Sample records for elasto-plastic fracture mechanics

  1. A physical mechanism based investigation on the elasto-plastic-damage behavior of anisotropic aluminum alloys under finite deformation

    NASA Astrophysics Data System (ADS)

    Chen, Cen; Liang, NaiGang; Liu, Fang; Fu, Qiang

    2014-03-01

    The elasto-plastic-damage behavior of anisotropic aluminum alloys is investigated under finite deformation using a physical mechanism based constitutive model. With an application to the structural calculation, the present model is used to describe and analyze the mechanical response of anisotropic 6260-T6 aluminum alloy extrusions. For the tensile specimens extracted along three different material orientations from the extruded aluminum profile, twelve simulations are carried out covering four different specimen geometries. The simulation results in force-displacement response and central logarithmic axial strain evolution are compared with experimental results. From the comparisons, it can be concluded that the present model has the capacity to describe the behavior of anisotropic material. From the force-displacement curves, the anisotropy is observed in different material orientations, and the physical mechanism of anisotropy is analyzed.

  2. Mechanics of a contracting reservoir in an elastic half-space with an intervening visco-elasto-plastic layer

    NASA Astrophysics Data System (ADS)

    Mossop, A.; Fredrich, J. T.

    2004-12-01

    The extraction of fluids from porous rocks within the Earth's crust leads to localised volume strains. These in turn induce stress changes and displacements in the surrounding rock mass. The relationships between these processes are governed by the constitutive properties of the rocks. For the case of a poroelastic fluid reservoir in a linear-elastic matrix the mechanics are relatively well known and understood. In this study we extend these models by investigating the case of a contracting rock body (caused by declining pore pressure) embedded within a linear-elastic half space, but with the addition of a visco-elasto-plastic layer between the contracting reservoir and the free surface. The problem is of growing importance as the exploitation of hydrocarbon reservoirs beneath salt bodies occurs at ever greater depths in the deepwater Gulf of Mexico. This is because the creep properties of salt are strongly temperature dependent, so that as depths increase, and hence ambient temperatures, creep can occur at a rate that is impossible to ignore over the reservoir lifecycle. The models are explored using a finite element approach and make use of sophisticated salt constitutive models and large-deformation three-dimensional geomechanical simulation codes; the reservoir deformations are governed by either poro-elastic or cap plasticity constitutive laws. However, a general behaviour pattern can be observed: the visco-elasto-plastic salt layer tends to decouple the deformation fields from the free surface with stress and displacements accentuated below the salt. The magnitude of the increased horizontal displacements below the salt layer are relatively independent of the layer thickness. The accentuated vertical displacements though are more strongly dependent on the thickness of the salt layer. This work was performed at Sandia National Laboratories funded by the US DOE under Contract DE-AC04-94AL85000. Sandia is a multiprogam laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration.

  3. A method to extract the mechanical properties of particles in collision based on a new elasto-plastic normal force–displacement model

    Microsoft Academic Search

    Xiang Zhang; Loc Vu-Quoc

    2002-01-01

    We present a general method to extract the elasto-plastic mechanical properties such as the coefficient of restitution, Young’s modulus, Poisson’s ratio, and the yield stress of granular materials from simple experimental measurements. These mechanical properties are important in the simulation of granular flows, but are not readily available and\\/or cannot be measured through direct experiments. The method developed here is

  4. Electromagnetic Elasto-Plastic Dynamic Response of Conductive Plate

    NASA Astrophysics Data System (ADS)

    Gao, Yuanwen

    2010-05-01

    Electromagnetic elasto-plastic dynamic response of a conductive plate in a magnetic pulse field are studied in this paper, the influence of the strain rate effect is investigated for the electromagnetic elasto-plastic deformation of the conductive plate. Basic governing equations are derived for electromagnetic field (eddy current), the elasto-plastic transient dynamic response and the heat transfer of a conductive rectangular plate, and then an appropriate numerical code is developed based on the finite element method to quantitatively simulate the magneto-elasto-plastic mechanical behaviors of the conductive rectangular plate. The Johnson-Cook model is employed to study the strain rate effect and temperature effect on the deformation of the plate. The dynamic response is explained with some characteristic curves of deformation, the eddy current, and the configurations, the temperature of the conductive plate. The numerical results indicate that the strain rate effect has to be considered for the conductive plates, especially for those with high strain rate sensitivity. Comparison of the influence of the temperature effect on the deformation of the plate with that of the strain rate effect shows that the influence of the temperature effect on the deformation of a plate is not significant.

  5. Elasto-Plastic FEM Stress Analysis and Mechanical Characteristics of Pipe Flange Connections with Non-Asbestos Gaskets under Internal Pressure

    NASA Astrophysics Data System (ADS)

    Takagi, Yoshio; Omiya, Yuya; Kobayashi, Takashi; Sawa, Toshiyuki

    The effects of the nominal diameter of pipe flange connections with non-asbestos spiral wound gaskets(SWG) under internal pressure on the mechanical characteristics such as the contact gasket stress distribution which governs the sealing performance, the load factor and the hub stress of the connections were evaluated. The stresses in the connections with the nominal diameters from 3” to 24” under internal pressure are analyzed using the elasto-plastic(EP) FEM analysis taking account the hysteresis and non-linearity of deformation behavior of the non-asbestos SWG. As a result, it is found that the variations in the contact gasket stress distributions are substantial due to the flange rotation in the connections with the larger nominal diameter. Leakage tests were conducted to measure the axial bolt forces (the load factor) and the hub stress. The results obtained from the EP-FEM analyses are fairly consistent with the experimental results concerning the variation in the axial bolt forces (the load factor) and the hub stress. Using the obtained contact gasket stress distributions and the fundamental relationship between the amount of leakage and the contact gasket stress, the amount of the leakage of the connections is estimated. It is observed that the sealing performance of the connections with larger nominal diameter is worse than that of the connection with smaller nominal diameter because of the flange rotation. The estimated results are in a fairly good agreement with the measured results. The difference in the hub stress between the EP-FEM and ASME code is demonstrated and the differences in the load factor and the sealing performance of the connections are shown between the asbestos and non-asbestos gaskets.

  6. Internal Stress in a Model Elasto-Plastic Fluid

    E-print Network

    Takeshi Ooshida; Ken Sekimoto

    2005-12-03

    Plastic materials can carry memory of past mechanical treatment in the form of internal stress. We introduce a natural definition of the vorticity of internal stress in a simple two-dimensional model of elasto-plastic fluids, which generates the internal stress. We demonstrate how the internal stress is induced under external loading, and how the presence of the internal stress modifies the plastic behavior.

  7. ARMA 10-473 Comparison between elasto-plastic and rigid-plastic cohesive surface

    E-print Network

    Regueiro, Richard A.

    ARMA 10-473 Comparison between elasto-plastic and rigid-plastic cohesive surface elements, CO 80309, U.S.A. Copyright 2010 ARMA, American Rock Mechanics Association This paper was prepared Lake City, UT June 27-30, 2010. This paper was selected for presentation at the symposium by an ARMA

  8. Modelling the Damage Induced by Pressure Transients in ElastoPlastic Pipes

    Microsoft Academic Search

    Felipe B. Freitas Rachid; Heraldo S. Costa Mattos

    1998-01-01

    This paper is concerned with the analysis of pressure transients in damageable elasto-plastic piping systems. The fluid dynamics and pipewall deformation are modelled by the classical water hammer theory, whereas pipewall mechanical behavior is described by an internal variable constitutive theory. The constitutive model coupling plasticity and damage used herein gives rise to a nonlinear hyperbolic problem in which the

  9. FE modeling of thermo-elasto-plastic finite deformation and its application in sheet warm forming

    Microsoft Academic Search

    H. L. Xing; A. Makinouchi

    2002-01-01

    In this paper, a strategy for analyzing a problem of the transient thermal coupling with the elastoplastic finite deformation is presented. A general constitutive equation is deduced by assuming the material properties to be temperature-dependent. The thermal and mechanical coupling problem is solved with a staggered algorithm, which partitions the coupled problem into an elasto-plastic problem at the known temperature

  10. Identification of rock mass properties in elasto-plasticity

    Microsoft Academic Search

    Desheng Deng; Duc Nguyen-Minh

    2003-01-01

    A simple and effective back analysis method has been proposed on the basis of a new criterion of identification, the minimization of error on the virtual work principle. This method works for both linear elastic and nonlinear elasto-plastic problems. The elasto-plastic rock mass properties for different criteria of plasticity can be well identified based on field measurements.

  11. Elasto-plastic contact between rollers

    NASA Astrophysics Data System (ADS)

    Chu, Kunliang; Li, Penghui

    1991-12-01

    Knowledge of the three-dimensional contact stress between roller and rolling road for a strain- hardening material in an elasto-plastic state is limited, to say the least. Mathematical analyses of stress for this problem meet with extreme difficulties. Therefore, experimental approaches are desirable. The experimental elasto-plastic stress analysis method proposed by A. R. Hunter is extended in this investigation. The model material is epoxy resin, which exhibits a frozen nonlinear effective stress-strain behavior similar to that of bearing steel when subjected to a thermal cycle whose maximum temperature is significantly less than the critical temperature of the material. This effective stress-strain curve and an effective birefringence- stress curve were obtained by subjecting uniaxial tensile specimens to constant stress and the appropriate thermal cycle. Then the model was subjected to the same thermal cycle and a uniform distributed load that would develop a plastic zone. The stress distributions on the contact surface and the plastic-zone expansion law were obtained from photomechanical analysis of the slices removed from the model. Several important conclusions were summed up that would greatly improve the roller bearing design.

  12. Coupled THM processes in EDZ of crystalline rocks using an elasto-plastic cellular automaton

    NASA Astrophysics Data System (ADS)

    Pan, Peng-Zhi; Feng, Xia-Ting; Huang, Xiao-Hua; Cui, Qiang; Zhou, Hui

    2009-05-01

    This paper aims at a numerical study of coupled thermal, hydrological and mechanical processes in the excavation disturbed zones (EDZ) around nuclear waste emplacement drifts in fractured crystalline rocks. The study was conducted for two model domains close to an emplacement tunnel; (1) a near-field domain and (2) a smaller wall-block domain. Goodman element and weak element were used to represent the fractures in the rock mass and the rock matrix was represented as elasto-visco-plastic material. Mohr-Coulomb criterion and a non-associated plastic flow rule were adopted to consider the viscoplastic deformation in the EDZ. A relation between volumetric strain and permeability was established. Using a self-developed EPCA2D code, the elastic, elasto-plastic and creep analyses to study the evolution of stress and deformations, as well as failure and permeability evolution in the EDZ were conducted. Results indicate a strong impact of fractures, plastic deformation and time effects on the behavior of EDZ especially the evolution of permeability around the drift.

  13. Investigation of Optimal Seismic Design Methodology for Piping Systems Supported by Elasto-plastic Dampers

    NASA Astrophysics Data System (ADS)

    Ito, Tomohiro; Michiue, Masashi; Fujita, Katsuhisa

    In this study, the applicability of a previously developed optimal seismic design methodology, which can consider the structural integrity of not only piping systems but also elasto-plastic supporting devices, is studied for seismic waves with various frequency characteristics. This methodology employs a genetic algorithm and can search the optimal conditions such as the supporting location and the capacity and stiffness of the supporting devices. Here, a lead extrusion damper is treated as a typical elasto-plastic damper. Numerical simulations are performed using a simple piping system model. As a result, it is shown that the proposed optimal seismic design methodology is applicable to the seismic design of piping systems subjected to seismic waves with various frequency characteristics. The mechanism of optimization is also clarified.

  14. Inverse approach to identification of material parameters of cyclic elasto-plasticity for component layers of a bimetallic sheet

    Microsoft Academic Search

    F. Yoshida; M. Urabe; R. Hino; V. V. Toropov

    2003-01-01

    The present paper proposes a novel approach to the identification of the mechanical properties of individual component layers of a bimetallic sheet. In this approach, a set of material parameters in a constitutive model of cyclic elasto-plasticity are identified for the two layers of the sheet simultaneously by minimizing the difference between the experimental results and the corresponding results of

  15. LaMEM: a Massively Parallel Staggered-Grid Finite-Difference Code for Thermo-Mechanical Modeling of Lithospheric Deformation with Visco-Elasto-Plastic Rheologies

    NASA Astrophysics Data System (ADS)

    Kaus, B.; Popov, A.

    2014-12-01

    The complexity of lithospheric rheology and the necessity to resolve the deformation patterns near the free surface (faults and folds) sufficiently well places a great demand on a stable and scalable modeling tool that is capable of efficiently handling nonlinearities. Our code LaMEM (Lithosphere and Mantle Evolution Model) is an attempt to satisfy this demand. The code utilizes a stable and numerically inexpensive finite difference discretization with the spatial staggering of velocity, pressure, and temperature unknowns (a so-called staggered grid). As a time discretization method the forward Euler, or a combination of the predictor-corrector and the fourth-order Runge-Kutta can be chosen. Elastic stresses are rotated on the markers, which are also used to track all relevant material properties and solution history fields. The Newtonian nonlinear iteration, however, is handled at the level of the grid points to avoid spurious averaging between markers and grid. Such an arrangement required us to develop a non-standard discretization of the effective strain-rate second invariant. Important feature of the code is its ability to handle stress-free and open-box boundary conditions, in which empty cells are simply eliminated from the discretization, which also solves the biggest problem of the sticky-air approach - namely large viscosity jumps near the free surface. We currently support an arbitrary combination of linear elastic, nonlinear viscous with multiple creep mechanisms, and plastic rheologies based on either a depth-dependent von Mises or pressure-dependent Drucker-Prager yield criteria.LaMEM is being developed as an inherently parallel code. Structurally all its parts are based on the building blocks provided by PETSc library. These include Jacobian-Free Newton-Krylov nonlinear solvers with convergence globalization techniques (line search), equipped with different linear preconditioners. We have also implemented the coupled velocity-pressure multigrid prolongation and restriction operators specific for staggered grid discretization. The capabilities of the code are demonstrated with a set of geodynamically-relevant benchmarks and example problems on parallel computers.This project is funded by ERC Starting Grant 258830

  16. An Elasto-Plastic Model of Avian Gastrulation

    PubMed Central

    2005-01-01

    The motions observed during avian gastrulation may be simply interpreted in terms of elasto-plastic flow of sheets. Such a model allows one to calculate the flow map inside the blastodisc, hence the evolution of its shape. In addition, the model predicts that there exists a region of high stress oriented radially from the caudal pole towards the center of the blastodisc, with a tensile component oriented orthoradially. If the stress generated by cellular motion is enough to provoke a crack in the extra cellular matrix, then mesoderm ingression proceeds through a “streak” (the primitive streak) oriented from the caudal pole inwards, which relieves the stress while it creates the three germ layers. The model predicts that crack opening is next followed by crack retreat (primitive streak retreat), as mesoderm ingression continues. As mesoderm ingression proceeds around the area pellucida, similar phenomena in the anterior pole may contribute to formation of the embryo. This gives a mechanical description of avian gastrulation which complements the biochemical approach. In addition, the model provides a simple explanation to the shape of the embryo at very early stages, and possibly an explanation of the entry point of the vitteline arteries into the mesoderm. PMID:19521523

  17. Micropillar Compression Technique Applied to Micron-Scale Mudstone Elasto-Plastic Deformation

    NASA Astrophysics Data System (ADS)

    Dewers, T. A.; Boyce, B.; Buchheit, T.; Heath, J. E.; Chidsey, T.; Michael, J.

    2010-12-01

    Mudstone mechanical testing is often limited by poor core recovery and sample size, preservation and preparation issues, which can lead to sampling bias, damage, and time-dependent effects. A micropillar compression technique, originally developed by Uchic et al. 2004, here is applied to elasto-plastic deformation of small volumes of mudstone, in the range of cubic microns. This study examines behavior of the Gothic shale, the basal unit of the Ismay zone of the Pennsylvanian Paradox Formation and potential shale gas play in southeastern Utah, USA. Precision manufacture of micropillars 5 microns in diameter and 10 microns in length are prepared using an ion-milling method. Characterization of samples is carried out using: dual focused ion - scanning electron beam imaging of nano-scaled pores and distribution of matrix clay and quartz, as well as pore-filling organics; laser scanning confocal (LSCM) 3D imaging of natural fractures; and gas permeability, among other techniques. Compression testing of micropillars under load control is performed using two different nanoindenter techniques. Deformation of 0.5 cm in diameter by 1 cm in length cores is carried out and visualized by a microscope loading stage and laser scanning confocal microscopy. Axisymmetric multistage compression testing and multi-stress path testing is carried out using 2.54 cm plugs. Discussion of results addresses size of representative elementary volumes applicable to continuum-scale mudstone deformation, anisotropy, and size-scale plasticity effects. Other issues include fabrication-induced damage, alignment, and influence of substrate. This work is funded by the US Department of Energy, Office of Basic Energy Sciences. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

  18. ElastoPlastic Failure Analysis of Composite Bolted Joints

    Microsoft Academic Search

    Yoshifumi Tsujimoto; Dale Wilson

    1986-01-01

    An elasto-plastic finite element analysis of pin loaded joints in laminated composites has been investigated and comparisons made with both existing 2-D linear elastic plane stress analytical solutions and experimental results for a graphite\\/epoxy laminate. The finite element analysis included nonlinear material behavior after initial failure by assuming an elastic-perfectly plastic bimodular material model. Laminated plate theory was used to

  19. LaMEM: a massively parallel 3D staggered-grid finite-difference code for coupled nonlinear themo-mechanical modeling of lithospheric deformation with visco-elasto-plastic rheology

    NASA Astrophysics Data System (ADS)

    Popov, Anton; Kaus, Boris

    2015-04-01

    This software project aims at bringing the 3D lithospheric deformation modeling to a qualitatively different level. Our code LaMEM (Lithosphere and Mantle Evolution Model) is based on the following building blocks: * Massively-parallel data-distributed implementation model based on PETSc library * Light, stable and accurate staggered-grid finite difference spatial discretization * Marker-in-Cell pedictor-corector time discretization with Runge-Kutta 4-th order * Elastic stress rotation algorithm based on the time integration of the vorticity pseudo-vector * Staircase-type internal free surface boundary condition without artificial viscosity contrast * Geodynamically relevant visco-elasto-plastic rheology * Global velocity-pressure-temperature Newton-Raphson nonlinear solver * Local nonlinear solver based on FZERO algorithm * Coupled velocity-pressure geometric multigrid preconditioner with Galerkin coarsening Staggered grid finite difference, being inherently Eulerian and rather complicated discretization method, provides no natural treatment of free surface boundary condition. The solution based on the quasi-viscous sticky-air phase introduces significant viscosity contrasts and spoils the convergence of the iterative solvers. In LaMEM we are currently implementing an approximate stair-case type of the free surface boundary condition which excludes the empty cells and restores the solver convergence. Because of the mutual dependence of the stress and strain-rate tensor components, and their different spatial locations in the grid, there is no straightforward way of implementing the nonlinear rheology. In LaMEM we have developed and implemented an efficient interpolation scheme for the second invariant of the strain-rate tensor, that solves this problem. Scalable efficient linear solvers are the key components of the successful nonlinear problem solution. In LaMEM we have a range of PETSc-based preconditioning techniques that either employ a block factorization of the velocity-pressure matrix, or treat it as a monolithic piece. In particular we have implemented the custom restriction-interpolation operators for the coupled Galerkin multigrid preconditioner. We have found that this type of algorithm is very robust with respect to the high grid resolutions and realistic viscosity variations. The coupled Galerking geometric multigrid implemented with the custom restriction-interpolation operators currently enables LaMEM to run efficiently with the grid sizes up to 1000-cube cells on the IBM Blue Gene/Q machines. This project is funded by ERC Starting Grant 258830 Computer facilities are provided by Jülich supercomputer center (Germany)

  20. A new thermo-elasto-plasticity constitutive theory for polycrystalline metals

    NASA Astrophysics Data System (ADS)

    Chen, Cen; Tang, Qiheng; Wang, Tzuchiang

    2015-06-01

    In this study, the behavior of polycrystalline metals at different temperatures is investigated by a new thermo-elasto-plasticity constitutive theory. Based on solid mechanical and interatomic potential, the constitutive equation is established using a new decomposition of the deformation gradient. For polycrystalline copper and magnesium, the stress-strain curves from 77 to 764 K (copper), and 77 to 870 K (magnesium) under quasi-static uniaxial loading are calculated, and then the calculated results are compared with the experiment results. Also, it is determined that the present model has the capacity to describe the decrease of the elastic modulus and yield stress with the increasing temperature, as well as the change of hardening behaviors of the polycrystalline metals. The calculation process is simple and explicit, which makes it easy to implement into the applications.

  1. Modelling and computation of instability phenomena in multisurface elasto-plasticity

    Microsoft Academic Search

    E. Sawischlewski; P. Steinmann; E. Stein

    1996-01-01

    This contribution is concerned with theoretical and numerical aspects of instability phenomena in multisurface elasto-plasticity which is the adequate constitutive framework for e.g. single crystal plasticity. To this end, the localization analysis for multisurface elasto-plasticity based on the additive decomposition of the geometrically linearized strain tensor is considered and the characteristic differences and similarities to the wellknown single surface case

  2. On a Paradox of Elasto-Plastic Tunnel Analysis

    NASA Astrophysics Data System (ADS)

    Cantieni, L.; Anagnostou, G.

    2011-03-01

    Elasto-plastic tunnel analysis may produce a paradox in the calculation of ground pressure whereby ground pressures appear to increase in relation to higher ground quality. More specifically, for an overstressed ground in combination with a stiff support, analysis may indicate greater loading of the support with a ground of high strength than with a ground of low strength (all of the other parameters being equal). This counter-intuitive outcome appears in all of the common calculation models (analytical plane strain analysis, numerical plane strain analysis and numerical axisymmetric analysis), although it does not correspond either to the ground behaviour that is intuitively expected or to ground behaviour observed in the field, thus raising doubts over the predictive power of common tunnel design calculations. The present paper discusses the assumptions made in the models that are responsible for the paradox: the assumption that ground behaviour is time-independent (whereas in reality overstressed ground generally creeps) and the assumption that the support operates with full stiffness close to the face (which is not feasible in reality due to the nature of construction procedures). When proper account is taken of either or both of these assumptions in more advanced models, the paradox disappears. As the models which generate the paradox are very commonly used in engineering and scientific practice, the investigations of the present paper may be of value, helping the engineer to understand the uncertainties inherent in the models and to arrive at a better interpretation of the results they produce.

  3. Investigation of Optimal Seismic Design Methodology for Piping Systems Supported by Elasto-Plastic Dampers

    NASA Astrophysics Data System (ADS)

    Ito, Tomohiro; Michiue, Masashi; Fujita, Katsuhisa

    In this study, the optimal seismic design methodology that can consider the structural integrity of not only the piping systems but also elasto-plastic supporting devices is developed. This methodology employs a genetic algorithm and can search the optimal conditions such as the supporting location, capacity and stiffness of the supporting devices. Here, a lead extrusion damper is treated as a typical elasto-plastic damper. Four types of evaluation functions are considered. It is found that the proposed optimal seismic design methodology is very effective and can be applied to the actual seismic design for piping systems supported by elasto-plastic dampers. The effectiveness of the evaluation functions is also clarified.

  4. Polycarbonate as an elasto-plastic material model for simulation of the microstructure hot imprint process.

    PubMed

    Narijauskait?, Birut?; Palevi?ius, Arvydas; Gaidys, Rimvydas; Janušas, Giedrius; Sakalys, Rokas

    2013-01-01

    The thermal imprint process of polymer micro-patterning is widely applied in areas such as manufacturing of optical parts, solar energy, bio-mechanical devices and chemical chips. Polycarbonate (PC), as an amorphous polymer, is often used in thermoforming processes because of its good replication characteristics. In order to obtain replicas of the best quality, the imprint parameters (e.g., pressure, temperature, time, etc.) must be determined. Therefore finite element model of the hot imprint process of lamellar periodical microstructure into PC has been created using COMSOL Multiphysics. The mathematical model of the hot imprint process includes three steps: heating, imprinting and demolding. The material properties of amorphous PC strongly depend on the imprint temperature and loading pressure. Polycarbonate was modelled as an elasto-plastic material, since it was analyzed below the glass transition temperature. The hot imprint model was solved using the heat transfer and the solid stress-strain application modes with thermal contact problem between the mold and polycarbonate. It was used for the evaluation of temperature and stress distributions in the polycarbonate during the hot imprint process. The quality of the replica, by means of lands filling ratio, was determined as well. PMID:23974153

  5. A posteriori error estimation and mesh adaptation for finite element models in elasto-plasticity

    Microsoft Academic Search

    Rolf Rannacher; Franz-Theo Suttmeier

    1999-01-01

    A new approach to a posteriori error estimation and adaptive mesh design based on techniques from optimal control is presented for primal-mixed finite element models in elasto-plasticity. This method uses global duality arguments for deriving weighted a posteriori error bounds for arbitrary functionals of the error representing physical quantities of interest. In these estimates local residuals of the computed solution

  6. Elasto-plastic analysis of interface layers for fiber reinforced metal matrix composites

    NASA Technical Reports Server (NTRS)

    Doghri, I.; Leckie, F. A.

    1991-01-01

    The mismatch in coefficients of thermal expansion (CTE) of fiber and matrix in metal matrix composites reinforced with ceramic fibers induces high thermal stresses in the matrix. Elasto-plastic analyses - with different degrees of simplification and modelization - show that an interface layer with a sufficiently high CTE can reduce the tensile hoop stress in the matrix substantially.

  7. Elasto-plastic analysis of interface layers for fiber reinforced metal matrix composites. Final Report

    SciTech Connect

    Doghri, I.; Leckie, F.A.

    1991-06-01

    The mismatch in coefficients of thermal expansion (CTE) of fiber and matrix in metal matrix composites reinforced with ceramic fibers induces high thermal stresses in the matrix. Elasto-plastic analyses - with different degrees of simplification and modelization - show that an interface layer with a sufficiently high CTE can reduce the tensile hoop stress in the matrix substantially.

  8. Critical state elasto-plastic constitutive models for soil failure in tillage - A review

    Microsoft Academic Search

    S. Karmakar; J. Sharma; R. L. Kushwaha

    2004-01-01

    On the other hand, if a particular stress path puts the stress state of the soil on or outside the yield locus, plastic or irrecoverable deformation of soil occurs. Elasto-plastic constitutive models help distinguish between the recoverable and irrecoverable deformations for understanding the stress strain behaviour of soil during loading and unloading. Kushwaha and Shen (1994) reported that a substantial

  9. ElastoPlastic Fatigue Life Improvement of Bolted Joints and Introducing FBI Method

    Microsoft Academic Search

    Peyman Honarmandi; Jean W. Zu; Kamran Behdinan

    2005-01-01

    The failures of bolted joints, which are the basic and popular fasteners in industry, are mostly due to fatigue. This paper presents an effective method to improve the elasto-plastic fatigue life of a bolt. A complete bolted joint is considered and modeled with the finite element approach to calculate stress and strain. The code based on crack initiation theory is

  10. Modeling subduction megathrust earthquakes: Insights from a visco-elasto-plastic analog model

    NASA Astrophysics Data System (ADS)

    Dominguez, Stéphane; Malavieille, Jacques; Mazzotti, Stéphane; Martin, Nicolas; Caniven, Yannick; Cattin, Rodolphe; Soliva, Roger; Peyret, Michel; Lallemand, Serge

    2015-04-01

    As illustrated recently by the 2004 Sumatra-Andaman or the 2011 Tohoku earthquakes, subduction megathrust earthquakes generate heavy economic and human losses. Better constrain how such destructive seismic events nucleate and generate crustal deformations represents a major societal issue but appears also as a difficult scientific challenge. Indeed, several limiting factors, related to the difficulty to analyze deformation undersea, to access deep source of earthquake and to integrate the characteristic time scales of seismic processes, must be overcome first. With this aim, we have developed an experimental approach to complement numerical modeling techniques that are classically used to analyze available geological and geophysical observations on subduction earthquakes. Objectives were to design a kinematically and mechanically first-order scaled analogue model of a subduction zone capable of reproducing megathrust earthquakes but also realistic seismic cycle deformation phases. The model rheology is based on multi-layered visco-elasto-plastic materials to take into account the mechanical behavior of the overriding lithospheric plate. The elastic deformation of the subducting oceanic plate is also simulated. The seismogenic zone is characterized by a frictional plate interface whose mechanical properties can be adjusted to modify seismic coupling. Preliminary results show that this subduction model succeeds in reproducing the main deformation phases associated to the seismic cycle (interseismic elastic loading, coseismic rupture and post-seismic relaxation). By studying model kinematics and mechanical behavior, we expect to improve our understanding of seismic deformation processes and better constrain the role of physical parameters (fault friction, rheology, ...) as well as boundary conditions (loading rate,...) on seismic cycle and megathrust earthquake dynamics. We expect that results of this project will lead to significant improvement on interpretation of geophysical data, satellite observations and seismological records.

  11. Theoretical and numerical aspects of fluid-saturated elasto-plastic soils

    SciTech Connect

    Ehlers, W. [Technische Hochschule Darmstadt (Germany)

    1995-12-31

    The theoretical and numerical treatment of fluid-saturated porous solid materials generally falls into the category of porous media models, which are described within the framework of the classical theory of mixtures extended by the concept of volume fractions (porous media theories). In particular, this concept allows for the description of saturated, unsaturated and empty porous matrix materials, thus offering a well-founded theoretical background for a lot of engineering problems occurring, for instance, in the fields of geomechanics (soil and rock mechanics as well as glacier and rock ice mechanics), oil producing industries, sintering technologies, biomechanics, etc. In the present contribution, theoretical and numerical studies are outlined to describe a two-phase material composed of an incompressible elasto-plastic soil matrix saturated by an incompressible viscous pore fluid. In this context, the phenomenon of phase incompressibility is well known as a microscopic effect not implying bulk incompressibility in the macro regime. This is seen from the fact that even if the material density functions of the individual constituents are constant during deformation, the corresponding bulk densities can still change through changes in the volume fractions. Within the framework of a pure mechanical theory, constitutive equations are given for both the solid and the fluid partial stress tensors and for the interaction force acting between the two materials. Concerning the porous soil matrix, the elastic properties are described by an elasticity law of Hookean type, while the plastic range is governed by a {open_quote}single surface{close_quote} yield function exhibiting a smooth and closed shape in the principal stress space together with a non-associated flow rule. The viscosity effects of the pore fluid are included in the fluid stress tensor and in the drag force.

  12. A 6-node co-rotational triangular elasto-plastic shell element

    NASA Astrophysics Data System (ADS)

    Li, Zhongxue; Xiang, Yu; Izzuddin, Bassam A.; Vu-Quoc, Loc; Zhuo, Xin; Zhang, Chuanjie

    2015-03-01

    A 6-node co-rotational triangular elasto-plastic shell element is developed. The local coordinate system of the element is defined by the vectors directing from one vertex to the other two vertices and their cross product. Based on such a co-rotational framework, the element rigid-body rotations are excluded in calculating the local nodal variables from the global nodal variables. The two smallest components of each nodal orientation vector are defined as rotational variables, resulting in the desired additive property for all nodal variables in a nonlinear incremental solution procedure. Different from other existing co-rotational finite element formulations, both the element tangent stiffness matrices in the local and in the global coordinate systems are symmetric owing to the commutativity of the nodal variables in calculating the second derivatives of the strain energy with respect to the local nodal variables and, through chain differentiation, with respect to the global nodal variables. For elasto-plastic analysis, the Maxwell-Huber-Hencky-von Mises yield criterion is employed together with the backward-Euler return-mapping method for the evaluation of the elasto-plastic stress state, where a consistent tangent modulus matrix is employed. To overcome locking problems, the assumed linear membrane strains and shear strains are obtained by using the line integration method proposed by MacNeal, and the assumed higher-order membrane strains are obtained by enforcing the stationarity of the mixed displacement-strain canonical functional, these assumed strains are then employed to replace the corresponding conforming strains. The reliability and convergence of the present 6-node triangular shell element formulation are verified through two elastic plate patch tests as well as two elastic and five elasto-plastic plate/shell problems undergoing large displacements and large rotations.

  13. Approximate local elasto-plastic solution for notched plates undergoing cyclic tensile loading

    Microsoft Academic Search

    H. S. da Costa Mattos; Paulo F. Soares Filho

    2010-01-01

    This work presents a simple methodology to estimate the inelastic stress and strain histories at the root of the notch of a thin elasto-plastic plate undergoing any complex non-monotonic tensile loading. It is proposed an extension of the classical Neuber and Linear projection rules to the case of non-monotonic loading. Using such extended projection techniques, the stress–strain curve at the

  14. A new multilayered visco-elasto-plastic experimental model to study strike-slip fault seismic cycle

    NASA Astrophysics Data System (ADS)

    Caniven, Y.; Dominguez, S.; Soliva, R.; Cattin, R.; Peyret, M.; Marchandon, M.; Romano, C.; Strak, V.

    2015-02-01

    Nowadays, technological advances in satellite imagery measurements as well as the development of dense geodetic and seismologic networks allow for a detailed analysis of surface deformation associated with active fault seismic cycle. However, the study of earthquake dynamics faces several limiting factors related to the difficulty to access the deep source of earthquake and to integrate the characteristic time scales of deformation processes that extend from seconds to thousands of years. To overcome part of these limitations and better constrain the role and couplings between kinematic and mechanical parameters, we have developed a new experimental approach allowing for the simulation of strike-slip fault earthquakes and analyze in detail hundreds of successive seismic cycle. Model rheology is made of multilayered visco-elasto-plastic analog materials to account for the mechanical behavior of the upper and lower crust and to allow simulating brittle/ductile coupling, postseismic deformation phase and far-field stress transfers. The kinematic evolution of the model surface is monitored using an optical system, based on subpixel spectral correlation of high-resolution digital images. First, results show that the model succeed in reproducing the deformation mechanisms and surface kinematics associated to the main phases of the seismic cycle indicating that model scaling is satisfactory. These results are comforted by using numerical algorithms to study the strain and stress distribution at the surface and at depth, along the fault plane. Our analog modeling approach appears, then, as an efficient complementary approach to investigate earthquake dynamics.

  15. A review of developments in the theory of elasto-plastic flow

    NASA Technical Reports Server (NTRS)

    Swedlow, J. L.

    1973-01-01

    The theory of elasto-plastic flow is developed so that it may accommodate features such as work-hardening, anisotropy, plastic compressibility, non-continuous loading including local or global unloading, and others. A complete theory is given in quasi-linear form; as a result, many useful attributes are accessible. Several integral theorems may be written, finite deformations may be incorporated, and efficient methods for solving problems may be developed; these and other aspects are described in some detail. The theory is reduced to special forms for 2-space, and extensive experience in solving such problems is cited.

  16. A variational formulation for the incremental homogenization of elasto-plastic composites

    NASA Astrophysics Data System (ADS)

    Brassart, L.; Stainier, L.; Doghri, I.; Delannay, L.

    2011-12-01

    This work addresses the micro-macro modeling of composites having elasto-plastic constituents. A new model is proposed to compute the effective stress-strain relation along arbitrary loading paths. The proposed model is based on an incremental variational principle (Ortiz, M., Stainier, L., 1999. The variational formulation of viscoplastic constitutive updates. Comput. Methods Appl. Mech. Eng. 171, 419-444) according to which the local stress-strain relation derives from a single incremental potential at each time step. The effective incremental potential of the composite is then estimated based on a linear comparison composite (LCC) with an effective behavior computed using available schemes in linear elasticity. Algorithmic elegance of the time-integration of J 2 elasto-plasticity is exploited in order to define the LCC. In particular, the elastic predictor strain is used explicitly. The method yields a homogenized yield criterion and radial return equation for each phase, as well as a homogenized plastic flow rule. The predictive capabilities of the proposed method are assessed against reference full-field finite element results for several particle-reinforced composites.

  17. Formation stability after hydraulic fracturing

    Microsoft Academic Search

    Panos Papanastasiou

    1999-01-01

    This paper investigates stress changes resulting from fracturing in a weak formation and estimates the reduced risk of formation failure. The analysis is based on fracture propagation and closure of a plane strain elasto-plastic fracture. It is shown that during fracture propagation the area near the fracture tip undergoes plastic deformation, with the result that the in situ stresses there

  18. Elastic and Elasto-Plastic Analysis of Gravity Dam-Foundation System without and with Shear Seams

    E-print Network

    Kumar, M. Jagadesh

    Elastic and Elasto-Plastic Analysis of Gravity Dam-Foundation System without and with Shear Seams hydro-power potential has been harnessed. Dams form a major component of a hydro-power project and apply. The interaction of the dam with the foundation, especially one with difficult or troublesome geology, needs

  19. An accurate elasto-plastic frictional tangential force displacement model for granular-flow simulations: Displacement-driven formulation

    NASA Astrophysics Data System (ADS)

    Zhang, Xiang; Vu-Quoc, Loc

    2007-07-01

    We present in this paper the displacement-driven version of a tangential force-displacement (TFD) model that accounts for both elastic and plastic deformations together with interfacial friction occurring in collisions of spherical particles. This elasto-plastic frictional TFD model, with its force-driven version presented in [L. Vu-Quoc, L. Lesburg, X. Zhang. An accurate tangential force-displacement model for granular-flow simulations: contacting spheres with plastic deformation, force-driven formulation, Journal of Computational Physics 196(1) (2004) 298-326], is consistent with the elasto-plastic frictional normal force-displacement (NFD) model presented in [L. Vu-Quoc, X. Zhang. An elasto-plastic contact force-displacement model in the normal direction: displacement-driven version, Proceedings of the Royal Society of London, Series A 455 (1991) 4013-4044]. Both the NFD model and the present TFD model are based on the concept of additive decomposition of the radius of contact area into an elastic part and a plastic part. The effect of permanent indentation after impact is represented by a correction to the radius of curvature. The effect of material softening due to plastic flow is represented by a correction to the elastic moduli. The proposed TFD model is accurate, and is validated against nonlinear finite element analyses involving plastic flows in both the loading and unloading conditions. The proposed consistent displacement-driven, elasto-plastic NFD and TFD models are designed for implementation in computer codes using the discrete-element method (DEM) for granular-flow simulations. The model is shown to be accurate and is validated against nonlinear elasto-plastic finite-element analysis.

  20. Exact Integration Of Uniaxial Elasto-Plastic Laws For Nonlinear Structural Analysis

    SciTech Connect

    Marmo, Francesco; Rosati, Luciano; Sessa, Salvatore [Dipartimento di Ingegneria Strutturale, Universita degli Studi di Napoli, Federico II, Via Claudio 21, 80125, Napoli (Italy)

    2008-07-08

    The recently formulated fiber-free approach [1,2] is used for the analytical integration of non-linear elastic and elasto-plastic normal stresses acting on beam cross sections. It is based on the subdivision of the section in suitable subdomains, which are updated during the analysis of the structural model, and the use of analytical formulas which require the constitutive law to be integrated four times as a maximum. In particular we illustrate the application of the fiber-free approach to the well known concrete model by Mander et al. [3] since its expression belongs to the set of countinous functions which do not admit a primitive. Some representative numerical tests highlight the correctness and the computational efficiency of the fiber-free approach with repsect to the traditional fiber approach, to date the only existing method to perform a non-linear sectional analysis.

  1. A highly accurate brick element based on a three-field variational principle for elasto-plastic analysis

    Microsoft Academic Search

    Yan P. Cao; N. Hu; H. Fukunaga; J. Lu; Zhen H. Yao

    2003-01-01

    In this paper, a penalty equilibrating 3-D mixed element based on a modified Hu–Washizu variational functional has been proposed to improve the accuracy of the elasto-plastic analysis for irregular meshes. In order to construct this element, a penalty term, which can enforce the stress components to satisfy the equilibrium equations in a weak form, is introduced into the Hu–Washizu three-field

  2. Dynamic quantized fracture mechanics

    Microsoft Academic Search

    N. M. Pugno; R. S. Ruoff

    2006-01-01

    A new quantum action-based theory, dynamic quantized fracture mechanics (DQFM), is presented that modifies continuum-based\\u000a dynamic fracture mechanics (DFM). The crack propagation is assumed as quantized in both space and time. The static limit case\\u000a corresponds to quantized fracture mechanics (QFM), that we have recently developed to predict the strength of nanostructures.\\u000a DQFM predicts the well-known forbidden strength and crack

  3. Quantized fracture mechanics

    Microsoft Academic Search

    Nicola M. Pugno; Rodney S. Ruoff

    2004-01-01

    A new energy-based theory, quantized fracture mechanics (QFM), is presented that modifies continuum-based fracture mechanics; stress- and strain-based QFM analogs are also proposed. The differentials in Griffith's criterion are substituted with finite differences; the implications are remarkable. Fracture of tiny systems with a given geometry and type of loading occurs at ‘quantized’ stresses that are well predicted by QFM: strengths

  4. Quantized fracture mechanics

    Microsoft Academic Search

    Nicola M. Pugno; Rodney S. Ruoff

    2004-01-01

    A new energy-based theory, quantized fracture mechanics (QFM), is presented that modifies continuum-based fracture mechanics; stress- and strain-based QFM analogs are also proposed. The differentials in Griffith's criterion are substituted with finite differences; the implications are remarkable. Fracture of tiny systems with a given geometry and type of loading occurs at 'quantized' stresses that are well predicted by QFM: strengths

  5. Quantized fracture mechanics

    NASA Astrophysics Data System (ADS)

    Pugno, Nicola M.; Ruoff, Rodney S.

    2004-09-01

    A new energy-based theory, quantized fracture mechanics (QFM), is presented that modifies continuum-based fracture mechanics; stress- and strain-based QFM analogs are also proposed. The differentials in Griffith's criterion are substituted with finite differences; the implications are remarkable. Fracture of tiny systems with a given geometry and type of loading occurs at 'quantized' stresses that are well predicted by QFM: strengths predicted by QFM are compared with experimental results on carbon nanotubes, ?-SiC nanorods, ?-Si3N4 whiskers, and polysilicon thin films; and also with molecular mechanics/dynamics simulation of fracture of carbon nanotubes and graphene with cracks and holes, and statistical mechanics-based simulations on fracture of two-dimensional spring networks. QFM is self-consistent, agreeing to first-order with linear elastic fracture mechanics (LEFM), and to second-order with non-linear fracture mechanics (NLFM). For vanishing crack length QFM predicts a finite ideal strength in agreement with Orowan's prediction. In contrast to LEFM, QFM has no restrictions on treating defect size and shape. The different fracture Modes (opening I, sliding II and tearing III), and the stability of the fracture propagations, are treated in a simple way.

  6. The Effective Fracture Toughness in Hydraulic Fracturing

    Microsoft Academic Search

    Panos Papanastasiou

    1999-01-01

    This paper examines the effective fracture toughness approach which is used in hydraulic fracturing in order to explain the\\u000a high net-pressures that are often observed in field operations. The effective fracture toughness is calculated using a fully\\u000a deterministic elasto-plastic hydraulic fracturing model. Rock is modelled by Mohr–Coulomb flow theory of plasticity for cohesive-frictional\\u000a dilatant material. Fluid flow is modelled by

  7. Comparison of isotropic elasto-plastic models for the plastic metric tensor $C_p=F_p^T\\, F_p$

    E-print Network

    Patrizio Neff; Ionel-Dumitrel Ghiba

    2014-10-08

    We discuss in detail existing isotropic elasto-plastic models based on 6-dimensional flow rules for the positive definite plastic metric tensor $C_p=F_p^T\\, F_p$ and highlight their properties and interconnections. We show that seemingly different models are equivalent in the isotropic case.

  8. Elasto-plastic bending of cracked plates, including the effects of crack closure. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Jones, D. P.

    1972-01-01

    A capability for solving elasto-plastic plate bending problems is developed using assumptions consistent with Kirchhoff plate theory. Both bending and extensional modes of deformation are admitted with the two modes becoming coupled as yielding proceeds. Equilibrium solutions are obtained numerically by determination of the stationary point of a functional which is analogous to the potential strain energy. The stationary value of the functional for each load increment is efficiently obtained through use of the conjugate gradient. This technique is applied to the problem of a large centrally through cracked plate subject to remote circular bending. Comparison is drawn between two cases of the bending problem. The first neglects the possibility of crack face interference with bending, and the second includes a kinematic prohibition against the crack face from passing through the symmetry plane. Results are reported which isolate the effects of elastoplastic flow and crack closure.

  9. Full-Field Strain Measurement On Titanium Welds And Local Elasto-Plastic Identification With The Virtual Fields Method

    SciTech Connect

    Tattoli, F.; Casavola, C. [Dipartimento di Ingegneria Meccanica e Gestionale, Politecnico di Bari, Viale Japigia 182, 70126 Bari (Italy); Pierron, F.; Rotinat, R.; Pappalettere, C. [Ecole Nationale Superieure d'Arts et Metiers, Rue Saint Dominique, BP508, 51006 Chalons en Champagne (France)

    2011-01-17

    One of the main problems in welding is the microstructural transformation within the area affected by the thermal history. The resulting heterogeneous microstructure within the weld nugget and the heat affected zones is often associated with changes in local material properties. The present work deals with the identification of material parameters governing the elasto--plastic behaviour of the fused and heat affected zones as well as the base material for titanium hybrid welded joints (Ti6Al4V alloy). The material parameters are identified from heterogeneous strain fields with the Virtual Fields Method. This method is based on a relevant use of the principle of virtual work and it has been shown to be useful and much less time consuming than classical finite element model updating approaches applied to similar problems. The paper will present results and discuss the problem of selection of the weld zones for the identification.

  10. A finite-element marker-in-cell simulation code for thermo-chemically coupled magma dynamics in a visco-elasto-plastic host rock

    NASA Astrophysics Data System (ADS)

    Keller, Tobias

    2014-05-01

    Many prominent geodynamic scenarios such as subduction zones, plate collision and orogeny formation, mid-ocean ridges, continental rifting, etc. involve a significant amount of active magmatism. However, many numerical simulations used to address related questions focus on the deformation of the solid rock phase only, sometimes taking into account the magma dynamics in the form of some parameterized weakening mechanism. On the other hand, simulations specifically developed for magma dynamics problems have largely been restricted to the context of mantle dynamics and are not designed to deal with brittle tectonic deformation of the rock matrix as it occurs in the lithosphere and crust. Here, a 2-D finite-element marker-in-cell numerical method is presented capable of simulating thermally and compositionally coupled two-phase flow problems in a realistically deforming mantle, lithosphere and crust. The modeling approach is based on a set of well accepted equations for the conservation of mass, momentum, energy and composition, completed by constitutive laws for visco-elasto-plastic shear and compaction stresses and a much simplified yet thermodynamically consistent melting model depending on temperature, pressure and composition. The simulation code is written in Matlab and is capable of solving up to 500k degrees of freedom (requiring 2m marker particles) within few minutes per time step on a standard desktop computer. Long-term simulations of that size require run times of one to three weeks. The non-linear system of equations is solved using a Picard iterative scheme, where the linearized system of equations is solved directly during each iterative step. Sufficient convergence is usually obtained within less than 10 non-linear iterations. Generally, this numerical method is versatile, accessible and efficient enough for a wide range of 2-D problems.

  11. Fracture mechanics validity limits

    NASA Technical Reports Server (NTRS)

    Lambert, Dennis M.; Ernst, Hugo A.

    1994-01-01

    Fracture behavior is characteristics of a dramatic loss of strength compared to elastic deformation behavior. Fracture parameters have been developed and exhibit a range within which each is valid for predicting growth. Each is limited by the assumptions made in its development: all are defined within a specific context. For example, the stress intensity parameters, K, and the crack driving force, G, are derived using an assumption of linear elasticity. To use K or G, the zone of plasticity must be small as compared to the physical dimensions of the object being loaded. This insures an elastic response, and in this context, K and G will work well. Rice's J-integral has been used beyond the limits imposed on K and G. J requires an assumption of nonlinear elasticity, which is not characteristic of real material behavior, but is thought to be a reasonable approximation if unloading is kept to a minimum. As well, the constraint cannot change dramatically (typically, the crack extension is limited to ten-percent of the initial remaining ligament length). Rice, et al investigated the properties required of J-type parameters, J(sub x), and showed that the time rate, dJ(sub x)/dt, must not be a function of the crack extension rate, da/dt. Ernst devised the modified-J parameter, J(sub M), that meets this criterion. J(sub M) correlates fracture data to much higher crack growth than does J. Ultimately, a limit of the validity of J(sub M) is anticipated, and this has been estimated to be at a crack extension of about 40-percent of the initial remaining ligament length. None of the various parameters can be expected to describe fracture in an environment of gross plasticity, in which case the process is better described by deformation parameters, e.g., stress and strain. In the current study, various schemes to identify the onset of the plasticity-dominated behavior, i.e., the end of fracture mechanics validity, are presented. Each validity limit parameter is developed in detail, and then data is presented and the various schemes for establishing a limit of the validity are compared. The selected limiting parameter is applied to a set of fracture data showing the improvement of correlation gained.

  12. A finite element formulation for evaluation of crack blunting effects in elasto-plastic solids

    NASA Technical Reports Server (NTRS)

    Osias, J. R.

    1975-01-01

    The sharp crack model allows the use of continuum analysis, linear elasticity, as a basic for predicting a micromechanical process, fracture, by providing a characterization of loading conditions affecting a very small volume of material. The model is described in detail.

  13. Fracture Mechanics and Failure Analysis

    E-print Network

    New South Wales, University of

    Analysis (Weeks 7-12) Prof Alan Crosky 10 General practice in failure analysis 7 11 Ductile and brittle Final exam Course Outline Fracture mechanics, remnant life assessment, general practice in failure

  14. Geometrically Frustrated Fracture Mechanics

    NASA Astrophysics Data System (ADS)

    Mitchell, Noah; Koning, Vinzenz; Vitelli, Vincenzo; Irvine, William T. M.

    2015-03-01

    When a flat elastic sheet is forced to conform to a surface with Gaussian curvature, stresses arise in the sheet. The mismatch between initial and final metrics gives rise to new fracture behavior which cannot be achieved by boundary loading alone. Using experiments of PDMS sheets frustrated on 3D-printed surfaces and a linearized analytical model, we demonstrate the ability of curvature to govern the sheets' fracture phenomenology. In this talk, we first show that curvature can both stimulate and suppress fracture initiation, depending on the position and orientation of the initial slit. Secondly, we show that curvature can steer the path of a crack as it propagates through the material. Lastly, the curvature can arrest cracks which would otherwise continue to propagate.

  15. Elasto-plastic analysis of a mode I edge crack with application to a surface notch.

    NASA Technical Reports Server (NTRS)

    Francis, P. H.

    1971-01-01

    A finite element analysis has been undertaken of the mechanical state of a plate containing a crack subjected to mode I loading. Specifically, a localized, well-defined surface depression (dimple) previously observed on the back surface of plate specimens immediately behind the plane of the crack was examined. The approach taken is concerned with defining more precisely the dimpling behavior as a function of relative flaw depth and applied stress level, as well as the development of the plastic zone at the crack tip.

  16. PLAN2D - A PROGRAM FOR ELASTO-PLASTIC ANALYSIS OF PLANAR FRAMES

    NASA Technical Reports Server (NTRS)

    Lawrence, C.

    1994-01-01

    PLAN2D is a FORTRAN computer program for the plastic analysis of planar rigid frame structures. Given a structure and loading pattern as input, PLAN2D calculates the ultimate load that the structure can sustain before collapse. Element moments and plastic hinge rotations are calculated for the ultimate load. The location of hinges required for a collapse mechanism to form are also determined. The program proceeds in an iterative series of linear elastic analyses. After each iteration the resulting elastic moments in each member are compared to the reserve plastic moment capacity of that member. The member or members that have moments closest to their reserve capacity will determine the minimum load factor and the site where the next hinge is to be inserted. Next, hinges are inserted and the structural stiffness matrix is reformulated. This cycle is repeated until the structure becomes unstable. At this point the ultimate collapse load is calculated by accumulating the minimum load factor from each previous iteration and multiplying them by the original input loads. PLAN2D is based on the program STAN, originally written by Dr. E.L. Wilson at U.C. Berkeley. PLAN2D has several limitations: 1) Although PLAN2D will detect unloading of hinges it does not contain the capability to remove hinges; 2) PLAN2D does not allow the user to input different positive and negative moment capacities and 3) PLAN2D does not consider the interaction between axial and plastic moment capacity. Axial yielding and buckling is ignored as is the reduction in moment capacity due to axial load. PLAN2D is written in FORTRAN and is machine independent. It has been tested on an IBM PC and a DEC MicroVAX. The program was developed in 1988.

  17. On the plumbing system of volcanic complexes: field constraints from the Isle of Skye (UK) and FEM elasto-plastic modelling including gravity and tectonics.

    NASA Astrophysics Data System (ADS)

    Bistacchi, A.; Pisterna, R.; Romano, V.; Rust, D.; Tibaldi, A.

