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1

A mechanical model for fiber reinforced composite materials with elasto-plastic matrix and interface debonding  

Microsoft Academic Search

The behaviour of fiber-reinforced composites is examined through the formulation of a non-linear constitutive law obtained through a physical-based approach. The elasto-plastic macro constitutive equations for such a class of materials, composed by a matrix phase with elasto-plastic behaviour and several fiber-reinforcing phases, is obtained by considering an imperfect bounds between the matrix and the fibers, i.e. a certain amount

Roberto Brighenti

2004-01-01

2

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

3

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

NASA Astrophysics Data System (ADS)

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

Mossop, A.; Fredrich, J. T.

2004-12-01

4

Elasto-plastic characteristics and mechanical properties of as-sprayed 8 mol% yttria-stabilized zirconia coating under nano-scales measured by nanoindentation  

NASA Astrophysics Data System (ADS)

The elasto-plastic characteristics and mechanical properties of as-received 8 mol% Y2O3-ZrO2 (8YSZ) coatings were studied by nanoindentation at ultra-low loads with a Berkovich indenter at room temperature. All experimental data including hardness H and elastic modulus E were analyzed by the Weibull statistical method due to the porous and heterogeneous nature of the tested samples. It was found that the hardness firstly exhibits interesting reverse indentation size effect, and then shows normal indentation size effect within different indentation scales. The average elastic modulus of 8YSZ was estimated as 214.8 ± 13.2 GPa. In order to reveal the elasto-plastic characteristics of 8YSZ at nano-scales, the distribution of resolved shear stresses underneath the indenter tip region was evaluated by Hertzian contact theory when the deformation behavior of 8YSZ changed from fully elastic to elasto-plastic stages. The results shed light on understanding possible foreign object damage mechanisms of thermal barrier coating systems.

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

2014-08-01

5

Fiber interactions and eective elasto-plastic properties of short-ber composites  

E-print Network

Fiber interactions and eective elasto-plastic properties of short-®ber composites Qing-Sheng Yang a , Qing-Hua Qin b,* a Department of Mechanics, Beijing Polytechnic University, Beijing 100022, China b

Qin, Qinghua

6

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

Microsoft Academic Search

The extraction of fluids from porous rocks within the Earth's crust leads to localised volume strains. These in turn induce stress changes and displacements in the surrounding rock mass. The relationships between these processes are governed by the constitutive properties of the rocks. For the case of a poroelastic fluid reservoir in a linear-elastic matrix the mechanics are relatively well

A. Mossop; J. T. Fredrich

2004-01-01

7

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

Microsoft Academic Search

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

H. L. Xing; A. Makinouchi

2002-01-01

8

Modelling the Damage Induced by Pressure Transients in ElastoPlastic Pipes  

Microsoft Academic Search

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

Felipe B. Freitas Rachid; Heraldo S. Costa Mattos

1998-01-01

9

Pressure transients in damageable elasto-plastic pipes  

SciTech Connect

This paper is concerned with the analysis of pressure transients in damageable elasto-plastic piping systems. The fluid dynamics and pipewall deformation are modeled by the classical water hammer theory, whereas pipewall mechanical behavior is described by an internal variable constitutive theory. The resulting nonlinear hyperbolic problem is numerically approximated by means of a technique based on an additive decomposition of the operator together with the Glimm`s method and a special Euler-type time integration scheme. Examples concerning the structural integrity analysis of a reservoir-pipe-valve installation where hydraulic transients are generated by valve slam are presented to illustrate the applicability of both the theory and numerical method.

Freitas Rachid, F.B.; Costa Mattos, H.S. [Univ. Federal Fluminense, Niteroi, Rio de Janeiro (Brazil)

1995-11-01

10

ElastoPlastic Failure Analysis of Composite Bolted Joints  

Microsoft Academic Search

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

Yoshifumi Tsujimoto; Dale Wilson

1986-01-01

11

The elasto-plastic response of underground excavations in rock masses that satisfy the Hoek–Brown failure criterion  

Microsoft Academic Search

This paper is intended to illustrate the relationship between the Hoek–Brown parameters describing the strength of rock masses and the mechanical response of underground openings.A formulation of the elasto-plastic behavior of rock in terms of the Hoek–Brown criterion is presented. The analysis assumes that the joint system present in the rock mass has no preferred orientation so that the medium

