits outstanding mechanical properties, especially a high fracture toughness. It is known that the basic building block of conch shell contains a high density of growth twins with average thickness of several nanometres, but their effects on the mechanical properties of the shell remain mysterious. Here we reveal a toughening mechanism governed by nanoscale twins in the conch shell. A combination of in situ fracture experiments inside a transmission electron microscope, large-scale atomistic simulations and finite element modelling show that the twin boundaries can effectively block crack propagation by inducing phase transformation and delocalization of deformation around the crack tip. This mechanism leads to an increase in fracture energy of the basic building block by one order of magnitude, and contributes significantly to that of the overall structure via structural hierarchy.

  14. Mechanical and hydraulic performance of sludge-mixed cement grout in rock fractures

    OpenAIRE

    Khomkrit Wetchasat; Kittitep Fuenkajorn

    2014-01-01

    The objective is to assess the performance of sludge mixed with commercial grade Portland cement type I for use in minimizing the permeability of fractured rock mass. The fractures were artificially made by applying a line load to sandstone block specimens. The sludge comprises over 80% of quartz with grain sizes less than 75 μm. The results indicate that the mixing ratios of sludge:cement (S:C) of 1:10, 3:10, 5:10 with water:cement ratio of 1:1 by weight are suitable for fracture gr...

  15. Fracture resistance curves and toughening mechanisms in polymer based dental composites

    DEFF Research Database (Denmark)

    De Souza, J.A.; Goutianos, Stergios; Skovgaard, M.;

    2011-01-01

    The fracture resistance (R-curve behaviour) of two commercial dental composites (Filtek Z350® and Concept Advanced®) were studied using Double Cantilever Beam sandwich specimens loaded with pure bending moments to obtain stable crack growth. The experiments were conducted in an environmental...... significantly higher fracture resistance than the composite with the coarser microstructure. The fracture properties were related to the flexural strength of the dental composites. The method, thus, can provide useful insight into how the microstructure enhances toughness, which is necessary for the future...

  16. Determination of the fracture mechanism of mild steel in an overprotective environment by slow strain rate testing

    Energy Technology Data Exchange (ETDEWEB)

    Yamaguchi, Y.; Nonaka, H. (Osaka Gas Co. Ltd. (Japan))

    1994-03-01

    The susceptibility and fracture mechanism of hydrogen-assisted cracking (HAC) of mild steel in an overprotective marine clay environment were investigated to identify cracking nucleation sites, crack initiation times, and cracking processes. Specimens were subjected to slow strain rate testing (SSRT) and to the fracture surface topography analysis (FRASTA) technique. The steel was susceptible to HAC in 30% marine clay. Microcrack initiation occurred at defects such as grain boundaries. Electron probe microanalysis (EPMA) showed manganous sulfide (MnS) existed near the crack initiation sites. H probably was trapped at the MnS sites and concentrated through the motion of dislocations when the crack initiated. The HAC mechanism in the soil environment was found to be similar to that of hydrogen-induced cracking (HIC).

  17. 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.

  18. Atomistic modeling of dropwise condensation

    Science.gov (United States)

    Sikarwar, B. S.; Singh, P. L.; Muralidhar, K.; Khandekar, S.

    2016-05-01

    The basic aim of the atomistic modeling of condensation of water is to determine the size of the stable cluster and connect phenomena occurring at atomic scale to the macroscale. In this paper, a population balance model is described in terms of the rate equations to obtain the number density distribution of the resulting clusters. The residence time is taken to be large enough so that sufficient time is available for all the adatoms existing in vapor-phase to loose their latent heat and get condensed. The simulation assumes clusters of a given size to be formed from clusters of smaller sizes, but not by the disintegration of the larger clusters. The largest stable cluster size in the number density distribution is taken to be representative of the minimum drop radius formed in a dropwise condensation process. A numerical confirmation of this result against predictions based on a thermodynamic model has been obtained. Results show that the number density distribution is sensitive to the surface diffusion coefficient and the rate of vapor flux impinging on the substrate. The minimum drop radius increases with the diffusion coefficient and the impinging vapor flux; however, the dependence is weak. The minimum drop radius predicted from thermodynamic considerations matches the prediction of the cluster model, though the former does not take into account the effect of the surface properties on the nucleation phenomena. For a chemically passive surface, the diffusion coefficient and the residence time are dependent on the surface texture via the coefficient of friction. Thus, physical texturing provides a means of changing, within limits, the minimum drop radius. The study reveals that surface texturing at the scale of the minimum drop radius does not provide controllability of the macro-scale dropwise condensation at large timescales when a dynamic steady-state is reached.

  19. Hydromechanical interactions in a fractured carbonate reservoir inferred from hydraulic and mechanical measurements

    OpenAIRE

    Cappa, Frédéric; Guglielmi, Yves; Fénart, Pascal; Merrien-Soukatchoff, Véronique; Thoraval, Alain

    2004-01-01

    10 pages; International audience; Hydromechanical coupled processes in a shallow fractured carbonate reservoir rock were investigated through field experiments coupled with analytical and numerical analyses. The experiments consist of hydraulic loading/unloading of a water reservoir in which fluid flow occurs mainly inside a heterogeneous fracture network made up of vertical faults and bedding planes. Hydromechanical response of the reservoir was measured using six pressure–normal displacemen...

  20. Fracture toughness correlation with microstructure and other mechanical properties in near-eutectoid steel

    OpenAIRE

    Sudhakar, KV; Murty, GS

    1998-01-01

    The variation of yield strength and fracture toughness was investigated for four different heat treatments attempted on specimens of a near-eutectoid steel. The aim of this study was to optimize the microstructure for simultaneous improvements in strength and toughness. Further, the fracture toughness deduced through empirical relations from tensile and charpy impact tests was compared with those measured directly according to ASTM Designation: E 399. Among the four different heat treatments ...

  1. A general mixed mode fracture mechanics test specimen: The DCB-specimen loaded with uneven bending moments

    Energy Technology Data Exchange (ETDEWEB)

    Soerensen, B.F.; Joergensen, K.; Oestergaard, R.C. [Risoe National Lab., Materials Dept., Roskilde (Denmark); Jacobsen, T.K. [LM Glasfiber A/S, Lunderskov (Denmark)

    2004-03-01

    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 ratio between the two applied moments, the full mode mixity range from pure mode I to pure mode II can be generated for the same specimen geometry. The specimen allows stable crack growth. In case of large scale crack bridging, mixed mode cohesive laws can be obtained by a J integral based approach. As a preliminary example, fracture of adhesive joints between two glass-fibre laminates was studied. The mixed mode fracture resistance increased with increasing crack length due to fibre cross over bridging, eventually reaching a steady-state level (R-curve behaviour). The steady-state fracture toughness level increased with increasing tangential crack opening displacement. Cohesive stresses were determined by a J integral approach. The deducted shear stress was found to be relative high ({approx} = 20 MPa) in comparison with the normal stress ({approx} = 1 MPa). (au)

  2. Effects of heat treatment and testing temperature on fracture mechanics behavior of low-Si CA-15 stainless steel

    Science.gov (United States)

    Hsu, Cheng-Hsun; Lee, Shen-Chih; Teng, Hwei-Yuan

    2004-02-01

    This research studied the effects of heat treatment and testing temperature on fracture mechanics behavior of Si-modified CA-15 martensitic stainless steel (MSS), which is similar to AISI 403 grade stainless steel, which has been widely used in wall and blanket structures and in the pipe of nuclear power plant reactors, turbine blades, and nozzles. The results indicated that fracture toughness of low-Si CA-15 MSS is better than that of AISI 403. The specimens of the low-Si CA-15 MSS after austenitization at 1010 °C and then tempering at 300 °C have higher plane-strain fracture toughness (K IC ) values for both 25 °C and -150 °C testing temperatures. However, the specimens tested at 150 °C cannot satisfy the plane-strain fracture toughness criteria. The fatigue crack growth rate is the slowest after austenitization at 1010 °C for 2 hours and tempering at 400 °C. Observing the crack propagation paths using a metallographic test, it was found that the cracking paths preferred orientation and branched along ferrite phase, owing to martensite-phase strengthening and grain-boundary-carbide retarding after 300 °C to 400 °C tempering. Also, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction analysis were performed to correlate the properties attained to the microstructural observation.

