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Sample records for elasto-plastic fracture mechanics

  1. Effects of mechanical properties and surface friction on elasto-plastic sliding contact

    E-print Network

    Dao, Ming

    Effects of mechanical properties and surface friction on elasto-plastic sliding contact S and many recent computational studies have established quantitative relationships between elasto-plastic systematically quantified the effect of the plastic deformation characteristics on the frictional sliding

  2. About contacts of adhesive, elasto-plastic, frictional powders Stefan Luding

    E-print Network

    Luding, Stefan

    About contacts of adhesive, elasto-plastic, frictional powders Stefan Luding Multi Scale Mechanics). The contact mechanics used involves elasto-plastic, viscous, frictional, and torque contributions. From the contact laws involving elasto-plastic repulsive forces, viscous dissipative forces, frictional forces

  3. 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.

  4. 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.

  5. Analysis and Research on Elasto-Plastic Response Spectra

    NASA Astrophysics Data System (ADS)

    Ding, Jianguo; Chen, Wei

    2010-05-01

    With the development of the seismic design theory, more and more attention is being paid to structural elastic-plastic analysis. As a kind of method for elasto-plastic analysis, elasto-plastic response spectra have an important role in providing seismic design rules and the related parameters. There are two kinds of elasto-plastic response spectra. One is constant-ductility strength demand spectrum; the other is constant-strength ductility demand spectrum. In this paper, the basic equation on elasto-plastic response spectra is established and the corresponding ductility demand spectra and strength demand spectra are calculated, based on time history analysis method. A detailed analysis of the proposed constant-strength ductility demand spectra is made, and the differences between bilinear restoring force model and trilinear restoring force model are found. The principles of establishing elasto-plastic design response spectra are elaborated by using the R-?-T relationship. Four kinds of elastic-plastic design response spectra are deduced, and are compared with each other in detail. Finally, the following recommendations are given: (1) bilinear system model can substitute trilinear system model when R is no more than 4; (2) Vidic's R-?-T relationship is recommended under the condition of hard soil and ??3; in other case, Berrill's R-?-T relationship is recommended to use.

  6. Micropillar compression technique applied to micron-scale mudstone elasto-plastic deformation.

    SciTech Connect

    Michael, Joseph Richard; Chidsey, Thomas; Heath, Jason E.; Dewers, Thomas A.; Boyce, Brad Lee; Buchheit, Thomas Edward

    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.

  7. 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

  8. Small strain elasto-plastic multiphase-field model

    NASA Astrophysics Data System (ADS)

    Schneider, Daniel; Schmid, Stefan; Selzer, Michael; Böhlke, Thomas; Nestler, Britta

    2015-01-01

    A small strain plasticity model, based on the principles of continuum mechanics, is incorporated into a phase-field model for heterogeneous microstructures in polycrystalline and multiphase material systems (Nestler et al., Phys Rev 71:1-6, 2005). Thereby, the displacement field is computed by solving the local momentum balance dynamically (Spatschek et al., Phys Rev 75:1-14, 2007) using the finite difference method on a staggered grid. The elastic contribution is expressed as the linear approximation according to the Cauchy stress tensor. In order to calculate the plastic strain, the Prandtl-Reuss model is implemented consisting of an associated flow rule in combination with the von Mises yield criterion and a linear isotropic hardening approximation. Simulations are performed illustrating the evolution of the stress and plastic strain using a radial return mapping algorithm for single phase system and two phase microstructures. As an example for interface evolution coupling with elasto-plastic effects, we present crack propagation simulations in ductile material.

  9. Thermo-elasto-plastic finite element analysis of quasi-state processes in Eulerian reference

    E-print Network

    Michaleris, Panagiotis

    Thermo-elasto-plastic finite element analysis of quasi-state processes in Eulerian reference frames ­ Incremental scheme ­ Fine mesh along entire heat source path ­ Lengthy computer runs · Elasto-Plasticity at times ti and ti-1, respectively. Penn State University 5 #12;Elasto-Plasticity Equilibrium: r(r, t) + b

  10. An elasto-plastic damage model cast in a co-rotational kinematic framework for large

    E-print Network

    Masud, Arif

    An elasto-plastic damage model cast in a co-rotational kinematic framework for large deformation an elasto-plastic damage model that is based on irreversible thermodynamics and internal state variable that is defined in terms of an internal damage variable of energy, along with a set of rate-independent elasto-plastic

  11. Ecient elasto-plastic simulation ICA, University of Stuttgart, Germany

    E-print Network

    Wieners, Christian

    EÃ?cient elasto-plastic simulation C. Wieners ICA, University of Stuttgart, Germany Summary. In this paper we describe a method for the construction of radial re- turn algorithms to the plasticity models plasticity, the constitutive equations are determined by the free energy functional and a monotone function

  12. Elasto-plastic properties of Cu-Nb nanolaminate

    NASA Astrophysics Data System (ADS)

    Betekhtin, V. I.; Kolobov, Yu. R.; Kardashev, B. K.; Golosov, E. V.; Narykova, M. V.; Kadomtsev, A. G.; Klimenko, D. N.; Karpov, M. I.

    2012-02-01

    The Young's modulus, internal friction, and microplastic flow stress in Cu-Nb nanolaminate has been determined by an acoustic technique. The influence of high hydrostatic compression (1 GPa) on these elasto-plastic properties of the nanolaminate has been studied.

  13. The method of lines in three dimensional fracture mechanics

    NASA Technical Reports Server (NTRS)

    Gyekenyesi, J.; Berke, L.

    1980-01-01

    A review of recent developments in the calculation of design parameters for fracture mechanics by the method of lines (MOL) is presented. Three dimensional elastic and elasto-plastic formulations are examined and results from previous and current research activities are reported. The application of MOL to the appropriate partial differential equations of equilibrium leads to coupled sets of simultaneous ordinary differential equations. Solutions of these equations are obtained by the Peano-Baker and by the recurrance relations methods. The advantages and limitations of both solution methods from the computational standpoint are summarized.

  14. Nonlinear elasto-plastic model for dense granular flow

    E-print Network

    Ken Kamrin

    2009-05-07

    This work proposes a model for granular deformation that predicts the stress and velocity profiles in well-developed dense granular flows. Recent models for granular elasticity (Jiang and Liu 2003) and rate-sensitive plastic flow (Jop et al. 2006) are reformulated and combined into one universal granular continuum law, capable of predicting flowing regions and stagnant zones simultaneously in any arbitrary 3D flow geometry. The unification is performed by justifying and implementing a Kroner-Lee elasto-plastic decomposition, with care taken to ensure certain continuum physical principles are necessarily upheld. The model is then numerically implemented in multiple geometries and results are compared to experiments and discrete simulations.

  15. An accurate elasto-plastic frictional tangential forcedisplacement model for granular-flow

    E-print Network

    Vu-Quoc, Loc

    An accurate elasto-plastic frictional tangential force­displacement model for granular 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

  16. 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)

  17. Modeling Elasto-Plastic Behavior of Polycrystalline Grain Structure of Steels at Mesoscopic Level

    E-print Network

    Cizelj, Leon

    Modeling Elasto-Plastic Behavior of Polycrystalline Grain Structure of Steels at Mesoscopic Level. The constitutive model of crystal grains utilizes anisotropic elasticity and crystal plasticity. Commercially be considered macroscopically homogeneous. Elastic and rate independent plastic deformation modes are considered

  18. Statistical Physics of Elasto-Plastic Steady States in Amorphous Solids: Finite Temperatures and Strain Rates

    E-print Network

    Smarajit Karmakar; Edan Lerner; Itamar Procaccia; Jacques Zylberg

    2010-06-18

    The effect of finite temperature $T$ and finite strain rate $\\dot\\gamma$ on the statistical physics of plastic deformations in amorphous solids made of $N$ particles is investigated. We recognize three regimes of temperature where the statistics are qualitatively different. In the first regime the temperature is very low, $Tstrain is quasi-static. In this regime the elasto-plastic steady state exhibits highly correlated plastic events whose statistics are characterized by anomalous exponents. In the second regime $T_{\\rm cross}(N)strain rate. The physical mechanism of the cross-over is different for increasing temperature and increasing strain rate, since the plastic events are still dominated by the mechanical instabilities (seen as an eigenvalue of the Hessian matrix going to zero), and the effect of temperature is only to facilitate the transition. A third regime occurs above the second cross-over temperature $T_{\\rm max}(\\dot\\gamma)$ where stress fluctuations become dominated by thermal noise. Throughout the paper we demonstrate that scaling concepts are highly relevant for the problem at hand, and finally we present a scaling theory that is able to collapse the data for all the values of temperatures and strain rates, providing us with a high degree of predictability.

  19. 3D Elasto-Plastic Stress Analysis by the Method of Arbitrary Lines

    NASA Astrophysics Data System (ADS)

    Kaminishi, Ken; Ando, Ryuma

    The method of arbitrary lines (MAL) constitutes a general dimensional reduction methodology for elliptic boundary value problems (BVP) in arbitrary two- and three-dimensional domains by solving systems of one-dimensional boundary value ordinary differential equations (ODEs). It has been already applied to two-dimensional problem, and the good results have been reported. In this work, we consider the extension of the MAL to three-dimensional elasto-plastic stress analysis. We first give the MAL formulation of three-dimensional elasto-plastic problems. Although the MAL formulation is derived from the principle of three-dimensional increment virtual work as well as the finite element method (FEM), the MAL is different from FEM in that displacement increment and virtual displacement increment are expressed continuous functions along one direction and shape-functions along other two directions. Substituting displacement increment and virtual displacement increment into the principle of three-dimensional increment virtual work, we have a system of ODEs. The three-dimensional elasto-plastic analysis of BGA model, which was a method of the solder joints of electronic component, was carried out. As results, it was confirmed that to solve 3D elasto-plastic problem at the good accuracy was possible by the MAL.

  20. 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.

  1. 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.

  2. REVERSING CYCLIC ELASTO-PLASTIC DEMANDS ON STRUCTURES DURING STRONG MOTION EARTHQUAKE EXCITATION.

    USGS Publications Warehouse

    Perez, V.; Brady, A.G.; Safak, E.

    1986-01-01

    Using the horizontal components from El Centro 1940, Taft 1952, and 4 accelerograms from the San Fernando earthquake of 2/9/71, the time history of the elasto-plastic displacement response was calculated for oscillators having periods within the range of 1 to 6 s and ductility factors within the range of 3 to 6. The Nth largest peak of the elasto-plastic response (N equals 2,4,8,16), when expressed as a percentage of maximum response (that is, N equals 1), is fairly independent of period within our period range. When considering only plastic peaks occurring, sometimes in a one-directional group of peaks, in the reverse direction from the preceding plastic peak, the amplitude of the Nth reversing plastic peak is similar to the Nth elastic peak, regardless of the ductility factor.

  3. 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

    2015-05-01

    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.

  4. The p-version of the finite element method in incremental elasto-plastic analysis

    NASA Technical Reports Server (NTRS)

    Holzer, Stefan M.; Yosibash, Zohar

    1993-01-01

    Whereas the higher-order versions of the finite elements method (the p- and hp-version) are fairly well established as highly efficient methods for monitoring and controlling the discretization error in linear problems, little has been done to exploit their benefits in elasto-plastic structural analysis. Aspects of incremental elasto-plastic finite element analysis which are particularly amenable to improvements by the p-version is discussed. These theoretical considerations are supported by several numerical experiments. First, an example for which an analytical solution is available is studied. It is demonstrated that the p-version performs very well even in cycles of elasto-plastic loading and unloading, not only as compared to the traditional h-version but also in respect to the exact solution. Finally, an example of considerable practical importance - the analysis of a cold-worked lug - is presented which demonstrates how the modeling tools offered by higher-order finite element techniques can contribute to an improved approximation of practical problems.

  5. The importance of visco-elasto-plastic rheology in numerical modeling of two-phase flow

    NASA Astrophysics Data System (ADS)

    Keller, T.; Kaus, B. J. P.

    2012-04-01

    We investigate the behaviour of a two-phase system that involves propagation of partial melt through a visco-elasto-plastic continental lithosphere and crust under ongoing tectonic deformation. Using two-dimensional numerical simulations we examine the coupled magmatic and tectonic processes leading to intrusive rock formation. The numerical modeling approach is based on the assumption that the melt fraction is equal to the porosity of the rock and that porosity changes reflect the compaction or dilation of the matrix framework due to visco-elasto-plastic processes. All modes of compaction are connected to the effective pressure, which can be understood as effective compaction/decompaction stress acting on the host rock. The rheology of the solid phase largely determines the mode and efficiency of melt transport. Therefore it is of considerable importance to formulate a realistic visco-elasto-plastic rheology. In the case of two-phase flow modeling, we additionally formulate a volumetric rheology to consitute compaction/decompaction deformation along with a standard deviatoric rheology for shear deformation. First results indicate that melt propagation is strongly related to the regional stress field, and that plastic failure zones (decompaction tubes, dikes and sills) form important conduits for the propagation of partial melt, especially through the more competent parts of lithosphere and crust. We may distinguish three distinct regimes of style and efficiency of melt propagation that occur at increasing competence of the host rock. A possible application of such models is to deepen the understanding of the processes involved in, and the geometry and field relations expected from, the emplacement of hydrated slab melts into the overriding continental plate in an ocean-continent subduction setting, covering rheological conditions in both the hot and weak asthenosphere as well as in the cooler and more rigid parts of lithosphere and crust.

  6. A numerical model for the thermo-elasto-plastic behaviour of a material

    NASA Technical Reports Server (NTRS)

    Ray, Sujit K.; Utki, Senol

    1989-01-01

    This paper presents a numerical model for the thermo-elasto-plastic behavior of an isotropic material. The model is based on the assumption that the yielding of the material obeys von Mises distortion energy theory and the material exhibits isotropic strain hardening. This unique model can be used both for isothermal and non-isothermal cases. The original formulation for the non-isothermal three-dimensional case has been specialized for plane stress conditions and the equations for the computation of warping and thickness change are provided. The finite element implementation of this model is also outlined.

  7. Proceedings of the Stockholm Music Acoustics Conference, August 6-9, 2003 (SMAC 03), Stockholm, Sweden BOWED STRING SIMULATION USING AN ELASTO-PLASTIC FRICTION MODEL

    E-print Network

    Avanzini, Federico

    , Sweden BOWED STRING SIMULATION USING AN ELASTO-PLASTIC FRICTION MODEL Stefania Serafin Federico Avanzini the interaction between the bow and the string is mod- eled using an elasto-plastic friction model, based on the observation that the interfacial rosin layer exhibits plastic deformation at the contact

  8. A single hardening elasto-plastic model for Kaolin clay with loading-history-dependent plastic potential function

    E-print Network

    Prashant, Amit

    A single hardening elasto-plastic model for Kaolin clay with loading-history- dependent plastic and failure criteria are found to be strongly dependent on the principal stress rotation angle () and plastic work. A unique plastic potential function determined solely by the current stress state

  9. Elasto-Plastic Analysis of Tee Joints Using HOT-SMAC

    NASA Technical Reports Server (NTRS)

    Arnold, Steve M. (Technical Monitor); Bednarcyk, Brett A.; Yarrington, Phillip W.

    2004-01-01

    The Higher Order Theory - Structural/Micro Analysis Code (HOT-SMAC) software package is applied to analyze the linearly elastic and elasto-plastic response of adhesively bonded tee joints. Joints of this type are finding an increasing number of applications with the increased use of composite materials within advanced aerospace vehicles, and improved tools for the design and analysis of these joints are needed. The linearly elastic results of the code are validated vs. finite element analysis results from the literature under different loading and boundary conditions, and new results are generated to investigate the inelastic behavior of the tee joint. The comparison with the finite element results indicates that HOT-SMAC is an efficient and accurate alternative to the finite element method and has a great deal of potential as an analysis tool for a wide range of bonded joints.

  10. On the symbolic manipulation and code generation for elasto-plastic material matrices

    NASA Technical Reports Server (NTRS)

    Chang, T. Y.; Saleeb, A. F.; Wang, P. S.; Tan, H. Q.

    1991-01-01

    A computerized procedure for symbolic manipulations and FORTRAN code generation of an elasto-plastic material matrix for finite element applications is presented. Special emphasis is placed on expression simplifications during intermediate derivations, optimal code generation, and interface with the main program. A systematic procedure is outlined to avoid redundant algebraic manipulations. Symbolic expressions of the derived material stiffness matrix are automatically converted to RATFOR code which is then translated into FORTRAN statements through a preprocessor. To minimize the interface problem with the main program, a template file is prepared so that the translated FORTRAN statements can be merged into the file to form a subroutine (or a submodule). Three constitutive models; namely, von Mises plasticity, Drucker-Prager model, and a concrete plasticity model, are used as illustrative examples.

  11. Model Experiments and Elasto-Plastic Finite Element Analysis about Seepage Failure of Sand Behind Fixed Sheet Pile

    NASA Astrophysics Data System (ADS)

    Okajima, Kenji; Tanaka, Tadatsugu; Zhang, Shanji; Komatsu, Takahiro

    Constructing civil engineering structures, temporaly or permanent water proofing sheet piles often are used. The stability of seepage failure are carefully applied to those sheet piles, although many troubles of seepage failure were reported. On this problem the predictive method of the deformation and critical water head is required. In this study we carried out the model experiments which were designed for studying the seepage failure of soil behind fixed sheet piles and our elasto-plastic finite element method was applied to verify the effectiveness. Terzaghi method is very famous method for this problem and Terzaghi method was investigated by experiments data. As a result, it was confirmed that elasto-plastic finite element method was effectiveness and Terzaghi method was useful for this problem.

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

    E-print Network

    Regueiro, Richard A.

    for presentation at the 44th US Rock Mechanics Symposium and 5th U.S.-Canada Rock Mechanics Symposium, held in Salt and embedded strong discontinuity finite element implementation of rock fracture Regueiro, R.A. and Yu, S, CO 80309, U.S.A. Copyright 2010 ARMA, American Rock Mechanics Association This paper was prepared

  13. Elasto-Plastic Constitutive Behavior in Three Lithofacies of the Cambrian Mt. Simon Sandstone, Illinois Basin, USA

    NASA Astrophysics Data System (ADS)

    Dewers, T.; Newell, P.; Broome, S. T.; Heath, J. E.; Bauer, S. J.

    2012-12-01

    The Mt. Simon Formation, a basal Cambrian sandstone underlying the Illinois Basin in the Central US, is a target for underground storage and waste injection which require an assessment of geomechanical behavior. The range of depositional environments, from braided streams and minor eolean features in the lower Mt Simon, to tidally-influenced near- and on-shore sands in the upper Mt. Simon, yield a heterogeneous formation with a range in porosity, permeability, and mechanical properties. We examine the experimental deformational behavior of three distinct Mt. Simon lithofacies via axisymmetric compressional testing. Initial yielding is confirmed with acoustic emissions in many of the tests and failure envelopes are determined for each lithofacies. The evolution of (assumed) isotropic elastic moduli are examined during testing by use of unload-reload cycles, which permit the separation of total measured strains into elastic and plastic (permanent) strains. The upper Mt Simon samples deform largely elastically at stresses encountered in the Illinois Basin, with very little modulus degradation. The lower Mt. Simon facies are weaker and deform plastically, with varying amounts of modulus degradation. Results are interpreted via petrographic observation of textural contrasts. This range in constitutive response is captured up to failure with a phenomenological elasto-plasticity model. Essential aspects to describe observed behavior used in the model include non-associative plasticity, stress-invariant dependent failure, an elliptical cap surface capturing shear effects on pore collapse, kinematic and isotropic hardening, nonlinear elasticity and elastic-plastic coupling, among other features. Static moduli derived from laboratory tests are compared to dynamic moduli from wellbore log response which can allow experimental results and model to be extrapolated to Mt. Simon occurrences across the basin. This work was funded in part by 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 and by the Department of Energy Office of Electricity. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  14. A new uniformly valid asymptotic integration algorithm for elasto-plastic-creep and unified viscoplastic theories including continuum damage

    NASA Technical Reports Server (NTRS)

    Chulya, A.; Walker, K. P.

    1989-01-01

    A new scheme to integrate a system of stiff differential equations for both the elasto-plastic creep and the unified viscoplastic theories is presented. The method has high stability, allows large time increments, and is implicit and iterative. It is suitable for use with continuum damage theories. The scheme was incorporated into MARC, a commercial finite element code through a user subroutine called HYPELA. Results from numerical problems under complex loading histories are presented for both small and large scale analysis. To demonstrate the scheme's accuracy and efficiency, comparisons to a self-adaptive forward Euler method are made.

  15. A new uniformly valid asymptotic integration algorithm for elasto-plastic creep and unified viscoplastic theories including continuum damage

    NASA Technical Reports Server (NTRS)

    Chulya, Abhisak; Walker, Kevin P.

    1991-01-01

    A new scheme to integrate a system of stiff differential equations for both the elasto-plastic creep and the unified viscoplastic theories is presented. The method has high stability, allows large time increments, and is implicit and iterative. It is suitable for use with continuum damage theories. The scheme was incorporated into MARC, a commercial finite element code through a user subroutine called HYPELA. Results from numerical problems under complex loading histories are presented for both small and large scale analysis. To demonstrate the scheme's accuracy and efficiency, comparisons to a self-adaptive forward Euler method are made.

  16. Fracture mechanics expert system

    NASA Technical Reports Server (NTRS)

    Powers, E.; Elfer, N.; Casadaban, C.

    1992-01-01

    Attention is given to fracture mechanics, an analytical method used extensively in the National Space Transportation System to conservatively predict the remaining service life of an article when a flaw or a material defect is detected. These analyses are performed on hardware containing material defects that have been detected by various nondestructive inspection techniques. An expert system being developed to streamline the process so that hardware dispositions may be obtained in a timely and consistent manner is discussed. The expert system reduces the potential for errors due to the manual transcription between the various software programs involved in completing a fracture mechanics analysis. NEXPERT Object, the expert system development shell selected for this purpose, allows the various software programs used in fracture mechanics analyses to be accessed and manipulated from the same platform.

  17. 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

    2015-10-29

    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.

  18. Mechanical and petrophysical study of fractured shale materials

    NASA Astrophysics Data System (ADS)

    Bonnelye, A.; Schubnel, A.; David, C.; Henry, P.; Guglielmi, Y.; Gout, C.; Dick, P.

    2013-12-01

    Understanding of the mechanical and physical properties of shales is of major importance in many fields such as faults hydro-mechanical behavior, cap-rock and unconventional reservoir studies or nuclear waste disposal. In particular, relationships between fluid transport properties, applied stress and textural anisotropy are critical both in intact and fractured shales. Therefore, these relations need to be investigated in the laboratory in order to have a better understanding on in-situ mechanisms. Hence, the mechanical behavior and the petrophysical properties of Toarcian shale of the Tournemire underground laboratory (France) have been investigated. The petrophysical properties have been measured along a 20 meters core drilled through a fault zone from the Tournemire tunnel. Along the core, P and S waves velocity and anisotropy, as well as magnetic susceptibility anisotropy and porosity were measured. In addition, conventional triaxial tests have been performed in order to determine the elasto-plastic yield envelope on three sets of samples with different orientations relative to bedding (0°, 45°, and 90° to the vertical axe). For each set, six experiments were carried out at increasing confining pressures (2.5, 5, 10, 20, 40, 80MPa). Experiments were performed in dry conditions, at a strain rate of 5x10-7 s-1 up to failure. During each experiment, P and S wave elastic velocities were continuously measured along different directions, in order to assess both P wave anisotropy and shear wave splitting and their evolutions with deformation. Our results show that brittle failure is preceded by the development of P wave anisotropy and shear wave splitting, due to crack re-opening and crack growth. However, the orientation of principal stress components relative to the bedding plane plays an important role on both the brittle strength, as well as on the magnitude of shear-enhanced P wave velocity anisotropy and S wave splitting. Our perspective is now to perform fluid injections, both at the field and laboratory scale and measure the evolution of hydraulic diffusivity by tracking the fluid front by both passive and active seismic measurements.

  19. Phase Field Fracture Mechanics.

    SciTech Connect

    Robertson, Brett Anthony

    2015-11-01

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

  20. An Optimized Elasto-Plastic Subgrade Reaction For Modeling The Response Of A Nonlinear Foundation For A Structural Analysis

    NASA Astrophysics Data System (ADS)

    Ray, Richard Paul

    2015-09-01

    Geotechnical and structural engineers are faced with a difficult task when their designs interact with each other. For complex projects, this is more the norm than the exception. In order to help bridge that gap, a method for modeling the behavior of a foundation using a simple elasto-plastic subgrade reaction was developed. The method uses an optimization technique to position 4-6 springs along a pile foundation to produce similar load deflection characteristics that were modeled by more sophisticated geotechnical finite element software. The methodology uses an Excel spreadsheet for accepting user input and delivering an optimized subgrade spring stiffness, yield, and position along the pile. In this way, the behavior developed from the geotechnical software can be transferred to the structural analysis software. The optimization is achieved through the solver add-in within Excel. Additionally, a beam on a nonlinear elastic foundation model is used to compute deflections of the optimized subgrade reaction configuration.

  1. 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.

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

    SciTech Connect

    Tattoli, F.; Casavola, C.; Pierron, F.; Rotinat, R.; Pappalettere, C.

    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.

  3. Fracture Mechanics and Failure Analysis

    E-print Network

    New South Wales, University of

    and brittle failure mechanisms 12 Cyclic fatigue failure mechanism 13 Stress corrosion cracking and hydrogen fracture, fatigue, stress corrosion cracking, hydrogen embrittlement, fracture criteria in design, fracture assisted crack growth. Assignment2 Linear Elastic Analysis Airy stress function, crack tip stresses, finite

  4. Linear elastic fracture mechanics primer

    NASA Technical Reports Server (NTRS)

    Wilson, Christopher D.

    1992-01-01

    This primer is intended to remove the blackbox perception of fracture mechanics computer software by structural engineers. The fundamental concepts of linear elastic fracture mechanics are presented with emphasis on the practical application of fracture mechanics to real problems. Numerous rules of thumb are provided. Recommended texts for additional reading, and a discussion of the significance of fracture mechanics in structural design are given. Griffith's criterion for crack extension, Irwin's elastic stress field near the crack tip, and the influence of small-scale plasticity are discussed. Common stress intensities factor solutions and methods for determining them are included. Fracture toughness and subcritical crack growth are discussed. The application of fracture mechanics to damage tolerance and fracture control is discussed. Several example problems and a practice set of problems are given.

  5. 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.

  6. Plane elasto-plastic analysis of v-notched plate under bending by boundary integral equation method. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Rzasnicki, W.

    1973-01-01

    A method of solution is presented, which, when applied to the elasto-plastic analysis of plates having a v-notch on one edge and subjected to pure bending, will produce stress and strain fields in much greater detail than presently available. Application of the boundary integral equation method results in two coupled Fredholm-type integral equations, subject to prescribed boundary conditions. These equations are replaced by a system of simultaneous algebraic equations and solved by a successive approximation method employing Prandtl-Reuss incremental plasticity relations. The method is first applied to number of elasto-static problems and the results compared with available solutions. Good agreement is obtained in all cases. The elasto-plastic analysis provides detailed stress and strain distributions for several cases of plates with various notch angles and notch depths. A strain hardening material is assumed and both plane strain and plane stress conditions are considered.

  7. A coupled ductile fracture phase-field model for crystal plasticity

    NASA Astrophysics Data System (ADS)

    Hernandez Padilla, Carlos Alberto; Markert, Bernd

    2015-08-01

    Nowadays crack initiation and evolution play a key role in the design of mechanical components. In the past few decades, several numerical approaches have been developed with the objective to predict these phenomena. The objective of this work is to present a simplified, nonetheless representative phenomenological model to predict the crack evolution of ductile fracture in single crystals. The proposed numerical approach is carried out by merging a conventional elasto-plastic crystal plasticity model and a phase-field model modified to predict ductile fracture. A two-dimensional initial boundary value problem of ductile fracture is introduced considering a single-crystal setup and Nickel-base superalloy material properties. The model is implemented into the finite element context subjected to a quasi-static uniaxial tension test. The results are then qualitatively analyzed and briefly compared to current benchmark results in the literature.

  8. Principles Of Linear Elastic Fracture Mechanics

    NASA Technical Reports Server (NTRS)

    Wilson, Christopher D.

    1994-01-01

    NASA technical memorandum discusses principles of linear elastic fracture mechanics. Emphasis on practical problems; intended especially to help structural engineers understand fracture-mechanics software.

  9. Fatigue crack propagation in a quasi one-dimensional elasto-plastic model

    E-print Network

    Tomás M. Guozden; Eduardo A. Jagla

    2012-06-27

    Fatigue crack advance induced by the application of cyclic quasistatic loads is investigated both numerically and analytically using a lattice spring model. The system has a quasi-one-dimensional geometry, and consists in two symmetrical chains that are pulled apart, thus breaking springs which connect them, and producing the advance of a crack. Quasistatic crack advance occurs as a consequence of the plasticity included in the springs which form the chains, and that implies a history dependent stress-strain curve for each spring. The continuous limit of the model allows a detailed analytical treatment that gives physical insight of the propagation mechanism. This simple model captures key features that cause well known phenomenology in fatigue crack propagation, in particular a Paris-like law of crack advance under cyclic loading, and the overload retardation effect.

  10. 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.

  11. 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.

  12. Modelling the graphite fracture mechanisms

    SciTech Connect

    Jacquemoud, C.; Marie, S.; Nedelec, M.

    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)

  13. Mode 2 fracture mechanics

    NASA Technical Reports Server (NTRS)

    Buzzard, Robert J.; Ghosn, Louis

    1988-01-01

    Current development of high-performance rolling element bearings for aircraft engines (up to 3 million DN, where DN is the product of shaft diameter in millimeters and speed in revolutions per minute) has aroused concern about fatigue crack growth in the inner bearing race that leads to catastrophic failure of the bearing and the engine. A failure sequence was postulated by Srawley, and an analytical program was undertaken to simulate fatigue crack propagation in the inner raceway of such a bearing. A fatigue specimen was developed at NASA by which fatigue data may be obtained relative to the cracking problems. The specimen may be used to obtain either mode 2 data alone or a combination of mixed-mode (1 and 2) data as well and was calibrated in this regard. Mixed-mode fracture data for M-50 bearing steel are presented, and a method for performing reversed-loading tests is described.

  14. Fracture mechanics of cellular glass

    SciTech Connect

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

    1981-02-01

    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.

  15. Fracture mechanics of cellular glass

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

    The fracture mechanics of cellular glasses (for the structural substrate of mirrored glass for solar 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. Previously announced in STAR as N82-11209

  16. 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.

  17. (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.

  18. Mechanical Coal-Face Fracturer

    NASA Technical Reports Server (NTRS)

    Collins, E. R., Jr.

    1984-01-01

    Radial points on proposed drill bit take advantage of natural fracture planes of coal. Radial fracture points retracted during drilling and impacted by piston to fracture coal once drilling halts. Group of bits attached to array of pneumatic drivers to fracture large areas of coal face.

  19. 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.

  20. FINITE FRACTURE MECHANICS OF MATRIX MICROCRACKING IN COMPOSITES

    E-print Network

    Nairn, John A.

    FINITE FRACTURE MECHANICS OF MATRIX MICROCRACKING IN COMPOSITES JOHN A. NAIRN INTRODUCTION damage following complex loading conditions. This chapter describes a fracture mechanics approach to the microcracking problem. A complicating feature of composite fracture mechanics analysis is that laminates often

  1. 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.

  2. Finite element methods in fracture mechanics

    NASA Technical Reports Server (NTRS)

    Liebowitz, H.; Moyer, E. T., Jr.

    1989-01-01

    Finite-element methodology specific to the analysis of fracture mechanics problems is reviewed. Primary emphasis is on the important algorithmic developments which have enhanced the numerical modeling of fracture processes. Methodologies to address elastostatic problems in two and three dimensions, elastodynamic problems, elastoplastic problems, special considerations for three-dimensional nonlinear problems, and the modeling of stable crack growth are reviewed. In addition, the future needs of the fracture community are discussed and open questions are identified.

  3. Fracture mechanisms and fracture control in composite structures

    NASA Astrophysics Data System (ADS)

    Kim, Wone-Chul

    Four basic failure modes--delamination, delamination buckling of composite sandwich panels, first-ply failure in cross-ply laminates, and compression failure--are analyzed using linear elastic fracture mechanics (LEFM) and the J-integral method. Structural failures, including those at the micromechanical level, are investigated with the aid of the models developed, and the critical strains for crack propagation for each mode are obtained. In the structural fracture analyses area, the fracture control schemes for delamination in a composite rib stiffener and delamination buckling in composite sandwich panels subjected to in-plane compression are determined. The critical fracture strains were predicted with the aid of LEFM for delamination and the J-integral method for delamination buckling. The use of toughened matrix systems has been recommended for improved damage tolerant design for delamination crack propagation. An experimental study was conducted to determine the onset of delamination buckling in composite sandwich panel containing flaws. The critical fracture loads computed using the proposed theoretical model and a numerical computational scheme closely followed the experimental measurements made on sandwich panel specimens of graphite/epoxy faceskins and aluminum honeycomb core with varying faceskin thicknesses and core sizes. Micromechanical models of fracture in composites are explored to predict transverse cracking of cross-ply laminates and compression fracture of unidirectional composites. A modified shear lag model which takes into account the important role of interlaminar shear zones between the 0 degree and 90 degree piles in cross-ply laminate is proposed and criteria for transverse cracking have been developed. For compressive failure of unidirectional composites, pre-existing defects play an important role. Using anisotropic elasticity, the stress state around a defect under a remotely applied compressive load is obtained. The experimentally observed complex compressive failure modes, such as shear crippling and pure compressive fiber failure of fibers are explained by the predicted stress distributions calculated in this work. These fracture analyses can be damage tolerant design methodology for composite structures. The proposed fracture criteria and the corresponding critical fracture strains provide the designer with quantitative guidelines for safe-life design. These have been incorporated into a fracture control plan for composite structures, which is also described. Currently, fracture control plans do not exist for composite structures; the proposed plan is a first step towards establishing fracture control and damage tolerant design methodology for this important class of materials.

  4. 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.

  5. Mechanisms for shrinkage fracturing at Meridiani Planum

    NASA Astrophysics Data System (ADS)

    Watters, W. A.; Squyres, S. W.

    2009-12-01

    We investigate the role of water in fracturing at Meridiani Planum with the aim of shedding light on the history of densely-fractured outcroppings of light-toned rocks at low-latitudes on Mars. The fractures that occur throughout the inter-crater plains at Meridiani exhibit many characteristics of shrinkage cracks: they have significant width (i.e., not hairline), commonly connect in 90-degree and 120-degree junctions, and exhibit a "hierarchical" organization: i.e., the longest fractures are widest, and narrower fractures terminate against wider fractures at 90-degree junctions (T-shaped). Using the Pancam and Navcam stereo-pair images acquired by the Opportunity rover, we have measured the geometric scaling of fracture networks at Meridiani (e.g., fracture width vs. fracture separation) as well as the total volume change. We have also characterized the diversity of patterns in detail, as well as the modification of fractures and polygonal "tiles" by wind-blown sand abrasion. Identical observations were carried-out for an analogue site where similar fractures are ubiquitous in the playas of Death Valley, California, and where modification processes are also comparable. By also estimating the expected volume change and results from numerical models of shrinkage fracturing, we evaluate the likelihood of three candidate contraction mechanisms: loss of water bound in hydrated minerals (dehydration), loss of water from pore spaces (desiccation), and contraction from cooling (thermal fracturing). The evidence to date favors the second of these (desiccation); this result would have significant implications for the history of Meridiani since the time when sulfate-rich sediments were deposited.

  6. 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.

  7. A review of fracture mechanics life technology

    NASA Technical Reports Server (NTRS)

    Besuner, P. M.; Harris, D. O.; Thomas, J. M.

    1986-01-01

    Lifetime prediction technology for structural components subjected to cyclic loads is examined. The central objectives of the project are: (1) to report the current state of the art, and (2) recommend future development of fracture mechanics-based analytical tools for modeling subcritical fatigue crack growth in structures. Of special interest is the ability to apply these tools to practical engineering problems and the developmental steps necessary to bring vital technologies to this stage. The authors conducted a survey of published literature and numerous discussions with experts in the field of fracture mechanics life technology. One of the key points made is that fracture mechanics analyses of crack growth often involve consideration of fatigue and fracture under extreme conditions. Therefore, inaccuracies in predicting component lifetime will be dominated by inaccuracies in environment and fatigue crack growth relations, stress intensity factor solutions, and methods used to model given loads and stresses. Suggestions made for reducing these inaccuracies include development of improved models of subcritical crack growth, research efforts aimed at better characterizing residual and assembly stresses that can be introduced during fabrication, and more widespread and uniform use of the best existing methods.

  8. Computational simulation methods for composite fracture mechanics

    NASA Technical Reports Server (NTRS)

    Murthy, Pappu L. N.

    1988-01-01

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

  9. Coupled thermal-hydrological-mechanical analyses of the YuccaMountain Drift Scale Test - Comparison of field measurements topredictions of four different numerical models

    SciTech Connect

    Rutqvist, J.; Barr, D.; Datta, R.; Gens, A.; Millard, A.; Olivella, S.; Tsang, C.-F.; Tsang, Y.

    2004-08-30

    The Yucca Mountain Drift Scale Test (DST) is a multiyear, large-scale underground heater test designed to study coupled thermal-hydrological-mechanical-chemical behavior in unsaturated fractured and welded tuff. As part of the international cooperative code-comparison project DECOVALEX, four research teams used four different numerical models to simulate and predict coupled thermal-hydrological-mechanical (THM) processes at the DST. The simulated processes included above-boiling temperature changes, liquid and vapor water movements, rock-mass stress and displacement, and THM-induced changes in fracture permeability. Model predictions were evaluated by comparison to measurements of temperature, water saturation,displacement, and air permeability. The generally good agreement between simulated and measured THM data shows that adopted continuum model approaches are adequate for simulating relevant coupled THM processes at the DST. Moreover, TM-induced rock-mass deformations were reasonably well predicted using elastic models, although some individual displacements appeared to be better captured using an elasto-plastic model. It is concluded that fracture closure/opening caused by change in normal stress across fractures is the dominant mechanism for TM-induced changes in intrinsic fracture permeability at the DST, whereas fracture shear dilation appears to be less significant. This indicates that TM-induced changes in intrinsic permeability at the DST, which are within one order of magnitude, tend to be reversible.

  10. 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.

  11. Analogy between fluid cavitation and fracture mechanics

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

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

  12. Fracture mechanics parameters for small fatigue cracks

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.

    1992-01-01

    This paper presents a review of some common small-crack test specimens, the underlying causes of the small-crack effect, and the fracture-mechanics parameters that have been used to correlate or predict their growth behavior. This review concentrates on continuum mechanics concepts and on the nonlinear behavior of small cracks. The paper reviews some stress-intensity factor solutions for small-crack test specimens and develops some simple elastic-plastic J integral and cyclic J integral expressions that include the influence of crack-closure. These parameters were applied to small-crack growth data on two aluminum alloys, and a fatigue life prediction methodology is demonstrated. For these materials, the crack-closure transient from the plastic wake was found to be the major factor in causing the small-crack effect.

  13. Numerical simulation of fracture set formation: A fracture mechanics model consistent with experimental observations

    NASA Astrophysics Data System (ADS)

    Renshaw, Carl E.; Pollard, David D.

    1994-05-01

    A physically based model for the evolution of a single set of planar, parallel fractures subject to a constant remote stress is presented. The model simulates the mechanical interaction between fractures using a recently developed approximation technique for stress analysis in elastic solids with many fractures. A comparison between experimental and numerical results shows that the model can accurately simulate the development of experimentally generated fracture sets. Once the flaw geometry is specified, only one parameter controls the geometric evolution of the frature set. This parameter, the velocity exponent, relates fracture propagation velocity to stress concentration at the fracture tip. Monte Carlo sensitivity analyses suggest that this parameter also control the extent to which fracture growth is concentrated within zones or clusters. Similar analyses suggest that the extent of fracture clustering is less sensitive to the flaw density.

  14. Mechanisms for fast flow in unsaturated fractured rock

    SciTech Connect

    Tokunaga, Tetsu K.; Wan, Jiamin

    1998-03-01

    Although fractures in rock are well-recognized as pathways for fast percolation of water, the possibility that fast flow could occur along unsaturated fracture pathways is commonly not considered in vadose zone hydrology. In this study, two mechanisms for fast flow along unsaturated fractures were investigated, film flow and surface zone flow. The importance of fracture surface roughness was demonstrated through experiments conducted on ceramic blocks having simple surface topographies. Those experiments showed that film flow on fracture surfaces is largely due to flow along continuous surface channels which become water-filled at near-zero matric (capillary) potentials. The second mechanism, surface zone flow, is important when the permeability of the rock along fractures (fracture skin) is significantly greater than that of the bulk rock matrix. Surface zone fast flow was demonstrated through water imbibition (sorptivity) experiments. These mechanisms help explain observations of rapid solute transport in unsaturated subsurface environments.

  15. Mechanism of diffusion-controlled brittle fracture

    SciTech Connect

    McMahon, C.J.

    1991-10-01

    Two generation of UHV testing systems were developed, one for testing pre-cracked specimens at constant displacement and the other at constant load, and they were supplemented by a computer-controlled potential-drop system for measurement of crack-growth rates. The latter system was also developed during this project. Experiments were carried out on the alloy Cu-8%Sn which was used as a model system for the phenomenon of diffusion-controlled fracture by intergranular decohesion resulting from the ingress of an embrittling element from a free surface as the result of an applied stress. The cracking phenomenon found earlier in alloy steels, and shown to be due to surface-adsorbed sulfur, was reproduced in the Cu-Sn alloy. This provided verification of the earlier proposed mechanism for the cracking phenomenon in the alloy steels, known as stress-relief cracking, and it also provided support for the hypothesis that the phenomenon was of a generic nature. In conjunction with the experimental work, the development of a quantitative theory of this class of brittle fracture, which we have termed dynamic embrittlement,'' was begun.