C. Carranza-Torres; C. Fairhurst

1999-01-01

12

Homogenization of two-phase elasto-plastic composite materials and structures  

Microsoft Academic Search

We develop homogenization schemes and numerical algorithms for two-phase elasto-plastic composite materials and structures. A Hill-type incremental formulation enables the simulation of unloading and cyclic loadings. It also allows to handle any rate-independent model for each phase. We study the crucial issue of tangent operators: elasto-plastic (or “continuum”) versus algorithmic (or “consistent”), and anisotropic versus isotropic. We apply two methods

I. Doghri; A. Ouaar

2003-01-01

13

Failure patterns in poro-elasto-plastic medium: Results from a two dimensional time-dependent pore-pressure model.  

NASA Astrophysics Data System (ADS)

Fluid flow in the earth is controlled primarily by fractures and fracture networks. These networks evolve over time in response to the regional stress field and local stress perturbations caused by faulting, while faulting can change the hydraulic properties by many orders of magnitude. Recent studies have shown that degassing of deeply trapped high pressure pockets can have a major influence on aftershock generation, but models of this process have been limited to a non-linear permeability model. They do not include the effects of shear and tensile cracking on the evolving permeability structure, nor do they include seepage forces (from pore pressure gradients) and their role in the initiation and propagation of fractures. We have developed a model of these processes by advancing the model of Rozhko et. al. (2007), who coupled steady state fluid flow in a deforming elasto-plastic media, to include fluid flow through evolving fracture networks. The elasto-plastic deformation code is coupled with a time-dependent Darcy fluid flow code, where permeability evolves in response to the growing fractures and a proxy crack aperture determined by the amount of accumulated plastic strain. We will present the results of simulations in which we study the effects of (1) rheological heterogeneities on fluid flow and crack initiation, (2) dynamic evolution of permeability as a function of plastic damage and (3) influence of the nucleation of new shear zones on patterns of fluid-flow. Reference: Rozhko, A. 2007. Role of seepage forces on hydraulic fracturing and failure patterns. Ph. D. thesis. University of Oslo.

Galvan, B.; Miller, S. A.; Kaus, B.

2009-04-01

14

Analysis of the elasto-plastic response of a polygonal packing Fernando Alonso Marroqu n and Hans Herrmann  

E-print Network

Analysis of the elasto-plastic response of a polygonal packing Fernando Alonso Marroqu#19;#16;n-dimensional packed samples of polygons using molecular dynamics simulation. The incremental elasto-plastic response parameter must be included, which takes into account the anisotropy of the elastic response. The plastic

Luding, Stefan

15

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

PubMed

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

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

2013-01-01

16

Polycarbonate as an Elasto-Plastic Material Model for Simulation of the Microstructure Hot Imprint Process  

PubMed Central

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

Narijauskaite, Birute; Palevicius, Arvydas; Gaidys, Rimvydas; Janusas, Giedrius; Sakalys, Rokas

2013-01-01

17

ElastoPlastic Fatigue Life Improvement of Bolted Joints and Introducing FBI Method  

Microsoft Academic Search

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

Peyman Honarmandi; Jean W. Zu; Kamran Behdinan

2005-01-01

18

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

NASA Technical Reports Server (NTRS)

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.

Doghri, I.; Leckie, F. A.

1991-01-01

19

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

E-print Network

available finite element code is applied to solve the boundary value problem defined at the macroscopic, apart the finite element discretization. The proposed model is then used to estimate the minimum size Polycrystalline material, elasto-plastic material behavior, mesoscale, Voronoi tessellation, finite elements

Cizelj, Leon

20

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

SciTech Connect

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

Ehlers, W. [Technische Hochschule Darmstadt (Germany)

1995-12-31

21

Gaussian excited elasto-plastic oscillator with rare visits to the plastic domain  

NASA Astrophysics Data System (ADS)

The probabilistic properties are modelled of the plastic displacement process component and the plastic work process of the response of a symmetric linear elasto-plastic oscillator excited by a stationary Gaussian process. Under the assumption of rare visits to the plastic domain these processes are taken to be homogeneous compound Poisson processes. The intensity and the jump statistics are derived by use of Slepian model process theory from the crossing properties at the elastic limits of the associated stationary Gaussian response and the corresponding Cramér-Leadbetter envelope process. The word "associated" refers to the linear elastic oscillator obtained from the elasto-plastic oscillator by letting the elastic limit go to infinity. Finally, an asymptotic distribution of the time to first passage of a given level is reported for each of the two compound Poisson processes.