  3. Application of the results of pipe stress analyses into fracture mechanics defect analyses for welds of nuclear piping components

    International Nuclear Information System (INIS)

    For the fracture mechanical assessment of postulated or detected crack-like defects in welds of piping systems it is necessary to know the stresses in the un-cracked component normal to the crack plane. Results of piping stress analyses may be used if these are evaluated for the locations of the welds in the piping system. Using stress enhancing factors (stress indices, stress factors) the needed stress components are calculated from the component specific sectional loads (forces and moments). For this procedure the tabulated stress enhancing factors, given in the standards (ASME Code, German KTA regulations) for determination and limitation of the effective stresses, are not always and immediately adequate for the calculation of the stress component normal to the crack plane. The contribution shows fundamental possibilities and validity limits for adoption of the results of piping system analyses for the fracture mechanical evaluation of axial and circumferential defects in welded joints, with special emphasis on typical piping system components (straight pipe, elbow, pipe fitting, T-joint). The lecture is supposed to contribute to the standardization of a code compliant and task-related use of the piping system analysis results for fracture mechanical failure assessment

  4. The role of stress state on the fracture toughness and toughening mechanisms of wrought molybdenum and molybdenum alloys

    International Nuclear Information System (INIS)

    Rolling unalloyed molybdenum, molybdenum alloys, and Oxide Dispersion Strengthened (ODS) molybdenum into sheet produces microstructures with elongated, pancake shaped grains that can result in anisotropic mechanical properties. In this work, unalloyed molybdenum, molybdenum alloys, and ODS molybdenum are rolled to thinner sheet and then subjected to tensile and fracture toughness testing and examination of the toughening mechanism. The ductile laminate toughening mechanism observed for wrought molybdenum results from a lower toughness in the short-transverse orientation that leads to separation of the layers of sheet-like grains of the microstructure along the grain boundaries in the regions of stress concentration. This splitting of the microstructure results in the formation of ligaments of grains, or non-constrained laminates, that are stretched to failure under a plane stress-state with large amounts of plastic deformation. The thinner specimens exhibit higher fracture toughness values and lower Ductile to Brittle Transition Temperature (DBTT) values than for thicker specimens machined from thicker starting material from the same alloy. The lower constraint of the thinner specimens tested in this work results in higher toughness and lower DBTT values. The finer grain size, finer precipitate size, and state of plane stress achieved for the thinner sheet specimens appears to enhance the ductile laminate toughening to result in higher fracture toughness and lower DBTT values. The detrimental effect of crack initiation from brittle carbides, oxides, and second phases is also observed to be diminished under a stress-state of plane stress.

  5. Mechanics of tidally driven fractures in Europa's ice shell and implications for seismic and radar profiling

    Science.gov (United States)

    Lee, S.; Pappalardo, R. T.; Makris, N. C.

    2005-12-01

    Among Europa's surface features, cycloidal cracks are probably the most important for proving the existence of a subsurface liquid ocean. This is because (1) there is strong evidence that they are caused by tidally induced stress [1], and (2) this stress likely only approaches the ice failure strength if an ocean is present. There are a number of outstanding issues, however, in quantitatively explaining cycloidal cracks. First, current estimates of the pure diurnal tidal stress necessary to cause cycloidal cracks even in the presence of an ocean [1,2] is well below the typical stress known to cause tensile failure in natural terrestrial ice [3]. Second, models of ridge formation suggest that cycloidal cracks penetrate through the entire brittle-ice layer [1,4], but current models limit the depth of tidally induced surface cracks to be less than 100 m even in the presence of an ocean [1,5]. Third, the 3-km/h crack propagation speed determined by [1] is three orders of magnitude lower than the roughly 2-km/s speed at which cracks are known to propagate in ice. Our goal is to quantitatively address these issues in a unified manner. To do this, a fracture mechanics model is developed for the initiation and propagation of a crack through an ice layer of finite thickness in the presence of gravitational overburden and porosity. It is shown that Europa's ice shell may be highly porous and salt-rich. This implies that the strength of Europa's outer ice shell may be sufficiently low to make the crack initiation strengths arrived at by current kinematic models [1,2] highly plausible, even though they are much lower than those typically measured for terrestrial ice. A model is developed for the stress intensity factor at a crack tip in an ice shell with finite thickness, gravitational overburden, and depth-dependent porosity. This leads to the conclusion that cycloids are generated as a sequence of discrete and near instantaneous fracture events, each of which penetrates

  6. Multi-Scale Modelling of Deformation and Fracture in a Biomimetic Apatite-Protein Composite: Molecular-Scale Processes Lead to Resilience at the μm-Scale.

    Science.gov (United States)

    Zahn, Dirk; Duchstein, Patrick

    2016-01-01

    Fracture mechanisms of an enamel-like hydroxyapatite-collagen composite model are elaborated by means of molecular and coarse-grained dynamics simulation. Using fully atomistic models, we uncover molecular-scale plastic deformation and fracture processes initiated at the organic-inorganic interface. Furthermore, coarse-grained models are developed to investigate fracture patterns at the μm-scale. At the meso-scale, micro-fractures are shown to reduce local stress and thus prevent material failure after loading beyond the elastic limit. On the basis of our multi-scale simulation approach, we provide a molecular scale rationalization of this phenomenon, which seems key to the resilience of hierarchical biominerals, including teeth and bone. PMID:27300748

  7. Effect of chemical environment and rock composition on fracture mechanics properties of reservoir lithologies in context of CO2 sequestration

    Science.gov (United States)

    Major, J. R.; Eichhubl, P.; Callahan, O. A.

    2015-12-01

    The coupled chemical and mechanical response of reservoir and seal rocks to injection of CO2 have major implications on the short and long term security of sequestered carbon. Many current numerical models evaluating behavior of reservoirs and seals during and after CO2 injection in the subsurface consider chemistry and mechanics separately and use only simple mechanical stability criteria while ignoring time-dependent failure parameters. CO2 injection irreversibly alters the subsurface chemical environment which can then affect geomechanical properties on a range of time scales by altering rock mineralogy and cements through dissolution, remobilization, and precipitation. It has also been documented that geomechanical parameters such as fracture toughness (KIC) and subcritical index (SCI) are sensitive to chemical environment. Double torsion fracture mechanics testing of reservoir lithologies under controlled environmental conditions relevant to CO2 sequestration show that chemical environment can measurably affect KIC and SCI. This coupled chemical-mechanical behavior is also influenced by rock composition, grains, amount and types of cement, and fabric. Fracture mechanics testing of the Aztec Sandstone, a largely silica-cemented, subarkose sandstone demonstrate it is less sensitive to chemical environment than Entrada Sandstone, a silty, clay-rich sandstone. The presence of de-ionized water lowers KIC by approximately 20% and SCI 30% in the Aztec Sandstone relative to tests performed in air, whereas the Entrada Sandstone shows reductions on the order of 70% and 90%, respectively. These results indicate that rock composition influences the chemical-mechanical response to deformation, and that the relative chemical reactivity of target reservoirs should be recognized in context of CO2 sequestration. In general, inert grains and cements such as quartz will be less sensitive to the changing subsurface environment than carbonates and clays.

  8. Strengthening mechanisms and fracture surface characteristics of silicate glass matrix composites with inclusion of alumina particles of different particle sizes

    International Nuclear Information System (INIS)

    Strengthening mechanisms of silicate glass by the inclusion of alumina particles of different volume fractions and different particle sizes are reported. The formulas of three responsible strengthening mechanisms, based on inclusion/crack interactions and interfacial elemental diffusion, were deduced; these include crack deflection, crack bridging and interdiffusion. The strength of the glass/alumina composites increased with inclusion fraction, but followed strengthening mechanisms that varied with alumina particle size. Crack deflection and bridging mechanisms dominated in strengthening for the glass/alumina (at mean particle size of 6 μm) composites while interdiffusion mechanism played a major role in the glass/alumina (at mean particle size of 1 μm) composites. The theoretical deduction of strengthening mechanisms depending on the particle size of alumina inclusions was demonstrated by the experimental strength data and fracture surface characteristics of the glass/alumina composites

  9. Structural properties of silver nanowires from atomistic descriptions

    Science.gov (United States)

    Jia, Jianming; Shi, Daning; Zhao, Jijun; Wang, Baolin

    2007-10-01

    The structural formation process and physical properties of silver nanowires were investigated via an unbiased genetic algorithm search using empirical potential combined with density-functional theory calculations. Some unexpected structural behaviors resulting from the intrinsic properties of silver were revealed. Two kinds of atomic arrangements, i.e., normal and abnormal configurations, appear alternately during the growth of wire, from which a (111) facet-based formation mechanism was observed. The excellent agreements between theoretical results and experimental observations on the structural motif, Young’s modulus, and shell effects of Ag nanowires indicate the importance of objective and precise atomistic descriptions in the study of nanosystems.