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  17. 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

  18. A Fracture-Mechanics-Based Approach to Fracture Control in Biomedical Devices Manufactured From Superelastic Nitinol Tube

    E-print Network

    Ritchie, Robert

    A Fracture-Mechanics-Based Approach to Fracture Control in Biomedical Devices Manufactured From: 10.1002/jbm.b.30840 Abstract: Several key fracture-mechanics parameters associated with the onset of subcritical and critical cracking, specifically the fracture toughness, crack-resistance curve, and fatigue

  19. Breakdown of Continuum Fracture Mechanics at the Nanoscale

    PubMed Central

    Shimada, Takahiro; Ouchi, Kenji; Chihara, Yuu; Kitamura, Takayuki

    2015-01-01

    Materials fail by the nucleation and propagation of a crack, the critical condition of which is quantitatively described by fracture mechanics that uses an intensity of singular stress field characteristically formed near the crack-tip. However, the continuum assumption basing fracture mechanics obscures the prediction of failure of materials at the nanoscale due to discreteness of atoms. Here, we demonstrate the ultimate dimensional limit of fracture mechanics at the nanoscale, where only a small number of atoms are included in a singular field of continuum stress formed near a crack tip. Surprisingly, a singular stress field of only several nanometers still governs fracture as successfully as that at the macroscale, whereas both the stress intensity factor and the energy release rate fail to describe fracture below a critically confined singular field of 2–3?nm, i.e., breakdown of fracture mechanics within the framework of the continuum theory. We further propose an energy-based theory that explicitly accounts for the discrete nature of atoms, and demonstrate that our theory not only successfully describes fracture even below the critical size but also seamlessly connects the atomic to macroscales. It thus provides a more universal fracture criterion, and novel atomistic insights into fracture. PMID:25716684

  20. A mesh-free approach to numerical rock mechanics simulations

    NASA Astrophysics Data System (ADS)

    Jansen, Gunnar; Galvan, Boris; Miller, Stephen

    2014-05-01

    Numerical simulation of the nucleation, growth, and coalescence of fracture networks is a fundamental aspect of lithospheric geodynamics and engineering applications such as enhanced geothermal systems, hydraulic fracturing and CO2 sequestration. Modeling the underlying mechanics is challenging because of several numerical difficulties. In particular, fracture path evolution predicted by mesh-based models can be heavily affected by numerical resolution of the chosen discretization scheme. Additionally, large deformations can lead to numerical errors associated with highly deformed elements. We are developing algorithms that simulate fracture nucleation and growth using mesh-free methods that overcome the difficulties arising from the mesh-sensitivity of conventional mesh-based methods. We implemented a mesh-free local Petrov-Galerkin method (MLPG), which is based on the local weak form of the problem under consideration. This method requires no mesh for interpolation or integration, and thus may be well-suited to handle strain localization occurring during fracture development. Interpolation is performed using moving least squares approximation (MLS) shape functions, and since nodal integration is performed locally, this approach can be parallelized efficiently. We present a mesh-free 2D elasto-plastic model for geomaterials that includes frictional hardening and cohesion softening using the Mohr-Coulomb failure criterion to simulate fracture network evolution and dynamic fracture propagation. Model performance is further enhanced through parallelization by utilising a hybrid CPU/GPU cluster using the PETSc library. We outline the implementation of the developed code, and evaluate its performance from a series of benchmark simulations.

  1. 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.

  2. 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.

  3. To mechanics of deformation, flow, and fracture

    E-print Network

    S. L. Arsenjev

    2008-09-23

    It is stated in the main in essence new approach to mechanics of the stressed state of the solid body from statistically isotropic material and the homogeneous liquid dynamics. The approach essence is in the detected property of the core-shell spontaneous structurization of internal energy of the solid and liquid bodies in its natural state and under action of external forces. The method elements of construction of physically adequate model of the stressed state of the solid and liquid bodies, reproduced exactly its behavior on the stages of elastic and plastic deformation, flow and fracture, are stated. It is adduced a number of the examples of the stressed state construction of the simple form bodies under action of its tension, compression, torsion and at its contact interaction. For the first time it is adduced structure of the principal - normal - stresses in cylindrical bar under action of the torsion moment. The detected property and the developed method is one of necessary bases for construction of physically adequate mathematical model of the stressed state of the body and fluid in contrast to traditional approach.

  4. Integration of NDE Reliability and Fracture Mechanics

    SciTech Connect

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

    1981-03-01

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

  5. Adaptive Finite-Element Computation In Fracture Mechanics

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

    Report discusses recent progress in use of solution-adaptive finite-element computational methods to solve two-dimensional problems in linear elastic fracture mechanics. Method also shown extensible to three-dimensional problems.

  6. A nonlinear high temperature fracture mechanics basis for strainrange partitioning

    NASA Technical Reports Server (NTRS)

    Kitamura, Takayuki; Halford, Gary R.

    1989-01-01

    A direct link was established between Strainrange Partitioning (SRP) and high temperature fracture mechanics by deriving the general SRP inelastic strain range versus cyclic life relationships from high temperature, nonlinear, fracture mechanics considerations. The derived SRP life relationships are in reasonable agreement based on the experience of the SRP behavior of many high temperature alloys. In addition, fracture mechanics has served as a basis for derivation of the Ductility-Normalized SRP life equations, as well as for examination of SRP relations that are applicable to thermal fatigue life prediction. Areas of additional links between nonlinear fracture mechanics and SRP were identified for future exploration. These include effects of multiaxiality as well as low strain, nominally elastic, long life creep fatigue interaction.

  7. Application of fracture mechanics to graphite under complex stress conditions

    NASA Technical Reports Server (NTRS)

    Yahr, G. T.; Valachovic, R. S.

    1974-01-01

    The purpose of this study was to examine the applicability of linear-elastic fracture mechanics to graphite under multiaxial stress conditions. The specimens were thick-walled graphite cylinders with flat heads which were internally pressurized. Two series of specimens were used. The first series had complete circumferential notches machined diagonally into the head-cylinder juncture region, while the second series was unnotched. The methods of linear-elastic fracture mechanics and a finite-element analysis were used to predict pressures to cause fracture for both notched and unnotched specimens.

  8. 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.

  9. Elastic-plastic fracture mechanics of compact bone

    NASA Astrophysics Data System (ADS)

    Yan, Jiahau

    Bone is a composite composed mainly of organics, minerals and water. Most studies on the fracture toughness of bone have been conducted at room temperature. Considering that the body temperature of animals is higher than room temperature, and that bone has a high volumetric percentage of organics (generally, 35--50%), the effect of temperature on fracture toughness of bone should be studied. Single-edged V-shaped notched (SEVN) specimens were prepared to measure the fracture toughness of bovine femur and manatee rib in water at 0, 10, 23, 37 and 50°C. The fracture toughness of bovine femur and manatee rib were found to decrease from 7.0 to 4.3 MPa·m1/2 and from 5.5 to 4.1 MPa·m1/2, respectively, over a temperature range of 50°C. The decreases were attributed to inability of the organics to sustain greater stresses at higher temperatures. We studied the effects of water and organics on fracture toughness of bone using water-free and organics-free SEVN specimens at 23°C. Water-free and organics-free specimens were obtained by placing fresh bone specimen in a furnace at different temperatures. Water and organics significantly affected the fracture toughness of bone. Fracture toughness of the water-free specimens was 44.7% (bovine femur) and 32.4% (manatee rib) less than that of fresh-bone specimens. Fracture toughness of the organics-free specimens was 92.7% (bovine femur) and 91.5% (manatee rib) less than that of fresh bone specimens. Linear Elastic Fracture Mechanics (LEFM) is widely used to study bone. However, bone often has small to moderate scale yielding during testing. We used J integral, an elastic-plastic fracture-mechanics parameter, to study the fracture process of bone. The J integral of bovine femur increased from 6.3 KJ/mm2 at 23°C to 6.7 KJ/mm2 at 37°C. Although the fracture toughness of bovine bone decreases as the temperature increases, the J integral results show a contrary trend. The energy spent in advancing the crack beyond the linear-elastic deformation was much greater than the energy spent in linear-elastic deformation. This could be because bone has at least four toughening mechanisms and a high volumetric percentage of organics (approximately 42% for bovine femur). The J integral is shown to better describe the fracture process of bovine femur and manatee rib.

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

    PubMed Central

    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

  11. Mechanics of dynamic fracture in notched polycarbonate

    NASA Astrophysics Data System (ADS)

    Faye, Anshul; Parmeswaran, Venkitanarayanan; Basu, Sumit

    2015-04-01

    Fracture toughness of brittle amorphous polymers (e.g. polymethyl methacrylate (PMMA)) has been reported to decrease with loading rate at moderate rates and increase abruptly thereafter to close to 5 times the static value at very high loading rates. Dynamic fracture toughness that is much higher than the static values has attractive technological possibilities. However, the reasons for the sharp increase remain unclear. Motivated by these observations, the present work focuses on the dynamic fracture behavior of polycarbonate (PC), which is also an amorphous polymer but unlike PMMA, is ductile at room temperature. Towards this end, a combined experimental and numerical approach is adopted. Dynamic fracture experiments at various loading rates are conducted on single edge notched (SEN) specimens with a notch of radius 150 ?m, using a Hopkinson bar setup equipped with ultra high-speed imaging (>105 fps) for real-time observation of dynamic processes during fracture. Concurrently, 3D dynamic finite element simulations are performed using a well calibrated material model for PC. Experimentally, we were able to clearly capture the intricate details of the process, for both slowly and dynamically loaded samples, of damage nucleation and growth ahead of the notch tip followed by unstable crack propagation. These observations coupled with fractography and computer simulations led us to conclude that in PC, the fracture toughness remains invariant with loading rate at Jfrac = 12 ± 3 kN / m for the entire range of loading rates (J ?) from static to 1 ×106 kN / m - s. However, the damage initiation toughness is significantly higher in dynamic loading compared to static situations. In dynamic situations, damage nucleation is quickly followed by initiation of radial crazes from around the void periphery that initiate and quickly bridge the ligament between the initial damaged region and the notch. Thus for PC, two criteria for two major stages in the failure process emerge. Firstly, a mean stress based defect initiation is suggested. The value of the critical mean stress for defect initiation under dynamic loading is found to be 115±5 MPa, which is significantly higher than its static value of 80 MPa. The critical normal plastic stretch needed for crazes to nucleate from the nucleated defect is estimated to be about 1.78±0.2.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    The initiation and propagation of tensile fractures in snow and ice are fundamental to numerous important physical processes in the cryosphere, from iceberg calving to ice shelf rift propagation to slab avalanche release. The heterogeneous nature of snow and ice, their proximity to the melting temperature, and the varied governing timescales typically lead to nonlinear fracture behavior which does not follow the predictions of Linear Elastic Fracture Mechanics (LEFM). Furthermore, traditional fracture mechanics is formally inapplicable for predicting crack initiation in the absence of a pre-existing flaw or stress concentration. An alternative to fracture mechanics is continuum damage mechanics, which accounts for the material degradation associated with cracking in a numerically efficient framework. However, damage models which are formulated locally (e.g. stress and strain are defined as point properties) suffer from mesh-sensitive crack trajectories, spurious localization of damage and improper fracture energy dissipation with mesh refinement. Nonlocal formulations of damage, which smear the effects of the material heterogeneity over an intrinsic length scale related to the material microstructure, overcome these difficulties and lead to numerically efficient and mesh-objective simulations of the tensile failure of heterogeneous materials. We present the results of numerical simulations of tensile fracture initiation and propagation in cohesive snow using a nonlocal damage model. Seventeen beam bending experiments, both notched and unnotched, were conducted using blocks of cohesive dry snow extracted from an alpine snowpack. Material properties and fracture parameters were calculated from the experimental data using beam theory and quasi-brittle fracture mechanics. Using these parameters, a nonlocal isotropic damage model was applied to two-dimensional finite element meshes of the same scale as the experiments. The model was capable of simulating the propagation of a tensile crack from an existing stress concentration as well as the initiation of a crack from a smooth boundary using the same model parameters and boundary conditions. Sensitivity analyses were conducted on the most uncertain model parameters. For the optimally paramaterized model, the simulated load-displacement curves agreed well with the experimental data, with the primary discrepancy related to the loss of elastic stability following peak load in the experiments. The spatial distribution of strain and damage is shown to support a quasi-brittle interpretation of the fracture physics for both crack initiation and crack propagation problems. These results provide a foundation for future predictive modeling applications related to the tensile fractures which release slab avalanches. We conclude by discussing the applicability of the nonlocal damage approach to a viscous or viscoelastic framework for simulating iceberg calving and the initiation and propagation of ice shelf rifts.

  13. 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.

  14. Fracture mechanics of monolayer molybdenum disulfide.

    PubMed

    Wang, Xiaonan; Tabarraei, Alireza; Spearot, Douglas E

    2015-05-01

    Molecular dynamics (MD) modeling is used to study the fracture toughness and crack propagation path of monolayer molybdenum disulfide (MoS(2)) sheets under mixed modes I and II loading. Sheets with both initial armchair and zigzag cracks are studied. The MD simulations predict that crack edge chirality, tip configuration and the loading phase angle influence the fracture toughness and crack propagation path of monolayer MoS(2) sheets. Furthermore, under all loading conditions, both armchair and zigzag cracks prefer to extend along a zigzag path, which is in agreement with the crack propagation path in graphene. A remarkable out-of-plane buckling can occur during mixed mode loading which can lead to the development of buckling cracks in addition to the propagation of the initial cracks. PMID:25834943

  15. Fracture mechanics of monolayer molybdenum disulfide

    NASA Astrophysics Data System (ADS)

    Wang, Xiaonan; Tabarraei, Alireza; Spearot, Douglas E.

    2015-05-01

    Molecular dynamics (MD) modeling is used to study the fracture toughness and crack propagation path of monolayer molybdenum disulfide (MoS2) sheets under mixed modes I and II loading. Sheets with both initial armchair and zigzag cracks are studied. The MD simulations predict that crack edge chirality, tip configuration and the loading phase angle influence the fracture toughness and crack propagation path of monolayer MoS2 sheets. Furthermore, under all loading conditions, both armchair and zigzag cracks prefer to extend along a zigzag path, which is in agreement with the crack propagation path in graphene. A remarkable out-of-plane buckling can occur during mixed mode loading which can lead to the development of buckling cracks in addition to the propagation of the initial cracks.

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

    SciTech Connect

    Ratigan, J.L.

    1981-06-01

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

  17. 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.

  18. Relating Cohesive Zone Model to Linear Elastic Fracture Mechanics

    NASA Technical Reports Server (NTRS)

    Wang, John T.

    2010-01-01

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

  19. Fracture mechanics life analytical methods verification testing

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

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

    SciTech Connect

    Tanaka, T.; Shimizu, S.; Ogata, Y.

    1997-04-01

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

  1. Measurements of residual stress in fracture mechanics coupons

    SciTech Connect

    Prime, Michael B; Hill, Michael R; Nav Dalen, John E

    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.

  2. Fracture mechanics approach for flip chip BGA design

    NASA Astrophysics Data System (ADS)

    Han, Jiang-Bo

    2000-10-01

    Die cracking and interfacial delamination are of major failure modes in IC packages. To these crack-related problems, design approaches based on traditional strength theories, are inadequate and insufficient. To achieve a more reliable and robust design, a fracture mechanics approach is needed. In this paper, fracture mechanics is applied to flip chip BGA design, assumed that the major potential failure mode is cracking of die from its backside. Fracture mechanics is integrated with the finite element analysis (FEA) and design of virtual experiments to analyze the effects of location and length of a die crack, and the effects of some key material properties and package dimensions on flip chip BGA reliability in terms of die cracking. The stress intensity factor and the strain energy release rate, are used as the design indices. The FEA is used as a numerical tool to calculate the fracture parameters. And the virtual DOE is employed to determine contributions of each design parameters to die cracking and their acceptable design windows. The investigation consists of three parts. The first is relations of length and location of a die crack with the fracture parameters. The relations are established through sweeping along crack length for a crack located in the center of die backside, and along the die backside surface. The critical crack length is determined. The second is the virtual DOE based on fracture mechanics. Several key material properties and cracking are calculated. From it, some generic design guidelines are made. The third part compares the virtual DOE design results between using the maximum normal stress (MNS) theory and using the fracture mechanics approach. The comparison gives a clear picture of the applicable range of the MNS theory. It is concluded that design optimization be a must in order to achieve a robust package design. Substrate and die thicknesses are the two most significant factors to die cracking of flip chip BGA. Increasing substrate thickness and reducing die thickness are the most effective measures to design a package with high resistance to die cracking. The fracture mechanics approach will produce more accurate design result than the MNS theory.

  3. Investigation of the fracture mechanics of boride composites

    NASA Technical Reports Server (NTRS)

    Clougherty, E. V.; Pober, R. L.; Kaufman, L.

    1972-01-01

    Significant results were obtained in fabrication studies of the role of metallic additives of Zr, Ti, Ni, Fe and Cr on the densification of ZrB2. All elemental additions lower the processing temperatures required to effect full densification of ZrB2. Each addition effects enhanced densification by a clearly distinguishable and different mechanism and the resulting fabricated materials are different. A significant improvement in strength and fracture toughness was obtained for the ZrB2/Ti composition. Mechanical characterization studies for the ZrB2/SiC/C composites and the new ZrB2/Metal materials produced data relevant to the effect of impacting load on measured impact energies, a specimen configuration for which controlled fracture could occur in a suitably hard testing apparatus, and fracture strength data. Controlled fracture--indicative of measurable fracture toughness--was obtained for the ZrB2-SiC-C composite, and a ZrB2/Ti composite fabricated from ZrB2 with an addition of 30 weight per cent Ti. The increased strength and toughness of the ZrB2/Ti composite is consistent with the presence of a significantly large amount of a fine grained acicular phase formed by reaction of Ti with ZrB2 during processing.

  4. 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.

  5. Hydraulic fracture extending into network in shale: reviewing influence factors and their mechanism.

    PubMed

    Ren, Lan; Zhao, Jinzhou; Hu, Yongquan

    2014-01-01

    Hydraulic fracture in shale reservoir presents complex network propagation, which has essential difference with traditional plane biwing fracture at forming mechanism. Based on the research results of experiments, field fracturing practice, theory analysis, and numerical simulation, the influence factors and their mechanism of hydraulic fracture extending into network in shale have been systematically analyzed and discussed. Research results show that the fracture propagation in shale reservoir is influenced by the geological and the engineering factors, which includes rock mineral composition, rock mechanical properties, horizontal stress field, natural fractures, treating net pressure, fracturing fluid viscosity, and fracturing scale. This study has important theoretical value and practical significance to understand fracture network propagation mechanism in shale reservoir and contributes to improving the science and efficiency of shale reservoir fracturing design. PMID:25032240

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

    PubMed Central

    Ren, Lan; Zhao, Jinzhou; Hu, Yongquan

    2014-01-01

    Hydraulic fracture in shale reservoir presents complex network propagation, which has essential difference with traditional plane biwing fracture at forming mechanism. Based on the research results of experiments, field fracturing practice, theory analysis, and numerical simulation, the influence factors and their mechanism of hydraulic fracture extending into network in shale have been systematically analyzed and discussed. Research results show that the fracture propagation in shale reservoir is influenced by the geological and the engineering factors, which includes rock mineral composition, rock mechanical properties, horizontal stress field, natural fractures, treating net pressure, fracturing fluid viscosity, and fracturing scale. This study has important theoretical value and practical significance to understand fracture network propagation mechanism in shale reservoir and contributes to improving the science and efficiency of shale reservoir fracturing design. PMID:25032240

  7. 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.

  8. 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.

  9. Fracture mechanics analysis of composite microcracking - Experimental results in fatigue

    NASA Technical Reports Server (NTRS)

    Nairn, J. A.; Liu, S.

    1990-01-01

    The Nairn (1989) variational mechanics analysis, which yields the energy release rate of a microcrack's formation between two existing microcracks, has proven useful in the fracture mechanics interpretation of cross-ply laminates' microcracking. Attention is presently given to the application of this energy release rate analysis to a fracture mechanics-based interpretation of microcrack formation during fatigue loading, for the case of fatigue experiments on three layups of Avimid K/IM6 laminates and four layups of Fiberite 934/T300 laminates. The single master Paris-law plot onto which the data from all layups of a given material system fall is claimed to offer a complete characterization of that system's microcrack-formation resistance during fatigue loading.

  10. Deformation and fracture of Macadamia nuts Part 2: Microstructure and fracture mechanics analysis of nutshell

    NASA Astrophysics Data System (ADS)

    Wang, Chun-Hui; Mai, Yiu-Wing

    A study of the microstructure and mechanical properties of Macadamia nutshells subjected to various heat treatments is given in Part 2 of this paper. It is found that the nutshell has a three-dimensional, close-packed, cell structure. The cells have a diameter to length ratio of about 1 to 3, and the orientation of the cells is reasonably isotropic with no apparent variation with either position or direction. The material behaves in a very brittle manner under tension and compression. Based on the elastic stress analysis of a nut under diametrical compression and the mechanical properties of the shell, it is shown that cracks that cause the final fracture are initiated from the inner surface beneath the loading point. A theoretical model is proposed and predictions of the fracture load for Macadamia nuts are in good agreement with experimental results.

  11. 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).

  12. Mechanical properties and fracture dynamics of silicene membranes.

    PubMed

    Botari, T; Perim, E; Autreto, P A S; van Duin, A C T; Paupitz, R; Galvao, D S

    2014-09-28

    As graphene has become one of the most important materials, there is renewed interest in other similar structures. One example is silicene, the silicon analogue of graphene. It shares some of the remarkable graphene properties, such as the Dirac cone, but presents some distinct ones, such as a pronounced structural buckling. We have investigated, through density functional based tight-binding (DFTB), as well as reactive molecular dynamics (using ReaxFF), the mechanical properties of suspended single-layer silicene. We calculated the elastic constants, analyzed the fracture patterns and edge reconstructions. We also addressed the stress distributions, unbuckling mechanisms and the fracture dependence on the temperature. We analysed the differences due to distinct edge morphologies, namely zigzag and armchair. PMID:25102369

  13. 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.

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

    SciTech Connect

    Wilkowski, G.M.; Olson, R.J.; Scott, P.M.

    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.

  15. Epidemiology and mechanisms of femur fractures in children.

    PubMed

    Loder, Randall T; O'Donnell, Patrick W; Feinberg, Judy R

    2006-01-01

    The most common pediatric orthopaedic injury requiring hospitalization is a femur fracture. This study aimed to identify the epidemiology and mechanisms of injury so that these injuries might be reduced through specifically targeted safety measures. Data for this study were culled from the 2000 Kids' Inpatient Database representing over 2.5 million pediatric hospital discharges. Of the nearly 10,000 femur fractures, 1076 (11%) occurred in children younger than 2 years; 2119 (21%) in children aged 2 to 5 years; 3237 (33%) in children aged 6 to 12 years; and 3528 (35%) in adolescents aged 13 to 18 years. The most (71%) occurred in male patients. Falls and motor vehicle collisions accounted for two thirds of those injuries, with the incidence of falls greater in the younger children and motor vehicle collisions more prevalent in older children. Fifteen percent of femoral fractures in children younger than 2 years were because of child abuse. Length of hospital stay, number of diagnoses and procedures, and hospital charges were greatest in the adolescent age group, likely because of high-energy trauma with resultant polytrauma. Hospital charges were more than 222 million dollars with the average charge over 2.5 times that in adolescents compared with infants/toddlers. Pediatric orthopaedists must continue to press for increased safety for our children, particularly adolescent motor vehicle safety. Abuse should be considered when a child younger than 2 years presents with a femoral fracture. PMID:16932091

  16. A field theory of distortion incompatibility for coupled fracture and plasticity

    NASA Astrophysics Data System (ADS)

    Fressengeas, Claude; Taupin, Vincent

    2014-08-01

    The displacement discontinuity arising between the crack surfaces is assigned to smooth areal/tensorial densities of crystal defects referred to as disconnections, through the incompatibility of the continuous distortion tensor. In a dual way, the disconnections are defined as line defects terminating surfaces where the displacement encounters a discontinuity. A conservation argument for their strength (the crack opening displacement) provides a natural framework for their dynamics in the form of a transport law for the disconnection densities. Similar methodology is applied to the discontinuity of the plastic displacement arising from the presence of dislocations in the body, which results in the concurrent involvement of the dislocation density tensor in the analysis. The present model can therefore be viewed as an extension of the mechanics of dislocation fields to the case where continuity of the body is disrupted by cracks. From the continuity of the elastic distortion tensor, it is expected that the stress field remains bounded everywhere in the body, including at the crack tip. Thermodynamic arguments provide the driving forces for disconnection and dislocation motion, and guidance for the formulation of constitutive relationships insuring non-negative dissipation. The conventional Peach-Koehler force on dislocations is retrieved in the analysis, and a Peach-Koehler-type force on disconnections is defined. A threshold in the disconnection driving force vs. disconnection velocity constitutive relationship provides for a Griffith-type fracture criterion. Application of the theory to the slit-crack (Griffith-Inglis crack) in elastic and elasto-plastic solids through finite element modeling shows that it allows recovering earlier results on the stress field around cracks, and that crack propagation can be consistently described by the transport scheme. Shielding/anti-shielding of cracks by dislocations is considered to illustrate the static/dynamic interactions between dislocations and disconnections resulting from the theory. Sample size effects on crack growth are evidenced in solids encountering plastic yielding.

  17. Mechanical and fracture behavior of calcium phosphate cements

    NASA Astrophysics Data System (ADS)

    Jew, Victoria Chou

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

  18. [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

  19. Mechanics and fracture of hybrid material interface bond

    NASA Astrophysics Data System (ADS)

    Wang, Jialai

    Considering current and future applications of hybrid materials and structures in civil engineering, the strength and durability of interface bond between the conventional materials and composites are critical to development of such products. Conventional methods mostly used for analysis of isotropic materials may not be well suitable or accurate enough for a system made of anisotropic materials with relatively low shear stiffness. A need exists for developing more accurate and explicit analytical solutions for hybrid material interface analysis and related novel experimental characterization techniques. In this study, a combined analytical and experimental approach to characterize hybrid material interface bond is developed. Using a shear deformable plate theory and an elastic interface model, a mechanics approach for interface analysis of hybrid material bond under general loading is first proposed. The resulting closed-form solution of interface stress distribution is used to compute strain energy release rate (SERB) and stress intensity factor (SIF) of the interface with or without adhesive bond. This approach is then extended to delamination of composite structures under generic loading conditions. Second, novel experimental approaches for characterization of hybrid material bonded interfaces are presented. To account for the crack tip deformations, a tapered beam on elastic foundation (TBEF) is developed. Based on the TBEF model, analysis and design of two novel fracture specimens, Tapered Double Cantilever Beam (TDCB) and Tapered End Notched Flexure (TENF), are proposed, and they are effectively used in fracture toughness tests of bonded interface under Mode-I and Mode-II loadings, respectively. A constant compliance rate change over certain crack length range is achieved for the TDCB and TENF specimens, and it alleviates the necessity of experimental compliance calibration tests. The fracture toughness data obtained from the experiments are useful to predict potential crack growth of adhesively bonded joints. In summary, a comprehensive study of mechanics and fracture of hybrid material interface bond is presented. The shear deformable-based mechanics and fracture model developed can be effectively and accurately used to predict the SERR and SIF of hybrid material interface bond, and the analysis and design of novel TDCB and TENF specimens provide useful and efficient techniques to experimentally characterize the hybrid material bonded interfaces.

  20. Mechanical Properties and Fracture Analysis of Mn-rich Ni-Mn-Ga Polycrystalline Alloys

    E-print Network

    Zheng, Yufeng

    Mechanical Properties and Fracture Analysis of Mn-rich Ni-Mn-Ga Polycrystalline Alloys Feng Chen1 memory alloy, mechanical properties, fracture mechanism, intergranular crack Abstract. In present paper, the mechanical properties and fracturegraphs of Mn-rich polycrystalline alloys are investigated by compression

  1. Variational fracture mechanics The fracture pattern in stressed bodies is defined through the minimization of a two-field pseudo-spatial-

    E-print Network

    Segatti, Antonio

    Variational fracture mechanics The fracture pattern in stressed bodies is defined through-deviatoric and masonry-like fractures. Remarkably, this latter formulation rigorously avoid material overlapping., Francfort, G. A. and J. J. Marigo, Numerical experiments in revisited brittle fracture. J. Mech. Phys

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

    PubMed

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

    2015-09-23

    In both research and industry, materials will be exposed to stresses, be it during fabrication, normal use, or mechanical failure. The response to external stress will have an important impact on properties, especially when atomic details govern the functionalities of the materials. This review aims at summarizing current research involving the responses of graphene and graphene materials to applied stress at the nanoscale, and to categorize them by stress-strain behavior. In particular, we consider the reversible functionalization of graphene and graphene materials by way of elastic deformation and strain engineering, the plastic deformation of graphene oxide and the emergence of such in normally brittle graphene, the formation of defects as a response to stress under high temperature annealing or irradiation conditions, and the properties that affect how, and mechanisms by which, pristine, defective, and polycrystalline graphene fail catastrophically during fracture. Overall we find that there is significant potential for the use of existing knowledge, especially that of strain engineering, as well as potential for additional research into the fracture mechanics of polycrystalline graphene and device functionalization by way of controllable plastic deformation of graphene. PMID:26325114

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  4. Probabilistic/Fracture-Mechanics Model For Service Life

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  5. Fracture mechanics analyses for skin-stiffener debonding

    NASA Technical Reports Server (NTRS)

    Raju, I. S.; Sistla, R.; Krishnamurthy, T.; Lotts, C. G.

    1993-01-01

    The debond configurations presently subjected to 3D FEM fracture mechanics analyses are respectively of the flange-skin strip and skin-stiffener configuration type. Two methods employing the virtual crack closure technique were used to evaluate the strain energy release rate, or 'G-value' distributions across the debond front. Both methods yielded nearly identical G-value distributions for the debond configurations studied; they were compared with plane strain and shell analyses results from the literature for the flange skin strip configuration, and found to be in good agreement. Mode II is dominant for the skin-stiffener debond configuration.

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

    SciTech Connect

    Gray, L.J.

    1990-11-09

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

  7. The fracture mechanics of human bone: influence of disease and treatment

    E-print Network

    Ritchie, Robert

    REVIEW The fracture mechanics of human bone: influence of disease and treatment Elizabeth of California, Berkeley, CA, USA. Aging and bone diseases are associated with increased fracture risk conditions such as aging and disease can significantly increase fracture risk. In simple terms, the reduced

  8. Mechanical Properties and Fracture Behavior of Nanoporous Au

    SciTech Connect

    Biener, J; Hodge, A M; Wang, Y M; Hayes, J R; Hamza, A V

    2005-06-16

    Nanoporous metals have recently attracted considerable interest fueled by potential sensor and actuator applications. From a material science point of view, one of the key issues in this context is the synthesis of nanoporous metals with both high tensile and compressive strength. Nanoporous gold (np-Au) has been suggested as a candidate material for this application due to its monolithic character. The material can be synthesized by electrochemically-driven dealloying of Ag-Au alloys, and exhibits an open sponge-like structure of interconnecting ligaments with a typical pore size distribution on the nanometer length scale. However, besides the observation of a ductile-brittle transition very little is known about the mechanical behavior of this material. Here, we present our results regarding the mechanical properties and the fracture behavior of np-Au. Depth-sensing nanoindentation reveals that the yield strength of np-Au is almost one order of magnitude higher than the value predicted by scaling laws developed for macroscopic open-cell foams. The unexpectedly high value of the yield strength indicates the presence of a distinct size effect of the mechanical properties due to the sub-micron dimensions of the ligaments, thus potentially opening a door to a new class of high yield strength--low density materials. The failure mechanism of np-Au under tensile stress was evaluated by microscopic examination of fracture surfaces using scanning electron microscopy. On a macroscopic level, np-Au is a very brittle material. However, microscopically np-Au is very ductile as ligaments strained by as much as 200% can be observed in the vicinity of crack tips. Cell-size effects on the microscopic failure mechanism were studied by annealing experiments whereby increasing the typical pore size/ligament diameter from {approx}100 nm to {approx}1{micro}m.

  9. 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.

  10. 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.

  11. Fundamental mechanisms of tensile fracture in aluminum sheet undirectionally reinforced with boron filament

    NASA Technical Reports Server (NTRS)

    Herring, H. W.

    1972-01-01

    Results are presented from an experimental study of the tensile-fracture process in aluminum sheet unidirectionally reinforced with boron filament. The tensile strength of the material is severely limited by a noncumulative fracture mechanism which involves the initiation and sustenance of a chain reaction of filament fractures at a relatively low stress level. Matrix fracture follows in a completely ductile manner. The minimum filament stress for initiation of the fracture mechanism is shown to be approximately 1.17 GN/sq m (170 ksi), and appears to be independent of filament diameter, number of filament layers, and the strength of the filament-matrix bond. All the commonly observed features of tensile fracture surfaces are explained in terms of the observed noncumulative fracture mechanism.

  12. Fracture Mechanics Modelling of an In Situ Concrete Spalling Experiment

    NASA Astrophysics Data System (ADS)

    Siren, Topias; Uotinen, Lauri; Rinne, Mikael; Shen, Baotang

    2015-07-01

    During the operation of nuclear waste disposal facilities, some sprayed concrete reinforced underground spaces will be in use for approximately 100 years. During this time of use, the local stress regime will be altered by the radioactive decay heat. The change in the stress state will impose high demands on sprayed concrete, as it may suffer stress damage or lose its adhesion to the rock surface. It is also unclear what kind of support pressure the sprayed concrete layer will apply to the rock. To investigate this, an in situ experiment is planned in the ONKALO underground rock characterization facility at Olkiluoto, Finland. A vertical experimental hole will be concreted, and the surrounding rock mass will be instrumented with heat sources, in order to simulate an increase in the surrounding stress field. The experiment is instrumented with an acoustic emission system for the observation of rock failure and temperature, as well as strain gauges to observe the thermo-mechanical interactive behaviour of the concrete and rock at several levels, in both rock and concrete. A thermo-mechanical fracture mechanics study is necessary for the prediction of the damage before the experiment, in order to plan the experiment and instrumentation, and for generating a proper prediction/outcome study due to the special nature of the in situ experiment. The prediction of acoustic emission patterns is made by Fracod 2D and the model later compared to the actual observed acoustic emissions. The fracture mechanics model will be compared to a COMSOL Multiphysics 3D model to study the geometrical effects along the hole axis.

  13. Microstructure evolution and mechanical behavior of bulk copper obtained by consolidation of micro- and nanopowders using equal-channel angular extrusion

    NASA Astrophysics Data System (ADS)

    Haouaoui, M.; Karaman, I.; Harwig, K. T.; Maier, H. J.

    2004-09-01

    The consolidation of copper micro- and nanoparticles (325 mesh, 130 nm, and 100 nm) was performed using room-temperature equal-channel angular extrusion (ECAE). The effects of extrusion route, number of passes, and extrusion rate on consolidation performance were evaluated. The evolution of the microstructure and the mechanical behavior of the consolidates were investigated and related to the processing route. Possible deformation mechanisms are proposed and compared to those in ECAE-processed bulk Cu. A combined high ultimate tensile stress (470 MPa) and ductility (˜20 pct tensile fracture strain) with near-elasto-plastic behavior was observed in consolidated 325-mesh Cu powder. On the other hand, early plastic instability took place, leading to a continuous softening in flow stress of bulk ECAE-processed copper. Increases in both strength and ductility were evident with an increasing number of passes in the bulk samples, which appears to be inconsistent with grain-boundary-moderated deformation mechanisms for a microstructure with an average grain size of 300 to 500 nm. Instead, this increase is attributed to microstructural refinement and to dynamic recovery and bimodal grain-size distribution. Near-perfect elastoplasticity in consolidated 325-mesh Cu powder is explained by a combined effect of strain hardening accommodated by large grains in the bimodal structure and softening caused by recovery mechanisms. Compressive strengths as high as 760 MPa were achieved in consolidated 130-nm copper powder. Although premature failure occurred during tensile loading in 130-nm consolidated powder, the fracture strength was still about 730 MPa. The present study shows that ECAE consolidation of nanoparticles opens a new possibility for the study of mechanical behavior of bulk nanocrystalline (NC) materials, as well as offering a new class of bulk materials for practical engineering applications.

  14. Fracture and mechanical stratigraphy for Mississippian-Pennsylvanian age carbonates, Ozark Dome, NW Arkansas

    NASA Astrophysics Data System (ADS)

    Peppers, M.; Burberry, C. M.

    2014-12-01

    Identifying natural fracture patterns in an area gives a detailed look into the local tectonic history. Comparing those fractures to the mechanical properties of the rocks provides key insights into predicting fractures in the subsurface. The Ozark Dome is an ideal study area for fracture research due to multiple fracturing events resulting from the multi-stage deformation Ouachita Orogeny during the late Paleozoic. This study used field observations of lithology and fracture attributes over ~10 outcrops in the Mississppian-Pennsylvanian (360-298 ma) carbonate sequence of the Ozark Plateau. Outcrops were chosen having excellent lithological exposure up the sequence from the Boone to Atoka formations and with 3D representations of the fracture patterns. In all, the area investigated covered nearly 60 square miles. Fracture attributes collected included fracture intensity, length, and abutting relationships; and rock hardness data collected from a Schmidt Hammer. Data was analyzed using programs such as Stereonet and MOVE structural software that generated rose diagrams, structural cross sections, and products. Initial results indicate 4 main fracture orientations that resulted from at least 3 discrete phases of deformation during the Miss-Penn. Initial results also indicate that the present-day mechanical stratigraphy is not the same one that existed during the deformation phases. Work done at the Tiger Blvd. outcrops showed at least 2 distinct mechanical units. Fractures observed at the outcrop did not respect mechanical bed boundaries, and showed no relationship to the differences in mechanical properties observed. This study will aid in the interpretation of fractures in regards to mechanical stratigraphy, which allows for a better understanding of subsurface fracture prediction in carbonate sequences worldwide. Finally, the fracture work here will also help in elucidating the tectonic history of the field area during the Mississippian and Pennsylvanian.

  15. Fracture of laminates: A computational damage mechanics approach

    SciTech Connect

    Allix, O.; Gornet, L.; Hochard, C.; Ladeveze, P.

    1995-12-31

    The present study describes the basic principles of a general damage computational approach for laminates and shows its prediction possibilities for simulating the complete fracture phenomenon in different cases involving both inner-ply damage mechanisms and delamination. Damage refers to the more and less gradual development of microvoids and microcracks which lead to macrocracks and then to rupture. Brittle and progressive damage mechanisms are both present. In composite structures, it may be the main mechanical phenomenon. For such materials, damage is generally of a highly complex nature. There are not a single but several damage mechanisms. For example, inside of classical carbon-fiber laminates the main damage mechanisms are: fiber breaking: transverse micro-cracking: the debonding of adjacent layer (i.e. delamination). In order to predict the state of deterioration, it is now usual to use models with internal damage variables. This classical framework is insufficient to properly describe the deterioration of structures and has led to many difficulties such as mesh-dependency. In fact, a key-point is to define the scale at which the damage mechanisms are described. In the case of composite, a pragmatic and efficient method is to describe the material, especially the damage mechanisms, on an intermediate and preferential scale called a {open_quotes}meso-scale{close_quotes}. To get a mesomodel, one has to add one more property: the {open_quotes}meso{close_quotes} damage state is locally uniform within each elementary constituent. Then, for laminates, the damage state is taken uniform in the thickness of the elementary ply. So a mesomodeling is not scale invariant as in the classical models in continuum mechanics. In the case of laminates, to avoid all spurious behaviour, one also models delay damage which ensures another physical property: the damage rate is bounded.

  16. 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.

  17. 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.

  18. 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.

  19. Fracture mechanics; Proceedings of the Seventeenth National Symposium, Albany, NY, August 7-9, 1984

    NASA Technical Reports Server (NTRS)

    Underwood, J. M. (editor); Chait, R. (editor); Smith, C. W. (editor); Wilhem, D. P. (editor); Andrews, W. A. (editor); Newman, J. C. (editor)

    1986-01-01

    The present conference gives attention to topics in the application of fracture mechanics, subcritical crack growth phenomena, fracture testing methods, ductile fracture behavior, and fracture mechanisms and their analysis. Specific papers treat the resistance curve approach to composite materials characterization, fracture toughness in ductile iron and cast steel, hold-time effects in elevated temperature fatigue crack propagation, creep crack growth under nonsteady conditions, viscoplastic fatigue in a superalloy at elevated temperatures, fracture testing with arc bend specimens, one-point bend impact test application, and a compact mode II fracture specimen. Also discussed are the computation of stable crack growth using the J-integral, the use of plastic energy dissipation to characterize crack growth, the extension of surface cracks under cyclic loading, the minimum time criterion for crack instability in structural materials, dynamic crack propagation and branching under biaxial loading, and boundary layer effects in cracked bodies.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  1. The importance of mechanics in the pathogenesis of fragility fractures of the femur and vertebrae

    PubMed Central

    Nardi, Alfredo; Ventura, Lorenzo; Rossini, Maurizio; Ramazzina, Emilio

    2010-01-01

    This review highlights the role played by mechanical imbalances in the pathogenesis of fragility fractures of the femur and vertebrae. Particular attention is paid to vertebral fractures, and the consequences arising from mechanical imbalances are analyzed and evaluated to determine how much they contribute to worsening vertebral deformity and creating a domino effect. PMID:22460018

  2. 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 ...

  3. 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. A 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.

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

    NASA Technical Reports Server (NTRS)

    Naik, Rajiv A.; Crews, John H., Jr.

    1992-01-01

    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, theory avoiding fractional effects. A 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.

  5. 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.

  6. 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.

  7. Numerical Assessment of the Progressive Rock Fracture Mechanism of Cracked Chevron Notched Brazilian Disc Specimens

    NASA Astrophysics Data System (ADS)

    Dai, F.; Wei, M. D.; Xu, N. W.; Ma, Y.; Yang, D. S.