Ditlevsen, O.

1991-03-01

22

Notch and mean stress effect in fatigue as phenomena of elasto-plastic inherent multiaxiality  

Microsoft Academic Search

The present paper summarises an attempt of estimating fatigue lifetime of notched metallic materials by directly accounting for the degree of multiaxiality of the local elasto-plastic stress\\/strain-fields acting on the fatigue process zone. In more detail, the proposed approach takes as its starting point the assumption that Stage I is the most important stage to be modelled to accurately estimate

L. Susmel; B. Atzori; G. Meneghetti; D. Taylor

2011-01-01

23

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

E-print Network

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

Kumar, M. Jagadesh

24

Elasto-Plastic Analysis of Tee Joints Using HOT-SMAC  

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

25

Prevention of cyclic instability at the modeling of elasto-plastic deformation at large strains under proportional and non-proportional loading  

NASA Astrophysics Data System (ADS)

The cyclic instability phenomenon is investigated at the modeling of large elasto-plastic strains. The instability is observed at large strains for some elasto-plastic material models with a kinematic hardening in contrast to the small strain case. The cyclic instability manifests itself as a changing of shape, sizes or location of the hysteresis loop during cycling. In partial case the cyclic instability leads to the stress ratcheting. Responses of 50 various models of elasto-plastic material have been considered under proportional loading (cyclic simple shear) and non-proportional loading (combined cyclic simple shear and tension-compression). Causes of the cyclic instability are analyzed and conditions ensuring the cyclic stability of elasto-plastic models are proposed.

Semenov, Artem S.; Melnikov, Boris E.; Gorokhov, Mikhail Yu.; Ulbricht, Volker

2007-04-01

26

Meso-mechanical constitutive model for ratchetting of particle-reinforced metal matrix composites  

Microsoft Academic Search

Based on the Eshelby equivalent inclusion theory and Mori–Tanaka averaging method, a meso-mechanical cyclic elasto-plastic constitutive model is proposed to predict the ratchetting of particle-reinforced metal matrix composites. In the proposed model, a Hill-typed incremental formulation is used to simulate the elasto-plastic responses of the composites during cyclic loading with assumptions of elastic particle, elasto-plastic metal matrix and perfect interfacial

Sujuan Guo; Guozheng Kang; Juan Zhang

2011-01-01

27

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

E-print Network

friction angles at peak and critical state ............................. 63 Figure 4. 7 Comparison of stress-strain behavior between an elasto-perfectly plasticity model and an elasto-plasticity model ......................................... 64... .................................................................. 90 Figure 5. 11 Deformed meshes with horizontal displacement contour ..................... 91 Figure 5. 12 Deviatoric stress and plastic strain distribution of test 3mm_sq_8 at peak and critical state (a) deviatoric stress (b) plastic...

Song, Ahran

2012-10-19

28

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

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

29

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

NASA Technical Reports Server (NTRS)

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.

Chulya, Abhisak; Walker, Kevin P.

1991-01-01

30

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

SciTech Connect

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.

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

2011-01-17

31

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

NASA Technical Reports Server (NTRS)

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.

Jones, D. P.

1972-01-01

32

Structural evolution of La-Cr-O thin film: Part II. Elasto-plastic properties by nanoindentation  

SciTech Connect

The goal of this research is to study the elasto-plastic properties of La–Cr–O thin films deposited by RF-magnetron sputtering on stainless steel interconnect materials after annealing at high temperatures in air. Elastic modulus, hardness and yield pressure derived from nanoindentation data are reported for thin films in different structural states. The amorphous film has an estimated elastic modulus of 174 GPa. The moduli of annealed films are calculated to be 150, 185 and 120 GPa after annealing at 500 °C, 600 °C and 800 °C, respectively. The film annealed at 800 °C has the lowest hardness and is dramatically different from the other structural states due to formation of the nanoporosity. The amorphous film and the films annealed at 500 °C and 600 °C both have hardness of 14 GPa, which is close to the value estimated by modeling.