    2009-04-01

    The plumbing system that connects a sub-volcanic magma reservoir to the surface has been the object of field characterization and mechanical modelling efforts since the pioneering work by Anderson (1936), who produced a detailed account of the spectacular Cullin Cone-sheet Complex (Isle of Skye, UK) and a geometrical and mechanical model aimed at defining the depth to the magma chamber. Since this work, the definition of the stress state in the half space comprised between the magma reservoir and the surface (modelled either as a flat surface or a surface comprising a volcanic edifice) was considered the key point in reconstructing dike propagation paths from the magma chamber. In fact, this process is generally seen as the propagation in an elastic media of purely tensional joints (mode I or opening mode propagation), which follow trajectories perpendicular to the least compressive principal stress axis. Later works generally used different continuum mechanics methodologies (analytic, BEM, FEM) to solve the problem of a pressure source (the magma chamber, either a point source or a finite volume) in an elastic (in some cases heterogeneous) half space (bounded by a flat topography or topped by a "volcano"). All these models (with a few limited exceptions) disregard the effect of the regional stress field, which is caused by tectonic boundary forces and gravitational body load, and consider only the pressure source represented by the magma chamber (review in Gudmundsson, 2006). However, this is only a (sometimes subordinate) component of the total stress field. Grosfils (2007) first introduced the gravitational load (but not tectonic stresses) in an elastic model solved with FEM in a 2D axisymmetric half-space, showing that "failure to incorporate gravitational loading correctly" affect the calculated stress pattern and many of the predictions that can be drawn from the models. In this contribution we report on modelling results that include: 2D axisymmetric or true 3D geometry; gravitational body load; anisotropic tectonic stresses; different shapes and depths of the magma chamber; different overpressure levels in the magma chamber; different shapes of the topographic surface (e.g. flat, volcano, caldera); linear-elastic or elasto-plastic Drucker-Prager rheology. The latter point, which in our opinion constitutes a fundamental improvement in the model, has proven necessary because in a purely elastic model the stress state would rise at levels that cannot be sustained by geologic materials. Particularly around and above the magma chamber, yielding is expected, influencing the stress field in the remaining modelling domain. The non-linear problem has been solved with the commercial finite element package Comsol Multiphysics, using a parametric solver. At the same time, a field structural analysis of the classical Cuillin Cone-sheet Complex has been performed. This analysis has shown that four distinct families of cone sheets of different age do exist. Among these, the sheets with the higher dip angle range (80-65°) are confirmed as purely tensional joints, but those with a lower dip angle range (60-40°) are quite often (when suitable markers are available) associated with a measurable shear component. Combining these new field observations with mechanical modelling results, we propose a new interpretation for the Cuillin Cone Sheet Complex. The plumbing system was composed by both purely tensional joints and mesoscopic faults with a shear component, produced in response to the regional stress field perturbed by the magma chamber, and later passively re-used as magma emplacement conduits. Under this assumption, the observed geometry of the Cuillin Cone-sheet Complex is consistent with a relatively shallow magma chamber with a flattened laccolite shape. The shape of the palaeotopography, now completely eroded, has also been considered, but is more weakly constrained by modelling results. References: Anderson E.M., 1936. The dynamics of the formation of cone-sheets, ring-dykes and cauldron subsidences.

  18. Modelling the graphite fracture mechanisms

    SciTech Connect

    Jacquemoud, C.; Marie, S. [CEA Saclay, Gif-sur-Yvette, (France); Nedelec, M. [IRSN/PSN-EXP/SES, Fontenay-aux-Roses, (France)

    2012-07-01

    In order to define a design criterion for graphite components, it is important to identify the physical phenomena responsible for the graphite fracture, to include them in a more effective modelling. In a first step, a large panel of experiments have been realised in order to build up an important database; results of tensile tests, 3 and 4 point bending tests on smooth and notched specimens have been analysed and have demonstrated an important geometry related effects on the behavior up to fracture. Then, first simulations with an elastic or an elastoplastic bilinear constitutive law have not made it possible to simulate the experimental fracture stress variations with the specimen geometry, the fracture mechanisms of the graphite being at the microstructural scale. That is the reason why a specific F.E. model of the graphite structure has been developed in which every graphite grain has been meshed independently, the crack initiation along the basal plane of the particles as well as the crack propagation and coalescence have been modelled too. This specific model has been used to test two different approaches for fracture initiation: a critical stress criterion and two criteria of fracture mechanic type. They are all based on crystallographic considerations as a global critical stress criterion gave unsatisfactory results. The criteria of fracture mechanic type being extremely unstable and unable to represent the graphite global behaviour up to the final collapse, the critical stress criterion has been preferred to predict the results of the large range of available experiments, on both smooth and notched specimens. In so doing, the experimental observations have been correctly simulated: the geometry related effects on the experimental fracture stress dispersion, the specimen volume effects on the macroscopic fracture stress and the crack propagation at a constant stress intensity factor. In addition, the parameters of the criterion have been related to experimental observations: the local crack initiation stress of 8 MPa corresponds to the non-linearity apparition on the global behavior observed experimentally and the the maximal critical stress defined for the particle of 30 MPa is equivalent to the fracture stress of notched specimens. This innovative combination of crack modelling and a local crystallographic critical stress criterion made it possible to understand that cleavage initiation and propagation in the graphite microstructure was driven by a mean critical stress criterion. (authors)

  19. Fracture mechanics of cellular glass

    NASA Technical Reports Server (NTRS)

    Zwissler, J. G.; Adams, M. A.

    1981-01-01

    The fracture mechanics of cellular glasses (for the structural substrate of mirrored glass for solr concentrator reflecting panels) are discussed. Commercial and developmental cellular glasses were tested and analyzed using standard testing techniques and models developed from linear fracture mechanics. Two models describing the fracture behavior of these materials were developed. Slow crack growth behavior in cellular glass was found to be more complex than that encountered in dense glasses or ceramics. The crack velocity was found to be strongly dependent upon water vapor transport to the tip of the moving crack. The existence of a static fatigue limit was not conclusively established, however, it is speculated that slow crack growth behavior in Region 1 may be slower, by orders of magnitude, than that found in dense glasses.

  20. Fracture mechanics estimates drillpipe fatigue

    SciTech Connect

    Kral, E.; Newlin, L.; Quan, S.S.; Sengupta, P.K.

    1984-08-06

    This first of two articles presents an alternative procedure based upon fracture mechanics. The computational bases for this procedure are presented. The contributions to the analysis of fatigue failure in drillpipes rotating in doglegs are discussed. In particular, the significant contributions of Lubinski and Hansford are reviewed.

  1. Structural reliability through fracture mechanics

    SciTech Connect

    Sinclair, G. (Carnegie Mellon Univ., Pittsburgh, PA (United States). Dept. of Mechanical Engineering)

    1993-06-01

    This article describes how engineers are using fracture mechanics to help them determine the potential severity of visible and seemingly invisible flaws in mechanical components. Nearly all mechanical engineering components contain flaws, albeit if only at the microscopic level. In service, these flaws can grow into small but visible cracks. To design for structural reliability under these circumstances, an engineer needs to know how and when the crack might grow further and run, with the component ultimately breaking apart. Fracture mechanics is the technology that helps to answer these questions. When cracks do suddenly run, the outcome is often dramatic and sometimes catastrophic. In 1987, while in flight, an aging Aloha Airlines 737 suddenly developed a hole in its side that was bigger than the main cabin door. This failure emphasizes the need for even greater vigilance with respect to this issue; the FAA is responding to this need. In all, fracture mechanics can be expected to play an important role in engineering for years to come.

  2. On a New Concept and Foundations of an Arbitrary Reference Configuration (ARC) Theory and Formulation for Computational Finite Deformation Applications—Part II: Elasto-Plasticity

    NASA Astrophysics Data System (ADS)

    Zhou, X.; Sha, D.; Tamma, K. K.

    2006-10-01

    Whereas in part I of the paper [1], we laid down the foundations towards a new arbitrary reference configuration (ARC) framework for computational elasticity finite deformation applications, here in part II of the paper we extend the developments to computational elasto-plasticity. Within the context of the ARC framework, the mid-point rule and the trapezoidal rule for computational plasticity are further investigated. The conclusions that the trapezoidal rule is indeed more suitable for computational plasticity in comparison to the mid-point rule, and the fact that the present ARC framework is more suitable for finite deformation problems in comparison with the widely adopted total Lagrangian formulation and the updated Lagrangian formulation, are finally drawn and established.

  3. (Fracture mechanics of inhomogeneous materials)

    SciTech Connect

    Bass, B.R.

    1990-10-01

    Discussions were held with Japanese researchers concerning (1) the Elastic-Plastic Fracture Mechanics in Inhomogeneous Materials and Structures (EPI) Program, and (2) ongoing large-scale pressurized- thermal-shock (PTS) experiments in Japan. In the EPI Program, major activities in the current fiscal year include round-robin analyses of measured data from inhomogeneous base metal/weld metal compact- tension (CT) specimens fabricated from welded plates of A533 grade B class 1 steel. The round-robin task involves participants from nine research organizations in Japan and is scheduled for completion by the end of 1990. Additional experiments will be performed on crack growth in inhomogeneous CT specimens and three-point bend (3PB) specimens 10 mm thick. The data will be compared with that generated previously from 19-mm-thick-specimens. A new type of inhomogeneous surface-cracked specimen will be tested this year, with ratio of crack depth to surface length (a/c) satisfying 0.2 {le} (a/c) {le} 0. 8 and using a 3PB type of applied load. Plans are under way to fabricate a new welded plate of A533 grade B class 1 steel (from a different heat than that currently being tested) in order to provide an expanded fracture-toughness data base. Other topics concerning fracture-prevention issues in reactor pressure vessels were discussed with each of the host organizations, including an overview of ongoing work in the Heavy-Section Steel Technology (HSST) Program.

  4. Fracture mechanics of cellular glass

    SciTech Connect

    Zwissler, J.G.; Adams, M.A.

    1981-02-01

    Cellular glasses are prime candidate materials for the structural substrate of mirrored glass for solar concentrator reflecting panels. These materials are brittle, however, and susceptible to mechanical failure from slow crack growth caused by a stress corrosion mechanism. The results are detailed of one part of a program established to develop improved cellular glasses and to characterize the behavior of these and commercially available materials. Commercial and developmental cellular glasses were tested and analyzed using standard testing techniques and models developed from linear fracture mechanics. Two models describing the fracture behavior of these materials are developed. Slow crack growth behavior in cellular glass was found to be more complex than that encountered in dense glasses or ceramics. The crack velocity was found to be strongly dependent upon water vapor transport to the tip of the moving crack. The existence of a static fatigue limit was not conclusively established, however, it is speculated that slow crack growth behavior in Region I may be slower, by orders of magnitude, than that found in dense glasses.

  5. Compendium of fracture mechanics problems

    NASA Technical Reports Server (NTRS)

    Stallworth, R.; Wilson, C.; Meyers, C.

    1990-01-01

    Fracture mechanics analysis results are presented from the following structures/components analyzed at Marshall Space Flight Center (MSFC) between 1982 and 1989: space shuttle main engine (SSME), Hubble Space Telescope (HST), external tank attach ring, B-1 stand LOX inner tank, and solid rocket booster (SRB). Results from the SSME high pressure fuel turbopump (HPFTP) second stage blade parametric analysis determine a critical flaw size for a wide variety of stress intensity values. The engine 0212 failure analysis was a time dependent fracture life assessment. Results indicated that the disk ruptured due to an overspeed condition. Results also indicated that very small flaws in the curvic coupling area could propagate and lead to failure under normal operating conditions. It was strongly recommended that a nondestructive evaluation inspection schedule be implemented. The main ring of the HST, scheduled to launch in 1990, was analyzed by safe-life and fail-safe analyses. First safe-life inspection criteria curves for the ring inner and outer skins and the fore and aft channels were derived. Afterwards the skins and channels were determined to be fail-safe by analysis. A conservative safe-life analysis was done on the 270 redesign external tank attach ring. Results from the analysis were used to determine the nondestructive evaluation technique required.

  6. Entablature: fracture types and mechanisms

    NASA Astrophysics Data System (ADS)

    Forbes, A. E. S.; Blake, S.; Tuffen, H.

    2014-05-01

    Entablature is the term used to describe zones or tiers of irregular jointing in basaltic lava flows. It is thought to form when water from rivers dammed by the lava inundates the lava flow surface, and during lava-meltwater interaction in subglacial settings. A number of different fracture types are described in entablature outcrops from the Búrfell lava and older lava flows in Þjórsárdalur, southwest Iceland. These are: striae-bearing, column-bounding fractures and pseudopillow fracture systems that themselves consist of two different fracture types—master fractures with dimpled surface textures and subsidiary fractures with curved striae. The interaction of pseudopillow fracture systems and columnar jointing in the entablature produces the chevron fracture patterns that are commonly observed in entablature. Cube-jointing is a more densely fractured version of entablature, which likely forms when more coolant enters the hot lava. The entablature tiers display closely spaced striae and dendritic crystal shapes which indicate rapid cooling. Master fracture surfaces show a thin band with an evolved composition at the fracture surface; mineral textures in this band also show evidence of quenching of this material. This is interpreted as gas-driven filter pressing of late-stage residual melt that is drawn into an area of low pressure immediately preceding or during master fracture formation by ductile extensional fracture of hot, partially crystallised lava. This melt is then quenched by an influx of water and/or steam when the master fracture fully opens. Our findings suggest that master fractures are the main conduit for coolant entering the lava flow during entablature formation.

  7. Nonlinear fracture mechanics. Volume 1. Time-dependent fracture

    SciTech Connect

    Saxena, A.; Landes, J.D.; Bassani, J.L.

    1989-01-01

    Various papers on time-dependent fracture in nonlinear fracture mechanics are presented. Individual subjects considered include: numerical study of non-steady-state creep at stationary crack tips, crack growth in small-scale creep, growth of macroscopic cracks by void coalescence under extensive creeping conditions, creep embrittlement susceptibility and creep crack growth behavior in low-alloy steels, and experimental determination of the high-temperature crack growth behavior of Incoloy 800H. Also discussed are: three-dimensional transient analysis of a dynamically loaded three-point-bend ductile fracture specimen, experimental study of the validity of a Delta J criterion for fatigue crack growth, combined-mode low-cycle fatigue crack growth under torsional loading, fatigue crack-tip mechanics in 7075-T6 aluminum alloy from high-sensitivity displacement field measurements, and nonlinear fracture of concrete and ceramics.

  8. Fracture healing: mechanisms and interventions

    PubMed Central

    Einhorn, Thomas A.; Gerstenfeld, Louis C.

    2015-01-01

    Fractures are the most common large-organ, traumatic injuries to humans. The repair of bone fractures is a postnatal regenerative process that recapitulates many of the ontological events of embryonic skeletal development. Although fracture repair usually restores the damaged skeletal organ to its pre-injury cellular composition, structure and biomechanical function, about 10% of fractures will not heal normally. This article reviews the developmental progression of fracture healing at the tissue, cellular and molecular levels. Innate and adaptive immune processes are discussed as a component of the injury response, as are environmental factors, such as the extent of injury to the bone and surrounding tissue, fixation and the contribution of vascular tissues. We also present strategies for fracture treatment that have been tested in animal models and in clinical trials or case series. The biophysical and biological basis of the molecular actions of various therapeutic approaches, including recombinant human bone morphogenetic proteins and parathyroid hormone therapy, are also discussed. PMID:25266456

  9. Equations For Selected Fracture-Mechanics Parameters

    NASA Technical Reports Server (NTRS)

    Bubsey, Raymond T.; Orange, Thomas W.; Pierce, William S.; Shannon, John L., Jr.

    1994-01-01

    Equations describing crack-mouth-opening displacements, stress-intensity factors, and related fracture-mechanics parameters of chevron-notched short bar and rod specimens presented in report. Equations in forms suitable for determining fracture toughnesses from maximum loads, for determining crack-extension-resistance curves, and for setting sensitivities of testing instruments. Useful in facilitating testing and interpretation of data from tests of brittle metals, ceramics, and glasses, formed into chevron-notched specimens for fracture testing according to concepts.

  10. Mechanics and direction of hydraulic fracturing

    Microsoft Academic Search

    Daneshy

    1973-01-01

    Use of the in situ principal stresses greatly simplifies the problems of hydraulic fracturing. For one thing, it reduces the number of stresses to 3, thus simplifying the mathematics. Besides, this choice is in harmony with laboratory observations of fracture propagation perpendicular to the least principal stress. In addition to underground stresses, hydraulic stress is also influenced by the mechanical

  11. Fracture mechanics evaluation of GaAs

    NASA Technical Reports Server (NTRS)

    Chen, C. P.

    1984-01-01

    A data base of mechanical and fracture properties for GaAs was generated. The data for single crystal GaAs will be used to design reusable GaAs solar modules. Database information includes; (1) physical property characterizations; (2) fracture behavior evaluations; and (3) strength of cells determined as a function of cell processing and material parameters.

  12. Mechanical behavior and fracture of graphene nanomeshes

    NASA Astrophysics Data System (ADS)

    Hu, Lin; Wyant, Spencer; Muniz, Andre R.; Ramasubramaniam, Ashwin; Maroudas, Dimitrios

    2015-01-01

    We study the mechanical behavior and fracture of graphene nanomeshes (GNMs) consisting of hexagonal lattices of unpassivated circular pores based on molecular-dynamics simulations of uniaxial tensile deformation tests. We analyze the GNMs' mechanical response as a function of their porosity for porosities up to 80%. We find that the fracture strain exhibits a minimum at a porosity ˜15%, which marks the onset of a transition in the mechanical behavior of the nanomeshes; beyond this critical porosity, the GNM ductility increases and the toughness remains practically constant with increasing porosity. The mechanism of crack initiation and propagation is characterized in both cases of mechanical response.

  13. Fracture mechanics analysis of delamination failures in IC packages

    Microsoft Academic Search

    Andrew A. O. Tay

    2009-01-01

    This paper describes the application of fracture mechanics to the analysis of delamination in IC packages. An introduction to the fundamentals of interfacial fracture mechanics will first be given together with a description of some numerical methods for calculating fracture mechanics parameters such as strain energy release rate and mode mixity. Fracture mechanics methodology will then be applied to analyze

  14. A Hierarchical Approach to Fracture Mechanics

    NASA Technical Reports Server (NTRS)

    Saether, Erik; Taasan, Shlomo

    2004-01-01

    Recent research conducted under NASA LaRC's Creativity and Innovation Program has led to the development of an initial approach for a hierarchical fracture mechanics. This methodology unites failure mechanisms occurring at different length scales and provides a framework for a physics-based theory of fracture. At the nanoscale, parametric molecular dynamic simulations are used to compute the energy associated with atomic level failure mechanisms. This information is used in a mesoscale percolation model of defect coalescence to obtain statistics of fracture paths and energies through Monte Carlo simulations. The mathematical structure of predicted crack paths is described using concepts of fractal geometry. The non-integer fractal dimension relates geometric and energy measures between meso- and macroscales. For illustration, a fractal-based continuum strain energy release rate is derived for inter- and transgranular fracture in polycrystalline metals.

  15. Rabotnov damageparameter and description of delayed fracture: Results, current status, application to fracture mechanics, and prospects

    NASA Astrophysics Data System (ADS)

    Stepanova, L. V.; Igonin, S. A.

    2015-03-01

    This paper presents a review of studies of delayed fracture and fracture mechanics problems in which the hypotheses and ideas of Yu. N. Rabotnov and L. M. Kachanov on the mechanisms of delayed fracture under creep conditions are extended to describe fracture processes using scalar and tensor measures of damage. The results of current research in the theory of elasticity, the mathematical theory of plasticity and creep, the mechanics of composites, and linear and nonlinear fracture mechanics, with material damage taken into account.

  16. Fracture mechanics of snow avalanches.

    PubMed

    Aström, J A; Timonen, J

    2001-07-01

    Dense snow avalanches are analyzed by modeling the snow slab as an elastic and brittle plate, attached by static friction to the underlying ground. The grade of heterogeneity in the local fracture (slip) thresholds, and the ratio of the average substrate slip threshold to the average slab fracture threshold, are the decisive parameters for avalanche dynamics. For a strong pack of snow there appears a stable precursor of local slips when the frictional contacts are weakened (equivalent to rising temperature), which eventually trigger a catastrophic crack growth that suddenly releases the entire slab. In the opposite limit of very high slip thresholds, the slab simply melts when the temperature is increased. In the intermediate regime, and for a homogeneous slab, the model display features typical of real snow avalanches. The model also suggests an explanation to why avalanches are impossible to forecast reliably based on precursor observations. This explanation may as well be applicable to other catastrophic rupture phenomena such as earthquakes. PMID:11461247

  17. Mechanical behavior, damage tolerance and durability of fiber metal laminates for aircraft structures

    Microsoft Academic Search

    Guocai Wu

    2005-01-01

    This study systematically explores the mechanical behavior, damage tolerance and durability of fiber metal laminates, a promising candidate materials system for next generation aerospace structures. The experimental results indicated that GLARE laminates exhibited a bilinear deformation behavior under static in-plane loading. Both an analytical constitutive model based on a modified classical lamination theory which incorporates the elasto-plastic behavior of aluminum

  18. Fracture Mechanics and Service Life Prediction Research

    NASA Astrophysics Data System (ADS)

    Liu, C. T.

    1999-09-01

    The main issues in service life prediction of solid rocket motors are the lack of a fundamental understanding of crack growth behavior under service loading conditions and a reliable methodology to predict crack growth. It is relatively unknown in the areas of microstructure effects on damage initiation and evolution, large deformation effect on crack growth, and the effects of mismatch of material properties of a bond system on the stress fields near the interfacial crack tip. This program consists of five major tasks: Task I predicting the initial crack length in high stress regions; Task II - crack instability and growth models; Task III - numerical modeling of crack growth; and Task IV - interfacial fracture of bimaterial bond systems. The program's basic approach involves a blend of analytical and experimental studies. In general, mechanisms and mechanics involved in cohesive fracture in a solid propellant and adhesive fracture in bond systems are emphasized. Program results will provide a basis for developing advanced crack growth and service life prediction technologies for predicting the service life of solid rocket motors. The implementation of these advanced technologies will not only increase the reliability of the solid rocket motors but also significantly reduce the motor replacement costs.

  19. Fracture mechanics methodology: Evaluation of structural components integrity

    NASA Astrophysics Data System (ADS)

    Sih, G. C.; de Oliveira Faria, L.

    1984-09-01

    The application of fracture mechanics to structural-design problems is discussed in lectures presented in the AGARD Fracture Mechanics Methodology course held in Lisbon, Portugal, in June 1981. The emphasis is on aeronautical design, and chapters are included on fatigue-life prediction for metals and composites, the fracture mechanics of engineering structural components, failure mechanics and damage evaluation of structural components, flaw-acceptance methods, and reliability in probabilistic design. Graphs, diagrams, drawings, and photographs are provided.

  20. Fracture of Sn-Ag-Cu Solder Joints on Cu Substrates. II: Fracture Mechanism Map

    NASA Astrophysics Data System (ADS)

    Kumar, P.; Huang, Z.; Dutta, I.; Sidhu, R.; Renavikar, M.; Mahajan, R.

    2012-02-01

    A methodology to construct fracture mechanism maps for Sn-3.8%Ag-0.7%Cu (SAC387) solder joints attached to Cu substrates has been developed. The map, which delineates the operative mechanisms of fracture along with corresponding joint fracture toughness values, is plotted in a space described by two microstructure-dependent parameters, with the abscissa describing the interfacial intermetallic compound (IMC) and the ordinate representing the strain-rate-dependent solder yield strength. The plot space encompasses the three major mechanisms by which joints fail, namely (i) cohesive fracture of solder, (ii) cleavage fracture of interfacial intermetallic compounds (IMC), and (iii) fracture of the solder-IMC interface. Line contours of constant fracture toughness values, as well as constant fraction of each of the above mechanisms, are indicated on the plots. The plots are generated by experimentally quantifying the dependence of the operative fracture mechanism(s) on the two microstructure-dependent parameters (IMC geometry and solder yield strength) as functions of strain rate, reflow parameters, and post-reflow aging. Separate maps are presented for nominally mode I and equi-mixed mode loading conditions (loading angle ? = 0° and 45°, respectively). The maps allow rapid assessment of the operative fracture mechanism(s) along with estimation of the expected joint fracture toughness value for a given loading condition (strain rate and loading angle) and joint microstructure without conducting actual tests, and may serve as a tool for both prediction and microstructure design.

  1. On Mechanisms of Hydraulic Fracturing in Cohesionless Materials

    Microsoft Academic Search

    R. S. Hurt; R. Wu; L. Germanovich; H. Chang; P. V. Dyke

    2005-01-01

    Based on the developed experimental techniques, hydraulic fracturing in particulate materials has been directly observed in the laboratory. We have conducted an experimental series by varying such controlling parameters as the properties of particulate materials and fracturing fluids, boundary conditions, initial stress states, and injection volumes and rates. As a result, we suggested some (hopefully, fundamental) mechanisms of hydraulic fracturing

  2. Patterns and perspectives in applied fracture mechanics

    SciTech Connect

    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.

  3. Mechanical Behavior of Carbide-free Medium Carbon Bainitic Steels

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoxu; Xu, Guang; Wang, Xiang; Embury, David; Bouaziz, Olivier; Purdy, Gary R.; Zurob, Hatem S.

    2013-11-01

    The effect of bainitic transformation time on the microstructure and mechanical properties was investigated in a steel containing 0.4 pct C-2.8 pct Mn-1.8 pct Si. The microstructure was characterized using optical and transmission electron microscopy; it consisted of bainitic ferrite, martensite, and retained austenite. The volume fraction of bainite increased from 0.4 for the shortest bainitic transformation time (30 minutes) to 0.9 at the longest time (120 minutes). The above microstructures exhibited an extended elasto-plastic transition leading to very high initial work-hardening rates. The work-hardening behavior was investigated in detail using strain-path reversals to measure the back stresses. These measurements point to a substantial kinematic hardening due to the mechanical contrast between the microstructural constituents. The onset of necking coincided with the saturation of kinematic hardening. Examination of the fracture surfaces indicated that the prior austenite grain boundaries play an important role in the fracture process.

  4. A chemo-mechanical model of lithiation in silicon

    NASA Astrophysics Data System (ADS)

    Yang, Hui; Fan, Feifei; Liang, Wentao; Guo, Xu; Zhu, Ting; Zhang, Sulin

    2014-10-01

    We present a chemo-mechanical model to investigate the lithiation-induced phase transformation, morphological evolution, stress generation and fracture in crystalline silicon nanowires (c-SiNWs). The model couples lithium (Li) diffusion with elasto-plastic deformation in a three-dimensional (3D) setting. Several key features observed from recent transmission electron microscopy (TEM) studies are incorporated into the model, including the sharp interface between the lithiated amorphous shell and unlithiated crystalline core, crystallographic orientation dependent Li-Si reaction rate, and large-strain plasticity. Our simulation results demonstrate that the model faithfully predicts the anisotropic swelling of lithiated SiNWs observed from previous experimental studies. Stress analysis from the finite-deformation model reveals that the SiNWs are prone to surface fracture at the angular sites where two adjacent {110} facets intersect, consistent with previous experimental observations. The mechanistic understanding of the morphological evolution and stress generation sheds light on the design of failure-resistant nanostructured electrodes. Our model offers a framework for the study of the chemo-mechanical degradation in high-capacity electrode materials.

  5. Discrete probability distributions for probabilistic fracture mechanics

    SciTech Connect

    Kurth, R.E.; Cox, D.C.

    1985-09-01

    Recently, discrete probability distributions (DPDs) have been suggested for use in risk analysis calculations to simplify the numerical computations which must be performed to determine failure probabilities. Specifically, DPDs have been developed to investigate probabilistic functions, that is, functions whose exact form is uncertain. The analysis of defect growth in materials by probabilistic fracture mechanics (PFM) models provides an example in which probabilistic functions play an important role. This paper compares and contrasts Monte Carlo simulation and DPDs as tools for calculating material failure due to fatigue crack growth. For the problem studied, the DPD method takes approximately one third the computation time of the Monte Carlo approach for comparable accuracy. It is concluded that the DPD method has considerable promise in low-failure-probability calculations of importance in risk assessment. In contrast to Monte Carlo, the computation time for the DPD approach is relatively insensitive to the magnitude of the probability being estimated.

  6. Reply to Davies: Hydraulic fracturing remains a possible mechanism for

    E-print Network

    Jackson, Robert B.

    LETTER Reply to Davies: Hydraulic fracturing remains a possible mechanism for observed methane in aquifers overlying the Marcellus formation but asserts that we prematurely ascribed its cause to hydraulic mechanisms were leaky gas well casings and the possibility that hydraulic fracturing might generate new

  7. Mixed-mode Mechanism of Hydraulic Fracture Segmentation

    NASA Astrophysics Data System (ADS)

    Hurt, R. S.; Germanovich, L.; Wu, R.

    2006-12-01

    Mixed-mode I+III loading is one of the primary causes of fracture front segmentation. Although such segmented fractures have been observed both in nature and laboratory, we are not aware of direct laboratory experiments on the mode III mechanism of segmentation of hydraulically induced fractures. In this work, we developed a laboratory technique and a theoretical model for studying not only the effect of mode III loading on the onset of hydraulic fracture segmentation, but also the effect of segmentation on the subsequent growth of hydraulic fractures. In quasi-brittle materials, even a small mode III component may cause fracture segmentation due to a tensile stress field induced near the fracture front [Rice, 1968]. Previously, this has been confirmed in experiments with non-hydraulic fractures [Knauss, 1970; Cooke and Pollard, 1996]. In one occasion, quasi-hydraulic fractures propagated in fast, uncontrollable manner [Sommer, 1969]. This is why, we focused on controlled hydraulic fractures with a rather small KIII/KI ratio (1-10 %). For mixed mode I+III experiments, we used transparent, cylindrical PMMA samples with circular internal fractures perpendicular to the sample axis. Fracture orientation was controlled by thermoelastic stresses induced in each sample by preheating it before creating a fracture. In order to apply mode III loading to the initial fracture, a constant torque was applied to the specimen while fluid was injected into the fracture at a constant rate to pressurize it and to induce mode I loading. The velocity of fracture propagation was constrained by controlling the rate of fluid injection. In spite of a small magnitude of the mode III component, we observed segmented fracture fronts in all tested samples. The segments had similar dimensions and shape elongated around the perimeter of the initial fracture. When the fractures were further pressurized by injecting additional fluid into the sample, second-order segments developed along the fronts of the first-order segments. The obtained results indicate that, similar to the case of non-hydraulic fractures, a KIII/KI ratio as small as 1 % is sufficient for fracture front segmentation, even in materials as homogeneous and fracture resistant as PMMA. In reality, a small component of mode III is always expected, for example, due to slight deviations of a fracture shape from planar or interaction with boundaries or other fractures. As a result, front segmentation (at an appropriate scale) is likely to accompany the growth of most (if not all) real, sufficiently large fractures (hydraulic or not) in quasi-brittle materials, which is consistent with many observations of hydraulic fractures and magmatic dikes. However, the described above shape of segments in stable, controllable hydraulic fractures, which appeared in our experiments, was dramatically different from narrow lance-like segments, elongated in the direction of growth, of uncontrollable, unstable, non-hydraulic fractures that were propagated in a similar setting [Sommer, 1969; Hull, 1995]. We also developed a simple theoretical model, which is based on the beam asymptotic approximation. It appears that mechanical interaction between the segments and the parent fracture can be taken into account by considering an effective single fracture of equal total size. The model has one fitting parameter and shows good agreement with the experimental observations.

  8. Compressive fracture morphology and mechanism of metallic glass

    NASA Astrophysics Data System (ADS)

    Qu, R. T.; Zhang, Z. F.

    2013-11-01

    We quantitatively investigated the fracture morphologies of Zr52.5Cu17.9Ni14.6Al10Ti5 and Pd78Cu6Si16 metallic glasses (MGs) under compression. The characteristic features of the compressive fracture morphology were captured, and the shear vein patterns were found to be not a one-to-one correspondence between two opposing fracture surfaces in an identical sample. This finding experimentally confirms that the compressive failure behaves in a fracture mode of pure shear (mode II). Quantitative measurements show that a ˜1 ?m thickness layer with materials not only inside but also adjacent to the major shear band contributes to the formation of shear vein patterns. The critical shear strain to break a shear band was found to be more than 105% and higher in more ductile MGs under compression than tension. Estimation on the temperature rise at the fracture moment indicates that only ˜5% of the total elastic energy stored in the sample converts into the heat required for melting the layer to form the vein patterns. The mode II fracture toughness was also estimated based on the quantitative measurements of shear vein pattern and found larger than the mode I fracture toughness. Finally, the deformation and fracture mechanisms of MGs under tension and compression were compared and discussed. These results may improve the understanding on the fracture behaviors and mechanisms of MGs and may provide instructions on future design for ductile MGs with high resistance for fracture.

  9. Fracture Mechanics for Composites: State of the Art and Challenges

    NASA Technical Reports Server (NTRS)

    Krueger, Ronald; Krueger, Ronald

    2006-01-01

    Interlaminar fracture mechanics has proven useful for characterizing the onset of delaminations in composites and has been used with limited success primarily to investigate onset in fracture toughness specimens and laboratory size coupon type specimens. Future acceptance of the methodology by industry and certification authorities however, requires the successful demonstration of the methodology on the structural level. In this paper, the state-of-the-art in fracture toughness characterization, and interlaminar fracture mechanics analysis tools are described. To demonstrate the application on the structural level, a panel was selected which is reinforced with stringers. Full implementation of interlaminar fracture mechanics in design however remains a challenge and requires a continuing development effort of codes to calculate energy release rates and advancements in delamination onset and growth criteria under mixed mode conditions.

  10. Mechanical and fracture behavior of bainitic rail steel

    Microsoft Academic Search

    H. A. Aglan; Z. Y. Liu; M. F. Hassan; M. Fateh

    2004-01-01

    Microstructural analysis of J6 bainitic rail steel was performed and the results compared with those for the microstructure of premium pearlitic rail steel. The mechanical properties, fracture behavior and fracture toughness of the J6 bainitic steel were evaluated and compared with those for a premium pearlitic rail steel. The microstructural origin of the strength and toughness of the bainitic steel

  11. Mechanical and thermal fracture of plastics under cyclic strains

    Microsoft Academic Search

    S. B. Ratner; V. I. Korobov; S. G. Agamalyan

    1972-01-01

    It is shown on the basis of the theory of cyclic strain-induced heating of plastics that two forms of fatigue fracture are possible (thermal and mechanical), this being reflected in the fact that the appropriate Wöhler curves consist of two branches. The conditions under which a transition from one form of fracture to another takes place are analyzed, and the

  12. “Electrochemical Shock” of Intercalation Electrodes: A Fracture Mechanics Analysis

    E-print Network

    Chiang, Yet-Ming

    Fracture of electrode particles due to diffusion-induced stress has been implicated as a possible mechanism for capacity fade and impedance growth in lithium-ion batteries. In brittle materials, including many lithium ...

  13. Material properties and fracture mechanics in relation to ceramic machining

    SciTech Connect

    Griffith, L.V.

    1993-12-02

    Material removal rate, surface finish, and subsurface damage are largely governed by fracture mechanics and plastic deformation, when ceramics are machined using abrasive methods. A great deal of work was published on the fracture mechanics of ceramics in the late 1970s and early 1980s, although this work has never resulted in a comprehensive model of the fixed abrasive grinding process. However, a recently published model describes many of the most important features of the loose abrasive machining process, for example depth of damage, surface roughness, and material removal rate. Many of the relations in the loose abrasive machining model can be readily discerned from fracture mechanics models, in terms of material properties. By understanding the mechanisms of material removal, from a material properties perspective, we can better estimate how one material will machine in relation to another. Although the fracture mechanics models may have been developed for loose abrasive machining, the principles of crack initiation and propagation are equally valuable for fixed abrasive machining. This report provides a brief review of fracture in brittle materials, the stress distribution induced by abrasives, critical indenter loads, the extension of cracks, and the relation of the fracture process to material removal.

  14. Fracture mechanics approaches in the analysis of strains and fractures of bodies with notches and scotches

    Microsoft Academic Search

    Yu. G. Matvienko

    2008-01-01

    Fracture mechanics models and criteria for bodies with cracks have been developed to analyze strains and fractures of bodies\\u000a with notches and scotches. Criterion equations and corresponding crack growth resistance diagrams for a body with a notch\\u000a taking into account the changes in the degree of strain constraint at the notch apex due to finiteness of its apex radius\\u000a rounding

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

    PubMed

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

    2013-01-01

    The characterization of fractured aquifers is commonly limited to the methodologies developed for unconsolidated porous media aquifers, which results in many uncertainties. Recent work indicates that fractured rocks remove more particulates than they are conventionally credited for. This research was designed to quantify the number of Escherichia coli RS2-GFP retained in single, saturated, variable-aperture fractures extracted from the natural environment. Conservative solute and E. coli RS2-GFP tracer experiments were used to elucidate the relationships between dominant retention mechanisms, aperture field characteristics, and flow rate. A non-destructive method of determining a surrogate measure of a coefficient of variation (COV(S)) for each fracture was used to better understand the transport behaviour of E. coli RS2-GFP. The results from this research all point to the importance of aperture field characterization in understanding the fate and transport of contaminants in fractured aquifers. The mean aperture was a very important characteristic in determining particulate recovery, so were matrix properties, COV(s), and flow rate. It was also determined that attachment is a much more significant retention mechanism than straining under the conditions employed in this research. Finally, it was demonstrated that the dominant retention mechanism in a fracture varies depending on the specific discharge. An improved understanding of the mechanisms that influence the fate and transport of contaminants through fractures will lead to the development of better tools and methodologies for the characterization of fractured aquifers, as well as the ability to manipulate the relevant mechanisms to increase or decrease retention, depending on the application. PMID:23127622

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

    PubMed

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

    2015-01-01

    Stimulated reservoir volume (SRV) fracturing in tight oil reservoirs often induces complex fracture-network growth, which has a fundamentally different formation mechanism from traditional planar bi-winged fracturing. To reveal the mechanism of fracture network propagation, this paper employs a modified displacement discontinuity method (DDM), mechanical mechanism analysis and initiation and propagation criteria for the theoretical model of fracture network propagation and its derivation. A reasonable solution of the theoretical model for a tight oil reservoir is obtained and verified by a numerical discrete method. Through theoretical calculation and computer programming, the variation rules of formation stress fields, hydraulic fracture propagation patterns (FPP) and branch fracture propagation angles and pressures are analyzed. The results show that during the process of fracture propagation, the initial orientation of the principal stress deflects, and the stress fields at the fracture tips change dramatically in the region surrounding the fracture. Whether the ideal fracture network can be produced depends on the geological conditions and on the engineering treatments. This study has both theoretical significance and practical application value by contributing to a better understanding of fracture network propagation mechanisms in unconventional oil/gas reservoirs and to the improvement of the science and design efficiency of reservoir fracturing. PMID:25966285

  17. Fracture initiation mechanisms in ?-alumina under hypervelocity impact

    Microsoft Academic Search

    Cheng Zhang; Rajiv K. Kalia; Aiichiro Nakano; Priya Vashishta

    2007-01-01

    Atomistic mechanisms of crack initiation and fracture in ?-alumina under hypervelocity impact are investigated using large-scale molecular-dynamics simulations involving 540×106 atoms. The simulations reveal crack initiation due to amorphization, structural phase changes, and interaction between high strain rate deformation modes, which can advance at sustained speeds of 8 km?s. Fracture toughness in the impact-damaged substrate is estimated to be around

  18. Fracture initiation mechanisms in alpha-alumina under hypervelocity impact

    Microsoft Academic Search

    Cheng Zhang; Rajiv K. Kalia; Aiichiro Nakano; Priya Vashishta

    2007-01-01

    Atomistic mechanisms of crack initiation and fracture in alpha-alumina under hypervelocity impact are investigated using large-scale molecular-dynamics simulations involving 540×106 atoms. The simulations reveal crack initiation due to amorphization, structural phase changes, and interaction between high strain rate deformation modes, which can advance at sustained speeds of 8 km\\/s. Fracture toughness in the impact-damaged substrate is estimated to be around

  19. RSRM nozzle actuator bracket/lug fracture mechanics qualification test

    NASA Astrophysics Data System (ADS)

    Kelley, Peggy

    1993-07-01

    This is the final report for the actuator bracket/lug fracture mechanics qualification test. The test plan (CTP-0071) outlined a two-phase test program designed to answer questions about the fracture criticality of the redesigned solid rocket motor (RSRM) nozzle actuator bracket. An analysis conducted using the NASA/FLAGRO fracture mechanics computer program indicated that the actuator bracket might be a fracture critical component. In the NASA/FLAGRO analysis, a simple lug model was used to represent the actuator bracket. It was calculated that the bracket would fracture if subjected to an actuator stall load in the presence of a 0.10 in. corner crack at the actuator attachment hole. The 0.10 in. crack size corresponds to the nondestructive inspection detectability limit for the actuator bracket. The inspection method used is the dye penetrant method. The actuator stall load (103,424 lb) is the maximum load which the actuator bracket is required to withstand during motor operation. This testing was designed to establish the accuracy of the analytical model and to directly determine whether the actuator bracket is capable of meeting fracture mechanics safe-life requirements.

  20. RSRM nozzle actuator bracket/lug fracture mechanics qualification test

    NASA Technical Reports Server (NTRS)

    Kelley, Peggy

    1993-01-01

    This is the final report for the actuator bracket/lug fracture mechanics qualification test. The test plan (CTP-0071) outlined a two-phase test program designed to answer questions about the fracture criticality of the redesigned solid rocket motor (RSRM) nozzle actuator bracket. An analysis conducted using the NASA/FLAGRO fracture mechanics computer program indicated that the actuator bracket might be a fracture critical component. In the NASA/FLAGRO analysis, a simple lug model was used to represent the actuator bracket. It was calculated that the bracket would fracture if subjected to an actuator stall load in the presence of a 0.10 in. corner crack at the actuator attachment hole. The 0.10 in. crack size corresponds to the nondestructive inspection detectability limit for the actuator bracket. The inspection method used is the dye penetrant method. The actuator stall load (103,424 lb) is the maximum load which the actuator bracket is required to withstand during motor operation. This testing was designed to establish the accuracy of the analytical model and to directly determine whether the actuator bracket is capable of meeting fracture mechanics safe-life requirements.

  1. Towards a fracture mechanics for brittle piezoelectric and dielectric materials

    Microsoft Academic Search

    Robert M. McMeeking

    2001-01-01

    A theoretical fracture mechanics for brittle piezoelectric and dielectric materials is developed consistent with standard features of elasticity and dielectricity. The influence of electric field and mechanical loading is considered in this approach and a Griffith style energy balance is used to establish the relevant energy release rates. Results are given for a finite crack in an infinite isotropic dielectric

  2. An Improved Probabilistic Fracture Mechanics Model for Pressurized Thermal Shock

    SciTech Connect

    Dickson, T.L.

    2001-10-29

    This paper provides an overview of an improved probabilistic fracture mechanics (PFM) model used for calculating the conditional probabilities of fracture and failure of a reactor pressure vessel (RPV) subjected to pressurized-thermal-shock (PTS) transients. The updated PFM model incorporates several new features: expanded databases for the fracture toughness properties of RPV steels; statistical representations of the fracture toughness databases developed through application of rigorous mathematical procedures; and capability of generating probability distributions for RPV fracture and failure. The updated PFM model was implemented into the FAVOR fracture mechanics program, developed at Oak Ridge National Laboratory as an applications tool for RPV integrity assessment; an example application of that implementation is discussed herein. Applications of the new PFM model are providing essential input to a probabilistic risk assessment (PRA) process that will establish an improved technical basis for re-assessment of current PTS regulations by the US Nuclear Regulatory Commission (NRC). The methodology described herein should be considered preliminary and subject to revision in the PTS re-evaluation process.

  3. Probabilistic fracture mechanics analysis of APT blanket tubes

    SciTech Connect

    Barsell, A. W. (Arthur W.); Kern, K. T. (Kristen T.)

    2001-01-01

    A probabilistic fracture mechanics (PFM) model that is specific to the Accelerator Production of Tritium (APT) helium tubes was developed. The model performs Monte Carlo analyses of potential failure modes caused by cyclic stresses generated by beam trips and depressurizations 60m normal operation, coupled with material aging due to irradiation. Dominant failure probabilities are due to crack through-growth while brittle fracture and ductile tearing have lower probability. Failure mechanisms of global plastic collapse and buckling or crack initiation mechanisms of fatigue or local fracture (upon loss of ductility) have negligible probability. For the population of (7,311) tubes in the APT blanket, the worst-case, annual probability of one tube failing is 3 percent. The probability of 2 or more failures is substantially lower; therefore, unavailability impacts are driven by single failure. The average annual loss of production (unavailability) is below about 0.2 percent. Helium outflow and water inflow rates were characterized for the failures.

  4. Fracture mechanics criteria for turbine engine hot section components

    NASA Technical Reports Server (NTRS)

    Meyers, G. J.

    1982-01-01

    The application of several fracture mechanics data correlation parameters to predicting the crack propagation life of turbine engine hot section components was evaluated. An engine survey was conducted to determine the locations where conventional fracture mechanics approaches may not be adequate to characterize cracking behavior. Both linear and nonlinear fracture mechanics analyses of a cracked annular combustor liner configuration were performed. Isothermal and variable temperature crack propagation tests were performed on Hastelloy X combustor liner material. The crack growth data was reduced using the stress intensity factor, the strain intensity factor, the J integral, crack opening displacement, and Tomkins' model. The parameter which showed the most effectiveness in correlation high temperature and variable temperature Hastelloy X crack growth data was crack opening displacement.

  5. Mechanical transport in two-dimensional networks of fractures

    SciTech Connect

    Endo, H.K.

    1984-04-01

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

  6. Constraints on the mantle and lithosphere dynamics from the observed geoid with the effect of visco-elasto-plastic rheology in the upper 300 km

    NASA Astrophysics Data System (ADS)

    Osei Tutu, Anthony; Steinberger, Bernhard; Rogozhina, Irina; Sobolev, Stephan

    2015-04-01

    Over the past decades rheological properties of the Earth's mantle and lithosphere have been extensively studied using numerical models calibrated versus a range of surface observations (e.g., free-air-gravity anomaly/geoid, dynamic topography, plate velocity, etc.).The quality of model predictions however strongly depends on the simplifying assumptions, spatial resolution and parameterizations adopted by numerical models. The geoid is largely (Hager & Richards, 1989) determined by both the density anomalies driving the mantle flow and the dynamic topography at the Earth surface and the core-mantle boundary. This is the effect of the convective processes within the Earth's mantle. The remainder is mostly due to strong heterogeneities in the lithospheric mantle and the crust, which also need to be taken into account. The surface topography caused by density anomalies both in the sub-lithospheric mantle and within the lithosphere also depends on the lithosphere rheology. Here we investigate the effects of complex lithosphere rheology on the modelled dynamic topography, geoid and plate motion using a spectral mantle flow code (Hager & O'Connell, 1981) considering radial viscosity distribution and a fully coupled code of the lithosphere and mantle accounting for strong heterogeneities in the upper mantle rheology in the 300 km depths (Popov & Sobolev, 2008). This study is the first step towards linking global mantle dynamics with lithosphere dynamics using the observed geoid as a major constraint. Here we present the results from both codes and compare them with the observed geoid, dynamic topography and plate velocities from GPS measurements. This method allows us to evaluate the effects of plate rheology (e.g., strong plate interiors and weak plate margins) and stiff subducted lithosphere on these observables (i.e. geoid, topography, plate boundary stresses) as well as on plate motion. This effort will also serve as a benchmark of the two existing numerical methods used. Finally, given significant dispersion of geodynamic predictions from different seismic tomography models currently available, we further look for seismic models that provide predictions closest to observations at both regional and global scales. References 1. Hager B.H & O'Connell R.J., 1981. A simple global model of plate dynamics and mantle convection, J.Geophys. Res. 86, 4843-4867 2. Popov A.A., Sobolev S.V., 2008. SLIM3D: A tool for three-dimensional thermo- mechanical modelling of lithospheric deformation with elasto-visco-plastic rheology, J.pepi.2008.03.007 3. Steinberger B., 2014. Dynamic topography: A comparison between observations and models based on seismic tomography. (Submitted) 4. Becker T and Boschi L., 2002, A comparison of tomographic and geodynamic mantle models. , J.Geophys. Res. 115, 0148-0227

  7. Mechanical stability of propped hydraulic fractures: A numerical study

    SciTech Connect

    Asgian, M.I.; Cundall, P.A. [Itasca Consulting Group Inc., Minneapolis, MN (United States); Brady, B.H. [Schlumberger Dowell, Tulsa, OK (United States). Applied Mechanics and Engineering Dept.

    1995-03-01

    Proppant is sometimes produced along with hydrocarbons in hydraulically fractured petroleum wells. Sometimes 10% to 20% of the proppant is backproduced, which can lead to damaged equipment and downtime. Furthermore, proppant flowback can lead to a substantial loss of fracture conductivity. A numerical study was conducted to help understand what conditions are likely to lead to proppant flowback. In the simulations, the mechanical interaction of a larger number (several thousand) individual proppant grains was modeled with a distinct-element-type code. The numerical simulations show that hydraulic fractures propped with cohesionless, unbonded proppant fail under closure stress at a critical ratio of mean grain diameter to fracture width. This is consistent with published laboratory studies. The simulations identify the mechanism (arch failure) that triggers the mechanical instability and also show that the primary way that drawdowns (less than {approx} 75 psi/ft) affect proppant flowback is to transport loose proppant grains in front of the stable arch to the wellbore. Drawdowns > 75 psi/ft are sufficient to destabilize the arch and to cause progressive failure of the propped fractures.

  8. Equine cortical bone exhibits rising R-curve fracture mechanics.

    PubMed

    Malik, C L; Stover, S M; Martin, R B; Gibeling, J C

    2003-02-01

    Previous studies of the fracture properties of cortical bone have suggested that the fracture toughness increases with crack length, which is indicative of rising R-curve behavior. Based on this indirect evidence and the similarity of bone to ceramic matrix composites, we hypothesized that bone would exhibit rising R-curve behavior in the transverse orientation and that the characteristics of the R-curves would be regionally dependent within the cortex due to variations in bone microstructure and toughening mechanisms. To test these hypotheses, we conducted R-curve experiments on specimens from equine third metacarpal bones using standard fracture mechanics testing methods. Compact type specimens from the dorsal and lateral regions in the middle of the diaphysis were oriented for crack propagation transverse to the longitudinal axis of the bone. The test results demonstrate that equine cortical bone exhibits rising R-curve behavior during transverse crack propagation as hypothesized. Statistical analyses of the crack growth initiation toughness, K0, the peak toughness, Kpeak, and the crack extension at peak toughness, deltaa, revealed significant regional differences in these characteristics. Specifically, the lateral cortex displayed higher crack growth initiation and peak toughnesses. The dorsal cortex exhibited greater crack extension at the peak of crack growth resistance. Scanning electron microscopy revealed osteon pullout on fracture surfaces from the dorsal cortex and but not in the lateral cortex. Taken together, the significant differences in R-curves and the SEM fractography indicate that the fracture mechanisms acting in equine cortical bone are regionally dependent. PMID:12547356

  9. The mechanisms of elbow fractures: an investigation using impact tests in vitro

    Microsoft Academic Search

    A. A. Amis; J. H. Miller

    1995-01-01

    Various mechanisms of injury have been hypothesized for each of the common elbow fractures, but few have been proved. This paper describes cadaveric experiments demonstrating some fracture mechanisms. Tests were performed at different angles of flexion, with impacts around the elbow or along the forearm bones. A range of fractures occurred. Radial head and coronoid fractures followed impact along the

  10. Measurements of residual stress in fracture mechanics coupons

    SciTech Connect

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

    2010-01-01

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

  11. Mechanical behavior of Al 2O 3-particle-reinforced 6061 aluminum alloy under uniaxial and multiaxial cyclic loading

    Microsoft Academic Search

    Z. Xia; F. Ellyin; G. Meijer

    1997-01-01

    Uniaxial and biaxial (proportional and non-proportional) strain-controlled tests were conducted to obtain mechanical properties of 6061 aluminum alloy reinforced with Al2O3 particles with 0.1 and 0.2 volume fractions. Thin-walled specimens were heat-treated in three groups, i.e. fully annealed (T0), solution and precipitation (T6) and as-extruded (F). The results indicaie that this composite material essentially has isotropic elasto-plastic properties similar to

  12. Finite deformation of elasto-plastic solids

    NASA Technical Reports Server (NTRS)

    Osias, J. R.

    1973-01-01

    A theoretical basis is established for analysis of finite deformation of metals. The observation that finite deformation of such elastoplastic materials may be viewed as a process rather than an event leads to derivation of a complete initial and boundary value problem distinguished by its quasilinear nature. This feature of the formulation motivates adoption of an incremental approach to numerical problem solving. Numerical solution capability is established for problems of plane stress and plane strain. The validity of the theory and numerical analysis is demonstrated by consideration of a number of problems of homogeneous finite deformation for which analytic solutions are available. Subsequently the analysis is employed for the investigation of necking in flat metal tensile bars. The results of this investigation provide the first full numerical solutions for tensile necking in plane stress and plane strain. In addition a basis is provided for assessment of the validity of stress-strain relations inferred from tensile test data.

  13. ON ADAPTIVE STRATEGIES AND ERROR CONTROL IN FRACTURE MECHANICS

    Microsoft Academic Search

    PER HEINTZ; KLAS SAMUELSSON

    2002-01-01

    Finite element approximations in elastic fracture mechanics are traditionally carried out on a priori constructed meshes with singularity elements that surrounds the crack tip. In this contribution we discuss an adaptive algorithm based on goal oriented error measures using ordinary elements and a p-refinement for the linearization of the secant forms. The numerical experiments show that good results can be

  14. Finite Element Simulation of Fracture Mechanism of Fibrous Food

    Microsoft Academic Search

    B. S. Sridhar; K. Sommer

    2011-01-01

    A Finite element model (FEM) was developed to simulate, analyze and to understand the finer mechanical interactions between the growing crack and the constituent material properties of turmeric (Curcuma longa) as a model material. The parameters varied were residual stress state, fiber orientation and interface bond. Fracture paths were predicted for fibers with respect to primary crack plane. FEM studies

  15. Structure, Mechanical Properties and Fracture Behavior of Organosilicate Glass

    E-print Network

    Structure, Mechanical Properties and Fracture Behavior of Organosilicate Glass Thin Films of Organosilicate Glass Thin Films Abstract Organosilicate glass (OSG) thin films with low permittivity made be finely tuned by changing the parameters during film deposition or post-treatments. Adding carbon content

  16. Mechanical fatigue and fracture of Nitinol S. W. Robertson*1

    E-print Network

    Ritchie, Robert

    Mechanical fatigue and fracture of Nitinol S. W. Robertson*1 , A. R. Pelton1 and R. O. Ritchie2 Nitinol, a near equiatomic intermetallic of nickel and titanium, is the most widely known and used shape transformation, Nitinol displays recoverable strains that are more than an order of magnitude greater than

  17. Fracture mechanics applied to the machining of brittle materials

    SciTech Connect

    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.