  10. Application of small specimens to fracture mechanics characterization of irradiated pressure vessel steels

    International Nuclear Information System (INIS)

    In this study, precracked Charpy V-notch (PCVN) specimens were used to characterize the fracture toughness of unirradiated and irradiated reactor pressure vessel steels in the transition region by means of three-point static bending. Fracture toughness at cleavage instability was calculated in terms of elastic-plastic KJc values. A statistical size correction based upon weakest-link theory was performed. The concept of a master curve was applied to analyze fracture toughness properties. Initially, size-corrected PCVN data from A 533 grade B steel, designated HSST Plate O2, were used to position the master curve and a 5% tolerance bound for KJc data. By converting PCVN data to IT compact specimen equivalent KJc data, the same master curve and 5% tolerance bound curve were plotted against the Electric Power Research Institute valid linear-elastic KJc database and the ASME lower bound KIc curve. Comparison shows that the master curve positioned by testing several PCVN specimens describes very well the massive fracture toughness database of large specimens. These results give strong support to the validity of KJc with respect to KIc in general and to the applicability of PCVN specimens to measure fracture toughness of reactor vessel steels in particular. Finally, irradiated PCVN specimens of other materials were tested, and the results are compared to compact specimen data. The current results show that PCVNs demonstrate very good capacity for fracture toughness characterization of reactor pressure vessel steels. It provides an opportunity for direct measurement of fracture toughness of irradiated materials by means of precracking and testing Charpy specimens from surveillance capsules. However, size limits based on constraint theory restrict the operational test temperature range for KJc data from PCVN specimens. 13 refs., 8 figs., 1 tab

  11. Research on structural integral assessment of cylinders with circumference cracks under pressurized thermal shock based on probabilistic fracture mechanics

    International Nuclear Information System (INIS)

    Background: Many investigations on the structural integrity assessment of reactor pressure vessel (RPV) under the pressure thermal stress (PTS) conditions have been performed. Probabilistic fracture mechanics (PFM) technique has been used for RPV PTS analysis since 1980. However, research on the structure integrity assessment techniques using the PFM method is insufficient in China to support the application of the method to be used for assessment of RPV under PTS conditions. Purpose: To gain the effective right assessment approach applied to Chinese RPV against PTS. Methods: Thermal stress distribution along the cylinder wall-thickness under PTS is firstly evaluated by FE in order to get the corresponding stress intensity factors (SIF) and to validate them with some available SIF solutions. The PFM analyses based on crack initiation are then performed under conditions of the crack size, fracture toughness and material yield stress. Both linear elastic fracture mechanics and R6 method are used in the analyses, and the sensitivity of uncertainties as well as the effect of the assessment method is discussed. Monte Carlo simulation is used to calculate the failure probability. Results: preliminary software is developed to perform the assessment for PTS analysis. The failure probability with R6 method is a little higher than with the linear elastic fracture mechanics approach. The effect of reference nil-ductility transition temperature RTNDT on the failure probability is more significant than other factors. Conclusions: Many uncertainties should be considered in RPV PTS analysis with PFM approach in the further, including the input parameters and failure models. Low RTNDT can extend the time of failure, and reduce the failure probability. (authors)

  12. Atomistic computer simulations a practical guide

    CERN Document Server

    Brazdova, Veronika

    2013-01-01

    Many books explain the theory of atomistic computer simulations; this book teaches you how to run them This introductory ""how to"" title enables readers to understand, plan, run, and analyze their own independent atomistic simulations, and decide which method to use and which questions to ask in their research project. It is written in a clear and precise language, focusing on a thorough understanding of the concepts behind the equations and how these are used in the simulations. As a result, readers will learn how to design the computational model and which parameters o

  13. Elastic stress transmission and transformation (ESTT) by confined liquid: A new mechanics for fracture in elastic lithosphere of the earth

    Science.gov (United States)

    Xu, Xing-Wang; Peters, Stephen G.; Liang, Guang-He; Zhang, Bao-Lin

    2016-03-01

    We report on a new mechanical principle, which suggests that a confined liquid in the elastic lithosphere has the potential to transmit a maximum applied compressive stress. This stress can be transmitted to the internal contacts between rock and liquid and would then be transformed into a normal compressive stress with tangential tensile stress components. During this process, both effective compressive normal stress and tensile tangential stresses arise along the liquid-rock contact. The minimum effective tensile tangential stress causes the surrounding rock to rupture. Liquid-driven fracture initiates at the point along the rock-liquid boundary where the maximum compressive stress is applied and propagates along a plane that is perpendicular to the minimum effective tensile tangential stress and also is perpendicular to the minimum principal stress. Liquid-driven fractures and dikes propagate along the axes of cylindrical zones that are perpendicular to the minimum compressive principal stress in rocks in non-tectonic regions. The minimum depth for liquid-driven fracture, which is induced by a spherical confined liquid and an isolated magma chamber in the elastic lithosphere, ranges from 2 to 6 km, whereas dikes with hemi-cylinder-shaped ends propagate upwards closer to the surface under gravity. Transmission of pumping pressure, i.e. the pressure differences on the underside of a dike that is connected with a chamber, from the source magma chamber to intermediate and shallow chambers increases liquid pressure and also the effective tensile tangential stress and therefore leads to new fractures and dike formation and to upwards transport of magmas that have stagnated in the intermediate chamber. Tectonic stress alters local stress fields in the surrounding country rocks and therefore synchronously varies the local effective tensile tangential stress and the nature and geometry of the liquid-driven fractures.

  14. 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

  15. High-temperature mechanical properties and fracture mechanisms of Al–Si piston alloy reinforced with in situ TiB2 particles

    International Nuclear Information System (INIS)

    In order to assess the high-temperature performance of aluminum–silicon alloy reinforced with titanium diboride particles as potential piston material, the tensile behaviors and fracture mechanisms of in situ 4 wt% TiB2/Al–Si composite were investigated in the temperature range 25–350 °C. The tensile results revealed that the composite exhibited higher modulus than the matrix alloy at all testing temperatures, but both the matrix alloy and the composite presented similar strength levels above 200 °C. The ductility of the composite was found to be lower than that of the unreinforced matrix alloy at 25 and 200 °C, but no obvious distinction was observed at 350 °C. The effects of temperature and the presence of TiB2 particles on tensile properties of the composite had been evaluated. Fractographic morphology studies were done using scanning electron microscope, which indicated that the fracture of the composite altered from brittle to ductile mode with temperature increasing. At 25 and 200 °C, fracture was dominated by cracked silicon particles and separated TiB2 particles, while decohesion at particle–matrix interface was prevalent at 350 °C. Analysis of the fracture surfaces also showed that regions of clustered TiB2 particles were found to be the locations prone to damage in the composite at both room and high temperatures

  16. High-temperature mechanical properties and fracture mechanisms of Al–Si piston alloy reinforced with in situ TiB{sub 2} particles

    Energy Technology Data Exchange (ETDEWEB)

    Han, Gang [School of Mechanical Engineering, Beijing Institute of Technology, 5 South Zhongguancun Street, Haidian District, Beijing 100081 (China); Zhang, Weizheng, E-mail: zhangwz@bit.edu.cn [School of Mechanical Engineering, Beijing Institute of Technology, 5 South Zhongguancun Street, Haidian District, Beijing 100081 (China); Zhang, Guohua; Feng, Zengjian; Wang, Yanjun [Shandong Binzhou Bohai Piston Co., Ltd., Binzhou 256602 (China)

    2015-05-01

    In order to assess the high-temperature performance of aluminum–silicon alloy reinforced with titanium diboride particles as potential piston material, the tensile behaviors and fracture mechanisms of in situ 4 wt% TiB{sub 2}/Al–Si composite were investigated in the temperature range 25–350 °C. The tensile results revealed that the composite exhibited higher modulus than the matrix alloy at all testing temperatures, but both the matrix alloy and the composite presented similar strength levels above 200 °C. The ductility of the composite was found to be lower than that of the unreinforced matrix alloy at 25 and 200 °C, but no obvious distinction was observed at 350 °C. The effects of temperature and the presence of TiB{sub 2} particles on tensile properties of the composite had been evaluated. Fractographic morphology studies were done using scanning electron microscope, which indicated that the fracture of the composite altered from brittle to ductile mode with temperature increasing. At 25 and 200 °C, fracture was dominated by cracked silicon particles and separated TiB{sub 2} particles, while decohesion at particle–matrix interface was prevalent at 350 °C. Analysis of the fracture surfaces also showed that regions of clustered TiB{sub 2} particles were found to be the locations prone to damage in the composite at both room and high temperatures.