Lugovy, M. (Drexel University, Philadelphia, PA); Coratolo, A. (Drexel University, Philadelphia, PA); Orlovskaya, N. (Michigan Technological University, Houghton, MI); Johnson, C.; Gemmen, R.S.

2007-01-22

33

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

NASA Astrophysics Data System (ADS)

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

Keller, Tobias

2014-05-01

34

Large-deformation, elasto-plastic analysis of frames under nonconservative loading, using explicitly derived tangent stiffnesses based on assumed stresses  

NASA Astrophysics Data System (ADS)

Simple and economical procedures for large-deformation elasto-plastic analysis of frames, whose members can be characterized as beams, are presented. An assumed stress approach is employed to derive the tangent stiffness of the beam, subjected in general to non-conservative type distributed loading. The beam is assumed to undergo arbitrarily large rigid rotations but small axial stretch and relative (non-rigid) point-wise rotations. It is shown that if a plastic-hinge method (with allowance being made for the formation of the hinge at an arbitrary location or locations along the beam) is employed, the tangent stiffness matrix may be derived in an explicit fashion, without numerical integration. Several examples are given to illustrate the relative economy and efficiency of the method in solving large-deformation elasto-plastic problems. The method is of considerable utility in analysing off-shore structures and large structures that are likely to be deployed in outerspace.

Kondoh, K.; Atluri, S. N.

1987-03-01

35

Large-deformation, elasto-plastic analysis of frames under nonconservative loading, using explicitly derived tangent stiffnesses based on assumed stresses  

Microsoft Academic Search

Simple and economical procedures for large-deformation elasto-plastic analysis of frames, whose members can be characterized as beams, are presented. An assumed stress approach is employed to derive the tangent stiffness of the beam, subjected in general to non-conservative type distributed loading. The beam is assumed to undergo arbitrarily large rigid rotations but small axial stretch and relative (non-rigid) point-wise rotations.

K. Kondoh; S. N. Atluri

1987-01-01

36

Inverse extraction of interfacial tractions from elastic and elasto-plastic far-fields by nonlinear field projection  

NASA Astrophysics Data System (ADS)

Determining the tractions along a surface or interface from measurement data in the far-fields of nonlinear materials is a challenging inverse problem which has significant engineering and nanoscience applications. Previously, a field projection method was established to identify the crack-tip cohesive zone constitutive relations in an isotropic elastic solid (Hong and Kim, 2003. J. Mech. Phys. Solids 51, 1267). In this paper, the field projection method is further generalized to extracting the tractions along interfaces bounded by nonlinear materials, both with and without pre-existing cracks. The new formulation is based on Maxwell-Betti's reciprocal theorem with a reciprocity gap associated with nonlinear materials. We express the unknown normal and shear tractions along the interface in terms of the Fourier series, and use specially constructed analytical auxiliary fields in the reciprocal theorem to extract the unknown Fourier coefficients from far-field data; the reciprocity gap in the formulation is iteratively determined with a set of numerical algorithms. Our detailed numerical experiments demonstrate that this nonlinear field projection method (NFPM) is well-suited for extracting the interfacial tractions from the far-field data of any nonlinear elastic or elasto-plastic material with known constitutive laws. Applications of the NFPM to experiments and atomistic simulations are discussed.

Chew, Huck Beng

2013-01-01

37

Shallow slip deficit due to large strike-slip earthquakes in dynamic rupture simulations with elasto-plastic off-fault response  

NASA Astrophysics Data System (ADS)