  18. FEA Based Tool Life Quantity Estimation of Hot Forging Dies Under Cyclic Thermo-Mechanical Loads

    NASA Astrophysics Data System (ADS)

    Behrens, B.-A.; Bouguecha, A.; Schäfer, F.; Hadifi, T.

    2011-01-01

    Hot forging dies are exposed during service to a combination of cyclic thermo-mechanical, tribological and chemical loads. Besides abrasive and adhesive wear on the die surface, fatigue crack initiation with subsequent fracture is one of the most frequent causes of failure. In order to extend the tool life, the finite element analysis (FEA) may serve as a means for process design and process optimisation. So far the FEA based estimation of the production cycles until initial cracking is limited as tool material behaviour due to repeated loading is not captured with the required accuracy. Material models which are able to account for cyclic effects are not verified for the fatigue life predictions of forging dies. Furthermore fatigue properties from strain controlled fatigue tests of relevant hot work steels are to date not available to allow for a close-to-reality fatigue life prediction. Two industrial forging processes, where clear fatigue crack initiation has been observed are considered for a fatigue analysis. For this purpose the relevant tool components are modelled with elasto-plastic material behaviour. The predicted sites, where crack initiation occurs, agree with the ones observed on the real die component.

  19. Physical and mechanical modelling of neutron irradiation effect on ductile fracture. Part 1. Prediction of fracture strain and fracture toughness of austenitic steels

    NASA Astrophysics Data System (ADS)

    Margolin, Boris; Sorokin, Alexander; Smirnov, Valeriy; Potapova, Vera

    2014-09-01

    A physical-and-mechanical model of ductile fracture has been developed to predict fracture toughness and fracture strain of irradiated austenitic steels taking into account stress-state triaxiality and radiation swelling. The model is based on criterion of plastic collapse of a material unit cell controlled by strain hardening of a material and criterion of voids coalescence due to channel shearing of voids. The model takes into account deformation voids nucleation and growth of deformation and vacancy voids. For justification of the model experimental data on fracture strain and fracture toughness of austenitic steel 18Cr-10Ni-Ti grade irradiated up to maximal dose 150 dpa with various swelling were used. Experimental data on fracture strain and fracture toughness were compared with the results predicted by the model. It has been shown that for prediction of the swelling effect on fracture toughness the dependence of process zone size on swelling should be taken into account.

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

    PubMed

    Birch, Aaron; Walsh, Ryan; Devita, Diane

    2013-03-01

    Since the first description of the Chance fracture in 1948, there have been few case reports of unique mechanisms causing this classical flexion-extension injury to the spine in motor vehicle accidents, sports injury, and falls. To our knowledge, this injury has not been reported from a fall with the mechanistic forces acting laterally on the spine and with spinal support in place. We present a 21-year-old male who slid down a flight of stairs onto his side wearing a heavy mountaineering style backpack, subsequently sustaining a Chance fracture of his first lumbar vertebrae. PMID:23599852

  1. A Computational Linear Elastic Fracture Mechanics-based Model for Alkali-Silica Reaction

    E-print Network

    Boyer, Edmond

    A Computational Linear Elastic Fracture Mechanics-based Model for Alkali-Silica Reaction Laurent: This poster presents a fracture mechanics model for Alkali-Silica Reaction. The model deals with the case

  2. Fracture mechanics analysis on the resistance of welded details under variable amplitude long life loading 

    E-print Network

    Zhou, Minjian

    1993-01-01

    amplitude fatigue limit. First of all, fracture mechanics models are established based on linear elastic fracture mechanics. Two methods are employed to compute the crack growth and fatigue life under variable amplitude fatigue long life loading...

  3. Optimal mechanical environment of the healing bone fracture/osteotomy.

    PubMed

    Mav?i?, Blaž; Antoli?, Vane

    2012-04-01

    The aim of this paper is to review recent experimental and clinical publications on bone biology with respect to the optimal mechanical environment in the healing process of fractures and osteotomies. The basic postulates of bone fracture healing include static bone compression and immobilisation/ fixation for three weeks and intermittent dynamic loading treatment afterwards. The optimal mechanical strain should be in the range of 100-2,000 microstrain, depending on the frequency of the strain application, type of bone and location in the bone, age and hormonal status. Higher frequency of mechanical strain application or larger number of repetition cycles result in increased bone mass at the healing fracture site, but only up to a certain limit, values beyond which no additional benefit is observed. Strain application and transition period from non-load-bearing to full load-bearing can be modified by implants allowing dynamisation of compression and generating strains at the fracture healing site in a controlled manner. PMID:22302177

  4. Fracture control methods for space vehicles. Volume 2: Assessment of fracture mechanics technology for space shuttle applications

    NASA Technical Reports Server (NTRS)

    Ehret, R. M.

    1974-01-01

    The concepts explored in a state of the art review of those engineering fracture mechanics considered most applicable to the space shuttle vehicle include fracture toughness, precritical flaw growth, failure mechanisms, inspection methods (including proof test logic), and crack growth predictive analysis techniques.

  5. Elastic plastic fracture mechanics methodology for surface cracks

    NASA Technical Reports Server (NTRS)

    Ernst, Hugo A.; Lambert, D. M.

    1994-01-01

    The Elastic Plastic Fracture Mechanics Methodology has evolved significantly in the last several years. Nevertheless, some of these concepts need to be extended further before the whole methodology can be safely applied to structural parts. Specifically, there is a need to include the effect of constraint in the characterization of material resistance to crack growth and also to extend these methods to the case of 3D defects. As a consequence, this project was started as a 36 month research program with the general objective of developing an elastic plastic fracture mechanics methodology to assess the structural reliability of pressure vessels and other parts of interest to NASA which may contain flaws. The project is divided into three tasks that deal with (1) constraint and thickness effects, (2) three-dimensional cracks, and (3) the Leak-Before-Burst (LBB) criterion. This report period (March 1994 to August 1994) is a continuation of attempts to characterize three dimensional aspects of fracture present in 'two dimensional' or planar configuration specimens (Chapter Two), especially, the determination of, and use of, crack face separation data. Also, included, are a variety of fracture resistance testing results (J(m)R-curve format) and a discussion regarding two materials of NASA interest (6061-T651 Aluminum alloy and 1N718-STA1 nickel-base super alloy) involving a bases for like constraint in terms of ligament dimensions, and their comparison to the resulting J(m)R-curves (Chapter Two).

  6. Mechanism-based approach for prediction of ductile fracture

    NASA Astrophysics Data System (ADS)

    Kim, Jin Kook

    Mechanism-based fracture mechanics attempts to link the micro-structural parameters and continuum properties of the material to the macroscopically measured fracture resistance. Two types of approaches have been proposed in the published literature to implement the mechanism-based concepts for the ductile fracture: explicit void representation and the continuum damage model. This study deals with both approaches. In the approach using explicit void representation, an array of micro-voids are assumed to pre-exist in the material and are modeled explicitly using refined finite elements in the 3-D small scale yielding (SSY) model to simulate the material failure process and ductile crack growth. A method to determine failure of the ligament between the crack tip and the nearest void is presented. The failure criterion is used to determine the fracture initiation toughness and J-R curve. The effect of void shape on the fracture toughness is examined. For the approach using a continuum damage model, a precise constitutive model for characterization of the void-containing material behavior during the ductile fracture process is needed. The Gurson-Tvergaard (GT) model is one of the widely used continuum damage models for materials containing spherical voids. A method to calibrate the two micromechanics parameters (q 1,q2) of the GT model is suggested in this study. It was found that these two parameters are functions of the initial void volume and the stress state of the void-containing material volume. The effects of the 3-D stress state, which can be expressed by the triaxiality stress ratio and the lode angle, on the parameters (q 1, q2) are discussed. A generalized numerical algorithm to calculate the consistent tangent stiffness was derived and applied to the Goludanu-Leblond-Devaux (GLD) continuum damage model for materials containing spheroidal shape voids. The performance comparison between the consistent tangent stiffness and the conventional continuum tangent stiffness demonstrates the significant improvement in convergence characteristics of the overall Newton iterations caused by using the consistent tangent matrix. The GLD model was implemented in ABAQUS via a user material subroutine. A series of parametric studies was conducted to demonstrate the application of the GLD model in fracture analysis.

  7. Effect of heat treatment on deformation and mechanical properties of 8 mol% yttria-stabilized zirconia by Berkovich nanoindentation

    NASA Astrophysics Data System (ADS)

    Mao, W. G.; Luo, J. M.; Dai, C. Y.; Shen, Y. G.

    2015-05-01

    The effect of thermal treatment on the elasto-plastic transition and mechanical properties of air plasma-sprayed 8 mol% Y2O3-stabilized ZrO2 (8YSZ) thermal barrier coatings was studied by nanoindentation test at ultra-low loads with a Berkovich indenter. The area contact function of the indenter was calibrated repeatedly under nano-scales, and the indenter tip radius was estimated under different indentation depths, respectively. Owing to the heterogeneous and porous microstructure, the scatter of all collected experimental data was analyzed by Weibull statistic method. It is interesting to observe that the hardness exhibits an apparent reverse indentation size effect under very small depths. The Young's modulus of 8YSZ varies with ranging from 213 to 246 GPa due to the sintering effect. True hardness of 8YSZ increases from as-received 72.9 GPa to a top value 79.7 GPa under 100 thermal cycles, and then slightly decreases from this value to 75.5 GPa under 175 thermal cycles. The pure elastic and elasto-plastic indentation curves were obtained by adjusting the indentation load magnitude. The elasto-plastic transition and resolved shear stress fields were discussed carefully from the use of energetic models and Hertzian contact theory.

  8. Mechanisms of particulate filled polypropylene finite plastic deformation and fracture

    Microsoft Academic Search

    I. L DUBNIKOVA; V. G OSHMYAN; A. YA GORENBERG

    1997-01-01

    The plastic deformation and fracture of aluminium hydroxide filled polypropylene has been investigated. A transition between\\u000a two mechanisms with an increase of the filler volume fraction has been observed. Below a critical filler volume content ?cr\\u000a ? 20 vol% (designated region 1) adhesive failure processes and polymer deformation in the neighbourhoods of different particles\\u000a occur in an uncorrelated manner. Above

  9. Fracture and Stress Evolution on Europa: New Insights Into Fracture Interpretation and Ice Thickness Estimates Using Fracture Mechanics Analyses

    NASA Technical Reports Server (NTRS)

    Kattenhorn, Simon

    2004-01-01

    The work completed during the funding period has provided many important insights into fracturing behavior in Europa's ice shell. It has been determined that fracturing through time is likely to have been controlled by the effects of nonsynchronous rotation stresses and that as much as 720 deg of said rotation may have occurred during the visible geologic history. It has been determined that there are at least two distinct styles of strike-slip faulting and that their mutual evolutionary styles are likely to have been different, with one involving a significant dilational component during shear motion. It has been determined that secondary fracturing in perturbed stress fields adjacent to older structures such as faults is a prevalent process on Europa. It has been determined that cycloidal ridges are likely to experience shear stresses along the existing segment portions as they propagate, which affects propagation direction and ultimately induces tailcracking at the segment tip than then initiates a new cycle of cycloid segment growth. Finally, it has been established that mechanical methods (e.g., flexure analysis) can be used to determine the elastic thickness of the ice shell, which, although probably only several km thick, is likely to be spatially variable, being thinner under bands but thicker under ridged plains terrain.

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

    SciTech Connect

    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.

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

    SciTech Connect

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

    1985-08-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

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

  13. A partitioned model order reduction approach to rationalise computational expenses in nonlinear fracture mechanics

    E-print Network

    Paris-Sud XI, Université de

    . In fracture mechanics, the initiation and propagation of cracks is the result of localised microscopic fracture mechanics P. Kerfriden1 , O. Goury1 , T. Rabczuk2 , S.P.A. Bordas1 1 Cardiff University, School of fracture. We show that coupling domain decomposition and projection- based model order reduction permits

  14. Two mechanisms of ductile fracture: void by void growth versus multiple void interaction

    E-print Network

    Hutchinson, John W.

    of ductile fracture. One is the interaction a single void with the crack tip characterizing initiation modeled in the literature on the mechanics of ductile fracture. One view has crack growth initiationTwo mechanisms of ductile fracture: void by void growth versus multiple void interaction Viggo

  15. A partitioned model order reduction approach to rationalise computational expenses in multiscale fracture mechanics

    E-print Network

    . In fracture mechanics, the initiation and propagation of cracks is the result of localised microscopic fracture mechanics P. Kerfriden1 , O. Goury1 , T. Rabczuk2 , S.P.A. Bordas1 1 Cardiff University, School of fracture. We show that coupling domain decomposition and projection-based model order reduction permits

  16. A partitioned model order reduction approach to rationalise computational expenses in multiscale fracture mechanics

    E-print Network

    Paris-Sud XI, Université de

    and the scale at which the phenomena of interest need to be described. In fracture mechanics, the initiation fracture mechanics P. Kerfriden, O. Goury, T. Rabczuk, S.P.A. Bordas May 2, 2012 Abstract 1 Introduction for predictive results. In any case, the local nature of fracture leads to large numerical models because sharp

  17. Elevated temperature fracture of RS/PM alloy 8009: part i. fracture mechanics behavior

    NASA Astrophysics Data System (ADS)

    Porr, William C.; Gangloff, Richard P.

    1994-02-01

    Increasing temperature and decreasing loading rate degrade the plane strain initiation ( K ICifrom the J integral) and growth (tearing modulus, T R) fracture toughnesses of RS/PM 8009 (Al-8.5Fe-1.3V-1.7Si, wt pct). K ICidecreases with increasing temperature from 25 ‡C to 175 ‡C (33 to 15 MPa?m for an extrusion and 28 to 11 MPa?m for hot cross-rolled plate) and further declines to 10 MPaVm at 316 ‡C without a minimum. T Ris greater than zero at all temperatures and is minimized at 200 ‡C. A four order-of-magnitude decrease in loading rate, at 175 ‡C, results in a 2.5-fold decrease in K ICiand a 5-fold reduction in T R. K ICiand T Rare anisotropic for extruded 8009 but are isotropic for cross-rolled plate. Cross rolling does not improve the magnitude or adverse temperature dependence of toughness. Delamination occurs along oxide-decorated particle boundaries for extruded but not cross-rolled 8009. Delamination toughening plays no role in the temperature dependence of K ICi, however, T Ris increased by this mechanism. Macroscopic work softening and flow localization do not occur for notch-root deformation; such uniaxial tensile phenomena may not be directly relevant to crack-tip fracture. Micromechanical modeling, employing temperature-dependent flow strength, modulus, and constrained fracture strain, reasonably predicts the temperature dependencies of K ICiand T Rfor 8009. While E and ?ys decrease with increasing temperature for all aluminum alloys, the strain to nucleate crack-tip damage dominates the fracture toughness of 8009 and decreases with increasing temperature for a range of constraint. Damage mechanisms for this novel behavior are evaluated in Part II.

  18. Application of elastic-plastic fracture mechanics to marine structures

    E-print Network

    Pathi, Amarkumar

    1991-01-01

    machine, and ASTM E 23 [21] guidelines were followed. Specimens machined from the center were engraved C and those machined from the sur- face were engraved S. The orientations of the EH 36 specimens and the HSLA 80 specimens were in the L-T direction... OF SCIENCE May 1991 Major Subject: Mechanical Engineering APPLICATION OF ELASTIC-PLASTIC FRACTURE MECHANICS TO MARINE STRUCTURES A Thesis by AMARI&UMAR PATEII Approved as to style and content by: Ted L. Anderson (C 'r of Commi e) Ravind ona ember...

  19. Fracture mechanics; Proceedings of the Twenty-first ASTM National Symposium, Annapolis, MD, June 28-30, 1988

    SciTech Connect

    Gudas, J.P.; Hackett, E.M.; Joyce, J.A.

    1990-01-01

    The papers presented in this volume provide an overview of recent theoretical and experimental research in various areas of fracture mechanics and its applications. The papers are grouped under the following headings: elastic-plastic fracture mechanics, dynamic fracture, transition fracture, micromechanics of fracture, computational mechanics, fracture mechanics applications, and fracture mechanics testing. Specific topics discussed include dynamic fracture behavior of a structural steel; finite element meshing criteria for crack problems; method and models for R-curve instability calculations; and closure measurements via a generalized threshold concept.

  20. [Radius fractures in children--causes and mechanisms of injury].

    PubMed

    Antabak, Anko; Stani?, Lana; Matkovi?, Nikša; Papeš, Dino; Romi?, Ivan; Fuchs, Nino; Lueti?, Tomislav

    2015-01-01

    Radius fractures are the most common fractures in childhood. The main mechanism of injury is fall onto an outstretched hand. This retrospective study analyzed the data on 201 children admitted for radius fractures at KBC-Zagreb in the period 2011-2013. The study included 85 girls (42.3%) and 116 boys (57.7%) . The average age of the children was 9.6 years. Radius was injured in the distal segment in 79.1% of children. The sites of injuries were: park, campi and beach (24.9% of all children), playground, skate park and swimming pool (23.9%), kindergarten or school (20.9%), at home and around the house (17.9%), in the street (11.4%) and in the store or at a hotel (0.9%). The boys were mostly injured at playgrounds, during skating and at swimming pools (37.1% of all boys), while girls were mostly injured in parks, camps and at beach (42.4% girls). Fall was the major cause of the injury (49.3%), and children usually fell during ice skating and skating (32.3% of all falls). In 20.4% the injury was caused by pushing and hitting. The smallest percentage (9.5%) of children were injured in traffic accidents while riding a bike (only one child was hit by a car). Sport related activities caused injuries in 53.7% of the cases. Sport activities are the most important cause of the radial fractures in the pediatric population and falls during sports are the main mechanism of injury. The peak incidence is at 12 years for boys and at 10 years for girls, so intervention and/or prevention should be aimed at the age groups. Preventive actions should be focused on injuries that tend to occur in parks, schools and during sport activities. PMID:26065283

  1. A dimensional decomposition method for stochastic fracture mechanics

    E-print Network

    Rahman, Sharif

    -integral and probability of fracture initiation for various cases including material gradation characteristics density of J-integral; Probability of fracture initiation; Decomposition method; Univariate decomposition and provides probabilistic characteristics of fracture initiation and growth of an existing crack, real

  2. HYDRO-MECHANICAL UPSCALING OF A FRACTURED ROCKMASS USING A 3D NUMERICAL APPROACH

    E-print Network

    Paris-Sud XI, Université de

    / 2 µ L) ij (2) = 2.45 10-7 m/s where: a (= 10-4 m) is the hydraulic aperture of the fracture; µ (= 10HYDRO-MECHANICAL UPSCALING OF A FRACTURED ROCKMASS USING A 3D NUMERICAL APPROACH Thoraval Alain compared with standard analytical approaches in the case of a simple fracture network. This method has been

  3. Z .Mechanics of Materials 28 1998 247262 Experimental and computational study of fracturing in an

    E-print Network

    Nemat-Nasser, Sia

    Z .Mechanics of Materials 28 1998 247­262 Experimental and computational study of fracturing, stress- and energy-based fracture criteria lead to fairly similar results. Theoretical studies show the fracture path along different cleavage planes. The experimental observations are compared

  4. Size and Temperature Effects on the Fracture Mechanisms of Silicon Nanowires: Molecular Dynamics

    E-print Network

    Cai, Wei

    Size and Temperature Effects on the Fracture Mechanisms of Silicon Nanowires: Molecular Dynamics. The fracture behavior of the NWs depends both on temperature and NW diameter. For NWs of di- ameter larger than 4 nm, cleavage fracture on the transverse (1 1 0) plane are predominantly observed at temperatures

  5. Title: Experimental Fracture Mechanics for the Bond between Composite Overlays and Concrete Substrate

    E-print Network

    Giurgiutiu, Victor

    should have high resistance to crack propagation, i.e. high fracture toughness. Crack initiation1 Title: Experimental Fracture Mechanics for the Bond between Composite Overlays and Concrete strength of composite overlays to concrete utilizing a fracture toughness test.. Specimen preparation, test

  6. NASGRO(registered trademark): Fracture Mechanics and Fatigue Crack Growth Analysis Software

    NASA Technical Reports Server (NTRS)

    Forman, Royce; Shivakumar, V.; Mettu, Sambi; Beek, Joachim; Williams, Leonard; Yeh, Feng; McClung, Craig; Cardinal, Joe

    2004-01-01

    This viewgraph presentation describes NASGRO, which is a fracture mechanics and fatigue crack growth analysis software package that is used to reduce risk of fracture in Space Shuttles. The contents include: 1) Consequences of Fracture; 2) NASA Fracture Control Requirements; 3) NASGRO Reduces Risk; 4) NASGRO Use Inside NASA; 5) NASGRO Components: Crack Growth Module; 6) NASGRO Components:Material Property Module; 7) Typical NASGRO analysis: Crack growth or component life calculation; and 8) NASGRO Sample Application: Orbiter feedline flowliner crack analysis.

  7. Development and application of an advanced ductile fracture mechanics methodology

    NASA Astrophysics Data System (ADS)

    Zhou, Zhen

    An advanced ductile fracture mechanics methodology is presented here. This methodology takes a load versus displacement result from a laboratory specimen test to predict the load versus displacement for a structural component containing crack-like defect. To use this methodology, three steps need to be followed. First a test record from laboratory experiment needs to be reduced into two pieces of information, the calibration function and the fracture toughness. The calibration function relates load, displacement and crack size. The fracture toughness relates crack driving force and crack extension in terms of a J-R curve. The second step is to transfer this information to a structural component to be analyzed. After the calibration function and the fracture toughness for the structural component are determined, the last step is to use a ductile fracture methodology proposed by Ernst and Landes to predict the load versus displacement behavior of the structural component. Traditionally the J-R curve has been developed according to the ASTM standard. Crack growth is usually estimated by instrumentation. This does not always work well for non-side grooved specimens and polymeric materials. To ensure accurate data reduction, the normalization method for J-R curve calculation is further developed by introducing the LMN function as the calibration function. The new version of the normalization method works well for both metallic and polymeric materials. It is more reliable and versatile than the compliance method. Two procedures for the determination of the LMN function are introduced. Two procedures are developed for generating the calibration function for a structural component of interest. One is the transformation procedure that can be applied to the case where the limit load solution for the structural component is known. The other procedure is based on numerical simulation incorporating with the load separation method.

  8. Application of probabilistic fracture mechanics to the PTS issue

    SciTech Connect

    Cheverton, R.D.; Ball, D.G.

    1985-01-01

    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.

  9. Coupled Flow and Mechanics in Porous and Fractured Media*

    NASA Astrophysics Data System (ADS)

    Martinez, M. J.; Newell, P.; Bishop, J.

    2012-12-01

    Numerical models describing subsurface flow through deformable porous materials are important for understanding and enabling energy security and climate security. Some applications of current interest come from such diverse areas as geologic sequestration of anthropogenic CO2, hydro-fracturing for stimulation of hydrocarbon reservoirs, and modeling electrochemistry-induced swelling of fluid-filled porous electrodes. Induced stress fields in any of these applications can lead to structural failure and fracture. The ultimate goal of this research is to model evolving faults and fracture networks and flow within the networks while coupling to flow and mechanics within the intact porous structure. We report here on a new computational capability for coupling of multiphase porous flow with geomechanics including assessment of over-pressure-induced structural damage. The geomechanics is coupled to the flow via the variation in the fluid pore pressures, whereas the flow problem is coupled to mechanics by the concomitant material strains which alter the pore volume (porosity field) and hence the permeability field. For linear elastic solid mechanics a monolithic coupling strategy is utilized. For nonlinear elastic/plastic and fractured media, a segregated coupling is presented. To facilitate coupling with disparate flow and mechanics time scales, the coupling strategy allows for different time steps in the flow solve compared to the mechanics solve. If time steps are synchronized, the controller allows user-specified intra-time-step iterations. The iterative coupling is dynamically controlled based on a norm measuring the degree of variation in the deformed porosity. The model is applied for evaluation of the integrity of jointed caprock systems during CO2 sequestration operations. Creation or reactivation of joints can lead to enhanced pathways for leakage. Similarly, over-pressures can induce flow along faults. Fluid flow rates in fractures are strongly dependent on the effective hydraulic aperture, which is a non-linear function of effective normal stress. The dynamically evolving aperture field updates the effective, anisotropic permeability tensor, thus resulting in a highly coupled multiphysics problem. Two models of geomechanical damage are discussed: critical shear-slip criteria and a sub-grid joint model. Leakage rates through the caprock resulting from the joint model are compared to those assuming intact material, allowing a correlation between potential for leakage and injection rates/pressures, for various in-situ stratigraphies. *This material is based upon work supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001114. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energys National Nuclear Security Administration under Contract DE-AC04-94AL85000.

  10. An experimental investigation into the mechanics of dynamic fracture

    NASA Astrophysics Data System (ADS)

    Ravi-Chandar, K.

    Current theories of dynamic fracture are based on elastodynamic analyses of mathematically sharp plane cracks and as such do not explain the observed terminal velocities or the phenomenon of crack branching satisfactorily. The present investigation addresses the above problems by using both microscopic and macroscopic interpretations. The experimental scheme that is used in this investigation is the configuration of a pressure loaded semi-infinite crack in an infinite medium. The loading is achieved through an electromagnetic device which provides highly repeatable loading. The method of caustics is used in conjunction with a high speed camera to obtain the time histories of the crack tip stress intensity factor and the crack position.The problems of crack initiation and crack arrest are explored. The stress intensity factor at initiation is found to be independent of the rate of applied loading when the latter is below about 10[^4]MPA/sec, but the initiation stress intensity factor increases considerably when the loading rate is increased further. Crack arrest is obtained in large specimen by using very low energy loading pulses. It was found that the stress intensity factor at crack arrest was constant and also that, within the time resolution of the high speed camera (5[milli]sec), the crack comes to a stop abruptly.The crack propagation and branching aspects were investigated first using post-mortem analysis of the fracture surfaces and high speed photomicrography to get an idea of the microscopic processes that occur in the fracure process. From this investigation, it was found that crack propagation involving high stress intensity factor and high velocity situations takes place by the growth and interaction of microcracks, due to the voids present in the material. A surprising result of this investigation was that cracks propagated at a constant velocity, although the stress intensity factor varied. Current theories of dynamic fracture cannot explain such behaviour. The crack branching process was found to be a continuous process arising out of propagation along a straight line. High speed photomicrographs of the branching process indicated the presence of a number of part-through attempted branches that interact with one another and finally the successful emergence of a few full fledged branches.The microscopic observations on the crack propagation and branching process leads to a new interpretation of dynamic fracture that attempts to qualitatively explain the constancy of the velocity of propagation, the terminal velocity and crack branching. The crack branching mechanism is a logical continuation of the mechanism for crack propagation.

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

    NASA Technical Reports Server (NTRS)

    Hanagud, S.; Uppaluri, B.

    1977-01-01

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

  12. On study of nonclassical problems of fracture and failure mechanics and related mechanisms

    Microsoft Academic Search

    Alexander N. Guz

    2009-01-01

    Nonclassical problems of fracture and failure mechanics that have been analyzed by the author and his collaborators at the\\u000a S. P. Timoshenko Institute of Mechanics (Kiev, National Academy of Sciences of Ukraine) during the past forty years are considered\\u000a in brief. The results of the analysis are presented in a form that would be quite informative for the majority of

  13. Elastic plastic fracture mechanics methodology for surface cracks

    NASA Technical Reports Server (NTRS)

    Ernst, Hugo A.; Boatwright, D. W.; Curtin, W. J.; Lambert, D. M.

    1993-01-01

    The Elastic Plastic Fracture Mechanics (EPFM) Methodology has evolved significantly in the last several years. Nevertheless, some of these concepts need to be extended further before the whole methodology can be safely applied to structural parts. Specifically, there is a need to include the effect of constraint in the characterization of material resistance to crack growth and also to extend these methods to the case of 3D defects. As a consequence, this project was started as a 36 month research program with the general objective of developing an EPFM methodology to assess the structural reliability of pressure vessels and other parts of interest to NASA containing defects. This report covers a computer modelling algorithm used to simulate the growth of a semi-elliptical surface crack; the presentation of a finite element investigation that compared the theoretical (HRR) stress field to that produced by elastic and elastic-plastic models; and experimental efforts to characterize three dimensional aspects of fracture present in 'two dimensional', or planar configuration specimens.

  14. Laser micromachining for fatigue and fracture mechanics applications

    NASA Astrophysics Data System (ADS)

    Gupta, M. C.; Li, B.; Gadag, S.; Chou, K. C.

    2010-04-01

    A laser micromachining (LMM) method to initiate flaws for fatigue and fracture mechanics applications is successfully demonstrated. Dynamic response of moving energy pulses during LMM of titanium alloy (Ti-3.5Al-2.5V) was numerically simulated by an integrated energy approach using temperature-dependent thermophysical properties and 3D heat transfer code. Stress and strain analyses were performed for a titanium tube of 9.53 mm outer diameter (OD) and 0.81 mm wall thickness (WT) with a 0.23 mm deep and 1.83-mm-long longitudinal laser micro-machined notch, using nonlinear finite element analysis (FEA). For comparison, an electric-discharge-machined (EDM) notched tube with the same notch profile as the laser-prepared tube was also investigated. The calculated hoop stress and strain amplitudes at the notch root of the EDM-prepared tube were approximately 64% and 63% of the stress and strain amplitudes in the laser-prepared tube, respectively, when two tubes were subjected to inner pressures for R ratio of 0.03 and ? P=45, 50, and 55 MPa. Fatigue life due to crack initiation process can be minimized using LMM method. The described LMM method is, therefore, more appropriate than EDM for accomplishing flaw formation to study fatigue and fracture behavior of various materials.

  15. Fracture Mechanics Analysis of LH2 Feed Line Flow Liners

    NASA Technical Reports Server (NTRS)

    James, Mark A.; Dawicke, David S.; Brzowski, Matthew B.; Raju, Ivatury S.; Elliott, Kenny B.; Harris, Charles E.

    2006-01-01

    Inspections of the Space Shuttle Main Engine revealed fatigue cracks growing from slots in the flow liner of the liquid hydrogen (LH2) feed lines. During flight, the flow liners experience complex loading induced by flow of LH2 and the resonance characteristics of the structure. The flow liners are made of Inconel 718 and had previously not been considered a fracture critical component. However, fatigue failure of a flow liner could have catastrophic effect on the Shuttle engines. A fracture mechanics study was performed to determine if a damage tolerance approach to life management was possible and to determine the sensitivity to the load spectra, material properties, and crack size. The load spectra were derived separately from ground tests and material properties were obtained from coupon tests. The stress-intensity factors for the fatigue cracks were determined from a shell-dynamics approach that simulated the dominant resonant frequencies. Life predictions were obtained using the NASGRO life prediction code. The results indicated that adequate life could not be demonstrated for initial crack lengths of the size that could be detected by traditional NDE techniques.

  16. Model for Fracturing Fluid Flowback and Characterization of Flowback Mechanisms 

    E-print Network

    Song, Bo

    2014-08-28

    A large volume of fracturing fluid that may include slick water and various sorts of additives is injected into shale formations along with proppant to create hydraulic fractures which define a stimulated shale volume a shale gas well will actually...

  17. A rare case of open bicondylar Hoffa fracture with extensor mechanism disruption

    PubMed Central

    Kini, Sunil Gurpur; Sharma, Mrinal; Raman, Rajeev

    2013-01-01

    The incidence of open bicondylar Hoffa fractures is extremely rare. We report one such case of a 42-year-old woman who presented to the emergency department with an open injury over the knee. Imaging revealed bicondylar Hoffa fracture. The patient was taken up for debridement and internal fixation. Intraoperative findings included an entrapped patella between the fracture fragments and extensor mechanism disruption. Hoffas fracture was fixed with lag screws and patellar tendon repaired on to the inferior patella. The patient was started on early postoperative range of motion exercises. The fracture united at 12?weeks with 120° knee flexion at 2?year follow-up. PMID:23645653

  18. Name of Lecture Linear Fracture Mechanics Term Autumn Semester

    E-print Network

    test 5. Fatigue & Stress Corrosion Cracking 6. Structural integrity evaluation process for a nuclear of elasticity & Stress Intensity factor 3. Crack Tip Plasticity 4. Fracture toughness and Fracture toughness the definitions of stress and strain in the first lecture, and it includes outline of the linear fracture

  19. Mechanical transport and porous media equivalence in anisotropic fracture networks

    Microsoft Academic Search

    H. K. Endo; P. A. Witherspoon

    1985-01-01

    The objective of this work is to investigate the directional characteristics of hydraulic effective porosity in an effort to understand porous medium equivalence for continuous and discontinuous fracture systems. Continuous systems contain infinitely long fractures. Discontinuous systems consist of fractures with finite lengths. The distribution of apertures (heterogeneity) has a major influence on the degree of porous medium equivalence for

  20. Fracture mechanics concepts in reliability analysis of monolithic ceramics

    NASA Technical Reports Server (NTRS)

    Manderscheid, Jane M.; Gyekenyesi, John P.

    1987-01-01

    Basic design concepts for high-performance, monolithic ceramic structural components are addressed. The design of brittle ceramics differs from that of ductile metals because of the inability of ceramic materials to redistribute high local stresses caused by inherent flaws. Random flaw size and orientation requires that a probabilistic analysis be performed in order to determine component reliability. The current trend in probabilistic analysis is to combine linear elastic fracture mechanics concepts with the two parameter Weibull distribution function to predict component reliability under multiaxial stress states. Nondestructive evaluation supports this analytical effort by supplying data during verification testing. It can also help to determine statistical parameters which describe the material strength variation, in particular the material threshold strength (the third Weibull parameter), which in the past was often taken as zero for simplicity.

  1. Linear Elastic Fracture Mechanics Pullout Analyses of Headed Anchors in Stressed Concrete

    E-print Network

    Ballarini, Roberto

    Linear Elastic Fracture Mechanics Pullout Analyses of Headed Anchors in Stressed Concrete R of headed anchors embedded in concrete with those developed using fracture mechanics. While provisions, no provisions are available for anchors embedded in prestressed concrete. This paper presents the results

  2. A BEM analysis of fracture mechanics in 2D anisotropic piezoelectric solids

    E-print Network

    Pan, Ernie

    A BEM analysis of fracture mechanics in 2D anisotropic piezoelectric solids Ernian Pan* Department-domain boundary element method (BEM) analysis of fracture mechanics in 2D anisotropic piezoelectric solids's functions for the anisotropic piezoelectric solids in an infinite plane, a half plane, and two joined

  3. Structural, mechanical properties and fracture mechanism of RuB(1.1).

    PubMed

    Pan, Yong; Guan, Weiming; Zheng, Weitao

    2014-04-01

    Polycrystalline RuB(1.1) has been prepared by using an arc-melting method and its structure and mechanical properties including elastic modulus, hardness and fracture behavior have been characterized. Also, the electronic structure and bond characteristics for this compound have been investigated by first-principles calculations. The lattice parameters of RuB(1.1) have been precisely determined by a Rietveld refinement. First-principles calculations show that this compound has a high bulk modulus and a big Poisson's ratio compared to RuB2. The measured hardness of ~10.6 GPa for RuB(1.1) is three times lower than the theoretical value. This low hardness can be attributed to bond characteristics such as the bonding state and orientation, and fracture mechanism, in which the features of the Ru-B bonds plays an important role in the hardness. We found that there is an isosceles triangle bonding state including the B-B and Ru-B bonds, and the two-dimensionally inclined Ru-B bonds along the a-b plane weaken the hardness and C33. The scanning electron microscopy images show that this RuB(1.1) compound exhibits a twinning fracture, and this fracture model is also confirmed by first-principle calculations. PMID:24496462

  4. Linear elastic fracture mechanics in anisotropic solids : application to fluid-driven crack propagation

    E-print Network

    Laubie, Hadrien Hyacinthe

    2013-01-01

    Fracture mechanics is a field of continuum mechanics with the objective to predict how cracks initiate and propagate in solids. It has a wide domain of application. While aerospace engineers want to make sure a defect in ...

  5. Investigation of translaminar fracture in fibrereinforced composite laminates---applicability of linear elastic fracture mechanics and cohesive-zone model

    NASA Astrophysics Data System (ADS)

    Hou, Fang

    With the extensive application of fiber-reinforced composite laminates in industry, research on the fracture mechanisms of this type of materials have drawn more and more attentions. A variety of fracture theories and models have been developed. Among them, the linear elastic fracture mechanics (LEFM) and cohesive-zone model (CZM) are two widely-accepted fracture models, which have already shown applicability in the fracture analysis of fiber-reinforced composite laminates. However, there remain challenges which prevent further applications of the two fracture models, such as the experimental measurement of fracture resistance. This dissertation primarily focused on the study of the applicability of LEFM and CZM for the fracture analysis of translaminar fracture in fibre-reinforced composite laminates. The research for each fracture model consisted of two sections: the analytical characterization of crack-tip fields and the experimental measurement of fracture resistance parameters. In the study of LEFM, an experimental investigation based on full-field crack-tip displacement measurements was carried out as a way to characterize the subcritical and steady-state crack advances in translaminar fracture of fiber-reinforced composite laminates. Here, the fiber-reinforced composite laminates were approximated as anisotropic solids. The experimental investigation relied on the LEFM theory with a modification with respect to the material anisotropy. Firstly, the full-field crack-tip displacement fields were measured by Digital Image Correlation (DIC). Then two methods, separately based on the stress intensity approach and the energy approach, were developed to measure the crack-tip field parameters from crack-tip displacement fields. The studied crack-tip field parameters included the stress intensity factor, energy release rate and effective crack length. Moreover, the crack-growth resistance curves (R-curves) were constructed with the measured crack-tip field parameters. In addition, an error analysis was carried out with an emphasis on the influence of out-of-plane rotation of specimen. In the study of CZM, two analytical inverse methods, namely the field projection method (FPM) and the separable nonlinear least-squares method, were developed for the extraction of cohesive fracture properties from crack-tip full-field displacements. Firstly, analytical characterizations of the elastic fields around a crack-tip cohesive zone and the cohesive variables within the cohesive zone were derived in terms of an eigenfunction expansion. Then both of the inverse methods were developed based on the analytical characterization. With the analytical inverse methods, the cohesive-zone law (CZL), cohesive-zone size and position can be inversely computed from the cohesive-crack-tip displacement fields. In the study, comprehensive numerical tests were carried out to investigate the applicability and robustness of two inverse methods. From the numerical tests, it was found that the field projection method was very sensitive to noise and thus had limited applicability in practice. On the other hand, the separable nonlinear least-squares method was found to be more noise-resistant and less ill-conditioned. Subsequently, the applicability of separable nonlinear least-squares method was validated with the same translaminar fracture experiment for the study of LEFM. Eventually, it was found that the experimental measurements of R-curves and CZL showed a great agreement, in both of the fracture energy and the predicted load carrying capability. It thus demonstrated the validity of present research for the translaminar fracture of fiber-reinforced composite laminates.

  6. Fracture mechanics analysis for various fiber/matrix interface loadings

    NASA Technical Reports Server (NTRS)

    Naik, R. A.; Crews, J. H., Jr.

    1991-01-01

    Fiber/matrix (F/M) cracking was analyzed to provide better understanding and guidance in developing F/M interface fracture toughness tests. Two configurations, corresponding to F/M cracking at a broken fiber and at the free edge, were investigated. The effects of mechanical loading, thermal cooldown, and friction were investigated. Each configuration was analyzed for two loadings: longitudinal and normal to the fiber. A nonlinear finite element analysis was performed to model friction and slip at the F/M interface. A new procedure for fitting a square-root singularity to calculated stresses was developed to determine stress intensity factors (K sub I and K sub II) for a bimaterial interface crack. For the case of F/M cracking at a broken fiber with longitudinal loading, crack tip conditions were strongly influenced by interface friction. As a result, an F/M interface toughness test based on this case was not recommended because nonlinear data analysis methods would be required. For the free edge crack configuration, both mechanical and thermal loading caused crack opening, thereby avoiding frictional effects. An F/M interface toughness test based on this configuration would provide data for K(sub I)/K(sub II) ratios of about 0.7 and 1.6 for fiber and radial normal loading, respectively. However, thermal effects must be accounted for in the data analysis.

  7. Mechanisms of fast fracture and arrest in steels

    Microsoft Academic Search

    R. G. Hoagland; A. R. Rosenfield; G. T. Hahn

    1972-01-01

    Studies of the unstable propagation and arrest of brittle fractures were conducted on four steels: plain carbon steel, 3 pct\\u000a Si steel, A-517, and 4340. Unstable fractures were initiated in double-cantilever-beam test specimens by forcing a wedge between\\u000a the two beams under compression. These fractures propagate at essentially constant wedge opening displacement and can be made\\u000a to arrest within the

  8. Fracture mechanics; Proceedings of the 22nd National Symposium, Atlanta, GA, June 26-28, 1990. Vols. 1 & 2

    NASA Technical Reports Server (NTRS)

    Ernst, Hugo A. (editor); Saxena, Ashok (editor); Mcdowell, David L. (editor); Atluri, Satya N. (editor); Newman, James C., Jr. (editor); Raju, Ivatury S. (editor); Epstein, Jonathan S. (editor)

    1992-01-01

    Current research on fracture mechanics is reviewed, focusing on ductile fracture; high-temperature and time-dependent fracture; 3D problems; interface fracture; microstructural aspects of fatigue and fracture; and fracture predictions and applications. Particular attention is given to the determination and comparison of crack resistance curves from wide plates and fracture mechanics specimens; a relationship between R-curves in contained and uncontained yield; the creep crack growth behavior of titanium alloy Ti-6242; a crack growth response in three heat resistant materials at elevated temperature; a crack-surface-contact model for determining effective-stress-intensity factors; interfacial dislocations in anisotropic bimaterials; an effect of intergranular crack branching on fracture toughness evaluation; the fracture toughness behavior of exservice chromium-molybdenum steels; the application of fracture mechanics to assess the significance of proof loading; and a load ratio method for estimating crack extension.

  9. Fracture mechanics; Proceedings of the 22nd National Symposium, Atlanta, GA, June 26-28, 1990. Vols. 1 & 2

    NASA Astrophysics Data System (ADS)

    Ernst, Hugo A.; Saxena, Ashok; McDowell, David L.; Atluri, Satya N.; Newman, James C., Jr.; Raju, Ivatury S.; Epstein, Jonathan S.

    Current research on fracture mechanics is reviewed, focusing on ductile fracture; high-temperature and time-dependent fracture; 3D problems; interface fracture; microstructural aspects of fatigue and fracture; and fracture predictions and applications. Particular attention is given to the determination and comparison of crack resistance curves from wide plates and fracture mechanics specimens; a relationship between R-curves in contained and uncontained yield; the creep crack growth behavior of titanium alloy Ti-6242; a crack growth response in three heat resistant materials at elevated temperature; a crack-surface-contact model for determining effective-stress-intensity factors; interfacial dislocations in anisotropic bimaterials; an effect of intergranular crack branching on fracture toughness evaluation; the fracture toughness behavior of exservice chromium-molybdenum steels; the application of fracture mechanics to assess the significance of proof loading; and a load ratio method for estimating crack extension. (For individual items see A93-31577 to A93-31616)

  10. A numerical study on intended and unintended failure mechanisms in blanking of sandwich plates

    NASA Astrophysics Data System (ADS)

    Chen, L.; Soyarslan, C.; Tekkaya, A. E.

    2013-05-01

    Metal-polymer-metal sandwich plates are widely used in the automotive and aerospace industry. As for different applications the sandwich plates can be divided into two types. They are sound-damping laminates with a polymer core much thinner than the metallic faces and low-density laminates with a core thickness of approximately 40-60% of the total thickness. One frequent process step in production of parts made of these plates is the blanking process whose hereditary effects draw the limits of further forming stages or service performance and life; e.g. the failure of the adhesive in the thermoplastic polymer interface affects the sound-damping efficiency intensively. With this motivation, we present FE simulation of an axi-symmetric blanking process of steel/polyethylene/steel sound-damping laminates. The mechanical behavior of the metallic layers was characterized by finite strain rate independent elasto-plasticity where progressive material deterioration and fracture are given account for using continuum damage mechanics (CDM). This material model is made accessible via implementations as VUMAT subroutines for ABAQUS/Explicit. Possible failure of the thermoplastic polymer which may lead to delamination of the metallic layers is modeled using ABAQUS built-in cohesive zone elements. The results show that existing intended and unintended failure modes, e.g. blanking of the metallic and thermoplastic polymer constituents as well as failure of polymer layer under shear and compression, can be effectively studied with the proposed framework for process enhancement. As a future work, a damage coupled nonlinear visco-elastic constitutive model will be devised for the simulation of the thermoplastic layer in low-density laminates.

  11. Fracture mechanics of a randomly heterogeneous double cantilever beam

    Microsoft Academic Search

    Eli Altus; Sefi Givli

    2004-01-01

    A Heterogeneous Double Cantilever Beam, commonly used for fracture energy measurements, is analyzed by the Functional Perturbation Method (FPM). External force and displacement are considered as functionals of materials morphology. Both stiffness and fracture energies are random fields, from which the average and variance of the external loading and displacement at the onset of crack growth are found explicitly. The

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    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.

  14. Dependence of the particle emission during the fracture of silica glass on its mechanical property

    Microsoft Academic Search

    T. Shiota; K. Yasuda; Y. Matsuo

    2008-01-01

    The emission intensities of photons, negative and positive charges during the fracture of silica glass and its bending strength were measured to investigate a dependence of such particle emission on the mechanical property. The emission intensities of these particles were sharply increased and showed peaks at the moment of the fracture. In the negative and positive charge emissions, there was

  15. Fracture Mechanics Analysis of Cracked Discs of Anisotropic Rock Using the

    E-print Network

    Pan, Ernie

    Fracture Mechanics Analysis of Cracked Discs of Anisotropic Rock Using the Boundary Element Method with the determi- nation of the deformability, tensile strength and fracturing of anisotropic rocks by diametral compression (Brazilian test) of discs of rock. It is shown how a new formulation of the Boundary Element

  16. Molecular dynamics simulations of atomic-level brittle fracture mechanisms in amorphous silica

    E-print Network

    Deymier, Pierre

    deformation prior to failure and consequently an amount of predictability, brittle frac- ture is suddenMolecular dynamics simulations of atomic-level brittle fracture mechanisms in amorphous silica Abstract We have examined the atomic dynamics of the brittle fracture process in amorphous silica using

  17. Fracture resistant bones: unusual deformation mechanisms of seahorse armor Michael M Porter1*

    E-print Network

    McKittrick, Joanna

    1 Fracture resistant bones: unusual deformation mechanisms of seahorse armor Michael M Porter1. Mimicking seahorse armor may lead to novel biomimetic technologies, such as flexible armor, fracture resistant structures, or prehensile robotics. Keywords: seahorse; natural armor; prehensile; bony plates 1

  18. Spartan Release Engagement Mechanism (REM) stress and fracture analysis

    NASA Technical Reports Server (NTRS)

    Marlowe, D. S.; West, E. J.

    1984-01-01

    The revised stress and fracture analysis of the Spartan REM hardware for current load conditions and mass properties is presented. The stress analysis was performed using a NASTRAN math model of the Spartan REM adapter, base, and payload. Appendix A contains the material properties, loads, and stress analysis of the hardware. The computer output and model description are in Appendix B. Factors of safety used in the stress analysis were 1.4 on tested items and 2.0 on all other items. Fracture analysis of the items considered fracture critical was accomplished using the MSFC Crack Growth Analysis code. Loads and stresses were obtaind from the stress analysis. The fracture analysis notes are located in Appendix A and the computer output in Appendix B. All items analyzed met design and fracture criteria.

  19. An extension of fracture mechanics/technology to larger and smaller cracks/defects

    PubMed Central

    Abé, Hiroyuki

    2009-01-01

    Fracture mechanics/technology is a key science and technology for the design and integrity assessment of the engineering structures. However, the conventional fracture mechanics has mostly targeted a limited size of cracks/defects, say of from several hundred microns to several tens of centimeters. The author and his group has tried to extend that limited size and establish a new version of fracture technology for very large cracks used in geothermal energy extraction and for very small cracks/defects or damage often appearing in the combination of mechanical and electronic components of engineering structures. Those new versions are reviewed in this paper. PMID:19907123

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

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

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

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

    SciTech Connect

    Bower, K.M.

    1996-06-01

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

  2. Calculations to Benchmark Probabilistic Fracture Mechanics Computer Codes

    SciTech Connect

    Simonen, Fredric A.; Gosselin, Stephen R.; Wilkowski, Gery M.; Rudland, David L.; Xu, H.

    2007-07-22

    This paper describes calculations to estimate component failure frequencies for components using the PRO-LOCA and PRAISE probabilistic fracture mechanics (PFM) computer codes. These calculations focused on the failure mechanism of intergranular stress corrosion cracking for operating conditions that were known to have failed field components. The objective was to benchmark the newly developed PRO-LOCA code against the older PRAISE code that had a much longer history of prior applications. Another objective was to determine the extent to which uncertainties and modeling assumptions may impact calculated probabilities. It was established that advanced modeling capabilities in the PRO-LOCA code simulated parameters that were treated deterministically by the PRAISE code. Excellent agreement of numerical results from the two codes was established once the PRO-LOCA code was applied using selective deterministic treatments. Benchmarking efforts described in a related paper have compared calculated frequencies with those estimated from plant operating experience. Sensitivity calculations have also been performed to address uncertainties associated with residual stresses and applied stresses and temperatures. The capabilities and limitations of the two PFM codes are described along with prior PFM applications to piping integrity issues. Model assumptions are described along with the uncertain nature of inputs and their impacts on calculated probabilities. Also described are calculations with the PRAISE code that have used an alternative crack initiation model based on laboratory data for crack initiation by PWSCC in Alloy-182. Sensitivity calculations with this model address the effects of uncertainties in levels of operating and residual stresses, uncertainties in plant operating conditions, and circumferential variations of stress.

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

    NASA Technical Reports Server (NTRS)

    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.

  4. Three-dimensional mixed mode linear elastic fracture mechanics analysis using domain interaction integrals

    E-print Network

    Esmen, Ekrem Alp, 1977-

    2004-01-01

    Three-dimensional mixed-mode linear elastic fracture mechanics analysis is presented using domain interaction integrals. An out-of-plane sinusoidal crack was analyzed using a commercially available finite element package ...

  5. Thermo-hydro-mechanical Analysis of Fractures and Wellbores in Petroleum/Geothermal Reservoirs 

    E-print Network

    Safariforoshani, Mohammadreza

    2013-08-09

    The thesis considers three-dimensional analyses of fractures and wellbores in low-permeability petroleum/geothermal reservoirs, with a special emphasis on the role of coupled thermo-hydro-mechanical processes. Thermoporoelastic displacement...

  6. Thermo-hydro-mechanical Analysis of Fractures and Wellbores in Petroleum/Geothermal Reservoirs

    E-print Network

    Safariforoshani, Mohammadreza

    2013-08-09

    The thesis considers three-dimensional analyses of fractures and wellbores in low-permeability petroleum/geothermal reservoirs, with a special emphasis on the role of coupled thermo-hydro-mechanical processes. Thermoporoelastic displacement...

  7. Mechanical and damage analysis along a flat-rolled wire cold forming schedule

    Microsoft Academic Search

    Thomas Massé; Yvan Chastel; Pierre Montmitonnet; Christian Bobadilla; Nicolas Persem; Sylvain Foissey

    Numerical simulation is used to study patented high-C steel flat-rolled wire cold forming processes. An elasto-plastic power\\u000a law, identified from mechanical tests, is used into Forge2005® finite element (FEM) package in order to describe the material\\u000a behaviour during wire drawing followed by cold rolling. A through-process approach has been favoured, transferring residual\\u000a wire-drawing stresses and strain into the flat-rolling preform.

  8. Spall fracture: methodological aspects, mechanisms and governing factors

    Microsoft Academic Search

    G. I. Kanel

    2010-01-01

    The dynamic tensile strength of materials at load durations of a few microseconds or less is studied by analyzing the spall\\u000a phenomena under shock pulse loading. The paper is devoted to discussing the methodology and capabilities of the technique\\u000a to measure spall strength, its error sources, spall fracture of materials of different classes and the factors governing the\\u000a high-rate fracture

  9. Mechanical design considerations for fracture-treating down casing strings

    SciTech Connect

    Clark, H.C.

    1987-06-01

    This paper deals with the design, handling, and cementing of a casting string that will ultimately encounter a fracture treatment. Various wellhead configurations are suggested that provide safe installations while allowing downhole treating-pressure monitoring and easy flowback operations. Solutions to logistical and operational problems faced with a casing treatment are recommended. A comparison of tubing vs. casing as the fracture-treating medium is also provided to show the substantial cost differences.