  17. Mechanical and hydraulic performance of sludge-mixed cement grout in rock fractures

    Directory of Open Access Journals (Sweden)

    Khomkrit Wetchasat

    2014-08-01

    Full Text Available The objective is to assess the performance of sludge mixed with commercial grade Portland cement type I for use in minimizing the permeability of fractured rock mass. The fractures were artificially made by applying a line load to sandstone block specimens. The sludge comprises over 80% of quartz with grain sizes less than 75 μm. The results indicate that the mixing ratios of sludge:cement (S:C of 1:10, 3:10, 5:10 with water:cement ratio of 1:1 by weight are suitable for fracture grouting. For S:C = 3:10, the compressive strength and elastic modulus are 1.22 MPa and 224 MPa which are comparable to those of bentonite mixed with cement. The shear strengths between the grouts and fractures surfaces are from 0.22 to 0.90 MPa. The S:C ratio of 5:10 gives the lowest permeability. The permeability of grouted fractures with apertures of 2, 10, and 20 mm range from 10-16 to 10-14 m2 and decrease with curing time.

  18. Mechanisms of Plastic and Fracture Instabilities for Alloy Development of Fusion Materials. Final Project Report for period July 15, 1998 - July 14, 2003

    Energy Technology Data Exchange (ETDEWEB)

    Ghoniem, N. M.

    2003-07-14

    The main objective of this research was to develop new computational tools for the simulation and analysis of plasticity and fracture mechanisms of fusion materials, and to assist in planning and assessment of corresponding radiation experiments.

  19. A thermo-hydro-mechanical coupled model in local thermal non-equilibrium for fractured HDR reservoir with double porosity

    Science.gov (United States)

    Gelet, R.; Loret, B.; Khalili, N.

    2012-07-01

    The constitutive thermo-hydro-mechanical equations of fractured media are embodied in the theory of mixtures applied to three-phase poroelastic media. The solid skeleton contains two distinct cavities filled with the same fluid. Each of the three phases is endowed with its own temperature. The constitutive relations governing the thermomechanical behavior, generalized diffusion and transfer are structured by, and satisfy, the dissipation inequality. The cavities exchange both mass and energy. Mass exchanges are driven by the jump in scaled chemical potential, and energy exchanges by the jump in coldness. The finite element approximation uses the displacement vector, the two fluid pressures and the three temperatures as primary variables. It is used to analyze a generic hot dry rock geothermal reservoir. Three parameters of the model are calibrated from the thermal outputs of Fenton Hill and Rosemanowes HDR reservoirs. The calibrated model is next applied to simulate circulation tests at the Fenton Hill HDR reservoir. The finer thermo-hydro-mechanical response provided by the dual porosity model with respect to a single porosity model is highlighted in a parameter analysis. Emphasis is put on the influence of the fracture spacing, on the effective stress response and on the permeation of the fluid into the porous blocks. The dual porosity model yields a thermally induced effective stress that is less tensile compared with the single porosity response. This effect becomes significant for large fracture spacings. In agreement with field data, fluid loss is observed to be high initially and to decrease with time.

  20. A composite material model for investigation of micro-fracture mechanism of brittle rock subjected to uniaxial compression

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A two-phase model of rock was proposed in order to investigate the mechanism of brittle fracture due to uniaxial compression, in which rock was considered to be a composite material consisting of hard grains and colloids. The stress state in colloid region near grains was calculated using Finite Element Metnod ( FEM). The influence of the tensile stresses on the crack initiation and failure process of brittle rock subjected to uniaxial compression was investigated by numerical experiments. The FE results show that tensile stresses are induced easily in the neighboring area of hard grains with the maximum value near grain boundaries. The distribution of tensile stresses depends on the relative position of hard grains. The cracks initiated just near the boundary area of hare grains, which was governed by tensile stress. These results dearly reveal the micro-fracture mechanism of brittle rock loaded by uniaxial compression. It can be concluded that the failure mode of brittle rock under uniaxial compression is still tensile fracture from the point view of microstructure. However,since the wide colloid region is still under compressive stress state, further propagation of boundary, cracks through this region obviously needs more external load, thus causing the uniaxial compressive strength of rock much higher than its tensile strength obtained via Brazilian (splitting) experiment.

  1. Mechanical characterization of a CO2 fractured reservoir by means of microseismicity induced by high pressure injection tests

    Science.gov (United States)

    De Simone, Silvia; Soler, Joaquim; Carrera, Jesus; Slooten, Luit Jan; Ortiz, Gema

    2014-05-01

    Reservoir characterization is an essential issue in geological storage of CO2 in Technological Development Plant (TDP). In particular, hydromechanical characterization of the caprock-reservoir system is crucial, in order to define the maximum suitable injection pressure and the in-situ mechanical properties. Thus, it is possible to conjecture the hydromechanical behavior of the system during CO2 injection. Microseismicity induced by fluid injection may be used as instruments to find out fractured reservoir properties. Indeed, the hydromechanical response is controlled by permeability (k), Young modulus (E) and Poisson ratio (ν). In caprock-reservoir systems, reservoir stiffness controls the stress transfer towards the caprock, where failure may occur. Therefore, the location of the microseismic hypocenters could give information on the reservoir stiffness. In this work we propose a simulation and calibration method of the microseismicity induced by high pressure fluid injection in a fractured reservoir. Coupled hydromechanical models are peformed. The methology is applied to a particular case study.

  2. Structural Integrity Assessment of High-Strength Anchor Bolt in Nuclear Power Plant based on Fracture Mechanics Concept

    Energy Technology Data Exchange (ETDEWEB)

    Lim, Eunmo; Huh, Namsu [Seoul Nat' l Univ. of Science and Technology, Seoul (Korea, Republic of); Shim, Heejin; Oh, Changkyun; Kim, Hyunsu [KEPCO Engineering and Construction Company, Inc., Yongin (Korea, Republic of)

    2013-07-15

    The failure of a bolted joint owing to stress corrosion cracking (Succ) has been considered one of the most important structural integrity issues in a nuclear power plant. In this study, the failure possibility of bolting, which is used to support the steam generator of a pressurized water reactor, owing to Succ and brittle fracture was evaluated in accordance with guidelines proposed by the Electric Power Research Institute, which are called the Reference Flaw Factor method. For this evaluation, first, detailed finite element stress analyses were conducted to obtain the actual nominal stresses of bolting in which either service loads or bolt preload were considered. Based on these nominal stresses, the structural integrity of bolting was addressed from the viewpoints of Succ and toughness. In addition, the accuracy of the EPRI Reference Flaw Factor for assessing bolting failure was investigated using finite element fracture mechanics analyses.

  3. 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.

  4. 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.

  5. Atomistic study on the FCC/BCC interface structure with {112}KS orientation

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Keonwook [Los Alamos National Laboratory; Beyerlein, Irene [Los Alamos National Laboratory

    2011-09-23

    In this study, atomistic simulation is used to explore the atomic interface structure, the intrinsic defect network, and mechanism of twin formation from the {112}KS Cu-Nb interface. The interface structure of different material systems AI-Fe and AI-Nb are also compared with Cu-Nb interface.

  6. The mechanics and physics of fracturing: application to thermal aspects of crack propagation and to fracking.

    Science.gov (United States)

    Cherepanov, Genady P

    2015-03-28

    By way of introduction, the general invariant integral (GI) based on the energy conservation law is presented, with mention of cosmic, gravitational, mass, elastic, thermal and electromagnetic energy of matter application to demonstrate the approach, including Coulomb's Law generalized for moving electric charges, Newton's Law generalized for coupled gravitational/cosmic field, the new Archimedes' Law accounting for gravitational and surface energy, and others. Then using this approach the temperature track behind a moving crack is found, and the coupling of elastic and thermal energies is set up in fracturing. For porous materials saturated with a fluid or gas, the notion of binary continuum is used to introduce the corresponding GIs. As applied to the horizontal drilling and fracturing of boreholes, the field of pressure and flow rate as well as the fluid output from both a horizontal borehole and a fracture are derived in the fluid extraction regime. The theory of fracking in shale gas reservoirs is suggested for three basic regimes of the drill mud permeation, with calculating the shape and volume of the local region of the multiply fractured rock in terms of the pressures of rock, drill mud and shale gas. PMID:25713454

  7. The mechanics and physics of fracturing: application to thermal aspects of crack propagation and to fracking.

    Science.gov (United States)

    Cherepanov, Genady P

    2015-03-28

    By way of introduction, the general invariant integral (GI) based on the energy conservation law is presented, with mention of cosmic, gravitational, mass, elastic, thermal and electromagnetic energy of matter application to demonstrate the approach, including Coulomb's Law generalized for moving electric charges, Newton's Law generalized for coupled gravitational/cosmic field, the new Archimedes' Law accounting for gravitational and surface energy, and others. Then using this approach the temperature track behind a moving crack is found, and the coupling of elastic and thermal energies is set up in fracturing. For porous materials saturated with a fluid or gas, the notion of binary continuum is used to introduce the corresponding GIs. As applied to the horizontal drilling and fracturing of boreholes, the field of pressure and flow rate as well as the fluid output from both a horizontal borehole and a fracture are derived in the fluid extraction regime. The theory of fracking in shale gas reservoirs is suggested for three basic regimes of the drill mud permeation, with calculating the shape and volume of the local region of the multiply fractured rock in terms of the pressures of rock, drill mud and shale gas.