    2015-03-01

    The International Society of Rock Mechanics (ISRM) suggested cracked chevron notched Brazilian disc method falls into a major testing category of rock fracture toughness measurement by virtue of chevron notched rock samples. A straight through crack front during the whole fracturing process is assumed in the testing principle but is never assessed. In this study, the progressive rock fracture mechanism of cracked chevron notched Brazilian disc rock specimens is numerically simulated for the first time. Two representative sample types with distinct geometry of notch ligaments are modelled. The assumption of a straight through crack front for chevron notched fracture samples is critically assessed. The results show that not only the notch tip but also the saw-cut chevron notch cracks during the experiments. The straight through crack front assumption is never satisfied in the realistic rock fracture progress of chevron notched disc samples. In addition, the crack features prominent curved front, far from being straight. In contrast to the sample type with narrow notch ligament, the acoustic emission (AE) of the simulation on the sample with wide notch ligament depicts obvious biased fracturing of the prescript fracturing route of the notch. The numerically observed progressive fracture mechanism calls for more attention on how to accurately calibrate the critical dimensionless stress intensity factor for a better measurement of Mode I fracture toughness via chevron notched samples.

  8. Mechanics of fracture under high-rate stress loading

    SciTech Connect

    Grady, D.

    1983-01-01

    The fracture properties of brittle materials subjected to impulsive or high rate loading is considered. Fracture is viewed as a microstructural process through the activation, growth and coalescence of a system of interacting cracks. The loading rate dependence of fracture stress is explained in terms of inertia of isolated cracks. The number of cracks participating in the fracture process, and the number and size of fragments in the failed material are related to both the inherent flaw structure and the rate of energy application required to sustain the system of growing cracks. Differences in loading conditions leading to material failure can result in vastly different fragment size distributions. These differences are compared with physically based statistical laws and possible relations to the loading conditions are explored. Lastly, continuum modelling of dynamic fracture focused toward computational analyses of complex applied problems is covered.

  9. 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.

  10. 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.

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

    SciTech Connect

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

    2009-02-01

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

  12. Quantitative safety analysis using fracture mechanics and ultrasonic stress measurements

    NASA Astrophysics Data System (ADS)

    Clark, Al V.; Anderson, Ted L.; Lozev, Margarit G.; Fuchs, P. A.

    1996-11-01

    Fracture mechanics can be applied to assess the safety of cracked bridge members. If crack length and stresses are known, the crack driving force (stress intensity factor, K) can be calculated. K was calculated for hot-rolled beams, as a function of crack length. K eventually becomes negative, indicating not further crack propagation. However a cracked girder will become compliant and 'shed' load to uncracked neighboring members. Our calculations show that the changes in both compliance and load-carrying capacity of the cracked girder are small until the girder is deeply cracked. A finite-element analysis of a cracked girder showed that by determining the bending stresses at about one beam depth from the crack it is possible to determine K. Measurement of these stresses was simulated in a field test. The method used small changes in sound speed to determine stress. The ultrasonic transducers used required no couplants and no surface preparation. They were also used to measure stresses in an integral backwall bridge.

  13. 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.

  14. Probalistic Finite Elements (PFEM) structural dynamics and fracture mechanics

    NASA Technical Reports Server (NTRS)

    Liu, Wing-Kam; Belytschko, Ted; Mani, A.; Besterfield, G.

    1989-01-01

    The purpose of this work is to develop computationally efficient methodologies for assessing the effects of randomness in loads, material properties, and other aspects of a problem by a finite element analysis. The resulting group of methods is called probabilistic finite elements (PFEM). The overall objective of this work is to develop methodologies whereby the lifetime of a component can be predicted, accounting for the variability in the material and geometry of the component, the loads, and other aspects of the environment; and the range of response expected in a particular scenario can be presented to the analyst in addition to the response itself. Emphasis has been placed on methods which are not statistical in character; that is, they do not involve Monte Carlo simulations. The reason for this choice of direction is that Monte Carlo simulations of complex nonlinear response require a tremendous amount of computation. The focus of efforts so far has been on nonlinear structural dynamics. However, in the continuation of this project, emphasis will be shifted to probabilistic fracture mechanics so that the effect of randomness in crack geometry and material properties can be studied interactively with the effect of random load and environment.

  15. THE COMPUTATION OF BOUNDS FOR THE EXACT ENERGY RELEASE RATES IN LINEAR FRACTURE MECHANICS

    E-print Network

    Peraire, Jaime

    of brittle fracture, fatigue, stress corrosion cracking, and to some extend for creep crack growth. Since equation. Introduction The accurate prediction of stress intensity factors in crack tips is essential for assessing the strength and life of structures using linear fracture mechanics theories. A crack is assumed

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

    PubMed

    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

  17. Understanding cracking failures of coatings: A fracture mechanics approach

    NASA Astrophysics Data System (ADS)

    Kim, Sung-Ryong

    A fracture mechanics analysis of coating (paint) cracking was developed. A strain energy release rate (G(sub c)) expression due to the formation of a new crack in a coating was derived for bending and tension loadings in terms of the moduli, thicknesses, Poisson's ratios, load, residual strain, etc. Four-point bending and instrumented impact tests were used to determine the in-situ fracture toughness of coatings as functions of increasing baking (drying) time. The system used was a thin coating layer on a thick substrate layer. The substrates included steel, aluminum, polycarbonate, acrylonitrile-butadiene-styrene (ABS), and Noryl. The coatings included newly developed automotive paints. The four-point bending configuration promoted nice transversed multiple coating cracks on both steel and polymeric substrates. The crosslinked type automotive coatings on steel substrates showed big cracks without microcracks. When theoretical predictions for energy release rate were compared to experimental data for coating/steel substrate samples with multiple cracking, the agreement was good. Crosslinked type coatings on polymeric substrates showed more cracks than theory predicted and the G(sub c)'s were high. Solvent evaporation type coatings on polymeric substrates showed clean multiple cracking and the G(sub c)'s were higher than those obtained by tension analysis of tension experiments with the same substrates. All the polymeric samples showed surface embrittlement after long baking times using four-point bending tests. The most apparent surface embrittlement was observed in the acrylonitrile-butadiene-styrene (ABS) substrate system. The impact properties of coatings as a function of baking time were also investigated. These experiments were performed using an instrumented impact tester. There was a rapid decrease in G(sub c) at short baking times and convergence to a constant value at long baking times. The surface embrittlement conditions and an embrittlement toughness were found upon impact loading. This analysis provides a basis for a quantitative approach to measuring coating toughness.

  18. 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.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

    Duchkov, A. A.; Stefanov, Yu. P.

    2015-10-01

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

  1. Mechanical properties of bioactive glass (13-93) scaffolds fabricated by robotic deposition for structural bone repair

    PubMed Central

    Liu, Xin; Rahaman, Mohamed N.; Hilmas, Gregory E.; Bal, B. Sonny

    2013-01-01

    There is a need to develop synthetic scaffolds for repairing large defects in load-bearing bones. Bioactive glasses have attractive properties as a scaffold material for bone repair, but data on their mechanical properties are limited. The objective of the present study was to comprehensively evaluate the mechanical properties of strong porous scaffolds of silicate 13-93 bioactive glass fabricated by robocasting. As-fabricated scaffolds with a grid-like microstructure (porosity = 47%; filament diameter = 330 ?m; pore width = 300) were tested in compressive and flexural loading to determine their strength, elastic modulus, Weibull modulus, fatigue resistance, and fracture toughness. Scaffolds were also tested in compression after they were immersed in simulated body fluid (SBF) in vitro or implanted in a rat subcutaneous model in vivo. As fabricated, the scaffolds had a strength = 86 ± 9 MPa, elastic modulus = 13 ± 2 GPa, and a Weibull modulus = 12 when tested in compression. In flexural loading, the strength, elastic modulus, and Weibull modulus were 11 ± 3 MPa, 13 ± 2 GPa, and 6, respectively. In compression, the as-fabricated scaffolds had a mean fatigue life of ~106 cycles when tested in air at room temperature or in phosphate-buffered saline at 37 °C under cyclic stresses of 1–10 MPa or 2–20 MPa. The compressive strength of the scaffolds decreased markedly during the first 2 weeks of immersion in SBF or implantation in vivo, but more slowly thereafter. The brittle mechanical response of the scaffolds in vitro changed to an elasto-plastic response after implantation for longer than 2–4 weeks in vivo. In addition to providing critically needed data for designing bioactive glass scaffolds, the results are promising for the application of these strong porous scaffolds in loaded bone repair. PMID:23438862

  2. Comparative mechanical properties of various Kirschner wire configurations in transverse and oblique phalangeal fractures.

    PubMed

    Viegas, S F; Ferren, E L; Self, J; Tencer, A F

    1988-03-01

    A biomechanical study assessed the comparative mechanical properties of various wire configurations used in transverse and oblique phalangeal fractures. The configurations included crossed, oblique, and intramedullary wire techniques using 0.028-inch diameter (d) or 0.035-inch d Kirschner (K) wires. Six different configurations were tested in both the oblique fracture pattern and in the transverse fracture pattern. The mechanical properties were determined after either oblique or transverse osteotomy and fixation of the proximal phalanx. Each fixation technique was tested in apex palmar, apex dorsal, and lateral bending, as well as in torsion and distraction. The results showed that of the configurations tested, four crossed 0.028-inch d Kirschner wires obtained the highest rigidity in the transverse fracture pattern and three oblique 0.035-inch d Kirschner wires obtained the highest rigidity in the oblique fracture pattern. PMID:3351253

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

  4. 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...

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

    E-print Network

    Zhou, Minjian

    1993-01-01

    Fracture mechanics approach has been used to analyze the behavior of fatigue resistance of welded details existing in highway steel bridges under variable amplitude long life loading which means most of the stress ranges will be below constant...

  6. 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.

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  10. A Fracture-Mechanical Model of Crack Growth and Interaction: Application to Pre-eruptive Seismicity

    NASA Astrophysics Data System (ADS)

    Matthews, C.; Sammonds, P.; Kilburn, C.

    2007-12-01

    A greater understanding of the physical processes occurring within a volcano is a key aspect in the success of eruption forecasting. By considering the role of fracture growth, interaction and coalescence in the formation of dykes and conduits as well as the source mechanism for observed seismicity we can create a more general, more applicable model for precursory seismicity. The frequency of volcano-tectonic earthquakes, created by fracturing of volcanic rock, often shows a short-term increase prior to eruption. Using fracture mechanics, the model presented here aims to determine the conditions necessary for the acceleration in fracture events which produces the observed pre-eruptive seismicity. By focusing on the cause of seismic events rather than simply the acceleration patterns observed, the model also highlights the distinction between an accelerating seismic sequence ending with an eruption and a short-term increase which returns to background levels with no activity occurring, an event also observed in the field and an important capability if false alarms are to be avoided. This 1-D model explores the effects of a surrounding stress field and the distribution of multi-scale cracks on the interaction and coalescence of these cracks to form an open pathway for magma ascent. Similarly to seismic observations in the field, and acoustic emissions data from the laboratory, exponential and hyperbolic accelerations in fracturing events are recorded. Crack distribution and inter-crack distance appears to be a significant controlling factor on the evolution of the fracture network, dominating over the effects of a remote stress field. The generality of the model and its basis on fundamental fracture mechanics results makes it applicable to studies of fracture networks in numerous situations. For example looking at the differences between high temperature fracture processes and purely brittle failure the model can be similarly applied to fracture dynamics in the edifice of a long repose volcano and a lava dome.

  11. 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.

  12. 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.

  13. The phase-field approach as a tool for experimental validations in fracture mechanics

    NASA Astrophysics Data System (ADS)

    Dally, Tim; Weinberg, Kerstin

    2015-05-01

    In a phase-field approach to fracture crack propagation is modeled by means of an additional continuous field. In this paper, two problems of linear elastic fracture mechanics are studied experimentally and numerically in order to evaluate the practicability of the phase-field approach and to validate the measured parameters. At first, a three-point bending experiment of silicon dies is simulated assuming static plate bending. Then, wave propagation and spallation in a Hopkinson bar test are analyzed in a dynamic regime. The simulations show that phase-field fracture reproduces the experimental results with high accuracy. The results are comparable to other fracture simulations, e.g., the cohesive element technique. In total, the phase-field approach to fracture is capable of tracking crack evolution in a very convenient and quantitatively correct way.

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

    SciTech Connect

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

    1991-01-01

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

  15. Spinal fractures in recreational bobsledders: an unexpected mechanism of injury

    PubMed Central

    Severson, Erik P.; Sofianos, Dmitri A.; Powell, Amy; Daubs, Michael; Patel, Rakesh; Patel, Alpesh A.

    2012-01-01

    Study design:?Retrospective case series and literature review. Objective:?To report and discuss spinal fractures occurring in recreational bobsledders. Summary of background data:?Spinal fractures have been commonly described following traumatic injury during a number of recreational sports. Reports have focused on younger patients and typically involved high-impact sports or significant injuries. With an aging population and a wider array of recreational sports, spinal injuries may be seen after seemingly benign activities and without a high-impact injury. Methods:?A retrospective review of two patients and review of the literature was performed. Results:?Two patients with spinal fractures after recreational bobsledding were identified. Both patients, aged 57 and 54 years, noticed a simultaneous onset of severe back pain during a routine turn on a bobsled track. Neither was involved in a high-impact injury during the event. Both patients were treated conservatively with resolution of symptoms. An analysis of the bobsled track revealed that potential forces imparted to the rider may be greater than the yield strength of vertebral bone. Conclusions:?Older athletes may be at greater risk for spinal fracture associated with routine recreational activities. Bobsledding imparts large amounts of force during routine events and may result in spinal trauma. Older patients, notably those with osteoporosis or metabolic bone disease, should be educated about the risks associated with seemingly benign recreational sports. PMID:23230417

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

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

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

  17. Nondestructive evaluation of mechanical and fracture characteristics of ferritic steels using automated ball identation testing

    SciTech Connect

    Murty, K.L.; Mathew, M.D.; Miraglia, P.Q.

    1997-12-01

    Mechanical properties of various ferritic steels commonly used for pressure boundary applications in light water reactors are characterized using a novel portable stress-strain microprobe (SSM) system. The SSM system utilizes an automated ball indentation (ABI) technique to measure yield strength, stress-strain curve, strength coefficient, and strain-hardening-exponent (uniform ductility). The technique is essentially nondestructive, albeit small indentations are left following the tests. These, however, leave surface compressive stresses that could actually retard crack initiation characteristics. The ABI-derived mechanical properties agreed with those obtained using conventional destructive tensile tests. To minimize specimen-to-specimen scatter, the grip/shoulder sections were used for ABI testing. In addition, the fracture properties are characterized in terms of a new fracture parameter, indentation energy to fracture (IEF), derived from the temperature variation of the true stress compared with true strain using the critical-stress-to-fracture concept.

  18. 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.

  19. Fracture mechanics; Proceedings of the Nineteenth National Symposium, San Antonio, TX, June 30-July 2, 1986

    SciTech Connect

    Cruse, T.A.

    1988-01-01

    The papers contained in this volume provide an overview of current theoretical and experimental research in the field of fracture mechanics. Topics discussed include three-dimensional issues, computational and analytical issues, damage tolerance and fatigue, elastoplastic fracture, dynamic inelastic fracture, and crack arrest theory and applications. Papers are presented on approximate methods for analysis of dynamic crack growth and arrest, constraint-loss model for the growth of surface fatigue cracks, fatigue crack growth in aircraft main landing gear wheels, and near-threshold crack growth in nickel-base superalloys.

  20. Experimental and theoretical fracture mechanics applied to volcanic conduits and domes

    NASA Astrophysics Data System (ADS)

    Sammonds, P.; Matthews, C.; Kilburn, C.; Smith, R.; Tuffen, H.; Meredith, P.

    2008-12-01

    We present an integrated modelling and experimental approach to magma deformation and fracture, which we attempt to validate against field observations of seismicity. The importance of fracture processes in magma ascent dynamics and lava dome growth and collapse are apparent from the associated seismicity. Our laboratory experiments have shown that brittle fracture of magma can occur at high temperature and stress conditions prevalent in the shallow volcanic system. Here, we use a fracture mechanics approach to model seismicity preceding volcanic eruptions. Starting with the fracture mechanics concept of a crack in an elastic body, we model crack growth around the volcanic conduit through the processes of crack interactions, leading either to the propagation and linkage of cracks, or crack avoidance and the inhibition of crack propagation. The nature of that interaction is governed by the temperature and plasticity of the magma. We find that fracture mechanics rules can account for the style of seismicity preceding eruptions. We have derived the changes in seismic b-value predicted by the model and interpret these in terms of the style of fracturing, fluid flow and heat transport. We compare our model with results from our laboratory experiments where we have deformed lava at high temperatures under triaxial stresses. These experiments were conducted in dry and water saturated conditions at effective pressures up to 10 MPa, temperatures up to 1000°C and strain rates from 10-4 s-1 to 10-6 s-1. The behaviour of these magmas was largely brittle under these conditions. We monitored the acoustic emission emitted and calculate the change in micro-seismic b-value with deformation. These we find are in accord with volcano seismicity and our fracture mechanics model.

  1. Development and fracture mechanics data for 6Al-6V-2 Sn titanium alloy

    NASA Technical Reports Server (NTRS)

    Fiftal, C. F.; Beck, E. J.

    1974-01-01

    Fracture mechanics properties of 6Al-6V-2Sn titanium in the annealed, solution-treated, and aged condition are presented. Tensile, fracture toughness, cyclic flaw growth, and sustained-load threshold tests were conducted. Both surface flaw and compact tension-specimen geometries were employed. Temperatures and/or environments used were -65 F (220 K) air, ambient, 300 F (422 K) air, and room-temperature air containing 10 and 100% relative humidity.

  2. 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.

  3. Fracture Mechanisms of Bone: A Comparative Study between Antler and Bovine Femur , F.A. Sheppard2

    E-print Network

    McKittrick, Joanna

    Fracture Mechanisms of Bone: A Comparative Study between Antler and Bovine Femur P.Y. Chen1 , F, University of California, San Diego, La Jolla, CA 92093-0411, U.S.A. ABSTRACT In this study, fracture conditions to study the effects of fiber orientation and hydration. Fracture toughness results

  4. Correlation between high resolution sequence stratigraphy and mechanical stratigraphy for enhanced fracture characteristic prediction

    NASA Astrophysics Data System (ADS)

    Al Kharusi, Laiyyan M.

    Sequence stratigraphy relates changes in vertical and lateral facies distribution to relative changes in sea level. These relative changes in carbonates effect early diagenesis, types of pores, cementation and dissolution patterns. As a result, in carbonates, relative changes in sea level significantly impact the lithology, porosity, diagenesis, bed and bounding surfaces which are all factors that control fracture patterns. This study explores these relationships by integrating stratigraphy with fracture analysis and petrophysical properties. A special focus is given to the relationship between mechanical boundaries and sequence stratigraphic boundaries in three different settings: (1) Mississippian strata in Sheep Mountain Anticline, Wyoming, (2) Mississippian limestones in St. Louis, Missouri, and (3) Pennsylvanian limestones intermixed with elastics in the Paradox Basin, Utah. The analysis of these sections demonstrate that a fracture hierarchy exists in relation to the sequence stratigraphic hierarchy. The majority of fractures (80%) terminate at genetic unit boundaries or the internal flooding surface that separates the transgressive from regressive hemicycle. Fractures (20%) that do not terminate at genetic unit boundaries or their internal flooding surface terminate at lower order sequence stratigraphic boundaries or their internal flooding surfaces. Secondly, the fracture spacing relates well to bed thickness in mechanical units no greater than 0.5m in thickness but with increasing bed thickness a scatter from the linear trend is observed. In the Paradox Basin the influence of strain on fracture density is illustrated by two sections measured in different strain regimes. The folded strata at Raplee Anticline has higher fracture densities than the flat-lying beds at the Honaker Trail. Cemented low porosity rocks in the Paradox Basin do not show a correlation between fracture pattern and porosity. However velocity and rock stiffness moduli's display a slight correlation to fracture spacing. Furthermore, bed thickness is found to be only one factor in determining fracture density but with increasing strain, internal bedforms and rock petrophysical heterogeneities influence fracture density patterns. This study illustrates how integrating sedimentologic and sequence stratigraphic interpretations with data on structural kinematics can lead to refined predictive understanding of fracture attributes.

  5. 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. PMID:26064297

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

    PubMed

    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. PMID:26064297

  7. 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.

  8. Modeling of Colloid Transport Mechanisms Facilitating Migration of Radionuclides in Fractured Media

    SciTech Connect

    Li Shihhai; Yang, H.-T.; Jen, C.-P.

    2004-12-15

    Performance assessments of high-level radioactive waste disposal have emphasized the role of colloids in the migration of radionuclides in the geosphere. The transport of colloids often brings them in contact with fracture surfaces or porous rock matrix. Colloids that attach to these surfaces are treated as being immobile and are called filtered colloids. The filtered colloids could be released into the fracture again; that is, the attachment of colloids may be reversible. Also, the colloids in the fracture could diffuse into the porous matrix rock. A methodology is proposed to evaluate a predictive model to assess transport within the fractured rock as well as various phenomenological coefficients employed in the different mechanisms, such as filtration, remobilization, and matrix diffusion of colloids. The governing equations of colloids considering mechanisms of the colloidal transport in the fractured media, including filtration, remobilization, and matrix diffusion, have been modeled and solved analytically in previous studies. In the present study, transport equations of colloids and radionuclides that consider the combination of the aforementioned transport mechanisms have also been solved numerically and investigated. The total concentration of mobile radionuclides in the fracture becomes lower because the concentration of mobile colloids in the fracture decreases when the filtration coefficient for colloids increases. Additionally, the concentration of mobile radionuclides was increased at any given time step due to the higher sorption partition coefficient of radionuclides associated with colloids. The results also show that the concentration of radionuclides in the fracture zone decreases when the remobilization coefficient of colloids or the percentages of the matrix diffusion flux of colloids increase.

  9. 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

  10. Modeling Fracture of Sn-Rich (Pb-Free) Solder Joints Under Mechanical Shock Conditions

    NASA Astrophysics Data System (ADS)

    Fei, Huiyang; Yazzie, Kyle; Chawla, Nikhilesh; Jiang, Hanqing

    2012-08-01

    With the increasing focus on developing environmentally benign electronic packages, lead-free solder alloys have received a great deal of attention. Mishandling of packages during manufacture, assembly, or by the user may cause solder joint failure. In this work, we conducted finite-element analysis to model solder joint fracture under dynamic loading conditions. The solder is modeled as a porous plastic material, and the intermetallic compound (IMC) material is characterized as an elastic material. The fracture of the solder is governed by void nucleation, and the IMC fracture is brittle in nature. The randomness of the void volume fraction in the solder and the defects in the IMC are considered and implemented in the finite-element package ABAQUS. The finite-element results show that the fracture mechanisms of the solder joints depend on the strain rate and IMC thickness. High strain rate and larger IMC thickness favor IMC-controlled fracture, which is brittle in nature. Low strain rate and smaller IMC thickness lead to solder-controlled fracture, which is governed by void growth and nucleation. Based on this finding, a mechanistic explanation for solder joint fracture is suggested.

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

    SciTech Connect

    Pyrack-Nolte, L.J.; Myer, L.R.; Cook, N.G.W.; Witherspoon, P.A.

    1987-01-01

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

  12. Updated Fatigue-Crack-Growth And Fracture-Mechanics Software

    NASA Technical Reports Server (NTRS)

    Forman, Royce G.; Shivakumar, Venkataraman; Newman, James C., Jr.

    1995-01-01

    NASA/FLAGRO 2.0 developed as analytical aid in predicting growth and stability of preexisting flaws and cracks in structural components of aerospace systems. Used for fracture-control analysis of space hardware. Organized into three modules to maximize efficiency in operation. Useful in: (1) crack-instability/crack-growth analysis, (2) processing raw crack-growth data from laboratory tests, and (3) boundary-element analysis to determine stresses and stress-intensity factors. Written in FORTRAN 77 and ANSI C.

  13. 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.

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

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

  15. Case histories involving fatigue and fracture mechanics; Proceedings of the Symposium, Charleston, SC, Mar. 21, 22, 1985

    NASA Technical Reports Server (NTRS)

    Hudson, C. Michael (editor); Rich, Thomas P. (editor)

    1986-01-01

    Papers are presented on cracking at nozzle corners in the nuclear pressure vessel industry, applied fracture mechanics for assessing defect significance in a crude oil pipeline, failure analysis of a large wind-tunnel compressor blade, analysis of a compressor-wheel failure, and preventing fracture by inspection and analysis. Consideration is also given to the fatigue crack growth predictions of welded aircraft structures containing flaws in the residual stress field, the fatigue and fracture mechanics analysis of a compression loaded aircraft structure, fracture of an aircraft horizontal stabilizer, fatigue life analysis of fuel tank skins under combined loads, and aircraft structural maintenance recommendations based on fracture mechanics analysis. Additional papers discuss an analysis of two metal-forming die failures, an analysis of a failed saw arbor, and the role of fracture mechanics in assessing the effect on fatigue life of design changes in welded fabrications.

  16. Glucocorticoids inhibit shaft fracture healing but not metaphyseal bone regeneration under stable mechanical conditions

    PubMed Central

    Sandberg, O. H.; Aspenberg, P.

    2015-01-01

    Objectives Healing in cancellous metaphyseal bone might be different from midshaft fracture healing due to different access to mesenchymal stem cells, and because metaphyseal bone often heals without a cartilaginous phase. Inflammation plays an important role in the healing of a shaft fracture, but if metaphyseal injury is different, it is important to clarify if the role of inflammation is also different. The biology of fracture healing is also influenced by the degree of mechanical stability. It is unclear if inflammation interacts with stability-related factors. Methods We investigated the role of inflammation in three different models: a metaphyseal screw pull-out, a shaft fracture with unstable nailing (IM-nail) and a stable external fixation (ExFix) model. For each, half of the animals received dexamethasone to reduce inflammation, and half received control injections. Mechanical and morphometric evaluation was used. Results As expected, dexamethasone had a strong inhibitory effect on the healing of unstable, but also stable, shaft fractures. In contrast, dexamethasone tended to increase the mechanical strength of metaphyseal bone regenerated under stable conditions. Conclusions It seems that dexamethasone has different effects on metaphyseal and diaphyseal bone healing. This could be explained by the different role of inflammation at different sites of injury. Cite this article: Bone Joint Res 2015;4:170–175. PMID:26490971

  17. 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.

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

    SciTech Connect

    Esaki, K.; Kimpara, I.; Kageyama, K.; Suzuki, T.; Ohsawa, I.

    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.

  19. Evaluation of fracture strength of metal/epoxy joint by interface mechanics

    SciTech Connect

    Nakai, Yoshikazu

    1995-11-01

    Tension tests of metal/epoxy joints with or without interface cracks were conducted and fracture criteria of the joints were discussed based on interface mechanics. The variation of the fracture strength of each specimen was large, and the strength showed Gaussian distribution. The fracture strength of smooth specimens was lower for wider specimens, but the cumulative probability of fracture of smooth specimens was not controlled by the stress singularity parameter. In interface cracked specimens, the cracks were propagated either along the interface or in epoxy resin, depending on crack length. When cracks propagated along the interface, the cumulative probability of the fracture of the specimen was controlled by the real part of the complex stress intensity factor along the interface, K{sub 1}. When cracks kinked to epoxy resin, the angle was almost identical to that of the maximum tangential stress, {sigma}{sub {theta}max}. In this case, the cumulative probability of fracture was controlled by the value of K{sub {theta}max}.

  20. Distal radius fractures: mechanisms of injury and strength prediction by bone mineral assessment.

    PubMed

    Augat, P; Iida, H; Jiang, Y; Diao, E; Genant, H K

    1998-09-01

    The strength of the radius depends on the mechanical properties of cancellous and cortical bone. By assessing both compartments quantitatively with bone densitometry, we tried to identify the specificity of each in predicting the load at which the distal radius will fracture. Twenty human cadaver forearms were scanned for bone mineral and geometric properties with quantitative computed tomography and dual x-ray absorptiometry. In both a neutral loading situation and one in which the wrist was extended 45 degrees, the load distribution was determined with pressure-sensitive films, and a fracture simulating a fall on the hand was produced with a material testing machine. Fractures that occur with the wrist in extension were produced by a central impact of the scaphoid onto the radiocarpal joint, and those that occur under neutral loading conditions were produced by a more commonly distributed loading pattern. The load at fracture was most specifically predicted (r2=0.74) by bone mineral and geometric measures of the cortex at the shaft of the radius. Bone mineral density measures of trabecular (r2=0.64) and total (r2=0.66) bone were less successful in predicting the fracture load. After adjustment for bone size, the geometric and density measures revealed similar specificity. Cortical bone, therefore, contributes significantly to the strength of the distal radius and may play an important role in the prediction of osteoporotic wrist fractures. PMID:9820289

  1. The imprint of hydro-mechanics of fractures in periodic pumping tests

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    Modelling of pressure transients recorded in wells allows for characterization of reservoirs surrounding the well. Simulation of pressure transients furthermore permits sensitivity studies for individual model parameters. We numerically simulated pumping tests in a vertical well intersecting a single horizontal fracture to evaluate the diagnostic potential of periodic pumping procedures for subsurface characterization. The pressure responses in the pumping and monitoring wells were analysed with respect to their sensitivity to geometrical and hydraulic properties of the fracture and of the surrounding rock material. We focused on interference analysis that for periodic pumping tests reduces to a consideration of amplitude ratio and phase shift between pressure transients recorded at an injection well and monitoring points. Fluid flow in the deformable fracture was modelled employing (1) a hybrid-dimensional hydro-mechanically coupled approach and (2) an uncoupled-diffusion equation. Results of both approaches were compared to quantify the effects of hydro-mechanical coupling. While in the uncoupled-diffusion approach a bulk storage capacity value is prescribed for the fracture, storage capacity is implicitly accounted for by the coupling in the hybrid-dimensional approach. Results reveal that hydro-mechanical coupling strongly affects the pressure transient at the pumping well and the monitoring points. Asymmetry of the pressure profiles between injection and production phases at the injection point is a peculiar characteristic of the hydro-mechanical results and is related to changes in fracture permeability with fluid pressure caused by fracture deformation. Further hydro-mechanical effects, such as reverse-pressure response, occur at monitoring points along the fracture domain, in particular at positions in the conduit where the contribution of diffusive pressure propagation remains small, that is, at monitoring distances large compared to classic scaling for penetration depth using hydraulic diffusivity. During periodic pumping tests the reverse response is potentially triggered various times within one period and thus chances to unequivocally recognize this effect are largely enhanced in comparison to conventional pulse or step testing procedures. The standard scaling relation for diffusion processes, often employed in the analysis of induced seismicity, has limited applicability to deformable fractures.

  2. Adaptive finite element methods for two-dimensional problems in computational fracture mechanics

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  3. 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.

  4. New computing systems and their impact on structural and fracture mechanics calculations

    NASA Technical Reports Server (NTRS)

    Liebowitz, Harold; Moyer, Thomas E., Jr.; Noor, Ahmed K.

    1991-01-01

    Advances made in computer technology and their impact on structural and fracture mechanics calculations are reviewed, and the computational needs for future structural systems are discussed. Special attention is given to the computer hardware, the network technology, the performance of new computing systems, and the supersystems and parallel processing and their impact on structure technology. The differences between different machines are identified.

  5. Heavy Section Steel Technology HSST eLib Computational Structural Fracture Mechanics Team

    E-print Network

    Heavy Section Steel Technology ­ HSST eLib Computational Structural Fracture Mechanics Team the reports generated by the Heavy-Section Steel Technology (HSST) program (JCN B0119) from the early 1970's welcome the opportunity to discuss your potential applications and ways that the Heavy-Section Steel

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

    SciTech Connect

    Reinhold H. Dauskardt

    2005-08-01

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

  7. Effects of carbon on fracture mechanisms in nanocrystalline BCC iron: Atomistic simulations

    NASA Astrophysics Data System (ADS)

    Hyde, Brian

    Atomistic computer simulations were performed using embedded atom method interatomic potentials in alpha-Fe with impurities and defects. The effects of intergranular carbon on fracture toughness and the mechanisms of fracture were investigated. It was found that as the average grain size changes the dominant energy release mechanism also changes. Because of this the role of the intergranular carbon changes and these mechanisms compete affecting the fracture toughness differently with changing grain size. Grain boundary accommodation mechanisms are seen to be dominant in the fracture of nanocrystalline alpha-Fe. To supplement this work we investigate grain boundary sliding using the Sigma = 5,(310)[001] symmetrical tilt grain boundary. We observe that in this special boundary sliding is governed by grain boundary dislocation activity with Burgers vectors belonging to the DSC lattice. The sliding process was found to occur through the nucleation and glide of partial grain boundary dislocations, with a secondary grain boundary structure playing an important role in the sliding process. Interstitial impurities and vacancies were introduced in the grain boundary to study their role as nucleation sites for the grain boundary dislocations. While vacancies and H interstitials act as preferred nucleation sites, C interstitials do not. This work was funded by the Office of Naval Research.

  8. Fractured rock stress-permeability relationships from in situ data and effects of temperature and chemical-mechanical couplings

    SciTech Connect

    Rutqvist, J.

    2014-09-19

    The purpose of this paper is to (i) review field data on stress-induced permeability changes in fractured rock; (ii) describe estimation of fractured rock stress-permeability relationships through model calibration against such field data; and (iii) discuss observations of temperature and chemically mediated fracture closure and its effect on fractured rock permeability. The field data that are reviewed include in situ block experiments, excavation-induced changes in permeability around tunnels, borehole injection experiments, depth (and stress) dependent permeability, and permeability changes associated with a large-scale rock-mass heating experiment. Data show how the stress-permeability relationship of fractured rock very much depends on local in situ conditions, such as fracture shear offset and fracture infilling by mineral precipitation. Field and laboratory experiments involving temperature have shown significant temperature-driven fracture closure even under constant stress. Such temperature-driven fracture closure has been described as thermal overclosure and relates to better fitting of opposing fracture surfaces at high temperatures, or is attributed to chemically mediated fracture closure related to pressure solution (and compaction) of stressed fracture surface asperities. Back-calculated stress-permeability relationships from field data may implicitly account for such effects, but the relative contribution of purely thermal-mechanical and chemically mediated changes is difficult to isolate. Therefore, it is concluded that further laboratory and in situ experiments are needed to increase the knowledge of the true mechanisms behind thermally driven fracture closure, and to further assess the importance of chemical-mechanical coupling for the long-term evolution of fractured rock permeability.

  9. Fractured rock stress-permeability relationships from in situ data and effects of temperature and chemical-mechanical couplings

    DOE PAGESBeta

    Rutqvist, J.

    2014-09-19

    The purpose of this paper is to (i) review field data on stress-induced permeability changes in fractured rock; (ii) describe estimation of fractured rock stress-permeability relationships through model calibration against such field data; and (iii) discuss observations of temperature and chemically mediated fracture closure and its effect on fractured rock permeability. The field data that are reviewed include in situ block experiments, excavation-induced changes in permeability around tunnels, borehole injection experiments, depth (and stress) dependent permeability, and permeability changes associated with a large-scale rock-mass heating experiment. Data show how the stress-permeability relationship of fractured rock very much depends on localmore »in situ conditions, such as fracture shear offset and fracture infilling by mineral precipitation. Field and laboratory experiments involving temperature have shown significant temperature-driven fracture closure even under constant stress. Such temperature-driven fracture closure has been described as thermal overclosure and relates to better fitting of opposing fracture surfaces at high temperatures, or is attributed to chemically mediated fracture closure related to pressure solution (and compaction) of stressed fracture surface asperities. Back-calculated stress-permeability relationships from field data may implicitly account for such effects, but the relative contribution of purely thermal-mechanical and chemically mediated changes is difficult to isolate. Therefore, it is concluded that further laboratory and in situ experiments are needed to increase the knowledge of the true mechanisms behind thermally driven fracture closure, and to further assess the importance of chemical-mechanical coupling for the long-term evolution of fractured rock permeability.« less

  10. 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.

  11. 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.

  12. 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

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

    PubMed

    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

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    Following an explosion of studies of silicon as a negative electrode for Li-ion batteries, the anomalous volumetric changes and fracture of lithiated single Si particles have attracted significant attention in various fields, including mechanics. However, in real batteries, lithiation occurs simultaneously in clusters of Si in a confined medium. Hence, understanding how the individual Si structures interact during lithiation in a closed space is necessary. Here, we demonstrate physical and mechanical interactions of swelling Si structures during lithiation using well-defined Si nanopillar pairs. Ex situ SEM and in situ TEM studies reveal that compressive stresses change the reaction kinetics so that preferential lithiation occurs at free surfaces when the pillars are mechanically clamped. Such mechanical interactions enhance the fracture resistance of lithiated Si by lessening the tensile stress concentrations in Si structures. This study will contribute to improved design of Si structures at the electrode level for high-performance Li-ion batteries.

  15. Fracture mechanics research at NASA related to the aging commercial transport fleet

    NASA Technical Reports Server (NTRS)

    Newman, James C., Jr.; Harris, Charles E.

    1992-01-01

    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 and an extensive testing program is under way to study fatigue crack growth and fracture in complex built-up shell structures. Innovative nondestructive examination technologies are also being developed to provide large area inspection capability to detect corrosion, disbonds, and cracks. Recent fracture mechanics results applicable to predicting the growth of cracks under monotonic and cyclic loading at rivets in fuselage lap-splice joints are reviewed.

  16. Phenomenological and mechanics aspects of nondestructive evaluation and characterization by sound and ultrasound of material and fracture properties

    NASA Technical Reports Server (NTRS)

    Fu, L. S. W.

    1982-01-01

    Developments in fracture mechanics and elastic wave theory enhance the understanding of many physical phenomena in a mathematical context. Available literature in the material, and fracture characterization by NDT, and the related mathematical methods in mechanics that provide fundamental underlying principles for its interpretation and evaluation are reviewed. Information on the energy release mechanism of defects and the interaction of microstructures within the material is basic in the formulation of the mechanics problems that supply guidance for nondestructive evaluation (NDE).

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

    SciTech Connect

    Zhang Jun; Li, Victor C

    2004-02-01

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

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

    SciTech Connect

    Derek Elsworth; Abraham Grader; Susan Brantley

    2007-04-25

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

  19. A three-dimensional stochastic rock mechanics model of engineered geothermal systems in fractured crystalline rock

    NASA Astrophysics Data System (ADS)

    Jing, Z.; Willis-Richards, J.; Watanabe, K.; Hashida, T.

    2000-10-01

    A three-dimensional (3-D) stochastic network model for simulating a hot dry rock (HDR) or hot wet rock (HWR) engineered geothermal system formed in fractured crystalline rock is presented. The model addresses the problems of fracture network characterization from in situ field data, such as fracture orientation, size, spacing, and other mechanical properties. The model can simulate the changes that occur within the rock mass during stimulation (i.e., large volume fluid injection at pressures sufficient to allow shear slip on natural fractures). It can also be used to simulate steady state circulation of the heat exchange system thus created and includes provision for predicting tracer response curves and heat extraction history. The model has been applied to data gathered during the stimulation and circulation of a 2.2-km-deep HDR reservoir at Hijiori, Japan. The predicted shape of the stimulated and shear-propped fractures closely matched the distribution of seismic source distribution of acoustic emission (AE), regardless of realization of the fracture network, suggesting that the geometry of the stimulated volume can be robustly predicted from knowledge of the fracture population and in situ stresses. However, hydraulic behavior and tracer tests during the circulation could only be satisfactorily simultaneously reproduced by a small subset of realizations. These selected realizations, obtained by matching initial circulation and tracer data, are considered to give the best prospect of satisfactory long-term thermal modeling. The success in simultaneously modeling diverse data (hydraulic, microseismic, and tracer) lends confidence to the thermal predictions. The results indicate that a large improvement in the long-term thermal performance of the Hijiori reservoir could result from increasing well spacing from 100 to 150 m without major degradation of the hydraulic performance.

  20. 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.

  1. Can deterministic mechanical size effects contribute to fracture and microdamage accumulation in trabecular bone?

    PubMed

    Siegmund, Thomas; Allen, Matthew R; Burr, David B

    2010-07-21

    Failure of bone under monotonic and cyclic loading is related to the bone mineral density, the quality of the bone matrix, and the evolution of microcracks. The theory of linear elastic fracture mechanics has commonly been applied to describe fracture in bone. Evidence is presented that bone failure can be described through a non-linear theory of fracture. Thereby, deterministic size effects are introduced. Concepts of a non-linear theory are applied to discern how the interaction among bone matrix constituents (collagen and mineral), microcrack characteristics, and trabecular architecture can create distinctively differences in the fracture resistance at the bone tissue level. The non-linear model is applied to interpret pre-clinical data concerning the effects of anti-osteoporotic agents on bone properties. The results show that bisphosphonate (BP) treatments that suppress bone remodeling will change trabecular bone in ways such that the size of the failure process zone relative to the trabecular thickness is reduced. Selective estrogen receptor modulators (SERMs) that suppress bone remodeling will change trabecular bone in ways such that the size of the failure process zone relative to the trabecular thickness is increased. The consequences of these changes are reflected in bone mechanical response and predictions are consistent with experimental observations in the animal model which show that BP treatment is associated with more brittle fracture and microcracks without altering the average length of the cracks, whereas SERM treatments lead to a more ductile fracture and mainly increase crack length with a smaller increase in microcrack density. The model suggests that BPs may be more effective in cases in which bone mass is very low, whereas SERMS may be more effective when milder osteoporotic symptoms are present. PMID:20398678

  2. 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.

  3. Metal cutting simulation of 4340 steel using an accurate mechanical description of meterial strength and fracture

    SciTech Connect

    Maudlin, P.J.; Stout, M.G.

    1996-09-01

    Strength and fracture constitutive relationships containing strain rate dependence and thermal softening are important for accurate simulation of metal cutting. The mechanical behavior of a hardened 4340 steel was characterized using the von Mises yield function, the Mechanical Threshold Stress model and the Johnson- Cook fracture model. This constitutive description was implemented into the explicit Lagrangian FEM continuum-mechanics code EPIC, and orthogonal plane-strain metal cutting calculations were performed. Heat conduction and friction at the toolwork-piece interface were included in the simulations. These transient calculations were advanced in time until steady state machining behavior (force) was realized. Experimental cutting force data (cutting and thrust forces) were measured for a planning operation and compared to the calculations. 13 refs., 6 figs.