  10. The peel test in experimental adhesive fracture mechanics

    NASA Technical Reports Server (NTRS)

    Anderson, G. P.; Devries, K. L.; Williams, M. L.

    1974-01-01

    Several testing methods have been proposed for obtaining critical energy release rate or adhesive fracture energy in bond systems. These tests include blister, cone, lap shear, and peel tests. Peel tests have been used for many years to compare relative strengths of different adhesives, different surface preparation techniques, etc. The present work demonstrates the potential use of the peel test for obtaining adhesive fracture energy values.

  11. Equine cortical bone exhibits rising R-curve fracture mechanics

    Microsoft Academic Search

    C. L. Malik; S. M. Stover; R. B. Martin; J. C. Gibeling

    2003-01-01

    Previous studies of the fracture properties of cortical bone have suggested that the fracture toughness increases with crack length, which is indicative of rising R-curve behavior. Based on this indirect evidence and the similarity of bone to ceramic matrix composites, we hypothesized that bone would exhibit rising R-curve behavior in the transverse orientation and that the characteristics of the R-curves

  12. Mechanical behavior and fracture characteristics of off-axis fiber composites. 2: Theory and comparisons

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.; Sinclair, J. H.

    1978-01-01

    The mechanical behavior and stresses inducing fracture modes of unidirectional high-modulus graphite-fiber/epoxy composites subjected to off-axis tensile loads were investigated theoretically. The investigation included the use of composite mechanics, combined-stress failure criteria, and finite-element stress analysis. The results are compared with experimental data and led to the formulation of criteria and convenient plotting procedures for identifying, characterizing, and quantifying these fracture modes.

  13. A new hydraulic fracture tip mechanism in a statistically homogeneous medium

    SciTech Connect

    Chudnovsky, A.; Fan, J.; Shulkin, Y. [Univ of Chicago, IL (United States)] [and others

    1996-12-31

    This paper presents a new hydraulic fracture (HF) tip mechanism observed in a statistically homogeneous porous rock. HF tip mechanisms are widely recognized to be responsible for discrepancies between field observations and HF model predictions. Current proposed tip mechanisms used in HF geometry simulations require field calibration and are not truly predictive based on lab- and/or field-scale material property data. Matching field pressure data often gives significantly different material property values from those measured in the lab. This paper reports studies of a hydraulic fracture created in an 18-inch cubic block of Lueders limestone that reveals random {open_quotes}bridges{close_quotes} connecting the opposing fracture faces. Observation of the bridges suggests the existence of a crack tip zone that resembles the process zone widely reported for various other materials. The existence of a process zone significantly changes many fracture parameters in comparison with linear fracture mechanics predictions (e.g., fracture length and width, net pressure, etc.). A new model is proposed to account for the observed crack tip process zone (PZ). The model is comprised of two complementary parts: (1) a statistical characterization and simulation of the bridging phenomenon, and (2) a thermodynamics-based model of the growth of the crack and PZ. The main challenges and future research topics in Hydraulic Fracturing are also discussed.

  14. Mechanical Properties of Rock Fractures derived from ultrasonic and numerical Data

    NASA Astrophysics Data System (ADS)

    Moellhoff, M.; Bean, C. J.; Meredith, P.

    2003-04-01

    Rock fracture properties including fracture stiffness and strength have a significant influence on many geophysical problems. We have recently developed and implemented a granular particle based numerical scheme for investigating wave propagation across confined unwelded fractures. Simulations predict that fracture stiffness can be determined directly from seismic data. In addition bi-compliant fracture stiffnesses can result in the generation of subtle non-linear wave effects, which are diagnostic of the fractures mechanical properties. We are conducting physical laboratory experiments to test the predictions of this recent numerical work. In particular we will investigate the effects of fracture cohesive properties, roughness and confining stress on fracture stiffness as measured dynamically from ultrasonic data in the laboratory. The laboratory experiment consists of a rock core sample with a single fracture. The ultrasonic transducers being used have a central frequency of 1MHz and the rock samples are between 4cm and 7cm long and 4cm in diameter. One transducer is fitted centrally on each end of the sample. This physical experiment is replicated in terms of rock grain size, external loading conditions and dynamic wave frequencies using the granular numerical scheme, greatly enhancing our interpretation of the physical seismograms.

  15. Integrity of the osteocyte bone cell network in osteoporotic fracture: Implications for mechanical load adaptation

    NASA Astrophysics Data System (ADS)

    Kuliwaba, J. S.; Truong, L.; Codrington, J. D.; Fazzalari, N. L.

    2010-06-01

    The human skeleton has the ability to modify its material composition and structure to accommodate loads through adaptive modelling and remodelling. The osteocyte cell network is now considered to be central to the regulation of skeletal homeostasis; however, very little is known of the integrity of the osteocyte cell network in osteoporotic fragility fracture. This study was designed to characterise osteocyte morphology, the extent of osteocyte cell apoptosis and expression of sclerostin protein (a negative regulator of bone formation) in trabecular bone from the intertrochanteric region of the proximal femur, for postmenopausal women with fragility hip fracture compared to age-matched women who had not sustained fragility fracture. Osteocyte morphology (osteocyte, empty lacunar, and total lacunar densities) and the degree of osteocyte apoptosis (percent caspase-3 positive osteocyte lacunae) were similar between the fracture patients and non-fracture women. The fragility hip fracture patients had a lower proportion of sclerostin-positive osteocyte lacunae in comparison to sclerostin-negative osteocyte lacunae, in contrast to similar percent sclerostin-positive/sclerostin-negative lacunae for non-fracture women. The unexpected finding of decreased sclerostin expression in trabecular bone osteocytes from fracture cases may be indicative of elevated bone turnover and under-mineralisation, characteristic of postmenopausal osteoporosis. Further, altered osteocytic expression of sclerostin may be involved in the mechano-responsiveness of bone. Optimal function of the osteocyte cell network is likely to be a critical determinant of bone strength, acting via mechanical load adaptation, and thus contributing to osteoporotic fracture risk.

  16. NETWORKS AND HETEROGENEOUS MEDIA Website: http://aimSciences.org c American Institute of Mathematical Sciences

    E-print Network

    DeSimone, Antonio

    friction, elasto­plasticity and fracture mechanics. The main results of our analysis are formulas giving is used as the key tool to interpret the experimental evidence. 1. Introduction. We consider liquid drops, a large pressure is exerted on a Cassie­Baxter (CB) drop (i.e., a drop which has vapor-filled cavities

  17. The application of fracture mechanics to failure analysis of photovoltaic solar modules

    NASA Technical Reports Server (NTRS)

    Chen, C. P.; Leipold, M. H.

    1981-01-01

    Cracking of silicon solar cells and solar module transparent cover panels such as glass or polymethylmethacrylate (PMMA) is a major cause of photovoltaic solar module failure in field service. Silicon and cover materials are brittle, and cracking of these materials is expected to result from the extension of preexisting flaws under stress. Study of the cracking mechanisms is therefore an appropriate area for the application of fracture mechanics principles. In this study, fracture mechanics techniques were employed to identify the mode of crack propagation, to examine the fracture-initiating flaw, to estimate the nature and magnitude of fracture stress in the field, and to predict analytically the service lifetime. Recommendations for corrective actions are also made.

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

    SciTech Connect

    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.

  19. Micro-mechanical analysis of damage growth and fracture in discontinuous fiber reinforced metal matrix composites

    NASA Technical Reports Server (NTRS)

    Goree, James G.; Richardson, David E.

    1991-01-01

    An experimental verification is presented for a new two parameter fracture model based on the equivalent remote biaxial stresses (ERBS). A detailed comparison is made between the new theory and the constant K(sub IC) approach of linear elastic fracture mechanics (LEFM). Fracture is predicted through a failure curve representing the change in a variable fracture toughness K(sub IC) with the ERBS ratio B(sub E). The nonsingular term (T) in the series expansion of the near crack-tip transverse stress is included in the model. Experimental results for polymethyl methacrylate (PPMA) show that the theory can account for the effects of geometry on fracture toughness as well as indicate the initiation of crack branching. It is shown that the new criterion predicts failure for PMMA with a 95 percent confidence zone which is nearly three times smaller than that of the LEFM K(sub IC) approach.

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

    PubMed

    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?fractures by emergency physicians later identified by radiologists was the same in both groups (7.7% vs 7.7%, P?=?0.984).While the same proportion of intoxicated patients presented more than 24?hours following injury, only intoxicated patients presented with craniofacial and cervical 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

  1. Tensile fracture resistance mechanisms in brittle polycrystals: An ultrasonics and in situ microscopy investigation

    NASA Astrophysics Data System (ADS)

    Swanson, Peter L.

    1987-07-01

    A zone of distributed microcracking is often suggested to accompany tensile macrocrack propagation in rocks and ceramics. The microcracking is said to be largely responsible for (1) high values of fracture energy, (2) increasing resistance to fracture with crack extension and (3) the dependence of fracture mechanics data on the experimental setup. In the present paper, the material breakdown processes in imperfectly elastic Westerly granite are investigated using ultrasonic wave probing and in situ microscopy during mode I fracture experiments. These observations are compared with an in situ reflection/transmission microscopy investigation of mode I fracture in a near-ideal elastic polycrystalline alumina (Al2O3). As defined by the spatial distribution of longitudinal and surface wave attenuation in wedge-loaded double-cantilever beam specimens of Westerly granite, the fracture process zone is elongate in the direction of fracture propagation (15-40 mm long by 1-2 grain dimensions wide; grain size 0.75 mm). As revealed by in situ reflection microscopy, the ultrasonic wave energy is partially transmitted through the developing fracture surfaces via two sources of crack interface traction: (1) remnant islands of unfractured material left behind the advancing fracture front and (2) geometrical interlocking of the microstructurally rough fracture surfaces. A similar zone of crack flank tractions is found in the alumina (greater than 2000 ?m long; grain size 20-100 ?m). No evidence of a diffuse kidney-shaped cloud of microcracking distributed ahead of the main fracture tip (predicted by many fracture models) was found in either material. Instead, interface-localized microcracking was observed to operate at positions where the tractions, or restraining forces, are transmitted across the nascent fracture surfaces. Crack flank tractions shield the main crack tip from high levels of stress and are relieved by friction-induced microcracking and microcrack rupture of intact-material bridges. As a consequence of the crack history dependence of the crack tip shielding, it is proposed that, even under small-scale inelastic deformation conditions appropriate to linear elastic fracture mechanics, neither R-curve behavior nor applied-KI/subcritical crack velocity relationships are intrinsic properties of these and similar materials.

  2. Sir Alan Cottrell and the Dislocation Mechanics of Fracturing

    E-print Network

    Maryland at College Park, University of

    strength and brittleness of crystals 9 #12;Theoretical Strength vs Smallest Crack Behaviour An attempt nucleation at a crack tip, Mater. Sci. Eng., 1, 251 (1966)10 Note by Wei Zhou: The paper assesses whether a crystal can break in a fully brittle manner or whether some plastic flow must accompany fracture

  3. Haptic Rendering of Cutting: A Fracture Mechanics Approach

    Microsoft Academic Search

    Mohsen Mahvash; Vincent Hayward

    2001-01-01

    Cutting a deformable body may be viewed as an in- terchange between three forms of energy: the elas- tic energy stored in the deformed body, the work done by a sharp tool as it moves against it, and the irreversible work spent in creating a fracture. Other dissipative phenomena such as friction can optionally also be considered. The force applied

  4. The creep fracture of wrought nickel-base alloys by a fracture mechanics approach

    Microsoft Academic Search

    S. Floreen

    1975-01-01

    Creep fracture in the 500 to 750°C temperature range was by an intergranular crack growth process involving the formation\\u000a of microcracks in grain boundaries slightly ahead of the main crack. The crack growth was proportional to an exponential power\\u000a of the stress intensity. Wide differences in cracking behavior were seen between different alloys, but their differences were\\u000a due primarily to

  5. Mechanical behavior and essential work of fracture of starch-based blown films

    NASA Astrophysics Data System (ADS)

    Nottez, M.; Chaki, S.; Soulestin, J.; Lacrampe, M. F.; Krawczak, P.

    2015-05-01

    A fracture mechanics approach (Essential Work of Fracture, EWF) was applied to assess the toughness of novel partly starch-grafted polyolefin blown films, compared to that of a neat polyethylene reference. Tests were performed on double-end notched samples. The digital image correlation method was used to monitor the deformation field around the notch. Regular tensile and tear tests were also carried out. The specific essential work of fracture is a characteristic which is much more sensitive to materials structural modifications than the tensile or tear properties.

  6. Tensile fracture mechanisms of ferritic/martensitic structural materials

    NASA Astrophysics Data System (ADS)

    Pan, Xiao

    Radiation-induced defect structures are known to elevate material yield strength and reduce material ductility so that small strains induce plastic instability. This process is commonly known as flow localization. Recent research indicates that the flow localization in face-centered cubic (FCC) materials is controlled by critical stress, the true stress of onset of necking. Critical stress dose not change with irradiation dose but has strong temperature dependence. Because critical stress acts as a material intrinsic property similar to yield strength, it is important to understand the controlling mechanism and the temperature dependence of critical stress. It is believed that critical stress is associated with critical interfacial strength between particle and matrix, which determines the void nucleation. Void nucleation has received extensive attention motivated by the need to enhance damage tolerance and avoid fracture in structural materials. Several initiation models have been built to predict critical interfacial strength of void nucleation. However, all of these models are limited because they were derived from post-deformation (static) micro-structural characterization, which contains no information about the dynamic processes involved in the evolution of failure. This dissertation project aims to examine the controlling mechanism of critical stress, and the effects of temperature and particle characters by investigating the void nucleation through in-situ tensile tests with high energy X-ray diffraction and small angle X-ray scattering. By combining stress and void evolution from X-ray experiments, the critical interfacial strength right at the beginning of void nucleation is directly measured for four types of Fe-Cr-C model alloys: Fe-9%Cr-0.1%C, Fe-9%Cr-0.5%C, Fe-12%Cr-0.2%C, and Fe-12%Cr-0.5%C, which are promising candidates for high-temperature advanced nuclear system applications. The effects of temperature, particle size, particle volume fraction, particle crystal orientation, and chemical composition on critical interfacial strength have been inspected thoroughly. Results from this study demonstrate that critical stress is strongly linearly correlated with critical interfacial strength. The effects of temperature and particle size on critical stress are correspondingly determined by how temperature and particle size influence critical interfacial strength. In addition, a new Micro-Structural Model (MSM) is developed to predict critical interfacial strength using macro tensile testing parameters. This MSM model is consistent with experimental measurements under all testing conditions. Pre-existing dislocation models are also evaluated by the X-ray measurements. Results show that the MSM model can provide better prediction than dislocation models. X-ray measurements and analysis not only support the hypothesis of the association between critical stress and critical interfacial strength, but also offer a new method to determine the true strain/stress behavior during deformation. This method is called the Universal Micro-structural Geometry-corrected Model (UMGM) in this dissertation. Due to the development of tri-axial stress and severe distortion of grain structure in the necking region, it is a challenge to determine the true strain/stress curve, a critical input in finite element modeling (FEM) analysis. Previous scholars have developed several analytical methods to characterize true strain/stress behavior after necking merely based on geometry correction or direct linear extrapolation. Grounded with experimental data, the UMGM provides empirical validation for these existing methods.

  7. A fully-coupled hydrological–mechanical–chemical model for fracture sealing and preferential opening

    Microsoft Academic Search

    Jishan Liu; Jinchang Sheng; A. Polak; D. Elsworth; H. Yasuhara; A. Grader

    2006-01-01

    A fully coupled hydrological–mechanical–chemical (HMC) model is developed and applied to explain enigmatic spontaneous changes in permeability that develop within a fracture in limestone under simulated in situ conditions (Water Resour Res 2004;40:W03502). The water flow-through test was concurrently monitored for water and dissolved mineral mass efflux and periodically imaged by X-ray CT to provide redundant constraints on fracture evolution

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

    NASA Astrophysics Data System (ADS)

    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 experimental results.

  9. PREDICTION OF PROXIMAL FEMORAL FRACTURE BY USING MECHANICAL QUASI-BRITTLE DAMAGE COUPLED WITH ANISOTROPIC BEHAVIOUR LAW

    E-print Network

    Boyer, Edmond

    applied stress, fracture toughness to determine the crack initiation and crack propagation behavior if if PREDICTION OF PROXIMAL FEMORAL FRACTURE BY USING MECHANICAL QUASI-BRITTLE DAMAGE COUPLED WITH ANISOTROPIC : abettamer2003@yahoo.com Introduction A femoral fracture caused by the osteoporosis becomes increasingly

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

    SciTech Connect

    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.

  11. Association of microstructural and mechanical properties of cancellous bone and their fracture risk assessment tool scores

    PubMed Central

    Wu, Dengke; Li, Xin; Tao, Cheng; Dai, Ruchun; Ni, Jiangdong; Liao, Eryuan

    2015-01-01

    This study is to investigate the association between fracture probabilities determined by using the fracture risk assessment tool (FRAX) and the microstructure and mechanical properties of femoral bone trabecula in osteoporosis (OP) and osteoarthritis (OA) patients with hip replacements. By using FRAX, we evaluated fracture risks of the 102 patients with bone replacements. Using micro CT scanning, we obtained the analysis parameters of microstructural properties of cancellous bone. Through morphometric observations, fatigue tests and compression tests, we obtained parameters of mechanical properties of cancellous bones. Relevant Pearson analysis was performed to investigate the association between the fracture probability and the microstructure and mechanical properties of femoral bone trabecula in patients. Fifteen risk factors in FRAX were compared between OP and OA patients. FRAX hip fracture risk score and major osteoporotic in OP and OA patients were significantly different. FRAX was associated with tissue bone mineral density and volumetric bone mineral density. Our study suggests that the probabilities of major osteoporotic and hip fracture using FRAX is associated with bone mass but not with micro bone quality.

  12. Atomistic and continuum modeling of mechanical properties of collagen: Elasticity, fracture, and self-assembly

    Microsoft Academic Search

    Markus J. Buehler

    2006-01-01

    We report studies of the mechanical properties of tropocollagen molecules under different types of mechanical loading including tension, compression, shear, and bending. Our modeling yields predictions of the fracture strength of single tropocollagen molecules and polypeptides, and also allows for quantification of the interactions between tropocollagen molecules. Atomistic modeling predicts a persistence length of tropocollagen molecules ? 23.4 nm, close

  13. Mechanical properties of two canine iliac fracture fixation systems 

    E-print Network

    VanGundy, Thomas Eugene

    1988-01-01

    hemi- pelves with implants. The osteotomy was standardized and oblique simulating a common clinical fracture. Forty specimens were tested once to failure (static testing). Ten specimens were tested in torsional loading. Ten specimens were tested... for stiffness, strength and cross sectional area for specimen groups in each testing mode. 15 LIST OF FIGURES Figure Page Length and position of osteotomy in relation to the iliac isthmus. . . . . . . . Radiograph of paired implant specimens illustrating...

  14. Fractural process and toughening mechanism of laminated ceramic composites

    Microsoft Academic Search

    Zhang Yafang; Tang Chun'an; Zhang Yongbin; Liang Zhenzao

    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

  15. Fatigue fracture mechanisms of Cu\\/lead-free solders interfaces

    Microsoft Academic Search

    Q. K. Zhang; Q. S. Zhu; Z. F. Zhang

    2010-01-01

    The fatigue fracture behaviors of a series of Cu\\/lead-free solder joints deformed under different directions of loadings were investigated in this study. Observation results showed that fatigue cracks generally initiate around the IMC\\/solder interface when the loading axis is vertical to the interface. For all the solder joints, the interfacial deformations are resulting from strain localization induced by the stain

  16. Mechanical properties of two canine iliac fracture fixation systems

    E-print Network

    VanGundy, Thomas Eugene

    1988-01-01

    to plate fixation for o lique canine iliac fracture fixation. The savings on implant fees and ease of lag screw application also may be a consideration for the veterinary surgeon. REFERENCES 1. Brinker WO, Piermattei DL, Flo GL. Handbook of Small..., for providng the funding that made this project possible. vi1 TABLE OF CONTENTS Page INTRODUCTION MATERIALS AND METHODS RESULTS Specimen Dimensions Static Testing Dynamic Testing DISCUSSION Pretesting Considerations Testing Considerations...

  17. Investigation of the fracture mechanics of boride composites

    NASA Technical Reports Server (NTRS)

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

    1971-01-01

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

  18. Fracture mechanics analyses of ceramic/veneer interface under mixed-mode loading.

    PubMed

    Wang, Gaoqi; Zhang, Song; Bian, Cuirong; Kong, Hui

    2014-11-01

    Few studies have focused on the interface fracture performance of zirconia/veneer bilayered structure, which plays an important role in dental all-ceramic restorations. The purpose of this study was to evaluate the fracture mechanics performance of zirconia/veneer interface in a wide range of mode-mixities (at phase angles ranging from 0° to 90°), and to examine the effect of mechanical properties of the materials and the interface on the fracture initiation and crack path of an interfacial crack. A modified sandwich test configuration with an oblique interfacial crack was proposed and calibrated to choose the appropriate geometry dimensions by means of finite element analysis. The specimens with different interface inclination angles were tested to failure under three-point bending configuration. Interface fracture parameters were obtained with finite element analyses. Based on the interfacial fracture mechanics, three fracture criteria for crack kinking were used to predict crack initiation and propagation. In addition, the effects of residual stresses due to coefficient of thermal expansion mismatch between zirconia and veneer on the crack behavior were evaluated. The crack initiation and propagation were well predicted by the three fracture criteria. For specimens at phase angle of 0, the cracks propagated in the interface; whereas for all the other specimens the cracks kinked into the veneer. Compressive residual stresses in the veneer can improve the toughness of the interface structure. The results suggest that, in zirconia/veneer bilayered structure the veneer is weaker than the interface, which can be used to explain the clinical phenomenon that veneer chipping rate is larger than interface delamination rate. Consequently, a veneer material with larger fracture toughness is needed to decrease the failure rate of all-ceramic restorations. And the coefficient of thermal expansion mismatch of the substrates can be larger to produce larger compressive stresses in the veneer. PMID:25123435

  19. A computational linear elastic fracture mechanics-based model for alkali-silica reaction Laurent Charpin,a

    E-print Network

    Boyer, Edmond

    A computational linear elastic fracture mechanics-based model for alkali-silica reaction Laurent mechanics model for alkali-silica reaction (ASR) is presented that deals with the case of a concrete made up words: Alkali-aggregate reaction, Free expansion, Linear Elastic Fracture Mechanics, Energy criterion

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

    PubMed

    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, P<0.05). Results of this study show that microstructure and material distribution based on micro-CT 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. PMID:24046532

  1. Chondral fracture of the lateral trochlea of the femur occurring in an adolescent: mechanism of injury.

    PubMed

    Oohashi, Yoshikazu; Oohashi, Yoshinori

    2007-11-01

    The trochlea of the femur is a very unusual site for chondral fracture. Little is known of the mechanism of injuries confined to the articular cartilage of the trochlea of the femur. A very unusual case of chondral fracture of the lateral trochlea of the femur occurring in an adolescent is reported here. The mechanism by which this injury occurred could be evaluated in this patient. The cartilage on the convex surface of the lateral trochlea was likely avulsed proximally by shear force of the patella during rapid extension of the weight-bearing knee from a flexed position. From a viewpoint of mechanism, this injury differs from the more usual osteochondral or chondral fractures of the weight bearing area of the femoral condyle, which are usually accompanied by twisting forces. PMID:17024462

  2. Hydraulic Aperture Reduction of Shale Fractures Due to Mechanical Stressing, with Characterization of Physical Fracture Evolution Using Comuted Tomography

    NASA Astrophysics Data System (ADS)

    Crandall, D.; Gill, M.; Moore, J.

    2014-12-01

    Flow in fractured shale is a topic of interest for both production from non-traditional fractured shale reservoirs and for estimating the leakage potential of sealing formations above geologic carbon dioxide repositories. The hydraulic aperture of a fracture quantifies how much fluid can be transported through a fracture, similarly to how permeability describes fluid flow through porous media. The advantage of defining the fracture hydraulic aperture as opposed to permeability, is that this property can be easily scaled up to fracture reservoir simulators. Many parameters affect the hydraulic aperture, however, including the fracture roughness, the physical aperture distribution, and the tortuosity of flow paths within the fracture.The computed tomography (CT) and flow facility at NETL has conducted an analysis of the changes in both physical and hydraulic aperture as fractures were subjected to varying external confining stresses. Changes in fracture geometry were tracked through the use of non-destructive CT imaging, allowing the determination of the physical aperture distribution, while hydraulic fracture apertures were derived from experimental fracture flow measurements. In order to evaluate the effects of fracture roughness and geometry, two fractures with different degrees of roughness were used. Tests were conducted with locally sourced shale.Experimental results show that the volume change in the fracture is a non-linear function of the confining pressure, and both physical and hydraulic apertures decrease rapidly as the fracture is first compressed.

  3. Probabilistic model for pressure vessel reliability incorporating fracture mechanics and nondestructive examination

    NASA Astrophysics Data System (ADS)

    Tow, David M.; Reuter, Walter G.

    1998-03-01

    A probabilistic model has been developed for predicting the reliability of structures based on fracture mechanics and the results of nondestructive examination (NDE). The distinctive feature of this model is the way in which inspection results and the probability of detection (POD) curve are used to calculate a probability density function (PDF) for the number of flaws and the distribution of those flaws among the various size ranges. In combination with a probabilistic fracture mechanics model, this density function is used to estimate the probability of failure (POF) of a structure in which flaws have been detected by NDE. The model is useful for parametric studies of inspection techniques and material characteristics.

  4. Permeability Evolution of Fractured Anhydrite Caused by Chemical and Mechanical Alteration

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    Geologic carbon sequestration requires competent structural seals (caprock) to prevent leakage over decadal time scales. Injection of large volumes of CO2 perturbs the target formation from chemical and mechanical equilibrium leading to the possible creation or enhancement of leakage pathways. We investigate the potential for leakage pathways (fractures) to grow over time under reservoir conditions in a series of anhydrite (Ca2SO4) cores. To simulate a potential leakage event in the laboratory, we fractured and jacketed the cores, and placed them in a flow-through reactor vessel. A high-pressure syringe pump applied confining stresses ranging from 7 to 17 MPa and another syringe pump pushed water through the sample at a constant flow rate with pressure control at the outlet. Effluent was sampled periodically and analyzed for Ca2+ and SO42- using an ion chromatograph. Before and after each experiment, we characterized the surfaces of the fractures using a high-resolution optical profilometer and a scanning electron microscope. Careful alignment of the surfaces during optical profiling allowed reproduction of the fracture aperture before and after each experiment. We present results from several experiments each carried out under different conditions in similar fractured anhydrite cores. One involved a well-mated pre-existing fracture and results showed that the permeability of the fractured core was similar to the intact rock matrix (O(10-18 m2); chemical alteration of the core was largely limited to the inflow face of the core and the fracture surfaces remained largely unaltered. To enhance permeability during subsequent experiments, we imposed a small (380 ?m) shear displacement between the fracture surfaces resulting in a four-order-of-magnitude increase in initial permeability. The first of these was run at a constant flow rate of 0.6 ml/min for a period of 7 days. The measured pressure gradient within the core increased slowly for a period of 4 days followed by a rapid increase in differential pressure corresponding to a two-order-of-magnitude decrease in permeability. During the experiment, the diameter of the core decreased by ~300 ?m at the inlet and a skin of gypsum (Ca2SO42H2O) was created along the length of the fracture. Dissolution of anhydrite and transition to gypsum of additional anhydrite weakened the fracture surfaces leading to closure of the fracture with a corresponding reduction in aperture and permeability. Additional experiments explore the influence of flow at a lower flow rate, which, in the absence of a large confining stress, has been shown to lead to the development of dissolution channels or wormholes.

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

    PubMed Central

    RIPPE, Marília Pivetta; SANTINI, Manuela Favarin; BIER, Carlos Alexandre Souza; BALDISSARA, Paolo; VALANDRO, Luiz Felipe

    2014-01-01

    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. PMID:25025556

  6. Nonlinear fracture mechanics analysis of end notched flexure specimen with tough interlayer

    SciTech Connect

    Esaki, K.; Kimpara, I.; Kageyama, K.; Suzuki, T.; Ohsawa, I. [Univ. of Tokyo (Japan). Dept. of Naval Architecture and Ocean Engineering

    1994-12-31

    An elastic-plastic analysis of the end notched flexure (ENF) specimen with tough interlayer is conducted by two-dimensional finite element modeling. Interlayer refers to a mixture of thermoplastic particles and thermoset base resin, selectively localized between laminae as a thin resin film. It is observed experimentally that plastic deformation in the interlayer has direct effect upon the interlaminar delamination growth and the toughness. The purpose of study is to evaluate Mode II interlaminar fracture toughness of interlayer-toughened composites with fracture mechanics parameter, J-integral, which is applicable to elastic-plastic regime. Effect of the material nonlinearity on the load versus crack shear displacement (CSD) diagram and J-integral is examined and limitation of linear elastic fracture mechanics approach to the tough composites is discussed.

  7. Mechanisms and impact of damage resulting from hydraulic fracturing. Topical report, May 1995-July 1996

    SciTech Connect

    Penny, G.S.; Conway, M.W.; Almond, S.W.; Himes, R.; Nick, K.E.

    1996-08-01

    This topical report documents the mechanisms of formation damage following hydraulic fracturing and their impact upon gas well productivity. The categories of damage reviewed include absolute or matrix permeability damage, relative permeability alterations, the damage of natural fracture permeability mechanisms and proppant conductivity impairment. Case studies are reviewed in which attempts are made to mitigate each of the damage types. Industry surveys have been conducted to determine the perceptions of the industry on the topic of formation damage following hydraulic fracturing and to identify key formations in which formation damage is a problem. From this information, technical hurdles and new technology needs are identified and estimates are made of the benefits of developing and applying minimum formation damage technology.

  8. Fracture mechanics of fiber-reinforced brittle-matrix composite materials

    SciTech Connect

    Gu Lixing.

    1991-01-01

    The fracture mechanics model of matrix cracking in uniaxially fiber-reinforced brittle matrix composites depends significantly on the load transfer mechanism between the fiber and the matrix. A model is developed theoretically under uniform tension in the direction parallel to the fibers and normal to the crack plane. It is assumed that the fibers are strong enough to remain intact when the matrix cracks. The different load transfer mechanisms are all based on a typical cylindrical composite cell. All load transfer mechanisms invoke equilibrium equations and continuity conditions in both the sliding and nonsliding regions. The methodology of analytical solution of the stress distribution in both the fiber and the matrix differ from other methods currently available in the literature. The fracture mechanics is described by micromechanics and macromechanics concepts, such as crack opening displacement and stress intensity factor. Parametric studies on the effects of material properties of the fiber and matrix are conducted to indicate the various influence of the properties.

  9. Fracture initiation mechanisms in -alumina under hypervelocity impact Cheng Zhang, Rajiv K. Kalia, Aiichiro Nakano, and Priya Vashishtaa

    E-print Network

    Southern California, University of

    Fracture initiation mechanisms in -alumina under hypervelocity impact Cheng Zhang, Rajiv K. Kalia; accepted 30 August 2007; published online 20 September 2007 Atomistic mechanisms of crack initiation and fracture in -alumina under hypervelocity impact are investigated using large-scale molecular

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

    NASA Astrophysics Data System (ADS)

    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 representative of the nonuniform fracture patterns observed in the HG-A microtunnel.

  11. Failure modes and fracture mechanisms in flexure of Kevlar-epoxy composites

    Microsoft Academic Search

    M. Davidovitz; A. Mittelman; I. Roman; G. Marom

    1984-01-01

    The results of testing in three-point bending of aramid fibre-reinforced epoxy composites are described. This loading mode has been chosen in order to increase the variety of failure modes and of fracture mechanisms. The main failure modes observed are tensile and delamination, with a transition at a fibre volume fraction of about 46%. This mode transition is detectable by monitoring

  12. Fracture toughening mechanism of shape memory alloys under mixed-mode loading due to martensite transformation

    Microsoft Academic Search

    Sung Yi; Shan Gao; Lianxi Shen

    2001-01-01

    This paper is devoted to the fracture toughening analysis of shape memory alloys (SMAs) with a macrocrack under mixed mode loads. The asymptotic analysis of the stress field and the derivation of the two-dimensional weight function for the semi-infinite crack in isotropic SMAs are investigated. The transformation boundaries for static crack and steady advanced crack are determined. The toughening mechanism

  13. Fracture mechanics testing on specimens with low constraint––standardisation activities within ISO and ASTM

    Microsoft Academic Search

    Karl-Heinz Schwalbe; James C. Newman; John L. Shannon

    2005-01-01

    Fracture mechanics tests are traditionally designed to measure material resistance to stable or unstable crack extension using specimens that are highly constrained to plastic deformation. For a variety of reasons, structural members may be made of thin gage-materials with inherently low constraint to plastic deformation. There is currently little guidance for measuring crack extension resistance under such conditions. The international

  14. Analysis of delamination in composite laminates under low-velocity impact. [Using fracture mechanics approach

    Microsoft Academic Search

    Jih Chanjiun

    1991-01-01

    Composite laminates subjected to foreign object impact often experience extreme damage that may not be visible on the impacted surface. This damage in the form of delamination may lead to significant reduction in compressive strength of the laminate. In this study, the fracture mechanics approach is employed to predict the extent of delamination for a given impact condition. Static linear

  15. Twenty years of fracture mechanics and flaw evaluation applications in the ASME Nuclear Code

    Microsoft Academic Search

    P. C. Riccardella; S. Yukawa

    1991-01-01

    The paper presents a retrospective on the development and applications of fracture mechanics-based toughness requirements and flaw evaluation methodology in Sections III and XI of the ASME Code. Section III developments range from the rules and requirements for thick section Class 1 pressure vessels to thinner section components in other Classes. Section XI applications include flaw acceptance standards and evaluation

  16. Quantifying Mechanical Properties in a Murine Fracture Healing System Using Inverse Modeling: Preliminary Work

    E-print Network

    Miga, Michael I.

    callus so that a clinician may detect and intervene in the event of a non-union. In addition-bearing mechanical properties of an experimental fracture callus system in response therapeutic intervention. To date, the challenge is that callus' often have a great deal of geometric complexity under similar initial conditions

  17. A fracture mechanics based fatigue life prediction for welded joints of square tubes

    Microsoft Academic Search

    J. M. Ferreira; A. H. Pereira; C. M. Branco

    1995-01-01

    Square tubes of mild and low alloy steels are extensively used in vehicle structures and offshore platforms. Despite this fact the fatigue behaviour of welded nodes of these tubes is not sufficiently known, especially in thin sections.The paper presents the results of fatigue life predictions based on fracture mechanics, in non-load carrying T and also load carrying cruciform joints. The

  18. A new fracture mechanics method to predict the fatigue life of welded cruciform joints

    Microsoft Academic Search

    Bimalendu Guha

    1995-01-01

    The fatigue life of MIG welded cruciform joint failing from root (LOP) region was successfully predicted using new fracture mechanics equations. These equations were developed by combining Paris' law and ?Ki-endurance equation and incorporating an integral factor (Ip) obtained by integrating Paris' equation. In the numerical formulation of the equation, the initiation life (Ni) and propagation life (Np) of the

  19. A fracture mechanics analysis of the popcorn cracking in the plastic IC packages

    Microsoft Academic Search

    Y. B. Park; Jin Yu

    1997-01-01

    Popcorn cracking phenomenon in surface mounted packages is treated by assuming an inherent edge crack at the die pad\\/EMC interface of a TQFP and subsequent interface delamination under thermal and\\/or vapor pressure loadings. Using the finite element methods and the methods of interface fracture mechanics, path independent energy release rate is calculated and compared to the interface toughness which is

  20. Vapor pressure analysis of popcorn cracking in plastic IC packages by fracture mechanics

    Microsoft Academic Search

    J. H. Lim; K. W. Lee; S. S. Park; Y. Y. Earmme

    1998-01-01

    Simulation studies of the popcorn cracking of plastic IC packages based on moisture diffusion analysis and fracture mechanics are performed. For analysis of the moisture diffusion during pre-conditioning and of the diffusion of heat and moisture during reflow soldering, the finite difference method with the one-dimensional Fick's law is applied to the epoxy molding compound (EMC) lying under the die

  1. Fracture mechanisms of the Strombus gigas conch shell: II-micromechanics analyses of multiple cracking

    E-print Network

    Ballarini, Roberto

    Fracture mechanisms of the Strombus gigas conch shell: II-micromechanics analyses of multiple shell of the giant Queen conch, Strombus gigas, are presented. The crossed lamellar microstructure pink Queen conch, Strombus gigas, is characterized by high toughness and moderate strength, a direct

  2. Application of fracture mechanics concepts to hierarchical biomechanics of bone and bone-like materials

    Microsoft Academic Search

    HUAJIAN GAO

    Fracture mechanics concepts are applied to gain some understanding of the hierarchical nanocomposite structures of hard biological tissues such as bone, tooth and shells. At the most elementary level of structural hierarchy, bone and bone-like materials exhibit a generic structure on the nanometer length scale consisting of hard mineral platelets arranged in a parallel staggered pattern in a soft protein

  3. Application of advanced fracture mechanics to the assessment of linepipe defects

    SciTech Connect

    Balsara, M.N. [British Gas plc, Cramlington (United Kingdom)

    1996-12-01

    The existing methods of failure assessment for steel pipelines are over 20 years old and are empirically based upon tensile properties of the pipe material. Recent advances in the understanding of defect failure processes (using advanced fracture mechanics concepts) have been significant and the pipeline industry has not yet applied these advances. This paper describes the application of these advanced fracture mechanics methods to a typical modern linepipe steel with the objective of producing more accurate failure predictions. Instrumented pipe ring experiments have been performed to establish failure conditions for axially flawed pipe sections of a grade X65 linepipe steel. The results from these experiments were used to establish the accuracy of the most recently published advanced fracture mechanics procedures (the British Standards Institute PD 6493 and the Central Electricity Generating Board R6 methodologies) for predicting failure conditions in flawed structures. The results of the study have demonstrated the potential for advanced fracture mechanics to provide more accurate predictions for the failure pressures of linepipe defects compared to conventional methods. Further studies are required to allow the above conclusion to be extended to other pipe geometries and materials.

  4. Analysis of failure of axle housing of crane truck with fracture mechanics

    Microsoft Academic Search

    Steven W. Bradley; Walter L. Bradley

    1995-01-01

    The failure of an axle housing in a crane truck has been successfully analyzed with the aid of fracture mechanics. The cause of failure was the field addition of stop blocks welded to the axle housing. The time from crack penetration of the axle housing to final failure was too short for the presence of such a crack to have

  5. A fracture mechanics approach to the crack formation in alkali-sensitive grains

    Microsoft Academic Search

    H. W. Reinhardt; O. Mielich

    2011-01-01

    The cause of cracking of slow\\/late aggregates is supposed to be due to gel pressure in the grain. The cracking of grains is approached with the aid of fracture mechanics and the decisive parameter for crack extension is the critical stress intensity factor. Various types of rock were stored in alkaline solution. The critical stress intensity factor was determined as

  6. Thermodynamic and fracture mechanical processes in the context of frost wedging in ice shelves

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    Ice shelves, the link between ice shields or glaciers and the ocean are sensitive elements of the polar environment. The ongoing break up and disintegration of huge ice shelf parts or entire ice shelf demands for an explication of the underlying processes. The first analyses of crack growth and break up events in ice shelves date back to more than half a century. Nevertheless, the mechanisms that trigger and influence the collapse of whole ice shelf parts are not yet fully understood. Popular presumptions link ice shelf disintegration to surface meltwater and hydro fracturing, explaining break up events in warm polar seasons. Fracture events during colder seasons are possibly triggered by more complex mechanisms. A well-documented break up event at the Wilkins Ice Shelf bridge inspires the possibility of frost wedging as disintegration cause. The present study shows a two-dimensional thermo-dynamical model simulating the growth of an ice lid in a water-filled crevasse for measured surface temperatures. The influence of the crevasse geometry and the ice shelf temperature are shown. The resulting lid thickness is then used for the linear elastic fracture mechanical analysis. The maximum crack depth is estimated by comparing the computed stress intensity factors to critical values KIc obtained from literature. The thermodynamic as well as the fracture mechanical simulation are performed using the commercial finite element code COMSOL. The computation of KI follows in post processing routines in MATLAB exploiting the benefits of the concept of configurational forces.

  7. Reinforcement delamination of metallic beams strengthened by FRP strips: Fracture mechanics based approach

    Microsoft Academic Search

    Pierluigi Colombi

    2006-01-01

    The delamination failure of metallic beams reinforced by externally bonded fibres reinforced polymers (FRP) is addressed in this paper and a simplified fracture mechanics based approach for the edge delamination of the reinforcement strips is illustrated. The criterion is based on the evaluation of the energy release rate (ERR) using both analytical and numerical models. The analytical models consist of

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

    PubMed Central

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

    2015-01-01

    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. PMID:26112834

  9. Mechanical properties and microstructure of an ? + ? titanium alloy with high strength and fracture toughness

    Microsoft Academic Search

    Yang Yu; Songxiao Hui; Wenjun Ye; Baiqing Xiong

    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\\u000a as an advanced structural material in aerospace and non-aerospace applications. Thermo-mechanical processes can be used to\\u000a optimize the relationship between its strength and fracture toughness. A Ti-62A alloy bar can be machined through a transus\\u000a ?-forged plus ?+? solution treated and aged specimen with

  10. Advances in Fatigue and Fracture Mechanics Analyses for Aircraft Structures

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.

    1999-01-01

    This paper reviews some of the advances that have been made in stress analyses of cracked aircraft components, in the understanding of the fatigue and fatigue-crack growth process, and in the prediction of residual strength of complex aircraft structures with widespread fatigue damage. Finite-element analyses of cracked structures are now used to determine accurate stress-intensity factors for cracks at structural details. Observations of small-crack behavior at open and rivet-loaded holes and the development of small-crack theory has lead to the prediction of stress-life behavior for components with stress concentrations under aircraft spectrum loading. Fatigue-crack growth under simulated aircraft spectra can now be predicted with the crack-closure concept. Residual strength of cracked panels with severe out-of-plane deformations (buckling) in the presence of stiffeners and multiple-site damage can be predicted with advanced elastic-plastic finite-element analyses and the critical crack-tip-opening angle (CTOA) fracture criterion. These advances are helping to assure continued safety of aircraft structures.

  11. Fracture mechanics approach to hydrogen assisted cracking: Analysis of the K -dominance condition

    Microsoft Academic Search

    J. Toribio; V. Kharin

    1999-01-01

    We summarize the achievements of a major research line at the Department of Materials Science of the University of La Corua\\u000a (Spain) in the field of environmentally-assisted cracking in general and hydrogen degradation in particular. We analyze the\\u000a meaning and significance of the fracture-mechanics approach to hydrogen-assisted cracking and study the problem ofK-dominance not only over the mechanical aspects of

  12. Fracture Mechanics Approach to Stress Corrosion Cracking of Pipeline Steels: When Hydrogen Is the Circumstance

    Microsoft Academic Search

    J. Toribio

    \\u000a Stress corrosion cracking is a problem of major concern in pipeline steels. This paper deals with the fracture mechanics approach\\u000a to the phenomenon. Paraphrasing the famous sentence by Ortega y Gasset “yo soy yo y mi circunstancia”, one could say that\\u000a the material is itself and its circumstance, the latter being the physico-chemical and mechanical environment. The paper analyzes\\u000a situations

  13. Hydromechanical modelling of geological CO2 storage and the study of possible caprock fracture mechanisms

    Microsoft Academic Search

    N. Guy; D. M. Seyedi; F. Hild

    2010-01-01

    The present study discusses the results of a large-scale finite element modelling of a hypothetical underground carbon dioxide (CO2) storage operation. The hydro-mechanical properties of the materials modelled are chosen to be representative of a potential injection site. For high injection rates, local effective stress modifications may lead to various fracture mechanisms induced by shear or tensile stresses depending on

  14. Elasto-plasticity in wrinkled polymerized lipid membranes

    NASA Astrophysics Data System (ADS)

    Chaieb, Sahraoui

    2014-01-01

    Biomembranes shown to behave like elastic sheets, can also suffer plastic deformations. Neutron scattering experiments on partially polymerised wrinkled membranes revealed that when a critical degree of polymerisation is crossed, the wrinkled membranes do not resume their spherical shapes. Instead they remain wrinkled and rigid while their non-polymerised counterparts resume their spherical floppy shapes. The yield stress of these membranes, measured for the first time via the fractal dimension, is intimately related to the degree of polymerisation probably through a 2D disorder that quenches the lateral diffusion of the lipid molecules. This work might shed light on the physical reason behind the irreversible deformation of echinocytes, acanthocytes and malaria infected red blood cells.

  15. Contributions to the anisotropic elasto-plastic analysis of shells

    E-print Network

    Kim, Do-Nyun

    2009-01-01

    Shells are probably the most widely used structural component in engineering and also in nature due to their high efficiency and excellent performance when properly designed. On the other hand, they can be very sensitive ...

  16. Elasto-plasticity in wrinkled polymerized lipid membranes

    PubMed Central

    Chaieb, Sahraoui

    2014-01-01

    Biomembranes shown to behave like elastic sheets, can also suffer plastic deformations. Neutron scattering experiments on partially polymerised wrinkled membranes revealed that when a critical degree of polymerisation is crossed, the wrinkled membranes do not resume their spherical shapes. Instead they remain wrinkled and rigid while their non-polymerised counterparts resume their spherical floppy shapes. The yield stress of these membranes, measured for the first time via the fractal dimension, is intimately related to the degree of polymerisation probably through a 2D disorder that quenches the lateral diffusion of the lipid molecules. This work might shed light on the physical reason behind the irreversible deformation of echinocytes, acanthocytes and malaria infected red blood cells. PMID:24424373

  17. The 1/r1/r singularity in weakly nonlinear fracture mechanics

    NASA Astrophysics Data System (ADS)

    Bouchbinder, Eran; Livne, Ariel; Fineberg, Jay

    2009-09-01

    Material failure by crack propagation essentially involves a concentration of large displacement-gradients near a crack's tip, even at scales where no irreversible deformation and energy dissipation occurs. This physical situation provides the motivation for a systematic gradient expansion of general nonlinear elastic constitutive laws that goes beyond the first order displacement-gradient expansion that is the basis for linear elastic fracture mechanics (LEFM). A weakly nonlinear fracture mechanics theory was recently developed by considering displacement-gradients up to second order. The theory predicts that, at scales within a dynamic lengthscale ? from a crack's tip, significant logr displacements and 1/r displacement-gradient contributions arise. Whereas in LEFM the 1/r singularity generates an unbalanced force and must be discarded, we show that this singularity not only exists but is also necessary in the weakly nonlinear theory. The theory generates no spurious forces and is consistent with the notion of the autonomy of the near-tip nonlinear region. The J-integral in the weakly nonlinear theory is also shown to be path-independent, taking the same value as the linear elastic J-integral. Thus, the weakly nonlinear theory retains the key tenets of fracture mechanics, while providing excellent quantitative agreement with measurements near the tip of single propagating cracks. As ? is consistent with lengthscales that appear in crack tip instabilities, we suggest that this theory may serve as a promising starting point for resolving open questions in fracture dynamics.

  18. Practical application of fracture mechanics with consideration of multiaxiality of stress state to degraded nuclear piping

    SciTech Connect

    Kussmaul, K.; Blind, D.; Herter, K.H.; Eisele, U.; Schuler, X. [Univ. of Stuttgart (Germany). Staatliche Materialpruefungsanstalt

    1995-11-01

    Within the scope of a research project nuclear piping components (T-branches and elbows) with dimensions like the primary coolant lines of PWR plants were investigated. In addition to the experimental full scale tests, extensive numerical calculations by means of the finite element method (FEM) as well as fracture mechanics analyses were performed. The applicability of these methods was verified by comparison with the experimental results. The calculation of fracture mechanics parameters as well as the calculated component stress enabled a statement on crack initiation. The failure behavior could be evaluated by means of the multiaxiality of stress state in the ligament (gradient of the quotient of the multiaxiality of stress state q). With respect to practical application on other pressurized components it is shown how to use the procedure (e.g. in a LBB analysis). A quantitative assessment with regard to crack initiation is possible by comparison of the effective crack initiation value J{sub ieff} with the calculated component stress. If the multiaxiality of stress state and the q gradient in the ligament of the fracture ligament of the fracture mechanics specimen and the pressurized component to be evaluated is comparable a quantitative assessment is possible as for crack extension and maximum load. If there is no comparability of the gradients a qualitative assessment is possible for the failure behavior.

  19. Coupled chemical alteration and mechanical deformation in fractures: Insights from laboratory-scale imaging

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    Perturbations from mechanical and chemical equilibrium can lead to significant alterations in fracture permeability and corresponding changes in fracture mechanical properties. Under conditions favoring mineral dissolution, alterations caused by chemical disequilibrium depend on the dimensionless Damkohler number (Da=kL/Vb, where k is an effective reaction rate, L is the length scale of the fracture, V is a mean flow velocity and b is the mean fracture aperture). At small values of Da, dissolution is relatively uniform throughout the fracture, whereas at high values of Da, instabilities in the reaction front lead to the formation of dissolution channels, and increased permeability at all values of Da. However, the addition of mechanical stresses can lead to contrasting behavior (i.e., either permeability increase or permeability decrease) due to the alteration of contact regions between the fracture surfaces. Quantifying the rates and relative impacts of different mechanisms in such experiments is necessary, particularly if we wish to use results to support predictions of field-scale behavior under different conditions. However, laboratory-scale experiments aimed at understanding coupled chemical and mechanical disequilibrium typically rely upon core-scale observations that provide insufficient details about the evolution of contacting asperities and the resulting stress induced deformation. We present results from a set of experiments in fractured cores through which we flowed reactive fluids. The cores were reservoir- and cap-rock (limestone and anhydrite, respectively) from the Weyburn CO2 sequestration project in Saskatchewan. In addition to differential pore pressures and effluent chemistry we measured the surface topography (+/- 1 ?m) of each sample before and after each experiment at high spatial resolution (20 x 20 ?m). We fabricated a jig for accurately aligning the halves of the core on the profilometer stage and developed and tested numerical routines for reconstructing fracture apertures from the measured surfaces. All cores were subjected to an effective confining stress of 14 MPa and reactive fluids (CO2-equilibrated brine or DI water) were flowed through the cores at different values of Da. The limestone cores showed increased fracture apertures at all values of Da. At the lowest value of Da, the core diameter decreased during the experiment, which was consistent with the measured erosion of contacting asperities contact. Thus, in these experiments, the rate of deformation was slower than the rate of chemical dissolution of the fracture surfaces. In the anhydrite cores, at the lowest value of Da, the permeability decreased by approximately two orders of magnitude to near the value of the intact core. This was consistent with the observed formation of a zone of gypsum adjacent to the fracture plane that deformed due to the confining stress. Results from these experiments are extended via numerical simulations of dissolution that consider the influence of stress-induced deformation of contacts and provide a means for studying the influence of the competing processes of mechanical deformation and mineral dissolution at much larger scales.

  20. Fracture mechanics of the cell wall of Chara corallina

    Microsoft Academic Search

    Geraldine A. Toole; Paul A. Gunning; Mary L. Parker; Andrew C. Smith; Keith W. Waldron

    2001-01-01

    .   Previous mechanical studies using algae have concentrated on cell extension and growth using creep-type experiments, but\\u000a there appears to be no published study of their failure properties. The mechanical strength of single large internode cell\\u000a walls (up to 2?mm diameter and 100?mm in length) of the charophyte (giant alga) Chara corallina was determined by dissecting cells to give sheets

  1. [Observations of the propagation velocity and formation mechanism of burst fractures caused by gunshot].

    PubMed

    König, H G; Schmidt, V

    1989-01-01

    In ballistic literature bursting fractures of the skull in gunshot wounds of the head are understood to be produced by the high pressure built up in the cranial cavity as a result of temporary cavity formation. On one hand there is known, that maximum expansion of the temporary cavity does not occur until some time after the bullet has passed through the skull. On the other hand there exist observations that bursting fractures originating from entrance hole traversed the skull more rapidly than did the projectile. In this paper there is presented a case with such a phenomenon in humerus. Since the determined fracture propagation velocity is very high, there is postulated a direct formation mechanism preceding the indirect effect of the temporary cavity. This hypothesis is confirmed by experiment. PMID:2818487

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

    NASA Astrophysics Data System (ADS)

    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.

  3. Electronics reliability fracture mechanics. Volume 1: Causes of failures of shop replaceable units and hybrid microcircuits

    NASA Astrophysics Data System (ADS)

    Kallis, J.; Buechler, D.; Erickson, J.; Westerhuyzen, D. V.; Strokes, R.

    1992-05-01

    This is the first of two volumes. The other volume (WL-TR-91-3119) is 'Fracture Mechanics'. The objective of the Electronics Reliability Fracture Mechanics (ERFM) program was to develop and demonstrate a life prediction technique for electronic assemblies, when subjected to environmental stress of vibration and thermal cycling, based upon the mechanical properties of the materials and packaging configurations which make up an electronic system. A detailed investigation was performed of the following two shop replaceable units (SRUs): Timing and Control Module (P/N 3562102) and Linear Regulator Module (P/N 3569800). The SRUs are in the Programmable Signal Processor (3137042) Line Replaceable Unit (LRU) of the Hughes AN/APG-63 Radar for the F-15 Aircraft.

  4. The Merging of Fatigue and Fracture Mechanics Concepts: A Historical Perspective

    NASA Technical Reports Server (NTRS)

    Newman, James C., Jr.