  8. 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

    using the crack flank displacements obtained from the FEA solution combined with measured mixed-mode fracture toughness values are used to determine the ultimate failure load. Experiments were conducted to compare against the analysis results. The comparison of numerical and experimentally achieved...

  9. Effect of orientation on the in vitro fracture toughness ofdentin: The role of toughening mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Nalla, R.K.; Kinney, J.H.; Ritchie, R.O.

    2003-01-28

    A micro-mechanistic understanding of bone fracture thatencompasses how cracks interact with the underlying microstructure anddefines their local failure mode is lacking, despite extensive research nthe response of bone to a variety of factors like aging, loading, and/ordisease.

  10. Mechanical Comparison of Headless Screw Fixation and Locking Plate Fixation for Talar Neck Fractures.

    Science.gov (United States)

    Karakasli, Ahmet; Hapa, Onur; Erduran, Mehmet; Dincer, Cemal; Cecen, Berivan; Havitcioglu, Hasan

    2015-01-01

    For talar neck fractures, open reduction and internal fixation have been thought to facilitate revascularization and prevent osteonecrosis. Newer screw systems allow for placement of cannulated headless screws, which provide compression by virtue of a variable pitch thread. The present study compared the biomechanical fixation strength of cannulated headless variable-pitch screw fixation and locking plate fixation. A reproducible talar neck fracture was created in 14 fresh cadaver talar necks. Talar head fixation was then performed using 2 cannulated headless variable-pitch 4-mm/5-mm diameter (4/5) screws (Acutrak; Acumed, Hillsboro, OR) and locking plate fixation. Headless variable-pitch screw fixation had lower failure displacement than did locking plate fixation. No statistically significant differences were found in failure stiffness, yield stiffness (p = .655), yield load (p = .142), or ultimate load between the 2 fixation techniques. Cannulated headless variable-pitch screw fixation resulted in better failure displacement than locking plate fixation in a cadaveric talus model and could be considered a viable option for talus fracture fixation. Headless, fully threaded, variable-pitch screw fixation has inherent advantages compared with locking plate fixation, because it might cause less damage to the articular surface and can compress the fracture for improved reduction. Additionally, plate fixation can increase the risk of avascular necrosis owing to the wider incision and dissection of soft tissues.

  11. Interaction of age and mechanical stability on bone defect healing: an early transcriptional analysis of fracture hematoma in rat.

    Directory of Open Access Journals (Sweden)

    Andrea Ode

    Full Text Available Among other stressors, age and mechanical constraints significantly influence regeneration cascades in bone healing. Here, our aim was to identify genes and, through their functional annotation, related biological processes that are influenced by an interaction between the effects of mechanical fixation stability and age. Therefore, at day three post-osteotomy, chip-based whole-genome gene expression analyses of fracture hematoma tissue were performed for four groups of Sprague-Dawley rats with a 1.5-mm osteotomy gap in the femora with varying age (12 vs. 52 weeks - biologically challenging and external fixator stiffness (mechanically challenging. From 31099 analysed genes, 1103 genes were differentially expressed between the six possible combinations of the four groups and from those 144 genes were identified as statistically significantly influenced by the interaction between age and fixation stability. Functional annotation of these differentially expressed genes revealed an association with extracellular space, cell migration or vasculature development. The chip-based whole-genome gene expression data was validated by q-RT-PCR at days three and seven post-osteotomy for MMP-9 and MMP-13, members of the mechanosensitive matrix metalloproteinase family and key players in cell migration and angiogenesis. Furthermore, we observed an interaction of age and mechanical stimuli in vitro on cell migration of mesenchymal stromal cells. These cells are a subpopulation of the fracture hematoma and are known to be key players in bone regeneration. In summary, these data correspond to and might explain our previously described biomechanical healing outcome after six weeks in response to fixation stiffness variation. In conclusion, our data highlight the importance of analysing the influence of risk factors of fracture healing (e.g. advanced age, suboptimal fixator stability in combination rather than alone.

  12. Testing continuum concepts for hydrogen embrittlement in metals using atomistics

    International Nuclear Information System (INIS)

    Hydrogen embrittlement is a pervasive mode of degradation in many metallic systems that can occur via several mechanisms. Here, the competition between dislocation emission and cleavage at a crack tip is evaluated in the presence of H. At this level, embrittlement is predicted when the critical stress intensity required for emission rises above that needed for cleavage, eliminating crack tip plasticity and blunting as toughening mechanisms. Continuum predictions for emission and cleavage are made using computed generalized stacking fault energies and surface energies in a model Ni–H system, and embrittlement is predicted at a critical H concentration. An atomistic model is then used to investigate actual crack tip behavior in the presence of controlled arrays of H atoms around the crack tip. The continuum models are accurate at low H concentrations, below the embrittlement point, but at higher H concentrations the models deviate from the atomistic behavior due to alternative dislocation emission modes. Additional H configurations are investigated to understand controlling features of the emission process. In no cases does crack propagation occur in preference to dislocation emission in geometries where emission is possible, indicating that embrittlement can be more complicated than envisioned by the basic brittle–ductile transition

  13. Evolution of limestone fracture permeability under coupled thermal, hydrologi-cal, mechanical, and chemical conditions

    Institute of Scientific and Technical Information of China (English)

    李凤滨; 盛金昌; 詹美礼; 徐力猛; 吴强; 贾春兰

    2014-01-01

    The effect of temperature on the rock fracture permeability is a very important factor in the prediction of the permeability of enhanced geothermal systems and in reservoir engineering. In this study, the flow-through experiments were conducted on a single limestone fracture at different temperatures of 25oC, 40oC and 60oC, and with differential pressures of 0.3 MPa and 0.4 MPa. The experimental results suggest a complex temporal evolution of the fracture aperture. The aperture increases considerably with increasing temperature and reduces gradually to a steady value at a stable temperature. The results of three short-term experiments (QT-1, QT-2, QT-3) indicate an exponential relationship between the permeability and the temperature change ratio (DT/T ) , which provides a further evidence that the rising temperature increases the aperture. It is shown that the changing temperature has its influence on two possible accounts:the chemical dissolution and the pressure dissolution. These two processes have opposite impacts on the fracture permeability. The chemical dissolution increases the permeability with a rising temperature while the pressure disso-lution reduces the permeability with a stable temperature. These make a very complex picture of the permeability evolution. Our results show that the fracture permeability reduces 39.2%when the temperature increases by 15oC (during the 25oC-40 C interval) and 42.6% when the temperature increases by 20oC (during the 40oC-60oC interval). It can be concluded that the permeability decreases to a greater extent for larger increases in temperature.

  14. Dynamic Mechanical Properties and Fracture Surface Morphologies of Core-Shell Rubber (CSR) Toughened Epoxy at Liquid Nitrogen (Ln2) Temperatures

    Science.gov (United States)

    Wang, J.; Magee, D.; Schneider, J. A.

    2009-01-01

    The dynamic mechanical properties and fracture surface morphologies were evaluated for a commercial epoxy resin toughened with two types of core-shell rubber (CSR) toughening agents (Kane Ace(Registered TradeMark) MX130 and MX960). The impact resistance (R) was evaluated by the resulting breaking energy measured in Charpy impact tests conducted on an instrumented drop tower. The resulting fracture surface morphologies were examined using Scanning Electron Microscopy (SEM). Fractographic observations of the CSR toughened epoxy tested at ambient temperature, showed a fracture as characterized by slender dendrite textures with large voids. The increasing number of dendrites and decreasing size of scale-like texture with more CSR particles corresponded with increased R. As the temperature decreased to Liquid Nitrogen (LN 2), the fracture surfaces showed a fracture characterized by a rough, torn texture containing many river markings and deep furrows.

  15. Micromechanics, Fracture Mechanics and Gas Permeability of Composite Laminates for Cryogenic Storage Systems

    Science.gov (United States)

    Choi, Sukjoo; Sankar, Bhavani; Ebaugh, Newton C.

    2005-01-01

    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 1/2. When the transverse crack propagates to a stiffer layer normal to the ply-direction, the singularity becomes less than 1/2 and vice versa. Finite element analysis is performed to predict the fracture toughness of a laminated beam subjected to fracture loads measured by four-point bending tests 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 difference of the 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

  16. Elastic-Plastic Fracture Mechanics Analysis of Critical Flaw Size in ARES I-X Flange-to-Skin Welds

    Science.gov (United States)

    Chell, G. Graham; Hudak, Stephen J., Jr.