  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. Understanding Irreversible Degradation of Nb3Sn Wires with Fundamental Fracture Mechanics

    SciTech Connect

    Zhai, Yuhu; Calzolaio, Ciro; Senatore, Carmine

    2014-08-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  7. Recent finite element studies in plasticity and fracture mechanics

    NASA Technical Reports Server (NTRS)

    Rice, J. R.; Mcmeeking, R. M.; Parks, D. M.; Sorensen, E. P.

    1979-01-01

    The paper reviews recent work on fundamentals of elastic-plastic finite-element analysis and its applications to the mechanics of crack opening and growth in ductile solids. The presentation begins with a precise formulation of incremental equilibrium equations and their finite-element forms in a manner valid for deformations of arbitrary magnitude. Special features of computational procedures are outlined for accuracy in view of the near-incompressibility of elastic-plastic response. Applications to crack mechanics include the analysis of large plastic deformations at a progressively opening crack tip, the determination of J integral values and of limitations to J characterizations of the intensity of the crack tip field, and the determination of crack tip fields in stable crack growth.

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

    SciTech Connect

    Li Helin; Zhang Yi; Deng Zengjie; Jin Dazeng

    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.

  9. Mechanical Behavior of Small-Scale Channels in Acid-etched Fractures 

    E-print Network

    Deng, Jiayao

    2011-02-22

    The conductivity of acid-etched fractures highly depends on spaces along the fracture created by uneven etching of the fracture walls remaining open after fracture closure. Formation heterogeneities such as variations of mineralogy and permeability...

  10. 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.

  11. Fracture mechanics correlation of boron/aluminum coupons containing stress risers

    NASA Technical Reports Server (NTRS)

    Adsit, N. R.; Waszczak, J. P.

    1975-01-01

    The mechanical behavior of boron/aluminum near stress risers has been studied and reported. This effort was directed toward defining the tensile behavior of both unidirectional and (0/ plus or minus 45) boron/aluminum using linear elastic fracture mechanics (LEFM). The material used was 5.6-mil boron in 6061 aluminum, consolidated using conventional diffusion bonding techniques. Mechanical properties are reported for both unidirectional and (0/ plus or minus 45) boron/aluminum, which serve as control data for the fracture mechanics predictions. Three different flawed specimen types were studied. In each case the series of specimens remained geometrically similar to eliminate variations in finite size correction factors. The fracture data from these tests were reduced using two techniques. They both used conventional LEFM methods, but the existence of a characteristic flaw was assumed in one case and not the other. Both the data and the physical behavior of the specimens support the characteristic flaw hypothesis. Cracks were observed growing slowly in the (0/ plus or minus 45) laminates, until a critical crack length was reached at which time catastrophic failure occurred.

  12. Probabilistic Fracture Mechanics Evaluation of Selected Passive Components – Technical Letter Report

    SciTech Connect

    Simonen, Fredric A.; Doctor, Steven R.; Gosselin, Stephen R.; Rudland, David L.; Xu, H.; Wilkowski, Gery M.; Lydell, Bengt O.

    2007-05-31

    This report addresses the potential application of probabilistic fracture mechanics computer codes to support the Proactive Materials Degradation Assessment (PMDA) program as a method to predict component failure probabilities. The present report describes probabilistic fracture mechanics calculations that were performed for selected components using the PRO-LOCA and PRAISE computer codes. The calculations address the failure mechanisms of stress corrosion cracking, intergranular stress corrosion cracking, and fatigue for components and operating conditions that are known to make particular components susceptible to cracking. It was demonstrated that the two codes can predict essentially the same failure probabilities if both codes start with the same fracture mechanics model and the same inputs to the model. Comparisons with field experience showed that both codes predict relatively high failure probabilities for components under operating conditions that have resulted in field failures. It was found that modeling assumptions and inputs tended to give higher calculated failure probabilities than those derived from data on field failures. Sensitivity calculations were performed to show that uncertainties in the probabilistic calculations were sufficiently large to explain the differences between predicted failure probabilities and field experience.

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

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

  14. International Journal of Rock Mechanics & Mining Sciences 45 (2008) 11951210 Consolidation settlements above deep tunnels in fractured crystalline

    E-print Network

    Eberhardt, Erik

    2008-01-01

    International Journal of Rock Mechanics & Mining Sciences 45 (2008) 1195­1210 Consolidation settlements above deep tunnels in fractured crystalline rock: Part 1--Investigations above the Gotthard associated with tunnelling in fractured crystalline rock masses is rarely considered to be large enough

  15. International Journal of Rock Mechanics & Mining Sciences 45 (2008) 12111225 Consolidation settlements above deep tunnels in fractured

    E-print Network

    Eberhardt, Erik

    2008-01-01

    International Journal of Rock Mechanics & Mining Sciences 45 (2008) 1211­1225 Consolidation settlements above deep tunnels in fractured crystalline rock: Part 2--Numerical analysis of the Gotthard of subsidence. Subsidence of this magnitude in relation to a deep tunnel excavated in fractured crystalline rock

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

    E-print Network

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

    2010-01-01

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

  17. Structure stability, fracture, and tuning mechanism of CdSe nanobelts

    NASA Astrophysics Data System (ADS)

    Wang, Zhongwu; Finkelstein, Ken; Ma, Chris; Wang, Zhong Lin

    2007-03-01

    High pressure synchrotron x-ray diffraction studies have been conducted to explore the structural stability, phase transformation, and resulting mechanisms of CdSe nanobelts. 25-nm-thick wurtzite CdSe nanobelts transform to a rocksalt structure with in situ fracture at 4.0GPa; this is greater than the transition pressure of 2.5GPa in bulk and 25nm nanoparticle. Decompression results in the formation of wurtzite and sphalerite at 1.2GPa. Total Gibbs free energy calculations demonstrate that the low surface energy ±{21¯0} facets are fully responsible for the enhancement of structure stability. A strongest particle size for the rocksalt phase was determined ˜12nm, providing a significant constraint for the fracture of nanobelts and size-tuned enhancement of mechanical properties.

  18. A variationally coupled FE-BE method for elasticity and fracture mechanics

    NASA Technical Reports Server (NTRS)

    Lu, Y. Y.; Belytschko, T.; Liu, W. K.

    1991-01-01

    A new method for coupling finite element and boundary element subdomains in elasticity and fracture mechanics problems is described. The essential feature of this new method is that a single variational statement is obtained for the entire domain, and in this process the terms associated with tractions on the interfaces between the subdomains are eliminated. This provides the additional advantage that the ambiguities associated with the matching of discontinuous tractions are circumvented. The method leads to a direct procedure for obtaining the discrete equations for the coupled problem without any intermediate steps. In order to evaluate this method and compare it with previous methods, a patch test for coupled procedures has been devised. Evaluation of this variationally coupled method and other methods, such as stiffness coupling and constraint traction matching coupling, shows that this method is substantially superior. Solutions for a series of fracture mechanics problems are also reported to illustrate the effectiveness of this method.

  19. 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

  20. 3D Modeling of Coupled Rock Deformation and Thermo-Poro-Mechanical Processes in Fractures 

    E-print Network

    Rawal, Chakra

    2012-07-16

    for the degree of DOCTOR OF PHILOSOPHY Approved by: Chair of Committee, Ahmad Ghassemi Committee Members, Stephen A. Holditch Peter P. Valk? Theofanis Strouboulis Head of Department, A. Daniel Hill May 2012 Major Subject: Petroleum... Engineering iii ABSTRACT 3D Modeling of Coupled Rock Deformation and Thermo-Poro-Mechanical Processes in Fractures. (May 2012) Chakra Rawal, B.E.; M.Sc., Tribhuvan University Chair of Advisory Committee: Dr. Ahmad Ghassemi Problems...

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

    NASA Technical Reports Server (NTRS)

    Updike, D. P.

    1975-01-01

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

  3. A new failure mechanism in thin film by collaborative fracture and delamination: Interacting duos of cracks

    NASA Astrophysics Data System (ADS)

    Marthelot, Joël; Bico, José; Melo, Francisco; Roman, Benoît

    2015-11-01

    When a thin film moderately adherent to a substrate is subjected to residual stress, the cooperation between fracture and delamination leads to unusual fracture patterns, such as spirals, alleys of crescents and various types of strips, all characterized by a robust characteristic length scale. We focus on the propagation of a duo of cracks: two fractures in the film connected by a delamination front and progressively detaching a strip. We show experimentally that the system selects an equilibrium width on the order of 25 times the thickness of the coating and independent of both fracture and adhesion energies. We investigate numerically the selection of the width and the condition for propagation by considering Griffith's criterion and the principle of local symmetry. In addition, we propose a simplified model based on the criterion of maximum of energy release rate, which provides insights of the physical mechanisms leading to these regular patterns, and predicts the effect of material properties on the selected width of the detaching strip.

  4. A new failure mechanism in thin film by collaborative fracture and delamination: interacting duos of cracks

    E-print Network

    Joel Marthelot; Jose Bico; Francisco Melo; Benoit Roman

    2015-09-20

    When a thin film moderately adherent to a substrate is subjected to residual stress, the cooperation between fracture and delamination leads to unusual fracture patterns, such as spirals, alleys of crescents and various types of strips, all characterized by a robust characteristic length scale. We focus on the propagation of a duo of cracks: two fractures in the film connected by a delamination front and progressively detaching a strip. We show experimentally that the system selects an equilibrium width on the order of 25 times the thickness of the coating and independent of both fracture and adhesion energies. We investigate numerically the selection of the width and the condition for propagation by considering Griffith's criterion and the principle of local symmetry. In addition, we propose a simplified model based on the criterion of maximum of energy release rate, which provides insights of the physical mechanisms leading to these regular patterns, and predicts the effect of material properties on the selected width of the detaching strip.

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

    SciTech Connect

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

    2008-01-01

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

  6. 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.

  7. Studying physical properties of deformed intact and fractured rocks by micro-scale hydro-mechanical-seismicity model

    NASA Astrophysics Data System (ADS)

    Raziperchikolaee, Samin

    The pore pressure variation in an underground formation during hydraulic stimulation of low permeability formations or CO2 sequestration into saline aquifers can induce microseismicity due to fracture generation or pre-existing fracture activation. While the analysis of microseismic data mainly focuses on mapping the location of fractures, the seismic waves generated by the microseismic events also contain information for understanding of fracture mechanisms based on microseismic source analysis. We developed a micro-scale geomechanics, fluid-flow and seismic model that can predict transport and seismic source behavior during rock failure. This model features the incorporation of microseismic source analysis in fractured and intact rock transport properties during possible rock damage and failure. The modeling method considers comprehensive grains and cements interaction through a bonded-particle-model. As a result of grain deformation and microcrack development in the rock sample, forces and displacements in the grains involved in the bond breakage are measured to determine seismic moment tensor. In addition, geometric description of the complex pore structure is regenerated to predict fluid flow behavior of fractured samples. Numerical experiments are conducted for different intact and fractured digital rock samples, representing various mechanical behaviors of rocks and fracture surface properties, to consider their roles on seismic and transport properties of rocks during deformation. Studying rock deformation in detail provides an opportunity to understand the relationship between source mechanism of microseismic events and transport properties of damaged rocks to have a better characterizing of fluid flow behavior in subsurface formations.

  8. A fracture mechanics specimen and loading device for the determination of fracture toughness under superimposed normal and shear modes of loading

    NASA Astrophysics Data System (ADS)

    Benitz, K.; Richard, H. A.

    1981-08-01

    A simple compact fracture-mechanics specimen and a loading device are suggested for the determination of fracture toughness under loading mode I, loading mode II, and a mixed loading mode. All specimens are photoelastically tested, and the device is demonstrated by applying superimposed normal and shear modes to the specimens. Force is applied at 0 deg for pure traction, between 0 and 90 deg for superimposed loading, and at 90 deg for pure shearing force. The ratio of crack depth to sample width (a/w) is determined to be not less than 0.5, and the stress intensity factor for the proposed fracture-mechanics specimen is presented as a function of the load application angle and the ratio a/w.

  9. 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

  10. J-integral Computations for Linear Elastic Fracture Mechanics in h,p,k Mathematical and Computational Framework

    E-print Network

    Nunez, Daniel

    2008-05-21

    This thesis presents an infrastructure for computations of the J-integral for mode I linear elastic fracture mechanics in h,p,k mathematical and computational framework using finite element formulations based on the Galerkin method with weak form...

  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

    are studied using a coupled thermo-hydro-mechanical (THM) analysis. The models are used to simulate microscopic and macroscopic fracture behaviors of laboratory-scale uniaxial and triaxial experiments on rock using an elastic/brittle damage model considering...

  12. Computational implementation of the multi-mechanism deformation coupled fracture model for salt

    SciTech Connect

    Koteras, J.R.; Munson, D.E.

    1996-05-01

    The Multi-Mechanism Deformation (M-D) model for creep in rock salt has been used in three-dimensional computations for the Waste Isolation Pilot Plant (WIPP), a potential waste, repository. These computational studies are relied upon to make key predictions about long-term behavior of the repository. Recently, the M-D model was extended to include creep-induced damage. The extended model, the Multi-Mechanism Deformation Coupled Fracture (MDCF) model, is considerably more complicated than the M-D model and required a different technology from that of the M-D model for a computational implementation.

  13. Study of fracture mechanisms of short fiber reinforced AS composite by acoustic emission technique

    SciTech Connect

    Kida, Sotoaki; Suzuki, Megumu

    1995-11-01

    The fracture mechanisms of short fiber reinforced AS composites are studied by acoustic emission technique for examining the effects of fiber contents. The loads P{sub b} and P{sub c} which the damage mechanisms change are obtained at the inflection points of the total AE energy curve the energy gradient method. The damages are generated by fiber breaking at the load point of P{sub b} and P{sub c} in B material, and by the fiber breaking and the debonding between resin and fiber at the load points of P{sub b} and P{sub c} in C material.

  14. Mechanical stress, fracture risk and beak evolution in Darwin's ground finches (Geospiza)

    PubMed Central

    Soons, Joris; Herrel, Anthony; Genbrugge, Annelies; Aerts, Peter; Podos, Jeffrey; Adriaens, Dominique; de Witte, Yoni; Jacobs, Patric; Dirckx, Joris

    2010-01-01

    Darwin's finches have radiated from a common ancestor into 14 descendent species, each specializing on distinct food resources and evolving divergent beak forms. Beak morphology in the ground finches (Geospiza) has been shown to evolve via natural selection in response to variation in food type, food availability and interspecific competition for food. From a mechanical perspective, however, beak size and shape are only indirectly related to birds' abilities to crack seeds, and beak form is hypothesized to evolve mainly under selection for fracture avoidance. Here, we test the fracture-avoidance hypothesis using finite-element modelling. We find that across species, mechanical loading is similar and approaches reported values of bone strength, thus suggesting pervasive selection on fracture avoidance. Additionally, deep and wide beaks are better suited for dissipating stress than are more elongate beaks when scaled to common sizes and loadings. Our results illustrate that deep and wide beaks in ground finches enable reduction of areas with high stress and peak stress magnitudes, allowing birds to crack hard seeds while limiting the risk of beak failure. These results may explain strong selection on beak depth and width in natural populations of Darwin's finches. PMID:20194171

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

    SciTech Connect

    Walter, Matthew; Yin, Shengjun; Stevens, Gary; Sommerville, Daniel; Palm, Nathan; Heinecke, Carol

    2012-01-01

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

  16. Investigation of the fracture mechanism in Ti-5Al-2.5Sn at cryogenic temperatures

    NASA Technical Reports Server (NTRS)

    Vanstone, R. H.; Low, J. R., Jr.; Shannon, J. L., Jr.

    1977-01-01

    The influence of microstructure on the fracture mechanism and plane-strain fracture toughness of Ti-5Al-2.5Sn was studied through the use of fractography and metallographic sectioning techniques. One-inch thick plates of extra low interstitial (ELI) and normal interstitial Ti-5Al-2.5Sn were mill annealed at 815 C followed by either air or furnace cooling. These variations in composition and cooling rate resulted in differences in the volume fraction and internal structure of the iron-stabilized phase, and in the crystallographic texture and ordering of the alpha matrix. The tensile properties of these plates were determined at 20 K, 77 K, and 295 K. The air-cooled ELI plate was the toughest material evaluated.

  17. 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.

  18. On a 2D hydro-mechanical lattice approach for modelling hydraulic fracture

    E-print Network

    Grassl, Peter; Gallipoli, Domenico; Wheeler, Simon J

    2014-01-01

    A 2D lattice approach to describe hydraulic fracturing is presented. The interaction of fluid pressure and mechanical response is described by Biot's theory. The lattice model is applied to the analysis of a thick-walled cylinder, for which an analytical solution for the elastic response is derived. The numerical results obtained with the lattice model agree well with the analytical solution. Furthermore, the coupled lattice approach is applied to the fracture analysis of the thick-walled cylinder. It is shown that the proposed lattice approach provides results that are independent of the mesh size. Moreover, a strong geometrical size effect on nominal strength is observed which lies between analytically derived lower and upper bounds. This size effect decreases with increasing Biot's coefficient.

  19. Correlation of Mechanical Properties with Fracture Surface Features in a Newly Developed Dual-Phase Steel

    NASA Astrophysics Data System (ADS)

    Mazaheri, Y.; Saeidi, N.; Kermanpur, A.; Najafizadeh, A.

    2015-04-01

    Dual-phase (DP) steels were produced by a newly developed method utilizing simple cold-rolling and subsequent short intercritical annealing of a martensite-ferrite duplex starting structure. Tensile testing revealed an excellent strength-elongation balance (UTS × UE ? 110-150 J/cm3) for the DP steels in comparison with the commercially used high strength steels. Fracture surfaces of the tensile specimens were studied by scanning electron microscopy analysis and image processing. Mechanical properties were correlated with fracture surface features. It was found that the variation of the total elongation and strength-elongation balance with the martensite volume fraction could be well correlated with the variation of the average dimple area. The variation of the yield strength and dimple areal density with the martensite volume fraction followed the same trend.

  20. NESC-VII: Fracture Mechanics Analyses of WPS Experiments on Large-scale Cruciform Specimen

    SciTech Connect

    Yin, Shengjun; Williams, Paul T; Bass, Bennett Richard

    2011-01-01

    This paper describes numerical analyses performed to simulate warm pre-stress (WPS) experiments conducted with large-scale cruciform specimens within the Network for Evaluation of Structural Components (NESC-VII) project. NESC-VII is a European cooperative action in support of WPS application in reactor pressure vessel (RPV) integrity assessment. The project aims in evaluation of the influence of WPS when assessing the structural integrity of RPVs. Advanced fracture mechanics models will be developed and performed to validate experiments concerning the effect of different WPS scenarios on RPV components. The Oak Ridge National Laboratory (ORNL), USA contributes to the Work Package-2 (Analyses of WPS experiments) within the NESCVII network. A series of WPS type experiments on large-scale cruciform specimens have been conducted at CEA Saclay, France, within the framework of NESC VII project. This paper first describes NESC-VII feasibility test analyses conducted at ORNL. Very good agreement was achieved between AREVA NP SAS and ORNL. Further analyses were conducted to evaluate the NESC-VII WPS tests conducted under Load-Cool-Transient- Fracture (LCTF) and Load-Cool-Fracture (LCF) conditions. This objective of this work is to provide a definitive quantification of WPS effects when assessing the structural integrity of reactor pressure vessels. This information will be utilized to further validate, refine, and improve the WPS models that are being used in probabilistic fracture mechanics computer codes now in use by the NRC staff in their effort to develop risk-informed updates to Title 10 of the U.S. Code of Federal Regulations (CFR), Part 50, Appendix G.

  1. 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.

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

    NASA Astrophysics Data System (ADS)

    Yeni, Yener Nail

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

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

    SciTech Connect

    Lee, Seok Woo; Lee, Hyun-Wook; Ryu, Ill; Nix, William D.; Gao, Huajian; Cui, Yi; /Stanford U., Materials Sci. Dept. /SLAC

    2015-06-01

    Following an explosion of studies of silicon as a negative electrode for Li-ion batteries, the anomalous volumetric changes and fracture of lithiated single Si particles have attracted significant attention in various fields, including mechanics. However, in real batteries, lithiation occurs simultaneously in clusters of Si in a confined medium. Hence, understanding how the individual Si structures interact during lithiation in a closed space is necessary. Herein, we demonstrate physical/mechanical interactions of swelling Si structures during lithiation using well-defined Si nanopillar pairs. Ex situ SEM and in situ TEM studies reveal that compressive stresses change the reaction kinetics so that preferential lithiation occurs at free surfaces when the pillars are mechanically clamped. Such mechanical interactions enhance the fracture resistance of This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Contract No. DE-AC02-76SF00515. SLAC-PUB-16300 2 lithiated Si by lessening the tensile stress concentrations in Si structures. This study will contribute to improved design of Si structures at the electrode level for high performance Li-ion batteries.

  4. A nonlinear fracture mechanics approach to the growth of small cracks

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.

    1983-01-01

    An analytical model of crack closure is used to study the crack growth and closure behavior of small cracks in plates and at notches. The calculated crack opening stresses for small and large cracks, together with elastic and elastic plastic fracture mechanics analyses, are used to correlate crack growth rate data. At equivalent elastic stress intensity factor levels, calculations predict that small cracks in plates and at notches should grow faster than large cracks because the applied stress needed to open a small crack is less than that needed to open a large crack. These predictions agree with observed trends in test data. The calculations from the model also imply that many of the stress intensity factor thresholds that are developed in tests with large cracks and with load reduction schemes do not apply to the growth of small cracks. The current calculations are based upon continuum mechanics principles and, thus, some crack size and grain structure exist where the underlying fracture mechanics assumptions become invalid because of material inhomogeneity (grains, inclusions, etc.). Admittedly, much more effort is needed to develop the mechanics of a noncontinuum. Nevertheless, these results indicate the importance of crack closure in predicting the growth of small cracks from large crack data.

  5. 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

  6. Consideration on the Mechanism of Microwave Emission Due to Rock Fracture

    NASA Astrophysics Data System (ADS)

    Takano, Tadashi; Sugita, Seiji; Yoshida, Shingo; Maeda, Takashi

    2010-05-01

    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 radiating wave with high accuracy. Accordingly, it was verified that a substantial power is emitted. The microwave emission phenomena were also observed on occasions of hypervelocity impact, and esteemed as phenomena generally associated with material destruction. Earthquakes and volcanic activities are association with rock fractures so that the microwave is expected to be emitted. Actually, the e emission was confirmed by the data analysis of the brightness temperature obtained by a remote sensing satellite, which flew over great earthquakes of Wuenchan and Sumatra, and great volcanic eruptions of Reventador and Chanten. It is important to show the microwave emission during rock fracture in natural phenomena. Therefore, the field test to detect the microwave due to the collapse of a crater cliff was planned and persecuted at the volcano of Miyake-jima about 100 km south of Tokyo. Volcanic activity may be more convenient than an earthquake because of the known location and time. As a result, they observed the microwave emission which was strongly correlated with the cliff collapses. Despite of the above-mentioned phenomenological fruits, the reason of the microwave emission is not fixed yet. We have investigated the mechanism of the emission in consideration of the obtained data in rock fracture experiments so far and the study results on material destruction by hypervelocity impact. This paper presents the proposal of the hypothesis and resultant discussions. The microwave sensors may be useful to monitor natural hazards such as an earthquake or a volcanic eruption, because the microwave due to rock fracture can penetrate the ionosphere and can be received by a satellite in orbit. However, the relation between a rock fracture and quakes has not been clarified at all, and is left to the future research. Please fill in your abstract text.

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

    NASA Astrophysics Data System (ADS)

    Poruks, Peter

    The fracture mechanisms of low carbon microalloyed plate steels based on the acicular ferrite + marten site/austenite microstructure (AF + M/A) are investigated. The final microstructure consists of a dispersed phase of submicron equi-axed martensite particles with a bainitic ferrite matrix. A series of plates with M/A volume fractions of 0.076--0.179 are studied. Brittle fracture is investigated by Instrumented Charpy impact testing of samples at -196°C and subsequent metallography. The M/A particles are identified as the crack nucleation sites and the cleavage fracture stress calculated to be 2400 MPa in a complete AF microstrucuture. This value is significantly larger than in steels that contain significant proportions of conventional bainite. Standard Charpy and Instrumented Charpy impact testing is conducted through a temperature range from -80 to + 22°C to study ductile fracture behaviour. The total absorbed energy is separated into energies of crack nucleation and of crack propagation. It is found that the energy of crack nucleation is weakly dependent on the volume fraction of M/A and completely independent of temperature over the range studied. The crack propagation energy varies significantly with both variables, decreasing with increased volume fraction of M/A and with decreasing temperature. The peak load in the instrumented Charpy data is used to calculate the dynamic fracture toughness, KId, which is found to be 105--120 MPa-m1/2. The void nucleation and void growth stages of ductile fracture are studied by metallographic examination of tensile bars. The sites of void nucleation are identified as inclusions and M/A particles. Voids nucleate at the M/A particles by decohesion of the particle-matrix interface. A constant void nucleation strain of epsilon = 0.90 +/- 0.05 is measured for all of the samples independent of the volume fraction of M/A. A stress-based criterion is used to predict void nucleation and the interface strength is determined to be 2500--2700 MPa. The void growth strains are measured and an inverse relationship is observed with decreasing void growth strain with increasing volume fraction of M/A. The data is compared to several models of void growth available in the literature and found to be in good agreement.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  9. Fracture Mechanisms of Zirconium Diboride Ultra-High Temperature Ceramics under Pulse Loading

    NASA Astrophysics Data System (ADS)

    Skripnyak, Vladimir V.; Bragov, Anatolii M.; Skripnyak, Vladimir A.; Lomunov, Andrei K.; Skripnyak, Evgeniya G.; Vaganova, Irina K.

    2015-06-01

    Mechanisms of failure in ultra-high temperature ceramics (UHTC) based on zirconium diboride under pulse loading were studied experimentally by the method of SHPB and theoretically using the multiscale simulation method. The obtained experimental and numerical data are evidence of the quasi-brittle fracture character of nanostructured zirconium diboride ceramics under compression and tension at high strain rates and the room temperatures. Damage of nanostructured porous zirconium diboride -based UHTC can be formed under stress pulse amplitude below the Hugoniot elastic limit. Fracture of nanostructured ultra-high temperature ceramics under pulse and shock-wave loadings is provided by fast processes of intercrystalline brittle fracture and relatively slow processes of quasi-brittle failure via growth and coalescence of microcracks. A decrease of the shear strength can be caused by nano-voids clusters in vicinity of triple junctions between ceramic matrix grains and ultrafine-grained ceramics. This research was supported by grants from ``The Tomsk State University Academic D.I. Mendeleev Fund Program'' and also N. I. Lobachevski State University of Nizhny Novgorod (Grant of post graduate mobility).

  10. A Review on Recent Contribution of Meshfree Methods to Structure and Fracture Mechanics Applications

    PubMed Central

    Daxini, S. D.; Prajapati, J. M.

    2014-01-01

    Meshfree methods are viewed as next generation computational techniques. With evident limitations of conventional grid based methods, like FEM, in dealing with problems of fracture mechanics, large deformation, and simulation of manufacturing processes, meshfree methods have gained much attention by researchers. A number of meshfree methods have been proposed till now for analyzing complex problems in various fields of engineering. Present work attempts to review recent developments and some earlier applications of well-known meshfree methods like EFG and MLPG to various types of structure mechanics and fracture mechanics applications like bending, buckling, free vibration analysis, sensitivity analysis and topology optimization, single and mixed mode crack problems, fatigue crack growth, and dynamic crack analysis and some typical applications like vibration of cracked structures, thermoelastic crack problems, and failure transition in impact problems. Due to complex nature of meshfree shape functions and evaluation of integrals in domain, meshless methods are computationally expensive as compared to conventional mesh based methods. Some improved versions of original meshfree methods and other techniques suggested by researchers to improve computational efficiency of meshfree methods are also reviewed here. PMID:24516359

  11. Fracture mechanisms of the SCS-6 fiber-reinforced titanium alloy matrix composites

    SciTech Connect

    Jeng Shwangming.

    1991-01-01

    Tensile, notched 3-point bending, low-cycle-fatigue and fatigue-crack-propagation tests were conducted at room temperature on the unidirectional SiC fiber-reinforced Ti-15V-3Cr-3Al-3Sn, Ti-6Al-4V and Ti-25Al-10Nb-3V-1Mo composites. Microstructural parameters controlling the deformation, damage initiation, and growth of the composites were investigated using metallographic technique and fractographic analysis. These parameters include interfacial reaction between fiber and matrix, interfacial mechanical properties, matrix toughness, fiber strength and loading conditions. The resulting deformation and fracture mechanisms of these composites under quasi-static and notched 3-point bend loading were classified on the basis of the ratio of the fiber strength ({delta}{sub f}) to interfacial shear strength ({tau}{sub i}) vs. matrix toughness. These failure mechanisms will provide a scientific basis for the development of an analytical model to predict the micro and macro-fracture processes of fiber-reinforced metal-matrix composites. Furthermore, the low-cycle-fatigue damage diagram was constructed using the maximum stress in the fiber vs. fatigue life.

  12. A review on recent contribution of meshfree methods to structure and fracture mechanics applications.

    PubMed

    Daxini, S D; Prajapati, J M

    2014-01-01

    Meshfree methods are viewed as next generation computational techniques. With evident limitations of conventional grid based methods, like FEM, in dealing with problems of fracture mechanics, large deformation, and simulation of manufacturing processes, meshfree methods have gained much attention by researchers. A number of meshfree methods have been proposed till now for analyzing complex problems in various fields of engineering. Present work attempts to review recent developments and some earlier applications of well-known meshfree methods like EFG and MLPG to various types of structure mechanics and fracture mechanics applications like bending, buckling, free vibration analysis, sensitivity analysis and topology optimization, single and mixed mode crack problems, fatigue crack growth, and dynamic crack analysis and some typical applications like vibration of cracked structures, thermoelastic crack problems, and failure transition in impact problems. Due to complex nature of meshfree shape functions and evaluation of integrals in domain, meshless methods are computationally expensive as compared to conventional mesh based methods. Some improved versions of original meshfree methods and other techniques suggested by researchers to improve computational efficiency of meshfree methods are also reviewed here. PMID:24516359

  13. Modeling and additive manufacturing of bio-inspired composites with tunable fracture mechanical properties.

    PubMed

    Dimas, Leon S; Buehler, Markus J

    2014-07-01

    Flaws, imperfections and cracks are ubiquitous in material systems and are commonly the catalysts of catastrophic material failure. As stresses and strains tend to concentrate around cracks and imperfections, structures tend to fail far before large regions of material have ever been subjected to significant loading. Therefore, a major challenge in material design is to engineer systems that perform on par with pristine structures despite the presence of imperfections. In this work we integrate knowledge of biological systems with computational modeling and state of the art additive manufacturing to synthesize advanced composites with tunable fracture mechanical properties. Supported by extensive mesoscale computer simulations, we demonstrate the design and manufacturing of composites that exhibit deformation mechanisms characteristic of pristine systems, featuring flaw-tolerant properties. We analyze the results by directly comparing strain fields for the synthesized composites, obtained through digital image correlation (DIC), and the computationally tested composites. Moreover, we plot Ashby diagrams for the range of simulated and experimental composites. Our findings show good agreement between simulation and experiment, confirming that the proposed mechanisms have a significant potential for vastly improving the fracture response of composite materials. We elucidate the role of stiffness ratio variations of composite constituents as an important feature in determining the composite properties. Moreover, our work validates the predictive ability of our models, presenting them as useful tools for guiding further material design. This work enables the tailored design and manufacturing of composites assembled from inferior building blocks, that obtain optimal combinations of stiffness and toughness. PMID:24700202

  14. Modeling mechanical degradation in lithium ion batteries during cycling: Solid electrolyte interphase fracture

    NASA Astrophysics Data System (ADS)

    Laresgoiti, Izaro; Käbitz, Stefan; Ecker, Madeleine; Sauer, Dirk Uwe

    2015-12-01

    During cycling, mechanical stresses can occur in the composite electrode, inside the active material, but also in the solid electrolyte interphase layer. A mechanical model is proposed based on a system made of a spherical graphite particle surrounded by the solid electrolyte interphase layer. During lithium intercalation or de-intercalation, stresses in the graphite are produced, governed by the diffusion induced stress phenomena and in the solid electrolyte interphase, driven by the graphite expansion. The stresses in both materials were simulated and a sensitivity analysis was performed to clarify the influence of principal parameters on both processes. Finally, assuming that the solid electrolyte interphase is the weakest material and therefore more prone to fracture than graphite, the experimental capacity fade during cycling was modeled based on its break and repair effect rather than on the fracture of the active material. The mechanical model of the solid electrolyte interphase was implemented in a single particle lithium ion battery model in order to reproduce capacity fade during battery lifetime. The model results were compared against cycle life aging experimental data, reproducing accurately the influence of the depth of discharge as well as the average state of charge on the capacity fade.

  15. Determination of stress intensity factors in three-dimensional problems of fracture mechanics

    NASA Astrophysics Data System (ADS)

    Tikhomirov, V. M.

    2014-09-01

    Dependences of displacements of the surface of a notch on the corresponding stress intensity factors were obtained for axisymmetric bodies with internal and external notches under different deformations (tensile, shear, bending, and torsion). An algorithm is proposed to determine the stress intensity factors of three types (opening mode, longitudinal shear, and transverse shear) from displacements of the notch surface near its tip. The effectiveness of the algorithm is shown, as an example, for numerical analysis of various three-dimensional problems of fracture mechanics.

  16. 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.

  17. Fracture mechanics. [review of fatigue crack propagation and technology of constructing safe structures

    NASA Technical Reports Server (NTRS)

    Hardrath, H. F.

    1974-01-01

    Fracture mechanics is a rapidly emerging discipline for assessing the residual strength of structures containing flaws due to fatigue, corrosion or accidental damage and for anticipating the rate of which such flaws will propagate if not repaired. The discipline is also applicable in the design of structures with improved resistance to such flaws. The present state of the design art is reviewed using this technology to choose materials, to configure safe and efficient structures, to specify inspection procedures, to predict lives of flawed structures and to develop reliability of current and future airframes.

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

    PubMed

    Lokhandwalla, M; Sturtevant, B

    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. PMID:10943929

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

    SciTech Connect

    Harris, D.O.; Lim, E.Y.; Dedhia, D.D.; Woo, H.H.; Chou, C.K.

    1982-06-01

    The efforts concentrated on modifications of the stratified Monte Carlo code called PRAISE (Piping Reliability Analysis Including Seismic Events) to make it more widely applicable to probabilistic fracture mechanics analysis of nuclear reactor piping. Pipe failures are considered to occur as the result of crack-like defects introduced during fabrication, that escape detection during inspections. The code modifications allow the following factors in addition to those considered in earlier work to be treated: other materials, failure criteria and subcritical crack growth characteristic; welding residual and vibratory stresses; and longitudinal welds (the original version considered only circumferential welds). The fracture mechanics background for the code modifications is included, and details of the modifications themselves provided. Additionally, an updated version of the PRAISE user's manual is included. The revised code, known as PRAISE-B was then applied to a variety of piping problems, including various size lines subject to stress corrosion cracking and vibratory stresses. Analyses including residual stresses and longitudinal welds were also performed.

  1. A New Approximate Fracture Mechanics Analysis Methodology for Composites with a Crack or Hole

    NASA Technical Reports Server (NTRS)

    Tsai, H. C.; Arocho, A.

    1990-01-01

    A new approximate theory which links the inherent flaw concept with the theory of crack tip stress singularities at a bi-material interface was developed. Three assumptions were made: (1) the existence of inherent flaw (i.e., damage zone) at the tip of the crack, (2) a fracture of the filamentary composites initiates at a crack lying in the matrix material at the interface of the matrix/filament, and (3) the laminate fails whenever the principal load-carrying laminae fails. This third assumption implies that for a laminate consisting of 0 degree plies, cracks into matrix perpendicular to the 0 degree filaments are the triggering mechanism for the final failure. Based on this theory, a parameter bar K sub Q which is similar to the stress intensity factor for isotropic materials but with a different dimension was defined. Utilizing existing test data, it was found that bar K sub Q can be treated as a material constant. Based on this finding a fracture mechanics analysis methodology was developed. The analytical results are correlated well with test results. This new approximate theory can apply to both brittle and metal matrix composite laminates with crack or hole.

  2. 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.

  3. Thermo-mechanically coupled fracture analysis of shape memory alloys using the extended finite element method

    NASA Astrophysics Data System (ADS)

    Hatefi Ardakani, S.; Ahmadian, H.; Mohammadi, S.

    2015-04-01

    In this paper, the extended finite element method is used for fracture analysis of shape memory alloys for both cases of super elastic and shape memory effects. Heat generation during the forward and reverse phase transformations can lead to temperature variation in the material because of strong thermo-mechanical coupling, which significantly influences the SMA mechanical behavior. First, the stationary crack mode is studied and the effects of loading rate on material behavior in the crack tip are examined. Then, the crack propagation analysis is performed in the presence of an initial crack by adopting a weighted averaging criterion, where the direction of crack propagation is determined by weighted averaging of effective stresses at all the integration points in the vicinity of the crack tip. Finally, several numerical examples are analyzed and the obtained results are compared with the available reference results.

  4. Chemical-mechanical interactions during natural fracture growth in tight gas and oil reservoirs: Implications for flow during reservoir charge and production

    NASA Astrophysics Data System (ADS)

    Eichhubl, Peter; Fall, Andras; Prodanovic, Masa; Tokan-Lawal, Adenike; Lander, Robert; Laubach, Steve

    2013-04-01

    Natural fractures in tight sandstone and shale reservoirs are characterized by partial to complete cementation. In all tight-gas sandstone reservoirs and suitable outcrop reservoir analogs, fractures frequently contain crack-seal quartz and carbonate cement that formed during incremental fracture opening. These synkinematic cements may be followed by blocky postkinematic cement occluding any residual fracture porosity. Fluid inclusion microthermometry combined with Raman analyses demonstrate that synkinematic cement formed under conditions close to maximum burial and incipient exhumation under elevated pore fluid pressures and over time spans of 10-50 m.y.. Fracture opening rates, integrated over the kinematic fracture aperture, are on the order of 10 microm/m.y. Based on the textural evidence of synkinematic cement growth, in combination with kinetic models of quartz cementation, we infer that these rates are comparable to rates of dissolution-precipitation reactions in the host rock, and of mass transfer between host rock and fracture. It is thus suggested that dissolution-precipitation creep is a dominant deformation mechanism allowing accommodation of permanent fracture strain under these deep-burial, diagenetically reactive conditions. Synkinematic mineral reactions in the host rock and precipitation of fracture lining cement guarantee that partially cemented natural fractures remain propped open and thus conductive under production conditions. However, cement linings and bridges can inhibit flow between micro-porous host rock and residual fracture porosity resulting in flow barriers. Complex pore geometry in partially cemented fractures may impede multiphase fracture flow and production. In shale, the interface between host rock and fracture cement is frequently mechanically weak potentially allowing fracture reactivation during well completion. Such artificially reactivated fractures may thus increase flow of production fluids even in formation containing otherwise sealed natural fractures.

  5. Chemical-mechanical interactions during natural fracture growth in tight gas and oil reservoirs: Implications for flow during reservoir charge and production

    NASA Astrophysics Data System (ADS)

    Eichhubl, P.; Fall, A.; Prodanovic, M.; Weisenberger, T.; Ukar, E.; Laubach, S.; Gale, J. F.

    2012-12-01

    Natural fractures in tight sandstone and shale reservoirs are characterized by partial to complete cementation. In all tight-gas sandstone reservoirs and suitable outcrop reservoir analogs, fractures frequently contain crack-seal quartz and carbonate cement that formed during incremental fracture opening. These synkinematic cements may be followed by blocky postkinematic cement occluding any residual fracture porosity. Fluid inclusion microthermometry combined with Raman analyses demonstrate that synkinematic cement formed under conditions close to maximum burial and incipient exhumation under elevated pore fluid pressures and over time spans of 10-40 m.y.. Fracture opening rates, integrated over the kinematic fracture aperture, are on the order of 10 ?m/m.y. Based on the textural evidence of synkinematic cement growth, in combination with kinetic models of quartz cementation, we infer that these rates are comparable to rates of dissolution-precipitation reactions in the host rock, and of mass transfer between host rock and fracture. It is thus suggested that dissolution-precipitation creep is a dominant deformation mechanism allowing accommodation of permanent fracture strain under these deep-burial, diagenetically reactive conditions. Synkinematic mineral reactions in the host rock and precipitation of fracture lining cement guarantee that partially cemented natural fractures remain propped open and thus conductive under production conditions. However, cement linings and bridges can inhibit flow between micro-porous host rock and residual fracture porosity resulting in flow barriers. Complex pore geometry in partially cemented fractures may impede multiphase fracture flow and production. In shale, the interface between host rock and fracture cement is frequently mechanically weak potentially allowing fracture reactivation during well completion. Such artificially reactivated fractures may thus increase flow of production fluids even in formation containing otherwise sealed natural fractures.

  6. 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.

  7. 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.

  8. An investigation on quench cracking behavior of superalloy Udimet 720LI using a fracture mechanics approach

    SciTech Connect

    Mao, J.; Keefer, V.L.; Chang, K.M.; Furrer, D.

    2000-04-01

    Quench cracking can be a serious problem in the heat treatment of high strength superalloys. A new fracture mechanics approach, quench cracking toughness (K{sub Q}), was introduced to evaluate the on-cooling quench cracking resistance of superalloy Udimet 720LI. A fully automatic computer controlled data acquisition and processing system was set up to track the on-cooling quenching process and to simulate the quench cracking. The influences of grain size, cooling rate, solution temperature, and alloy processing routes on quench cracking resistance were investigated. Research results indicate that quench cracking revealed a typical brittle and intergranular failure at high temperatures, which causes a lower quench cracking toughness in comparison to fracture toughness at room temperature. Fine grain structures show the higher quench cracking resistance and lower failure temperatures than intermediate grain structures at the same cooling rates. Moreover, higher cooling rate results in lower cracking toughness under the same grain size structures. In comparison of processing routes, powder metallurgy (PM) alloys show higher cracking resistance than cast and wrought (CW) alloys for fine grain structures at the same cooling rates. However, for immediate grain structure, there is no obvious difference of K{sub Q} between the two processing route in this study.