    1997-01-01

    The seventh Jerry L. Swedlow Memorial Lecture presents a review of some of the technical developments, that have occurred during the past 40 years, which have led to the merger of fatigue and fracture mechanics concepts. This review is made from the viewpoint of 'crack propagation.' As methods to observe the 'fatigue' process have improved, the formation of fatigue micro-cracks have been observed earlier in life and the measured crack sizes have become smaller. These observations suggest that fatigue damage can now be characterized by 'crack size.' In parallel, the crack-growth analysis methods, using stress-intensity factors, have also improved. But the effects of material inhomogeneities, crack-fracture mechanisms, and nonlinear behavior must now be included in these analyses. The discovery of crack-closure mechanisms, such as plasticity, roughness, and oxide/corrosion/fretting product debris, and the use of the effective stress-intensity factor range, has provided an engineering tool to predict small- and large-crack-growth rate behavior under service loading, conditions. These mechanisms have also provided a rationale for developing, new, damage-tolerant materials. This review suggests that small-crack growth behavior should be viewed as typical behavior, whereas large-crack threshold behavior should be viewed as the anomaly. Small-crack theory has unified 'fatigue' and 'fracture mechanics' concepts; and has bridged the cap between safe-life and durability/damage-tolerance design concepts.

  5. The merging of fatigue and fracture mechanics concepts: a historical perspective

    NASA Astrophysics Data System (ADS)

    Newman, J. C.

    1998-07-01

    In this review, some of the technical developments that have occurred during the past 40 years are presented which have led to the merger of fatigue and fracture mechanics concepts. This review is made from the viewpoint of “crack propagation”. As methods to observe the “fatigue” process have improved, the formation of fatigue micro-cracks have been observed earlier in life and the measured crack sizes have become smaller. These observations suggest that fatigue damage can now be characterized by “crack size”. In parallel, the crack-growth analysis methods, using stress-intensity factors, have also improved. But the effects of material inhomogeneities, crack-fracture mechanisms, and nonlinear behavior must now be included in these analyses. The discovery of crack-closure mechanisms, such as plasticity, roughness, and oxide/corrosion/fretting product debris, and the use of the effective stress-intensity factor range, has provided an engineering tool to predict small- and large-crack-growth rate behavior under service loading conditions. These mechanisms have also provided a rationale for developing new, damage-tolerant materials. This review suggests that small-crack growth behavior should be viewed as typical behavior, whereas large-crack threshold behavior should be viewed as the anomaly. Small-crack theory has unified “fatigue” and “fracture mechanics” concepts; and has bridged the gap between safe-life and durability/damage-tolerance design concepts.

  6. The merging of fatigue and fracture mechanics concepts: A historical perspective

    SciTech Connect

    Newman, J.C. Jr. [NASA Langley Research Center, Hampton, VA (United States)

    1997-12-31

    The seventh Jerry L. Swedlow Memorial Lecture presents a review of some of the technical developments, that have occurred during the past 40 years, which have led to the merger of fatigue and fracture mechanics concepts. This review is made from the viewpoint of crack propagation. As methods to observe the fatigue process have improved, the formation of fatigue micro-cracks have been observed earlier in life and the measured crack sizes have become smaller. These observations suggest that fatigue damage can now be characterized by crack size. In parallel, the crack-growth analysis methods, using stress-intensity factors, have also improved. But the effects of material inhomogeneities, crack-fracture mechanisms, and nonlinear behavior must now be included in these analyses. The discovery of crack-closure mechanisms, such as plasticity, roughness, and oxide/corrosion/fretting product debris, and the use of the effective stress-intensity factor range, has provided an engineering tool to predict small- and large-crack-growth rate behavior under service loading conditions. These mechanisms have also provided a rationale for developing new, damage-tolerant materials. This review suggests that small-crack growth behavior should be viewed as typical behavior, whereas large-crack threshold behavior should be viewed as the anomaly. Small-crack theory has unified fatigue and fracture mechanics concepts; and has bridged the gap between safe-life and durability/damage-tolerance design concepts. 192 refs.

  7. Fracture mechanisms and mechanics of an 18-4-1 high speed steel

    Microsoft Academic Search

    A. S. Wronski; M. M. Rebbeck; S. A. Amen

    1988-01-01

    Cast, wrought, and directly sintered smooth and precracked beam specimens of BT1 steels were studied in three- and four-point bending at room temperature. Following austenitization at 1250° C and tempering between 500 and 560° C, brittle fracture strengths varied between 1.1 and 2.8 GN m-2 and the fracture toughness of the materials was in the range 18 to 25 MN

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

    PubMed Central

    2012-01-01

    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 osteoporotic hip fractures. The developed model is suitable for being used in individualized cases. The model might better identify at-risk individuals in early stages of osteoporosis and might be helpful for treatment decisions. PMID:23151049

  9. Study on predicting residual life of elevator links by fracture mechanics approach

    SciTech Connect

    Li Helin; Zhang Yi; Deng Zengjie [China National Petroleum Corp., Xi`an, Shaanxi (China). Tubular Goods Research Center; Jin Dazeng [Xi`an Jiaotong Univ., Xi`an, Shaanxi (China)

    1995-12-31

    On the basis of investigation, failure and fracture analysis of elevator links, residual life prediction of links using fracture mechanics approach is studied, and mechanical properties, fracture toughness value K{sub IC} and fatigue crack propagation rage da/dN of the steel for elevator links are determined. Using the relation between stress intensity factor K{sub I} and the strain-energy release rate, the two-dimensional conversion thickness finite element method has been used to calculate the stress intensity factors K{sub I} for dangerous sections in the ring part of links. Furthermore, the reliability of calculations of the finite element stress intensity factors K{sub I} for dangerous sections of elevator links and the residual life computation for links are verified by fatigue tests of actual links. Finally, the experimental verification of computed results by 150T link fractured at site indicates that the computed critical crack lengths and residual life tally well with those measured and meet the needs of oil drilling.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  11. Cellular and molecular mechanisms of accelerated fracture healing by COX2 gene therapy: studies in a mouse model of multiple fractures.

    PubMed

    Lau, K-H William; Kothari, Vishal; Das, Amitava; Zhang, Xiao-Bing; Baylink, David J

    2013-04-01

    This study sought to determine the cellular and molecular mechanisms of cyclooxygenase-2 (COX2) gene therapy to accelerate fracture repair in a mouse multiple tibial fractures model. The lenti-COX2 (or lenti-gfp control vector) was injected into fractures on day 1 post-fracture. At days 3-7, the COX2 treatment increased Sdf1-, Cxcr4-, Nes-, and Podxl-expressing mesenchymal stem cells (MSCs) within fracture calluses, suggesting an enhanced MSC recruitment or expansion. The COX2-treated mice formed smaller cartilaginous calluses that had less cartilage tissues than control mice. The expression of Sox9 mRNA was 7-fold less in COX2-treated than in control calluses at day 14, implying that COX2 reduces chondrocytic differentiation of MSCs. The therapy also enhanced angiogenesis as reflected by increased immunostaining of CD31, vWF, and ?-SMA over controls in the cartilaginous callus at day 14-21. At which time, the COX2 gene therapy promoted bony remodeling of the cartilaginous callus to bridge the fracture gap that was accompanied by 2-fold increase in osteoclasts along the surface of the woven bone and an onset of osteogenesis. Blocking angiogenesis with daily injection of endostatin from day 4 to day 10 into fracture sites blocked the COX2-mediated reduction of callus size that was associated with an increase in hypertrophic chondrocytes and concomitant reduction in osteoclasts. In conclusion, COX2 accelerates fracture healing in part through three biological actions: 1) increased recruitment/expansion of MSCs; 2) decreased cartilaginous callus formation; and 3) increased angiogenesis-dependent cartilage remodeling. These effects were associated with an earlier onset of bony bridging of the fracture gap. PMID:23314071

  12. Mechanisms for rate effects on interlaminar fracture toughness of carbon\\/epoxy and carbon\\/PEEK composites

    Microsoft Academic Search

    K. Friedrich; R. Walter; L. A. Carlsson; A. J. Smiley; J. W. Gillespie

    1989-01-01

    The objective of this study was to investigate strain-rate dependent energy absorption mechanisms during interlaminar fracture of thermosetting (epoxy) and thermoplastic (PEEK) uni directional carbon fibre (CF) composites. A simple model addressing the translation of matrix toughness to mode I and mode II interlaminar toughness of the composite is presented, in conjunction with a fractographic examination of the fracture surfaces

  13. Simulation of fluid flow mechanisms in high permeability zones (Super-K) in a giant naturally fractured carbonate reservoir 

    E-print Network

    Abu-Hassoun, Amer H.

    2009-05-15

    the Super-K Zone was investigated. It is known that these zones are connected to naturally occurring fractures. Fluid flow in naturally fractured reservoirs is a very difficult mechanism to understand. To accomplish this mission, the Super-K Zone...

  14. MECHANICAL PROPERTIES AND FRACTURE MECHANISMS OF BURN RESISTANT Ti25V-15Cr2Al0.2C ALLOYS

    Microsoft Academic Search

    T. UDOMPHOL; P. BOWEN

    This current work focused on an assessment of mechanical properties and fracture behaviour of a burn resistant Ti-25V-15Cr-2Al-0.2C alloy, which is designed for aerospace applications up to service temperatures of 450 to 500°C. Alloy microstructure consists of an equiaxed or elongated beta matrix phase with elliptical shaped carbide particles. Thermomechanical processes applied influence morphologies and sizes of the beta grains

  15. Nonlinear fracture mechanics-based analysis of thin wall cylinders

    NASA Technical Reports Server (NTRS)

    Brust, Frederick W.; Leis, Brian N.; Forte, Thomas P.

    1994-01-01

    This paper presents a simple analysis technique to predict the crack initiation, growth, and rupture of large-radius, R, to thickness, t, ratio (thin wall) cylinders. The method is formulated to deal both with stable tearing as well as fatigue mechanisms in applications to both surface and through-wall axial cracks, including interacting surface cracks. The method can also account for time-dependent effects. Validation of the model is provided by comparisons of predictions to more than forty full scale experiments of thin wall cylinders pressurized to failure.

  16. Application of elastic-plastic fracture mechanics to marine structures 

    E-print Network

    Pathi, Amarkumar

    1991-01-01

    machine, and ASTM E 23 [21] guidelines were followed. Specimens machined from the center were engraved C and those machined from the sur- face were engraved S. The orientations of the EH 36 specimens and the HSLA 80 specimens were in the L-T direction... employed to characterize the mechanical prop- erties of both the steels. The test specimens were made according to the ASTM E 8 standards [22] as shown in Figure II. 2. The load was applied to each tensile specimen at a known rate so that the deformation...

  17. Unusual Mechanism of Injury Resulting in a Thoracic Chance Fracture in a Rodeo Athlete: A Case Report

    PubMed Central

    Boham, Mikaela; O'Connell, Kim

    2014-01-01

    Objective: To introduce the characteristics of a Chance fracture and increase awareness of the mechanism of injury that may occur during athletic activity. Background: A T12 Chance fracture was diagnosed in an 18-year-old male rodeo athlete. The rider was forced into extreme lumbothoracic hyperflexion when the horse bucked within the chute, pinning the rider's legs to his chest. Differential Diagnosis: Burst fracture, abdominal organ rupture, spinal dislocation, spinal cord injury, disk herniation, pars interarticularis fracture, spinal nerve injury, paralysis. Treatment: The patient underwent an open reduction and fixation of the thoracic fracture. Posterior stabilization was obtained with nonsegmental instrumentation. Allograft and autografts were used for posterolateral arthrodesis at T11–T12 and T12–L1. Uniqueness: Motor vehicle crashes with occupants wearing lap-type–only restraints account for nearly all previously reported Chance fractures. When only lap seatbelts are worn, the pelvis is stabilized, and the torso continues moving forward with impact. The stabilized body segment for this individual was reversed. Nearly 3 years after the initial surgery, fixation, and infection, the bareback rider has returned to full participation in rodeo. Conclusions: To our knowledge, this is the first reported diagnosis of a T12 Chance fracture in a rodeo athlete. When animals buck, athletes can be forced into hyperflexion, exposing them to Chance fractures. Therefore, anyone treating rodeo athletes must suspect possible spinal fracture when this mechanism is present and must treat all athletes with early conservative management and hospital referral. PMID:24520836

  18. Mechanical properties and fracture behavior of an ultrafine-grained Al20 wt pct Si alloy

    Microsoft Academic Search

    Soon-Jik Hong; C. Suryanarayana

    2005-01-01

    The effect of powder particle size on the microstructure, mechanical properties, and fracture behavior of Al-20 wt pct Si\\u000a alloy powders was studied in both the gas-atomized and extruded conditions. The microstructure of the as-atomized powders\\u000a consisted of fine Si particles and that of the extruded bars showed a homogeneous distribution of fine eutectic Si and primary\\u000a Si particles embedded

  19. Linear elastic vs elastic-plastic fracture mechanics methods in nuclear vessel integrity assessments

    Microsoft Academic Search

    JoséRicardo Tarpani; Dirceu Spinelli

    1997-01-01

    This paper compares analytical failure predictions for a flawed PWR vessel from linear elastic and elastic-plastic fracture mechanics, as currently permissible by ASME code. The significant conservatism under upper-shelf conditions provided by the first approach has been quantified in terms of internal pressure and wall-thickness strain gradient. Monotonic crack growth withstood by the assessed component has been evaluated through several

  20. Application of Fracture Mechanics Concepts to Hierarchical Biomechanics of Bone and Bone-like Materials

    Microsoft Academic Search

    Huajian Gao

    2006-01-01

    Fracture mechanics concepts are applied to gain some understanding of the hierarchical nanocomposite structures of hard biological\\u000a tissues such as bone, tooth and shells. At the most elementary level of structural hierarchy, bone and bone-like materials\\u000a exhibit a generic structure on the nanometer length scale consisting of hard mineral platelets arranged in a parallel staggered\\u000a pattern in a soft protein

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

  2. The Fatigue and Durability Behaviour of Automotive Adhesives. Part I: Fracture Mechanics Tests

    Microsoft Academic Search

    J. K. Jethwa; A. J. Kinloch

    1997-01-01

    A fracture mechanics approach has been successfully used to examine the cyclic fatigue behaviour of adhesively-bonded joints, which consisted of aluminium-alloy or electro-galvanised (EG) steel substrates bonded using toughened-epoxy structural paste-adhesives. The adhesive systems are typical of those being considered for use, or in use, for bonding load-bearing components in the automobile industry. The results were plotted in the form

  3. Interpenetrating microstructure and fracture mechanism of NiAl\\/TiC composites by pressureless melt infiltration

    Microsoft Academic Search

    M. X Gao; Y Pan; F. J Oliveira; J. L Baptista; J. M Vieira

    2004-01-01

    NiAl\\/TiC composites with TiC content of 86–92 vol.% were prepared by pressureless melt infiltration. The high content of TiC and consequent TiC particles joining were obtained by pre-sintering of the as-pressed TiC preform before infiltration. Mechanical properties including bending strength, Vickers hardness, fracture toughness and Young's modulus were measured. The microstructure of the composites is characterized by the three-dimensional interpenetration

  4. American Society of Biomechanics Journal of Biomechanics Award 2013: cortical bone tissue mechanical quality and biological mechanisms possibly underlying atypical fractures.

    PubMed

    Geissler, Joseph R; Bajaj, Devendra; Fritton, J Christopher

    2015-04-13

    The biomechanics literature contains many well-understood mechanisms behind typical fracture types that have important roles in treatment planning. The recent association of "atypical" fractures with long-term use of drugs designed to prevent osteoporosis has renewed interest in the effects of agents on bone tissue-level quality. While this class of fracture was recognized prior to the introduction of the anti-resorptive bisphosphonate drugs and recently likened to stress fractures, the mechanism(s) that lead to atypical fractures have not been definitively identified. Thus, a causal relationship between these drugs and atypical fracture has not been established. Physicians, bioengineers and others interested in the biomechanics of bone are working to improve fracture-prevention diagnostics, and the design of treatments to avoid this serious side-effect in the future. This review examines the mechanisms behind the bone tissue damage that may produce the atypical fracture pattern observed increasingly with long-term bisphosphonate use. Our recent findings and those of others reviewed support that the mechanisms behind normal, healthy excavation and tunnel filling by bone remodeling units within cortical tissue strengthen mechanical integrity. The ability of cortical bone to resist the damage induced during cyclic loading may be altered by the reduced remodeling and increased tissue age resulting from long-term bisphosphonate treatment. Development of assessments for such potential fractures would restore confidence in pharmaceutical treatments that have the potential to spare millions in our aging population from the morbidity and death that often follow bone fracture. PMID:25683519

  5. Incorporation of Interfacial Intermetallic Morphology in Fracture Mechanism Map for Sn-Ag-Cu Solder Joints

    NASA Astrophysics Data System (ADS)

    Huang, Z.; Kumar, P.; Dutta, I.; Sidhu, R.; Renavikar, M.; Mahajan, R.

    2014-01-01

    A fracture mechanism map (FMM) is a powerful tool which correlates the fracture behavior of a material to its microstructural characteristics in an explicit and convenient way. In the FMM for solder joints, an effective thickness of the interfacial intermetallic compound (IMC) layer ( t eff) and the solder yield strength ( ? ys,eff) are used as abscissa and ordinate axes, respectively, as these two predominantly affect the fracture behavior of solder joints. Earlier, a definition of t eff, based on the uniform thickness of IMC ( t u) and the average height of the IMC scallops ( t s), was proposed and shown to aptly explain the fracture behavior of solder joints on Cu. This paper presents a more general definition of t eff that is more widely applicable to a range of metallizations, including Cu and electroless nickel immersion gold (ENIG). Using this new definition of t eff, mode I FMM for SAC387/Cu joints has been updated and its validity was confirmed. A preliminary FMM for SAC387/Cu joints with ENIG metallization is also presented.

  6. A new approach to the modeling and analysis of fracture through an extension of continuum mechanics to the nanoscale 

    E-print Network

    Sendova, Tsvetanka Bozhidarova

    2009-05-15

    The dissertation focuses on the analysis, through combined analytical and numerical techniques, of the partial differential equations arising from a new approach to modeling brittle fracture, based on extension of continuum mechanics...

  7. A new approach to the modeling and analysis of fracture through an extension of continuum mechanics to the nanoscale

    E-print Network

    Sendova, Tsvetanka Bozhidarova

    2009-05-15

    The dissertation focuses on the analysis, through combined analytical and numerical techniques, of the partial differential equations arising from a new approach to modeling brittle fracture, based on extension of continuum mechanics...

  8. A study of fracture mechanisms in ATD roller bearing

    NASA Technical Reports Server (NTRS)

    Zee, Ralph H.

    1990-01-01

    The purpose was to investigate how microstructures, especially anisotropy, affects internal stresses and the overall mechanical response of bearings. Samples with the stress axis along the aligned carbide direction possessed high modulus values compared to those with their axis perpendicular to the carbide stringers. The difference in the modulus was found to be more than a factor of two. A series of experiments was conducted on rolled samples to further investigate this effect; the two sets of results were consistent with each other. The degree of anisotropy of the microstructure in terms of the carbide and matrix orientations was determined using x-ray diffraction. The stress state determination was conducted using neutron diffraction. It was found that there was little variation in the distribution of the internal stresses amongst different samples, indicating that small changes in the processing and geometrical conditions did not result in significant variations in the internal stress. A nominal tensile hoop stress of 39 ksi was obtained for the inner raceway. Furthermore, during the course of the investigation, it was apparent that there was a need to determine the stress state induced by the shrink fitting process. Therefore, a series of experiments was conducted using strain gages to identify the stress distribution in a shrink fitting process in three different types of geometries. Correlations were obtained to estimate the highest stress values in the outer and inner groove geometry. A finite element program based on the ANSYS system was developed to compute the stress distribution in the inner raceway geometry. This analysis indicates that the highest tensile stress in the system occurs at the ID of the ring with a stress value of over 5 times that of the applied radial stress. Results from all these facets were correlated with one another. It appears that the material does not fail as a result of any one single factor, but results from a combination of the various factors investigated.

  9. Effect of the notch opening angle on the mechanical properties and fracture morphology of mild steel samples at different strain rates

    NASA Astrophysics Data System (ADS)

    Savenkov, G. G.; Barakhtin, B. K.; Bragov, A. M.; Shchukina, E. V.

    2013-07-01

    The mechanical properties of notched samples of St.10 steel under tension at different strain rates were studied. Fracture surfaces of the notched samples after the dynamic bending were investigated, the mechanisms of plastic deformation and fracture were determined, and the fractal dimension of the fracture contours were obtained.

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

    NASA Astrophysics Data System (ADS)

    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.

  11. Transformation of creep stresses in ice shelves for fracture mechanical analyses

    NASA Astrophysics Data System (ADS)

    Plate, C.; Müller, R.; Humbert, A.; Wilkens, N.; Gross, D.

    2012-04-01

    Recent disintegrations of ice shelves and calving at ice fronts require a better understanding of fracture mechanical processes involved in these events. Previous studies on cracks in ice shelves with different stress states, density profiles and material parameters highlighted the dependence of the crack criticality on the choice of boundary conditions and the applied material law. To this end, we present different approaches how to transfer the flow induced viscous stresses into the fracture mechanical analysis for the study of vertical and horizontal crack scenarios. The numerical simulations are performed using Finite Elements and the concept of configurational forces for the evaluation of stress intensity factors. This approach is rather flexible and can account for inhomogeneous material properties, volume forces and crack face loadings, e.g. due to additional water pressure. The methods are applied to 2-dimensional geometries under various loading conditions and material parameters. The methods are validated using data from the literature and the results are compared to fracture events that have been documented using remote sensing data analysis.

  12. Finite Element Study of the Mechanical Response in Spinal Cord during the Thoracolumbar Burst Fracture

    PubMed Central

    Wu, Zi-Xiang; Qiu, Tian-Xia; Teo, Ee-Chon; Lei, Wei

    2012-01-01

    Background The mechanical response of the spinal cord during burst fracture was seldom quantitatively addressed and only few studies look into the internal strain of the white and grey matters within the spinal cord during thoracolumbar burst fracture (TLBF). The aim of the study is to investigate the mechanical response of the spinal cord during TLBF and correlate the percent canal compromise (PCC) with the strain in the spinal cord. Methodology/Principal Findings A three-dimensional (3D) finite element (FE) model of human T12-L1 spinal cord with visco-elastic property was generated based on the transverse sections images of spinal cord, and the model was validated against published literatures under static uniaxial tension and compression. With the validated model, a TLBF simulation was performed to compute the mechanical strain in the spinal cord with the PCC. Linear regressions between PCC and strain in the spinal cord show that at the initial stage, with the PCC at 20%, and 45%, the corresponding mechanical strains in ventral grey, dorsal grey, ventral white, dorsal white matters were 0.06, 0.04, 0.12, 0.06, and increased to 0.14, 0.12, 0.23, and 0.13, respectively. At the recoiled stage, when the PCC was decreased from 45% to 20%, the corresponding strains were reduced to 0.03, 0.02, 0.04 and 0.03. The strain was correlated well with PCC. Conclusions/Significance The simulation shows that the strain in the spinal cord correlated well with the PCC, and the mechanical strains in the ventral regions are higher than those in the dorsal regions of spinal cord tissue during burst fracture, suggesting that the ventral regions of the spinal cord may susceptible to injury than the dorsal regions. PMID:23028426

  13. A fracture mechanics study of the turbine wheel in the Space Shuttle auxiliary power unit

    NASA Technical Reports Server (NTRS)

    Forman, R. G.

    1985-01-01

    The experimental and analytical efforts performed for fracture control of the Space Shuttle auxiliary power unit (APU) wheel are described and a summary of fracture mechanics concepts relevant to safe-life analysis of fatigue loaded parts is given. An environmental crack growth test program is conducted by NASA on candidate wheel materials exposed to decomposed hydrazine which is found to be no more severe in causing crack growth than an environment of high-temperature air. Details of the crack growth testing and the safe-life analysis are presented. The results show that special nondestructive examination is needed for the APU wheel to meet the required mission life for either the maximum design or expected speed-range operations.

  14. A nonlocal continuum damage mechanics approach to simulation of creep fracture in ice sheets

    NASA Astrophysics Data System (ADS)

    Duddu, Ravindra; Waisman, Haim

    2013-06-01

    We present a Lagrangian finite element formulation aimed at modeling creep fracture in ice-sheets using nonlocal continuum damage mechanics. The proposed formulation is based on a thermo-viscoelastic constitutive model and a creep damage model for polycrystalline ice with different behavior in tension and compression. In this paper, mainly, we detail the nonlocal numerical implementation of the constitutive damage model into commercial finite element codes (e.g. Abaqus), wherein a procedure to handle the abrupt failure (rupture) of ice under tension is proposed. Then, we present numerical examples of creep fracture under four-point bending, uniaxial tension, and biaxial tension in order to illustrate the viability of the current approach. Finally, we present simulations of creep crack propagation in idealized rectangular ice slabs so as to estimate calving rates at low deformation rates. The examples presented demonstrate the mesh size and mesh directionality independence of the proposed nonlocal implementation.

  15. Quantifying mechanical properties in a murine fracture healing system using inverse modeling: preliminary work

    NASA Astrophysics Data System (ADS)

    Miga, Michael I.; Weis, Jared A.; Granero-Molto, Froilan; Spagnoli, Anna

    2010-03-01

    Understanding bone remodeling and mechanical property characteristics is important for assessing treatments to accelerate healing or in developing diagnostics to evaluate successful return to function. The murine system whereby mid-diaphaseal tibia fractures are imparted on the subject and fracture healing is assessed at different time points and under different therapeutic conditions is a particularly useful model to study. In this work, a novel inverse geometric nonlinear elasticity modeling framework is proposed that can reconstruct multiple mechanical properties from uniaxial testing data. To test this framework, the Lame' constants were reconstructed within the context of a murine cohort (n=6) where there were no differences in treatment post tibia fracture except that half of the mice were allowed to heal 4 days longer (10 day, and 14 day healing time point, respectively). The properties reconstructed were a shear modulus of G=511.2 +/- 295.6 kPa, and 833.3+/- 352.3 kPa for the 10 day, and 14 day time points respectively. The second Lame' constant reconstructed at ?=1002.9 +/-42.9 kPa, and 14893.7 +/- 863.3 kPa for the 10 day, and 14 day time points respectively. An unpaired Student t-test was used to test for statistically significant differences among the groups. While the shear modulus did not meet our criteria for significance, the second Lame' constant did at a value p<0.0001. Traditional metrics that are commonly used within the bone fracture healing research community were not found to be statistically significant.

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

    NASA Astrophysics Data System (ADS)

    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. Tensile fractures can occur when the hoop stress exerted on the outer shell exceeds its tensile strength. The molten conduit material is then likely to flow into the newly formed fracture, depending on its viscosity and the fracture dimensions, allowing comparisons to be made between the temperature and intrusions dynamics of the simulated dyke process. As a starting point, we are now testing an analogue material to replace the magma to avoid complex multi-phase rheology (bubbles, crystals) and the need for high experimental temperatures, relying of maintaining similar temperature/viscosity ratios between magma/country rock in the laboratory and the field. We chose PMMA (commonly known as plexiglass) for this task as it displays a large range in viscosities (log(visc)range = 10 -1) with temperatures between 100 and 300 °C, making it an excellent analogue material. In the future experiments at higher temperatures will be conducted with NIST-glasses and field collected glasses. 2D and 3D imaging of post-deformation samples show no preferential location of the fractures. Fractures are formed both around and trough crystals. Some evidence suggests the formation of microcracks and linking up as predicted by Griffith's theory. Correcting for apparatus distortion and friction of o-rings and the filler material we can calculate the conduit stress and arrive at a tensile strength values for different basement rock types in the order of 1-15 MPa.

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

    PubMed

    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

  18. The Relationships between Weight Functions, Geometric Functions, and Compliance Functions in Linear Elastic Fracture Mechanics

    E-print Network

    Yuan, Rong

    2007-01-01

    G and fracture resistance R as G ? R (initiation), and ? G ?fracture resistance in isotropic elastic material, and also formulated a criterion for crack initiationinitiation [2]. As both notches experience the same bending moment, when one fractures,

  19. Breaking the limits of structural and mechanical imaging of the heterogeneous structure of coal macerals

    NASA Astrophysics Data System (ADS)

    Collins, L.; Tselev, A.; Jesse, S.; Okatan, M. B.; Proksch, R.; Mathews, J. P.; Mitchell, G. D.; Rodriguez, B. J.; Kalinin, S. V.; Ivanov, I. N.

    2014-10-01

    The correlation between local mechanical (elasto-plastic) and structural (composition) properties of coal presents significant fundamental and practical interest for coal processing and for the development of rheological models of coal to coke transformations. Here, we explore the relationship between the local structural, chemical composition, and mechanical properties of coal using a combination of confocal micro-Raman imaging and band excitation atomic force acoustic microscopy for a bituminous coal. This allows high resolution imaging (10s of nm) of mechanical properties of the heterogeneous (banded) architecture of coal and correlating them to the optical gap, average crystallite size, the bond-bending disorder of sp2 aromatic double bonds, and the defect density. This methodology allows the structural and mechanical properties of coal components (lithotypes, microlithotypes, and macerals) to be understood, and related to local chemical structure, potentially allowing for knowledge-based modeling and optimization of coal utilization processes.

  20. Breaking the limits of structural and mechanical imaging of the heterogeneous structure of coal macerals.

    PubMed

    Collins, L; Tselev, A; Jesse, S; Okatan, M B; Proksch, R; Mathews, J P; Mitchell, G D; Rodriguez, B J; Kalinin, S V; Ivanov, I N

    2014-10-31

    The correlation between local mechanical (elasto-plastic) and structural (composition) properties of coal presents significant fundamental and practical interest for coal processing and for the development of rheological models of coal to coke transformations. Here, we explore the relationship between the local structural, chemical composition, and mechanical properties of coal using a combination of confocal micro-Raman imaging and band excitation atomic force acoustic microscopy for a bituminous coal. This allows high resolution imaging (10s of nm) of mechanical properties of the heterogeneous (banded) architecture of coal and correlating them to the optical gap, average crystallite size, the bond-bending disorder of sp(2) aromatic double bonds, and the defect density. This methodology allows the structural and mechanical properties of coal components (lithotypes, microlithotypes, and macerals) to be understood, and related to local chemical structure, potentially allowing for knowledge-based modeling and optimization of coal utilization processes. PMID:25299223

  1. Effect of hydrogen on the mechanical properties and fracture behavior of high-purity aluminium

    SciTech Connect

    Zeides, F.

    1986-01-01

    A study of hydrogen effects was conducted on 99.999% pure aluminum. Hydrogen was introduced into the material by means of a corrosion process. Two corrosive media were used; deionized pure water and an alkaline solution. The former was used for dynamic hydrogen charging during mechanical tests and the latter for hydrogen precharging. The corrosion reaction in the dynamic charging was intensified by application of weak ultrasonic oscillations. It was found that hydrogen changed the response of the material to plastic deformation causing softening and plastic-deformation localization on the macroscale and slip-line coarsening as well as an increase in their waviness on the microscale. Hydrogen modified the fracture mode, changing it from a totally ductile, chisel point type to a more brittle transgranular or intergranular fracture. The hydrogen-induced fracture modification is believed to result from the plastic-deformation modification and from the effect of hydrogen on microvoid nucleation. Hydrogen charging resulted in the formation of bulk vacancy clusters, a linear-dimensions shrinkage, and grain growth.

  2. Study on life extension of aged RPV material based on probabilistic fracture mechanics: Japanese round robin

    SciTech Connect

    Yagawa, G.; Yoshimura, S. (Univ. of Tokyo (Japan)); Handa, N. (Toshiba Corp., Tokyo (Japan)) (and others)

    1995-02-01

    This paper is concerned with round-robin analyses of probabilistic fracture mechanics (PFM) problems of aged RPV material. Analyzed here is a plate with a semi-elliptical surface crack subjected to various cyclic tensile and bending stresses. A depth and an aspect ratio of the surface crack are assumed to be probabilistic variables. Failure probabilities are calculated using the Monte Carlo methods with the importance sampling or the stratified sampling techniques. Material properties are chosen from the Marshall report, the ASME Code Section XI, and the experiments on a Japanese RPV material carried out by the Life Evaluation (LE) subcommittee of the Japan Welding Engineering Society (JWES), while loads are determined referring to design loading conditions of pressurized water reactors (PWR). Seven organizations participate in this study. At first, the procedures for obtaining reliable PFM solutions with low failure probabilities are examined by solving a unique problem with seven computer programs. The seven solutions agree very well with one another, i.e., by a factor of 2 to 5 in failure probabilities. Next, sensitivity analyses are performed by varying fracture toughness values, loading conditions, and pre and in-service inspections. Finally, life extension simulations based on the PFM analyses are performed. It is clearly demonstrated from these analyses that failure probabilities are so sensitive to the change of fracture toughness values that the degree of neutron irradiation significantly influences the judgment of plant life extension.

  3. Alteration of Fractured Rocks Due to Coupled Chemical and Mechanical Processes: High-Resolution Simulations and Experimental Observations

    NASA Astrophysics Data System (ADS)

    Ameli, Pasha

    Engineering activities such as enhanced geothermal energy production and improved oil recovery techniques are heavily dependent on the permeability of the subsurface, while others such as CO2 sequestration and nuclear waste disposal rely on the efficiency of rock formations as transport barriers. In either case fractures provide the main pathways for fluid flow and transport, especially in rocks with lower matrix porosity. Laboratory experiments aimed at quantifying the chemo-mechanical responses of fractures have shown a range of results, some of which contradict simple conceptual models. For example, under conditions favoring mineral dissolution, where one would expect an overall increase in permeability, experiments show that permeability increases under some conditions and decreases under others. Recent experiments have attempted to link these core-scale observations to the relevant small-scale processes occurring within fractures. Results suggest that the loss of mechanical strength in asperities due to chemical alteration may cause non-uniform deformation and alteration of fracture apertures. However, due to the lack of direct micro-scale measurements of the coupled chemical and mechanical processes that lead to alteration of contacting fracture surfaces, our ability to predict the long-term evolution of fractures is still limited. To explore the processes that control permeability evolution, I developed a computational model that uses micro-scale surface roughness and explicitly couples dissolution and elastic deformation to calculate local alterations in fracture aperture under chemical and mechanical stresses. A depth-averaged algorithm of fracture flow is used to model reactive transport and chemical alteration of the fracture surfaces. Then, I deform the resulting altered fracture-surfaces using an algorithm that calculates the elastic deformation. The results of the model are compared with flow-through experiments conducted on fractured limestone. The fracture apertures are mapped before and after the experiments. These detailed aperture measurements are used as input to the new coupled model. The experiments cover a wide range of transport and reaction conditions; some exhibited negligible reaction-induced deformation and formation of distinct dissolution channels and others more uniform dissolution and measurable deformation caused by dissolution. Simulation results predict these general trends and the small-scale details in regions of contacting asperities.

  4. A deterministic method for probabilistic fracture mechanics and its application to an analysis of LWR piping

    SciTech Connect

    Akiba, Hiroshi; Yoshimura, Shinobu; Yagawa, Genki

    1995-11-01

    This paper proposes a new method for Probabilistic Fracture Mechanics (PFM). The present method give a time-evolution law of a distribution function of a crack geometry, which is obtained from initial random variables and a deterministic time-evolution law of the variables. A numerical example of a Light Water Reactor (LWR)`s piping problem is solved by the present method and the results are compared with those of the Monte Carlo (MC) method. Both results agree sufficiently well, while CPU time of the present method is remarkably short.

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

    NASA Technical Reports Server (NTRS)

    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.

  6. Basilar Artery Occlusion Following C1 Lateral Mass Fracture Managed by Mechanical and Pharmacological Thrombolysis

    Microsoft Academic Search

    Patrick A. Sugrue; Ziad A. Hage; Daniel L. Surdell; Mina Foroohar; John Liu; Bernard R. Bendok

    2009-01-01

    Background  Vertebral artery injury following cervical spine trauma can be associated with stroke. We present a case of a C1 fracture\\u000a resulting in vertebral artery dissection and neurological decline as a result of basilar artery occlusion treated with chemical\\u000a and mechanical thrombolysis resulting in basilar artery patency and clinical improvement.\\u000a \\u000a \\u000a \\u000a Case description  The patient is a 43-year-old female who was involved in

  7. Vena Tech LGM filter retrieval 16 years after implantation: piecemeal removal by intentional mechanical fracture.

    PubMed

    Kuo, William T; Deso, Steven E; Robertson, Scott W

    2013-11-01

    A 48-year-old man presented with symptomatic inferior vena cava (IVC) occlusion from a chronically thrombosed and embedded Vena Tech LGM filter resulting in exercise intolerance from diminished cardiac preload and postthrombotic syndrome from chronic venous insufficiency. The patient was treated using a new PRIME technique--Piecemeal Removal by Intentional MEchanical fracture--to achieve successful filter retrieval 16 years after implantation. Removal of the obstructing filter permitted endovascular IVC recanalization with restoration of venous outflow and alleviation of venous obstructive symptoms. Cardiac preload was restored, allowing the patient to resume long-distance running, and he successfully completed a half-marathon 3 months after treatment. PMID:24160825

  8. Recent fracture mechanics results from NASA research related to the aging commercial transport fleet

    NASA Technical Reports Server (NTRS)

    Harris, Charles E.

    1991-01-01

    NASA is conducting the Airframe Structural Integrity Program in support of the aging commercial transport fleet. This interdisciplinary program is being worked in cooperation with the U.S. airframe manufacturers, airline operators, and the FAA. Advanced analysis methods are under development to predict the fatigue crack growth in complex built-up shell structures. Innovative nondestructive examination technologies are also under development to provide large area inspection capability to detect corrosion, disbonds, and fatigue cracks. Recent fracture mechanics results applicable to predicting the growth of cracks initiating at the rivets of fuselage splice joints are reviewed.

  9. Fracture mechanics model of stone comminution in ESWL and implications for tissue damage

    NASA Astrophysics Data System (ADS)

    Lokhandwalla, Murtuza; Sturtevant, Bradford

    2000-07-01

    Focused shock waves administered during extracorporeal shock-wave lithotripsy (ESWL) cause stone fragmentation. The process of stone fragmentation is described in terms of a dynamic fracture process. As is characteristic of all brittle materials, fragmentation requires nucleation, growth and coalescence of flaws, caused by a tensile or shear stress. The mechanisms, operative in the stone, inducing these stresses have been identified as spall and compression-induced tensile microcracks, nucleating at pre-existing flaws. These mechanisms are driven by the lithotripter-generated shock wave and possibly also by cavitation effects in the surrounding fluid. In this paper, the spall mechanism has been analysed, using a cohesive-zone model for the material. The influence of shock wave parameters, and physical properties of stone, on stone comminution is described. The analysis suggests a potential means to exploit the difference between the stone and tissue physical properties, so as to make stone comminution more effective, without increasing tissue damage.

  10. Interface Effects on the Fracture Mechanism of a High-Toughness Aluminum-Composite Laminate

    NASA Astrophysics Data System (ADS)

    Cepeda-Jiménez, C. M.; Pozuelo, M.; García-Infanta, J. M.; Ruano, O. A.; Carreño, F.

    2009-01-01

    The microstructure and the mechanical properties of a multilayer composite laminate based on aluminum 7075 and 2024 alloys produced by hot roll bonding were examined. The composite laminate has been tested at room temperature under Charpy-impact tests, three-point bend tests, and shear tests on the interfaces. The toughness of the post-rolling tempered and T6-treated composite laminate, measured by impact- absorbed energy in the crack-arrester orientation, was more than 20 times higher than that of the monolithic Al 7075 alloy and 7 times higher than that of Al 2024 alloy. The outstanding toughness increase of the composite laminate in the post-rolling tempered and T6-treated condition is mainly due to the mechanism of “interface predelamination.” By this fracture mechanism, the interfaces are debonded before the main crack reaches them, warranting delamination in all interfaces. Therefore, delamination and crack renucleation in every layer are responsible for the improvement in toughness.

  11. Source Mechanisms of Low Frequency Seismicity in a Hydraulic Fracturing Context

    NASA Astrophysics Data System (ADS)

    Zecevic, M.; Daniel, G.; Hubans, F.; Gouedard, P.

    2014-12-01

    In recent years, long-period long-duration (LPLD) events have been observed during hydraulic fracturing of hydrocarbon reservoirs (Das & Zoback, 2013). LPLDs are low-amplitude signals lasting from tens of seconds to minutes. Their source mechanisms are not fully understood. However, as they are remarkably similar in character to tectonic tremors it has been suggested that they may also have comparable source models. Current models suggest that a tectonic tremor consists of numerous slow-slip earthquakes superposed on each other to form continuous waveforms (Shelley et al., 2007). These slow-slip earthquakes are thought to be a result of shear slip on faults close to failure with low confining pressure, most likely due to the presence of fluid with pore pressures close to lithostatic pressures (Peng & Gomberg, 2010). This study aims to further understand the source mechanism of LPLDs. A hydraulic fracturing dataset containing thousands of located microseismic earthquakes (MEQs) and numerous LPLDs is presented. The MEQs are located around the injection stages whereas the LPLDs are clustered in a limited region within the reservoir. This clustering suggests that LPLDs can only be generated where the conditions in the reservoir are favorable. These results correspond with the possibility that LPLDs are manifestations of slow-slip, with the source locations confined by variations in the mechanical properties of the reservoir. To test this hypothesis a further understanding of the mechanisms of LPLDs and the stress field in which they occur is needed. However, calculating focal mechanisms for LPLDs is difficult due to their emergent onset and lack of clear phases. Consequently, LPLDs must be put into context with the observed MEQs. We will present the spatial distribution of the focal mechanisms of the MEQs and analyze our findings with respect to the occurrence of the LPLD events.

  12. Fracture mechanics investigations on high-temperature gas-cooled reactor materials

    SciTech Connect

    Krompholz, K.; Bodmann, E.; Gnirss, G.K.; Huthmann, H.

    1984-08-01

    The prototype nuclear process heat plant and the high-temperature gas-cooled reactor need materials that can withstand temperatures up to 1223 K (950/sup 0/C). An elaboration of fracture mechanics concepts that holds for the complete temperature regime must consider all possible phenomena like creep damage and precipitation during exposure, etc. In tests on the Inconel-617, Hastelloy-X, and Nimonic-86 alloys with respect to fatigue crack growth, creep crack growth, and toughness (J integral R curves) up to 1273 K (1000/sup 0/C), the first creep crack growth results were obtained in helium to compare with the air results. It was shown that pure fatigue crack growth behavior can be described by linear elastic fracture mechanics up to 1273 K. An example of Hastelloy-X at 1223 K proves that evaluating fatigue crack growth according to the J intergral concept gives, within a small scatterband, the same results as by following the linear elastic concept. Hastelloy-X shows a decreasing fracture toughness with increasing temperatures. It is emphasized that the J integral concept holds only if creep deformation can be neglected. The experimental evidence at highest temperatures shows that the J integral R curve is not at all similar to that found at lower temperatures under ideal conditions. Creep crack growth for Nimonic-86 at 1073 less than or equal to T/K less than or equal to 1273 shows that crack growth at 1223 K in helium is found to be larger than in air. Problems arise when correlating the creep crack growth results. The application of the energy rate integral C* seems promising, but this has yet to be proven. A combination of long-term creep with fatigue crack growth is presently impossible.

  13. Mechanical properties and fracture toughness of organo-silicate glass (OSG) low- k dielectric thin films for microelectronic applications

    Microsoft Academic Search

    J. B. Vella; I. S. Adhihetty; K. Junker; A. A. Volinsky

    2003-01-01

    The integration of chemical vapor deposited organo-silicate glass (OSG) interlayer dielectrics (ILD) has challenged the IC industry to formulate new methods of metrology and characterization. The impact of nanoindentation to understand and screen for integrated circuit failure mechanisms that are mainly predicated upon OSG nano-porosity is discussed. Failure modes include poor mechanical strength, low material stiffness, and brittle fracture due

  14. Fracture mechanics based design for radioactive material transport packagings -- Historical review

    SciTech Connect

    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.

  15. Simulating Thermal-Hydrologic-Mechanical-Chemical Evolution Surrounding Fluid Injection in a Fractured Porous Geothermal Reservoir

    NASA Astrophysics Data System (ADS)

    Taron, J.; Min, K.; Elsworth, D.

    2006-12-01

    Computational analysis is conducted on the coupled thermal-hydrologic-mechanical-chemical (THMC) behavior of a stimulated EGS geothermal reservoir. Numerical analyses utilize a newly developed simulator capable of examining THMC processes in fractured porous geologic media. The simulator links the thermal-hydrologic- chemical (THC) computational code TOUGHREACT with the mechanical (M) capability of FLAC3D, where the response of pore fluid pressure to mechanical disturbance is treated as an undrained system and mineral precipitation/dissolution generates porosity and permeability change within each dual-permeability continuum. Non-linear permeability response to thermal-hydrologic-mechanical (THM) mechanisms is accommodated via embryonic mechanical and transport constitutive laws, and is considered to act in union with permeability changes associated with the removal or addition of minerals within the system. This construct is applied to the geometry of an injector-withdrawal doublet within the Coso Geothermal field, where in situ stress conditions, thermal state, and mineralogical composition at 3000m depth are extracted from recorded field data. Initial results for feasible parametric settings show that permeability reduction in the vicinity of a cool (80°C) injection well may be significant, within an order of magnitude, and accompanied by large (MPa) changes in the stress field throughout the reservoir for imposed boundary conditions of constant stress.

  16. Fracture and Damage Mechanics of Marginal Weakening and Rifting in Pine Island Glacier Ice Shelf

    NASA Astrophysics Data System (ADS)

    Borstad, C. P.; Rignot, E. J.; Larour, E. Y.

    2013-12-01

    The southern ice shelf of Pine Island Glacier has experienced at least seven major tabular calving events since 1973. The most recent calving in July 2013 was the culmination of a rift that initiated further upstream than any in the observational record. Here, we apply fracture and damage mechanics to analyze the pattern, location, and relationship between marginal weakening and rifting over time for the ice shelf. We compute spatially variable maps of ice rigidity for the years 1996 and 2007 using an inverse control method implemented in the Ice Sheet System Model (ISSM). We derive a new theoretical relation for the creep of a damaged ice shelf and use this relation, combined with an analytical temperature calculation for the ice shelf, to partition the inverted rigidity into solutions for damage and backstress for the ice shelf. We find that damage in the shear margins has increased in magnitude and spatial extent over time, in agreement with the amount of marginal weakening necessary for analytical centerline velocity calculations to be consistent with observations. We apply Linear Elastic Fracture Mechanics (LEFM) to analyze the conditions under which rifts originate in the ice shelf. All rifts observed over the last 40 years have been located adjacent to or downstream of an ice rumple located along the northern shear margin of the ice shelf. Prior to 2001, the rifts appeared to initiate in the center of the ice shelf and propagate symmetrically outward and transverse to the flow. Since 2001, however, the rifts have initiated from existing marginal fractures in the wake of the ice rumple. This change in behavior is explained by the loss of buttressing from the ice rumple as the ice upstream has thinned and weakened. Simple LEFM considerations predict that rifts may form more frequently in the future, as propagating a fracture from the edge of a plate is easier, for a given stress, than from the middle. Furthermore, given the reduced buttressing near the front of the ice shelf, future rifts are increasingly likely to originate further upstream than observed previously.

  17. Computational mechanics

    SciTech Connect

    Raboin, P J

    1998-01-01

    The Computational Mechanics thrust area is a vital and growing facet of the Mechanical Engineering Department at Lawrence Livermore National Laboratory (LLNL). This work supports the development of computational analysis tools in the areas of structural mechanics and heat transfer. Over 75 analysts depend on thrust area-supported software running on a variety of computing platforms to meet the demands of LLNL programs. Interactions with the Department of Defense (DOD) High Performance Computing and Modernization Program and the Defense Special Weapons Agency are of special importance as they support our ParaDyn project in its development of new parallel capabilities for DYNA3D. Working with DOD customers has been invaluable to driving this technology in directions mutually beneficial to the Department of Energy. Other projects associated with the Computational Mechanics thrust area include work with the Partnership for a New Generation Vehicle (PNGV) for ''Springback Predictability'' and with the Federal Aviation Administration (FAA) for the ''Development of Methodologies for Evaluating Containment and Mitigation of Uncontained Engine Debris.'' In this report for FY-97, there are five articles detailing three code development activities and two projects that synthesized new code capabilities with new analytic research in damage/failure and biomechanics. The article this year are: (1) Energy- and Momentum-Conserving Rigid-Body Contact for NIKE3D and DYNA3D; (2) Computational Modeling of Prosthetics: A New Approach to Implant Design; (3) Characterization of Laser-Induced Mechanical Failure Damage of Optical Components; (4) Parallel Algorithm Research for Solid Mechanics Applications Using Finite Element Analysis; and (5) An Accurate One-Step Elasto-Plasticity Algorithm for Shell Elements in DYNA3D.

  18. Aspects of equivalence between contact mechanics and fracture mechanics: theoretical connections and a life-prediction methodology for fretting-fatigue

    Microsoft Academic Search

    A. E. Giannakopoulos; T. C. Lindley; S. Suresh

    1998-01-01

    We identify aspects of quantitative equivalence between contact mechanics and fracture mechanics via asymptotic matching. An analogy is invoked between the geometry of the near-tip regions of cracked specimens and that of the sharp-edged contact region between two contacting surfaces. We then demonstrate that the asymptotic elastic stress and strain fields around the rim of the contact region, as derived

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

    NASA Astrophysics Data System (ADS)

    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-and long-term high temperature effects.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    SciTech Connect

    Dickson, T.L.

    1993-04-01

    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.

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

    SciTech Connect

    Dickson, T.L.

    1993-01-01

    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.

  3. Evaluation of hydrogen pressure vessels using slow strain rate testing and fracture mechanics analysis

    SciTech Connect

    Murray, S.H. [National Aeronautics and Space Administration, Kennedy Space Center, FL (United States). Materials Science Div.; Desai, V.H. [Univ. of Central Florida, Orlando, FL (United States)

    1998-12-31

    A total of 108 seamless, forged pressure vessels, fabricated from ASTM A372 type IV (UNS K14508) and type V low alloy steel, are currently in 4,200 psi (29 MPa) gaseous hydrogen (GH{sub 2}) service at the Kennedy Space Center`s (KSC) Space Shuttle Launch Complex 39 (LC-39). The vessels were originally used in 6,000 psi (41 MPa) GH{sub 2} service during the Apollo program. NASA recently received a letter of warning from the manufacturer of the vessels stating that the subject vessels should be now be removed from GH{sub 2} service due to the fact that the ultimate tensile strength (UTS) of many of the vessels exceeds the maximum limit of 126 ksi (869 MPa) now imposed on A372 steel intended for GH{sub 2} service, and therefore are susceptible to hydrogen environment embrittlement. Due to the expense associated with vessel replacement, it was decided to determine by testing and analysis whether or not the vessels needed to be removed from GH{sub 2} service. Slow strain rate testing was performed under hydrogen charging conditions to determine the value of the threshold fracture toughness for sustained loading crack growth in GH{sub 2}, (K{sub H}) for the vessel material, this value was then used in a fracture mechanics safe-life analysis (a 20-year service life was modeled) that indicated the vessels are safe for continued use.

  4. The Hall-Petch relationship and mechanisms of fracture in B2 compounds

    SciTech Connect

    Baker, I.

    1991-03-01

    This report is concerned with studies of the Hall-Petch relationship and Mechanisms of fracture in B2 compounds. It covers the period from April 1st 1990 to March 1st 1991. TEM in-situ straining studies have been performed on NiAl and FeAl, some in collaboration with Dr. J. A. Horton at ORNL. Both materials show intense activity ahead of transgranular cracks in thin foils. Thin foils of NiAl show cell structures after in-situ straining which are very similar to those in samples taken from bulk deformed material. Studies of the fracture behavior as a function of stoichiometry have been completed for both FeAl and NiAl. ALCHEMI studies have been performed on a number of B2 compounds (NiAl + V and FeAl + Cr) and L1{sub 2} compounds (Ni{sub 3}Al + Hf and Al{sub 3}Ti + Ni) in order to determine the site occupancy of the ternary addition. Alloys of CoAl, FeCo, NiAl + B, FeAl + Cr and CuZn have been cast and further processing has been initiated. TEM examination of dislocations in FeCo has been started.

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

    SciTech Connect

    Dickson, T.L.; Cheverton, R.D.; Bryson, J.W.; Bass, B.R.; Shum, D.K.M.; Keeney, J.A. [Oak Ridge National Lab., TN (United States)

    1993-08-01

    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.