    2008-01-01

    NASA's Ares 1 Upper Stage Simulator (USS) is being fabricated from welded A516 steel. In order to insure the structural integrity of these welds it is of interest to calculate the critical initial flaw size (CIFS) to establish rational inspection requirements. The CIFS is in turn dependent on the critical final flaw size (CFS), as well as fatigue flaw growth resulting from transportation, handling and service-induced loading. These calculations were made using linear elastic fracture mechanics (LEFM), which are thought to be conservative because they are based on a lower bound, so called elastic, fracture toughness determined from tests that displayed significant plasticity. Nevertheless, there was still concern that the yield magnitude stresses generated in the flange-to-skin weld by the combination of axial stresses due to axial forces, fit-up stresses, and weld residual stresses, could give rise to significant flaw-tip plasticity, which might render the LEFM results to be non-conservative. The objective of the present study was to employ Elastic Plastic Fracture Mechanics (EPFM) to determine CFS values, and then compare these values to CFS values evaluated using LEFM. CFS values were calculated for twelve cases involving surface and embedded flaws, EPFM analyses with and without plastic shakedown of the stresses, LEFM analyses, and various welding residual stress distributions. For the cases examined, the computed CFS values based on elastic analyses were the smallest in all instances where the failures were predicted to be controlled by the fracture toughness. However, in certain cases, the CFS values predicted by the elastic-plastic analyses were smaller than those predicted by the elastic analyses; in these cases the failure criteria were determined by a breakdown in stress intensity factor validity limits for deep flaws (a greater than 0.90t), rather than by the fracture toughness. Plastic relaxation of stresses accompanying shakedown always increases the

  17. Hydraulic Fracture Containment in Sand

    NARCIS (Netherlands)

    Dong, Y.

    2010-01-01

    The mechanism of hydraulic fracturing in soft, high permeability material is considered fundamentally different from that in hard, low permeability rock, where a tensile fracture is created and conventional linear elastic fracture mechanics (LEFM) applies. The fracturing and associated modeling work

  18. A Thermo-Hydro-Mechanical modeling of fracture opening and closing due heat extraction from geothermal reservoir

    Science.gov (United States)

    Nand Pandey, Sachchida; Chaudhuri, Abhijit; Kelkar, Sharad

    2015-04-01

    Increasing the carbon dioxide concentration in atmosphere become challenging task for the scientific community. To achieve the sustainable growth with minimum pollution in atmosphere requires the development of low carbon technology or switch towards renewable energy. Geothermal energy is one of the promising source of clean energy. Geothermal energy is also considered a sustainable, reliable and least-expensive. This study presents a numerical modeling of subsurface heat extraction from the reservoir. The combine flow, heat transfer and geo-mechanical problem are modeled using FEHM code, which was validated against existing field data, numerical code and commercial software. In FEHM the flow and heat transfer in reservoir are solved by control volume method while for mechanical deformation finite element technique is used. The 3-D computational domain (230m × 200m × 1000m) has single horizontal fault/fracture, which is located at 800 m depth from the ground surface. The fracture connects the injection and production wells. The distance between the wells is 100 m. A geothermal gradient 0.08 °C/m is considered. The temperatures at top and bottom boundaries are held fixed as 20 and 100 °C respectively. The zero heat and mass flux boundary conditions are imposed to all vertical side boundaries of the domain. The simulation results for 100 days suggests that the computational domain is sufficiently large as the temperature along the vertical boundaries are not affected by cold-water injection. To model the thermo-poro-elastic deformation, zero all three components of displacement are specified as zero at the bottom. The zero stress condition along all other boundaries allows the boundaries to move freely. The temperature and pressure dependent fluid properties such as density and viscosity with single phase flow in saturated medium is considered. We performed a series of thermo-hydro-mechanical (THM) simulations to show aperture alteration due to cold

  19. The complementary roles of fracture mechanics and non-destructive examination in the safety assessment of components

    International Nuclear Information System (INIS)

    This document presents the various speeches of the workshop of the Committee on Safety of Nuclear Installations (CSNI) that took place in Wuerenligen, Switzerland, in October 1988. The speeches deal with the roles of Non-Destructive Examination (NDE) and Fracture Mechanics (FM) in the safety assessment of reactor components, such as pressure vessels. Some calibration standards and reference values of defects are presented, and several NDE and FM methods for the assessment of components are described. Separate abstracts were prepared for all the papers in this volume. (TEC)

  20. The effect of coating/substrate interface curvature on fracture of Si-Al-N coatings subjected to mechanical loading

    Science.gov (United States)

    Shugurov, Artur

    2015-10-01

    The effect of curvature of the film/substrate interface on the fracture mechanisms of Si-Al-N coatings on Cu substrates subjected to uniaxial tension and alternating bending is studied. Local interface curvature due to substrate surface roughening caused by its plastic deformation in the course of the uniaxial tension is shown to have a profound effect on their delamination and buckling. Interface curvature induced by specimen bending promotes kinking of through-the-coating cracks at the interface that is followed by delamination and spalling of the coatings.

  1. Numerical simulation of a class of models that combine several mechanisms of dissipation: Fracture, plasticity, viscous dissipation

    Science.gov (United States)

    Bonnetier, Eric; Jakabčin, Lukáš; Labbé, Stéphane; Replumaz, Anne

    2014-08-01

    We study a class of time evolution models that contain dissipation mechanisms exhibited by geophysical materials during deformation: plasticity, viscous dissipation and fracture. We formally prove that they satisfy a Clausius-Duhem type inequality. We describe a semi-discrete time evolution associated with these models, and report numerical 1D and 2D traction experiments, that illustrate that several dissipation regimes can indeed take place during the deformation. Finally, we report 2D numerical simulation of an experiment by Peltzer and Tapponnier, who studied the indentation of a layer of plasticine as an analogue model for geological materials.

  2. The life estimation of turbine rotor through fracture mechanics and fatigue analysis

    International Nuclear Information System (INIS)

    Stress analysis for High Pressure Turbine Rotor of Korea Nuclear Power Unit 9/10 was carried out by finite element method. And, using the greatest value of stress output, the maximum allowable non-metallic inclusion size and the operating cycle limit at bore surface were calculated through linear elastic fracture mechnics and low cycle fatigue theory respectively; the inclusion smaller than 14.3mm in length was safe from brittle fracture regardless of its existing position and crack initiating life was 3886 cycles under the most severe starting condition. FEM program TDROTOR(Temperature Distribution of was developed to calculate temperature distribution of Rotor by heat transfer from hot steam, and centrifugal, thermal and total stress components were calculated by SAROTOR(Stress Analysis of ROTOR). Both FEM codes used axi-symmetric, quadrilateral element, and plasticity was not considered. (Author)

  3. A fracture mechanics model to describe the buckling behavior of  lightly rc columns

    OpenAIRE

    Porras Soriano, Rocio; Ruiz Carmona, Jacinto; Ruiz Lopez, Gonzalo Francisco; Yu, Chengxiang

    2013-01-01

    In order to correctly model the behavior of slender columns made of lightly reinforced concrete (RC) sub- jected to buckling load, both tensile fracture and compressive damage should be taken into account. In this work, we propose to consider both failure types as cohesive cracks, governed by a bilinear cohesive law for traction or a linear-decreasing softening equation for compression. Since the columns are lightly reinforced, we assume only one single crack is to propagate at the column cen...

  4. Fracture mechanics characterisation of the WWER-440 reactor pressure vessel beltline welding seam

    Energy Technology Data Exchange (ETDEWEB)

    Viehrig, Hans-Werner [Forschungszentrum Dresden-Rossendorf, P.O. Box 510119, 01314 Dresden (Germany)], E-mail: H.W.Viehrig@fzd.de; Schuhknecht, Jan [Forschungszentrum Dresden-Rossendorf, P.O. Box 510119, 01314 Dresden (Germany)

    2009-04-15

    The master curve (MC) approach as standardised in the ASTM Standard Test Method E1921 was applied to weld metal of the reactor pressure vessel (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 orientation of the specimens within the welding seam is TL and TS according to ASTM E399. The fracture toughness values measured on the SE(B) specimens with both orientations follow the course of the master curve. Nearly all values lie within the fracture toughness curves for 2% and 98% fracture probability. There is a strong variation of the reference temperature T{sub 0} through the thickness of the welding seam, which can be explained by microstructural differences. The scatter is more pronounced for the TS SE(B) specimens. It can be shown that specimens with TL and TS orientation in the welding seam have a differentiating and integrating behaviour, respectively.