  9. Mechanism of diffusion-controlled brittle fracture. Final report, April 1, 1987--July 31, 1991

    SciTech Connect

    McMahon, C.J.

    1991-10-01

    Two generation of UHV testing systems were developed, one for testing pre-cracked specimens at constant displacement and the other at constant load, and they were supplemented by a computer-controlled potential-drop system for measurement of crack-growth rates. The latter system was also developed during this project. Experiments were carried out on the alloy Cu-8%Sn which was used as a model system for the phenomenon of diffusion-controlled fracture by intergranular decohesion resulting from the ingress of an embrittling element from a free surface as the result of an applied stress. The cracking phenomenon found earlier in alloy steels, and shown to be due to surface-adsorbed sulfur, was reproduced in the Cu-Sn alloy. This provided verification of the earlier proposed mechanism for the cracking phenomenon in the alloy steels, known as stress-relief cracking, and it also provided support for the hypothesis that the phenomenon was of a generic nature. In conjunction with the experimental work, the development of a quantitative theory of this class of brittle fracture, which we have termed ``dynamic embrittlement,`` was begun.

  10. 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.

    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.

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

    SciTech Connect

    Murray, S.H.; Desai, V.H.

    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.

  12. Fundamental Mechanisms of Tensile Fracture in Aluminum Sheet Unidirectionally Reinforced with Boron Filament. Ph.D. Thesis - Virginia Polytechnic Inst.

    NASA Technical Reports Server (NTRS)

    Herring, H. W.

    1971-01-01

    Results are presented from an experimental research effort to gain a more complete understanding of the physics of tensile fracture in unidirectionally reinforced B-Al composite sheet. By varying the degree of filament degradation resulting from fabrication, composite specimens were produced which failed in tension by the cumulative mode, the noncumulative mode, or by any desired combination of the two modes. Radiographic and acoustic emission techniques were combined to identify and physically describe a previously unrecognized fundamental fracture mechanism which was responsible for the noncumulative mode. The tensile strength of the composite was found to be severely limited by the noncumulative mechanism which involved the initiation and sustenance of a chain reaction of filament fractures at a relatively low stress level followed by ductile fracture of the matrix. The minimum average filament stress required for initiation of the fracture mechanism was shown to be approximately 170 ksi, and appeared to be independent of filament diameter, number of filament layers, and the identity of the matrix alloy.

  13. Complementary hydro-mechanical coupled finite/discrete element and microseismic modelling to predict hydraulic fracture propagation in tight shale reservoirs

    NASA Astrophysics Data System (ADS)

    Profit, Matthew; Dutko, Martin; Yu, Jianguo; Cole, Sarah; Angus, Doug; Baird, Alan

    2015-11-01

    This paper presents a novel approach to predict the propagation of hydraulic fractures in tight shale reservoirs. Many hydraulic fracture modelling schemes assume that the fracture direction is pre-seeded in the problem domain discretisation. This is a severe limitation as the reservoir often contains large numbers of pre-existing fractures that strongly influence the direction of the propagating fracture. To circumvent these shortcomings, a new fracture modelling treatment is proposed where the introduction of discrete fracture surfaces is based on new and dynamically updated geometrical entities rather than the topology of the underlying spatial discretisation. Hydraulic fracturing is an inherently coupled engineering problem with interactions between fluid flow and fracturing when the stress state of the reservoir rock attains a failure criterion. This work follows a staggered hydro-mechanical coupled finite/discrete element approach to capture the key interplay between fluid pressure and fracture growth. In field practice, the fracture growth is hidden from the design engineer and microseismicity is often used to infer hydraulic fracture lengths and directions. Microseismic output can also be computed from changes of the effective stress in the geomechanical model and compared against field microseismicity. A number of hydraulic fracture numerical examples are presented to illustrate the new technology.

  14. Identification of fracture mechanisms of fiberglass laminate based on the acoustic emission data

    NASA Astrophysics Data System (ADS)

    Panteleev, Ivan; Naimark, Oleg

    2015-10-01

    This work is devoted to classification of the acoustic emission pulses on the base of cluster analysis of acoustic emission data registered during quasistatic uniaxial tensile of fiberglass laminate samples. There were established characteristic parameters and stages of acoustic emission for each type of fracture: matrix fracture, fiber fracture, fiber/matrix debonding, delamination.

  15. 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

  16. Fracture mechanics of matrix cracking and delamination in glass/epoxy laminates

    NASA Technical Reports Server (NTRS)

    Caslini, M.; Zanotti, C.; Obrien, T. K.

    1986-01-01

    This study focused on characterizing matrix cracking and delamination behavior in multidirectional laminates. Static tension and tension-tension fatigue tests were conducted on two different layups. Damage onset, accumulation, and residual properties were measured. Matrix cracking was shown to have a considerable influence on residual stiffness of glass epoxy laminates, and could be predicted reasonably well for cracks in 90 deg piles using a simple shear lag analysis. A fracture mechanics analysis for the strain energy release rate associated with 90 deg ply-matrix crack formation was developed and was shown to correlate the onset of 90 deg ply cracks in different laminates. The linear degradation of laminate modulus with delamination area, previously observed for graphite epoxy laminates, was predicted for glass epoxy laminates using a simple rule of mixtures analysis. The strain energy release rate associated with edge delamination formation under static and cyclic loading was difficult to analyze because of the presence of several contemporary damage phenomena.

  17. A probabilistic fracture mechanics approach for structural reliability assessment of space flight systems

    NASA Technical Reports Server (NTRS)

    Sutharshana, S.; Creager, M.; Ebbeler, D.; Moore, N.

    1992-01-01

    A probabilistic fracture mechanics approach for predicting the failure life distribution due to subcritical crack growth is presented. A state-of-the-art crack propagation method is used in a Monte Carlo simulation to generate a distribution of failure lives. The crack growth failure model expresses failure life as a function of stochastic parameters including environment, loads, material properties, geometry, and model specification errors. A stochastic crack growth rate model that considers the uncertainties due to scatter in the data and mode misspecification is proposed. The rationale for choosing a particular type of probability distribution for each stochastic input parameter and for specifying the distribution parameters is presented. The approach is demonstrated through a probabilistic crack growth failure analysis of a welded tube in the Space Shuttle Main Engine. A discussion of the results from this application of the methodology is given.

  18. The role of fracture mechanics in the design of fuel tanks in space vehicles

    NASA Technical Reports Server (NTRS)

    Denton, S. J.; Liu, C. K.

    1976-01-01

    With special reference to design of fuel tanks in space vehicles, the principles of fracture mechanics are reviewed. An approximate but extremely simple relationship is derived among the operating stress level, the length of crack, and the number of cycles of failure. Any one of the variables can be computed approximately from the knowledge of the other two, if the loading schedule (mission of the tank) is not greatly altered. Two sample examples illustrating the procedures of determining the allowable safe operating stress corresponding to a set of assumed loading schedule are included. The selection of sample examples is limited by the relatively meager available data on the candidate material for various stress ratios in the cycling.

  19. DEFORMATION AND FRACTURE OF POORLY CONSOLIDATED MEDIA - Borehole Failure Mechanisms in High-Porosity Sandstone

    SciTech Connect

    Bezalel c. Haimson

    2005-06-10

    We investigated failure mechanisms around boreholes and the formation of borehole breakouts in high-porosity sandstone, with particular interest to grain-scale micromechanics of failure leading to the hitherto unrecognized fracture-like borehole breakouts and apparent compaction band formation in poorly consolidated granular materials. We also looked at a variety of drilling-related factors that contribute to the type, size and shape of borehole breakouts. The objective was to assess their effect on the ability to establish correlations between breakout geometry and in situ stress magnitudes, as well as on borehole stability prediction, and hydrocarbon/water extraction in general. We identified two classes of medium to high porosity (12-30%) sandstones, arkosic, consisting of 50-70% quartz and 15 to 50% feldspar, and quartz-rich sandstones, in which quartz grain contents varied from 90 to 100%. In arkose sandstones critical far-field stress magnitudes induced compressive failure around boreholes in the form of V-shaped (dog-eared) breakouts, the result of dilatant intra-and trans-granular microcracking subparallel to both the maximum horizontal far-field stress and to the borehole wall. On the other hand, boreholes in quartz-rich sandstones failed by developing fracture-like breakouts. These are long and very narrow (several grain diameters) tabular failure zones perpendicular to the maximum stress. Evidence provided mainly by SEM observations suggests a failure process initiated by localized grain-bond loosening along the least horizontal far-field stress springline, the packing of these grains into a lower porosity compaction band resembling those discovered in Navajo and Aztec sandstones, and the emptying of the loosened grains by the circulating drilling fluid starting from the borehole wall. Although the immediate several grain layers at the breakout tip often contain some cracked or even crushed grains, the failure mechanism enabled by the formation of the compaction band is largely non-dilatant, a major departure from the dilatant mechanism observed in Tablerock sandstone. The experimental results suggest that unlike our previous assertion, the strength of grain bonding and the mineral composition, rather than the porosity, are major factors in the formation of compaction bands and the ensuing fracture-like breakouts. Some breakout dimensions in all rocks were correlatable to the far-field principal stresses, and could potentially be used (in conjunction with other information) as indicators of their magnitudes. However, we found that several factors can significantly influence breakout geometry. Larger boreholes and increased drilling-fluid flow rates produce longer fracture-like breakouts, suggesting that breakouts in field-scale wellbores could reach considerable lengths. On the other hand, increased drilling-fluid weight and increased drill-bit penetration rate resulted in a decrease in breakout length. These results indicate that breakout growth can be controlled to some degree by manipulating drilling variables. Realizing how drilling variables impact borehole breakout formation is important in understanding the process by which breakouts form and their potential use as indicators of the far-field in situ stress magnitudes and as sources of sand production. As our research indicates, the final breakout size and mechanism of formation can be a function of several variables and conditions, meaning there is still much to be understood about this phenomenon.

  20. 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.

  1. 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.

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

    SciTech Connect

    Yin, Shengjun; Bass, Bennett Richard; Stevens, Gary; Kirk, Mark

    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.

  3. 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...

  4. 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.

  5. Mechanics of tungsten blistering II: Analytical treatment and fracture mechanical assessment

    NASA Astrophysics Data System (ADS)

    Li, Muyuan; You, Jeong-Ha

    2015-10-01

    Since a decade the blistering of pure tungsten under hydrogen implantation has been one of the major research topics in relation to the plasma-wall interaction of tungsten-armored first wall. Overall blistering may reduce the erosion lifetime of the wall. Mature blisters grown by high internal pressure are likely to burst leading to exfoliation of the surface. Therefore, the control and suppression of blistering is an important concern for sustainable operation of the tungsten-armored plasma-facing components. In this context, a quantitative assessment of the mechanical conditions for blister bulging and growth is an important concern. In this article a theoretical framework is presented to describe the bulging deformation of tungsten blisters and to estimate the mechanical driving force of blister growth. The validity of the analytical formulations based on the theory of elastic plates is evaluated with the help of finite element analysis. Plastic strains and J-integral values at the blister boundary edge are assessed by means of numerical simulation. Extensive parametric studies were performed for a range of blister geometry (cap aspect ratio), gas pressure, yield stress and hardening rate. The characteristic features of the blistering mechanics are discussed and the cracking energy is quantitatively estimated for the various combinations of parameters.

  6. 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

  7. 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.

  8. 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.

  9. Homogenized Finite Element Analysis on Effective Elastoplastic Mechanical Behaviors of Composite with Imperfect Interfaces

    PubMed Central

    Jiang, Wu-Gui; Zhong, Ren-Zhi; Qin, Qing H.; Tong, Yong-Gang

    2014-01-01

    A three-dimensional (3D) representative volume element (RVE) model was developed for analyzing effective mechanical behavior of fiber-reinforced ceramic matrix composites with imperfect interfaces. In the model, the fiber is assumed to be perfectly elastic until its tensile strength, and the ceramic material is modeled by an elasto-plastic Drucker-Prager constitutive law. The RVE model is then used to study the elastic properties and the tensile strength of composites with imperfect interfaces and validated through experiments. The imperfect interfaces between the fiber and the matrix are taken into account by introducing some cohesive contact surfaces. The influences of the interface on the elastic constants and the tensile strengths are examined through these interface models. PMID:25522170

  10. Homogenized finite element analysis on effective elastoplastic mechanical behaviors of composite with imperfect interfaces.

    PubMed

    Jiang, Wu-Gui; Zhong, Ren-Zhi; Qin, Qing H; Tong, Yong-Gang

    2014-01-01

    A three-dimensional (3D) representative volume element (RVE) model was developed for analyzing effective mechanical behavior of fiber-reinforced ceramic matrix composites with imperfect interfaces. In the model, the fiber is assumed to be perfectly elastic until its tensile strength, and the ceramic material is modeled by an elasto-plastic Drucker-Prager constitutive law. The RVE model is then used to study the elastic properties and the tensile strength of composites with imperfect interfaces and validated through experiments. The imperfect interfaces between the fiber and the matrix are taken into account by introducing some cohesive contact surfaces. The influences of the interface on the elastic constants and the tensile strengths are examined through these interface models. PMID:25522170

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

    SciTech Connect

    Du Yongfeng; Li Hui

    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.

  12. A witnessed case of a classic metaphyseal fracture caused during IV line placement in a child: Insight into mechanism of injury.

    PubMed

    Burrell, Tanya; Opfer, Erin; Berglund, Lisa; Lowe, Lisa H; Anderst, James

    2015-10-01

    Recent publications argue that classic metaphyseal fractures are caused by rickets as opposed to trauma. Previous case reports of accidental traumatic classic metaphyseal fractures have been discounted due to lack of identification of the fracture at the time of the traumatic event, and lack of an evaluation for boney metabolic disorders. We report a case of a 20 day old male with a diagnosis of congenital vertical talus who sustained a classic metaphyseal fracture of the distal tibia during manipulation in preparation for intravenous line placement. The mechanics of the event causing the classic metaphyseal fracture were witnessed and accompanied by an audible "pop". Prior x-rays of the tibia demonstrate normal osseous morphology, and an evaluation for boney metabolic disorders was normal. This case identifies a traumatic classic metaphyseal fracture and provides insight into the types of forces necessary to cause such a fracture. PMID:26344460

  13. Mechanical properties of the dentinoenamel junction: AFM studies of nanohardness, elastic modulus, and fracture.

    PubMed

    Marshall, G W; Balooch, M; Gallagher, R R; Gansky, S A; Marshall, S J

    2001-01-01

    The dentinoenamel junction (DEJ) is a complex and poorly defined structure that unites the brittle overlying enamel with the dentin that forms the bulk of the tooth. In addition, this structure appears to confer excellent toughness and crack deflecting properties to the tooth, and has drawn considerable interest as a biomimetic model of a structure uniting dissimilar materials. This work sought to characterize the nanomechanical properties in the region of the DEJ using modified AFM based nanoindentation to determine nanohardness and elastic modulus. Lines of indentations traversing the DEJ were made at 1-2 microm intervals from the dentin to enamel along three directions on polished sagittal sections from three third molars. Nanohardness and elastic modulus rose steadily across the DEJ from bulk dentin to enamel. DEJ width was estimated by local polynomial regression fits for each sample and location of the mechanical property curves for the data gradient from enamel to dentin, and gave a mean value of 11.8 microm, which did not vary significantly with intratooth location or among teeth. Nanoindentation was also used to initiate cracks in the DEJ region. In agreement with prior work, it was difficult to initiate cracks that traversed the DEJ, or to produce cracks in the dentin. The fracture toughness values for enamel of 0.6-0.9 MPa . m(1/2) were in good agreement with recent microindentation fracture results. Our results suggest that the DEJ displays a gradient in structure and that nanoindenation methods show promise for further understanding its structure and function. PMID:11077406

  14. 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.

  15. Fracture mechanics investigation of oil shale to aid in understanding the explosive fragmentation process. Final technical report, January 1983-July 1984

    SciTech Connect

    Chong, K.P.

    1984-09-01

    This report summarizes goals and findings achieved in developing technologies to improve the overall efficiency of oil shale recovery processes. The objectives are to (a) develop theoretical fracture mechanics tools that are applicable to transversely isotropic materials such as sedimentary rock, more particularly oil shale; and (b) develop a fracture mechanics test procedure that can be conveniently used for rock specimens. Such a test procedure would: utilize the geometry of a typical rock core for the test; require a minimum amount of specimen machining; and provide meaningful, reproducible data that corresponds well to test data obtained from conventional fracture mechanics tests. Critical review of the state-of-the-art of fracture mechanics on layered rocks has been completed. Recommendations are made for innovative and promising methods for oil shale fracture mechanics. Numerical and analytical studies of mixed mode fracture mechanics are investigated. Transversely isotropic properties of oil shale are input using isoparametric finite elements with singular elements at the crack tip. The model is a plate with an edge crack whose angle with the edge varies to study the effect of mixed mode fracture under various conditions. The three-dimensional plate is in tension, and stress, energy methods are used in the fracture analysis. Precracked disks of oil shale cored perpendicular to bedding planes are analyzed numerically. Stress intensity factors are determined by (i) strain energy method, and (ii) elliptic simulation method. 47 refs., 12 figs., 1 tab.

  16. 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.

  17. Fracture mechanics by three-dimensional crack-tip synchrotron X-ray microscopy

    PubMed Central

    Withers, P. J.

    2015-01-01

    To better understand the relationship between the nucleation and growth of defects and the local stresses and phase changes that cause them, we need both imaging and stress mapping. Here, we explore how this can be achieved by bringing together synchrotron X-ray diffraction and tomographic imaging. Conventionally, these are undertaken on separate synchrotron beamlines; however, instruments capable of both imaging and diffraction are beginning to emerge, such as ID15 at the European Synchrotron Radiation Facility and JEEP at the Diamond Light Source. This review explores the concept of three-dimensional crack-tip X-ray microscopy, bringing them together to probe the crack-tip behaviour under realistic environmental and loading conditions and to extract quantitative fracture mechanics information about the local crack-tip environment. X-ray diffraction provides information about the crack-tip stress field, phase transformations, plastic zone and crack-face tractions and forces. Time-lapse CT, besides providing information about the three-dimensional nature of the crack and its local growth rate, can also provide information as to the activation of extrinsic toughening mechanisms such as crack deflection, crack-tip zone shielding, crack bridging and crack closure. It is shown how crack-tip microscopy allows a quantitative measure of the crack-tip driving force via the stress intensity factor or the crack-tip opening displacement. Finally, further opportunities for synchrotron X-ray microscopy are explored. PMID:25624521

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

    NASA Technical Reports Server (NTRS)

    Gangloff, Richard P.; Kim, Sang-Shik

    1993-01-01

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

  19. Mechanics of two interacting magma-driven fractures: A numerical study

    NASA Astrophysics Data System (ADS)

    Zhang, Xi; Bunger, Andrew P.; Jeffrey, Robert G.

    2014-11-01

    To understand magma focusing from broad melting zones in the crust, propagation in brittle rocks of two interacting dikes ascending from a single deep source has been modeled using a time-dependent plane strain hydraulic fracturing model. The source is assumed to generate a constant influx rate to feed the dike growth, which is also aided by buoyancy effects. In contrast to uncoupled model results, the simultaneous parallel growth of two dikes to a certain distance is found to occur provided that the two dikes are initially of different heights, which might be produced either by previous magma intrusion or during nucleation. The shorter dike will chase the longer one and they can either progressively merge or continue subparallel growth at a reduced spacing, depending on the deviator stress between the vertical and horizontal stresses and the initial lateral separation, with parameters given in dimensionless forms. Numerical results reveal the mechanics for simultaneous ascents of two subparallel dikes, in that dike interaction can produce a low-stress field, which is just above the tip of the shorter dike, favorable to growth of the shorter dike. The energy analysis indicates that the energy required for two subparallel dikes is less than that for a single dike during the late-time buoyancy-viscosity propagation stage where considerable ascent occurs. This growth behavior might provide the mechanism for simultaneous, instead of sequential, growth of various dikes in a single set.

  20. Liquid metal embrittlement of T91 and 316L steels by heavy liquid metals: A fracture mechanics assessment

    NASA Astrophysics Data System (ADS)

    Auger, T.; Hamouche, Z.; Medina-Almazàn, L.; Gorse, D.

    2008-06-01

    LME of the martensitic T91 and the austenitic 316L steels have been investigated in the CCT geometry in the plane-stress condition. Using such a geometry, premature cracking induced by a liquid metal (PbBi and Hg) can be studied using a fracture mechanics approach based on CTOD, J-? a and fracture assessment diagram. One is able to measure a reduction of the crack tip blunting and a reduction of the energy required for crack propagation induced by the liquid metal. In spite of some limitations, this qualitative evaluation shows that liquid metals do not induce strong embrittlement on steels in plane-stress condition. Rather, the effect of the liquid metal seems to promote a fracture mode by plastic collapse linked with strain localization. It indicates that the materials, in spite of a potential embrittlement, should still be acceptable in terms of safety criteria.

  1. 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.

  2. Fracture Profile and Crack Propagation of Ultra-High Strength Hot-Stamped Boron Steel During Mechanical Trimming Process

    NASA Astrophysics Data System (ADS)

    Han, Xianhong; Yang, Kun; Chen, Sisi; Chen, Jun

    2015-10-01

    Mechanical trimming process for ultra-high strength boron steel after hot stamping was carried out in this study. Shear and tensile tests were designed to analyze the influences of stress state on the fracture mode; trimmed fracture surface and profile were observed and compared to other commonly used steels such as DP980 and Q235 etc.; the crack propagation during trimming process was studied through step-by-step tests. The observation and analysis reveal that the fracture mode of hot-stamped boron steel is highly related to the stress state, it belongs to cleavage fracture on low stress triaxiality but dimple fracture on high stress triaxiality. Such phenomenon is reflected in the trimming process, during which the stress state changes from shear-dominated state to tensile-dominated state. In addition, the burnish zone of trimmed boron steel is much smaller than other high strength steels, and the profile of cutting surface shows an `S'-like shape which is destructive to the trimming tool. Moreover, during the trimming process, most martensite laths near the cutting edge are stretched and rotated markedly to the direction of the shear band, and the main crack expands along those grain boundaries, which may penetrate through a few martensite laths and form small crack branches.

  3. Discrete element simulations to assess controls on landslide size in heterogeneous slopes: The roles of fractures and mechanical stratigraphy

    NASA Astrophysics Data System (ADS)

    Katz, O.; Morgan, J. K.

    2009-04-01

    Landslides of different sizes, from different locations around the globe, triggered by different mechanisms, all seem to follow similar size-distributions, consisting of a maximum frequency at the small landslide side of the distribution and a power-law tail toward the large landslide side. Here we carry out numerical simulations using the discrete element method (DEM) to better understand the physics behind this distinctive landslide size distribution, and in particular, to determine what controls the shape of the power law tail. Previous studies have suggested that the power-law tail is a result of large, deep seated landslides that occur in the fractured and layered deep part of the slope. We modeled 2D slopes constructed of numerous spheres simulating material with friction and cohesion. The simulated slope length is 2500 m with height (H) range of 500 m-1000 m; slope angle is fixed at 70 degrees. To determine landslide size, we measured the landslide surface length from the scarp to the toe, and the landslide thickness as the maximum distance from the slope surface to the sliding surface. Failure in mechanically homogeneous slopes initiates at the slope-foot and propagates to slope-crest forming a discrete sliding plane. Landslides (slumps) developed encompass the entire slope height (i.e. maximum size) with size dependent on H and a self-similar shape, producing a constant ratio of landslide thickness to surface length. Slumps developed in slopes containing 500 randomly distributed and oriented fractures produce landslides that are smaller than maximum size (as fracture length increases from 10 m to 100 m, landslide size increases from 0.75 of maximum size to the maximum size.). The sliding surface uses the preexisting fractures to propagate from slope-foot to crest. Landslides developed in slopes with a weak dipping layer are of rock-slide type and have geometries and dimensions reflecting the layer depth relative to the slope height. The above observations highlight the importance of fractures and stratigraphy in determining the size distribution of large, deep-seated landslides. Longer fractures in otherwise homogeneous slopes readily coalesce to form continuous, through-going failure surfaces, thereby producing larger landslides than observed in slopes containing short, distributed fractures or no fractures. Heterogeneous mechanical layering also promotes large deep-seated landslides, by defining weak slip surfaces that cut the entire slope. These results confirm the importance of slope heterogeneity in defining the power-law tail of landslide size distributions.

  4. Architecture, fracture system, mechanical properties and permeability structure of a fault zone in Lower Triassic sandstone, Upper Rhine Graben

    NASA Astrophysics Data System (ADS)

    Bauer, Johanna F.; Meier, Silke; Philipp, Sonja L.

    2015-04-01

    Close to the western Upper Rhine Graben Main Fault, Alsace, a NNE-SSW-striking fault zone, crosscutting porous, thick bedded Lower Triassic Bunter sandstone was investigated in detail, including its architecture, discontinuity system, mechanical rock properties and implications on its permeability structure and fault zone type. Field observations indicate a three-part fault zone structure including core-, transition- and damage zone. The at least 14 m thick fault core is composed of various slip surfaces and deformation bands, which encompass fractured host rock lenses. When connected, host rock lenses may transport fluids through the core zone. Adjacent transition zones are highly fractured in R1-orientation, show folded beds and contain P1-oriented deformation bands. R1 and P1-fractures are synthetic shear fractures and project with an acute angle (10-20°) toward the fault plane. Only in the damage zone, fault-parallel striking fractures occur. Here, increasing fracture apertures and connectivity may increase the permeability toward the fault core. Mechanical rock properties from 12 rock samples (Young's modulus, uniaxial compressive strength, tensile strength) measured in all the parts of the fault zone, show highest values within the transition zone. In-situ measurements of rebound-hardnesses with a Schmidt-Hammer and analytical approaches, however, indicate that effective Young's moduli are two to sixteen times lower than the Young's moduli of intact rock. Values clearly decrease toward the fault core, even in the transition zone and are in average lower than effective Young's moduli in the damage zone. Although many fault zones in sandstone are sealing structures these field study show, that fault zones in porous sandstone may allow fluid flow.

  5. Nose fracture

    MedlinePLUS

    Fracture of the nose; Broken nose; Nasal fracture; Nasal bone fracture; Nasal septal fracture ... A fractured nose is the most common fracture of the face. It ... with other fractures of the face. Sometimes a blunt injury can ...

  6. 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

  7. 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.

  8. 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

    2015-04-01

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

  9. Micro-mechanical investigation for effects of helium on grain boundary fracture of austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Miura, Terumitsu; Fujii, Katsuhiko; Fukuya, Koji

    2015-02-01

    Effects of helium (He) on grain boundary (GB) fracture of austenitic stainless steel were investigated by micro-tensile tests. Micro-bicrystal tensile specimens were fabricated for non-coincidence site lattice boundaries of He ion-irradiated 316 stainless steel by focused ion beam (FIB) micro-processing. Micro-tensile tests were conducted in a vacuum at room temperature in the FIB system. Specimens containing more than 2 at.% He fractured at GBs. The criteria for brittle fracture occurrence on GBs were: (1) He concentrations higher than 2 at.%; (2) formation of He bubbles on the GBs with less than a 5 nm spacing; and (3) matrix hardening to more than 4.6 GPa (nano-indentation hardness). The fracture stress of GB brittle fracture was lower for a specimen with higher He concentration while the size and areal density of the GB He bubbles were the same. The specimens that contained 10 at.% He and had been annealed at 923 K after irradiation fractured at the GB nominally in a brittle manner; however the inter-bubble matrix at the GB experienced ductile fracture. The annealing caused He bubbles to grow but decreased the areal density so that the spacing of the GB He bubbles widened and the hardness decreased, therefore the fracture mode changed from brittle to ductile. The findings revealed that He promotes GB fracture by weakening the GB strength and hardening the matrix due to the formation of He bubbles both on GBs and in the matrix. In addition, the findings suggested that GB segregated He atoms may have a role in GB fracture.

  10. 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

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

    NASA Technical Reports Server (NTRS)

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

    2007-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

  13. A review of path-independent integrals in elastic-plastic fracture mechanics, task 4

    NASA Technical Reports Server (NTRS)

    Kim, K. S.

    1985-01-01

    The path independent (P-I) integrals in elastic plastic fracture mechanics which have been proposed in recent years to overcome the limitations imposed on the J integral are reviewed. The P-I integrals considered herein are the J integral by Rice, the thermoelastic P-I integrals by Wilson and Yu and by Gurtin, the J* integral by Blackburn, the J sub theta integral by Ainsworth et al., the J integral by Kishimoto et al., and the delta T sub p and delta T* sub p integrals by Atluri et al. The theoretical foundation of these P-I integrals is examined with emphasis on whether or not path independence is maintained in the presence of nonproportional loading and unloading in the plastic regime, thermal gradients, and material inhomogeneities. The similarities, differences, salient features, and limitations of these P-I integrals are discussed. Comments are also made with regard to the physical meaning, the possibility of experimental measurement, and computational aspects.

  14. A review of path-independent integrals in elastic-plastic fracture mechanics

    NASA Technical Reports Server (NTRS)

    Kim, Kwang S.; Orange, Thomas W.

    1988-01-01

    The objective of this paper is to review the path-independent (P-I) integrals in elastic plastic fracture mechanics which have been proposed in recent years to overcome the limitations imposed on the J-integral. The P-I integrals considered are the J-integral by Rice (1968), the thermoelastic P-I integrals by Wilson and Yu (1979) and Gurtin (1979), the J-integral by Blackburn (1972), the J(theta)-integral by Ainsworth et al. (1978), the J-integral by Kishimoto et al. (1980), and the Delta-T(p) and Delta T(p)-asterisk integrals by Alturi et al. (1982). The theoretical foundation of the P-I integrals is examined with an emphasis on whether or not the path independence is maintained in the presence of nonproportional loading and unloading in the plastic regime, thermal gradient, and material inhomogeneities. The simularities, difference, salient features, and limitations of the P-I integrals are discussed. Comments are also made with regard to the physical meaning, the possibility of experimental measurement, and computational aspects.

  15. 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.

    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.

  16. 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.

  17. 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.

  18. 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.

  19. Application of fracture mechanics and half-cycle theory to the prediction of fatigue life of aerospace structural components

    NASA Technical Reports Server (NTRS)

    Ko, William L.

    1989-01-01

    The service life of aircraft structural components undergoing random stress cycling was analyzed by the application of fracture mechanics. The initial crack sizes at the critical stress points for the fatigue crack growth analysis were established through proof load tests. The fatigue crack growth rates for random stress cycles were calculated using the half-cycle method. A new equation was developed for calculating the number of remaining flights for the structural components. The number of remaining flights predicted by the new equation is much lower than that predicted by the conventional equation. This report describes the application of fracture mechanics and the half-cycle method to calculate the number of remaining flights for aircraft structural components.

  20. Brittle Fracture Mechanics of Snow : In Situ Testing and Distinct Element Modeling

    NASA Astrophysics Data System (ADS)

    Faillettaz, J.; Daudon, D.; Louchet, F.

    A snow slab avalanche release usually results from the rupture of the snow cover at the interface between an upper layer (slab) and an underlying substrate. Amazingly, the models proposed so far to predict this kind of rupture were only based on continuum mechanics, as they did not take into account the existing cracks or cohesion defects at the interface between the two layers, and their possible unstable propagation that eventually triggers the avalanche. This is why the present work, essentially devoted to human triggered avalanches, is based instead on Griffith's fracture approach, widely used in modelling brittle fracture of materials. The possible rupture scenario involves a propagation in a shear mode of a "basal crack" nucleated and gradually grown at the interface by the skier's weight, followed by a mode I opening and propagation of a "crown crack" at the top of the sheared zone. Different avalanche sizes are predicted according whether the basal crack propagation reaches or not the Griffith's instabil- ity size before crown crack opening (Louchet 2000). Accurate predictions therefore require a precise knowledge of snow toughness values in both modes. A theoretical estimation of toughness considering snow as an ice foam was proposed by Kirchner and Michot (2000), but the question of whether these results may be extended to an assembly of sintered grains is still open. A mode I toughness measurement of snow was also published for the first time by Kirchner and Michot on samples gathered in the Vosges range. In the present work, we developed an experimental set similar to Michot's, in order to measure mode I toughness: a vertical crack of increasing size is gradually machined from the top surface in an horizontal snow beam until failure takes place under its own weight. The toughness value is computed from the snow weight and the crack length at the onset of rapid crack propagation. A similar device was designed for mode II testing, but is still under development. The experimental cam- paign carried out in the Alps during the 2000-2001 winter on homogeneous sintered snow with a density of 200 kg/m3 (typical of a snow slab) gave results of the same or- der of magnitude as Michot's. A numerical modeling of these toughness experiments was performed using a distinct element code, considering snow as a cohesive granu- lar material. Both crack propagation and rupture patterns are in close agreement with experiments. References: Kirchner, Michot, Suzuki 2000 Fracture thoughness of snow in tension 1 Philisophical Magazine A, vol 80,N5, p1265-1272. Louchet 2001,A transition in dry snow slab avalanche triggering modes, Annales de glaciologie, vol 32,Symphosium on Snow, Avalanches and Impact of the Frest Cover, Innsbruck,Austria,22-26 may 2000, p2285-289 2

  1. Structure, mechanical properties and fracture behavior of organosilicate glass thin films

    NASA Astrophysics Data System (ADS)

    Lin, Youbo

    2007-12-01

    Organosilicate glass (OSG) thin films with low permittivity made by means of plasma enhanced chemical vapor deposition are the inter-metal insulator in advanced integrated circuits. These materials are employed to reduce the interconnect delay and power consumption associated with the inter-line capacitance. However the implementation of OSG is hampered by its poor mechanical properties and susceptibility to stress-corrosion cracking. In this work, we present a study of the structure evolution of OSG under various processing conditions, as well as the impact of structure and environment on the mechanical properties and fracture behavior. We will show that the composition and structure of OSG can be finely tuned by changing the parameters during film deposition or post-treatments. Adding carbon content in the film lowers the density and reduces the dielectric constant, accompanied by a decrease of the network connectivity. Ultraviolet-cure is very effective in crosslinking and stabilizing the network structure without causing significant increase in permittivity. With the assist of a structure model, we determined the infrared absorption inverse cross-sections that may be used to analyze infrared spectra of other OSG films. The mechanical properties of OSG are very sensitive to the network structure. Both the mean connectivity number and networking bond density correlate well with mechanical properties. The comparison of cohesive and adhesion energies reveals that plasma treatments substantially enhance the adhesion. However, the enhancement diminishes when the films are exposed to reactive environments. Our study shows that the adhesion energy at given crack velocity changes linearly with the logarithm of the water partial pressure in ambient, or with pH value in aqueous environment. On the other hand, water degrades the electrical property and adhesion when absorbed. We found that the water diffusion in OSG film stacks is very fast, reversible under mild annealing; and the activation energy is low (˜0.27 eV), consistent with an interfacial diffusion process. These findings can be applied to assess the reliability of OSG-containing thin film structures in microelectronics.

  2. Application of fracture mechanics to predict the strength of filament-wound composite specimens with surface damage

    NASA Technical Reports Server (NTRS)

    Morris, D. H.; Harris, C. E.

    1988-01-01

    The strength of a thick surface notched filament wound graphite/epoxy tensile specimen was predicted using fracture mechanics analysis. The prediction model depended upon the depth of the surface notch and upon the type of failure. Specimens failed in two stages: first a sublaminate with thickness equal to the depth of the surface cut, and second, for increasing load, a sublaminate with thickness equal to the initial thickness minus the cut depth. Analytical predictions and experimental data were in good agreement.

  3. 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.

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

    SciTech Connect

    Nyilas, A.; Mitterbacher, H.

    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.

  5. 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.

  6. 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 ...

  7. FRACTURE MECHANISM OF A BAINITE STEEL IN PRECRACKED AND NOTCHED SPECIMENS

    E-print Network

    Qin, Qinghua

    in Charpy V-notch impact energy. They attributed this to the variation of cleavage fracture stress specimen. Currently, bainite steels have been increasing used in pressure vessels and piping industries due

  8. 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.

  9. 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.

  10. Petrophysical and Mechanical Properties of Fractured Aquifers in the Northern Newark Basin: Implications for Carbon Sequestration

    NASA Astrophysics Data System (ADS)

    Zakharova, N. V.; Goldberg, D.; Collins, D.; Olsen, P. E.

    2012-12-01

    One of the key factors in predicting the performance of low-permeability fractured reservoirs is a detailed understanding of the in-situ state of stress and the distribution and orientation of natural fractures and faults. In this study we analyze borehole geophysical data from a deep characterization well in the northern Newark Basin, a candidate CO2-storage site, and provide petrophysical and geomechanical characterization of fractured sedimentary and igneous formations. Previous studies in the northern Newark basin demonstrated no unique relationship between hydraulic conductivity and degree of fracturing, fracture apertures or orientation. Therefore, in the absence of hydraulic testing data predicting fracture behavior under CO2 injection condition presents a significant challenge for baseline formation characterization. Moreover, fluid injection in deep wells can cause reactivation of existing faults or new fracture initiation due to significant increase in the pore pressure. We analyze electrical resistivity images and full-wave sonic data to constrain the state of the current in-situ stress in the northern Newark basin, and to evaluate how the interaction between in-situ stress and the distribution and orientation of natural fractures influences their hydraulic properties. We then combine it with the full suite of wireline logs to describe petrophysical, hydraulic, and geomechanical properties of the fractured aquifers at the locality. The Sandia Technologies, LLC Tandem Lot #1 geologic characterization well (Rockland County, NY) is about 6,800 ft deep and transects Triassic terrestrial sediments and the Palisades diabase sill that are both characterized by abundant natural fractures. A suite of standard wireline logs, high-resolution electrical resistivity images and full-wave sonic data were collected in the borehole but no hydraulic data or in-situ stress estimates are available. Borehole breakouts are clearly observed in the resistivity images in distinct sedimentary layers and strike predominantly SSE-NNW. In the Palisades sill breakouts are absent but the wellbore is consistently enlarged by up to 4 inches in the SE-NW direction (nominal hole diameter is 8.5 in). Drilling-induced tensile fractures and drilling-enhanced natural fractures appear in the tensile quadrants striking NE-SW. Preliminary analysis of sonic wavefields also suggest the NE orientation of the fast shear azimuth. For a vertical borehole these factors indicate maximum horizontal stress in the NE-SW direction, and are consistent with earthquake focal plane solutions and previous stress direction estimates in the Newark Basin. Borehole images also provide an excellent tool to describe natural fracture distribution and orientation. Combined with other petrophysical data such as core-calibrated density log, elastic moduli and stress-induced shear-wave anisotropy indicator, they allow to constrain geomechanical properties of the formation and to predict fracture behavior for potential CO2 injection conditions.

  11. Mechanisms affecting the transport and retention of bacteria, bacteriophage and microspheres in laboratory-scale saturated fractures

    NASA Astrophysics Data System (ADS)

    Seggewiss, G.; Dickson, S. E.

    2013-12-01

    Groundwater is becoming an increasingly important water source due to the ever-increasing demands from agricultural, residential and industrial consumers. In search of more secure sources, wells are routinely finished over large vertical depths in bedrock aquifers, creating new hydraulic pathways and thus increasing the risk of cross contamination. Moreover, hydraulic pathways are also being altered and created by increasing water withdrawal rates from these wells. Currently, it is not well understood how biological contaminants are transported through, and retained in, fractured media thereby making risk assessment and land use decisions difficult. Colloid transport within fractured rock is a complex process with several mechanisms affecting transport and retention, including: advection, hydrodynamic dispersion, diffusion, size exclusion, adsorption, and decay. Several researchers have investigated the transport of bacteria, bacteriophage, and microspheres (both carboxylated and plain) to evaluate the effects of surface properties and size on transport and retention. These studies have suggested that transport is highly dependent on the physico-chemical properties of the particle, the fracture, and the carrying fluid. However, these studies contain little detail regarding the specific mechanisms responsible for transport beyond speculating about their existence. Further, little work has been done to compare the transport of these particulate materials through the same fracture, allowing for direct observations based on particulate size and surface properties. This research examines the similarities and differences in transport and retention between four different particles through two different laboratory-scale, saturated fractures. This work is designed to explore the effects of particle size, surface properties, ionic strength of the carrying solution, and aperture field characteristics on transport and retention in single, saturated fractures. The particulates chosen for this work include E.coli RS2-GFP, MS2, and carboxylated microspheres with diameters of 0.0425 ?m and 0.525 ?m. The results of this work will contribute to the understanding of risk posed by contaminants to bedrock aquifer sources. Dolomite rock samples were collected from the DoLime quarry in Guelph, Ontario. A single fracture was induced in the sample by applying a uniaxial force. Lengthwise edges were sealed to create no-flow boundaries, and flow cells were fitted on the up- and down-stream ends of the fracture. Aperture size and variability were characterized using hydraulic and solute tracer tests. Particulate tracer tests were conducted by injecting a pulse of particles (E.coli RS2-GFP, MS2, or microspheres) into the upstream flow cell, and measuring the subsequent effluent concentration profile. From these tests, the percent recovery and mean residence time of the particulate were analyzed. Generally, it was found that microspheres are a poor indication of biological particulate transport, likely due to differences in surface properties affecting the retention mechanisms. This talk will provide an analysis of the breakthrough curves, with specific details regarding the transport and retention mechanisms for the various types and sizes of particles employed in these experiments.

  12. Influence of Ni addition on mechanical properties and fracture behaviors of Ir-15Nb two-phase refractory superalloys

    SciTech Connect

    Gu, Yuefeng; Yamabe-Mitarai, Y.; Ro, Y.; Yokokawa, T.; Harada, H.