  6. A micromodel investigation of two-phase matrix-fracture transfer mechanisms

    Microsoft Academic Search

    E. R. Rangel-German; A. R. Kovscek

    2006-01-01

    Micromodels employing a two-dimensional representation of pore space were used to observe directly (via microscope) water imbibition into a matrix and matrix-fracture interactions between wetting and nonwetting fluids. Within a single field of view, some pores are responsible for the uptake of water, whereas immediately adjacent pores expel nonwetting phase into the fracture. When water flow through fractures is relatively

  7. International Journal of Rock Mechanics & Mining Sciences 44 (2007) 739757 Computer simulation of hydraulic fractures

    E-print Network

    Peirce, Anthony

    2007-01-01

    of hydraulic fractures J. Adachia , E. Siebritsb , A. Peircec,Ã, J. Desrochesd a Schlumberger Data of hydraulic fracturing models for use in the petroleum and other industries. We discuss scaling laws and the propagation regimes that control the growth of hydraulic fractures from the laboratory to the field scale. We

  8. Reference stress based fracture mechanics analysis for circumferential through-wall cracked pipes: experimental validation

    Microsoft Academic Search

    Yun-Jae Kim; Nam-Su Huh; Young-Jin Kim

    2003-01-01

    This paper presents experimental validation of the reference stress based J estimates for circumferential through-wall cracked (TWC) pipes, recently proposed by the authors. Using the pipe test data for circumferential TWC pipes given in the Pipe Fracture Encyclopedia [Pipe Fracture Test Data, vol. 3, Battelle, 1997], the predicted fracture initiation and instability loads according to the proposed reference stress method

  9. Recursive distribution method for probabilistic fracture mechanics and its application to evaluation of LWR piping

    SciTech Connect

    Akiba, Hiroshi; Suzuki, Masabumi [Allied Engineering Corporation, Tokyo (Japan); Yoshimura, Shinobu; Yagawa, Genki [Univ. of Tokyo (Japan)

    1996-12-01

    The present authors have previously developed a new method for Probabilistic Fracture Mechanics (PFM), which they call Recursive Distribution (RD) method. The method is based on the construction of the Lebesgue-Stieltjes measure through a deterministic mapping defining a crack growth process. In the present paper, its theoretical background is first discussed, and the Lebesgue decomposition of the measure is given. Then a numerical example of a Light Water Reactor (LWR)`s piping problem is solved by the present method, and the results are compared with those of the Monte Carlo (MC) method. In addition to leakage probability, a variation in stress cycles of the marginal distribution of an aspect ratio of a semi-elliptical surface crack is calculated, which will be used in a study on LBB evaluation.

  10. A fracture mechanics analysis of impact damage in a thick composite laminate

    NASA Technical Reports Server (NTRS)

    Poe, C. C., Jr.

    1985-01-01

    Graphite/epoxy filament-wound cases (FWC) for the solid rocket motors of the space shuttle are being made by NASA. The FWC cases are wound with AS4W graphite fiber impregnated with an epoxy resin and are about 1.4 inches or more thick. Graphite-epoxy composite laminates, unlike metals, can be damaged easily by low velocity impacts of objects like dropped tools. The residual tension strength of the FWC laminate, after impact, is being studied at Langley Research Center. The conditions that give minimum visual evidence of damage are being emphasized. A fracture mechanics analysis was developed to predict the residual strength, after impact, using radiographs to measure the size of the damage and an equivalent surface crack to represent the damage.

  11. Addendum to the User Manual for NASGRO Elastic-Plastic Fracture Mechanics Software Module

    NASA Technical Reports Server (NTRS)

    Gregg, M. Wayne (Technical Monitor); Chell, Graham; Gardner, Brian

    2003-01-01

    The elastic-plastic fracture mechanics modules in NASGRO have been enhanced by the addition of of the following: new J-integral solutions based on the reference stress method and finite element solutions; the extension of the critical crack and critical load modules for cracks with two degrees of freedom that tear and failure by ductile instability; the addition of a proof test analysis module that includes safe life analysis, calculates proof loads, and determines the flaw screening 1 capability for a given proof load; the addition of a tear-fatigue module for ductile materials that simultaneously tear and extend by fatigue; and a multiple cycle proof test module for estimating service reliability following a proof test.

  12. Natural Fracture Characterization by Source Mechanism Estimation and Semi-Stochastic Generation of Discrete Fracture Networks Using Microseismic and Core Data 

    E-print Network

    Sotelo Gamboa, Edith

    2014-11-12

    The overall goal of this study is to generate discrete fracture networks using microseismic and core data from a natural fractured reservoir that has been hydraulically stimulated. To improve fracture characterization, a methodology based on source...

  13. A mechanical comparison between conventional and modified angular plates for proximal humeral fractures.

    PubMed

    Carrera, Eduardo F; Nicolao, Fabio A; Netto, Nicola Archetti; Carvalho, Renato L; Dos Reis, Fernando B; Giordani, Enrico José

    2008-01-01

    The objective of this study is to present a modified angular blade plate for fixing 2-part and even 3-part fractures of the proximal humerus, as well as the results of the comparative mechanical test between the conventional angular blade plate and this new modified plate. The plates were tested in flexion and rotational trials in a wooden model that simulated a 2-part humeral fracture of the proximal extremity. The results (mean +/- SD) of bending strength and stiffness obtained after testing showed findings of 601 +/- 349 N and 0.5 +/- 0.2 N/mm, respectively, for the conventional plate and 4005 +/- 164 N and 3.9 +/- 0.7 N/mm, respectively, for the modified plate. The torsional stiffness test showed findings of 1.26 +/- 0.09 KN.mm degrees for the conventional plate and 1.74 +/- 0.21 KN.mm degrees for the modified plate. The test of torsional moment showed findings of 57.0 +/- 7.6 KN.mm for the conventional plate and 115.2 +/- 9.3 KN.mm for the modified plate. The test of angular displacement at the torsional moment showed findings of 50.8 degrees +/- 7.2 degrees for the conventional plate and 70.2 degrees +/- 2.6 degrees for the modified plate. The results of the mechanical trials of flexion and rotation were superior for the modified angular blade plate compared with the conventional angular blade plate. PMID:18359646

  14. Stress and Fracture Mechanics Analyses of Boiling Water Reactor and Pressurized Water Reactor Pressure Vessel Nozzles

    SciTech Connect

    Yin, Shengjun [ORNL; Bass, Bennett Richard [ORNL; Stevens, Gary [U.S. Nuclear Regulatory Commission; Kirk, Mark [NRC

    2011-01-01

    This paper describes stress analysis and fracture mechanics work performed to assess boiling water reactor (BWR) and pressurized water reactor (PWR) nozzles located in the reactor pressure vessel (RPV) adjacent to the core beltline region. Various RPV nozzle geometries were investigated: 1. BWR recirculation outlet nozzle; 2. BWR core spray nozzle3 3. PWR inlet nozzle; ; 4. PWR outlet nozzle; and 5. BWR partial penetration instrument nozzle. The above nozzle designs 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-license (EOL) to require evaluation as part of establishing the allowed limits on heatup, cooldown, and hydrotest (leak test) conditions. These nozzles analyzed represent one each of the nozzle types potentially requiring evaluation. The purpose of the analyses performed on these nozzle designs was as follows: To model and understand differences in pressure and thermal stress results using a two-dimensional (2-D) axi-symmetric finite element model (FEM) versus a three-dimensional (3-D) FEM for all nozzle types. In particular, the ovalization (stress concentration) effect of two intersecting cylinders, which is typical of RPV nozzle configurations, was investigated; To verify the accuracy of a selected linear elastic fracture mechanics (LEFM) hand solution for stress intensity factor for a postulated nozzle corner crack for both thermal and pressure loading for all nozzle types; To assess the significance of attached piping loads on the stresses in the nozzle corner region; and To assess the significance of applying pressure on the crack face with respect to the stress intensity factor for a postulated nozzle corner crack.

  15. Fracture Mechanical Analysis of Frost Wedging in Ice Shelves as Break-Up Mechanism

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    Disintegration events in ice shelves have been the subject of extensive investigations in the past years, however comprehensive explanations applicable to a majority of events are still missing. A popular assumption made by Scambos et al. (2000) [1] links disintegration events to a general thinning of the ice shelf in conjunction with growing melt-water ponds leading to hydro fractures. This explanation seems reasonable for break-up events that happened in Antarctic summers. Large parts of the Wilkins Ice Shelf, however broke-up in fall and winter periods. Therefore, the aim of the present study is to analyse the possibility of frost wedging of water filled surface crevasses in an ice shelf as a source of break-up events. Configurational forces are used to assess crack criticality. The simulations are performed on a 2-dimensional single crack with a mode-I type load, body forces and additional crack-face pressure due to freezing of the water. Depth-dependent density profiles are considered. The relevant parameters, Young's modulus, Poisson's ratio and external loading are obtained from literature, remote sensing data analysis and modelling of the ice dynamics. The investigation is performed using the finite element software COMSOL. The simulations show that in comparison to water filled crevasses without ice, thin layers of frozen water may lead to a decreasing criticality at the crack tip as long as the ice 'bridge' is allowed to take tensile loads. An increasing crack criticality can be seen for thicker layers of ice. The results are compared to findings from previous finite element analyses of dry and water filled cracks as presented in Plate et al. (2012) [2]. [1] Scambos, T., Hulbe, C., Fahnestock, M., & Bohlander, J. (2000). The link between climate warming and break-up of ice shelves in the Antarctic Peninsula. Journal of Glaciology, 46(154), 516-530. [2] Plate, C., Müller, R., Humbert, A., & Gross, D. (2012). Evaluation of the criticality of cracks in ice shelves using finite element simulations. The Cryosphere, 6(5), 973-984.

  16. Microstructural effects on fracture behavior of particulate composites: Investigation of toughening mechanisms using optical and boundary element methods

    NASA Astrophysics Data System (ADS)

    Kitey, Rajesh

    Particulate polymer composites are used in a variety of engineering applications. These are generally two phase materials with polymeric phase reinforced by a filler phase to improve overall mechanical, thermal and/or dielectric functionalities. From a mechanical perspective, polymers when filled with stiffer particulates generally show enhanced elastic properties and creep resistance. Achieving similar improvement in failure characteristics has not been consistent due to a lack of thorough understanding of microstructural and loading rate effects. This dissertation addresses a few of these issues by studying effects of filler particle size, filler size distribution and filler-matrix adhesion strength on fracture behavior under quasi-static and dynamic loading conditions. Glass-filled epoxy composites consisting of solid spherical particles are studied in this research. Spherical particles of mean dia. (D) 7 mum to 200 mum are used to reinforce epoxy matrix at a constant volume fraction (Vf = 10%) and two different filler-matrix strengths, weak and strong. Optical interferometry in conjunction with high-speed photography is used to quantify crack growth and deformation histories during impact loading. Although elastic characteristics remain unaffected by microstructural variations, significant differences in fracture behaviors are seen. Both weakly and strongly bonded particles in the matrix show higher values of steady-state dynamic fracture toughness, KIss, relative to unfilled material. Filler particle size affects KIss significantly when particles are weakly bonded to the matrix but not when bonded strongly. Weakly bonded fillers result in consistently higher KIss values compared to strongly bonded counterparts. A particle size of 35 mum appears to be the optimum at the chosen Vf. The KIss of two inter-mixed particle sizes (each of 5% Vf) is bounded by the KIss values of the composite with corresponding single particle size. Fracture surface micromeasurements show that fracture toughness cannot be correlated with average fracture surface roughness Ra as in neat polymers. Therefore, a model for calculating fracture induced roughness, Raf, a component of Ra representative of the fracture process, is proposed. A linear relationship between macroscopically measured fracture toughness KIss and microstructure dependent quantity Raf/ D is demonstrated. Crack front deflection, attraction, twisting and blunting are some of the micromechanisms responsible for the observed fracture characteristics in particle reinforced composites. (Abstract shortened by UMI.)

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

    NASA Astrophysics Data System (ADS)

    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.

  18. Earthquake Induced Damage Mechanism of Long Period Structures Using Energy Response

    SciTech Connect

    Du Yongfeng; Li Hui [Western Engineering Research Center for Disaster Mitigation in Civil Engineering of Ministry of Education, Lanzhou, 730050 (China); Institute of Earthquake Protection and Disaster Mitigation, Lanzhou University of Technology, Lanzhou, 730050 (China)

    2008-07-08

    This paper presents a method of expounding the damage of RC long period frame structure using energy analysis method. Since the damage of structures usually occurs under major earthquakes, the structure is assumed to be in elasto-plastic state, and degraded Bouc-Wen model is used to describe the hysteretic component of the restoring force. A double index damage criterion defined by the maximum drift and energy absorption is used as the damage criterion. The energy transferring relation in a structure is derived, and both momentary and cumulative energy response is used to reflect the delay of the collapse of a long period structure. The mechanism of collapse delay of the long period structure is suggested through a numerical example combing the energy response and time history response.

  19. The effect of carbon nanotubes and graphene on the mechanical properties of multi-component polymeric composites

    NASA Astrophysics Data System (ADS)

    Dervishi, Enkeleda; Hategekimana, Festus; Boyer, Laurent; Watanabe, Fumiya; Mustafa, Thikra; Biswas, Abhijit; Biris, Alexandru R.; Biris, Alexandru S.

    2013-12-01

    Two types of nano-materials (nanotubes and graphene) were incorporated at different concentrations into a bio-compatible polymer matrix, and the mechanical properties of the composite films were studied. Although both nanomaterials improved the mechanical attributes of the polymer, it was found that the composites containing the nanotube-graphene mixture exhibited significantly superior elasto-plastic properties. This work presents a facile technique of fabricating nano-composites that could be scaled up and applied to various types of polymers. These multi-component films have the potential to be used in a wide range of applications including bio-medicine and photovoltaics, as well as the military and automotive industry.

  20. Mechanical models of fracture reactivation and slip on bedding surfaces during folding of the asymmetric anticline at Sheep Mountain, Wyoming

    Microsoft Academic Search

    Pablo F. Sanz; David D. Pollard; Patricia F. Allwardt; Ronaldo I. Borja

    2008-01-01

    We use finite element methods to investigate the reactivation of fractures (opening and shearing) and the development of bedding-surface slip during the deformation of the asymmetric anticline at Sheep Mountain, Wyoming. A series of numerical simulations were run to show the effect of mechanical stratigraphy, layer thickness, slip on bedding surfaces, and tectonic shortening of the fold on the response

  1. Hydraulic Fracture Containment in Sand

    Microsoft Academic Search

    Y. Dong

    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 is then a relatively new area. Particularly, the fracture containment in layered formations remains unknown. This research is aiming

  2. Magnesium alloys as body implants: fracture mechanism under dynamic and static loadings in a physiological environment.

    PubMed

    Choudhary, Lokesh; Raman, R K Singh

    2012-02-01

    It is essential that a metallic implant material possesses adequate resistance to cracking/fracture under the synergistic action of a corrosive physiological environment and mechanical loading (i.e. stress corrosion cracking (SCC)), before the implant can be put to actual use. This paper presents a critique of the fundamental issues with an assessment of SCC of a rapidly corroding material such as magnesium alloys, and describes an investigation into the mechanism of SCC of a magnesium alloy in a physiological environment. The SCC susceptibility of the alloy in a simulated human body fluid was established by slow strain rate tensile (SSRT) testing using smooth specimens under different electrochemical conditions for understanding the mechanism of SCC. However, to assess the life of the implant devices that often possess fine micro-cracks, SCC susceptibility of notched specimens was investigated by circumferential notch tensile (CNT) testing. CNT tests also produced important design data, i.e. threshold stress intensity for SCC (KISCC) and SCC crack growth rate. Fractographic features of SCC were examined using scanning electron microscopy. The SSRT and CNT results, together with fractographic evidence, confirmed the SCC susceptibility of both smooth and notched specimens of a magnesium alloy in the physiological environment. PMID:22075121

  3. Performance of multiple fractured horizontal wells in shale gas reservoirs with consideration of multiple mechanisms

    NASA Astrophysics Data System (ADS)

    Wang, Hai-Tao

    2014-03-01

    Gas flow in shales is believed to result from a combination of several mechanisms, including desorption, diffusion, viscous flow and the effect of stress-sensitivity of reservoir permeability. However, little work has been done in literature to simultaneously incorporate all these mechanisms in well testing models for shale gas reservoirs. This paper presents a new well testing model for multiple fractured horizontal wells (MFHW) in shale gas reservoirs with consideration of desorption, diffusive flow, viscous flow and stress-sensitivity of reservoir permeability. Comparing with current well testing models for MFHW, the model presented here takes into consideration more mechanisms controlling shale gas flow, which is more in line with the actual reservoir situation. Laplace transformation, point source function, perturbation method, numerical discrete method and Gaussian elimination method are employed to solve the well testing model. The pressure transient responses are then inverted into real time space with Stehfest numerical inversion algorithm. Type curves are plotted, and different flow regimes in shale gas reservoirs are identified. The effects of relevant parameters are analyzed as well. The presented model can be used to interpret pressure data more accurately for shale gas reservoirs and provide more accurate dynamic parameters which are important for efficient reservoir development.

  4. On the mechanical interaction between a fluid-filled fracture and the earth's surface

    USGS Publications Warehouse

    Pollard, D.D.; Holzhausen, G.

    1979-01-01

    The mechanical interaction between a fluid-filled fracture (e.g., hydraulic fracture joint, or igneous dike) and the earth's surface is analyzed using a two-dimensional elastic solution for a slit of arbitrary inclination buried beneath a horizontal free surface and subjected to an arbitrary pressure distribution. The solution is obtained by iteratively superimposing two fundamental sets of analytical solutions. For uniform internal pressure the slit behaves essentially as if it were in an infinite region if the depth-to-center is three times greater than the half-length. For shallower slits interaction with the free surface is pronounced: stresses and displacements near the slit differ by more than 10% from values for the deeply buried slit. The following changes are noted as the depth-to-center decreases: 1. (1) the mode I stress intensity factor increases for both ends of the slit, but more rapidly at the upper end; 2. (2) the mode II stress-intensity factor is significantly different from zero (except for vertical slits) suggesting propagation out of the original plane of the slit; 3. (3) displacements of the slit wall are asymmetric such that the slit gaps open more widely near the upper end. Similar changes are noted if fluid density creates a linear pressure gradient that is smaller than the lithostatic gradient. Under such conditions natural fractures should propagate preferentially upward toward the earth's surface requiring less pressure as they grow in length. If deformation near the surface is of interest, the model should account explicitly for the free surface. Stresses and displacements at the free surface are not approximated very well by values calculated along a line in an infinite region, even when the slit is far from the line. As depth-to-center of a shallow pressurized slit decreases, the following changes are noted: 1. (1) displacements of the free surface increase to the same order of magnitude as the displacements of the slit walls, 2. (2) tensile stresses of magnitude greater than the pressure in the slit are concentrated along the free surface. The relative surface displacements over a shallow vertical slit are downward over the slit and upward to both sides of this area. The tensile stress acting parallel to the free surface over a shallow vertical slit is concentrated in two maxima adjacent to a point of very low stress immediately over the slit. The solution is used to estimate the length-to-depth ratio at which igneous sills have gained sufficient leverage on overlying strata to bend these strata upward and form a laccolith. The pronounced mode II stress intensity associated with shallow horizontal slits explains the tendency for some sills to climb to higher stratigraphie horizons as they grow in length. The bimodal tensile stress concentration over shallow vertical slits correlates qualitatively with the distribution of cracks and normal faults which flank fissure eruptions on volcanoes. The solution may be used to analyze surface displacements and tilts over massive hydraulic fractures in oil fields and to understand the behavior of hydraulic fractures in granite quarries. ?? 1979.

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

    SciTech Connect

    Robert Podgorney; Chuan Lu; Hai Huang

    2012-01-01

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

  6. Fracture mechanisms in ferroelectric-ferroelastic lead zirconate titanate (Zr:Ti = 0. 54:0. 46) ceramics

    Microsoft Academic Search

    Karun Mehta; Anil V. Virkar

    1990-01-01

    Fracture toughness, {ital K}{sub IC}, of a single-phase commercial lead zirconate titanate (PZT) ceramic of tetragonal structure was measured using the single edge notched beam method above and below the Curie temperature. Domain switching (poling) under electrical and mechanical loading was examined using x-ray diffraction. Surface grinding, electrical poling, and mechanical poling caused crystallographic texture. Similar texture, indicative of domain

  7. Formation of conical fractures in sedimentary basins: Experiments involving pore fluids and implications for sandstone intrusion mechanisms

    NASA Astrophysics Data System (ADS)

    Mourgues, R.; Bureau, D.; Bodet, L.; Gay, A.; Gressier, J. B.

    2012-01-01

    Large sand intrusions often exhibit conical morphologies analogous to magmatic intrusions such as saucer-shaped or cup-shaped sills. Whereas some physical processes may be similar, we show with scaled experiments that the formation of conical sand intrusions may be favoured by the pore-pressure gradients prevailing in the host rock before sand injection. Our experiments involve injecting air into a permeable and cohesive analogue material to produce hydraulic fractures while controlling the pore pressure field. We control the state of overpressure in the overburden by applying homogeneous basal pore pressure, and then adding a second local pore pressure field by injecting air via a central injector to initiate hydraulic fractures near the injection point. In experiments involving small vertical effective stresses (small overburden, or high pore fluid overpressure), the fracturing pressure ( ?fract) is supralithostatic and two dipping fractures are initiated at the injection point forming a conical structure. From theoretical considerations, we predict that high values of ?fract are due to strong cohesion or high pore fluid overpressure distributed in the overburden. Such conditions are favoured by the pore pressure/stress coupling induced by both pore pressure fields. The dips of cones can be accounted for elastic-stress rotation occurring around the source. Contrary to magmatic chamber models, the aqueous fluid overpressure developed in a parent sandbody (and prevailing before the formation of injectites) may diffuse into the surrounding overburden, thus favouring stress rotation and the formation of inclined sheets far from the parent source. For experiments involving higher vertical effective stresses (thick overburden or low pore fluid overpressure), the fracturing pressure is lower than the lithostatic stress, and a single fracture is opened in mode I which then grows vertically. At a critical depth, the fracture separates into two dilatant branches forming a flat cone. We make use of a P.I.V. (Particle Imaging Velocimetry) technique to analyse plastic deformation, showing that these inclined fractures are opened in mixed modes. Close to the surface, they change into steep shear bands where fluids can infiltrate. The final morphology of the fracture network is very similar to the common tripartite architecture of various injection complexes, indicating that different mechanisms may be involved in the formation of dykes. Feeder dykes under the sill zones may open as tensile fractures, while overlying dykes may be guided by the deformation induced by the growth of sills. These deformation conditions may also favour the formation of fluid escape structures and pockmarks.

  8. Experimental investigation of the effect of coupled processes (Thermo-Hydro-Mechanical-Chemical) on CO2 flow through fractured caprock

    NASA Astrophysics Data System (ADS)

    McCraw, Claire; Edlmann, Katriona; McDermott, Christopher

    2013-04-01

    In order for geological storage of CO2 to be effective in mitigation of anthropogenically induced climate change, the occurrence of CO2 leakage from the storage reservoir to the surface must be negligible. One of the key potential pathways for CO2 leakage is escape through macroscopic fractures or faults in caprock overlying the storage reservoir. The laboratory investigation of fracture permeability to CO2 under a range of in-situ temperature and pressure conditions, using typical caprock samples, will improve understanding of the flow and transport properties of CO2 under typical geological storage conditions. Knowledge gained from such laboratory investigations will be critical for development of accurate models of CO2 flow and transport in the subsurface, which in turn will inform on leakage risk and site suitability. Experimental equipment has been designed and built at the University of Edinburgh that allows investigation of CO2 flow through 38mm diameter rock samples under realistic reservoir/overburden conditions of temperature (up to 80°C) and pressure (up to 60MPa). The fractured rock sample is contained within a Hassler-type uniaxial pressure cell and CO2 flow through the sample is controlled via high precision, high pressure syringe pumps. Fluid pressures upstream and downstream of the sample, and the confining pressure, are continuously monitored. Single phase CO2 flow experiments have been conducted on artificial planar fractures within a variety of representative caprock samples. The effect on fracture permeability of varying: (i) effective stress (confining pressure); (ii) temperature; and (iii) fluid pressure has been investigated. The impact of mineralogy has also been considered through comparison of results obtained from samples of differing rock type. Initial results and findings from the experiments are presented. A discussion of the use of the experimental results for development of coupled process (thermo-hydro-mechanical and chemical) single fracture benchmark models is also included. Proposed future experimental work, which includes investigation of natural fractures, is outlined.

  9. Fracture-mechanics data deduced from thermal-shock and related experiments with LWR pressure-vessel material

    SciTech Connect

    Cheverton, R.D.; Canonico, D.A.; Iskander, S.K.; Bolt, S.E.; Holz, P.P.; Nanstad, R.K.; Stelzman, W.J.

    1982-01-01

    Pressurized water reactors (PWRs) are susceptible to certain types of hypothetical accidents that can subject the reactor pressure vessel to severe thermal shock, that is, a rapid cooling of the inner surface of the vessel wall. The thermal-shock loading, coupled with the radiation-induced reduction in the material fracture toughness, introduces the possibility of propagation of preexistent flaws and what at one time were regarded as somewhat unique fracture-oriented conditions. Several postulated reactor accidents have been analyzed to discover flaw behavior trends; seven intermediate-scale thermal-shock experiments with steel cylinders have been conducted; and corresponding materials characterization studies have been performed. Flaw behavior trends and related fracture-mechanics data deduced from these studies are discussed.

  10. Mechanical properties and fracture characteristics of CNTs-doped W-Nb alloys

    NASA Astrophysics Data System (ADS)

    Sha, J. J.; Hao, X. N.; Li, J.; Dai, J. X.; Yang, X. L.; Yoon, H. K.

    2014-12-01

    W-based alloys are currently considered promising candidates for high heat flux components in future fusion reactors. In this work, the strength and fracture toughness of CNTs-doped W-Nb alloys fabricated by hot pressing were measured by three-point bending tests on smooth and single edge notched beams, respectively, and the fracture characteristics were observed by scanning electron microscopy. The result indicated that the bending strength and fracture toughness increased with increasing the Nb content. Combining with the microstructure analysis on the fracture surface, it was found that the increased Nb content could refine the microstructure and form the oriented Nb(W) solid solutions, which increases the number of crack deflections and total fracture paths and enhanced the strength and fracture toughness.

  11. Rib stress fractures among rowers: definition, epidemiology, mechanisms, risk factors and effectiveness of injury prevention strategies.

    PubMed

    McDonnell, Lisa K; Hume, Patria A; Nolte, Volker

    2011-11-01

    Rib stress fractures (RSFs) can have serious effects on rowing training and performance and accordingly represent an important topic for sports medicine practitioners. Therefore, the aim of this review is to outline the definition, epidemiology, mechanisms, intrinsic and extrinsic risk factors, injury management and injury prevention strategies for RSF in rowers. To this end, nine relevant books, 140 journal articles, the proceedings of five conferences and two unpublished presentations were reviewed after searches of electronic databases using the keywords 'rowing', 'rib', 'stress fracture', 'injury', 'mechanics' and 'kinetics'. The review showed that RSF is an incomplete fracture occurring from an imbalance between the rate of bone resorption and the rate of bone formation. RSF occurs in 8.1-16.4% of elite rowers, 2% of university rowers and 1% of junior elite rowers. Approximately 86% of rowing RSF cases with known locations occur in ribs four to eight, mostly along the anterolateral/lateral rib cage. Elite rowers are more likely to experience RSF than nonelite rowers. Injury occurrence is equal among sweep rowers and scullers, but the regional location of the injury differs. The mechanism of injury is multifactorial with numerous intrinsic and extrinsic risk factors contributing. Posterior-directed resultant forces arising from the forward directed force vector through the arms to the oar handle in combination with the force vector induced by the scapula retractors during mid-drive, or repetitive stress from the external obliques and rectus abdominis in the 'finish' position, may be responsible for RSF. Joint hypomobility, vertebral malalignment or low bone mineral density may be associated with RSF. Case studies have shown increased risk associated with amenorrhoea, low bone density or poor technique, in combination with increases in training volume. Training volume alone may have less effect on injury than other factors. Large differences in seat and handle velocity, sequential movement patterns, higher elbow-flexion to knee-extension strength ratios, higher seat-to-handle velocity during the initial drive, or higher shoulder angle excursion may result in RSF. Gearing may indirectly affect rib loading. Increased risk may be due to low calcium, low vitamin D, eating disorders, low testosterone or use of depot medroxyprogesterone injections. Injury management involves 1-2 weeks cessation of rowing with analgesic modalities followed by a slow return to rowing with low-impact intensity and modified pain-free training. Some evidence shows injury prevention strategies should focus on strengthening the serratus anterior, strengthening leg extensors, stretching the lumbar spine, increasing hip joint flexibility, reducing excessive protraction, training with ergometers on slides or floating-head ergometers, and calcium and vitamin D supplementation. Future research should focus on the epidemiology of RSF over 4-year Olympic cycles in elite rowers, the aetiology of the condition, and the effectiveness of RSF prevention strategies for injury incidence and performance in rowing. PMID:21985212

  12. Probability of pipe fracture in the primary coolant loop of a PWR plant. Volume 5. Probabilistic fracture mechanics analysis. Load Combination Program Project I final report

    SciTech Connect

    Harris, D.O.; Lim, E.Y.; Dedhia, D.D.

    1981-06-01

    The primary purpose of the Load Combination Program covered in this report is to estimate the probability of a seismic induced LOCA in the primary piping of a commercial pressurized water reactor (PWR). Best estimates, rather than upper bound results are desired. This was accomplished by use of a fracture mechanics model that employs a random distribution of initial cracks in the piping welds. Estimates of the probability of cracks of various sizes initially existing in the welds are combined with fracture mechanics calculations of how these cracks would grow during service. This then leads to direct estimates of the probability of failure as a function of time and location within the piping system. The influence of varying the stress history to which the piping is subjected is easily determined. Seismic events enter into the analysis through the stresses they impose on the pipes. Hence, the influence of various seismic events on the piping failure probability can be determined, thereby providing the desired information.

  13. A Numerical Study on Generation Mechanism of Vertical Cracks in Top Coat of TBCs During APS Deposition

    NASA Astrophysics Data System (ADS)

    Ito, K.; Kuriki, H.; Enoki, M.

    2015-06-01

    Clarification of crack generation mechanism in the top coat of the thermal barrier coatings (TBCs) during atmospheric plasma spray process is important to improve the reliability of TBC. In this study, finite element analyses of stress and strain during the deposition process were conducted with layer-by-layer method to understand the cracking behaviors. Stress relaxation by generation of vertical cracks was expressed as an elasto-plastic behavior of the coating. The effects of pre-heating temperature of the substrate and plasma power on crack development were analyzed by changing of the initial and atmospheric temperatures in simulation, respectively. The simulation results of radial strain explained the experimental results of crack monitoring by non-contact laser acoustic emission method.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    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 125 {mm}3 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 (P < 0.05 ). 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.

  15. Mechanical testing and macro-mechanical finite element simulation of the deformation, fracture, and short circuit initiation of cylindrical Lithium ion battery cells

    NASA Astrophysics Data System (ADS)

    Greve, Lars; Fehrenbach, Clemens

    2012-09-01

    A quasi-static mechanical abuse test program on cylindrical Lithium ion battery cells has been performed at a state of charge (SoC) of 0%. The investigated load cases involved radial crushing, local lateral indentation and global three-point bending of the cell. During the tests, the punch load, the punch displacement, the cell voltage and the temperature development of the cell have been monitored using an infrared camera and temperature sensors. After the test, the cells have been analysed using computer tomography. It is indicated that macroscopic jelly roll fracture on a global scale initiates the internal short circuits, revealed by a sudden decrease of the global mechanical load due to the rupture, followed by a drop of the measured voltage and immediate increase in cell temperature. A macro-mechanical finite element crash simulation model has been established for the cell housing and the jelly roll. The classical stress-based criterion after Mohr and Coulomb (MC) has been applied to predict fracture and the initiation of an internal short circuit of the jelly roll. The MC criterion correctly represents the punch displacement to fracture, where the predicted fracture locations correspond to the observed locations of the internal short circuits of the cells.

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

    NASA Astrophysics Data System (ADS)

    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.

  17. A finite element analysis of dynamic fracture initiation by ductile failure mechanisms in a 4340 steel

    Microsoft Academic Search

    M. Jha; R. Narasimhan

    1992-01-01

    In some recent dropweight impact experiments [5] with pre-notched bend specimens of 4340 steel, it was observed that considerable crack tunneling occurred in the interior of the specimen prior to gross fracture initiation on the free surfaces. The final failure of the side ligaments happened because of shear lip formation. The tunneled region is characterized by a flat, fibrous fracture

  18. Shear Fracture Precipitated by Strain Softening as a Mechanism of Dry Slab Avalanche Release

    Microsoft Academic Search

    David M. McClung

    1979-01-01

    .Snow stratigraphy studies at the fracture lines of dry slab avalanches often indicate a situation that consists of a harder thick layer overlying a thin weak layer. Prefracture stress conditions and progressive fracture of snow slabs are discussed here from the point of view that slow shear failure in the weak layer results in Griffith-like critical lengths there, resulting in

  19. Fracture mechanisms of the Strombus gigas conch shell: II-micromechanics analyses of multiple cracking and large-scale crack bridging

    Microsoft Academic Search

    Shekhar Kamat; Hannes Kessler; Roberto Ballarini; Maissarath Nassirou; Arthur. H. Heuer

    2004-01-01

    Micromechanics analyses of the dominant energy-dissipating mechanisms responsible for the resistance to catastrophic fracture of the aragonitic shell of the giant Queen conch, Strombus gigas, are presented. The crossed lamellar microstructure of the shell is associated with a work of fracture that is three orders of magnitude higher than that of non-biogenic aragonite [J. Mater. Sci. 6 (1996) 6583]. Previous

  20. Deferoxamine restores callus size, mineralization and mechanical strength in fracture healing after radiotherapy

    PubMed Central

    Donneys, Alexis; Ahsan, Salman; Perosky, Joseph E.; Deshpande, Sagar S.; Tchanque-Fossuo, Catherine N.; Levi, Benjamin; Kozloff, Ken M.; Buchman, Steven R.

    2013-01-01

    Background Therapeutic augmentation of fracture site angiogenesis with Deferoxamine (DFO) has proven to increase vascularity, callus size and mineralization in long-bone fracture models. We posit that the addition of DFO would enhance pathological fracture healing in the setting of radiotherapy in a model where non-unions are the most common outcome. Methods Sprague-Dawley rats (n = 35) were divided into 3 groups. Fracture (Fx), radiated fracture (XFx) and radiated fracture + DFO (XFxDFO). Groups XFx and XFxDFO received a human equivalent dose of radiotherapy (7 Gy/day × 5 days = 35 Gy) 2 weeks prior to mandibular osteotomy and external fixation. The XFxDFO group received injections of DFO into the fracture callus after surgery. Following a 40-day healing period, mandibles were dissected, clinically assessed for bony-union, imaged with Micro-CT, and tension tested to failure. Results Compared to radiated fractures, metrics of callus size, mineralization and strength in DFO treated mandibles were significantly increased. These metrics were restored to a level demonstrating no statistical difference from control fractures. In addition we observed an increased rate of achieving bony unions in the XFxDFO treated group when compared to XFx (67% vs. 20% respectively). Conclusions Our data demonstrate near total restoration of callus size, mineralization, and biomechanical strength, as well as a 3-fold increase in the rate of union with the use of DFO. Our results suggest that the administration of DFO may have the potential for clinical translation as a new treatment paradigm for radiation induced pathologic fractures. Level of Evidence Animal study, not gradable for level of evidence. PMID:23629110

  1. Development of Probabilistic Fracture Mechanics Analysis Code for Pipes with Stress Corrosion Cracks

    NASA Astrophysics Data System (ADS)

    Machida, Hideo; Arakawa, Manabu; Yamashita, Norimichi; Yoshimura, Shinobu

    Risk-Informed integrity management methodologies have been developed for Japanese nuclear power plants. One of the issues of concern is the reliability assessment of piping with flaws due to stress corrosion cracking (SCC). Therefore, the probabilistic fracture mechanics analysis code has been developed, which can perform the reliability assessment for austenitic stainless steel piping with flaws due to SCC. This paper describes technical basis of this code. This method is based on Monte-Carlo technique considering many sample cases in a piping section, where the initiation and growth of cracks are calculated and piping failures, including leaks and rapture, are evaluated. A notable feature is that multiple cracks can be treated, consequently, assessment of coalescence of cracks and intricate break evaluation of piping section have been included. Moreover, the in-service inspection (ISI) and integrity evaluation by Fitness-for-Service (FFS) code are integrated into the analysis, and the contribution to failure probability decrease can be assessed. Key parameters are determined on a probability basis with the designated probability type throughout the procedure. Size, location and time of crack initiation, coefficients of crack growth due to SCC and factors for piping failure are included in those parameters. With this method the reliability level of the piping through the operation periods can be estimated and the contribution of various parameters including ISI can be quantitatively evaluated.

  2. NASCRAC - A computer code for fracture mechanics analysis of crack growth

    NASA Technical Reports Server (NTRS)

    Harris, D. O.; Eason, E. D.; Thomas, J. M.; Bianca, C. J.; Salter, L. D.

    1987-01-01

    NASCRAC - a computer code for fracture mechanics analysis of crack growth - is described in this paper. The need for such a code is increasing as requirements grow for high reliability and low weight in aerospace components. The code is comprehensive and versatile, as well as user friendly. The major purpose of the code is calculation of fatigue, corrosion fatigue, or stress corrosion crack growth, and a variety of crack growth relations can be selected by the user. Additionally, crack retardation models are included. A very wide variety of stress intensity factor solutions are contained in the code, and extensive use is made of influence functions. This allows complex stress gradients in three-dimensional crack problems to be treated easily and economically. In cases where previous stress intensity factor solutions are not adequate, new influence functions can be calculated by the code. Additional features include incorporation of J-integral solutions from the literature and a capability for estimating elastic-plastic stress redistribution from the results of a corresponding elastic analysis. An example problem is presented which shows typical outputs from the code.

  3. Computational and numerical aspects of using the integral equation method for adhesive layer fracture mechanics analysis

    SciTech Connect

    Giurgiutiu, V.; Ionita, A.; Dillard, D.A.; Graffeo, J.K. [Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States)

    1996-12-31

    Fracture mechanics analysis of adhesively bonded joints has attracted considerable attention in recent years. A possible approach to the analysis of adhesive layer cracks is to study a brittle adhesive between 2 elastic half-planes representing the substrates. A 2-material 3-region elasticity problem is set up and has to be solved. A modeling technique based on the work of Fleck, Hutchinson, and Suo is used. Two complex potential problems using Muskelishvili`s formulation are set up for the 3-region, 2-material model: (a) a distribution of edge dislocations is employed to simulate the crack and its near field; and (b) a crack-free problem is used to simulate the effect of the external loading applied in the far field. Superposition of the two problems is followed by matching tractions and displacements at the bimaterial boundaries. The Cauchy principal value integral is used to treat the singularities. Imposing the traction-free boundary conditions over the entire crack length yielded a linear system of two integral equations. The parameters of the problem are Dundurs` elastic mismatch coefficients, {alpha} and {beta}, and the ratio c/H representing the geometric position of the crack in the adhesive layer.

  4. COMPARISON OF THE TRADITIONAL STRENGTH OF MATERIALS APPROACH TO DESIGN WITH THE FRACTURE MECHANICS APPROACH

    SciTech Connect

    Z. Ceylan

    2002-04-30

    The objective of this activity is to show that the use of the traditional strength of materials approach to the drip shield and the waste package (WP) designs is bounding and appropriate when compared to the fracture mechanics approach. The scope of this activity is limited to determining the failure assessment diagrams for the two materials at issue: Ti-7 and Alloy 22. This calculation is intended for use in support of the license application design of the drip shield and the WP. This activity is associated with the drip shield and the WP designs. The activity evaluation for work package number P32 12234F2, included in ''Technical Work Plan for: Waste Package Design Description for LA'' (Ref. 1, p. A-6), has determined that the development of this document is subject to ''Quality Assurance Requirements and Description'' requirements. The control of the electronic management of data is accomplished in accordance with the methods specified in Reference 1, Section 10. AP-3.124, ''Design Calculations and Analysis'' (Ref. 2), is used to develop and document the calculation.

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

    NASA Technical Reports Server (NTRS)

    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.

  6. Fracture mechanics assessment of PWR vessel integrity incorporating dynamic crack arrest data above 220 MPa radical m

    SciTech Connect

    Dickson, T.L.; Cheverton, R.D.

    1991-01-01

    The present rules and criteria regarding the PTS issue, as established by the US Nuclear Regulatory Commission (NRC), are the PTS rule (Code of Federal Regulations, 1985) and Nuclear Regulatory Guide 1.154 (Regulatory Guide 1.154, 1987). The PTS rule specifics screening criteria in the form of limiting values of reference nil ductility temperature (RT{sub NDT}) of the reactor pressure vessel. Also, the PTS rule requires that a plant specific safety analysis must be performed for any plant that a utility seeks to operate beyond the screening criteria. Nuclear Regulatory Guide 1.154 provides guidance for utilities on how to perform the plant specific analysis. It references the IPTS study as an acceptable methodology for performing the probabilistic fracture mechanics portion of the plant specific analysis and specifies that the frequency of vessel failure due to PTS shall not exceed 5 {times} 10{sup {minus}6} failures per reactor year. Since the IPTS Program was completed, the Heavy Section Steel Technology (HSST) Program has conducted several large specimen fracture mechanics experiments which demonstrated that prototypical reactor pressure vessel steels are capable of arresting a crack propagating in the cleavage mode at fracture toughness values considerably above 220 MPa{radical}m, the implicit limit of the American Society of Mechanical Engineers (ASME) Code and the maximum value included in the IPTS studies. The purpose of this paper is to investigate the potential impact of the enhanced crack arrest data on the results of probabilistic fracture mechanics analyses. 12 refs., 5 figs.

  7. Fracture mechanism and toughness of the welding heat-affected zone in structural steel under static and dynamic loading

    Microsoft Academic Search

    H. Qiu; H. Mori; M. Enoki; T. Kishi

    2000-01-01

    Due to the influence of the welding thermal cycle, the toughness of structural steel generally degenerates. Recently, the\\u000a intercritically reheated coarse-grained heat-affected zone (IC CG HAZ) was found to demonstrate the worst toughness in welded\\u000a joint, which was associated with its fracture mechanism. In this article, two IC CG HAZs of a structural steel were prepared\\u000a by welding thermal-cycle simulation

  8. The effect of nonsetting calcium hydroxide on root fracture and mechanical properties of radicular dentine: a systematic review.

    PubMed

    Yassen, G H; Platt, J A

    2013-02-01

    The aim of this review was to identify and analyse all studies related to the effect of nonsetting calcium hydroxide [Ca(OH)(2)] on root fracture and various mechanical properties of radicular dentine. A PubMed search was conducted using the keywords 'calcium hydroxide' and 'dentistry' combined with MeSH terms 'tooth fractures' or 'mechanical phenomena' or 'compressive strength'. The search was expanded by including Embase and Web of Science databases, using the keywords 'calcium hydroxide' and 'root' and 'fracture'. The search was supplemented by checking the reference lists from each selected article. Each study had to meet the following criteria to be selected for review: (i) Inclusion of at least one experimental group with root or radicular dentine either filled with or exposed to nonsetting Ca(OH)(2); (ii) inclusion of at least one appropriate control group; and (iii) a minimum of five samples per experimental group. Only articles written in English were included. Of the 16 studies selected initially, 12 in vitro studies fulfilled the selection criteria for inclusion in the final review. No clinical studies that directly supported the correlation between Ca(OH)(2) intracanal dressing and root fracture were found in the literature. However, the majority of in vitro studies showed reduction in the mechanical properties of radicular dentine after exposure to Ca(OH)(2) for 5 weeks or longer. Conversely, the data were inconclusive regarding whether Ca(OH)(2) exposure for 1 month or less had a negative effect on the mechanical properties of radicular dentine. PMID:22970899

  9. Future target for geothermal development -- Fractal Fracture Mechanics and its application to conceptual HDR reservoir design

    SciTech Connect

    Takahashi, Hideaki; Watanable, Kimio; Hashida, Toshiyuki

    1995-01-26

    A simple model is proposed for water/rock interaction in rock fractures through which geothermal water flows. Water/rock interaction experiments were carried out at high temperature and pressure (200-350 C, 18 MPa) in order to obtain basic solubility and reaction rate data. Based on the experimental data, changes of idealized fracture apertures with time are calculated numerically. The results of the calculations show that the precipitation from water can lead to plugging of the fractures under certain conditions. Finally, the results are compared with the experimental data.

  10. FRACTURE MECHANICAL MEASUREMENTS WITH COMMERCIAL STAINLESS STEELS AT 4 K AND WITH CP-TITANIUM AT 173 K

    SciTech Connect

    Nyilas, A. [Cryogenic Engineering and Materials Expertise, CEME, 76297 Stutensee (Germany); Mitterbacher, H. [Linde AG, Engineering Division, Materials Technology, 82049 Pullach (Germany)

    2010-04-08

    Using the JETT (J-Evaluation on Tensile Test) technique, measurements have been performed with commercial stainless steels in forged and cast condition for the reason of an assessment for low temperature service down to 4 K. These steels frequently used for industrial applications are designated by German Werkstoff (WNr) 1.4308 and 1.4408 cast stainless steels and a forged material with the number 1.4307. The fracture toughness tests at 4 K with forged material 1.4307 comprised apart from the base metal also the weld zone and additionally the 5% and 8% pre-strained conditions of the base metal. Fracture toughness reduced slightly for cold worked condition gradually as well as for the weld joint. The Reliability of the JETT measurements has been also checked using the ASTM E 1820--99a standard. In addition, to these measurements, commercial pure ASTM grade 2 titanium (WNr 3.7035) has been also examined using the same JETT method for the reason of industrial application and the requirement of minimum fracture toughness of 100 MPasq root(m) was fulfilled at 173 K. Furthermore, test results performed at 7 K of pure titanium plate material (ASTM grade 1) with respect to fracture mechanical JETT method are presented.

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

    NASA Astrophysics Data System (ADS)

    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.

  12. Induced seismicity of a normal blind undetected reservoir-bounding fault influenced by dissymmetric fractured damage zones

    NASA Astrophysics Data System (ADS)

    Rohmer, J.

    2014-04-01

    Fluid injection in deep sedimentary porous formations might induce shear reactivation of reservoir bounding faults. Here, we focus on `blind' 1000-m-long normal faults (with shear displacement ?10 m), which can hardly be detected using conventional seismic surveys, but might potentially induce seismicity felt on surface. The influence of the dissymmetry in the internal structure of the fractured damage zone DZ is numerically investigated by using 2-D plane-strain finite-element simulations of a 1500-m-deep fluid injection into a porous reservoir. The problem is solved within the framework of fully saturated isothermal elasto-plastic porous media by both accounting for fault slip weakening and shear-induced degradation of fault core permeability. The numerical results show that the presence of a thick fractured hanging wall's DZ (with Young's modulus decreasing with the distance to the fault core due to the presence of fractures) strongly controls the magnitude M of the seismic event induced by the rupture. In the case modelled, M changed by more than 1.0 unit when the DZ thickness is varied from 5 to 50 m (M ranges from ˜0.1 to ˜1.5, i.e. from a `low' to a `low-to-moderate' seismicity activity). However, further extending DZ up to 90 m has little effect and the relationship reaches a quasi-horizontal plateau. This tendency is confirmed considering other initial conditions and injection scenarios. Finally, the presence of a thicker footwall DZ appears to lower the influence of hanging wall's DZ, but with lesser impact than the degree of fracturing.

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

    SciTech Connect

    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.

  14. Computational fracture mechanics estimation of the strength of deep-water welded constructions

    NASA Astrophysics Data System (ADS)

    Il'in, A. V.; Filin, V. Yu.

    2013-04-01

    The principles of estimating the strength of deep-water engineering constructions using the brittle fracture prevention criterion are presented. They are based on the experimental results and theoretical developments accumulated in our works.

  15. Ductile fracture at intermediate stress triaxialities : experimental investigations and micro-mechanical modeling

    E-print Network

    Dunand, Matthieu

    2013-01-01

    Accurate predictions of the onset of ductile fracture play an increasingly important role in the design of lightweight sheet metal structures. With the development of virtual prototyping practices, most transportation ...

  16. Mechanical Behavior of Small-Scale Channels in Acid-etched Fractures 

    E-print Network

    Deng, Jiayao

    2011-02-22

    . A large number of deep, narrow channels through the entire fracture leads to high conductivity when the rock is strong enough to resist closure stress effectively. Based on extensive numerical experiments, I developed the new correlations in three...

  17. Fracture mechanics data for 2024-T861 and 2124-T851 aluminum

    NASA Technical Reports Server (NTRS)

    Pionke, L. J.; Linback, R. K.

    1974-01-01

    The fracture toughness and fatigue flaw growth characteristics of 2024-T861 and 2124-T851 aluminum were evaluated under plane stress conditions. Center cracked tension specimens were employed to evaluate these properties under a number of different test conditions which included variations in specimen thickness, specimen orientation, test environment, and initial flaw size. The effect of buckling was also investigated for all tests of thin gage specimens, and the effect of frequency and stress ratio was evaluated for the cyclic tests. Fracture toughness test results were analyzed and presented in terms of fracture resistance curves; fatigue flaw growth data was analyzed using empirical rate models. The results of the study indicate that both fracture toughness and resistance to fatigue crack growth improve with increasing temperature and decreasing thickness. The presence of buckling during testing of thin gage panels was found to degrade the resistance to fatigue flaw growth only at elevated temperatures.

  18. On the application of linear elastic fracture mechanics to hard steels

    Microsoft Academic Search

    Hokan Johansson

    1978-01-01

    The fracture toughness of a high speed steel (M3-2PM) and a tool steel (AISI 01) was assessed by the application of LEFM in\\u000a a nonconventional manner. The point of fracture initiation in bend test specimens was identified in a scanning electron microscope\\u000a and the shape of the inclusion sites found was approximated by ellipses to allow a critical stress intensity

  19. Fracture energy vs. internal bond strength – mechanical characterization of wood-based panels

    Microsoft Academic Search

    Jörn Rathke; Gerhard Sinn; Michael Harm; Alfred Teischinger; Martin Weigl; Ulrich Müller

    2012-01-01

    A new testing method measuring the specific fracture energy of wood-based panels in Mode I is proposed. Three types of wood-based panels, i.e. oriented strand board (OSB), particleboard (PB) and medium density fibreboard (MDF) are investigated, using fracture energy and the industrial European standard method of internal bond strength according to EN 319. Double cantilever beam specimens are notched in

  20. Mechanical behavior of polycrystalline ceramics: Brittle fracture of SiC-Si3N4 materials

    NASA Technical Reports Server (NTRS)

    Ceipold, M. H.; Kapadia, C. M.; Kelkar, A. H.

    1972-01-01

    Research on the fracture behavior of silicon nitride and silicon carbide is reported along with the role of anion impurities in the fabrication and behavior of magnesium oxide. The results of a survey of crack propagation in SiC and Si3N4 are presented. Studies in the following areas are reported: development of a fracture toughness testing technique, constant moment beam, microcrack examination, and etching techniques.

  1. Development of a balanced experimental-computational approach to understanding the mechanics of proximal femur fractures.

    PubMed

    Helgason, B; Gilchrist, S; Ariza, O; Chak, J D; Zheng, G; Widmer, R P; Ferguson, S J; Guy, P; Cripton, P A

    2014-06-01

    The majority of people who sustain hip fractures after a fall to the side would not have been identified using current screening techniques such as areal bone mineral density. Identifying them, however, is essential so that appropriate pharmacological or lifestyle interventions can be implemented. A protocol, demonstrated on a single specimen, is introduced, comprising the following components; in vitro biofidelic drop tower testing of a proximal femur; high-speed image analysis through digital image correlation; detailed accounting of the energy present during the drop tower test; organ level finite element simulations of the drop tower test; micro level finite element simulations of critical volumes of interest in the trabecular bone. Fracture in the femoral specimen initiated in the superior part of the neck. Measured fracture load was 3760N, compared to 4871N predicted based on the finite element analysis. Digital image correlation showed compressive surface strains as high as 7.1% prior to fracture. Voxel level results were consistent with high-speed video data and helped identify hidden local structural weaknesses. We found using a drop tower test protocol that a femoral neck fracture can be created with a fall velocity and energy representative of a sideways fall from standing. Additionally, we found that the nested explicit finite element method used allowed us to identify local structural weaknesses associated with femur fracture initiation. PMID:24629624

  2. The Relationships between Weight Functions, Geometric Functions,and Compliance Functions in Linear Elastic Fracture Mechanics

    SciTech Connect

    Yuan, Rong

    2007-02-06

    Linear elastic fracture mechanics is widely used in industry because it established simple and explicit relationships between the permissible loading conditions and the critical crack size that is allowed in a structure. Stress intensity factors are the above-mentioned functional expressions that relate load with crack size through geometric functions or weight functions. Compliance functions are to determine the crack/flaw size in a structure when optical inspection is inconvenient. As a result, geometric functions, weight functions and compliance functions have been intensively studied to determine the stress intensity factor expressions for different geometries. However, the relations between these functions have received less attention. This work is therefore to investigate the intrinsic relationships between these functions. Theoretical derivation was carried out and the results were verified on single-edge cracked plate under tension and bending. It is found out that the geometric function is essentially the non-dimensional weight function at the loading point. The compliance function is composed of two parts: a varying part due to crack extension and a constant part from the intact structure if no crack exists. The derivative of the compliance function at any location is the product of the geometric function and the weight function at the evaluation point. Inversely, the compliance function can be acquired by the integration of the product of the geometric function and the weight function with respect to the crack size. The integral constant is just the unchanging compliance from the intact structure. Consequently, a special application of the relations is to obtain the compliance functions along a crack once the geometric function and weight functions are known. Any of the three special functions can be derived once the other two functions are known. These relations may greatly simplify the numerical process in obtaining either geometric functions, weight functions or compliance functions for new test geometries.

  3. The solution of hypersingular integral equations with applications in acoustics and fracture mechanics

    NASA Astrophysics Data System (ADS)

    St.John, Richard S.