  5. Proppant backproduction during hydraulic fracturing -- A new failure mechanism for resin-coated proppants

    Energy Technology Data Exchange (ETDEWEB)

    Vreeburg, R.J.; Roodhart, L.P.; Davies, D.R.; Penny, G.S. (STIM-LAB Inc., Duncan, OK (United States))

    1994-10-01

    Backproduction of proppant from hydraulically fractured wells, particularly those completed in the northern European Rotliegend formation, is a major operational problem, necessitating costly and manpower-intensive surface-handling procedures. Further, the development of unmanned platform operations offshore, required in today's economic climate, is impossible as long as this problem remains unsolved. The most cost-effective potential solution to this problem is provided by curable resin-coated proppant (RCP), which consolidates in the fracture. Early field trials with RCP's, however, were not completely effective in stopping the backproduction of proppant. Typically, some 10% of the total volume of RCP placed in the fracture was backproduced. The authors performed a laboratory study to help clarify the effect of curing temperature, water production rate, proppant size, and stress cycling on the integrity of RCP packs. The experiments confirmed the field experience that stress cycling has a dramatic effect on proppant backproduction of commercial RCP packs. The number of applied stress cycles (i.e., the number of times the well is shut in) and the initial RCP pack strength appear to be the dominant factors that govern proppant backproduction. Dedicated experiments are therefore required to evaluate the use of RCP's to eliminate proppant backproduction for a particular field application.

  6. Type I collagen degradation during tissue repair: comparison of mechanisms following fracture and acute coronary syndromes.

    Science.gov (United States)

    Stansfield, Rachel; Gossiel, Fatma; Morton, Allison; Newman, Christopher; Eastell, Richard

    2014-12-01

    There is turnover of type I collagen during tissue repair. The degradation of type I collagen by matrix metalloproteinases (MMPs) is reflected by serum ICTP and that by cathepsins by CTX-I. There is evidence for increases in ICTP after acute coronary syndromes (ACS) and in CTX-I during fracture repair. The involvement of the MMP pathway in fracture repair and cathepsins after myocardial infarction is unclear. We studied 74 men; 22 were admitted to the hospital on the day of their ACS (ST or non-ST elevation myocardial infarction) (mean age 56 years, range 39 to 82) and 9 attended hospital on the day of their tibial shaft fracture (mean age 33 years, range 21 to 79); we had 43 age-matched controls (mean age 54 years, range 20 to 82). Subjects with ACS and tibial shaft fracture were followed up for up to one year; control subjects were used to establish a reference interval. We measured serum ICTP by ELISA (reference interval 1.1 to 17.6 ng/mL) and CTX-I by chemiluminescence (reference interval 0.094 to 0.991 ng/mL). After ACS, the mean ICTP increased from 5.41 to 6.60 ng/mL within one day of admission (p<0.05); the mean CTX-I increased from 0.263 to 0.414 ng/mL (p<0.05). In two cases, the CTX increased to above the reference interval. After tibial shaft fracture, the mean ICTP increased from 5.51 to maximum of 8.71 ng/mL within 28 days of admission (p<0.01); the mean CTX increased from 0.200 to 0.374 ng/mL (p<0.001). In four cases, the CTX increased to above the reference interval. We conclude that the MMP and cathepsin pathways are both implicated in tissue repair in the bone and heart. This may have clinical implications; drugs that block either pathway (TIMPs, cathepsin K inhibitors) may affect the repair of both tissues. PMID:25193029

  7. Viscoelastic Fracturing As a Migration and Expulsion Mechanism for Hydrocarbons in Shales: Analog Experiments

    Science.gov (United States)

    Van Damme, H.

    2014-12-01

    We report the results of simple laboratory experiments aimed at mimicking the generation, migration, and expulsion process of oil or gas from soft clayey sediments, triggered by thermal decomposition of organic matter. In previously published work, we showed that the injection of fluids into a soft sediment layer confined within a quasi-2D Hele-Shaw cell led to the transition from a viscous fingering invasion regime to a viscoelastic fracturing regime. The transition is controlled by the ratio of the characteristic times for the invasion process and for the structural relaxation in the sediment, respectively (Deborah number). Here we show that expulsion is a discontinuous quasi-periodic process, driven by the elastic energy stored in the embedding layers. We report also about two sets of experiments aimed at understanding the conditions in which fluid generation from multiple sources can generate a highly connected network of fractures for expulsion. In a first set of experiments, a Hele-Shaw cell with multiple injection points and multiple outlets was used. It is shown that, due to attractive elastic interactions between cracks, a network spontaneously forms as soon as invasion proceeds in the viscoelastic regime. On the contrary, no network of migration paths is forming in the viscous fingering regime, due to the effective repulsion of the fluid channels. In the second set of analog experiments, we used a thermostated mini-Hele-Shaw cell, the gap of which was filled with a strong clay mud in which microcrystals of reactive organic matter (azoisobutyronitrile, AIBN) are dispersed, or with a mud prepared with clay particles on which the organic matter was pre-impregnated. AIBN decomposes around 70°C, releasing nitrogen gas. It was again observed that, depending on the viscoelastic properties of the clay matrix, gas evolution occurs either by formation and coalescence of bubbles, or by formation of a percolating network of fractures. The length of the fracture

  8. Fracture mechanics characteristics and associated safety margins for integrity assessment; Bruchmechanische Kennwerte und zugeordnete Sicherheitsfaktoren bei Integritaetsanalysen

    Energy Technology Data Exchange (ETDEWEB)

    Roos, E.; Schuler, X.; Stumpfrock, L.; Silcher, H. [Stuttgart Univ. (DE). Materialpruefungsanstalt (MPA)

    2008-07-01

    Within the integrity assessment of components and structural members of plants safety margins have to be applied, whose magnitude depend on several factors. Important factors influencing the magnitude of the safety margins are as for instance: Material behaviour (ductile / brittle behaviour), the event to be considered (local deformation / fracture), possible consequences of failure (human health, environmental damage, economic consequences) and many others. One important factor also is the fact, how precisely and reliably the appropriate material characteristics can be determined and how precisely and reliably the components behaviour can be predicted and assessed by means of this material characteristic. In contemporary safety assessment procedures by means of fracture mechanics evaluation tools (e.g. [1]) a concept of partial safety margins is proposed for application. The basic idea with this procedure is that only those sources of uncertainty have to be considered, which are relevant or may be relevant for the structure to be considered. For this purpose each source of possible uncertainty has to be quantified individually, finally only those singular safety margins are superimposed to a total safety margin which are relevant. The more the uncertainties have to be taken into account, the total safety margin to be applied, consequently will be larger. If some sources of uncertainty can be eliminated totally or can be minimized (for instance by a more reliable calculational procedure of the component loading or by more precise material characteristics), the total safety margin can be reduced. In this contribution the different procedures for the definition of safety margins within the integrity assessment by means of fracture mechanics procedures will be discussed. (orig.)

  9. 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.

  10. 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

    2016-01-01

    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.

  11. Atomistic spin dynamics and surface magnons

    International Nuclear Information System (INIS)

    Atomistic spin dynamics simulations have evolved to become a powerful and versatile tool for simulating dynamic properties of magnetic materials. It has a wide range of applications, for instance switching of magnetic states in bulk and nano-magnets, dynamics of topological magnets, such as skyrmions and vortices and domain wall motion. In this review, after a brief summary of the existing investigation tools for the study of magnons, we focus on calculations of spin-wave excitations in low-dimensional magnets and the effect of relativistic and temperature effects in such structures. In general, we find a good agreement between our results and the experimental values. For material specific studies, the atomistic spin dynamics is combined with electronic structure calculations within the density functional theory from which the required parameters are calculated, such as magnetic exchange interactions, magnetocrystalline anisotropy, and Dzyaloshinskii–Moriya vectors. (topical review)

  12. Effective Transparency: A Test of Atomistic Laser-Cluster Models

    CERN Document Server

    Pandit, Rishi; Teague, Thomas; Hartwick, Zachary; Bigaouette, Nicolas; Ramunno, Lora; Ackad, Edward

    2016-01-01

    The effective transparency of rare-gas clusters, post-interaction with an extreme ultraviolet (XUV) pump pulse, is studied by using an atomistic hybrid quantum-classical molecular dynamics model. We find there is an intensity range in which an XUV probe pulse has no lasting effect on the average charge state of a cluster after being saturated by an XUV pump pulse: the cluster is effectively transparent to the probe pulse. The range of this phenomena increases with the size of the cluster and thus provides an excellent candidate for an experimental test of the effective transparency effect. We present predictions for the clusters at the peak of the laser pulse as well as the experimental time-of-flight signal expected along with trends which can be compared with. Significant deviations from these predictions would provide evidence for enhanced photoionization mechanism(s).