    1999-07-01

    Ir-based alloys with fcc-L1{sub 2} two-phase coherent structure, which are called refractory superalloys, have good potentiality as structure materials used at ultra-high temperatures up to 2,000 C. Preliminary results showed that the refractory superalloys failed predominantly by brittle intergranular fracture at room temperature even though they showed higher strength at that temperature. This paper will present the influence of nickel (Ni) addition on mechanical properties and fracture behaviors of one of these alloys, Ir-15at%Nb. The results indicated that Ni addition was beneficial to the compression ductility and strength of two-phase Ir-15at%Nb alloy when Ni content was below the optimum content.

  13. Fracture mechanics and statistical modeling of ternary blends of polylactide/ethylene-acrylate copolymer /wood-flour composites

    NASA Astrophysics Data System (ADS)

    Afrifah, Kojo Agyapong

    This study examined the mechanisms of toughening the brittle bio-based poly(lactic acid) (PLA) with a biodegradable rubbery impact modifier to develop biodegradable and cost effective PLA/wood-flour composites with improved impact strength, toughness, high ductility, and flexibility. Semicrystalline and amorphous PLA grades were impact modified by melt blending with an ethylene-acrylate copolymer (EAC) impact modifier. EAC content was varied to study the effectiveness and efficiency of the impact modifier in toughening the semicrystalline and amorphous grades of the PLA. Impact strength was used to assess the effectiveness and efficiency of the EAC in toughening the blends, whereas the toughening mechanisms were determined with the phase morphologies and the miscibilities of the blends. Subsequent tensile property analyses were performed on the most efficiently toughened PLA grade. Composites were made from PLA, wood flour of various particle sizes, and EAC. Using two-level factorial design the interaction between wood flour content, wood flour particle size, and EAC content and its effect on the mechanical properties of the PLA/wood-flour composites was statistically studied. Numerical optimization was also performed to statistically model and optimize material compositions to attain mechanical properties for the PLA/wood-flour composites equivalent to at least those of unfilled PLA. The J-integral method of fracture mechanics was applied to assess the crack initiation (Jin) and complete fracture (J f) energies of the composites to account for imperfections in the composites and generate data useful for engineering designs. Morphologies of the fractured surfaces of the composites were analyzed to elucidate the failure and toughening mechanisms of the composites. The EAC impact modifier effectively improved the impact strength of the PLA/EAC blends, regardless of the PLA type. However, the EAC was more efficient in the semicrystalline grades of PLA compared to the amorphous grade. The semicrystalline blends showed decreased tensile strength and modulus with increased impact modifier content. In contrast, the ductility, elongation at break, and energy to break increased significantly. Mechanisms of toughening of PLA with EAC included impact modifier debonding, fibrillization, crack bridging and matrix shear yielding resulting in a ductile behavior. Increasing the EAC content in PLA/wood-flour composites enhanced the impact strength and elongation at break, but reduced the tensile modulus and strength of the composites. Composites with fine wood particles showed greater improvement in elongation at break than those with coarse particles; an opposite trend was observed for impact strength, tensile modulus and tensile strength. Numerical optimization produced two scenarios based on materials compositions to produce composites with similar mechanical properties as unfilled PLA. These optimization solutions were successfully validated experimentally. The crack initiation (Jin) and complete fracture (Jf) energies of unmodified PLA/wood-flour composites showed the deleterious effect of wood fiber incorporation into the plastic matrix by significantly decreasing the fracture toughness of PLA as the wood flour content increased. By contrast, impact modification of wood plastic composites with EAC significantly increased both the resistance to crack initiation (Jin) and complete fracture (Jf). Microscopic morphological studies revealed that the major mechanisms of toughening was through the EAC existing as separate domains in the bulk matrix of the composites which tended to act as stress concentrators that initiated local yielding of the matrix around crack tips and enhanced the toughness of the composites.

  14. The Mechanisms of Dispersion Strengthening and Fracture in Al-based XD (TM) Alloys

    NASA Technical Reports Server (NTRS)

    Aiken, R. M., Jr.

    1990-01-01

    The influence of reinforcement size, volume fraction, and matrix deformation behavior on room and elevated temperature strength, and the fracture toughness of metal matrix composites of both pure aluminum and Al(4 percent)Cu(1.5 percent)Mg with 0 to 15 vol percent TiB2 were examined. Higher TiB2 volume fractions increased the tensile yield strength both at room and elevated temperatures, and reduced the elongation to fracture. Tensile tests also indicate that small particles provided a greater increase in strength for a given volume fraction than larger particles, whereas elongation to fracture appeared to be insensitive to reinforcement size. The fracture toughness of the Al(4 percent)Cu(1.5 percent)Mg alloys decreased rapidly with TiB2 additions of 0 to 5 vol percent and more slowly with TiB2 additions of 5 to 15 vol percent. Fracture toughness appears to be independent of TiB2 particle size. The isothermal-aging response of the precipitation strengthened Al(4 percent)Cu(1.5 percent)Mg alloys was not altered by the presence of TiB2.

  15. 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

  16. 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

  17. Materials and mechanics of rate effects in brittle fracture. Progress report, October 1979-October 1980

    SciTech Connect

    Burns, S.J.

    1980-01-01

    Energy balance methods have been used to find the crack driving force in elastic fractures. The fracture toughness of cracked steel bars have been measured using these techniques. Crack tip dislocations have been shown to protect the crack tip by having a stress intensity value that is opposite in sign from the applied stress intensity value. Thus, crack tip dislocation plasticity shields the crack from the external stress intensity factor. In the fatigue of LiF single crystals a relationship between monotonic and fatigue hardening responses has been established using a statistical model for fatigue deformation.

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

    NASA Technical Reports Server (NTRS)

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

    2009-01-01

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

  19. Fracture of disordered solids in compression as a critical phenomenon. I. Statistical mechanics formalism

    E-print Network

    Toussaint, Renaud

    from the energy balance of brittle fracture. The laws of thermodynamics, the partition function contact, we expect that once shear strain is applied and cracks begin to arrive in the system-solid materials are in compression and then have an additional deviatoric strain applied to them, small stable

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

    PubMed

    Cherepanov, Genady P

    2015-03-28

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

  1. Effect of strain rate and temperature on mechanical properties and fracture mode of high strength

    E-print Network

    Espinosa, Horacio D.

    lower the Peierls stress for screw dislocations in body-centered cubic iron. The fracture mode because the screw dislocations have a high Peierls stress. At room temper- ature or above, thermal energy is high enough to allow a screw dislocation lying in its Peierls valley to form a double kink

  2. 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.

  3. 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.

  4. Concurrent recordings of Electrical Current Emissions and Acoustic Emissions detected from marble specimens subjected to mechanical stress up to fracture

    NASA Astrophysics Data System (ADS)

    Stavrakas, I.; Hloupis, G.; Triantis, D.; Vallianatos, F.

    2012-04-01

    The emission of electrical signals during the application of mechanical stress on brittle geo-materials (the so called Pressure Stimulated Current - PSC[1,2]), provides significant information regarding the mechanical status of the studied rock sample, since PSCs are originated as a result of the opening of cracks and microfractures[3]. The latter mechanism for the creation of PSCs it is straightforward to associated with the recording of acoustic emissions (AE). To justify the common origin of PSCs and AE due to opening of cracks, a combined study was performed implicating the concurrent recording of electric current emissions and AE on marble samples when they are subjected to linearly increasing mechanical load up to the fracture. The electric signal detected is recorded by an ultra sensitive electrometer (Keithley 6514). The sensor used for detecting the electric current is a pair of gold plated electrodes adapted bilaterally on the sample found under axial mechanical stress[4]. The AE were recorded through the Physical Acoustics PCI-2 Acquisition System. The experimental results prove the strong association of the recorded electrical signals and the corresponding acoustic emissions justifying their common origin due to opening of microfractures. Furthermore, when the applied mechanical load exceeds the yield stress then an increasing of PSCs amplitude along with that of AE rate is observed. Acknowledgments. This work was partly supported by the THALES Program of the Ministry of Education of Greece and the European Union in the framework of the project entitled "Integrated understanding of Seismicity, using innovative Methodologies of Fracture mechanics along with Earthquake and non extensive statistical physics - Application to the geodynamic system of the Hellenic Arc. SEISMO FEAR HELLARC".

  5. Fracture Education in Engineering.

    ERIC Educational Resources Information Center

    Sidey, D.; And Others

    Fracture mechanics is a multidisciplinary topic which is being introduced to undergraduate engineering students in such courses as materials engineering. At a recent Conference on Fracture held at the University of Waterloo, a session was devoted to fracture education. Some of the ideas presented at that session are included and discussed here.…

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

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Shugurov, Artur

    2015-10-01

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

  8. 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.

  9. 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.

  10. 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.

  11. 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. )

    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.

  12. Reaction mechanisms, microstructure, and fracture properties of thermoplastic polysulfone-modified epoxy resin

    SciTech Connect

    Min, B.G.; Stachurski, Z.H. . Dept. of Materials Engineering); Hodgkin, J.H. . 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.

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

    NASA Astrophysics Data System (ADS)

    Van Damme, H.

    2014-12-01

    We report the results of simple laboratory experiments aimed at mimicking the generation, migration, and expulsion process of oil or gas from soft clayey sediments, triggered by thermal decomposition of organic matter. In previously published work, we showed that the injection of fluids into a soft sediment layer confined within a quasi-2D Hele-Shaw cell led to the transition from a viscous fingering invasion regime to a viscoelastic fracturing regime. The transition is controlled by the ratio of the characteristic times for the invasion process and for the structural relaxation in the sediment, respectively (Deborah number). Here we show that expulsion is a discontinuous quasi-periodic process, driven by the elastic energy stored in the embedding layers. We report also about two sets of experiments aimed at understanding the conditions in which fluid generation from multiple sources can generate a highly connected network of fractures for expulsion. In a first set of experiments, a Hele-Shaw cell with multiple injection points and multiple outlets was used. It is shown that, due to attractive elastic interactions between cracks, a network spontaneously forms as soon as invasion proceeds in the viscoelastic regime. On the contrary, no network of migration paths is forming in the viscous fingering regime, due to the effective repulsion of the fluid channels. In the second set of analog experiments, we used a thermostated mini-Hele-Shaw cell, the gap of which was filled with a strong clay mud in which microcrystals of reactive organic matter (azoisobutyronitrile, AIBN) are dispersed, or with a mud prepared with clay particles on which the organic matter was pre-impregnated. AIBN decomposes around 70°C, releasing nitrogen gas. It was again observed that, depending on the viscoelastic properties of the clay matrix, gas evolution occurs either by formation and coalescence of bubbles, or by formation of a percolating network of fractures. The length of the fracture network is initially linearly related to the Total (reactive) Organic Matter content. The expulsion process is remarkably effective in the fracturing regime (close to 100 percent), even at vey low TOC (below 0.5 percent). The relevance of these experiments for oil and gas migration in natural conditions will be discussed.

  14. On the Mechanisms for Defeating AP Projectiles

    NASA Astrophysics Data System (ADS)

    Rosenberg, Z.; Dekel, E.; Ashuach, Y.; Yeshurun, Y.

    The important mechanisms for defeating armor piercing (AP) projectiles are reviewed in this paper. These mechanisms are based on the compressive strength of the target material (its inherent resistance to penetration) and on the asymmetrical forces which it exerts on the threat, through proper geometrical arrangements. We discuss the basic features of the resistance to penetration, starting with the classical analysis of the cavity expansion process in elasto-plastic solids. This property of the target is responsible for the deceleration of hard cored projectiles and for the erosion of long rods, under normal impact conditions. We then discuss the asymmetrical interaction of AP projectiles with inclined plates (metals and polymers) and with ceramic spheres. These asymmetric forces are responsible for their deflection and breakup. Our work combines experimental observations with numerical simulations and engineering models, which enhance the understanding of the various phenomena encountered in these complex situations. This understanding is necessary for optimizing the performance of any armor design against a given threat.

  15. 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.

  16. 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.

    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.

  17. 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.

    1990-01-01

    The near-crack-tip stresses in any planar coupon of arbitrary geometry subjected to mode 1 loading may be equated to those in an infinite center-cracked panel subjected to the appropriate equivalent remote biaxial stresses (ERBS). Since this process can be done for all such mode 1 coupons, attention may be focused on the behavior of the equivalent infinite cracked panel. To calculate the ERBS, the constant term in the series expansion of the crack-tip stress must be retained. It is proposed that the ERBS may be used quantitatively to explain different fracture phenomena such as crack branching.

  18. Structure, Mechanics and Flow Properties of Fractured Shale: Core-Scale Experimentation and In-situ Imaging

    NASA Astrophysics Data System (ADS)

    Abdelmalek, B. F.; Karpyn, Z.; Liu, S.

    2014-12-01

    Over the last several years, hydrocarbon exploitation and development in North America has been heavily centered on shale gas plays. However, the physical attributes of shales and their manifestation on transport properties and storage capacity remain poorly understood. Therefore, more experimentally based data are needed to fill the gaps in understanding both transport and storage of fluids in shale. The proposed work includes installation and testing of an experimental system which is capable of monitoring the dynamic evolution of shale core permeability under variable loading conditions and in coordination with X-ray microCT imaging. The goal of this study is to better understand and quantify fluid flow patterns and associated transport dynamics of fractured shale samples. The independent variables considered in this study are: mechanical loading and pore pressure. The mechanical response of shale core is captured for different loading paths. To best replicate the in-situ production scenario, the pore pressure is progressively depleted to mimic pressure decline. During the course of experimentation, permeability is estimated using the pulse-decay method under tri-axial stress boundary conditions. Simultaneously, X-ray microCT imaging is used with a tracer gas that is allowed to flow through the sample as an illuminating agent. In the presence of an illuminating agent, either Xenon or Krypton, the X-ray CT scanner can image fractures, global pathways and diffusional fronts in the matrix, as well as sorption sites that reflect heterogeneities in the sample and localized deformation. Anticipated results from these experiments will help quantify permeability evolution as a function of different loading conditions and pore pressure depletion. Also, the X-ray images will help visualize the change of flow patterns and the intensity of sorption as a function of mechanical loading and pore pressure.

  19. Seismic imaging of hydraullically-stimulated fractures: A numerical study of the effect of the source mechanism

    E-print Network

    Shabelansky, Andrey Hanan

    2012-01-01

    We present a numerical study of seismic imaging of hydraulically stimulated fractures using a single source from an adjacent fracturing-process. The source is either a point force generated from the perforation of the ...

  20. Shatter cones - An outstanding problem in shock mechanics. [geological impact fracture surface in cratering

    NASA Technical Reports Server (NTRS)

    Milton, D. J.

    1977-01-01

    Shatter cone characteristics are surveyed. Shatter cones, a form of rock fracture in impact structures, apparently form as a shock front interacts with inhomogeneities or discontinuities in the rock. Topics discussed include morphology, conditions of formation, shock pressure of formation, and theories of formation. It is thought that shatter cones are produced within a limited range of shock pressures extending from about 20 to perhaps 250 kbar. Apical angles range from less than 70 deg to over 120 deg. Tentative hypotheses concerning the physical process of shock coning are considered. The range in shock pressures which produce shatter cones might correspond to the range in which shock waves decompose into elastic and deformational fronts.

  1. Trans-Endplate Pedicle Pillar System in Unstable Spinal Burst Fractures: Design, Technique, and Mechanical Evaluation

    PubMed Central

    Zhao, Chunfeng; Hongo, Michio; Ilharreborde, Brice; Zhao, Kristin D.; Currier, Bradford L.; An, Kai-Nan

    2015-01-01

    Background Short-segment pedicle screw instrumentation (SSPI) is used for unstable burst fractures to correct deformity and stabilize the spine for fusion. However, pedicle screw loosening, pullout, or breakage often occurs due to the large moment applied during spine motion, leading to poor outcomes. The purpose of this study was to test the ability of a newly designed device, the Trans-Endplate Pedicle Pillar System (TEPPS), to enhance SSPI rigidity and decrease the screw bending moment with a simple posterior approach. Methods Six human cadaveric spines (T11-L3) were harvested. A burst fracture was created at L1, and the SSPI (Moss Miami System) was used for SSPI fixation. Strain gauge sensors were mounted on upper pedicle screws to measure screw load bearing. Segmental motion (T12-L2) was measured under pure moment of 7.5 Nm. The spine was tested sequentially under 4 conditions: intact; first SSPI alone (SSPI-1); SSPI+TEPPS; and second SSPI alone (SSPI-2). Results SSPI+TEPPS increased fixation rigidity by 41% in flexion/extension, 28% in lateral bending, and 37% in axial rotation compared with SSPI-1 (P<0.001), and it performed even better compared to SSPI-2 (P<0.001 for all). Importantly, the bending moment on the pedicle screws for SSPI+TEPPS was significantly decreased 63% during spine flexion and 47% in lateral bending (p<0.001). Conclusion TEPPS provided strong anterior support, enhanced SSPI fixation rigidity, and dramatically decreased the load on the pedicle screws. Its biomechanical benefits could potentially improve fusion rates and decrease SSPI instrumentation failure. PMID:26502352

  2. An a-posteriori error estimator for linear elastic fracture mechanics using the stable generalized/extended finite element method

    NASA Astrophysics Data System (ADS)

    Lins, R. M.; Ferreira, M. D. C.; Proença, S. P. B.; Duarte, C. A.

    2015-10-01

    In this study, a recovery-based a-posteriori error estimator originally proposed for the Corrected XFEM is investigated in the framework of the stable generalized FEM (SGFEM). Both Heaviside and branch functions are adopted to enrich the approximations in the SGFEM. Some necessary adjustments to adapt the expressions defining the enhanced stresses in the original error estimator are discussed in the SGFEM framework. Relevant aspects such as effectivity indexes, error distribution, convergence rates and accuracy of the recovered stresses are used in order to highlight the main findings and the effectiveness of the error estimator. Two benchmark problems of the 2-D fracture mechanics are selected to assess the robustness of the error estimator hereby investigated. The main findings of this investigation are: the SGFEM shows higher accuracy than G/XFEM and a reduced sensitivity to blending element issues. The error estimator can accurately capture these features of both methods.

  3. 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.

  4. 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.

  5. Brittle Fracture Ductile to Brittle transition

    E-print Network

    Subramaniam, Anandh

    FRACTURE Brittle Fracture Ductile to Brittle transition Fracture Mechanics T.L. Anderson CRC sulphur in steel Residual stress Continuity of the structure Microcracks #12;Fracture Brittle Ductile Factors affecting fracture Strain rate State of stress Temperature #12;Behaviour described Terms Used

  6. 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.

  7. A comprehensive study on the damage tolerance of ultrafine-grained copper

    PubMed Central

    Hohenwarter, A.; Pippan, R.

    2012-01-01

    In this study the fracture behavior of ultrafine-grained copper was assessed by means of elasto-plastic fracture mechanics. For the synthesis of the material high pressure torsion was used. The fracture toughness was quantitatively measured by JIC as a global measure by recording the crack growth resistance curve. Additionally, the initiation toughness in terms of the crack opening displacement (CODi) was evaluated as a local fracture parameter. The results presented here exhibit a low fracture initiation toughness but simultaneously a remarkably high fracture toughness in terms of JIC. The origin of the large difference between these two parameters, peculiarities of the fracture surface and the fracture mechanical performance compared to coarse grained copper will be discussed. PMID:23471016

  8. 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. ...

  9. 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.

  10. The role of stress-state on the deformation and fracture mechanism of hydrided and non-hydrided Zircaloy-4

    NASA Astrophysics Data System (ADS)

    Cockeram, B. V.; Hollenbeck, J. L.

    2015-12-01

    Zircaloy-4 was tested at room-temperature over a range of hydrogen content between 10 and 200 ppm, and stress-states between a triaxiality of -0.23 and 0.9. Triaxiality (?) is defined as the ratio of hydrostatic stress to von Mises stress and was controlled through use of select mechanical test specimen designs. Testing of smooth and notched tensile specimens (? = 0.33 to 0.9) results in an increase in the stress to initiate plastic deformation and a decrease in strain to failure at higher values of ?. Increases in triaxiality are shown to have a more significant effect on reducing the strain to failure when the material is hydrided. Increases in strain to failure are observed at lower values of triaxiality for dual keyhole specimens (? = 0.1) and compression specimens (? = -0.17 to -0.23), with hydrided material showing much less decrement in strain to failure at these lower triaxialities. Examinations of microstructure are used to show that a change in mechanism for deformation and fracture with triaxiality can explain these differences in mechanical behavior and a model is developed to describe the observed changes in strain to failure with stress-state.

  11. Development of a Titanium Plate for Mandibular Angle Fractures with a Bone Defect in the Lower Border: Finite Element Analysis and Mechanical Test

    PubMed Central

    Goulart, Douglas Rangel; Kemmoku, Daniel Takanori; Noritomi, Pedro Yoshito

    2015-01-01

    ABSTRACT Objectives The aim of the present study was to develop a plate to treat mandibular angle fractures using the finite element method and mechanical testing. Material and Methods A three-dimensional model of a fractured mandible was generated using Rhinoceros 4.0 software. The models were exported to ANSYS®, in which a static application of displacement (3 mm) was performed in the first molar region. Three groups were assessed according to the method of internal fixation (2 mm system): two non-locking plates; two locking plates and a new design locking plate. The computational model was transferred to an in vitro experiment with polyurethane mandibles. Each group contained five samples and was subjected to a linear loading test in a universal testing machine. Results A balanced distribution of stress was associated with the new plate design. This plate modified the mechanical behavior of the fractured region, with less displacement between the fractured segments. In the mechanical test, the group with two locking plates exhibited greater resistance to the 3 mm displacement, with a statistically significant difference when compared with the new plate group (ANOVA, P = 0.016). Conclusions The new plate exhibited a more balanced distribution of stress. However, the group with two locking plates exhibited greater mechanical resistance. PMID:26539287

  12. Fracture Mechanics of Thin, Cracked Plates Under Tension, Bending and Out-of-Plane Shear Loading

    NASA Technical Reports Server (NTRS)

    Zehnder, Alan T.; Hui, C. Y.; Potdar, Yogesh; Zucchini, Alberto

    1999-01-01

    Cracks in the skin of aircraft fuselages or other shell structures can be subjected to very complex stress states, resulting in mixed-mode fracture conditions. For example, a crack running along a stringer in a pressurized fuselage will be subject to the usual in-plane tension stresses (Mode-I) along with out-of-plane tearing stresses (Mode-III like). Crack growth and initiation in this case is correlated not only with the tensile or Mode-I stress intensity factor, K(sub I), but depends on a combination of parameters and on the history of crack growth. The stresses at the tip of a crack in a plate or shell are typically described in terms of either the small deflection Kirchhoff plate theory. However, real applications involve large deflections. We show, using the von-Karman theory, that the crack tip stress field derived on the basis of the small deflection theory is still valid for large deflections. We then give examples demonstrating the exact calculation of energy release rates and stress intensity factors for cracked plates loaded to large deflections. The crack tip fields calculated using the plate theories are an approximation to the actual three dimensional fields. Using three dimensional finite element analyses we have explored the relationship between the three dimensional elasticity theory and two dimensional plate theory results. The results show that for out-of-plane shear loading the three dimensional and Kirchhoff theory results coincide at distance greater than h/2 from the crack tip, where h/2 is the plate thickness. Inside this region, the distribution of stresses through the thickness can be very different from the plate theory predictions. We have also explored how the energy release rate varies as a function of crack length to plate thickness using the different theories. This is important in the implementation of fracture prediction methods using finite element analysis. Our experiments show that under certain conditions, during fatigue crack growth, the presence of out-of-plane shear loads induces a great deal of contact and friction on the crack surfaces, dramatically reducing crack growth rate. A series of experiments and a proposed computational approach for accounting for the friction is discussed.

  13. U.S. National Committee for Rock Mechanics; and Conceptual model of fluid infiltration in fractured media. Project summary, July 28, 1997--July 27, 1998

    SciTech Connect

    1998-09-01

    The title describes the two tasks summarized in this report. The remainder of the report contains information on meetings held or to be held on the subjects. The US National Committee for Rock Mechanics (USNC/RM) provides for US participation in international activities in rock mechanics, principally through adherence to the International Society for Rock Mechanics (ISRM). It also keeps the US rock mechanics community informed about new programs directed toward major areas of national concern in which rock mechanics problems represent critical or limiting factors, such as energy resources, excavation, underground storage and waste disposal, and reactor siting. The committee also guides or produces advisory studies and reports on problem areas in rock mechanics. A new panel under the auspices of the US National Committee for Rock Mechanics has been appointed to conduct a study on Conceptual Models of Fluid Infiltration in Fractured Media. The study has health and environmental applications related to the underground flow of pollutants through fractured rock in and around mines and waste repositories. Support of the study has been received from the US Nuclear Regulatory Commission and the Department of Energy`s Yucca Mountain Project Office. The new study builds on the success of a recent USNC/RM report entitled Rock Fractures and Fluid Flow: Contemporary Understanding and Applications (National Academy Press, 1996, 551 pp.). A summary of the new study is provided.

  14. 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.

  15. 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

  16. Impact induced failure of cartilage-on-bone following creep loading: a microstructural and fracture mechanics study.

    PubMed

    Thambyah, Ashvin; Zhang, Geran; Kim, Woong; Broom, Neil D

    2012-10-01

    Cartilage-on-bone samples obtained from healthy bovine patellae, with or without prior static compression (i.e. creep) at 2MPa for 3h, were delivered a single impact via an instrumented pendulum indenter at a velocity of 1.13m/s and an energy of 2.2J. Mechanical data was obtained and microstructural assessment of the region of failure was carried out using differential interference contrast (DIC) optical imaging. In addition, a fibrillar-level structural analysis using scanning electron microscopy (SEM) was conducted on a control batch of non-impacted samples that were subjected to either creep or non-creep loading protocols. Arising from the impact event the deepest levels of crack penetration into the articular cartilage occurred in those samples subjected to prior creep loading. Further the crack depth was inversely proportional to the rebound velocity of the indenter. By contrast, those impacted samples not subjected to prior creep loading had only short obliquely patterned microcracks confined to the upper one-third of the full cartilage depth. Ultrastructurally the creep-loaded cartilage matrix exhibited a substantial radial collapse or compaction of the fibrillar network in its primary radial zone. The increase in crack length in the prior creep-loaded cartilage is consistent with a reduction in its dissipative properties as indicated by a reduction in rebound velocity. An interpretation is offered in terms of classical fracture mechanics theory. PMID:22784816

  17. The Behavior of Water in Collagen and Hydroxyapatite Sites of Cortical Bone: Fracture, Mechanical Wear, and Load Bearing Studies

    PubMed Central

    Gul-E-Noor, Farhana; Singh, Chandan; Papaioannou, Antonios; Sinha, Neeraj; Boutis, Gregory S.

    2015-01-01

    The mechanical properties of cortical bone, which is largely comprised of collagen, hydroxyapatite, and water, are known to hinge on hydration. Recently, the characteristics of water in bone have drawn attention as potential markers of bone quality. We report on the dynamics, diffusion, population, and exchange of water in cortical bone by NMR relaxation and diffusion methodologies. Relaxation measurements over timescales ranging from 0.001 to 4.2 s reveal two distinguishable water environments. Systematic exposure to ethylenediaminetetraacetic acid or collagenase reveals one peak in our 2D relaxation map belonging to water present in the hydroxyapatite rich environment, and a second peak with shorter relaxation times arising from a collagen rich site. Diffusion-T2 measurements allowed for direct measurement of the diffusion coefficient of water in all observable reservoirs. Further, deuterium relaxation methods were applied to study cortical bone under an applied force, following mechanical wear or fracture. The tumbling correlation times of water reduce in all three cases, indicating that water dynamics may be used as a probe of bone quality. Lastly, changes in the relative populations and correlation times of water in bone under an applied force suggest that load bearing occurs largely in the collagen rich environment and is reversible. PMID:26659838

  18. Progressive Fracture of Composite Structures

    NASA Technical Reports Server (NTRS)

    Chamis, Christos C.; Minnetyan, Levon

    2008-01-01

    A new approach is described for evaluating fracture in composite structures. This approach is independent of classical fracture mechanics parameters like fracture toughness. It relies on computational simulation and is programmed in a stand-alone integrated computer code. It is multiscale, multifunctional because it includes composite mechanics for the composite behavior and finite element analysis for predicting the structural response. It contains seven modules; layered composite mechanics (micro, macro, laminate), finite element, updating scheme, local fracture, global fracture, stress based failure modes, and fracture progression. The computer code is called CODSTRAN (Composite Durability Structural ANalysis). It is used in the present paper to evaluate the global fracture of four composite shell problems and one composite built-up structure. Results show that the composite shells and the built-up composite structure global fracture are enhanced when internal pressure is combined with shear loads.

  19. 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.

  20. Isogeometric Boundary Element Analysis with elasto-plastic inclusions. Part 1: Plane problems

    E-print Network

    Beer, Gernot; Zechner, Jürgen; Dünser, Christian; Fries, Thomas-Peter

    2015-01-01

    In this work a novel approach is presented for the isogeometric Boundary Element analysis of domains that contain inclusions with different elastic properties than the ones used for computing the fundamental solutions. In addition the inclusion may exhibit inelastic material behavior. In this paper only plane stress/strain problems are considered. In our approach the geometry of the inclusion is described using NURBS basis functions. The advantage over currently used methods is that no discretization into cells is required in order to evaluate the arising volume integrals. The other difference to current approaches is that Kernels of lower singularity are used in the domain term. The implementation is verified on simple finite and infinite domain examples with various boundary conditions. Finally a practical application in geomechanics is presented.

  1. 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.

  2. Distribution-enhanced homogenization framework and model for heterogeneous elasto-plastic problems

    NASA Astrophysics Data System (ADS)

    Alleman, Coleman; Luscher, D. J.; Bronkhorst, Curt; Ghosh, Somnath

    2015-12-01

    Multi-scale computational models offer tractable means to simulate sufficiently large spatial domains comprised of heterogeneous materials by resolving material behavior at different scales and communicating across these scales. Within the framework of computational multi-scale analyses, hierarchical models enable unidirectional transfer of information from lower to higher scales, usually in the form of effective material properties. Determining explicit forms for the macroscale constitutive relations for complex microstructures and nonlinear processes generally requires numerical homogenization of the microscopic response. Conventional low-order homogenization uses results of simulations of representative microstructural domains to construct appropriate expressions for effective macroscale constitutive parameters written as a function of the microstructural characterization. This paper proposes an alternative novel approach, introduced as the distribution-enhanced homogenization framework or DEHF, in which the macroscale constitutive relations are formulated in a series expansion based on the microscale constitutive relations and moments of arbitrary order of the microscale field variables. The framework does not make any a priori assumption on the macroscale constitutive behavior being represented by a homogeneous effective medium theory. Instead, the evolution of macroscale variables is governed by the moments of microscale distributions of evolving field variables. This approach demonstrates excellent accuracy in representing the microscale fields through their distributions. An approximate characterization of the microscale heterogeneity is accounted for explicitly in the macroscale constitutive behavior. Increasing the order of this approximation results in increased fidelity of the macroscale approximation of the microscale constitutive behavior. By including higher-order moments of the microscale fields in the macroscale problem, micromechanical analyses do not require boundary conditions to ensure satisfaction of the original form of Hill's lemma. A few examples are presented in this paper, in which the macroscale DEHF model is shown to capture the microscale response of the material without re-parametrization of the microscale constitutive relations.

  3. On the symbolic manipulation and code generation for elasto-plastic material matrices

    NASA Technical Reports Server (NTRS)

    Chang, T. Y.; Saleeb, A. F.; Wang, P. S.; Tan, H. Q.

    1986-01-01

    A computerized procedure for symbolic manipulations and FORTRAN code generation of elastoplastic material matrix for finite element applications is presented. Special emphasis is placed on expression simplifications during intermediate derivations, optimal code generation, and interface with the main program. A systematic procedure is outlined to avoid redundant algebraic manipulations. Symbolic expressions of the derived material stiffness matrix are automatically converted to RATFOR code which is then translated into FORTRAN statements through a preprocessor. To minimize the interface problem with the main program, a template file is prepared so that the translated FORTRAN statements can be merged into the file to form a subroutine (or a submodule). Three constitutive models; namely, von Mises plasticity, the Drucker-Prager model, and a concrete plasticity model, are used as illustrative examples.

  4. Evolution of swelling pressure of cohesive-frictional, rough and elasto-plastic granulates

    E-print Network

    Luding, Stefan

    to the integration of Newton's equa- tions of motion for the translational and rotational degrees of freedom: f i d element model (DEM), force-laws, fric- tion, rolling- and torsion resistance, adhesion, elasto, up to a state where a target volume fraction is reached. Alternative laws for the growth rate

  5. Elasto-plastic stress analysis of thick-walled FGM pipes

    SciTech Connect

    Figueiredo, Fabio; Borges, Lavinia; Rochinha, Fernando

    2008-02-15

    The paper is concerned with quasi-static deformation processes of elastic-plastic FGM structures. It is assumed that the structures undergo small strain and the material properties of the graded layer are modeled by the modified rule of mixtures approximation. The elastic domain for ductile phases is defined through the Von Mises yield criterion. The mathematical problem consists of a variational equation that represents the equilibrium of the body and a variational inequality expressing the plastic strain rate evolution. An iterative method for solving this nonlinear system, combining a finite element approximation and an incremental-iterative scheme, is proposed. The results of some numerical experiments comparing the plastic response of tubes with abrupt transition to different configurations obtained using smooth transitions containing FGM layers between the two dissimilar materials are provided.

  6. Elasto-Plasticity Behavior of Type 5000 and 6000 Aluminum Alloy Sheets and Its Constitutive Modeling

    SciTech Connect

    Tamura, Shohei; Sumikawa, Satoshi; Hamasaki, Hiroshi; Yoshida, Fusahito; Uemori, Takeshi

    2010-06-15

    To examine the deformation characteristic of type 5000 and 6000 aluminum alloy sheets, uniaxial tension, biaxial stretching and in-plane cyclic tension-compression experiments were performed, and from these, r-values (r{sub 0}, r{sub 45} and r{sub 90}), yield loci and cyclic stress-strain responses were obtained. For the accurate description of anisotropies of the materials, high-ordered anisotropic yield functions, such as Gotoh's biquadratic yield function and Barlat's Yld2000-2d, are necessary. Furthermore, for the simulation of cyclic behavior, an advanced kinematic hardening model, such as Yoshida-Uemori model (Y-U model), should be employed. The effect of the selection of material models on the accuracy of the springback prediction was discussed by performing hat bending FE simulation using several yield functions and two types of hardening laws (the isotropic hardening model and Y-U model).

  7. Numerical study on dynamic compressive deformation and elasto-plastic wave propagation of foam materials

    NASA Astrophysics Data System (ADS)

    Tanigaki, Kenichi; Idouji, Toru; Horikawa, Keitaro; Kobayashi, Hidetoshi; Ogawa, Kinya

    2015-09-01

    Finite element models of closed-cell foam structures were created using the three-dimensional Voronoi tessellation method coupled with the random sequential addition algorithm. The dynamic compressive deformation behaviors of the models were numerically studied using LS-DYNA code. The deformation mode of the models changed gradually as the deformation rate increases. Also, the generation and the propagation of plastic wave was clearly observed with the rate of 100 m/s. The longitudinal elastic wave velocity showed a weak negative dependency on the deformation rate although the strain rate dependence of material properties was not considered. Furthermore, a prediction method for the dynamic stress state on the impact side based on the static stress-strain relationship was presented.

  8. A new multilayered visco-elasto-plastic experimental model to study strike-slip

    E-print Network

    Cattin, Rodolphe

    University, Clayton, Victoria, Australia Abstract Nowadays, technological advances in satellite imagery 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

  9. Toward a Hybrid-Trefftz element with a hole for elasto-plasticity?

    NASA Astrophysics Data System (ADS)

    Leconte, Nicolas; Langrand, Bertrand; Markiewicz, Eric

    2008-08-01

    The paper deals with the modelling of riveted assemblies for full-scale complete aircraft crashworthiness. Many comparisons between experiments and FE computations of bird impacts onto aluminium riveted panels have shown that macroscopic plastic strains were not sufficiently developed (and localised) in the riveted shell FE in the impact area. Consequently, FE models never succeed in initialising and propagating the rupture in the sheet metal plates and along rivet rows as shown by experiments, without calibrating the input data (especially the damage and failure properties of the riveted shell FE). To model the assembly correctly, it appears necessary to investigate on FE techniques such as Hybrid-Trefftz finite element method (H-T FEM). Indeed, perforated FE plates developed for elastic problems, based on a Hybrid-Trefftz formulation, have been found in the open literature. Our purpose is to find a way to extend this formulation so that the super-element can be used for crashworthiness. To reach this aim, the main features of an elastic Hybrid-Trefftz plate are presented and are then followed by a discussion on the possible extensions. Finally, the interpolation functions of the element are evaluated numerically.

  10. Fracture Modeling and Flow Behavior in Shale Gas Reservoirs Using Discrete Fracture Networks 

    E-print Network

    Ogbechie, Joachim Nwabunwanne

    2012-02-14

    Fluid flow process in fractured reservoirs is controlled primarily by the connectivity of fractures. The presence of fractures in these reservoirs significantly affects the mechanism of fluid flow. They have led to problems ...

  11. Mode and mechanism of fatigue fracture of a pearlitic steel in hydrogen

    NASA Technical Reports Server (NTRS)

    Lo, S. H.; Johnson, H. H.

    1986-01-01

    It is presently suggested that there are two mechanisms that cause fatigue crack initiation in a specimen subjected to a hydrogen environment: either a critical concentration of hydrogen is attained within the specimen, causing Mode I crack initiation, or the presence of some hydrogen (below critical concentration) promotes the early onset of plastic instability at the sites of maximum strain. It is further suggested that in the static loading condition, a high hydrogen concentration may be attained by way of mechanical factors, causing Mode I crack initiation. While cyclic fatigue specimens exhibited Mode II crack initiation in air, only Mode I crack initiation emerged in a hydrogen environment.

  12. Ankle Fractures

    MedlinePLUS

    .org Ankle Fractures (Broken Ankle) Page ( 1 ) A broken ankle is also known as an ankle “fracture.” This means that one or more of the bones that make up the ankle joint are broken. A fractured ankle can range ...

  13. Fracture Mechanism and Toughness Optimization of Macroscopic Thick Graphene Oxide Film

    PubMed Central

    Ye, Shibing; Chen, Bin; Feng, Jiachun

    2015-01-01

    Combined high strength and toughness of film materials are rather important for their industrial applications. As a new class of films, graphene oxide films (GOFs) attract intense attention in many applications but are frequently divergent, inconsistent, and poorly reproducible in their mechanical properties. In this study, we first demonstrate that different chemical compositions and assembly structures probably are responsible for the difference in elongations between cast GOFs and filtration GOFs. Comprehensive analysis of the morphologies and mechanical properties indicates that the enhanced elongation of the thick cast GOFs is mainly attributed to the presence of a unique skin-wrinkles-skin structure, which more easily forms in cast GOFs than in filtration counterparts. On the basis of this finding, we attempt to optimize the strength-toughness performance of the cast GOFs by adjusting their structures. With an appropriate thickness of 12.5??m, the GOFs can achieve an ultrahigh toughness up to 4.37?MJ m?3, which is even comparable to the polymer-toughening graphene/GO-based paper-like materials. Such an optimization of the mechanical properties from the perspective of skin-wrinkles-skin structure appears to be a universal approach that could be extended to a variety of other film materials. PMID:26310835

  14. 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

  15. Fracture and damage; Winter Annual Meeting of the American Society of Mechanical Engineers, Anaheim, CA, Nov. 8-13, 1992

    NASA Technical Reports Server (NTRS)

    Nagar, Arvind (editor)

    1992-01-01

    The latest developments in the area of fracture and damage at high temperatures are discussed, in particular: modeling; analysis and experimental techniques for interface damage in composites including the effects of residual stresses and temperatures; and crack growth, inelastic deformation and fracture parameters for isotropic materials. Also included are damage modeling and experiments at elevated temperatures.

  16. Characterization of the mechanisms controlling the permeability changes of fractured cements flowed through by CO2-rich brine.

    PubMed

    Abdoulghafour, H; Luquot, L; Gouze, P

    2013-09-17

    Experiments were conducted to assess the potential impact of fractured well-cement degradation on leakage rate. Permeability was monitored while CO2-enriched reservoir-equilibrated brine was flowed at constant rate through a single fracture in a class G cement core under conditions mimicking geologic sequestration environments (temperature 60 °C, pressure 10 MPa). The results demonstrate that, at least for the conditions used in the experiment, an initial leakage in a 42 ?m aperture fracture (permeability = 1.5 × 10(-10) m(2)) can be self-mitigated due to the decrease of the fracture hydraulic aperture after about 15 h. This decrease results from the development of continuous highly hydrated amorphous Si-rich alteration products at the edge of the fracture and the dense carbonation of the bulk cement that mitigate the penetration of the alteration front. PMID:23937192

  17. Effect of processing, sterilization and crosslinking on UHMWPE fatigue fracture and fatigue wear mechanisms in joint arthroplasty.

    PubMed

    Ansari, Farzana; Ries, Michael D; Pruitt, Lisa

    2016-01-01

    Ultra high molecular weight polyethylene (UHMWPE) has been used as a bearing surface in total joint replacements (TJR) for nearly five decades. This semi-crystalline polymer has extraordinary energetic toughness owing to its high molecular weight and entanglement density. However, it is challenged by a need to offer a combined resistance to fatigue, wear and oxidation in vivo. The processing, sterilization treatment, and microstructural tailoring of UHMWPE has evolved considerably in the past 50 years but an optimized microstructure remains elusive. This review seeks to provide an overview of this processing history to address two primary questions: First, how does microstructure affect fatigue fracture and fatigue wear mechanisms in UHMWPE? And second, can microstructure be optimized to provide resistance to fatigue, oxidation and wear in vivo? Previous literature demonstrates that while crosslinking improves resistance to adhesive/abrasive wear, it also reduces resistance to fatigue crack propagation and fatigue wear by restricting molecular mobility and rendering the polymer more brittle. Crystallinity improves fatigue resistance but generally increases elastic modulus and concomitant contact stresses in vivo. The presence of fusion defects or oxidation reduces further fatigue resistance and enhances fatigue wear. Thus, UHMWPE microstructural evolution comes with trade-offs. Currently there is no singular formulation of UHMWPE that is ideal for all TJR applications. PMID:26386167

  18. Is there a role for vitamin C in preventing osteoporosis and fractures? A review of the potential underlying mechanisms and current epidemiological evidence.