    The numerical solution of two classes of hypersingular integral equations is addressed. Both classes are integral equations of the first kind, and are hypersingular due to a kernel containing a Hadamard singularity. The convergence of a Galerkin method and a collocation method is discussed and computationally efficient algorithms are developed for each class of hypersingular integral equation. Interest in these classes of hypersingular integral equations is due to their occurrence in many physical applications. In particular, investigations into the scattering of acoustic waves by moving objects and the study of dynamic Griffith crack problems has necessitated a computationally efficient technique for solving such equations. Fracture mechanic studies are performed using the aforementioned techniques. We focus our studies on problems addressing the Stress Intensity Factors (SIF) of a finite Griffith crack scattering an out of plane shear wave. In addition, we consider the problem of determining the SIF of two parallel Griffith cracks and two perpendicular Griffith cracks. It is shown that the method is very accurate and computationally efficient. In acoustics, we first consider the moving wing problem. For this problem we wish to find the sound produced by the interaction of a moving wing with a known incident sound source. Although this problem is relatively simple, it is a good precursor to the two-dimensional, finite, moving duct problem. The bulk of the research is focused on solving the two- dimensional, finite, moving duct problem. Here we look at sound propagation and radiation from a finite, two- dimensional, moving duct with a variety of inlet configurations. In particular, we conduct studies on the redirection of sound by a so-called scarf inlet design. In said designs, we are able to demonstrate the ability to redirect sound away from sensitive areas.

  4. Unique pumping-out fracturing mechanism of a polymer-shelled contrast agent: an acoustic characterization and optical visualization.

    PubMed

    Kothapalli, Satya V V N; Daeichin, Verya; Mastik, Frits; Brodin, Lars Åke; Janerot-Sjoberg, Birgitta; Paradossi, Gaio; de Jong, Nico; Grishenkov, Dmitry

    2015-03-01

    This work describes the fracturing mechanism of air-filled microbubbles (MBs) encapsulated by a cross-linked poly(vinyl alcohol) (PVA) shell. The radial oscillation and fracturing events following the ultrasound exposure were visualized with an ultrahigh-speed camera, and backscattered timedomain signals were acquired with the acoustic setup specific for harmonic detection. No evidence of gas emerging from defects in the shell with the arrival of the first insonation burst was found. In optical recordings, more than one shell defect was noted, and the gas core was drained without any sign of air extrusion when several consecutive bursts of 1 MPa amplitude were applied. In acoustic tests, the backscattered peak-to-peak voltage gradually reached its maximum and exponentially decreased when the PVA-based MB suspension was exposed to approximately 20 consecutive bursts arriving at pulse repetition frequencies of 100 and 500 Hz. Taking into account that the PVA shell is porous and possibly contains large air pockets between the cross-linked PVA chains, the aforementioned acoustic behavior might be attributed to pumping gas from these pockets in combination with gas release from the core through shell defects. We refer to this fracturing mechanism as pumping-out behavior, and this behavior could have potential use for the local delivery of therapeutic gases, such as nitric oxide. PMID:25768814

  5. Fracture mechanics characterization of welds: Fatigue life analysis of notches at welds: J(sub Ic) fracture toughness tests for weld metal

    NASA Astrophysics Data System (ADS)

    Underwood, John H.

    1995-03-01

    In this report two methods of fracture analysis of welds will be emphasized, one addressing fatigue life testing and analysis of notches at welds, and the other addressing the final fracture of the welded component and the fracture toughness tests used to characterize final fracture. These fatigue and fracture methods will be described by referring to recent work from the technical literature and from the U.S. Army Armament Research, Development, and Engineering Center, primarily fracture case study and fracture test method development investigations. A brief general summary will be given of fatigue and fracture methods and concepts that have application to welded structures. Specific fatigue crack initiation tests and analysis methods will be presented, using example results from a welded stainless steel box beam of a cannon carriage. Recent improvements and simplifications in J.integral fracture toughness tests will be described, particularly those related to welds. Fracture toughness measurements for various stainless steel weld metals and heat treatments will also be described.

  6. Competition of Fracture Mechanisms in Monolithic Dental Ceramics: Flat Model Systems

    PubMed Central

    Zhang, Yu; Kim, Jae-Won; Bhowmick, Sanjit; Thompson, Van P.; Rekow, E. Dianne

    2015-01-01

    Monolithic (single layer) glass-ceramic restorations often fail from chipping and fracture. Using blunt indentation of a model flat porcelain-like brittle layer bonded onto a dentin-like polymer support system, a variety of fatigue fracture modes has been identified and analyzed: outer cone, inner cone, and median cracks developing in the near-contact region at the occlusal surface; radial cracks developing at the internal cementation surface along the loading axis. Our findings indicate that monolithic glass-ceramic layers are vulnerable to both occlusal surface damage and cementation internal surface fracture. Clinical issues in the longevity of ceramic restorations are discussed in relation to biting force, physical properties of ceramic crowns and luting cement, and thicknesses of ceramic and cement layers. PMID:18478533

  7. Interaction of Age and Mechanical Stability on Bone Defect Healing: An Early Transcriptional Analysis of Fracture Hematoma in Rat

    PubMed Central

    Ode, Andrea; Duda, Georg N.; Geissler, Sven; Pauly, Stephan; Ode, Jan-Erik; Perka, Carsten; Strube, Patrick

    2014-01-01

    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. PMID:25187955

  8. A partitioned model order reduction approach to rationalise computational expenses in nonlinear fracture mechanics

    PubMed Central

    Kerfriden, P.; Goury, O.; Rabczuk, T.; Bordas, S.P.A.

    2013-01-01

    We propose in this paper a reduced order modelling technique based on domain partitioning for parametric problems of fracture. We show that coupling domain decomposition and projection-based model order reduction permits to focus the numerical effort where it is most needed: around the zones where damage propagates. No a priori knowledge of the damage pattern is required, the extraction of the corresponding spatial regions being based solely on algebra. The efficiency of the proposed approach is demonstrated numerically with an example relevant to engineering fracture. PMID:23750055

  9. Non-Linear Flow, Fracture, Mechanical Quenching, and Computer Modeling of a Glass Cylinder Pressed Between Parallel Plates.

    NASA Astrophysics Data System (ADS)

    Sakoske, George Emil

    Analytical, experimental, and computer modeling studies are conducted for axial pressing of a glass cylinder between parallel plates. The classic "no-slip" parallel plate equation is derived from fundamental fluid mechanics with no geometric limitations and its validity is proved for transient and steady state low Reynold's number flow. Similarly, a "perfect-slip" solution yields the fiber elongation equation sigma = 3etadotvarepsilon. These limiting boundary conditions are studied experimentally by pressing directly on graphite and mica providing slip mechanisms, and non-deformable metal discs for no-slip. Linear, non-linear flow, and elastic fracture are observed by varying time scale over which strain is applied, theta, in relationship to glass structural relaxation time, tau. Linear flow is measured for tau<fracture. Ability to transmit shearing stresses and breakdown of "slip" boundary material is discussed. Fracture occurs as stresses increase within the sample for increasing time and rates. Cracks are driven by hoop and radial stresses where the origin and mode is a function of pressing rate. A Maxwell fluid finite element model is developed which uses experimental parameters as input. FEM results show general agreement with analytical solutions. A viscous heating analysis brings insight to stress overshoot and rate dependent shape. Conduction and radiation are shown to be important mechanisms affecting the bulge shape. Heat transfer to thermal boundaries is limited by the glass conductivity. Internal stress distributions and fracture modes are predicted. Shearing stresses are the significant component which may nucleate cracks that are then driven by radial and hoop stresses. Mechanical quench experiments demonstrate stress -strain induced lattice structure deformations. At T = 570^circC a 110 MPa mechanical quench increases density ~0.13% and produces internal axial compression and biaxial hoop-radial tension of ~10 MPa. Dilatometric recoveries show radial strain increases ~ 0.08% and axial strain decreases ~ 0.25% correlating to density changes and the phenomenon known as "delayed elasticity".

  10. Relative Permeability Through Fractures

    E-print Network

    Stanford University

    SGP-TR-170 Relative Permeability Through Fractures Gracel P. Diomampo August 2001 Financial support, California #12;#12;v Abstract The mechanism of two-phase flow through fractures is of importance in understanding many geologic processes. Currently, two-phase flow through fractures is still poorly understood

  11. Numerical Modeling of Hydraulic Fracture Propagation Using Thermo-hydro-mechanical Analysis with Brittle Damage Model by Finite Element Method 

    E-print Network

    Min, Kyoung

    2013-07-16

    Better understanding and control of crack growth direction during hydraulic fracturing are essential for enhancing productivity of geothermal and petroleum reservoirs. Structural analysis of fracture propagation and impact ...

  12. Ris-R-1394(EN) A general mixed mode fracture mechan-

    E-print Network

    with uneven bending moments Bent F. Sørensen, Kenneth Jørgensen, Torben K. Jacobsen, and Rasmus C. Østergaard and multilayers. The specimen is a double cantilever beam specimen loaded with uneven bending moments at the two integral based ap- proach. As a preliminary example, fracture of adhesive joints between two glass

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

    Microsoft Academic Search

    Stephen L. Karner

    2006-01-01

    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

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

    Microsoft Academic Search

    Sonja Leonie Philipp; Dorothea Reyer

    2010-01-01

    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

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

    SciTech Connect

    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.

  16. Mechanical behavior of polycrystalline ceramics: Brittle fracture of Si C - Si3N4 materials

    NASA Technical Reports Server (NTRS)

    Leipold, M. H.; Kapadia, C. M.; Kelkar, A. H.

    1973-01-01

    The results are described of the final stage of the research involving the role of anions in the behavior of magnesium oxide, as well as the continued efforts of the fracture behavior of silicon nitride materials. These efforts, particularly the first, are further sub-divided in subsections describing individual types of behavior of materials.

  17. Contact-induced Damage in Ceramic Coatings on Compliant Substrates: Fracture Mechanics and Design

    Microsoft Academic Search

    Young-Woo Rhee; Hae-Won Kim; Yan Deng; Brian R. Lawn

    2001-01-01

    Simple explicit relations are presented for the onset of com- peting fracture modes in ceramic coatings on compliant sub- strates from Hertzian-like contacts. Special attention is given to a deleterious mode of radial cracking that initiates at the lower coating surface beneath the contact, in addition to traditional cone cracking and quasiplasticity in the near- contact area. The critical load

  18. Mechanical test in-situ fracture device for Auger electron spectroscopy

    NASA Technical Reports Server (NTRS)

    Moorhead, R. D.

    1975-01-01

    An in-situ fracture device for Auger spectroscopy was described. The device is designed to handle small tensile specimens or small double cantilever beam specimens and is fully instrumented with load and displacement transducers so that quantitative stress-strain measurements can be made directly. Some initial test results for specimens made from 4130 and 1020 steel were presented.

  19. Consideration on the Mechanism of Microwave Emission Due to Rock Fracture

    Microsoft Academic Search

    Tadashi Takano; Seiji Sugita; Shingo Yoshida; Takashi Maeda

    2010-01-01

    Microwave emission due to rock fracture was found at 300 MHz, 2 GHz, and 22 GHz, and its power was calibrated in laboratory for the first time in the world. The observed waveform is impulsive, and contains correspondent frequency component inside the envelope at each frequency band. At such high frequencies, the electro-magnetic signal power can be calibrated as a

  20. A fracture mechanics approach to prediction of pitting under fretting fatigue conditions

    Microsoft Academic Search

    O. P. Datsyshyn; V. M. Kadyra

    2006-01-01

    Within the framework of the calculational model for investigation of fatigue fracture and estimation of durability of bodies contacting under fretting fatigue conditions, the pitting formation in these bodies has been simulated and investigated. It is assumed, that a pit is generated by a surface macrocrack, which previously appeared on the contact zone, and developed due to its cyclic filling

  1. Design characteristics, primary stability and risk of fracture of orthodontic mini-implants: Pilot scan electron microscope and mechanical studies

    PubMed Central

    Walter, André; Winsauer, Heinz; Marcé-Nogué, Jordi; Mojal, Sergi

    2013-01-01

    Objectives: Orthodontic mini-implants (OMIs) are increasingly used in orthodontics but can fail for various reasons. This study investigates the effects of OMI design characteristics on the mechanical properties in artificial bone. Material and Methods: Twelve self-drilling OMIs (2 small, 6 medium, 4 large) from 8 manufacturers were tested for their primary stability in simulated medium-high cancellous bone and the risk to fracture in high-density methacrylate blocks. For the assessments of the maximum insertion torque (IT) and torsional fracture (TF) 5 of each OMI were used and for the pull-out strength (POS) 10. The OMIs were inserted with a torque screwdriver (12 sec/360°) until the bottom at 8 mm depth was reached. OMI designs were analyzed with a scan electron microscope (SEM). Results: SEM images revealed a great variation in product refinement. In the whole sample, a cylindrical OMI shape was associated with higher POS (p<0.001) but lower IT (p=0.002) values. The outer and inner OMI diameters were design characteristics well correlated with POS, IT and TF values (ranging from 0.601 to 0.961). Greater thread depth was related to greater POS values (r= 0.628), although OMIs with similar POS values may have different IT values. Thread depth and pitch had some impact on POS. TF depended mainly on the OMI inner (r= 0.961) and outer diameters (r=0.892). A thread depth to outer diameter ratio close to 40% increased TF risk. Conclusions: Although at the same insertion depth the OMI outer and inner diameters are the most important factors for primary stability, other OMI design characteristics (cylindrical vs. conical, thread design) may significantly affect primary stability and torsional fracture. This needs to be considered when selecting the appropriate OMI for the desired orthodontic procedures. Key words:Orthodontic mini-implants, primary stability, insertion torque, pullout strength, torsional fracture. PMID:23722125

  2. Observation of mechanical fracture and corresponding domain structure changes of polycrystalline PbTiO{sub 3} nanotubes.

    SciTech Connect

    Choi, H.; Hong, S.; Kim, Y.; Kim, M.; Sung, T.-H.; Shin, H.; No, K. (Materials Science Division); (Korea Advanced Inst. of Science and Technology); (Max Planck Inst. of Microstructure Physics); (Kookmin Univ.); (Hanyang Univ.)

    2011-02-01

    PbTiO{sub 3} (PTO) nanotubes (NTs) were synthesized at various temperatures by gas phase reaction between PbO gas and anatase TiO{sub 2} NTs and characterized by piezoresponse force microscopy (PFM). PTO ferroelectric phase was synthesized at as low as 400 C as evidenced by PFM domain images and piezoresponse hysteresis loop measurement. Furthermore, the PTO NTs fabricated at above 500 C underwent mechanical fracture through development of nanocracks due to grain growth, leading to ferroelectric domains with larger size and lower aspect ratio.

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

    NASA Astrophysics Data System (ADS)

    Bonnetier, Eric; Jakab?in, 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.

  4. Kinetics of Failure Rate Accumulation and TiNi Shape Memory Effect Alloy Fracture Under Mechanical Cycling

    NASA Astrophysics Data System (ADS)

    Bondarev, A. B.; Khusainov, M. A.; Plastilina, G. V.; Andreev, V. A.

    2010-06-01

    Wire specimens, d = 0.1 mm, made of Ti-(50.6-50.8)at.%-Ni alloy were exposed to thermo-mechanical treatment (TMT), thus making the samples straight and providing them with high superelasticity (?se). It was established that the most effective method of TMT is annealing with deformation at 500 and 300 °C. The optimum mode of treatment was used in the research of mechanical fatigue of alloys with high superelastic properties. Two stages characterizing the alloy behavior under mechanical cycling were found out: failure accumulation and fracture. It was shown that the duration of the cycles is determined by the value of the preset deformation (?set) in relation to the deformation on the plateau-shaped area. The results of low-cycle fatigue of the alloys under investigation were processed by means of the method of least squares. The equations of prognosis of longetivity at the preset level of deformation are presented.

  5. Atlas fractures

    Microsoft Academic Search

    S. Schären; B. Jeanneret

    1999-01-01

    Summary  \\u000a Fractures of the atlas account for 1–2 % of all vertebral fractures. We divide atlas fractures into 5 groups: isolated fractures\\u000a of the anterior arch of the atlas, isolated fractures of the posterior arch, combined fractures of the anterior and posterior\\u000a arch (so-called Jefferson fractures), isolated fractures of the lateral mass and fractures of the transverse process. Isolated\\u000a fractures

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

    NASA Astrophysics Data System (ADS)

    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-water injection. The initial fracture aperture was taken 1mm. The Young's modulus of rock matrix and joint stiffness were taken as 15GPa and 15GPa/m respectively. Our results show that the contraction of rock due to cooling causes the opening of the fracture near injection well. However in some regions where temperature drop is insignificant the compressive stress develops and fracture closes. As the heat extraction continues with time, further contraction of rock causes more aperture growth between the wells. For the above-mentioned computational domain, due to cold-water (20 °C) at mass flow rate 4kg/s, the aperture in the vicinity of the injection well increases by 75%. Our simulation for joint stiffness equal to 50GPa/m, show that the magnitudes of normal tensile and compressive stresses in the fracture/joint are almost same but the aperture alteration is proportionally reduced. Since the joint stiffness is a nonlinear function of opening, it is important to include a suitable nonlinear model for joint opening/closing while simulating the fracture transmissivity alter during heat extraction.

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

    NASA Technical Reports Server (NTRS)

    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 investigate the effect of cryogenic cycling on permeability for various composite material systems. Textile composites have lower permeability than laminated composites even with increasing number of cryogenic cycle. Nano-particles dispersed in laminated composites do not show improvement on permeability. The optical inspection is performed to investigate the microcrack propagation and void content in laminated composites and compared the microscopic results before and after cryogenic cycling.

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

    SciTech Connect

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

    1993-06-01

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

  9. [Investigation of mechanical properties of materials used for functional stabilization in pilon fractures].

    PubMed

    Sto?ko, I V; Béts, G V; Béts, I G; Karpinski?, M Iu

    2014-02-01

    Existing methods of surgical treatment of the pilon fractures do not provide early functional rehabilitation of patients. The lack of confidence in secure fixation of fragments in significant quantity of patients causes necessity to apply a plaster immobilization during long time. While seeking possibilities of early functional treatment of the pilon fractures there was proposed a theory of "functional stabilization" (instead of "artificial", but necessary plaster immobilization), materials and technologies for its realization. For substantiating, from the biomechanical point of view, of expediency of a new materials (Softcost, Scotchcost) application the data about their physic-chemical properties were adduced, and in particular, there were studied the bowing values, depending on loading, and modules of elasticity of these materials. PMID:24923122

  10. Containment of massive hydraulic fractures

    Microsoft Academic Search

    E. R. Simonson; A. S. Abou-Sayed; R. J. Clifton

    1976-01-01

    Hydraulic fracture containment is discussed from the point of view of linear elastic fracture mechanics. Three cases are analyzed: (a) Effect of different material properties for the pay zone and the barrier formation, (b) Characteristic of fracture propagation into region of varying in situ stress and (c) Effect of hydrostatic pressure gradients on fracture propagation into overlying or underlying barrier

  11. Fracture Mechanics of Metals: Some Features of Crack Initiation and Crack Propagation

    Microsoft Academic Search

    A. J. Krasowsky

    \\u000a The main features are considered concerning the crack initiation and crack propagation events during the fracture toughness\\u000a measurements at static and dynamic loading with respect to perfectly brittle, quasi-brittle and ductile behavior of material.\\u000a The relationships are described between seven different stages of loading process and corresponding stages of the crack tip\\u000a plastic zone evolution as well as the appearances

  12. Reaction mechanisms, microstructure, and fracture properties of thermoplastic polysulfone-modified epoxy resin

    Microsoft Academic Search

    B.-G. Min; Z. H. Stachurski; J. H. Hodgkin

    1993-01-01

    The microstructure and fracture properties of diglycidyl ether of bisphenol A (DGEBA) epoxy resins modified with phenolic hydroxyl-terminated polysulfone (PSF) and cured with diaminodiphenyl sulfone (DDS) hardener have been investigated as a function of the molecular weight and concentration of PSF. The microstructure changed from a typical particulate structure to a phase-inverted structure as the molecular weight and\\/or the concentration

  13. Fracture mechanisms of the Strombus gigas conch shell: implications for the design of brittle laminates

    Microsoft Academic Search

    L. T. Kuhn-Spearing; H. Kessler; E. Chateau; R. Ballarini; A. H. Heuer; S. M. Spearing

    1996-01-01

    Flexural strength, crack-density evolution, work of fracture, and critical strain energy release rates were measured for wet and dry specimens of the Strombus gigas conch shell. This shell has a crossed-lamellar microarchitecture, which is layered at five distinct length scales and can be considered a form of ceramic “plywood”. The shell has a particularly high ceramic (mineral) content (99.9 wt%),

  14. Title: Can mechanics explain the development neurofibromatosis type 1 and fracture in the lower tibia?

    E-print Network

    Wolper, Pierre

    about in 3500, neurofibromatosis type 1 (NF1) is one of the most common heritable disorders. People with the disease typically have freckles and the distinctive café-au-lait spots. A primary concern for NF1 patients://www.aeschylus-philanthropy.eu/index.php/b/project/bone4kids. Tibial fractures in patients with NF1 typically occur in the lower third of the bone (distal

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

    SciTech Connect

    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.

  16. Reaction mechanisms, microstructure, and fracture properties of thermoplastic polysulfone-modified epoxy resin

    SciTech Connect

    Min, B.G.; Stachurski, Z.H. (Monash Univ., Clayton, Victoria (Australia). Dept. of Materials Engineering); Hodgkin, J.H. (CSIRO, Clayton, Victoria (Australia). Div. of Chemicals and Polymers)

    1993-11-10

    The microstructure and fracture properties of diglycidyl ether of bisphenol A (DGEBA) epoxy resins modified with phenolic hydroxyl-terminated polysulfone (PSF) and cured with diaminodiphenyl sulfone (DDS) hardener have been investigated as a function of the molecular weight and concentration of PSF. The microstructure changed from a typical particulate structure to a phase-inverted structure as the molecular weight and/or the concentration of the modifier increased. The fracture toughness, measured by compact tension tests, increased with the microstructural changes toward the phase-inverted structure. The level of minor reactions such as etherification and homopolymerization reactions increased with increasing molecular weight and/or concentration of the modifier, in line with the tendencies observed in microstructure and fracture toughness. In the system containing 20 wt% of M[sub n] 10,000 PSF, about 30% of the epoxy groups were consumed by etherification and homopolymerization reactions, whereas none of these reactions occurred in the unmodified system. The increase in minor reactions in the modified systems may be to be due to the restricted molecular mobility, resulting from the increase of system viscosity caused by the modification.

  17. An elastic-plastic fracture mechanics analysis of weld-toe surface cracks in fillet welded T-butt joint

    SciTech Connect

    Fu, B. [British Gas plc, Newcastle upon Tyne (United Kingdom). Engineering Research Station

    1994-12-31

    This paper describes an elastic-plastic fracture mechanics (EPFM) study of shallow weld-toe cracks. Two limiting crack configurations, plane strain edge crack and semi-circular surface crack in fillet welded T-butt plate joint, were analyzed using the finite element method. Crack depth ranging from 2 to 40% of plate thickness were considered. The elastic-plastic analysis, assuming power-law hardening relationship and Mises yield criterion, was based on incremental plasticity theory. Tension and bending loads applied were monotonically increased to a level causing relatively large scale yielding at the crack tip. Effects of weld-notch geometry and ductile material modeling on prediction of fracture mechanics characterizing parameter were assessed. It was found that the weld-notch effect reduces and the effect of material modeling increases as crack depth increases. Material modeling is less important than geometric modeling in analysis of very shallow cracks but is more important for relatively deeper cracks, e.g. crack depth more than 20% of thickness. The effect of material modeling can be assessed using a simplified structural model. Weld magnification factors derived assuming linear elastic conditions can be applied to EPFM characterization.

  18. Understanding the Degradation of Silicon Electrodes for Lithium-Ion Batteries Using Acoustic Emission and Fracture Mechanics

    NASA Astrophysics Data System (ADS)

    Daniel, Claus

    2012-02-01

    Silicon is a promising anode material for lithium-ion battery application due to its high specific capacity, low cost, and abundance. However, when silicon is lithiated at room temperature, it can undergo a volume expansion in excess of 280%, which leads to an extensive fracturing. This is thought to be a primary cause of the rapid decay in cell capacity routinely observed. We have developed a special cell design which allows us to monitor acoustic emissions stemming from mechanical events in the cell and allow for detailed structural analysis using X-ray diffraction with an internal standard. The combined result from acoustic emissions and X-ray diffraction allow for a first of its kind detailed look at how silicon anodes degrade and together with presented theories of fracture mechanics enable a material engineering approach to optimize its long term behavior. In collaboration with Kevin Rhodes and Sergiy Kalnaus.[4pt] Parts of this research were performed at the High Temperature Materials Laboratory, a national user facility sponsored by the same office.

  19. Contaminant transport in fractured porous media: Analytical solution for a single fracture

    Microsoft Academic Search

    D. H. Tang; E. O. Frind; E. A. Sudicky

    1981-01-01

    A general analytical solution is developed for the problem of contaminant transport along a discrete fracture in a porous rock matrix. The solution takes into account advective transport in the fracture, longitudinal mechanical dispersion in the fracture, molecular diffusion in the fracture fluid along the fracture axis, molecular diffusion from the fracture into the matrix, adsorption onto the face of

  20. Culture-independent pilot study of microbiota colonizing open fractures and association with severity, mechanism, location, and complication from presentation to early outpatient follow-up.

    PubMed

    Hannigan, Geoffrey D; Hodkinson, Brendan P; McGinnis, Kelly; Tyldsley, Amanda S; Anari, Jason B; Horan, Annamarie D; Grice, Elizabeth A; Mehta, Samir

    2014-04-01

    Precise identification of bacteria associated with post-injury infection, co-morbidities, and outcomes could have a tremendous impact in the management and treatment of open fractures. We characterized microbiota colonizing open fractures using culture-independent, high-throughput DNA sequencing of bacterial 16S ribosomal RNA genes, and analyzed those communities with respect to injury mechanism, severity, anatomical site, and infectious complications. Thirty subjects presenting to the Hospital of the University of Pennsylvania for acute care of open fractures were enrolled in a prospective cohort study. Microbiota was collected from wound center and adjacent skin upon presentation to the emergency department, intraoperatively, and at two outpatient follow-up visits at approximately 25 and 50 days following initial presentation. Bacterial community composition and diversity colonizing open fracture wounds became increasingly similar to adjacent skin microbiota with healing. Mechanism of injury, severity, complication, and location were all associated with various aspects of microbiota diversity and composition. The results of this pilot study demonstrate the diversity and dynamism of the open fracture microbiota, and their relationship to clinical variables. Validation of these preliminary findings in larger cohorts may lead to the identification of microbiome-based biomarkers of complication risk and/or to aid in management and treatment of open fractures. PMID:24395335

  1. Proceedings of the Joint IAEA/CSNI Specialists` Meeting on Fracture Mechanics Verification by Large-Scale Testing held at Pollard Auditorium, Oak Ridge, Tennessee

    SciTech Connect

    Pugh, C.E.; Bass, B.R.; Keeney, J.A. [comps.] [Oak Ridge National Lab., TN (United States)

    1993-10-01

    This report contains 40 papers that were presented at the Joint IAEA/CSNI Specialists` Meeting Fracture Mechanics Verification by Large-Scale Testing held at the Pollard Auditorium, Oak Ridge, Tennessee, during the week of October 26--29, 1992. The papers are printed in the order of their presentation in each session and describe recent large-scale fracture (brittle and/or ductile) experiments, analyses of these experiments, and comparisons between predictions and experimental results. The goal of the meeting was to allow international experts to examine the fracture behavior of various materials and structures under conditions relevant to nuclear reactor components and operating environments. The emphasis was on the ability of various fracture models and analysis methods to predict the wide range of experimental data now available. The individual papers have been cataloged separately.

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

    NASA Astrophysics Data System (ADS)

    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 in the range of millimetres to a very few centimetres and can be linked to annual groundwater fluctuations. Due to pore pressure variations HM coupling can influence seepage forces and effective stresses in the rock mass. Effective stress changes can adversely affect the stability and deformation behaviour of deep-seated rock slides by influencing the shear strength or the time dependent (viscous) material behaviour of the basal shear zone. The shear strength of active shear zones is often reasonably well described by Coulomb's law. In Coulomb's law the operative normal stresses to the shear surface/zone are effective stresses and hence pore pressures which should be taken into account reduces the shear strength. According to the time dependent material behaviour a few effective stress based viscous models exists which are able to consider pore pressures. For slowly moving rock slides HM coupling could be highly relevant when low-permeability clayey-silty shear zones (fault gouges) are existing. An important parameters therefore is the hydraulic diffusivity, which is controlled by the permeability and fluid-pore compressibility of the shear zone, and by fluid viscosity. Thus time dependent pore pressure diffusion in the shear zone can either control the stability condition or the viscous behaviour (creep) of the rock slide. Numerous cases studies show that HM coupling can effect deformability, shear strength and time dependent behaviour of fractured rock masses. A process-based consideration can be important to avoid unexpected impacts on infrastructures and to understand complex rock mass as well rock slide behaviour.

  3. Prediction of the Time Course of Callus Stiffness as a Function of Mechanical Parameters in Experimental Rat Fracture Healing Studies - A Numerical Study

    PubMed Central

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

    2014-01-01

    Numerous experimental fracture healing studies are performed on rats, in which different experimental, mechanical parameters are applied, thereby prohibiting direct comparison between each other. Numerical fracture healing simulation models are able to predict courses of fracture healing and offer support for pre-planning animal experiments and for post-hoc comparison between outcomes of different in vivo studies. The aims of this study are to adapt a pre-existing fracture healing simulation algorithm for sheep and humans to the rat, to corroborate it using the data of numerous different rat experiments, and to provide healing predictions for future rat experiments. First, material properties of different tissue types involved were adjusted by comparing experimentally measured callus stiffness to respective simulated values obtained in three finite element (FE) models. This yielded values for Young’s moduli of cortical bone, woven bone, cartilage, and connective tissue of 15,750 MPa, 1,000 MPa, 5 MPa, and 1 MPa, respectively. Next, thresholds in the underlying mechanoregulatory tissue differentiation rules were calibrated by modifying model parameters so that predicted fracture callus stiffness matched experimental data from a study that used rigid and flexible fixators. This resulted in strain thresholds at higher magnitudes than in models for sheep and humans. The resulting numerical model was then used to simulate numerous fracture healing scenarios from literature, showing a considerable mismatch in only 6 of 21 cases. Based on this corroborated model, a fit curve function was derived which predicts the increase of callus stiffness dependent on bodyweight, fixation stiffness, and fracture gap size. By mathematically predicting the time course of the healing process prior to the animal studies, the data presented in this work provides support for planning new fracture healing experiments in rats. Furthermore, it allows one to transfer and compare new in vivo findings to previously performed studies with differing mechanical parameters. PMID:25532060

  4. Corrosion fatigue of iron-chromium-nickel alloys: Fracture mechanics and chemistry

    SciTech Connect

    Wei, R.P.

    1990-11-29

    Peak bare-surface current densities based on the scratched electrode test are seriously in error and repasivation rates grossly overestimated. Influences of potential and pH on reactions of bare surfaces are better understood. Correlation between charge transfer and corrosion fatigue crack growth response was established for Fe18Cr12Ni alloy in deaerated 0.6N NaCl at RT. Strong correlation was established between morphology of corrosion fatigue fracture surfaces and cracking in hydrogen charged samples. Attempts at growing bicrystals by strain annealing were not successful.

  5. Corrosion fatigue of iron-chromium-nickel alloys: Fracture mechanics, microstructure and chemistry

    SciTech Connect

    Wei, R.P.

    1993-01-25

    Phase transformation and cracking during RT aging of charged, high-purity Fe18Cr12Ni alloy and commerical 304 ss were examined; results show that [epsilon]* (hcp) hydride formed on Fe18Cr12Ni upon charging, and it decomposed rapidly to form first [epsilon] and then [alpha]' martensite. Morphology of fracture surfaces of Fe18Cr12Ni produced by corrosion fatigue in NaCl solutions and in hydrogen was found to be identical. Effort was made to examine the approaches and methodologies used in service life predictions and reliability analyses.

  6. Developments in fracture mechanics test methods standardization; Proceedings of the Symposium, St. Louis, Mo., May 4, 1976

    NASA Technical Reports Server (NTRS)

    Brown, W. F., Jr.; Kaufman, J. G.

    1977-01-01

    Experience in plane-strain fracture toughness testing per ASTM Method E 399 is considered along with fracture toughness testing using the C-shaped specimen, an analysis of radially cracked ring segments subject to forces and couples, compliance calibration of specimens used in the R-curve practice, heavy-section fracture toughness screening specimen, and sharply notched cylindrical tension specimens for screening plane-strain fracture toughness. Attention is also given to an investigation of some problems in developing standards for precracked Charpy specimen strength ratios, fracture testing with surface crack specimens, and the estimation of plane strain fracture toughness values from slow bend precracked Charpy specimen strength ratios.

  7. Coupled quantum mechanical\\/molecular mechanical modeling of the fracture of defective carbon nanotubes and graphene sheets

    Microsoft Academic Search

    Roopam Khare; Steven L. Mielke; Jeffrey T. Paci; Sulin Zhang; Roberto Ballarini; George C. Schatz; Ted Belytschko

    2007-01-01

    Coupled quantum mechanical\\/molecular mechanical (QM\\/MM) calculations were used to study the effects of large defects and cracks on the mechanical properties of carbon nanotubes and graphene sheets. The semi-empirical method PM3 was used to treat the QM subdomains and a Tersoff-Brenner potential was used for the molecular mechanics; some of the QM calculations were also done using density functional theory

  8. Coupled quantum mechanical/molecular mechanical modeling of the fracture of defective carbon nanotubes and graphene sheets

    E-print Network

    Ballarini, Roberto

    of large defects and cracks on the mechanical properties of carbon nanotubes and graphene sheets. The semi.50.Ah, 81.07.De I. INTRODUCTION Due to their favorable mechanical properties, carbon nanotubes CNTs-quantities of perfect CNTs or graphene sheets may prove challenging; in practice, mechanical properties will often

  9. Joint location and source mechanism inversion of microseismic events: benchmarking on seismicity induced by hydraulic fracturing

    NASA Astrophysics Data System (ADS)

    Anikiev, D.; Valenta, J.; Stan?k, F.; Eisner, L.

    2014-07-01

    Seismic monitoring can greatly benefit from imaging events with a low signal-to-noise ratio (SNR) as the number of the events with a low signal grows exponentially. One way to detect weaker events is improvement of a SNR by migration-type stacking of waveforms from multiple stations. We have developed a new method of location of seismic events that involves stacking of seismic phases and amplitudes along diffraction traveltime curves to suppress noise and detect seismic events with a SNR lower than that on individual receivers. The stacking includes polarity correction based on a simultaneous seismic moment tensor inversion and detection algorithm on the stack function. We applied this method to locate microseismicity induced by hydraulic fracturing. First we calibrated the velocity model by locating perforation shots at known locations. Then we processed 3 d of data from microseismic monitoring of shale stimulation and benchmarked migration-type locations of the largest events that were manually located. The detected and located events induced by hydraulic fracturing in this case study are mostly shear events forming narrow bands along the maximum horizontal stress direction approximately 100 m above the injection intervals. The proposed technique is fully automated and feasible for real-time seismic monitoring.

  10. Induced stress changes and associated fracture development as a result of deglaciation on the Zugspitzplatt, SE Germany

    NASA Astrophysics Data System (ADS)

    Leith, Kerry; Kupp, Jan; Geisenhof, Benedikt; Krautblatter, Michael

    2015-04-01

    Bedrock stresses in alpine regions result from the combined effects of exhumation, tectonics, topography, inelastic strain (e.g. fault displacement and fracture formation), and external loading. Gravitational loading by glacial ice can significantly affect near-surface stress magnitudes, although the nature of this effect and it's impact on stress distributions and bedrock fracturing is strongly dependent on the stress history of the bedrock landscape. We assess the effects of recent (post-Little Ice Age , ~1850 AD) and future deglaciation on bedrock stresses in the region of the Zugspitzplatt, a glaciated plateau surrounded by 1500 m high bedrock walls in SE Germany. We address this by undertaking a 2-D elasto-plastic finite element method analysis of stress changes and fracture propagation due to repeated glacial - interglacial cycles. Our model is initialised with upper crustal stresses in equilibrium with bedrock strength and regional tectonics, and we then simulate two cycles of major Pleistocene glaciation and deglaciation in order to dissipate stress concentrations and incorporate path-dependent effects of glacial loading on the landscape. We then simulate a final glacial cycle, and remove 1 m of bedrock to approximate glacial erosion across the topography. Finally, ice levels are reduced in accordance with known late-glacial and recent ice retreat, allowing us to compare relative stress changes and predicted patterns of fracture propagation to observed fracture distributions on the Zugspitzplatt. Model results compare favourably to observed fracture patterns, and indicate the plateau is likely to be undergoing N-S extension as a result of deglaciation, with a strong reduction of horizontal stress magnitudes beneath the present-day Schneeferner glacier. As each glacial cycle has a similar effect on the plateau, it is likely that surficial stresses are slightly tensile, and each cycle of deglaciation produces additional sub-vertical tensile fractures, which are then exploited by the karst groundwater system. Here we show how stress histories and brittle deformation in near-surface stress models can provide a better understanding of long-term rock slope evolution and failure as well as karst co-evolution in Alpine Environments.

  11. Fractography: Determining the sites of fracture initiation

    Microsoft Academic Search

    John J. Mecholsky

    1995-01-01

    Fractography is the analysis of fracture surfaces. Here, it refers to quantitative fracture surface analysis (FSA) in the context of applying the principles of fracture mechanics to the topography observed on the fracture surface of brittle materials. The application of FSA is based on the principle that encoded on the fracture surface of brittle materials is the entire history of

  12. Containment of Massive Hydraulic Fractures

    Microsoft Academic Search

    E. R. Simonson; A. S. Abou-Sayed; R. J. Clifton

    1978-01-01

    Based on two-dimensional analyses of three cases involving the relationship of linear fracture mechanics to the containment of massive hydraulic fractures (MHF), Terra Tek Inc. concluded that the mechanical properties of the pay zone and the barrier formation, as well as the minimum horizontal in situ stresses for these layers, play important roles in the prediction of hydraulic-fracture containment. The

  13. Cleavage Fracture Modeling of Pressure Vessels Under Transient Thermo-Mechanical Loading

    SciTech Connect

    Qian, Xudong [National University of Singapore; Dodds, Robert [University of Illinois; Yin, Shengjun [ORNL; Bass, Bennett Richard [ORNL

    2008-01-01

    Abstract The next generation of fracture assessment procedures for nuclear reactor pressure vessels (RPVs) will combine nonlinear analyses of crack-front response with stochastic treatments of crack size, shape, orientation, location, material properties and thermal-pressure transients. The projected computational demands needed to support stochastic approaches with detailed 3-D, nonlinear stress analyses of vessels containing defects appear well beyond current and near-term capabilities. In the interim, 2-D models be-come appealing to approximate certain classes of critical flaws in RPVs, and have computational demands within reach for stochastic frameworks. The present work focuses on the capability of 2-D models to provide values for the Weibull stress fracture parameter with accuracy comparable to those from very detailed 3-D models. Weibull stress approaches provide one route to connect nonlinear vessel response with fracture toughness values measured using small laboratory specimens. The embedded axial flaw located in the RPV wall near the cladding-vessel interface emerges from current linear-elastic, stochastic investigations as a critical contributor to the conditional probability of initiation. Three different types of 2-D models reflecting this configuration are subjected to a thermal-pressure transient characteristic of a critical pressurized thermal shock event. The plane-strain, 2-D models include: the modified boundary layer (MBL) model, the middle tension (M(T)) model, and the 2-D RPV model. The 2-D MBL model provides a high quality estimate for the Weibull stress but only in crack-front regions with a positive T-stress. For crack-front locations with low constraint (T-stress < 0), the M(T) specimen provides very accurate Weibull stress values but only for pressure load acting alone on the RPV. For RPVs under a combined thermal-pressure transient, Weibull stresses computed from the 2-D RPV model demonstrate close agreement with those computed from the corresponding crack-front locations in the 3-D RPV model having large negative T-stresses. Applications of this family of 2-D models provide Weibull stress values in excellent agreement with very detailed 3-D models while retaining practical levels of computational effort.

  14. The effect of friction stir processing on the microstructure, mechanical properties and fracture behavior of investment cast titanium aluminum vanadium

    NASA Astrophysics Data System (ADS)

    Pilchak, Adam L.

    The use of investment cast titanium components is becoming increasingly common in the aerospace industry due to the ability to produce large, one-piece components with complex geometries that were previously fabricated by mechanically fastening or welding multiple smaller parts together. However, the coarse, fully lamellar microstructure typical of investment cast alpha + beta titanium alloys results in relatively poor fatigue strength compared to forged titanium products. As a result, investment castings are not considered for use in fatigue limited structures. In recent years, friction stir processing has emerged as a solid state metalworking technique capable of substantial microstructure refinement in aluminum and nickel-aluminum-bronze alloys. The purpose of the present study is to determine the feasibility of friction stir processing and assess its effect on the microstructure and mechanical properties of the most widely used alpha + beta titanium alloy, Ti-6Al-4V. Depending on processing parameters, including tool travel speed, rotation rate and geometry, the peak temperature in the stir zone was either above or below the beta transus. The resulting microstructures consisted of either ˜1 mum equiaxed a grains, ˜25 mum prior beta grains containing a colony alpha + beta microstructure or a combination of 1 mum equiaxed alpha and fine, acicular alpha + beta. The changes in microstructure were characterized with scanning and transmission electron microscopy and electron backscatter diffraction. The texture in the stir zone was nearly random for all processing conditions, however, several components of ideal simple shear textures were observed in both the hexagonal close packed alpha and the body centered cubic beta phases which provided insight into the operative grain refinement mechanisms. Due to the relatively small volume of material affected by friction stir processing, conventionally sized test specimens were unable to be machined from the stir zone. Thus, the mechanical properties were investigated using micropillar compression and microtensile specimens. The effect of friction stir processing on crack initiation resistance was assessed using high cycle fatigue tests conducted in four-point bend which put only the stir zone in maximum tension. The results indicated that at constant stress amplitude, there was greater than an order of magnitude increase in fatigue life after friction stir processing. In addition, the fatigue strength of the investment cast material was improved between 20 pct. and 60 pct. by friction stir processing. These improvements have been verified with a statistically significant number of tests. Finally, the wide range of microstructures created by friction stir processing provided an opportunity to study the effect of underlying microstructure on the fracture behavior of alpha + beta titanium alloys. For this purpose, high resolution fractography coupled with quantitative tilt fractography and electron backscatter diffraction was used to provide a direct link between microstructure, crystallography and fracture topography. These techniques have been used extensively to study the early stages of post-initiation crack growth in Ti-6Al-4V, especially at low stress intensity ranges (DeltaK) in the as-cast material. A limited number of experiments were also performed on Ti-6Al-4V specimens in other microstructural conditions to assess the generality of the detailed results obtained for the fully lamellar material. The results show that fracture topography depends strongly on DeltaK and microstructural length scale. In addition, many of the features observed on the fracture surface were directly related to the underlying crystallographic orientation.

  15. Mechanical assessment of local bone quality to predict failure of locked plating in a proximal humerus fracture model.

    PubMed

    Röderer, Götz; Brianza, Stefano; Schiuma, Damiano; Schwyn, Ronald; Scola, Alexander; Gueorguiev, Boyko; Gebhard, Florian; Tami, Andrea

    2013-09-01

    The importance of osteoporosis in proximal humerus fractures is well recognized. However, the local distribution of bone quality in the humeral head may also have a significant effect because it remains unclear in what quality of bone screws of standard implants purchase. The goal of this study was to investigate whether the failure of proximal humerus locked plating can be predicted by the DensiProbe (ARI, Davos, Switzerland). A 2-part fracture with metaphyseal impaction was simulated in 12 fresh-frozen human cadaveric humeri. Using the DensiProbe, local bone quality was determined in the humeral head in the course of 6 proximal screws of a standard locking plate (Philos; Synthes GmbH, Solothurn, Switzerland). Cyclic mechanical testing with increasing axial loading until failure was performed. Bone mineral density (BMD) significantly correlated with cycles until failure. Head migration significantly increased between 1000 and 2000 loading cycles and significantly correlated with BMD after 3000 cycles. DensiProbe peak torque in all screw positions and their respective mean torque correlated significantly with the BMD values. In 3 positions, the peak torque significantly correlated with cycles to failure; here BMD significantly influenced mechanical stability. The validity of the DensiProbe was proven by the correlation between its peak torque measurements and BMD. The correlation between the peak torque and cycles to failure revealed the potential of the DensiProbe to predict the failure of locked plating in vitro. This method provides information about local bone quality, potentially making it suitable for intraoperative use by allowing the surgeon to take measures to improve stability. PMID:24025003

  16. Training and Research on Probabilistic Hydro-Thermo-Mechanical Modeling of Carbon Dioxide Geological Sequestration in Fractured Porous Rocks

    SciTech Connect

    Gutierrez, Marte

    2013-05-31

    Colorado School of Mines conducted research and training in the development and validation of an advanced CO{sub 2} GS (Geological Sequestration) probabilistic simulation and risk assessment model. CO{sub 2} GS simulation and risk assessment is used to develop advanced numerical simulation models of the subsurface to forecast CO2 behavior and transport; optimize site operational practices; ensure site safety; and refine site monitoring, verification, and accounting efforts. As simulation models are refined with new data, the uncertainty surrounding the identified risks decrease, thereby providing more accurate risk assessment. The models considered the full coupling of multiple physical processes (geomechanical and fluid flow) and describe the effects of stochastic hydro-mechanical (H-M) parameters on the modeling of CO{sub 2} flow and transport in fractured porous rocks. Graduate students were involved in the development and validation of the model that can be used to predict the fate, movement, and storage of CO{sub 2} in subsurface formations, and to evaluate the risk of potential leakage to the atmosphere and underground aquifers. The main major contributions from the project include the development of: 1) an improved procedure to rigorously couple the simulations of hydro-thermomechanical (H-M) processes involved in CO{sub 2} GS; 2) models for the hydro-mechanical behavior of fractured porous rocks with random fracture patterns; and 3) probabilistic methods to account for the effects of stochastic fluid flow and geomechanical properties on flow, transport, storage and leakage associated with CO{sub 2} GS. The research project provided the means to educate and train graduate students in the science and technology of CO{sub 2} GS, with a focus on geologic storage. Specifically, the training included the investigation of an advanced CO{sub 2} GS simulation and risk assessment model that can be used to predict the fate, movement, and storage of CO{sub 2} in underground formations, and the evaluation of the risk of potential CO{sub 2} leakage to the atmosphere and underground aquifers.

  17. Fracture prediction in metal sheets

    E-print Network

    Lee, Young-Woong

    2005-01-01

    One of the most important failure modes of thin-walled structures is fracture. Fracture is predominantly tensile in nature and, in most part, is operated by the physical mechanisms of void nucleation, growth, and linkage. ...

  18. Subsurface Crack Initiation and Propagation Mechanism under the Super-Long Fatigue Regime for High Speed Tool Steel (JIS SKH51) by Fracture Surface Topographic Analysis

    Microsoft Academic Search

    Kazuaki Shiozawa; Yuuichi Morii; Seiichi Nishino

    2006-01-01

    In order to study the subsurface crack initiation and propagation mechanism of high strength steel under a very high cycle fatigue regime, computational simulation with fracture surface topographic analysis (FRASTA) was carried out for subsurface fatigue crack initiated specimens of high speed tool steel (JIS SKH51) obtained from the rotating bending fatigue test in air. A remarkable area formed around

  19. Fracture corridors in carbonates

    NASA Astrophysics Data System (ADS)

    Chatelée, Sébastien; Lamarche, Juliette; Gauthier, Bertrand D. M.

    2015-04-01

    Among fractures, Fracture Corridors (FC) are anomalous structures made of highly persistent fracture clusters having a strong effect on multi-phase fluid flow in the subsurface. While mechanical and geological conditions for diffuse fracture systems are well constrained, FC genetic conditions remain a matter of questioning. FC can be localized in larger structures such as folds and fault zones but recent studies suggest that a large amount of fractures and FC also arise as distributed in the host rock and formed in tabular layers during burial with early rock mechanical differentiation. In addition, while the mechanical stratigraphy is of prime importance for fracture stratigraphy, it is still unknown which factor prevails on FC genesis among the local versus regional stress-state, the host rock mechanical stratigraphy or the sedimentary facies. We present a study of fractures in a 400×300 m wide quarry (Calvisson, SE France) dug in homogeneous marly limestones of Hauterivian age. The quarry exhibits diffuse fractures as well as 16 FC. The aim of this study is to reveal the genetics factor for FC development, their global geometry and internal morphologic variations, but also to clear the impact of fracture corridors on diffuse fracture. For that, we measured >2500 fractures (strike, dip, spacing, filling, aperture, etc.) and studied microstructures in 80 thin sections. We calculated fracture density and acquired LiDAR data with >90 million points with a resolution of 4 to 15mm. Diffuse fractures are organized as two perpendicular sets, a main set NE-SW-trending and minor set NW-SE-trending. The FC have the same trend, but the NW-SE trend prevail on the NE-SW one. The LiDAR acquisition allows to visualize the 3D lateral continuity with corridors with a minimal extension of 30m. We distinguish 4 internal morphologic types in FC, depending on fracture morphology, occurrence of breccia and number of zones. The types may occur in a single FC with a lateral transition from one type to another. Fracture density study shows that diffuse fracture increase around FC. FC growth and variability was not dependent on facies variations, as they are inexistent in the quarry. The result of this study allows to interpret geomechanical behaviors and geological history of fractures and fracture corridors in carbonates.

  20. A fracture mechanics approach for estimating fatigue crack initiation in carbon and low-alloy steels in LWR coolant environments

    SciTech Connect

    Park, H. B.; Chopra, O. K.

    2000-04-10

    A fracture mechanics approach for elastic-plastic materials has been used to evaluate the effects of light water reactor (LWR) coolant environments on the fatigue lives of carbon and low-alloy steels. The fatigue life of such steel, defined as the number of cycles required to form an engineering-size crack, i.e., 3-mm deep, is considered to be composed of the growth of (a) microstructurally small cracks and (b) mechanically small cracks. The growth of the latter was characterized in terms of {Delta}J and crack growth rate (da/dN) data in air and LWR environments; in water, the growth rates from long crack tests had to be decreased to match the rates from fatigue S-N data. The growth of microstructurally small cracks was expressed by a modified Hobson relationship in air and by a slip dissolution/oxidation model in water. The crack length for transition from a microstructurally small crack to a mechanically small crack was based on studies on small crack growth. The estimated fatigue S-N curves show good agreement with the experimental data for these steels in air and water environments. At low strain amplitudes, the predicted lives in water can be significantly lower than the experimental values.

  1. Evaluation of the relationship between fracture conductivity, fracture fluid production, and effective fracture length

    NASA Astrophysics Data System (ADS)

    Lolon, Elyezer P.

    Low-permeability gas wells often produce less than predicted after a fracture treatment. One of the reasons for this is that fracture lengths calculated after stimulation are often less than designed lengths. While actual fracture lengths may be shorter due to fracture growth out of zone, improper proppant settling, or proppant flowback, short calculated fracture lengths can also result from incorrect analysis techniques. It is known that fracturing fluid that remains in the fracture and formation after a hydraulic fracture treatment can decrease the productivity of a gas well by reducing the relative permeability to gas in the region invaded by this fluid. However, the relationships between fracture fluid cleanup, effective fracture length, and well productivity are not fully understood. In this work I used reservoir simulation to determine the relationship between fracture conductivity, fracture fluid production, effective fracture length, and well productivity. I simulated water saturation and pressure profiles around a propped fracture, tracked gas production along the length of the propped fracture, and quantified the effective fracture length (i.e., the fracture length under single-phase flow conditions that gives similar performance as for multiphase flow conditions), the "cleanup" fracture length (i.e., the fracture length corresponding to 90% cumulative gas flow rate into the fracture), and the "apparent" fracture length (i.e., the fracture length where the ratio of multiphase to single-phase gas entry rate profiles is unity). This study shows that the proppant pack is generally cleaned up and the cleanup lengths are close to designed lengths in relatively short times. Although gas is entering along entire fracture, fracturing fluid remains in the formation near the fracture. The water saturation distribution affects the gas entry rate profile, which determines the effective fracture length. Subtle changes in the gas rate entry profile can result in significant changes in effective fracture length. The results I derived from this work are consistent with prior work, namely that greater fracture conductivity results in more effective well cleanup and longer effective fracture lengths versus time. This study provides better explanation of mechanisms that affect fracturing fluid cleanup, effective fracture length, and well productivity than previous work.

  2. Advances in Fatigue and Fracture Mechanics Analyses for Metallic Aircraft Structures

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.

    2000-01-01

    This paper reviews some of the advances that have been made in stress analyses of cracked aircraft components, in the understanding of the fatigue and fatigue-crack growth process, and in the prediction of residual strength of complex aircraft structures with widespread fatigue damage. Finite-element analyses of cracked metallic structures are now used to determine accurate stress-intensity factors for cracks at structural details. Observations of small-crack behavior at open and rivet-loaded holes and the development of small-crack theory has lead to the prediction of stress-life behavior for components with stress concentrations under aircraft spectrum loading. Fatigue-crack growth under simulated aircraft spectra can now be predicted with the crack-closure concept. Residual strength of cracked panels with severe out-of-plane deformations (buckling) in the presence of stiffeners and multiple-site damage can be predicted with advanced elastic-plastic finite-element analyses and the critical crack-tip-opening angle (CTOA) fracture criterion. These advances are helping to assure continued safety of aircraft structures.