  13. Quantum-based Atomistic Simulation of Transition Metals

    Energy Technology Data Exchange (ETDEWEB)

    Moriarty, J A; Benedict, L X; Glosli, J N; Hood, R Q; Orlikowski, D A; Patel, M V; Soderlind, P; Streitz, F H; Tang, M; Yang, L H

    2005-08-29

    First-principles generalized pseudopotential theory (GPT) provides a fundamental basis for transferable multi-ion interatomic potentials in d-electron transition metals within density-functional quantum mechanics. In mid-period bcc metals, where multi-ion angular forces are important to structural properties, simplified model GPT or MGPT potentials have been developed based on canonical d bands to allow analytic forms and large-scale atomistic simulations. Robust, advanced-generation MGPT potentials have now been obtained for Ta and Mo and successfully applied to a wide range of structural, thermodynamic, defect and mechanical properties at both ambient and extreme conditions of pressure and temperature. Recent algorithm improvements have also led to a more general matrix representation of MGPT beyond canonical bands allowing increased accuracy and extension to f-electron actinide metals, an order of magnitude increase in computational speed, and the current development of temperature-dependent potentials.

  14. 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.

  15. Hydromechanical coupling in fractured rock masses: mechanisms and processes of selected case studies

    Science.gov (United States)

    Zangerl, Christian

    2015-04-01

    Hydromechanical (HM) coupling in fractured rock play an important role when events including dam failures, landslides, surface subsidences due to water withdrawal or drainage, injection-induced earthquakes and others are analysed. Generally, hydromechanical coupling occurs when a rock mass contain interconnected pores and fractures which are filled with water and pore/fracture pressures evolves. In the on hand changes in the fluid pressure can lead to stress changes, deformations and failures of the rock mass. In the other hand rock mass stress changes and deformations can alter the hydraulic properties and fluid pressures of the rock mass. Herein well documented case studies focussing on surface subsidence due to water withdrawal, reversible deformations of large-scale valley flanks and failure as well as deformation processes of deep-seated rock slides in fractured rock masses are presented. Due to pore pressure variations HM coupling can lead to predominantly reversible rock mass deformations. Such processes can be considered by the theory of poroelasticity. Surface subsidence reaching magnitudes of few centimetres and are caused by water drainage into deep tunnels are phenomenas which can be assigned to processes of poroelasticity. Recently, particular focus was given on large tunnelling projects to monitor and predict surface subsidence in fractured rock mass in oder to avoid damage of surface structures such as dams of large reservoirs. It was found that surface subsidence due to tunnel drainage can adversely effect infrastructure when pore pressure drawdown is sufficiently large and spatially extended and differential displacements which can be amplified due to topographical effects e.g. valley closure are occurring. Reversible surface deformations were also ascertained on large mountain slopes and summits with the help of precise deformation measurements i.e. permanent GPS or episodic levelling/tacheometric methods. These reversible deformations are often

  16. Fracture mechanics and subcritical crack growth approach to model time-dependent failure in brittle rock

    OpenAIRE

    Rinne, Mikael

    2008-01-01

    Subcritical crack growth (SCG) takes place when a crack is stressed below its short-term strength. This slow fracturing process may lead to an accelerating crack velocity and to a sudden unstable failure event. SCG is thought to play an important role in long-term rock stability at all scales, ranging from laboratory samples to earthquake-generating faults. SCG can be detected as rock loosening or as sudden rock movements around excavations. A time-dependent crack growth model is develop...

  17. The formation of carbon nanostructures by in situ TEM mechanical nanoscale fatigue and fracture of carbon thin films

    Energy Technology Data Exchange (ETDEWEB)

    Wang, J J; Lockwood, A J; Peng, Y; Xu, X; Inkson, B J [Department of Engineering Materials, University of Sheffield, Sheffield S1 3JD (United Kingdom); Bobji, M S, E-mail: beverley.inkson@sheffield.ac.u [Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012, Karnataka (India)

    2009-07-29

    A technique to quantify in real time the microstructural changes occurring during mechanical nanoscale fatigue of ultrathin surface coatings has been developed. Cyclic nanoscale loading, with amplitudes less than 100 nm, is achieved with a mechanical probe miniaturized to fit inside a transmission electron microscope (TEM). The TEM tribological probe can be used for nanofriction and nanofatigue testing, with 3D control of the loading direction and simultaneous TEM imaging of the nano-objects. It is demonstrated that fracture of 10-20 nm thick amorphous carbon films on sharp gold asperities, by a single nanoscale shear impact, results in the formation of <10 nm diameter amorphous carbon filaments. Failure of the same carbon films after cyclic nanofatigue, however, results in the formation of carbon nanostructures with a significant degree of graphitic ordering, including a carbon onion.

  18. Effects of fibre content on mechanical properties and fracture behaviour of short carbon fibre reinforced geopolymer matrix composites

    Indian Academy of Sciences (India)

    Tiesong Lin; Dechang Jia; Meirong Wang; Peigang He; Defu Liang

    2009-02-01

    Geopolymer matrix composites reinforced with different volume fractions of short carbon fibres (Cf/geopolymer composites) were prepared and the mechanical properties, fracture behaviour and microstructure of as-prepared composites were studied and correlated with fibre content. The results show that short carbon fibres have a great strengthening and toughening effect at low volume percentages of fibres (3.5 and 4.5 vol.%). With the increase of fibre content, the strengthening and toughening effect of short carbon fibres reduce, possibly due to fibre damage, formation of high shear stresses at intersect between fibres and strong interface cohesion of fibre/matrix under higher forming pressure. The property improvements are primarily based on the network structure of short carbon fibre preform and the predominant strengthening and toughening mechanisms are attributed to the apparent fibre bridging and pulling-out effect.

  19. Fluid mechanics and rock fracture kinetics of fracture mesh system in tight sand gas reservoirs%致密砂岩气藏缝网系统渗流力学和岩石断裂动力学

    Institute of Scientific and Technical Information of China (English)

    赵海峰; 蒋迪; 石俊

    2016-01-01

    Based on fluid mechanics equations and the Galerkin method,a finite element model has been established to simulate fracture mesh seepage field of horizontal wells volume fracturing,and the relationship between fracture mesh conductivity and production has been studied under different fracture mesh scale.Unlike shale gas,fracture mesh scale is not the bigger the better for tight sand stone gas.It should be maintained in a small-to-medium scale (0.1≤FCI≤0.25) and a high conductivity main fracture is also required.From production-SRV curve,it is found that there exists a critical SRV value (optimal value),and the production increase is significantly smaller when SRV is beyond the critical value.In practice,together with FCI,the critical SRV value can be used to determine cluster spacing and number of clusters in horizontal well fracturing.This paper has studied the process conditions to form small-to-medium scale fracture mesh.An analytic relationship among fracturing fluid pump rate,viscosity,rock dynamic fracture toughness,elastic modulus,Poisson' s ratio,stress,natural fracture parameters and fracture net pressure is given by rock fracture kinetics,and then the optimized pump rate to form small-to-medium scale fracture mesh is determined by dynamic extension conditions on the fracture mesh edge.%基于渗流力学方程和伽辽金法建立水平井体积压裂缝网渗流场的有限元模型,研究了不同缝网形式与规模下产能随缝网导流能力的变化关系,研究发现致密砂岩与页岩不同,压裂的缝网规模并非越大越好,而应该维持在中小规模(0.1≤FCI≤0.25),且需要高导流能力的支撑主缝.在确定了裂缝形态的基础上,计算得到产能与SRV曲线,研究发现存在SRV临界值(优化值),若SRV超出临界值,产能增幅明显变小.在压裂实践中可由SRV临界值和FCI值,确定水平井分段压裂簇间距和簇数之间的关系.研究了形成中小规模缝网对应的施工条件,首先

  20. Galeazzi fracture.

    Science.gov (United States)

    Atesok, Kivanc I; Jupiter, Jesse B; Weiss, Arnold-Peter C

    2011-10-01

    Galeazzi fracture is a fracture of the radial diaphysis with disruption at the distal radioulnar joint (DRUJ). Typically, the mechanism of injury is forceful axial loading and torsion of the forearm. Diagnosis is established on radiographic evaluation. Underdiagnosis is common because disruption of the ligamentous restraints of the DRUJ may be overlooked. Nonsurgical management with anatomic reduction and immobilization in a long-arm cast has been successful in children. In adults, nonsurgical treatment typically fails because of deforming forces acting on the distal radius and DRUJ. Open reduction and internal fixation is the preferred surgical option. Anatomic reduction and rigid fixation should be followed by intraoperative assessment of the DRUJ. Further intraoperative interventions are based on the reducibility and postreduction stability of the DRUJ. Misdiagnosis or inadequate management of Galeazzi fracture may result in disabling complications, such as DRUJ instability, malunion, limited forearm range of motion, chronic wrist pain, and osteoarthritis.