    PubMed

    Finck, Henriette; Hart, Andrew R; Jennings, Amy; Welch, Ailsa A

    2014-12-01

    Osteoporosis and related fractures are a major global health issue, but there are few preventative strategies. Previously reported associations between higher intakes of fruits and vegetables and skeletal health have been suggested to be partly attributable to vitamin C. To date, there is some evidence for a potential role of vitamin C in osteoporosis and fracture prevention but an overall consensus of published studies has not yet been drawn. The present review aims to provide a summary of the proposed underlying mechanisms of vitamin C on bone and reviews the current evidence in the literature, examining a potential link between vitamin C intake and status with osteoporosis and fractures. The Bradford Hill criteria were used to assess reported associations. Recent animal studies have provided insights into the involvement of vitamin C in osteoclastogenesis and osteoblastogenesis, and its role as a mediator of bone matrix deposition, affecting both the quantity and quality of bone collagen. Observational studies have provided some evidence for this in the general population, showing positive associations between dietary vitamin C intake and supplements and higher bone mineral density or reduced fracture risk. However, previous intervention studies were not sufficiently well designed to evaluate these associations. Epidemiological data are particularly limited for vitamin C status and for fracture risk and good-quality randomised controlled trials are needed to confirm previous epidemiological findings. The present review also highlights that associations between vitamin C and bone health may be non-linear and further research is needed to ascertain optimal intakes for osteoporosis and fracture prevention. PMID:25412684

  19. Surgical Management of Patellar Fractures.

    PubMed

    Kakazu, Rafael; Archdeacon, Michael T

    2016-01-01

    The patella plays a crucial role in the extensor mechanism to increase the mechanical advantage of the quadriceps. Fractures can be classified based on displacement, comminution, and fracture pattern, which often guide treatment. Modern treatment options include internal fixation using tension bands with Kirschner wires or cannulated screws, lag screw fixation, partial patellectomy, and rarely total patellectomy. Nondisplaced, closed patellar fractures or fractures with less than 2-mm articular steps can be successfully treated conservatively. Open fractures, articular step of 2 mm or greater, and loss of knee extension are indications for surgical intervention. PMID:26614923

  20. 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).

  1. Mechanical behavior of composite materials: Elastic moduli, nonlinear behavior, and fracture

    NASA Astrophysics Data System (ADS)

    Seo, Minwhan

    This thesis introduces two methods relating to the mechanical behavior of continuous fiber composites. First, an analytical method is introduced to predict the elastic properties of fiber reinforced composites. Although several other analytical methods are available, they are limited in material types or internal geometries. The present method is more general than other methods. In the present method, the fibers are assumed to be arranged in a periodic manner in the matrix. The method provides solutions for various types of composite materials including hybrid composites and thick-interface composites. The results show good agreement with experimental data. Second, a finite element analysis technique to model the nonlinear behavior of orthotropic materials in a finite element analysis program is introduced. The present finite element method models post-yield behavior with a general-purpose FEA package. User-defined elements and material models are not required. The method uses springs between the nodes to correct post-yield behavior, and utilizes the plastic theory (Hill's criteria and work-hardening rule) that is built into the FEA package. The results show that the present method can correctly present the nonlinear behavior of composite materials.

  2. Small Molecule Inhibition of the TNF Family Cytokine CD40 Ligand Through a Subunit Fracture Mechanism

    SciTech Connect

    L Silvian; J Friedman; K Strauch; T Cachero; E Day; F Qian; B Cunningham; A Fung; L Sun; et al.

    2011-12-31

    BIO8898 is one of several synthetic organic molecules that have recently been reported to inhibit receptor binding and function of the constitutively trimeric tumor necrosis factor (TNF) family cytokine CD40 ligand (CD40L, aka CD154). Small molecule inhibitors of protein-protein interfaces are relatively rare, and their discovery is often very challenging. Therefore, to understand how BIO8898 achieves this feat, we characterized its mechanism of action using biochemical assays and X-ray crystallography. BIO8898 inhibited soluble CD40L binding to CD40-Ig with a potency of IC{sub 50} = 25 {mu}M and inhibited CD40L-dependent apoptosis in a cellular assay. A co-crystal structure of BIO8898 with CD40L revealed that one inhibitor molecule binds per protein trimer. Surprisingly, the compound binds not at the surface of the protein but by intercalating deeply between two subunits of the homotrimeric cytokine, disrupting a constitutive protein-protein interface and breaking the protein's 3-fold symmetry. The compound forms several hydrogen bonds with the protein, within an otherwise hydrophobic binding pocket. In addition to the translational splitting of the trimer, binding of BIO8898 was accompanied by additional local and longer-range conformational perturbations of the protein, both in the core and in a surface loop. Binding of BIO8898 is reversible, and the resulting complex is stable and does not lead to detectable dissociation of the protein trimer. Our results suggest that a set of core aromatic residues that are conserved across a subset of TNF family cytokines might represent a generic hot-spot for the induced-fit binding of trimer-disrupting small molecules.

  3. 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.

  4. 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

  5. Assessment of Fracture Repair.

    PubMed

    Cook, Gillian E; Bates, Brent D; Tornetta, Paul; McKee, Michael D; Morshed, Saam; Slobogean, Gerard P; Schemitsch, Emil H

    2015-12-01

    Assessment of fracture union is a critical concept in clinical orthopaedics; however, there is no established "gold standard" for fracture healing. This review provides an overview of the problems related to the assessment of fracture healing, examines currently available tools to determine union, discusses the role of functional outcomes in the assessment of fracture healing, and finally evaluates healing outcome measures as they pertain to fracture trials. Because there is no universally accepted method to determine fracture healing, orthopaedic surgeons must rely on a range of tools that can include: radiographic assessment, mechanical assessment, serologic markers, and clinical evaluation (including functional outcomes). When used in conjunction, these tools can help to improve the sensitivity and specificity of determining fracture union. This is furthermore relevant when conducting fracture healing trials, for which there is little consensus between surgeons or the Food and Drug Administration as to optimal study endpoints. Such studies should therefore include a composite outcome measure consisting of radiographic and functional assessments to increase the quality and consistency of fracture healing trials. PMID:26584269

  6. Fracture of synthetic diamond M. D. Droty

    E-print Network

    Ritchie, Robert

    Fracture of synthetic diamond M. D. Droty Ctystallume, 3506 Bassett Street, Santa Clara, California 1995) The fracture behavior of synthetic diamond has been investigated using indentation methods and by the tensile testing of pre-notched fracture-mechanics type samples. Specifically, the fracture toughness

  7. Evaluation of Stress Corrosion Cracking Susceptibility Using Fracture Mechanics Techniques, Part 1. [environmental tests of aluminum alloys, stainless steels, and titanium alloys

    NASA Technical Reports Server (NTRS)

    Sprowls, D. O.; Shumaker, M. B.; Walsh, J. D.; Coursen, J. W.

    1973-01-01

    Stress corrosion cracking (SSC) tests were performed on 13 aluminum alloys, 13 precipitation hardening stainless steels, and two titanium 6Al-4V alloy forgings to compare fracture mechanics techniques with the conventional smooth specimen procedures. Commercially fabricated plate and rolled or forged bars 2 to 2.5-in. thick were tested. Exposures were conducted outdoors in a seacoast atmosphere and in an inland industrial atmosphere to relate the accelerated tests with service type environments. With the fracture mechanics technique tests were made chiefly on bolt loaded fatigue precracked compact tension specimens of the type used for plane-strain fracture toughness tests. Additional tests of the aluminum alloy were performed on ring loaded compact tension specimens and on bolt loaded double cantilever beams. For the smooth specimen procedure 0.125-in. dia. tensile specimens were loaded axially in constant deformation type frames. For both aluminum and steel alloys comparative SCC growth rates obtained from tests of precracked specimens provide an additional useful characterization of the SCC behavior of an alloy.

  8. 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.

  9. 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.

  10. Facial fractures.

    PubMed Central

    Carr, M. M.; Freiberg, A.; Martin, R. D.

    1994-01-01

    Emergency room physicians frequently see facial fractures that can have serious consequences for patients if mismanaged. This article reviews the signs, symptoms, imaging techniques, and general modes of treatment of common facial fractures. It focuses on fractures of the mandible, zygomaticomaxillary region, orbital floor, and nose. Images p520-a p522-a PMID:8199509

  11. A microstructural study of the extension-to-shear fracture transition in Carrara Marble 

    E-print Network

    Rodriguez, Erika

    2005-11-01

    Triaxial extension experiments on Carrara Marble demonstrate that there is a continuous transition from extension to shear fracture on the basis of mechanical behavior, macroscopic fracture orientation and fracture morphology where hybrid fractures...

  12. Experimental study of step-displacement hydraulic fracturing on naturally fractured shale outcrops

    NASA Astrophysics Data System (ADS)

    Cheng, Wan; Jin, Yan; Chen, Mian

    2015-08-01

    Low porosity and permeability make it extremely difficult to develop shale oil and gas reservoirs. The stimulated reservoir volume is believed to have potential to obtain industry production by multi-stage or simultaneous fracturing in horizontal wells. The formation mechanism of network hydraulic fractures in fractured shale reservoirs remains poorly understood. In this article, a true tri-axial hydraulic fracturing system associated acoustic emission monitor was deployed to simulate hydraulic fracturing on shale outcrops. Results showed that the properties of natural fractures (such as aperture, orientation), compared to the viscosity and displacement of the fracturing fluid, affect the propagation direction of hydraulic fractures more predominantly. Each natural fracture in a natural fracture network can independently affect the hydraulic fracture. Low displacement (below the diffusion ability of a reservoir) fracturing tends to connect pre-existing fractures, while high displacement (surpass the diffusion ability of a reservoir) tends to create new fractures. After the breakdown pressure, an increase in injection rate results in more acoustic emission energy and induces new fractures. These results suggest that step-displacement fracturing technology is a possible mechanism to obtain effective fracture networks. Such an understanding would help to avoid unproductive, or sometimes destructive, costly segments of the hydraulic fracturing treatment design.

  13. Mechanical properties of heterophase polymer blends of cryogenically fractured soy flour composite filler and poly(styrene-butadiene)

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Reinforcement effect of cryogenically fractured soy Flour composite filler in soft polymer was investigated in this study. Polymer composites were prepared by melt-mixing polymer and soy flour composite fillers in an internal mixer. Soy flour composite fillers were prepared by blending aqueous dis...

  14. 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

    and fractures were treated as two systems. Reservoir management practices and decisions should be very carefully reviewed and executed in this dual continuum reservoir based on the results of this work. Studying this dual media flow behavior is vital for better...

  15. 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 wood and wood composites develop process zones often consisting of fibers bridging the crack surfaces. After crack initiation, a process zone develops causing the toughness (or R curve) to increase

  16. Quantitative, Structural and Image-based Mechanical Analysis of Nonunion Fracture Repaired by Genetically Engineered Mesenchymal Stem Cells

    PubMed Central

    Kallai, Ilan; van Lenthe, G. Harry; Ruffoni, Davide; Zilberman, Yoram; Müller, Ralph; Pelled, Gadi; Gazit, Dan

    2010-01-01

    Stem cell-mediated gene therapy for fracture repair, utilizes genetically engineered mesenchymal stem cells (MSCs) for the induction of bone growth and is considered a promising approach in skeletal tissue regeneration. Previous studies have shown that murine nonunion fractures can be repaired by implanting MSCs over-expressing recombinant human bone morphogenetic protein-2 (rhBMP-2). Nanoindentation studies of bone tissue induced by MSCs in a radius fracture site indicated similar elastic modulus compared to intact murine bone, eight weeks post treatment. In the present study we sought to investigate temporal changes in microarchitecture and biomechanical properties of repaired murine radius bones, following the implantation of MSCs. High resolution micro computed tomography (Micro-CT) was performed 10 and 35 weeks post MSC implantation, followed by micro finite element (Micro-FE) analysis. The results have shown that the regenerated bone tissue remodels over time, as indicated by a significant decrease in bone volume, total volume and connectivity density combined with an increase in mineral density. In addition, the axial stiffness of limbs repaired with MSCs was 2 to 1.5 times higher compared to the contralateral intact limbs, at 10 and 35 weeks post treatment. These results could be attributed to the fusion that occurred between in the ulna and radius bones. In conclusion, although MSCs induce bone formation, which exceeds the fracture site, significant remodeling of the repair callus occurs over time. In addition, limbs treated with an MSC graft demonstrated superior biomechanical properties, which could indicate the clinical benefit of future MSC application in nonunion fracture repair. PMID:20471652

  17. Quantitative, structural, and image-based mechanical analysis of nonunion fracture repaired by genetically engineered mesenchymal stem cells.

    PubMed

    Kallai, Ilan; van Lenthe, G Harry; Ruffoni, Davide; Zilberman, Yoram; Müller, Ralph; Pelled, Gadi; Gazit, Dan

    2010-08-26

    Stem cell-mediated gene therapy for fracture repair, utilizes genetically engineered mesenchymal stem cells (MSCs) for the induction of bone growth and is considered a promising approach in skeletal tissue regeneration. Previous studies have shown that murine nonunion fractures can be repaired by implanting MSCs over-expressing recombinant human bone morphogenetic protein-2 (rhBMP-2). Nanoindentation studies of bone tissue induced by MSCs in a radius fracture site indicated similar elastic modulus compared to intact murine bone, eight weeks post-treatment. In the present study we sought to investigate temporal changes in microarchitecture and biomechanical properties of repaired murine radius bones, following the implantation of MSCs. High-resolution micro-computed tomography (micro-CT) was performed 10 and 35 weeks post MSC implantation, followed by micro-finite element (micro-FE) analysis. The results have shown that the regenerated bone tissue remodels over time, as indicated by a significant decrease in bone volume, total volume, and connectivity density combined with an increase in mineral density. In addition, the axial stiffness of limbs repaired with MSCs was 2-1.5 times higher compared to the contralateral intact limbs, at 10 and 35 weeks post-treatment. These results could be attributed to the fusion that occurred in between the ulna and radius bones. In conclusion, although MSCs induce bone formation, which exceeds the fracture site, significant remodeling of the repair callus occurs over time. In addition, limbs treated with an MSC graft demonstrated superior biomechanical properties, which could indicate the clinical benefit of future MSC application in nonunion fracture repair. PMID:20471652

  18. Modeling of Acid Fracturing in Carbonate Reservoirs 

    E-print Network

    Al Jawad, Murtada s

    2014-06-05

    The acid fracturing process is a thermal, hydraulic, mechanical, and geochemical (THMG)-coupled phenomena in which the behavior of these variables are interrelated. To model the flow behavior of an acid into a fracture, mass and momentum balance...

  19. FY07 LDRD Final Report A Fracture Mechanics and Tribology Approach to Understanding Subsurface Damage on Fused Silica during Grinding and Polishing

    SciTech Connect

    Suratwala, T I; Miller, P E; Menapace, J A; Wong, L L; Steele, R A; Feit, M D; Davis, P J; Walmer, C D

    2008-02-05

    The objective of this work is to develop a solid scientific understanding of the creation and characteristics of surface fractures formed during the grinding and polishing of brittle materials, specifically glass. In this study, we have experimentally characterized the morphology, number density, and depth distribution of various surface cracks as a function of various grinding and polishing processes (blanchard, fixed abrasive grinding, loose abrasive, pitch polishing and pad polishing). Also, the effects of load, abrasive particle (size, distribution, foreign particles, geometry, velocity), and lap material (pitch, pad) were examined. The resulting data were evaluated in terms of indentation fracture mechanics and tribological interactions (science of interacting surfaces) leading to several models to explain crack distribution behavior of ground surfaces and to explain the characteristics of scratches formed during polishing. This project has greatly advanced the scientific knowledge of microscopic mechanical damage occurring during grinding and polishing and has been of general interest. This knowledge-base has also enabled the design and optimization of surface finishing processes to create optical surfaces with far superior laser damage resistance. There are five major areas of scientific progress as a result of this LDRD. They are listed in Figure 1 and described briefly in this summary below. The details of this work are summarized through a number of published manuscripts which are included this LDRD Final Report. In the first area of grinding, we developed a technique to quantitatively and statistically measure the depth distribution of surface fractures (i.e., subsurface damage) in fused silica as function of various grinding processes using mixtures of various abrasive particles size distributions. The observed crack distributions were explained using a model that extended known, single brittle indentation models to an ensemble of loaded, sliding particles. The model illustrates the importance of the particle size distribution of the abrasive and its influence on the resulting crack distribution. The results of these studies are summarized in references 1-7. In the second area of polishing, we conducted a series of experiments showing the influence of rogue particles (i.e., particles in the polishing slurry that are larger than base particles) on the creation of scratches on polished surfaces. Scratches can be thought of a as a specific type of sub-surface damage. The characteristics (width, length, type of fractures, concentration) were explained in terms of the rogue particle size, the rogue particle material, and the viscoelastic properties of the lap. The results of these studies are summarized in references 6-7. In the third area of etching, we conducted experiments aimed at understanding the effect of HF:NH{sub 4}F acid etching on surface fractures on fused silica. Etching can be used as a method: (a) to expose sub-surface mechanical damage, (b) to study the morphology of specific mechanical damage occurring by indentation, and (c) to convert a ground surface containing a high concentration of sub-surface mechanical damage into surface roughness. Supporting models have been developed to describe in detail the effect of etching on the morphology and evolution of surface cracks. The results of these studies are summarized in references 8-9. In the fourth area of scratch forensics or scratch fractography, a set of new scratch forensic rule-of-thumbs were developed in order to aid the optical fabricator and process engineer to interpret the cause of scratches and digs on surfaces. The details of how these rules were developed are described in each of the references included in this summary (1-9). Figure 2 provides as a summary of some of the more commonly used rules-of-thumbs that have been developed in this study. In the fifth and final area of laser damage, we demonstrated that the removal of such surface fractures from the surface during optical fabrication can dramatically improve the laser damage.

  20. Thermally and compositionally coupled simulations of magma ascent, differentiation and emplacement

    NASA Astrophysics Data System (ADS)

    Keller, T.

    2013-12-01

    A wide range of physically and chemically coupled mechanisms contribute to the problem of magma ascent and differentiation from an upper mantle melt source through lithosphere and crust towards its emplacement or eruption. The thermodynamics of the petrological system involved are complex and therefore challenging to represent with a simple model. Additionally, the mechanics of melt ascent and emplacement in a host rock undergoing both ductile creep and brittle fracture requires the use of a realistic visco-elasto-plastic rheology. A novel numerical method is proposed to simulate a thermally and compositionally coupled two-phase flow problem applied to magma ascent, compositional differentiation and emplacement tectonics in a visco-elasto-plastically deforming 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 thermodynamically consistent melting model depending on temperature, pressure and composition. The method is applied to the context of continental arc magmatism, where magmas derived from melting processes in the mantle wedge above a subduction zone ascend through a cool and mechanically strong continental lithosphere undergoing tectonic deformation. The results demonstrate that some important features known from geological and petrological studies of continental arc magmatism may be reproduced numerically to a good first order. The proposed method opens up the opportunity to study the physics of magmatic systems in geodynamics through a fully coupled and self-consistent numerical model of thermally and compositionally coupled two-phase flow.

  1. Cancellous bone lamellae strongly affect microcrack propagation and apparent mechanical properties: Separation of patients with osteoporotic fracture from normal controls using a 2D nonlinear finite element method (biomechanical stereology)

    PubMed Central

    Wang, Xiang; Zauel, Roger R.; Rao, D. Sudhaker; Fyhrie, David P.

    2009-01-01

    Biomechanical stereology is proposed as a two-dimensional (2D) finite element (FE) method to estimate the ability of bone tissue to sustain damage and to separate patients with osteoporotic fracture from normal controls. Briefly, 2D nonlinear compact tension FE models were created from quantitative back scattered electron images taken of iliac crest bone specimens collected from the individuals with or without osteoporotic fracture history. The effects of bone mineral microstructure on predicted bone fracture toughness and microcrack propagation were examined. The 2D FE models were used as surrogates for the real bone tissues. The calculated microcrack propagation results and bone mechanical properties were examined as surrogates for measurements from mechanical testing of actual specimens. The results for the 2D FE simulation separated patients with osteoporotic fracture from normal controls even though only the variability in tissue mineral microstructure was used to build the models. The models were deliberately created to ignore all differences in mean mineralization. Hence, the current results support the following hypotheses: (1) that material heterogeneity is important to the separation of patients with osteoporotic fracture from normal controls and; and (2) that 2D nonlinear finite element modeling can produce surrogate mechanical parameters that separate patients with fracture from normal controls. PMID:18378204

  2. Hip fracture - discharge

    MedlinePLUS

    Inter-trochanteric fracture repair - discharge; Subtrochanteric fracture repair - discharge; Femoral neck fracture repair - discharge; Trochanteric fracture repair - discharge; Hip pinning surgery - ...

  3. The mechanisms of dispersion strengthening and fracture in Al-based XD(tm) alloys, part 1

    NASA Technical Reports Server (NTRS)

    Aikin, R. M., Jr.

    1990-01-01

    The influence of reinforcement size, volume fraction, and matrix deformation behavior on room and elevated temperature strength; the fracture toughness; and the fatigue crack growth rate of metal matrix composites of Al-4(pct)Cu-1.5(pct)Mg with TiB2 were examined. The influence of reinforcement volume fraction was also examined for pure aluminum with TiB2. Higher TiB2 volume fractions increased the tensile yield strength at both room and elevated temperatures, and reduced the elongation to fracture. Tensile tests also indicate that small particles provided a greater increase in strength for a given volume fraction than larger particles, whereas elongation to fracture appeared to be insensitive to reinforcement size. Interparticle spacing appears to be the factor that controls the strength of these alloys, with the exact nature of the dependence relying on the nature of dislocation slip in the matrix (planar vs. diffuse). The isothermal aging response of the precipitation strengthened Al-4(pct)Cu-1.5(pct)Mg alloys was not accelerated by the presence of TiB2. Cold work prior to artificial aging created additional geometrically necessary dislocations which serve as heterogeneous nucleation sites leading to accelerated aging, a finer precipitate size, and an increase in the strength of the alloy.

  4. Treatment of Thoracolumbar Fracture

    PubMed Central

    Kim, Byung-Guk; Shin, Dong-Eun

    2015-01-01

    The most common fractures of the spine are associated with the thoracolumbar junction. The goals of treatment of thoracolumbar fracture are leading to early mobilization and rehabilitation by restoring mechanical stability of fracture and inducing neurologic recovery, thereby enabling patients to return to the workplace. However, it is still debatable about the treatment methods. Neurologic injury should be identified by thorough physical examination for motor and sensory nerve system in order to determine the appropriate treatment. The mechanical stability of fracture also should be evaluated by plain radiographs and computed tomography. In some cases, magnetic resonance imaging is required to evaluate soft tissue injury involving neurologic structure or posterior ligament complex. Based on these physical examinations and imaging studies, fracture stability is evaluated and it is determined whether to use the conservative or operative treatment. The development of instruments have led to more interests on the operative treatment which saves mobile segments without fusion and on instrumentation through minimal invasive approach in recent years. It is still controversial for the use of these treatments because there have not been verified evidences yet. However, the morbidity of patients can be decreased and good clinical and radiologic outcomes can be achieved if the recent operative treatments are used carefully considering the fracture pattern and the injury severity. PMID:25705347

  5. Multiscale Multifunctional Progressive Fracture of Composite Structures

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.; Minnetyan, L.

    2012-01-01

    A new approach is described for evaluating fracture in composite structures. This approach is independent of classical fracture mechanics parameters like fracture toughness. It relies on computational simulation and is programmed in a stand-alone integrated computer code. It is multiscale, multifunctional because it includes composite mechanics for the composite behavior and finite element analysis for predicting the structural response. It contains seven modules; layered composite mechanics (micro, macro, laminate), finite element, updating scheme, local fracture, global fracture, stress based failure modes, and fracture progression. The computer code is called CODSTRAN (Composite Durability Structural ANalysis). It is used in the present paper to evaluate the global fracture of four composite shell problems and one composite built-up structure. Results show that the composite shells. Global fracture is enhanced when internal pressure is combined with shear loads. The old reference denotes that nothing has been added to this comprehensive report since then.

  6. Mechanical behaviors of the dispersion nuclear fuel plates induced by fuel particle swelling and thermal effect II: Effects of variations of the fuel particle diameters

    NASA Astrophysics Data System (ADS)

    Ding, Shurong; Wang, Qiming; Huo, Yongzhong

    2010-02-01

    In order to predict the irradiation mechanical behaviors of plate-type dispersion nuclear fuel elements, the total burnup is divided into two stages: the initial stage and the increasing stage. At the initial stage, the thermal effects induced by the high temperature differences between the operation temperatures and the room temperature are mainly considered; and at the increasing stage, the intense mechanical interactions between the fuel particles and the matrix due to the irradiation swelling of fuel particles are focused on. The large-deformation thermo-elasto-plasticity finite element analysis is performed to evaluate the effects of particle diameters on the in-pile mechanical behaviors of fuel elements. The research results indicate that: (1) the maximum Mises stresses and equivalent plastic strains at the matrix increase with the fuel particle diameters; the effects of particle diameters on the maximum first principal stresses vary with burnup, and the considered case with the largest particle diameter holds the maximum values all along; (2) at the cladding near the interface between the fuel meat and the cladding, the Mises stresses and the first principal stresses undergo major changes with increasing burnup, and different variations exist for different particle diameter cases; (3) the maximum Mises stresses at the fuel particles rise with the particle diameters.

  7. The medial periosteal hinge, a key structure in fractures of the proximal humerus: a biomechanical cadaver study of its mechanical properties.

    PubMed

    Kralinger, F; Unger, S; Wambacher, M; Smekal, V; Schmoelz, W

    2009-07-01

    The medial periosteal hinge plays a key role in fractures of the head of the humerus, offering mechanical support during and after reduction and maintaining perfusion of the head by the vessels in the posteromedial periosteum. We have investigated the biomechanical properties of the medial periosteum in fractures of the proximal humerus using a standard model in 20 fresh-frozen cadaver specimens comparable in age, gender and bone mineral density. After creating the fracture, we displaced the humeral head medial or lateral to the shaft with controlled force until complete disruption of the posteromedial periosteum was recorded. As the quality of periosteum might be affected by age and bone quality, the results were correlated with the age and the local bone mineral density of the specimens measured with quantitative CT. Periosteal rupture started at a mean displacement of 2.96 mm (SD 2.92) with a mean load of 100.9 N (SD 47.1). The mean maximum load of 111.4 N (SD 42.5) was reached at a mean displacement of 4.9 mm (SD 4.2). The periosteum was completely ruptured at a mean displacement of 34.4 mm (SD 11.1). There was no significant difference in the mean distance to complete rupture for medial (mean 35.8 mm (SD 13.8)) or lateral (mean 33.0 mm (SD 8.2)) displacement (p = 0.589). The mean bone mineral density was 0.111 g/cm(3) (SD 0.035). A statistically significant but low correlation between bone mineral density and the maximum load uptake (r = 0.475, p = 0.034) was observed. This study showed that the posteromedial hinge is a mechanical structure capable of providing support for percutaneous reduction and stabilisation of a fracture by ligamentotaxis. Periosteal rupture started at a mean of about 3 mm and was completed by a mean displacement of just under 35 mm. The microvascular situation of the rupturing periosteum cannot be investigated with the current model. PMID:19567866

  8. The Effects of Fracture Orientation and Anisotropy on Hydraulic Fracture Conductivity in the Marcellus Shale 

    E-print Network

    McGinley, Mark John

    2015-05-12

    of hydraulically-induced fractures. Ultimately, the experiments conducted as part of this work show that fracture conductivity trends are strongly tied to both proppant concentration and the rock’s mechanical properties....

  9. FRACTURING FLUID CHARACTERIZATION FACILITY

    SciTech Connect

    Subhash Shah

    2000-08-01

    Hydraulic fracturing technology has been successfully applied for well stimulation of low and high permeability reservoirs for numerous years. Treatment optimization and improved economics have always been the key to the success and it is more so when the reservoirs under consideration are marginal. Fluids are widely used for the stimulation of wells. The Fracturing Fluid Characterization Facility (FFCF) has been established to provide the accurate prediction of the behavior of complex fracturing fluids under downhole conditions. The primary focus of the facility is to provide valuable insight into the various mechanisms that govern the flow of fracturing fluids and slurries through hydraulically created fractures. During the time between September 30, 1992, and March 31, 2000, the research efforts were devoted to the areas of fluid rheology, proppant transport, proppant flowback, dynamic fluid loss, perforation pressure losses, and frictional pressure losses. In this regard, a unique above-the-ground fracture simulator was designed and constructed at the FFCF, labeled ''The High Pressure Simulator'' (HPS). The FFCF is now available to industry for characterizing and understanding the behavior of complex fluid systems. To better reflect and encompass the broad spectrum of the petroleum industry, the FFCF now operates under a new name of ''The Well Construction Technology Center'' (WCTC). This report documents the summary of the activities performed during 1992-2000 at the FFCF.

  10. Fracture mechanical behavior of red sandstone containing a single fissure and two parallel fissures after exposure to different high temperature treatments

    NASA Astrophysics Data System (ADS)

    Yang, Sheng-Qi; Jing, Hong-Wen; Huang, Yan-Hua; Ranjith, P. G.; Jiao, Yu-Yong

    2014-12-01

    A detailed understanding of the brittle deformation behavior of sandstone containing pre-existing flaws at elevated temperatures is a key concern in underground engineering. In this research, uniaxial compression tests were performed to evaluate the effect of high temperature treatments (300, 600 or 900 °C) on the strength, deformability and fracture coalescence behavior of a sandstone containing either a single fissure or two parallel fissures. All experiments focused on rectangular prismatic (80 × 160 × 30 mm) specimens of red sandstone. Constant strain rate experiments were performed on either: (1) specimens that contained a single 2 mm-wide fissure or (2) specimens that contained two 2 mm-wide parallel fissures. The specimens containing either one or two fissures were either left at room temperature (i.e., no heat treatment), or heat treated to 300, 600 or 900 °C prior to experimentation. The results demonstrated that, in all cases, the strength and stiffness of red sandstone was increased at 300 °C, before decreasing up to our maximum temperature of 900 °C. However, the peak strain at failure always showed an increase when the temperature was increased. The crack initiation, propagation and coalescence process were monitored during the deformation using both photographic monitoring and acoustic emission (AE) monitoring techniques. The monitoring results showed that the cracking process depended on both the fissure geometry and the heat treatment temperature. The potential mechanisms causing the differences in the mechanical behavior observed with increasing temperature are discussed, as is the influence of the single fissure and the two parallel fissures on the crack evolution process. These results are important and valuable to understand the fracture mechanism of rock engineering in deep underground mining excavations and nuclear waste depositories.

  11. Mechanical thrombectomy using Rotarex system and stent-in-stent placement for treatment of distal femoral artery occlusion secondary to stent fracture – a case report and literature review

    PubMed Central

    Dys, Krzysztof; Drelichowska-Durawa, Justyna; Do?ega-Kozierowski, Bartosz; Lis, Micha?; Sokratous, Kyriakos; Iwanowski, Wojciech; Drelichowski, Stanis?aw; Witkiewicz, Wojciech

    2013-01-01

    Summary Background: Treatment of peripheral arterial diseases may be distinguished into conservative and interventional management; the latter is divided into surgical and endovascular procedures. Management of peripheral artery stenosis and occlusion with vascular stents is associated with the risk of late complications such as restenosis, stent fracture or dislocation. Case Report: A 62-year-old woman with generalized atherosclerosis, particularly extensive in lower limb arteries, was admitted to the Department of Angiology 11 months after having an endovascular procedure performed due to critical ischemia of left lower limb. Because of stent occlusion, a decision to perform angiographic examination of lower limb arteries was made. Examination revealed occlusion of the superficial femoral artery along its entire length, including previously implanted stents. Distal stent was fractured with slight dislocation of the proximal segment. A decision was made to perform mechanical thrombectomy using a Rotarex system followed by a stent-in-stent placement procedure. Follow-up angiography and ultrasound scan performed 24 hours after the procedure revealed a patent vessel with satisfactory blood flow. Discussion: Nowadays, imaging diagnostics of peripheral artery stenosis involves non-invasive examinations such as ultrasound, minimally invasive examinations such as angio-MRI and MDCT, or invasive examinations such as DSA and IVUS. DSA examinations are used to confirm significant stenosis or occlusion of a vessel, particularly when qualifying a patient for endovascular treatment. Due to their anatomic location, the superficial femoral artery and the popliteal artery are subject to various forces e.g. those exerted by the working muscles. Mechanical thrombectomy and atherectomy are efficient methods of arterial recanalization used in the treatment of acute, subacute or even chronic occlusions or stenosis of peripheral vessels. Conclusions: Frequency of angioplasty and vascular stent implantation procedures is increased in patients with peripheral arterial disease, thus increasing the incidence of reported early and late complications such as acute stent thrombosis, restenosis and stent fractures. The Rotarex transcutaneous mechanical thrombectomy system is an efficient method of treating occlusions in arterial stents. It is also safe when performed by experienced operators. PMID:24115965

  12. An automated dynamic fracture procedure and a continuum damage mechanics based model for finite element simulations of delamination failure in laminated composites

    NASA Astrophysics Data System (ADS)

    Aminjikarai Vedagiri, Srinivasa Babu

    An active field of research that has developed due to the increasing use of computational techniques like finite element simulations for analysis of highly complex structural mechanics problems and the increasing use of composite laminates in varied industries such as aerospace, automotive, bio-medical, etc. is the development of numerical models to capture the behavior of composite materials. One of the big challenges not yet overcome convincingly in this field is the modeling of delamination failure which is one of the primary modes of damage in composite laminates. Hence, the primary aim of this work is to develop two numerical models for finite element simulations of delamination failure in composite laminates and implement them in the explicit finite element software DYNA3D/LS-DYNA. Dynamic fracture mechanics is an example of a complex structural analysis problem for which finite element simulations seem to be the only possible way to extract detailed information on sophisticated physical quantities of the crack-tip at any instant of time along a highly transient history of fracture. However, general purpose, commercial finite element software which have capabilities to do fracture analyses are still limited in their use to stationary cracks and crack propagation along trajectories known a priori. Therefore, an automated dynamic fracture procedure capable of simulating dynamic propagation of through-thickness cracks in arbitrary directions in linear, isotropic materials without user-intervention is first developed and implemented in DYNA3D for its default 8-node solid (brick) element. Dynamic energy release rate and stress intensity factors are computed in the model using integral expressions particularly well-suited for the finite element method. Energy approach is used to check for crack propagation and the maximum circumferential stress criterion is used to determine the direction of crack growth. Since the re-meshing strategy used to model crack growth explicitly in the model induces spurious high-frequency oscillations in the finite element results after crack initiation, a "gradual nodal release" procedure is implemented as part of the model to overcome this problem. Also, an in-built contact algorithm of DYNA3D is modified to adapt it to the remeshing strategy to maintain proper contact conditions at newly added elements. Finally, the model is suitably modified for simulating delamination failure in laminated composites and used to predict delamination resistance characteristics which are important considerations for effective use of composite structures. Continuum damage mechanics is a popular approach for modeling the in-plane failure modes in composites. However, its applicability to modeling delamination has not been sufficiently analyzed yet. Hence, as the second part of this dissertation work, a new material model is developed for unidirectional polymer matrix composites in which this approach is used to predict delamination failure and used to perform a qualitative study of the damage mechanics approach to modeling delamination. The new material model is developed using micro-mechanics and accounts for the strain-rate dependent behavior of polymer matrix composites. It is implemented for three different element formulations with different transverse shear strain assumptions and the effect of these assumptions on the delamination prediction using this approach is analyzed.

  13. Mechanics of Jointed and Faulted Rock, Rossmanith (ed) 0 1995 Balkema, Rotterdam. ISBN 90 54 10 54 7 0 Seismic properties of a general fracture

    E-print Network

    Edinburgh, University of

    and fracture systems are also crucial for hydrocarbon production, control and manipulation of water supplies events induced by hydraulic fracturing. The effect of a thin weak elastic layer was investigated by Jones

  14. Growth Kinematics of Opening-Mode Fractures

    NASA Astrophysics Data System (ADS)

    Eichhubl, P.; Alzayer, Y.; Laubach, S.; Fall, A.

    2014-12-01

    Fracture aperture is a primary control on flow in fractured reservoirs of low matrix permeability including unconventional oil and gas reservoirs and most geothermal systems. Guided by principles of linear elastic fracture mechanics, fracture aperture is generally assumed to be a linear function of fracture length and elastic material properties. Natural opening-mode fractures with significant preserved aperture are observed in core and outcrop indicative of fracture opening strain accommodated by permanent solution-precipitation creep. Fracture opening may thus be decoupled from length growth if the material effectively weakens after initial elastic fracture growth by either non-elastic deformation processes or changes in elastic properties. To investigate the kinematics of fracture length and aperture growth, we reconstructed the opening history of three opening-mode fractures that are bridged by crack-seal quartz cement in Travis Peak Sandstone of the SFOT-1 well, East Texas. Similar crack-seal cement bridges had been interpreted to form by repeated incremental fracture opening and subsequent precipitation of quartz cement. We imaged crack-seal cement textures for bridges sampled at varying distance from the tips using scanning electron microscope cathodoluminescence, and determined the number and thickness of crack-seal cement increments as a function of position along the fracture length and height. Observed trends in increment number and thickness are consistent with an initial stage of fast fracture propagation relative to aperture growth, followed by a stage of slow propagation and pronounced aperture growth. Consistent with fluid inclusion observations indicative of fracture opening and propagation occurring over 30-40 m.y., we interpret the second phase of pronounced aperture growth to result from fracture opening strain accommodated by solution-precipitation creep and concurrent slow, possibly subcritical, fracture propagation. Similar deformation mechanisms are envisioned to govern fracture growth over shorter timescales in reactive chemical subsurface environments including CO2 reservoirs, organic-rich shales, and geothermal systems.

  15. Facial nerve palsy after mandibular fracture.

    PubMed

    Weinberg, M J; Merx, P; Antonyshyn, O; Farb, R

    1995-05-01

    A 19-year-old man sustained a right parasymphyseal fracture and bilateral condylar neck fractures in a motor vehicle accident. The parasymphyseal fracture was treated by open reduction and internal fixation, and the subcondylar fractures were treated with closed reduction and maxillomandibular fixation. Three days postoperatively, a near-complete left facial nerve palsy developed. Facial nerve recovery was not full. The literature is reviewed, and possible mechanisms of this rare and devastating complication are discussed. PMID:7639495

  16. Fracture phenomena have been extensively studied in the last several decades, and continuum mechanics-based approaches, such as Finite Element Methods (FEM), are widely used for simulation.

    E-print Network

    Fracture phenomena have been extensively studied in the last several decades, and continuum-known issue of this approach is the stress singularity at the crack tip/front. Another known issue of fracture) and Peridynamics, have certain advantages while modeling various fracture problems of solids due to their intrinsic

  17. Ductile fracture mechanism of low-temperature In-48Sn alloy joint under high strain rate loading.

    PubMed

    Kim, Jong-Woong; Jung, Seung-Boo

    2012-04-01

    The failure behaviors of In-48Sn solder ball joints under various strain rate loadings were investigated with both experimental and finite element modeling study. The bonding force of In-48Sn solder on an Ni plated Cu pad increased with increasing shear speed, mainly due to the high strain-rate sensitivity of the solder alloy. In contrast to the cases of Sn-based Pb-free solder joints, the transition of the fracture mode from a ductile mode to a brittle mode was not observed in this solder joint system due to the soft nature of the In-48Sn alloy. This result is discussed in terms of the relationship between the strain-rate of the solder alloy, the work-hardening effect and the resulting stress concentration at the interfacial regions. PMID:22849101

  18. The laser ablation model development of glass substrate cutting assisted with the thermal fracture and ultrasonic mechanisms

    NASA Astrophysics Data System (ADS)

    Huang, Kuo-Cheng; Hsiao, Wen-Tse; Hwang, Chi-Hung; Lin, Ru-Li; Andrew Yeh, Jer-Liang

    2015-04-01

    This study presents three hybrid processing models for cutting a glass substrate, and compares their cutting speeds. The three models are (I) thermal fracture cutting technology (TFCT)-assisted laser ablation, (II) ultrasonic-assisted laser ablation, and (III) ultrasonic and TFCT-assisted laser ablation. In the experiment, a 12 W 355 nm Nd:YVO4 laser system, a 40 W CO2 laser and an ultrasonic transducer were used to cut 3 mm thick soda-lime glasses. Lasers and ultrasonic transducers were used as heat sources and vibration sources, respectively. Results show that the surface morphology of the soda-lime glass sheet depends on the processing models. After cutting, the surface and cross-sectional morphology of glass substrate were observed using a portable digital microscope and residual stresses were also evaluated thanks to a photoelasticity instrument.

  19. Application of fracture mechanics and half-cycle method to the prediction of fatigue life of B-52 aircraft pylon components

    NASA Technical Reports Server (NTRS)

    Ko, W. L.; Carter, A. L.; Totton, W. W.; Ficke, J. M.

    1989-01-01

    Stress intensity levels at various parts of the NASA B-52 carrier aircraft pylon were examined for the case when the pylon store was the space shuttle solid rocket booster drop test vehicle. Eight critical stress points were selected for the pylon fatigue analysis. Using fracture mechanics and the half-cycle theory (directly or indirectly) for the calculations of fatigue-crack growth ,the remaining fatigue life (number of flights left) was estimated for each critical part. It was found that the two rear hooks had relatively short fatigue life and that the front hook had the shortest fatigue life of all the parts analyzed. The rest of the pylon parts were found to be noncritical because of their extremely long fatigue life associated with the low operational stress levels.

  20. Fracture Reactivation in Chemically Reactive Rock Systems

    NASA Astrophysics Data System (ADS)

    Eichhubl, P.; Hooker, J. N.