  3. 3D Modeling of Coupled Rock Deformation and Thermo-Poro-Mechanical Processes in Fractures

    E-print Network

    Rawal, Chakra

    2012-07-16

    Problems involving coupled thermo-poro-chemo-mechanical processes are of great importance in geothermal and petroleum reservoir systems. In particular, economic power production from enhanced geothermal systems, effective water-flooding of petroleum...

  4. 3D Modeling of Coupled Rock Deformation and Thermo-Poro-Mechanical Processes in Fractures 

    E-print Network

    Rawal, Chakra

    2012-07-16

    Problems involving coupled thermo-poro-chemo-mechanical processes are of great importance in geothermal and petroleum reservoir systems. In particular, economic power production from enhanced geothermal systems, effective ...

  5. A comparison of the stress corrosion cracking susceptibility of commercially pure titanium grade 4 in Ringer's solution and in distilled water: a fracture mechanics approach.

    PubMed

    Roach, Michael D; Williamson, R Scott; Thomas, Joseph A; Griggs, Jason A; Zardiackas, Lyle D

    2014-01-01

    From the results of laboratory investigations reported in the literature, it has been suggested that stress corrosion cracking (SCC) mechanisms may contribute to early failures in titanium alloys that have elevated oxygen concentrations. However, the susceptibility of titanium alloys to SCC in physiological environments remains unclear. In this study, a fracture mechanics approach was used to examine the SCC susceptibility of CP titanium grade 4 in Ringer's solution and distilled de-ionized (DI) water, at 37°C. The study duration was 26 weeks, simulating the non-union declaration of a plated fracture. Four wedge loads were used corresponding to 86-95% of the alloy's ligament yield load. The longest cracks were measured to be 0.18 mm and 0.10 mm in Ringer's solution and DI water, respectively. SEM analysis revealed no evidence of extensive fluting and quasi-cleavage fracture features which, in literature reports, were attributed to SCC. We thus postulate that the Ringer's solution accelerated the wedge-loaded crack growth without producing the critical stresses needed to change the fracture mechanism. Regression analysis of the crack length results led to a significant best-fit relationship between crack growth velocity (independent variable) and test electrolyte, initial wedge load, and time of immersion of specimen in electrolyte (dependent variables). PMID:23852924

  6. The location and extent of exfoliation of clay on the fracture mechanisms in nylon 66-based ternary nanocomposites.

    PubMed

    Dasari, Aravind; Yu, Zhong-Zhen; Mai, Yiu-Wing; Yang, Mingshu

    2008-04-01

    The primary focus of this work is to elucidate the location and extent of exfoliation of clay on fracture (under both static and dynamic loading conditions) of melt-compounded nylon 66/clay/SEBS-g-MA ternary nanocomposites fabricated by different blending sequences. Distinct microstructures are obtained depending on the blending protocol employed. The state of exfoliation and dispersion of clay in nylon 66 matrix and SEBS-g-MA phase are quantified and the presence of clay in rubber is shown to have a negative effect on the toughness of the nanocomposites. The level of toughness enhancement of ternary nanocomposites depends on the blending protocol and the capability of different fillers to activate the plastic deformation mechanisms in the matrix. These mechanisms include: cavitation of SEBS-g-MA phase, stretching of voided matrix material, interfacial debonding of SEBS-g-MA particles, debonding of intercalated clay embedded inside the SEBS-g-MA phase, and delamination of intercalated clay platelets. Based on these results, new insights and approaches for the processing of better toughened polymer ternary nanocomposites are discussed. PMID:18572592

  7. Application of different fatigue strength criteria to shot peened notched components. Part 1: Fracture Mechanics based approaches

    NASA Astrophysics Data System (ADS)

    Bagherifard, Sara; Colombo, Chiara; Guagliano, Mario

    2014-01-01

    Fatigue strength assessment of notched components is an essential step within their design process. It is well known that shot peening strongly increases the fatigue strength of mechanical structures. However, the contribution of shot peening to fatigue strength is generally underestimated by engineering design codes. This is due to the difficulty of defining a general fatigue design approach that is able to correctly and quantitatively consider the effect of shot peening, in terms of residual stresses, surface work hardening and surface roughness alteration. This work critically evaluates the criteria available in the literature that have been applied to shot peened notched specimens. The entire work is divided in two parts. In the first part, fatigue strength evaluation methods based on fracture mechanics concepts are applied to notched shot peened specimens tested under different fatigue loading conditions. The second part, on the other hand, studies two recognized local stress approaches. Comparison of the results highlights the restrictions of each approach and the field in which it can be successfully applied; where possible, appropriate corrections were introduced in order to obtain a better agreement with the practical condition and the experimental data.

  8. Fracture of glass

    NASA Technical Reports Server (NTRS)

    Henshaw, John M.

    1993-01-01

    The objectives of this educational exercise are the following: to observe and understand the fracture behavior of a brittle material; and to quantify the effects of various treatments on that material designed to modify its strength. A brief introduction to beam bending, fracture mechanics, influence of surface defects, residual stress, and static fatigue is presented. A test procedure for specimen testing is also presented.

  9. Development of the program SPECEL: A special element for elasto-plastic crack tip analysis

    NASA Technical Reports Server (NTRS)

    Swedlow, J. L.

    1974-01-01

    Theory is stated in terms of increments of displacement and stress, and of instantaneous or accumulated values of stress. The equilibrium equations, in the absence of body forces, are written, along with constitutive relations for plane strain.

  10. Theoretical Development of an Orthotropic Elasto-Plastic Generalized Composite Material Model

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.; Carney, Kelly S.; DuBois, Paul; Hoffarth, Canio; Harrington, Joseph; Subramanian, Rajan; Blankenhorn, Gunther

    2014-01-01

    The need for accurate material models to simulate the deformation, damage and failure of polymer matrix composites is becoming critical as these materials are gaining increased usage in the aerospace and automotive industries. While there are several composite material models currently available within LS-DYNA (Registered), there are several features that have been identified that could improve the predictive capability of a composite model. To address these needs, a combined plasticity and damage model suitable for use with both solid and shell elements is being developed and is being implemented into LS-DYNA as MAT_213. A key feature of the improved material model is the use of tabulated stress-strain data in a variety of coordinate directions to fully define the stress-strain response of the material. To date, the model development efforts have focused on creating the plasticity portion of the model. The Tsai-Wu composite failure model has been generalized and extended to a strain-hardening based orthotropic material model with a non-associative flow rule. The coefficients of the yield function, and the stresses to be used in both the yield function and the flow rule, are computed based on the input stress-strain curves using the effective plastic strain as the tracking variable. The coefficients in the flow rule are computed based on the obtained stress-strain data. The developed material model is suitable for implementation within LS-DYNA for use in analyzing the nonlinear response of polymer composites.

  11. Theoretical Development of an Orthotropic Elasto-Plastic Generalized Composite Material Model

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert; Carney, Kelly; DuBois, Paul; Hoffarth, Canio; Harrington, Joseph; Rajan, Subramaniam; Blankenhorn, Gunther

    2014-01-01

    The need for accurate material models to simulate the deformation, damage and failure of polymer matrix composites is becoming critical as these materials are gaining increased usage in the aerospace and automotive industries. While there are several composite material models currently available within LSDYNA (Livermore Software Technology Corporation), there are several features that have been identified that could improve the predictive capability of a composite model. To address these needs, a combined plasticity and damage model suitable for use with both solid and shell elements is being developed and is being implemented into LS-DYNA as MAT_213. A key feature of the improved material model is the use of tabulated stress-strain data in a variety of coordinate directions to fully define the stress-strain response of the material. To date, the model development efforts have focused on creating the plasticity portion of the model. The Tsai-Wu composite failure model has been generalized and extended to a strain-hardening based orthotropic yield function with a nonassociative flow rule. The coefficients of the yield function, and the stresses to be used in both the yield function and the flow rule, are computed based on the input stress-strain curves using the effective plastic strain as the tracking variable. The coefficients in the flow rule are computed based on the obtained stress-strain data. The developed material model is suitable for implementation within LS-DYNA for use in analyzing the nonlinear response of polymer composites.

  12. Multilevel Computation in Civil Engineering Based on Multimodel ElastoPlastic Analysis

    Microsoft Academic Search

    B. E. Melnikov; A. S. Semenov

    Creation of hierarchical sequence of the plastic and viscoplastic models according to different levels of structure approximations is considered. Developed strategy of multimodel analysis, which consists of creation of the inelastic models library, determination of selection criteria system and caring out of multivariant sequential clarifying computations, is described. Application of the multimodel approach in numerical computations has demonstrated possibility of

  13. MATERIAL STABILITY ANALYSIS BASED ON THE LOCAL AND GLOBAL ELASTO-PLASTIC TANGENT OPERATORS

    E-print Network

    Boyer, Edmond

    . The approach applies mainly to non associated materials such as soils. The analysis usually performed of the failure mode even for non homogeneous boundary value problems. 1 INTRODUCTION Prediction of failure in geomaterials has not yet been completely clarified. This paper proposes an original approach providing some

  14. Elasto-plastic analysis of a right-angle bent bar structure

    SciTech Connect

    Nishimura, Tetsu; Nemoto, Osamu [Nihon Univ., Tokyo (J); Yanase, Hiroyasu [Hitachi Co., Ltd., Mobara, Chiba (Japan). Production Engineering Dept.

    1996-12-01

    The limit analysis for a plastic analysis of structures usually employs an interaction curve. The plastic deformation is believed to proceed to the normal direction on the interaction curve (normality rule) in this analysis. It is supposed without doubt that the normality rule, suggested by R. Hill and D.C. Drucker for the conventional plastic flow, can be applied for the generalized plastic deformation. However, the previous studies show that the radiality rule is reasonable rather than the normality rule for the plastic deformation. In this research, the collapse load on the radiality rule and the normality rule is discussed with investigating the deformational behavior of the right-angle bent bar structure introduced by Heyman.

  15. FEM-FDM coupled liquefaction analysis of a porous soil using an elasto-plastic model

    Microsoft Academic Search

    Fusao Oka; Atsushi Yashima; Toru Shibata; Mitsuru Kato; Ryosuke Uzuoka

    1994-01-01

    The phenomenon of liquefaction is one of the most important subjects in Earthquake Engineering and Coastal Engineering. In the present study, the governing equations of such coupling problems as soil skeleton and pore water are obtained through application of the two-phase mixture theory. Using au-p (displacement of the solid phase-pore water pressure) formulation, a simple and practical numerical method for

  16. The application of fracture mechanics to failure analysis of photovoltaic solar modules

    Microsoft Academic Search

    C. P. Chen; M. H. Leipold

    1981-01-01

    Cracking of silicon solar cells and solar module transparent cover panels such as glass or polymethylmethacrylate (PMMA) is a major cause of photovoltaic solar module failure in field service. Silicon and cover materials are brittle, and cracking of these materials is expected to result from the extension of preexisting flaws under stress. Study of the cracking mechanisms is therefore an

  17. Research on fatigue behavior evaluation and fatigue fracture mechanisms of cruciform welded joints

    Microsoft Academic Search

    J. L. Fan; X. L. Guo; C. W. Wu; Y. G. Zhao

    2011-01-01

    The applications of infrared thermographic method and the relationship between the microstructures and mechanical properties of materials were reviewed. Experimental tests, using the thermographic method, have been carried out in order to evaluate the fatigue behavior of cruciform welded joints subjected to a high mean stress. A good agreement was achieved between the predicted values and those obtained by the

  18. Mechanical characteristics and morphological effect of complex crossed structure in biomaterials: fracture mechanics and microstructure of chalky layer in oyster shell.

    PubMed

    Lee, Seung-Woo; Jang, Young-Nam; Ryu, Kyoung-Won; Chae, Soo-Chun; Lee, Yun-Hee; Jeon, Chi-Wan

    2011-01-01

    The complex crossed structures with a polymorph of calcite, termed a chalky layer, which make up much of the shell of an oyster, are composed of flames and leaflets. Two layers, folia and the chalky layer in the giant Pacific oyster (Crassostrea gigas) were examined using SEM (scanning electron microscope), micro-area-XRD (X-ray diffraction) and FT-IR (Fourier transform infrared spectrometer) to determine their morphologies and component characteristics. The chalky layer was also tested using microindentation to assess its mechanical properties, and a microcrack was generated to study the fracture mechanism of the chalky layer. From an analysis of the secondary protein structure, it was shown that the ordered structures of the two layers, ?-helix and ?-structure, are similar but that the unordered structures are different. Moreover, the foliated rods at the interface of the chalky layer play a key role in the crystal growth of the chalky layers. Comparing the morphology and the preferred orientation of foliated laths, the advantages of the relatively high density and low hardness of the chalky layer have interesting implications regarding the development of sophisticated complex composites. PMID:20888246

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

    Microsoft Academic Search

    Ram B. Bhagat; Joseph C. Conway; Maurice F. Amateau; R. A. Brezler

    1996-01-01

    Relatively low fracture toughness of WC-Co materials compared to high speed tool steels is a major concern. Tungsten carbide tools may exhibit sudden brittle fracture at high stresses such as are encountered in shear and slitter knives. This has limited the use of tungsten carbide tools to certain applications in spite of their high hardness and wear resistance. The objective

  20. Deformation and Fracture Behavior of Alumina Particle-Reinforced Al 6061-T6 Composite during Dynamic Mechanical Loading

    Microsoft Academic Search

    A. G. Odeshi; G. M. Owolabi; M. N. K. Singh; M. N. Bassim

    2007-01-01

    Alumina particle-reinforced aluminum 6061-T6 composites are subjected to deformation at high strain rates in torsion and in compression using Hopkinson bars. The volume content of alumina particles in the aluminum alloy are 10 and 20 pct. While occurrence of adiabatic shear bands is evident under compression, the specimens fractured rapidly in torsion at high strain rates. Fracture occurs in both

  1. A three-dimensional numerical investigation of fracture initiation by ductile failure mechanisms in a 4340 steel

    Microsoft Academic Search

    R. Narasimhan; A. J. Rosakis; B. Moran

    1992-01-01

    Fracture initiation in ductile metal plates occurs due to substantial tunneling of the crack in the interior of the specimen followed by final failure of side ligaments by shear lip formation. The tunneled region is characterized by a flat, fibrous fracture surface. This phenomenon is clearly exhibited in a recent experimental investigation [8] performed on pre-notched plates of a ductile

  2. Fracture Modeling of Crack Propagation in Wood and Wood Composites Including Crack Tip Processes and Fiber Bridging Mechanics

    E-print Network

    Nairn, John A.

    1 Fracture Modeling of Crack Propagation in Wood and Wood Composites Including Crack Tip Processes, Corvallis, Oregon, USA Abstract Many materials develop process zones during fracture. For example, solid. After crack initiation, a process zone develops causing the toughness (or R curve) to increase

  3. New probabilistic fracture mechanics approach with neural network-based crack modeling: Its application to multiple cracks problem

    SciTech Connect

    Yoshimura, Shinobu; Lee, J.S.; Yagawa, Genki [Univ. of Tokyo (Japan); Sugioka, Kiyoshi; Kawai, Tadahiko [Science Univ. of Tokyo (Japan)

    1995-11-01

    Studies on efficient utilization and life extension of operating nuclear power plants (NPPs) have become increasingly important since ages of the first-generation NPPs are approaching their design lives. In order to predict a remaining life of each plant, it is necessary to select those critical components that strongly influence the plant life, and to evaluate their remaining lives by considering aging effects of materials and other factors. This paper proposes a new method to incorporate sophisticated crack models, such as interaction and coalescence of multiple surface cracks, into probabilistic fracture mechanism (PFM) computer programs using neural networks. First, hundreds of finite element (FE) calculations of a plate containing multiple surface cracks are performed by parametrically changing crack parameters such as sizes and locations. A fully automated 3D FE analysis system is effectively utilized here. Second, the back-propagation neural network is trained using the FE solutions, i.e. crack parameters vs. their corresponding stress intensity factors (SIFs). After a sufficient number of training iterations, the network attains an ability to promptly output SIFs for arbitrary combinations of crack parameters. The well trained network is then incorporated into the parallel PFM program which runs on one of massively parallel computers composed of 512 processing units. To demonstrate its fundamental performances, the present computer program is applied to evaluate failure probabilities of aged reactor pressure vessels considering interaction and coalescence of two dissimilar semi-elliptical surface cracks.

  4. Study of a flight monitor for jet engine disk cracks using the critical length criterion of fracture mechanics

    NASA Technical Reports Server (NTRS)

    Barranger, J. P.

    1974-01-01

    A disk crack detector is discussed which is intended to operate while in flight. The crack detector monitors the disk rim for radial surface cracks emanating from the blade root interface. An eddy current type sensor with a remotely located capacitance-resistance bridge and signal analyzer is able to detect reliably a simulated crack 1/8 in. long. The sensor was tested at rim velocities of 600 fps and at 1000 F. Fracture mechanics is used to calculate the critical crack length. Knowledge of the crack growth rate permits the calculation of the number of stress cycles remaining for the detected crack to grow to critical size. A plot is presented of the remaining life as a function of the critical crack length and the operating stress. It is shown that for a disk of Inconel 718 a through-the-thickness crack operating under a rim stress of 50 kpsi has a critical length of 0.7-in. and a remaining life of 130 flights.

  5. Numerical modelling of hydrologically-driven slope instability by means of porous media mechanics

    NASA Astrophysics Data System (ADS)

    Kakogiannou, Evanthia; Sanavia, Lorenzo; Lora, Marco; Schrefler, Bernhard

    2015-04-01

    Heavy rainfall can trigger slope failure which generally involves shallow soil deposit of different grading and origin usually in a state of partial saturation. In this case of slope instability, the behaviour of the soil slope is closely related not only to the distribution of pore-water pressure but also to the stress state during rainfall infiltration involving both mechanical and hydrological processes. In order to understand better these physical key processes, in this research work, the modelling of rainfall induced slope failure is considered as a coupled variably saturated hydro-mechanical problem. Therefore, the geometrically linear finite element code Comes-Geo for non-isothermal elasto-plastic multiphase solid porous materials is used, as developed by B.A. Schrefler and his co-workers. In this context, a detailed numerical analysis of an experimental slope stability test due to rainfall infiltration is presented. The main goals of this work are to understand the triggering mechanisms during the progressive failure, the effect of using different constitutive models of the mechanical soil behavior on the numerical results and the use of the second order work criterion on the detection of slope instability.

  6. Structure parameters governing fracture toughness of engineering materials

    Microsoft Academic Search

    A. J. Krasowsky; G. Pluvinage

    1993-01-01

    1. Of the two concepts of brittle fracture of engineering materials based on the “decohesion” and “coalescence” fracture mechanisms, respectively, the first reflects the threshold fracture toughness for materials of perfect structure, the second — the minimal fracture toughness of the material of a real structure. Since the “coalescence” fracture mechanism is observed with most engineering materials and requires higher

  7. In-situ Fracture Studies and Modeling of the Toughening Mechanism Present in Wrought LCAC, TZM, and ODS Molybdenum Flat Products

    SciTech Connect

    Cockerman, B. V. and Chan, K. S.

    2007-07-01

    In-situ testing, ultrasonic C-scans, and metallography were used to show that a crack-divider delamination form of thin-sheet toughening occurs in wrought Low Carbon Arc Cast (LCAC) unalloyed molybdenum, Oxide Dispersion Strengthened (ODS) molybdenum, and TZM molybdenum at temperatures {ge} the Ductile to Brittle Transition Temperature (DBTT). Cracking along boundaries relieves mechanical constraint to free ligaments that may plastically stretch to produce toughening. Anisotropy in fracture toughness with lower values in the short-transverse direction is shown to produce the crack divider delaminations at the crack tip in the LT and TL orientations. The delamination zone increases with increasing stress-intensity to sizes significantly larger than the plastic zone, which leads to large increases in fracture toughness by the thin sheet toughening mechanism. Fracture in ODS Mo-alloys proceeds mainly along grain boundaries to produce small ligaments that exhibit ductility for both LT and TL orientations resulting in a lower DBTT and higher toughness values at lower temperatures than observed in LCAC and TZM. A combination of grain boundary fracture and cleavage is prevalent in LCAC molybdenum and TZM. The predominance for microcracking along grain boundaries to leave fine, ductile ligaments in ODS molybdenum can be attributed to a fine-grained microstructure with {approx} 1-2 {micro}m thickness of sheet-like grains. The presence of mixed grain boundary fracture and cleavage in LCAC and TZM can be attributed to a microstructure with a larger thickness of sheet-like grains (4-15 {micro}m).

  8. Fracture healing in mice lacking Pten in osteoblasts: a micro-computed tomography image-based analysis of the mechanical properties of the femur.

    PubMed

    Collins, Caitlyn J; Vivanco, Juan F; Sokn, Scott A; Williams, Bart O; Burgers, Travis A; Ploeg, Heidi-Lynn

    2015-01-21

    In the United States, approximately eight million osseous fractures are reported annually, of which 5-10% fail to create a bony union. Osteoblast-specific deletion of the gene Pten in mice has been found to stimulate bone growth and accelerate fracture healing. Healing rates at four weeks increased in femurs from Pten osteoblast conditional knock-out mice (Pten-CKO) compared to wild-type mice (WT) of the same genetic strain as measured by an increase in mechanical stiffness and failure load in four-point bending tests. Preceding mechanical testing, each femur was imaged using a Skyscan 1172 micro-computed tomography (?CT) scanner (Skyscan, Kontich, Belgium). The present study used µCT image-based analysis to test the hypothesis that the increased femoral fracture force and stiffness in Pten-CKO were due to greater section properties with the same effective material properties as that of the WT. The second moment of area and section modulus were computed in ImageJ 1.46 (National Institutes of Health) and used to predict the effective flexural modulus and the stress at failure for fourteen pairs of intact and callus WT and twelve pairs of intact and callus Pten-CKO femurs. For callus and intact femurs, the failure stress and tissue mineral density of the Pten-CKO and WT were not different; however, the section properties of the Pten-CKO were more than twice as large 28 days post-fracture. It was therefore concluded, when the gene Pten was conditionally knocked-out in osteoblasts, the resulting increased bending stiffness and force to fracture were due to increased section properties. PMID:25498366

  9. Evaluation of the Impact of Thermal-Hydrological-Mechanical Couplings in Bentonite and Near-Field Rock Barriers of a Nuclear Waste Repository in Sparsely Fractured Hard Rock

    Microsoft Academic Search

    J. Rutqvist; M. Chijimatsu; L. Jing; A. Millard; T. S. Nguyen; A. Rejeb; Y. Sugita; C. F. Tsang

    2004-01-01

    As part of the international DECOVALEX III project and the European BENCHPAR project, this paper evaluates the impact of thermal-hydrological-mechanical (THM) couplings on the performance of a bentonite back-filled nuclear waste repository in sparsely fractured hard rock. The significance of THM coupling on the performance of a hypothetical repository is evaluated by several independent coupled numerical analyses. Moreover, the influence

  10. Fluids double-fracturing genetic mechanism and mineralization of gold-copper of the breccia pipe at Qibaoshan in Shandong Province

    Microsoft Academic Search

    Xingwang Xu; Xinping Cai; Dajun Qin; Jie Wang; Guanghe Liang; Xiaoyun Zhang; Lijin Liu

    2000-01-01

    After studying the characteristics and special texture of the fluidogenous tectonics, mineral assemblage in the cemented vein\\u000a between breccia and their special distribution, and stress analyzing the joint structures in and around the breccia pipe,\\u000a it is found that the observed phenomena are caused by a new tectonic dynamic mechanics of fluid—double-fracturing caused by\\u000a temperature and pressure of fluids and

  11. The effect of low-dose neutron irradiation on mechanical properties, electrical resistivity and fracture of NiAl bronze for ITER

    Microsoft Academic Search

    V. Barabash; A. Pokrovsky; S. Fabritsiev

    2007-01-01

    Nickel–aluminum bronze is a candidate material for several applications for ITER in-vessel components such as divertor and blanket attachments and remote handling equipment. This paper presents the first results of an experimental investigation of the effect of neutron irradiation on mechanical properties, fracture characteristics and electrical resistivity of NiAl bronze. Specimens of NiAl bronze were irradiated at 150°C and 300°C

  12. 3D Modeling of fracture of brittle rock using Lattice Solid Model with rotational mechanism

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Abe, S.; Latham, S.; Mora, P.

    2004-12-01

    The Lattice Solid Model (LSMearth) is a particle based model similar to the Discrete Element Model (DEM). The current LSMerath includes only radial interaction between two linked particles, involving only translational motions of particles. In this study, we extend the LSM by introducing full rigidity interactions between particles and full degrees of freedom for a single particle. In the new model, for each particle we introduce six degrees of freedom: 3 for translational motion, and 3 for orientation. Six kinds of relative motions are permitted, and six interactions are transferred, i.e., radial, two shearing forces, twisting and two bending torques. Particle motion is decomposed into translational motion of the center of mass and rotation about the center. The former is solved using conventional Molecular Dynamics algorithms. The latter is integrated using Fincham's leap-frog algorithm using quaternion representation of orientations. The relative rotation between two particles is decomposed into two sequence-independent rotations. Using such decomposition, all interactions due to the relative translational and rotational motions between interactive rigid bodies can be uniquely determined. We carried out several tests on 3-D rock failure under uni-axial compression and frictional instability between two blocks. Compared with the simulations without the single particle rotational mechanism, the new simulation results match more closely with experimental results

  13. Corrosion fatigue of iron-chromium-nickel alloys: Fracture mechanics, microstructure and chemistry

    SciTech Connect

    Wei, R.P.

    1992-01-29

    This progress report briefly summarizes the research performed under the referenced grant for the period from 1 December 1990 to 31 December 1991, and contains a cumulative listing of technical presentations and publications dating back to 1 June 1988. Under this grant, a multi-disciplinary research program is undertaken to address certain fundamental issues relating to corrosion fatigue crack growth in structurally important alloys in aqueous environments. The principal goal of the research is to develop and expand the scientific understanding of the processes that control corrosion fatigue crack growth, particularly for ferrous alloys in terms of the controlling mechanical and chemical/electrochemical processes and their interactions with the microstructure. Focus is placed upon the austenitic iron-chromium-nickel (FeCrNi) alloys because of the need to resolve certain mechanistic issues and because of extensive utilization of these alloys in the power generation and chemical industries. Emphasis is given to the growth of short (small) cracks at low growth rates because crack growth in this regime is expected to be more sensitive to changes in external chemical/electrochemical variables.

  14. Dry snow slab shear fracture speeds

    Microsoft Academic Search

    D. M. McClung

    2007-01-01

    Dry snow slab avalanches release by propagating shear fractures within thin weak layers underneath thicker, stronger planar slabs. In this paper, measured shear fracture speeds from small scale snow slabs are compared with theoretical estimates compatible with dynamic fracture mechanics. Given the important physical quantities including density and elastic shear modulus, it is concluded that estimated snow slab shear fracture

  15. Melt fracturing and healing: A mechanism for degassing and origin of silicic obsidian

    USGS Publications Warehouse

    Cabrera, A.; Weinberg, R.F.; Wright, H.M.N.; Zlotnik, S.; Cas, Ray A.F.

    2011-01-01

    We present water content transects across a healed fault in pyroclastic obsidian from Lami pumice cone, Lipari, Italy, using synchrotron Fourier transform infrared spectroscopy. Results indicate that rhyolite melt degassed through the fault surface. Transects define a trough of low water content coincident with the fault trace, surrounded on either side by high-water-content plateaus. Plateaus indicate that obsidian on either side of the fault equilibrated at different pressure-temperature (P-T) conditions before being juxtaposed. The curves into the troughs indicate disequilibrium and water loss through diffusion. If we assume constant T, melt equilibrated at pressures differing by 0.74 MPa before juxtaposition, and the fault acted as a low-P permeable path for H2O that diffused from the glass within time scales of 10 and 30 min. Assuming constant P instead, melt on either side could have equilibrated at temperatures differing by as much as 100 ??C, before being brought together. Water content on the fault trace is particularly sensitive to post-healing diffusion. Its preserved value indicates either higher temperature or lower pressure than the surroundings, indicative of shear heating and dynamic decompression. Our results reveal that water contents of obsidian on either side of the faults equilibrated under different P-T conditions and were out of equilibrium with each other when they were juxtaposed due to faulting immediately before the system was quenched. Degassing due to faulting could be linked to cyclical seismic activity and general degassing during silicic volcanic activity, and could be an efficient mechanism of producing low-water-content obsidian. ?? 2011 Geological Society of America.

  16. Enhanced fatigue endurance of metallic glasses through a staircase-like fracture mechanism.

    PubMed

    Gludovatz, Bernd; Demetriou, Marios D; Floyd, Michael; Hohenwarter, Anton; Johnson, William L; Ritchie, Robert O

    2013-11-12

    Bulk-metallic glasses (BMGs) are now candidate materials for structural applications due to their exceptional strength and toughness. However, their fatigue resistance can be poor and inconsistent, severely limiting their potential as reliable structural materials. As fatigue limits are invariably governed by the local arrest of microscopically small cracks at microstructural features, the lack of microstructure in monolithic glasses, often coupled with other factors, such as the ease of crack formation in shear bands or a high susceptibility to corrosion, can lead to low fatigue limits (some ~1/20 of their tensile strengths) and highly variable fatigue lives. BMG-matrix composites can provide a solution here as their duplex microstructures can arrest shear bands at a second phase to prevent cracks from exceeding critical size; under these conditions, fatigue limits become comparable with those of crystalline alloys. Here, we report on a Pd-based glass that similarly has high fatigue resistance but without a second phase. This monolithic glass displays high intrinsic toughness from extensive shear-band proliferation with cavitation and cracking effectively obstructed. We find that this property can further promote fatigue resistance through extrinsic crack-tip shielding, a mechanism well known in crystalline metals but not previously reported in BMGs, whereby cyclically loaded cracks propagate in a highly "zig-zag" manner, creating a rough "staircase-like" profile. The resulting crack-surface contact (roughness-induced crack closure) elevates fatigue properties to those comparable to crystalline alloys, and the accompanying plasticity helps to reduce flaw sensitivity in the glass, thereby promoting structural reliability. PMID:24167284

  17. Enhanced fatigue endurance of metallic glasses through a staircase-like fracture mechanism

    PubMed Central

    Gludovatz, Bernd; Demetriou, Marios D.; Floyd, Michael; Hohenwarter, Anton; Johnson, William L.; Ritchie, Robert O.

    2013-01-01

    Bulk-metallic glasses (BMGs) are now candidate materials for structural applications due to their exceptional strength and toughness. However, their fatigue resistance can be poor and inconsistent, severely limiting their potential as reliable structural materials. As fatigue limits are invariably governed by the local arrest of microscopically small cracks at microstructural features, the lack of microstructure in monolithic glasses, often coupled with other factors, such as the ease of crack formation in shear bands or a high susceptibility to corrosion, can lead to low fatigue limits (some ?1/20 of their tensile strengths) and highly variable fatigue lives. BMG-matrix composites can provide a solution here as their duplex microstructures can arrest shear bands at a second phase to prevent cracks from exceeding critical size; under these conditions, fatigue limits become comparable with those of crystalline alloys. Here, we report on a Pd-based glass that similarly has high fatigue resistance but without a second phase. This monolithic glass displays high intrinsic toughness from extensive shear-band proliferation with cavitation and cracking effectively obstructed. We find that this property can further promote fatigue resistance through extrinsic crack-tip shielding, a mechanism well known in crystalline metals but not previously reported in BMGs, whereby cyclically loaded cracks propagate in a highly “zig-zag” manner, creating a rough “staircase-like” profile. The resulting crack-surface contact (roughness-induced crack closure) elevates fatigue properties to those comparable to crystalline alloys, and the accompanying plasticity helps to reduce flaw sensitivity in the glass, thereby promoting structural reliability. PMID:24167284

  18. The XV-th Meeting of European Working Group on Acoustic emission FRACTURE MECHANISMS IN SINGLE CRYSTAL COMPOSITES

    E-print Network

    Wadley, Haydn

    single crystals of aluminum which contain a single axial fiber of SiC. These were prepared by directional fractures. Figure I shows the stress-strain and AE-strain curves for a slowly solidified composite

  19. Deformation and Fracture Behavior of Alumina Particle-Reinforced Al 6061-T6 Composite during Dynamic Mechanical Loading

    Microsoft Academic Search

    A. G. Odeshi; G. M. Owolabi; M. N. K. Singh; M. N. Bassim

    2007-01-01

    Alumina particle-reinforced aluminum 6061-T6 composites are subjected to deformation at high strain rates in torsion and in\\u000a compression using Hopkinson bars. The volume content of alumina particles in the aluminum alloy are 10 and 20 pct. While occurrence\\u000a of adiabatic shear bands is evident under compression, the specimens fractured rapidly in torsion at high strain rates. Fracture\\u000a occurs in both testing

  20. Effect of Interfacial Microstructure Evolution on Mechanical Properties and Fracture Behavior of Friction Stir-Welded Al-Cu Joints

    NASA Astrophysics Data System (ADS)

    Xue, P.; Xiao, B. L.; Ma, Z. Y.

    2015-07-01

    The interfacial microstructure evolution of Al-Cu joints during friction stir welding and post-welding annealing and its influence on the tensile strength and the fracture behavior were investigated in detail. An obvious interface including three sub-layers of ?-Al, Al2Cu, and Al4Cu9 intermetallic compound (IMC) layers is generated in the as-FSW joint. With the development of annealing process, the ?-Al layer disappeared and a new IMC layer of AlCu formed between initial two IMC layers of Al2Cu and Al4Cu9. The growth rate of IMC layers was diffusion controlled before the formation of Kirkendall voids, with activation energy of 117 kJ/mol. When the total thickness of IMC layers was less than the critical value of 2.5 ?m, the FSW joints fractured at the heat-affected zone of Al side with a high ultimate tensile strength (UTS) of ~100 MPa. When the thickness of IMC layers exceeded 2.5 ?m, the joints fractured at the interface. For relatively thin IMC layer, the joints exhibited a slightly decreased UTS of ~90 MPa and an inter-granular fracture mode with crack propagating mainly between the Al2Cu and AlCu IMC layers. However, when the IMC layer was very thick, crack propagated in the whole IMC layers and the fracture exhibited trans-granular mode with a greatly decreased UTS of 50-60 MPa.

  1. Effect of Interfacial Microstructure Evolution on Mechanical Properties and Fracture Behavior of Friction Stir-Welded Al-Cu Joints

    NASA Astrophysics Data System (ADS)

    Xue, P.; Xiao, B. L.; Ma, Z. Y.

    2015-04-01

    The interfacial microstructure evolution of Al-Cu joints during friction stir welding and post-welding annealing and its influence on the tensile strength and the fracture behavior were investigated in detail. An obvious interface including three sub-layers of ?-Al, Al2Cu, and Al4Cu9 intermetallic compound (IMC) layers is generated in the as-FSW joint. With the development of annealing process, the ?-Al layer disappeared and a new IMC layer of AlCu formed between initial two IMC layers of Al2Cu and Al4Cu9. The growth rate of IMC layers was diffusion controlled before the formation of Kirkendall voids, with activation energy of 117 kJ/mol. When the total thickness of IMC layers was less than the critical value of 2.5 ?m, the FSW joints fractured at the heat-affected zone of Al side with a high ultimate tensile strength (UTS) of ~100 MPa. When the thickness of IMC layers exceeded 2.5 ?m, the joints fractured at the interface. For relatively thin IMC layer, the joints exhibited a slightly decreased UTS of ~90 MPa and an inter-granular fracture mode with crack propagating mainly between the Al2Cu and AlCu IMC layers. However, when the IMC layer was very thick, crack propagated in the whole IMC layers and the fracture exhibited trans-granular mode with a greatly decreased UTS of 50-60 MPa.

  2. Avulsion fractures in athletes.

    PubMed Central

    Orava, S.; Ala-Ketola, L.

    1977-01-01

    34 cases of avulsion fractures are described. Each fracture took place during athletic training or competition. Excepting six sportsmen participating in a general fitness programme, every patient was an active competitive athlete. There were six women and 28 men; their average age was 20.1 years, raised by a few middle-aged "fitness sportsmen". Most avulsion fractures took place in sprinters and hurdlers; next were middle and long distance renner, footballers, fitness joggers, skiers and ice-hockey players. The most usual location of a fracture was the anterior pelvic spines; avulsion fractures were also detected in various parts of lower limbs. There were fewer avulsion fractures in the area of the trunk and upper extremities. Roetgenologically, the diagnosis of an avulsion fracture is generally easy to make. However, the diagnosis is facilitated by knowing the mechanism of the injury, the technique of the athletic event, and some of the training methods. Generally, a fracture heals well, even if it requires both sufficient immobilisation and some delay in resuming physical exertion. PMID:884433

  3. Fracture opening/propagation behavior and their significance on pressure-time records during hydraulic fracturing

    SciTech Connect

    Takashi Kojima; Yasuhiko Nakagawa; Koji Matsuki; Toshiyuki Hashida

    1992-01-01

    Hydraulic fracturing with constant fluid injection rate was numerically modeled for a pair of rectangular longitudinal fractures intersecting a wellbore in an impermeable rock mass, and numerical calculations have been performed to investigate the relations among the form of pressure-time curves, fracture opening/propagation behavior and permeability of the mechanically closed fractures. The results have shown that both permeability of the fractures and fluid injection rate significantly influence the form of the pressure-time relations on the early stage of fracture opening. Furthermore it has been shown that wellbore pressure during fracture propagation is affected by the pre-existing fracture length.

  4. Particle transport in unsaturated fractured chalk under arid A series of field and laboratory experiments were conducted to study the mechanisms of particle

    E-print Network

    Weisbrod, Noam

    Particle transport in unsaturated fractured chalk under arid conditions Abstract A series of field fractures in vadose chalk. Experiments of intermittent flow events along fracture surfaces were carried out

  5. Simulation of Hydraulic Fracturing in Low-Permeability Reservoirs

    Microsoft Academic Search

    A. Settari; H. S. Price

    1984-01-01

    Computer-based numerical simulation can be used as a tool for analysis of fracturing treatments and prediction of postfracturing well performance. The physical problem studied involves fracture mechanics, fluid flow, and heat transfer both in the fracture and in the reservoir. The numerical model predicts fracture extension, length, and width; proppant transport and settlement; fracture closure; cleanup; and postfracturing performance under

  6. Contaminant transport in fractured porous media: Analytical solutions for a system of parallel fractures

    Microsoft Academic Search

    E. A. Sudicky; E. O. Frind

    1982-01-01

    An exact analytical solution is developed for the problem of transient contaminant transport in discrete parallel fractures situated in a porous rock matrix. The solution takes into account advective transport in the fractures, molecular diffusion and mechanical dispersion along the fracture axes, molecular diffusion from the fracture to the porous matrix, adsorption onto the face of the matrix, adsorption within

  7. Simulations of mechanical failure in ice: Implications of terrestrial fracture models as applied to they icy satellites of the outer solar system

    NASA Astrophysics Data System (ADS)

    Walker, C. C.; Bassis, J. N.

    2011-12-01

    At the South Pole of Enceladus, a small icy moon orbiting Saturn, is a heavily fractured ice plain surrounded by a nearly-circular mountain range. Remarkably, the Cassini orbiter detected jets of water emanating from the icy shell and into space, originating from 4 parallel "tiger stripe" rifts within the center of the ice plain. The tiger stripes imaged on Enceladus are morphologically similar to rifts observed to form under extensional stress regimes in terrestrial ice shelves; the putative subsurface ocean hypothesized beneath the icy shell strengthens the analogy that their formation may have similar mechanical origins. Past studies have also suggested that the tiger stripes are the result of a process similar to that of mid-ocean ridge spreading on the Earth, but it remains to be seen whether or not such motion is consistent with the mountainous features seen at the circular cliff-like boundary of the region. In an attempt to understand the formation of these tiger stripes and their relationship to the observed mountain chains, we apply a conceptual model in which the ice is considered to be less like a continuous fluid body and, instead, behaves like a granular material made up of discrete blocks of ice. The tidal forces on the small moon tug on the shell enough that it has been cracked many times over, motivating the assumption that the ice exists in a continuum between wholly intact ice and highly pre-fractured ice. We employ several experimental setups with the intention of mapping the deformation of the south polar segment of the shell, to determine the processes that may contribute to its observed morphological state. These setups range from large scale topographical models, e.g., simulating the build up of mountains and processes that lead to overall elevation differences in the region, to small-scale, and focus on the more detailed level of fracturing. We explore our ice-shelf rifting analogy by modeling both icy moon fracturing and ice shelf rifting to compare and contrast the failure modes that we observe, results that bolster both our comparative platform and, importantly, our understanding of fracture in ice shelves on the Earth as well. A similar approach could be applied to the chaos regions of Europa, where fractures are prevalent and whose underlying causes are not well understood.

  8. Ruptures along a frictional interface are described by Fracture Mechanics: Experiments in a "Laboratory Earthquake" along both dry and lubricated interfaces

    NASA Astrophysics Data System (ADS)

    Fineberg, J.; Svetlizky, I.; Bayart Schweizer, E.

    2014-12-01

    A dry frictional interface is composed of an ensemble of discrete contacts whose real contact area is orders of magnitude smaller than the nominal one. Slip is initiated when contacts are broken via propagating ruptures. Characterization of the dynamic fields that drive these ruptures and how they couple to the dissipative mechanisms on the interface are critical to our fundamental understanding of both frictional motion and earthquake dynamics. We experimentally investigate ruptures along rough spatially extended interfaces bounded by the same type of material. We perform simultaneous high-speed measurements (at ?sec time scale) of the real contact area and the strain fields in the region surrounding propagating rupture tips. These measurements enable us to uncover the breakdown process near the tip of the slipping zone for rapidly propagating ruptures ranging from slow rupture fronts (~0.01CR) to nearly the Rayleigh wave speed, CR~1255m/s. These rupture fronts are quantitatively described by classical singular solutions for rapid shear cracks. These singular solutions, originally derived to describe brittle fracture, are in excellent agreement with the experiments for slow propagation, whereas some significant discrepancies arise as the rupture velocity approaches CR. The energy dissipated by the fracture of the contacts (fracture energy) is nearly constant throughout the entire rupture velocity range, while the size of the dissipative zone undergoes a 'Lorentz-like' contraction as the rupture velocity approaches CR. We then turn to both fully lubricated and partially lubricated interfaces and compare the dynamic strain fields measured to those of dry interfaces. The results of these studies are surprising. We will show that: Rapid rupture fronts still propagate in the stick-slip regime Although decreasing the overall friction coefficient along the interface, the addition of a lubricant significantly increases the fracture energy at the rupture tip In the fully lubricated case, the form of the fields surrounding the rupture tip may belong to a different class of solutions than the classical solutions given by dynamic shear fracture. This coupling between friction and fracture is critical to our fundamental understanding of frictional motion and related processes, such as earthquake dynamics.

  9. Small strain vs large strain formulation in computational mechanics

    Microsoft Academic Search

    René Chambon

    2002-01-01

    This paper is a short introduction to a comparison of the large strain formulation with respect to the small strain one. It is restricted to quasi static monophasic problems. It is intended, in this introduction, to clearly separate the balance equations and the constitutive models. Consequently large strain formulation of an elasto plastic constitutive equation is out of the scope

  10. Effects of Rotation Rates on Microstructure, Mechanical Properties, and Fracture Behavior of Friction Stir-Welded (FSW) AZ31 Magnesium Alloy

    NASA Astrophysics Data System (ADS)

    Yang, J.; Wang, D.; Xiao, B. L.; Ni, D. R.; Ma, Z. Y.

    2013-01-01

    Three rotation rates were selected for friction stir welded (FSW) rolled AZ31 plates, at a constant welding speed of 100 mm/minutes. As the rotation rate was increased from 800 and 2000 to 3500 rpm, the nugget shape varied from a basin- or ellipse-shaped homogeneous structure to a two-layer structure. The grain characteristic was similar in the nugget zones (NZs) at 800 and 2000 rpm, with the column-rotated basal plane. However, at 3500 rpm, the equiaxed fine grains and column-rotated basal plane were found in the lower zone of the two-layer structure, while elongated coarse grains and the basal plane with little inclination comparable to that in the parent material (PM) were detected in the upper zone. Tensile tests indicated that the fracture behaviors of the FSW AZ31 joints at 800 and 2000 rpm were similar with the weak zones being located at the NZ middle and along the boundary between the NZ and the thermo-mechanically affected zone, while contrasting fracture features were found at 3500 rpm. The ultimate tensile strength (UTS) of the joints increased as the rotation rate increased, with the highest UTS being about 95 pct of the PM at 3500 rpm. The variations in the strength and fracture behavior of the joints with the rotation rate were accounted for by the variation in the texture.

  11. The influence of mechanical stimulus on the pattern of tissue differentiation in a long bone fracture — an FEM study

    Microsoft Academic Search

    T. N. Gardner; T. Stoll; L. Marks; S. Mishra; M. Knothe Tate

    2000-01-01

    2D, coronal plane, finite elements models (FEMs) were developed from orthogonal radiographs of a diaphyseal tibial fracture and its reparative tissue at four different time points during healing. Each callus was separated into regions of common tissue histology by computerised radiographic analysis. Starting point values of tissue material properties from the literature were refined by the model to simulate exactly

  12. KINEMATIC AND MECHANICAL CHANGES IN THE DISTAL RADIOULNAR JOINT (DRUJ) OF PATIENTS WITH MALUNITED DISTAL RADIUS FRACTURES

    E-print Network

    Laidlaw, David

    DISTAL RADIUS FRACTURES +*Crisco, JJ; **Marai, GE; **Laidlaw, DH; *Moore, DC; *Akelman, E +*Department challenging. Using markerless bone registration [1], we recently demonstrated that in patients with no ulnar ultimately affect long- term clinical outcome. To test this hypothesis, we developed a novel technique

  13. International Conference on Fracture Mechanics of Concrete and Concrete Structures (FraMCoS-V), April 2004, Vail, Colorado

    E-print Network

    Mobasher, Barzin

    : The role of fibers on the tensile stress strain response and the fracture toughness of cement based debonding and pullout of fibers as closing pressure distribution which is expressed as tensile stress crack on glass fiber composites. Keywords: R-Curves, fiber reinforced concrete, closing pressure, stress

  14. Effect of niobium filaments on mechanical response and fracture characteristics of dispersion strengthened copper alloy and copper–niobium microcomposite

    Microsoft Academic Search

    T. S Srivatsan; J. D Troxell

    1999-01-01

    In this study, the microstructure, tensile deformation, cyclic stress amplitude-controlled fatigue and final fracture behavior of a microcomposite based on an oxide dispersion strengthened copper matrix were examined. Specimens of the microcomposite and an unreinforced dispersion strengthened copper counterpart were cyclically deformed, over a range of cyclic stress amplitudes, at both ambient and elevated temperatures. Increase in test temperature was

  15. EXTRACTION OF FRACTURE-MECHANICS AND TRANSMISSION-ELECTRON-MICROSCOPY SAMPLES FROM TRITIUM-EXPOSED RESERVOIRS USING ELECTRIC-DISCHARGE MACHINING

    SciTech Connect

    Morgan, M; Ken Imrich, K; Michael Tosten, M

    2006-08-31

    The Enhanced Surveillance Campaign is funding a program to investigate tritium aging effects on the structural properties of tritium reservoir steels. The program is designed to investigate how the structural properties of reservoir steels change during tritium service and to examine the role of microstructure and reservoir manufacturing on tritium compatibility. New surveillance tests are also being developed that can better gauge the long-term effects of tritium and its radioactive decay product, helium-3, on the properties of reservoir steels. In order to conduct these investigations, three types of samples are needed from returned reservoirs: tensile, fracture mechanics, and transmission-electron microscopy (TEM). An earlier report demonstrated how the electric-discharge machining (EDM) technique can be used for cutting tensile samples from serial sections of a 3T reservoir and how yield strength, ultimate strength and elongation could be measured from those samples. In this report, EDM was used successfully to section sub-sized fracture-mechanics samples from the inner and outer walls of a 3T reservoir and TEM samples from serial sections of a 1M reservoir. This report fulfills the requirements for the FY06 Level 3 milestone, TSR 15.1 ''Cut Fracture-Mechanics Samples from Tritium-Exposed Reservoir'' and TSR 15.2 ''Cut Transmission-electron-microscopy foils from Tritium-Exposed Reservoir'' for the Enhance Surveillance Campaign (ESC). This was in support of ESC L2-1870 Milestone-''Provide aging and lifetime assessments of selected components and materials for multiple enduring stockpile systems''.

  16. Processing and mechanical properties of high temperature/high performance composites. Mechanism-based constitutive laws and design. Book 1. Annual report, 1 March 1992-28 February 1994

    SciTech Connect

    Evans, A.G.; Leckie, F.A.

    1994-03-01

    This document discusses the following: (1) Materials selection and innovation in design; (2) Elasto-plastic analysis of interface layers for fiber-reinforced metal-matrix composites; (3) Modeling of anisotropic behavior of weakly bonded fiber reinforced MMCs; (4) On the tensile properties of a fiber reinforced titanium matrix composite; (5) Control of strength anisotropy of metal matrix fiber composites; (6) inelastic strains due to matrix cracking in unidirectional fiber-reinforced composites; (7) Location and ultimate tensile strength of fiber-reinforced ceramic-matrix composites; (8) Matrix cracking and debonding of ceramic-matrix composites; (9) Matrix cracking of cross-ply ceramic composites; (10) Transverse cracking in fiber-reinforced brittle matrix, cross-ply laminates; (11) The mechanisms of deformation and failure in carbon matrix composites subject to tensile and shear loading; (12) Uncoupled and coupled approaches to predict crack-initiation in fiber-reinforced ceramic-matrix composites; (13) Stress corrosion cracking in a unidirectional ceramic-matrix composite; (14) Effects of gauge length on the tensile strength of SiC fibers; (15) Tunneling cracks in constrained layers; (16) The effect of interfacial properties on the flow strength of discontinuous reinforced metal matrix composites; (17) On dislocation storage and the mechanical response of fine scale microstructures; and (18) Effect of microstructural parameters on the yield strength of Al-4%Mg/Al2O3P composites.

  17. [Hip fractures].

    PubMed

    Weisová, Drahomíra; Salášek, Martin; Pavelka, Tomáš

    2013-01-01

    Hip fractures are ranked among the frequent injuries. These fractures have been often coupled with high energy trauma in children and in patients with normal bone structure, low energy trauma and osteoporotic fracture (fragility fracture) is typical in elder patients. Hip fractures are divided into five groups: femoral head fracture, femoral neck fracture, pertrochanteric, intertrochateric and subtrochanteric fracture. Surgical treatment is indicated in all patients unless contraindications are present. Long bed rest has been accompanied by a high risk of development of thromboembolic disease, pneumonia and bed sore. Healing in the wrong position and nonunions are often the result of conservative treatment. Screw osteosynthesis is performed in isolated femoral head factures. Three cannulated screws or a DHS plate (dynamic hip screw) are used in fractures of the femoral neck with normal femoral head perfusion, total hip replacement is recommended in elder patients and in case of loss of blood supply of the femoral head. Pertrochanteric and intertrochanteric fractures can be stabilized by the femoral nails (PFN, PFN A, PFH - proximal femoral nail), nails are suitable for minimally invasive insertion and provide higher stability in the shaft, or plates (DHS) designed for stable pertronchanteric and intertrochanteric fractures. Subtrochanteric fractures can be fixed also intramedullary (nails - PFN long, PFN A long) and extramedullary (plates - DCS dynamic condylar screw, proximal femoral LCP - locking compression plate). Open reduction with internal plate fixation is advantageous for pathological fractures, as biopsy sampling can be performed. Hip fracture rehabilitation is integral part of the treatment, including walking on crutches or with a walker with partial weight bearing for at least six weeks. PMID:24131459

  18. The Hall-Petch relationship and mechanisms of fracture in B2 compounds. Third year progress report

    SciTech Connect

    Baker, I.

    1992-12-30

    A study was initiated in 1987 to examine structure and properties of grain boundaries in the B2 ordered alloys FeAl and NiAl. This project continued from 1990, with initial emphasis on CoAl, FeCo, and CuZn, but with continued work on FeAl and NiAl. Effect of alloy composition on structure/chemistry and properties of grain boundaries were examined by measuring yield strength vs grain size, measuring grain boundary composition using a scanning Auger electron microprobe, examining dislocation/grain boundary interactions during in-situ straining in TEM, and determining fracture modes and assessing strain extent at fracture surfaces using selected area channeling patterns. Progress during the last 3 years is reviewed.

  19. ELASTIC-PLASTIC FRACTURE MECHANICS FOR TWO-DIMENSIONAL STABLE CRACK GROWTH AND INSTABILITY AS APPLIED TO PVC PIPE MATERIAL

    Microsoft Academic Search

    A. A. EL BADAWY; M. YOUNAN

    The objective of the presented work is to evaluate the fracture resistance ofPVC pipe material based on curved three point bend specimens cut directly from the pipe. Two experimental techniques have been implemented: The multiple specimen approach (Begley and Landes method), ASTM method for the determination of the critical value of the J-integral Old. The J-R curve is determined from

  20. Leakage losses from a hydraulic fracture and fracture propagation

    Microsoft Academic Search

    Robert E. Johnson; Craig W. Gustafson

    1988-01-01

    The fluid mechanics of viscous fluid injection into a fracture embedded in a permeable rock formation is studied. Coupling between flow in the fracture and flow in the rock is retained. The analysis is based on a perturbation scheme that assumes the depth of penetration of the fluid into the rock is small compared to the characteristic length w30\\/k, where