    2013-12-01

    Reactivation of existing fractures is a fundamental process of brittle failure that controls the nucleation of earthquake ruptures, propagation and linkage of hydraulic fractures in oil and gas production, and the evolution of fault and fracture networks and thus of fluid and heat transport in the upper crust. At depths below 2-3 km, and frequently shallower, brittle processes of fracture growth, linkage, and reactivation compete with chemical processes of fracture sealing by mineral precipitation, with precipitation rates similar to fracture opening rates. We recently found rates of fracture opening in tectonically quiescent settings of 10-20 ?m/m.y., rates similar to euhedral quartz precipitation under these conditions. The tendency of existing partially or completely cemented fractures to reactivate will vary depending on strain rate, mineral precipitation kinetics, strength contrast between host rock and fracture cement, stress conditions, degree of fracture infill, and fracture network geometry. Natural fractures in quartzite of the Cambrian Eriboll Formation, NW Scotland, exhibit a complex history of fracture formation and reactivation, with reactivation involving both repeated crack-seal opening-mode failure and shear failure of fractures that formed in opening mode. Fractures are partially to completely sealed with crack-seal or euhedral quartz cement or quartz cement fragmented by shear reactivation. Degree of cementation controls the tendency of fractures for later shear reactivation, to interact elastically with adjacent open fractures, and their intersection behavior. Using kinematic, dynamic, and diagenetic criteria, we determine the sequence of opening-mode fracture formation and later shear reactivation. We find that sheared fracture systems of similar orientation display spatially varying sense of slip We attribute these inconsistent directions of shear reactivation to 1) a heterogeneous stress field in this highly fractured rock unit and 2) variations in the degree of fracture cement infill in fractures of same orientation, allowing fractures to reactivate at times when adjacent, more cemented fractures remain dormant. The observed interaction of chemical and mechanical fracture growth and sealing processes in this chemically reactive and heavily deformed rock unit results in a complex fracture network geometry not generally observed in less chemically reactive, shallower crustal environments.

  1. Fractured Petroleum Reservoirs

    SciTech Connect

    Firoozabadi, Dr. Abbas

    2000-01-18

    In this report the results of experiments of water injection in fractured porous media comprising a number of water-wet matrix blocks are reported for the first time. The blocks experience an advancing fracture-water level (FWL). Immersion-type experiments are performed for comparison; the dominant recovery mechanism changed from co-current to counter-current imbibition when the boundary conditions changed from advancing FWL to immersion-type. Single block experiments of co-current and counter-current imbibition was performed and co-current imbibition leads to more efficient recovery was found.

  2. Mechanical enhancement of woven composites with radially aligned carbon nanotubes (CNTs) : investigation of Mode I fracture toughness

    E-print Network

    Wicks, Sunny S

    2010-01-01

    Composites have seen an increasing role in aerospace structures that demand lightweight, strong, and stiff materials. Composites are attractive structural materials with outstanding mechanical and physical properties, as ...

  3. Continuum Mechanics and Thermodynamics manuscript No. (will be inserted by the editor)

    E-print Network

    frictional cracks and elasto-plastic zones. The proposed theory combines micromechanical and thermodynamic thermodynamics · micromechanics · frictional cracks · plasticity · dissipation 1 Introduction A wide variety@lmt.ens-cachan.fr H. Trumel CEA, DAM Le Ripault F-37260 Monts, France. Tel.: (33) 2 47 34 44 12 Fax: (33) 2 47 34 E

  4. Fracture toughness testing data: A technology survey and bibliography

    NASA Technical Reports Server (NTRS)

    Stuhrke, W. F.; Carpenter, J. L., Jr.; Moya, N.; Mandel, G.

    1975-01-01

    Announced survey includes reports covering fracture toughness testing for various structural materials including information on plane strain and developing areas of mixed mode and plane strain test conditions. Bibliography references cite work and conclusions in fracture toughness testing and application of fracture toughness test data, and in fracture mechanics analysis.

  5. Kevlar fiber-epoxy adhesion and its effect on composite mechanical and fracture properties by plasma and chemical treatment

    SciTech Connect

    Shyu, S.S.; Wu, S.R.; Sheu, G.S.

    1996-12-31

    Kevlar 49 fibers were surface modified by gas (ammonia, oxygen, and water vapor) plasmas etching and chlorosulfonation and subsequent reaction with some reagents (glycine, deionized water, ethylenediamine, and 1-butanol) to improve the adhesion to epoxy resin. After these treatments, the changes in fiber topography, chemical compositions of the fiber surfaces and the surface functional groups introduced to the surface of fibers were identified by SEM XPS and static SIMS. Interlaminar shear strength (ILSS) and T-peel strength between the fiber and epoxy resin were markedly improved by gas plasma and chlorosulfonation (0.1% and 0.25% ClSO{sub 3}H at 30 s). However, it is clear from the similar G{sub IC} values of the treated and untreated fiber composites that the fiber/matrix interfacial bond strength is only a minor contributor to G{sub IC}. SEM was also used to study the surface topography of the fracture surfaces of composites in T-peel test.

  6. Formability Prediction Of Aluminum Sheet In Automotive Applications

    NASA Astrophysics Data System (ADS)

    Leppin, Christian; Daniel, Dominique; Shahani, Ravi; Gese, Helmut; Dell, Harry

    2007-05-01

    In the following paper, a full mechanical characterization of the AA6016 T4 aluminum alloy car body sheet DR100 is presented. A comprehensive experimental program was performed to identify and model the orthotopic elasto-plastic deformation behavior of the material and its fracture characteristics including criteria for localized necking, ductile fracture and shear fracture. The commercial software package MF GenYld + CrachFEM in combination with the explicit finite element code Ls-Dyna is used to validate the quality of the material model with experiments, namely, prediction of the FLD, deep drawing with a cross-shaped punch and finally, analysis of a simplified hemming process using a solid discretization of the problem. The focus is on the correct prediction of the limits of the material in such processes.

  7. Particulate fracture during deformation

    NASA Astrophysics Data System (ADS)

    Llorca, J.; Martin, A.; Ruiz, J.; Elices, M.

    1993-07-01

    The mechanisms of deformation and failure in a 2618 Al alloy reinforced with 15 vol pct SiC particilates were studied and compared with those of the unreinforced alloy, processed by spray forming as well. Tensile and fracture toughness tests were carried out on naturally aged and peak-aged specimens. The broken specimens were sliced through the middle, and the geometric features of fractured and intact particulates were measured. The experimental observations led to the conclusion that failure took place by the progressive fracture of the particulates until a critical volume fraction was reached. An influence of the particulate size and aspect ratio on the probability of fracture was found, the large and elongated particulates being more prone to fail, and the fracture stress in the particulates seemed to obey the Weibull statistics. The dif- ferences in ductility found between the naturally aged and peak-aged composites were explained in terms of the number of broken particulates as a function of the applied strain. Numerical simulations of the deformation process indicated that the stresses acting on the particulates are higher in the peak-aged material, precipitating the specimen failure. Moreover, the compressive residual stresses induced on the SiC during water quenching delayed the onset of particulate breakage in the naturally aged material.

  8. Fracture healing redefined.

    PubMed

    Braun, B J; Rollmann, M; Veith, N; Pohlemann, T

    2015-12-01

    It is well established that local mechanical conditions and interfragmentary movement are important factors for successful bone healing and may vary dramatically with patient fracture-load and activity. Up until now however it was technically impossible to use these key influence parameters in the aftercare treatment process of human lower extremity fractures. We propose a theory that with state of the art sensor technology these biomechanical influences can not only be monitored in vivo, but also used for individualized therapy protocols. Local measurement systems for fracture healing are available but remain research tools, due to various technical issues. To investigate the biomechanical influences on healing right away surrogate sensor tools are needed. Various gait characteristics have been proposed as surrogate measures. Currently available sensor tools could be modified with the appropriate support structure to allow such measurements continuously over the course of a fracture healing. Interdisciplinary work between clinicians, software engineers with computer and biomechanical simulations is needed. Through such a sensor system human boundary conditions for fracture healing could not only be defined for the first time, but also used for a unique, extendible aftercare system. With this tool critical healing situations would be detected much earlier and could be prevented with easy activity modifications, reducing patient and socioeconomic burden of disease. The hypothesis, necessary tools and support structures are presented. PMID:26364044

  9. Application of a fracture mechanics model of seismic slip to slickenside data from the Black Mountain Frontal Fault Zone, Death Valley, California

    SciTech Connect

    Myers, R.D.; Pavlis, T.L. . Dept. of Geology and Geophysics)

    1992-01-01

    The fault arrays within fault zones are commonly highly organized, suggesting that simple processes are controlling the overall evolution of the system. Most analyses of slip data depend upon a dynamic interpretation, typically formulated as an inverse modeling scheme. A more realistic forward model of the finite kinematics should be provided by consideration of secondary stresses due to proximity of a rupture front. Approximating the secondary stress field using linear elastic fracture mechanics, the merits of the homogeneous dynamic theory can be evaluated by comparison with results from simulations of superimposed slip events. It was found that sets of randomly oriented fractures may record numerous overlapping slip events and large variations in lineation orientation accompany spatial variations in rupture termination, complexities not represented in a dynamic scenario. A robust feature of slip sets formed in an odd axis stress state are ubiquitous great circle distributions of M-poles the pole to which lies collinear to the odd axis. The computer model was field tested using fault geometries measured in the Black Mountain Frontal Fault Zone. Results of this modeling shed light on several features commonly observed in slickenside data sets, including; bi-clustering and great circle distributions of lineations, curvilinear slickensided surfaces, great circle M-pole distributions and anomalous lineation clusters with respect to movement on nearby major faults. These observations can be explained by combinations of; incomplete resetting, incrementally shallowing fault planes, spatial variations in fault terminations, incremental and conjugate slip about an inclined principle stress. These results strongly suggest that thorough documentation of local fault geometries is essential for proper interpretation of slip data obtained from large fault zones and that a regional dynamic approach may be overly simplistic in such studies.

  10. Sub-discretized surface model with application to contact mechanics in multi-body simulation

    SciTech Connect

    Johnson, S; Williams, J

    2008-02-28

    The mechanics of contact between rough and imperfectly spherical adhesive powder grains are often complicated by a variety of factors, including several which vary over sub-grain length scales. These include several traction factors that vary spatially over the surface of the individual grains, including high energy electron and acceptor sites (electrostatic), hydrophobic and hydrophilic sites (electrostatic and capillary), surface energy (general adhesion), geometry (van der Waals and mechanical), and elasto-plastic deformation (mechanical). For mechanical deformation and reaction, coupled motions, such as twisting with bending and sliding, as well as surface roughness add an asymmetry to the contact force which invalidates assumptions for popular models of contact, such as the Hertzian and its derivatives, for the non-adhesive case, and the JKR and DMT models for adhesive contacts. Though several contact laws have been offered to ameliorate these drawbacks, they are often constrained to particular loading paths (most often normal loading) and are relatively complicated for computational implementation. This paper offers a simple and general computational method for augmenting contact law predictions in multi-body simulations through characterization of the contact surfaces using a hierarchically-defined surface sub-discretization. For the case of adhesive contact between powder grains in low stress regimes, this technique can allow a variety of existing contact laws to be resolved across scales, allowing for moments and torques about the contact area as well as normal and tangential tractions to be resolved. This is especially useful for multi-body simulation applications where the modeler desires statistical distributions and calibration for parameters in contact laws commonly used for resolving near-surface contact mechanics. The approach is verified against analytical results for the case of rough, elastic spheres.

  11. Laboratory study of mechanical and petrophysical properties of both intact and naturally fractured shale samples from the Tournemire Underground Research Laboratory

    NASA Astrophysics Data System (ADS)

    David, C.; Bonnelye, A.; Schubnel, A.; Henry, P.; Guglielmi, Y.; Gout, C.; Dick, P.

    2014-12-01

    Understanding the mechanical and physical properties of fractured shales is of major importance in many fields such as the study of cap rock integrity or targets for radioactive waste disposal. In particular, relationships between fluid transport properties and textural anisotropy are critical. Therefore, these relations need to be investigated on real fault samples. This study in collaboration with IRSN and Total deals with the mechanical and petrophysical characterization of core samples from the Tournemire Underground Research Laboratory in Southern France. Three boreholes crossing a major fault at different angles have been investigated. The cores retrieved were carefully sampled and give access to the three major areas defining the fault zone: 1) the intact zone, 2) the damaged zone and 3) the fault core. The goal of the study is to perform several petrophysical measurements on the same specimens sampled at different distances from the fault core. These include multidirectional measurements of P and S waves under preserved humidity conditions, magnetic susceptibility measurements and pore size distribution characterization through the BET gas adsorption method. Some preliminary results show an evolution of the anisotropy with the distance to the fault core (anisotropy reversal). The boreholes that were sampled were drilled to perform hydromechanical in situ testing, therefore one of our objectives is also to compare the hydromechanical properties obtained in the mesoscale experiments in situ to the petrophysical measurements in the lab. Mechanical tests were also performed on intact samples in order to understand the mechanisms of deformation of the studied shale, depending on the orientation of the maximal applied stress with respect to bedding.

  12. Statistical Physics of Fracture

    SciTech Connect

    Alava, Mikko; Nukala, Phani K; Zapperi, Stefano

    2006-05-01

    Disorder and long-range interactions are two of the key components that make material failure an interesting playfield for the application of statistical mechanics. The cornerstone in this respect has been lattice models of the fracture in which a network of elastic beams, bonds, or electrical fuses with random failure thresholds are subject to an increasing external load. These models describe on a qualitative level the failure processes of real, brittle, or quasi-brittle materials. This has been particularly important in solving the classical engineering problems of material strength: the size dependence of maximum stress and its sample-to-sample statistical fluctuations. At the same time, lattice models pose many new fundamental questions in statistical physics, such as the relation between fracture and phase transitions. Experimental results point out to the existence of an intriguing crackling noise in the acoustic emission and of self-affine fractals in the crack surface morphology. Recent advances in computer power have enabled considerable progress in the understanding of such models. Among these partly still controversial issues, are the scaling and size-effects in material strength and accumulated damage, the statistics of avalanches or bursts of microfailures, and the morphology of the crack surface. Here we present an overview of the results obtained with lattice models for fracture, highlighting the relations with statistical physics theories and more conventional fracture mechanics approaches.

  13. CONSTRAINT EFFECT IN FRACTURE WHAT IS IT

    SciTech Connect

    Lam, P; Prof. Yuh J. Chao, P

    2008-10-29

    The meaning of the phrase 'constraint effect in fracture' has changed in the past two decades from 'contained plasticity' to a broader description of 'dependence of fracture toughness value on geometry of test specimen or structure'. This paper will first elucidate the fundamental mechanics reasons for the apparent 'constraint effects in fracture', followed by outlining a straightforward approach to overcoming this problem in both brittle (elastic) and ductile (elastic-plastic) fracture. It is concluded by discussing the major difference in constraint effect on fracture event in elastic and elastic-plastic materials.

  14. Geomechanical Simulation of Fluid-Driven Fractures

    SciTech Connect

    Makhnenko, R.; Nikolskiy, D.; Mogilevskaya, S.; Labuz, J.

    2012-11-30

    The project supported graduate students working on experimental and numerical modeling of rock fracture, with the following objectives: (a) perform laboratory testing of fluid-saturated rock; (b) develop predictive models for simulation of fracture; and (c) establish educational frameworks for geologic sequestration issues related to rock fracture. These objectives were achieved through (i) using a novel apparatus to produce faulting in a fluid-saturated rock; (ii) modeling fracture with a boundary element method; and (iii) developing curricula for training geoengineers in experimental mechanics, numerical modeling of fracture, and poroelasticity.

  15. Fracture types (1) (image)

    MedlinePLUS

    ... fracture which goes at an angle to the axis Comminuted - a fracture of many relatively small fragments Spiral - a fracture which runs around the axis of the bone Compound - a fracture (also called ...

  16. Effects of fracture reactivation and diagenesis on fracture network evolution: Cambrian Eriboll Formation, NW Scotland

    NASA Astrophysics Data System (ADS)

    Hooker, J. N.; Eichhubl, P.; Xu, G.; Ahn, H.; Fall, A.; Hargrove, P.; Laubach, S.; Ukar, E.

    2011-12-01

    The Cambrian Eriboll Formation quartzarenites contain abundant fractures with varying degrees of quartz cement infill. Fractures exist that are entirely sealed; are locally sealed by bridging cements but preserve pore space among bridges; are mostly open but lined with veneers of cement; or are devoid of cement. Fracture propagation in the Eriboll Formation is highly sensitive to the presence of pre-existing fractures. Fracture reactivation occurs in opening mode as individual fractures repeatedly open and are filled or bridged by syn-kinematic cements. As well, reactivation occurs in shear as opening of one fracture orientation coincides with shear displacement along pre-existing fractures of different orientations. The tendency for pre-existing fractures to slip varies in part by the extent of cement infill, yet we observe shear and opening-mode reactivation even among sealed fractures. Paleotemperature analysis of fluid inclusions within fracture cements suggests some fractures now in outcrop formed deep in the subsurface. Fractures within the Eriboll Formation may therefore affect later fracture propagation throughout geologic time. With progressive strain, fault zones develop within fracture networks by a sequence of opening-mode fracture formation, fracture reactivation and linkage, fragmentation, cataclasis, and the formation of slip surfaces. Cataclasite within fault zones is commonly more thoroughly cemented than fractures in the damage zone or outside the fault zone. This variance of cement abundance is likely the result of (1) continued exposure of freshly broken quartz surfaces within cataclasite, promoting quartz precipitation, and (2) possibly more interconnected pathways for mass transfer within the fault zone. Enhanced cementation of cataclasite results in strengthening or diagenetic strain hardening of the evolving fault zone. Further slip is accommodated by shear localization along discrete slip surfaces. With further linkage of fault segments, new, more favorably oriented slip surfaces form while earlier formed slip surfaces become inactive and cemented. This interaction between mechanical processes of fault-fracture network evolution with cementation leads to complex fault systems with heterogeneous permeability structure.

  17. Isolated medial cuneiform fractures: report of two cases and review of the literature.

    PubMed

    Guler, Ferhat; Baz, Ali Bulent; Turan, Adil; Kose, Ozkan; Akalin, Serdar

    2011-10-01

    Although fractures of the midfoot are common, cuneiform fractures are rarely seen. These fractures are frequently associated with other fractures of the midfoot such as Lisfranc fracture-dislocations. However, isolated cuneiform fractures are extremely rare, with few cases reported in the relevant literature. Herein, the authors report 2 cases of isolated medial cuneiform fractures. One of the patients was treated with headless screw fixation due to displacement in fracture configuration, and the other was treated conservatively. Fractures were united without any complication in both patients. In this report, the authors discuss the mechanism of injury, diagnostic challenges, and treatment options of isolated medial cuneiform fractures. PMID:21926363

  18. An experimental study on fracture mechanical behavior of rock-like materials containing two unparallel fissures under uniaxial compression

    NASA Astrophysics Data System (ADS)

    Huang, Yan-Hua; Yang, Sheng-Qi; Tian, Wen-Ling; Zeng, Wei; Yu, Li-Yuan

    2015-09-01

    Strength and deformability characteristics of rock with pre-existing fissures are governed by cracking behavior. To further research the effects of pre-existing fissures on the mechanical properties and crack coalescence process, a series of uniaxial compression tests were carried out for rock-like material with two unparallel fissures. In the present study, cement, quartz sand, and water were used to fabricate a kind of brittle rock-like material cylindrical model specimen. The mechanical properties of rock-like material specimen used in this research were all in good agreement with the brittle rock materials. Two unparallel fissures (a horizontal fissure and an inclined fissure) were created by inserting steel during molding the model specimen. Then all the pre-fissured rock-like specimens were tested under uniaxial compression by a rock mechanics servo-controlled testing system. The peak strength and Young's modulus of pre-fissured specimen all first decreased and then increased when the fissure angle increased from 0° to 75°. In order to investigate the crack initiation, propagation and coalescence process, photographic monitoring was adopted to capture images during the entire deformation process. Moreover, acoustic emission (AE) monitoring technique was also used to obtain the AE evolution characteristic of pre-fissured specimen. The relationship between axial stress, AE events, and the crack coalescence process was set up: when a new crack was initiated or a crack coalescence occurred, the corresponding axial stress dropped in the axial stress-time curve and a big AE event could be observed simultaneously. Finally, the mechanism of crack propagation under microscopic observation was discussed. These experimental results are expected to increase the understanding of the strength failure behavior and the cracking mechanism of rock containing unparallel fissures.

  19. Gravity-Driven Hydraulic Fractures

    NASA Astrophysics Data System (ADS)

    Germanovich, L. N.; Garagash, D.; Murdoch, L. C.; Robinowitz, M.

    2014-12-01

    This study is motived by a new method for disposing of nuclear waste by injecting it as a dense slurry into a hydraulic fracture that grows downward to great enough depth to permanently isolate the waste. Disposing of nuclear waste using gravity-driven hydraulic fractures is mechanically similar to the upward growth of dikes filled with low density magma. A fundamental question in both applications is how the injected fluid controls the propagation dynamics and fracture geometry (depth and breadth) in three dimensions. Analog experiments in gelatin [e.g., Heimpel and Olson, 1994; Taisne and Tait, 2009] show that fracture breadth (the short horizontal dimension) remains nearly stationary when the process in the fracture "head" (where breadth is controlled) is dominated by solid toughness, whereas viscous fluid dissipation is dominant in the fracture tail. We model propagation of the resulting gravity-driven (buoyant or sinking), finger-like fracture of stationary breadth with slowly varying opening along the crack length. The elastic response to fluid loading in a horizontal cross-section is local and can be treated similar to the classical Perkins-Kern-Nordgren (PKN) model of hydraulic fracturing. The propagation condition for a finger-like crack is based on balancing the global energy release rate due to a unit crack extension with the rock fracture toughness. It allows us to relate the net fluid pressure at the tip to the fracture breadth and rock toughness. Unlike the PKN fracture, where breadth is known a priori, the final breadth of a finger-like fracture is a result of processes in the fracture head. Because the head is much more open than the tail, viscous pressure drop in the head can be neglected leading to a 3D analog of Weertman's hydrostatic pulse. This requires relaxing the local elasticity assumption of the PKN model in the fracture head. As a result, we resolve the breadth, and then match the viscosity-dominated tail with the 3-D, toughness-dominated head to obtain a complete closed-form solution. We then analyze the gravity fracture propagation in conditions of either continuous injection or finite volume release for sets of parameters representative of dense waste injection technique and low viscosity magma diking.

  20. On constitutive relations at finite strain - Hypo-elasticity and elasto-plasticity with isotropic or kinematic hardening

    NASA Technical Reports Server (NTRS)

    Atluri, S. N.

    1984-01-01

    Nagtegaal and de Jong (1982) have studied stresses generated by simple finite shear in the case of elastic-plastic and rigid-plastic materials which exhibit anisotropic hardening. They reported that the shear stress is oscillatory in time. It was found that the occurrence of such an 'anomaly' is not restricted to anisotropic plasticity. Similar behavior in finite shear may result even in the case of hypoelasticity and classical isotropic hardening plasticity theory. The present investigation is concerned with the central problem of 'generalizing' with respect to the finite strain case, taking into account the constitutive relations of infinitesimal strain theories of classical plasticity with isotropic or kinematic hardening. The problem of hypoelasticity is also considered. It is shown that current controversies surrounding the choice of stress rate in the finite-strain generalizations of the constitutive relations and the anomalies surrounding kinematic hardening plasticity theory are easily resolvable.

  1. The influence of crack closure and elasto-plastic flow on the bending of a cracked plate

    NASA Technical Reports Server (NTRS)

    Jones, D. P.; Swedlow, J. L.

    1975-01-01

    The influence of crack closure and elastoplastic flow on the bending behavior of thin cracked plates is investigated using an incremental elastoplastic plate bending finite element computer program. The finite element program was developed using assumptions consistent with Kirchhoff fourth-order plate theory while the material property treatment permits general isotropic work hardening with local elastic unloading. 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.

  2. Study of the Elasto-plastic Properties of Mineralized Biomaterials via Synchrotron High-energy X-ray Diffraction

    NASA Astrophysics Data System (ADS)

    Deymier-Black, Alix Christine

    Synchrotron high-energy X-ray diffraction was employed to investigate the strains in the hydroxyapatite (HAP) platelets and mineralized collagen fibrils in bovine dentin and cortical bone. The HAP and the fibrillar apparent moduli, defined as the applied stress divided by the phase strain, in dentin were measured as 27+/-7.2 and 16+/-4.9 GPa. The HAP apparent modulus ( EHAPapp ) is less than the lower bound calculated for EHAPapp from the Voigt model. This discrepancy is probably due to stress concentrators or decreases in the HAP Young's modulus due to size or composition effects. EHAPapp and Efibapp in dentin vary significantly within a single tooth in both the apical-cervical direction and the buccal-lingual direction. However, the variation between teeth is minimal. The HAP and fibrillar apparent moduli are not affected by freezing in dentin or by X-ray irradiation in bone and dentin. X-ray irradiation causes a decrease in HAP residual strain in bone. This decrease suggests the presence of HAP-collagen interfacial damage. It was determined from the HAP 00.2 peak broadening that irradiation damage mostly affects the HAP unit cells which are under the highest strain. From this it was theorized that irradiation may damage highly-strained bonds at stress concentrators and/or calcium-mediated electrostatic bonds. The fact that the apparent modulus does not change with irradiation suggests that the interfacial damage must be reversible. Bone and dentin both undergo creep when loaded to high stresses. At low irradiation doses, both the fibrillar and HAP strains increase with creep time indicating that load is being transferred from the matrix to the HAP. However, at high doses, the strain on the HAP decreases with creep time. This supports the interfacial damage theory which would allow the HAP to release its elastic load upon interfacial debonding. At -80 MPa, beyond a dose of 50 kGy, the rate of change in HAP strain with time begins to increase, becoming positive at ˜115 kGy. After 300 kGy the HAP strain rate decreases and plateaus probably due to stiffening of the matrix through cross-linking. The HAP and fibrillar strain rate in irradiated bone and dentin samples increase with increased temperature and applied load.

  3. Size effects in the conical indentation of an elasto-plastic solid , V.S. Deshpande b

    E-print Network

    Fleck, Norman A.

    , N.A. Fleck b,n a Laboratoire de Me´canique des Solides, C.N.R.S. UMR7649, De´partement de Me´canique of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, UK a r t i c l e i n f o Article

  4. Deformation Analysis of Sand Specimens using 3D Digital Image Correlation for the Calibration of an Elasto-Plastic Model 

    E-print Network

    Song, Ahran

    2012-10-19

    on the boundary of the specimen. A comparison between the axisymmetic model predictions and the experimental observations showed good agreement, for both the global and local behavior, in the case of different sand specimen configuration, including loose, dense...

  5. NFFLOW: A reservoir simulator incorporating explicit fractures (SPE 153890)

    SciTech Connect

    Boyle, E.J.; Sams, W.N.

    2012-01-01

    NFFLOW is a research code that quickly and inexpensively simulates flow in moderately fractured reservoirs. It explicitly recognizes fractures separately from rock matrix. In NFFLOW fracture flow is proportional to the pressure gradient along the fracture, and flow in the rock matrix is determined by Darcy’s Law. The two flow mechanisms are coupled through the pressure gradient between a fracture and its adjacent rock matrix. Presented is a promising change to NFFLOW that allows for flow across a rock matrix block.

  6. Active monitoring of hydraulic and mechanical properties variations during the hydraulic stimulation of a fractured porous reservoir: Some preliminary results from the HPPP Project

    NASA Astrophysics Data System (ADS)

    Cappa, F.; Guglielmi, Y.

    2010-12-01

    A new protocol of active geophysical monitoring is used to investigate the downhole changes in the hydromechanical response of a naturally porous reservoir layer with 80° dipping fractures where permeability was artificially enhanced by a hydraulic jacking test conducted by a step-wise increase of the fluid pressure. The protocol, called the High-Pulse Poroelasticity Protocol (HPPP) (http://hppp.unice.fr/), is focusing on controlled-impulsive source repeated observations and interpretation of rock properties changes over the seismic band of frequencies. The excitation source corresponds to a fast hydraulic pulse imposed in a small section of a borehole. The source is monitored with a special borehole probe based on fiber-optic sensors which allow dynamic fluid pressure/3D-mechanical deformation measurements, with reflection of light at specific wavelength from Fabry-Pérot or fiber Bragg gratings mounted between inflatable packers. Within the injection zone, fluid pressure and deformation waves of 1 to 500 Hz and static hydraulic diffusion are simultaneously measured to quantify the hydromechanical couplings Two identical pressure pulses were performed to test the rock three-dimensionnal mechanical response before and after the jacking test. It clearly appears that (1) the magnitude of the rock deformation is a factor of 3 higher, and (2) the principal deformation component pitch is rotated of about 20° with more radial deformation of the layer after the jacking test. Those preliminary tests show that the HPPP protocol can actively improve downhole monitoring of both hydraulic and mechanical bulk properties changes of rocks under strong dynamic stress-flow couplings.

  7. Mechanical characterization and modeling of non-linear deformation and fracture of a fiber reinforced metal matrix composite

    NASA Technical Reports Server (NTRS)

    Jansson, S.

    1991-01-01

    The nonlinear anisotropic mechanical behavior of an aluminum alloy metal matrix composite reinforced with continuous alumina fibers was determined experimentally. The mechanical behavior of the composite were modeled by assuming that the composite has a periodical microstructure. The resulting unit cell problem was solved with the finite element method. Excellent agreement was found between theoretically predicted and measured stress-strain responses for various tensile and shear loadings. The stress-strain responses for transverse and inplane shear were found to be identical and this will provide a simplification of the constitutive equations for the composite. The composite has a very low ductility in transverse tension and a limited ductility in transverse shear that was correlated to high hydrostatic stresses that develop in the matrix. The shape of the initial yield surface was calculated and good agreement was found between the calculated shape and the experimentally determined shape.

  8. Naturally fractured reservoirs: Optimized E and P strategies using a reaction-transport-mechanical simulator in an integrated approach. Summary of project accomplishments; Final report, September 30, 1998

    SciTech Connect

    Ortoleva, P.J.; Sundberg, K.R.; Hoak, T.E.

    1998-12-01

    Major accomplishments of this project occurred in three primary categories: (1) fractured reservoir location and characteristics prediction for exploration and production planning; (2) implications of geologic data analysis and synthesis for exploration and development programs; and (3) fractured reservoir production modeling. The results in each category will be discussed in turn. Seven detailed reports have been processed separately.

  9. Mixed-mode fracture of human cortical bone Elizabeth A. Zimmermann a,b

    E-print Network

    Ritchie, Robert

    Mixed-mode fracture of human cortical bone Elizabeth A. Zimmermann a,b , Maximilien E. Launey Available online 1 July 2009 Keywords: Human cortical bone Mixed-mode fracture Fracture toughness Fracture mechanisms a b s t r a c t Although the mode I (tensile opening) fracture toughness has been the focus

  10. Fracture Management

    MedlinePLUS

    Fracture Management 804 W. Diamond Ave., Ste. 210 Gaithersburg, MD 20878 (800) 981-2663 (301) 947-0083 Fax: (301) 947-0456 Internet: www.oif.org ... osteogenesis imperfecta contact: Osteogenesis Imperfecta Foundation 804 W. Diamond Avenue, Suite 210, Gaithersburg, MD 20878 Tel: 800- ...

  11. Condylar fractures.

    PubMed

    Sawhney, Raja; Brown, Ryan; Ducic, Yadranko

    2013-10-01

    The purpose of this article is to review the basic indications for different treatments of condylar and subcondylar fractures. It also reviews the steps of different surgical approaches to access the surgical area and explains the pros and cons of each procedure. PMID:24138737

  12. NUMERICAL SIMULATION FOR MECHANICAL BEHAVIOR OF U10MO MONOLITHIC MINIPLATES FOR RESEARCH AND TEST REACTORS

    SciTech Connect

    Hakan Ozaltun & Herman Shen

    2011-11-01

    This article presents assessment of the mechanical behavior of U-10wt% Mo (U10Mo) alloy based monolithic fuel plates subject to irradiation. Monolithic, plate-type fuel is a new fuel form being developed for research and test reactors to achieve higher uranium densities within the reactor core to allow the use of low-enriched uranium fuel in high-performance reactors. Identification of the stress/strain characteristics is important for understanding the in-reactor performance of these plate-type fuels. For this work, three distinct cases were considered: (1) fabrication induced residual stresses (2) thermal cycling of fabricated plates; and finally (3) transient mechanical behavior under actual operating conditions. Because the temperatures approach the melting temperature of the cladding during the fabrication and thermal cycling, high temperature material properties were incorporated to improve the accuracy. Once residual stress fields due to fabrication process were identified, solution was used as initial state for the subsequent simulations. For thermal cycling simulation, elasto-plastic material model with thermal creep was constructed and residual stresses caused by the fabrication process were included. For in-service simulation, coupled fluid-thermal-structural interaction was considered. First, temperature field on the plates was calculated and this field was used to compute the thermal stresses. For time dependent mechanical behavior, thermal creep of cladding, volumetric swelling and fission induced creep of the fuel foil were considered. The analysis showed that the stresses evolve very rapidly in the reactor. While swelling of the foil increases the stress of the foil, irradiation induced creep causes stress relaxation.

  13. A mechanical chest compressor closed-loop controller with an effective trade-off between blood flow improvement and ribs fracture reduction.

    PubMed

    Zhang, Guang; Wu, Taihu; Song, Zhenxing; Wang, Haitao; Lu, Hengzhi; Wang, Yalin; Wang, Dan; Chen, Feng

    2015-06-01

    Chest compression (CC) is a significant emergency medical procedure for maintaining circulation during cardiac arrest. Although CC produces the necessary blood flow for patients with heart arrest, improperly deep CC will contribute significantly to the risk of chest injury. In this paper, an optimal CC closed-loop controller for a mechanical chest compressor (OCC-MCC) was developed to provide an effective trade-off between the benefit of improved blood perfusion and the risk of ribs fracture. The trade-off performance of the OCC-MCC during real automatic mechanical CCs was evaluated by comparing the OCC-MCC and the traditional mechanical CC method (TMCM) with a human circulation hardware model based on hardware simulations. A benefit factor (BF), risk factor (RF) and benefit versus risk index (BRI) were introduced in this paper for the comprehensive evaluation of risk and benefit. The OCC-MCC was developed using the LabVIEW control platform and the mechanical chest compressor (MCC) controller. PID control is also employed by MCC for effective compression depth regulation. In addition, the physiological parameters model for MCC was built based on a digital signal processor for hardware simulations. A comparison between the OCC-MCC and TMCM was then performed based on the simulation test platform which is composed of the MCC, LabVIEW control platform, physiological parameters model for MCC and the manikin. Compared with the TMCM, the OCC-MCC obtained a better trade-off and a higher BRI in seven out of a total of nine cases. With a higher mean value of cardiac output (1.35 L/min) and partial pressure of end-tidal CO2 (15.7 mmHg), the OCC-MCC obtained a larger blood flow and higher BF than TMCM (5.19 vs. 3.41) in six out of a total of nine cases. Although it is relatively difficult to maintain a stable CC depth when the chest is stiff, the OCC-MCC is still superior to the TMCM for performing safe and effective CC during CPR. The OCC-MCC is superior to the TMCM in performing safe and effective CC during CPR and can be incorporated into the current version of mechanical CC devices for high quality CPR, in both in-hospital and out-of-hospital CPR settings. PMID:25735437

  14. Insight from modelling discrete fractures using GEOCRACK

    SciTech Connect

    DuTeaux, Robert; Swenson, Daniel; Hardeman, Brian

    1996-01-24

    This work analyzes the behavior of a numerical geothermal reservoir simulation with flow only in discrete fractures. GEOCRACK is a 2-D finite element model developed at Kansas State University for the Hot Dry Rock (HDR) research at Los Alamos National Laboratory. Its numerical simulations couple the mechanics of discrete fracture behavior with the state of earth stress, fluid flow, and heat transfer. This coupled model could also be of value for modeling reinjection and other reservoir operating strategies for liquid dominated fractured reservoirs. Because fracture surfaces cool quickly by fluid convection, and heat does not conduct quickly from the interior of reservoir rock, modeling the injection of cold fluid into a fractured reservoir is better simulated by a model with discrete fractures. This work contains knowledge gained from HDR reservoir simulation and continues to develop the general concept of heat mining, reservoir optimization. and the sensitivity of simulation to the uncertainties of fracture spacing and dynamic flow dispersion.

  15. Multiple-Code BenchMaek Simulation Stidy of Coupled THMC Processes IN the EXCAVATION DISTURBED ZONE Associated with Geological Nuclear Waste Repositories

    SciTech Connect

    J. Rutqvist; X. Feng; J. Hudson; L. Jing; A. Kobayashi; T. Koyama; P.Pan; H. Lee; M. Rinne; E. Sonnenthal; Y. Yamamoto

    2006-05-08

    An international, multiple-code benchmark test (BMT) study is being conducted within the international DECOVALEX project to analyze coupled thermal, hydrological, mechanical and chemical (THMC) processes in the excavation disturbed zone (EDZ) around emplacement drifts of a nuclear waste repository. This BMT focuses on mechanical responses and long-term chemo-mechanical effects that may lead to changes in mechanical and hydrological properties in the EDZ. This includes time-dependent processes such as creep, and subcritical crack, or healing of fractures that might cause ''weakening'' or ''hardening'' of the rock over the long term. Five research teams are studying this BMT using a wide range of model approaches, including boundary element, finite element, and finite difference, particle mechanics, and elasto-plastic cellular automata methods. This paper describes the definition of the problem and preliminary simulation results for the initial model inception part, in which time dependent effects are not yet included.

  16. Fracture characterization of clays and clay-like materials using flattened Brazilian Test

    E-print Network

    Agaiby, Shehab Sherif Wissa

    2013-01-01

    Fracture mechanics has been used for many years to study the mechanical behavior of brittle and quasi-brittle materials like concrete, rock, wood, and ceramics. To date, the application of fracture mechanics to soils has ...

  17. The effect of particulate fracture in determining fracture toughness of metal matrix composites

    SciTech Connect

    Lucas, J.P.; Liaw, P.K.; Stephens, J.J.; Nunes, J.

    1990-12-31

    Although the fracture toughness of discontinuous reinforced metal matrix composites (DR MMCs) is reduced significantly in comparison to its matrix alloy, the fracture mode remains ductile for all Al- based materials studied. Failure of DR MMCs occurs ultimately by void growth and coalescence in the matrix phase, similar to unreinforced material. Brittle fracture of the particulates also contributes to the microfracture process and thus to fracture toughness. Fracture surface, metallographic, and acoustic emission results indicate that particulates contained in the process zone fracture either by single-faceted or multi-faceted cracking ahead of the main crack. Moreover, fracture of primary void initiating particulates depends on the reinforcement type, size, and the particulate/matrix interface microstructure. These factors influence the stress level at which void nucleation occurs at particulates. Fractographic evidence indicates that void nucleation and growth begin at a low nominal level of stress in particular for large particulates exhibiting extensive interfacial precipitation. Fracture of reinforcing particulates encompassed in the crack tip process zone has a strong effect on the fracture toughness of MMCs. Emphasis is placed on the role of particulate cracking and the mechanism of interparticulate ligament failure in determining the fracture toughness. In addition, fracture toughness results obtained by short bar and conventional compact tension methods were found to be in remarkable agreement. Using a stress-modified strain criterion continuum model for ductile fracture, the fracture toughness of particulate reinforced metal matrix composites is described reasonably well.

  18. Prediction of fatigue life of high-heat-load components made of oxygen-free copper by comparing with Glidcop

    PubMed Central

    Takahashi, Sunao; Sano, Mutsumi; Watanabe, Atsuo; Kitamura, Hideo

    2013-01-01

    Following a successful study on the prediction of fatigue life of high-heat-load components made of Glidcop, the thermal limitation of oxygen-free copper (OFC), which is used more commonly than Glidcop, has been studied. In addition to its general mechanical properties, the low-cycle-fatigue (LCF) and creep properties of OFC were investigated in detail and compared with those of Glidcop. The breaking mode of OFC, which was observed to be completely different from that of Glidcop in a fatigue fracture experiment, clarified the importance of considering the creep–fatigue interaction. An additional LCF test with compressive strain holding was conducted so that the creep–fatigue life diagram for out-of-phase thermal fatigue could be obtained on the basis of the strain-range partitioning method. The life predicted from elasto-plastic creep analysis agreed well with that determined from the void ratio estimated in the fatigue fracture experiment. PMID:23254657

  19. Failure analysis of a cracked plate based on endochronic plastic theory coupled with damage

    NASA Astrophysics Data System (ADS)

    Chow, C. L.; Chen, X. F.

    1993-03-01

    An anisotropic model of damage mechanics for ductile fracture incorporating the endochronic theory of plasticity is presented in order to take into account material deterioration during plastic deformation. An alternative form of endochronic (internal time) theory which is actually an elasto-plastic damage theory with isotropic-nonlinear kinematic hardening is developed for ease of numerical computation. Based on this new damage model, a finite element algorithm is formulated and then employed to characterize the fracture of thin aluminum plate containing a center crack. A new criterion termed as Y(sub R)-criterion is proposed to define both the crack initiation angle and load. Experiments have been conducted to verify the validity of the proposed damage model and it is found that the theoretical crack initiation loads correspond closely with the measured values.

  20. Geomechanics of fracture caging in wellbores

    NASA Astrophysics Data System (ADS)

    Weijermars, Ruud; Zhang, Xi; Schultz-Ela, Dan

    2013-06-01

    This study highlights the occurrence of so-called `fracture cages' around underbalanced wellbores, where fractures cannot propagate outwards due to unfavourable principal stress orientations. The existence of such cages is demonstrated here by independent analytical and numerical methods. We explain the fracture caging mechanism and pinpoint the physical parameters and conditions for its control. This new insight has great practical relevance for the effectiveness and safety of drilling operations in general, and hydraulic fracturing in particular. Fracture caging runaway poses a hazard for drilling operations in overpressured formations. Recognition of the fracture caging mechanism also opens up new opportunities for controlled engineering of its effects by the manipulation of the Frac number in wells in order to bring more precision in the fracking process of tight formations.