Slip inversions of geodetic data from several large (magnitude ˜7) strike-slip earthquakes point to coseismic slip deficit at shallow depths (<3-4 km), that is, coseismic slip appears to decrease towards the Earth surface. While the inferred slip distribution may be consistent with laboratory-derived rate and state friction laws suggesting that the uppermost brittle crust may be velocity strengthening, there remains a question of how the coseismic slip deficit is accommodated throughout the earthquake cycle. The consequence of velocity-strengthening fault friction at shallow depths is that the deficit of coseismic slip is relieved by post-seismic afterslip and interseismic creep. However, many seismic events with inferred shallow slip deficit were not associated with either resolvable shallow interseismic creep or robust shallow afterslip. Hence, the origin of shallow 'slip deficit' remains uncertain. In this study, we investigate whether inelastic failure in the shallow crust due to dynamic earthquake rupture can explain the inferred deficit of shallow slip. Evidence for such failure is emerging from geologic, seismic and geodetic observations. We find that the amount of shallow slip deficit is proportional to the amount of inelastic deformation near the Earth surface. Such deformation occurs under a wide range of parameters that characterize rock strength in the upper crust. However, the largest magnitude of slip deficit in models accounting for off-fault yielding is 2-4 times smaller than that inferred from kinematic inversions of geodetic data. To explain this discrepancy, we further explore to what extent assumptions in the kinematic inversions may bias the inferred slip distributions. Inelastic deformation in the shallow crust reduces coseismic strain near the fault, introducing an additional 'artificial' deficit of up to 10 per cent of the maximum slip in inversions of geodetic data that are based on purely elastic models. The largest magnitude of slip deficit in our models combined with the bias in inversions accounts for up to 25 per cent of shallow slip deficit, which is comparable, but still smaller than 30-60 per cent deficit inferred from kinematic inversions. We discuss potential mechanisms that may account for the remaining discrepancy between slip deficit predicted by elasto-plastic rupture models and that inferred from inversions of space geodetic data.

Kaneko, Y.; Fialko, Y.

2011-09-01

38

Linear elastic fracture mechanics primer  

NASA Technical Reports Server (NTRS)

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.

Wilson, Christopher D.

1992-01-01

39

Linear elastic fracture mechanics primer  

NASA Astrophysics Data System (ADS)

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.

Wilson, Christopher D.

1992-07-01

40

The frictional sliding response of elasto-plastic materials in contact with a conical indenter  

Microsoft Academic Search

Over the past decade, many computational studies have explored the mechanics of normal indentation. Quantitative relationships have been well established between the load–displacement hysteresis response and material properties. By contrast, very few studies have investigated broad quantitative aspects of the effects of material properties, especially plastic deformation characteristics, on the frictional sliding response of metals and alloys. The response to

S. Bellemare; M. Dao; S. Suresh

2007-01-01

41

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

E-print Network

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.

Tomás M. Guozden; Eduardo A. Jagla

2012-06-27

42

Two-temperature hydrodynamics of laser-generated ultrashort shock waves in elasto-plastic solids  

NASA Astrophysics Data System (ADS)

Shock-wave generation by ultrashort laser pulses opens new doors for study of hidden processes in materials happened at an atomic-scale spatiotemporal scales. The poorly explored mechanism of shock generation is started from a short-living two-temperature (2T) state of solid in a thin surface layer where laser energy is deposited. Such 2T state represents a highly non-equilibrium warm dense matter having cold ions and hot electrons with temperatures of 1-2 orders of magnitude higher than the melting point. Here for the first time we present results obtained by our new hybrid hydrodynamics code combining detailed description of 2T states with a model of elasticity together with a wide-range equation of state of solid. New hydro-code has higher accuracy in the 2T stage than molecular dynamics method, because it includes electron related phenomena including thermal conduction, electron-ion collisions and energy transfer, and electron pressure. From the other hand the new code significantly improves our previous version of 2T hydrodynamics model, because now it is capable of reproducing the elastic compression waves, which may have an imprint of supersonic melting like as in MD simulations. With help of the new code we have solved a difficult problem of thermal and dynamic coupling of a molten layer with an uniaxially compressed elastic solid. This approach allows us to describe the recent femtosecond laser experiments.

Ilnitsky, Denis K.; Khokhlov, Viktor A.; Inogamov, Nail A.; Zhakhovsky, Vasily V.; Petrov, Yurii V.; Khishchenko, Konstantin V.; Migdal, Kirill P.; Anisimov, Sergey I.

2014-05-01

43

Inverse analyses in fracture mechanics  

Microsoft Academic Search

The present purpose is a survey of some engineering-oriented research results which may be representative of the main issues in the title subject. Some recent or current developments are pointed out in the growing area of fracture mechanics centered on the calibration of cohesive fracture models for quasi-brittle materials, by approaches which combine experimentation, experiment simulation and minimisation of the

G. Maier; M. Bocciarelli; G. Bolzon; R. Fedele

44

Elasto-plastic contact analysis of an ultra-high molecular weight polyethylene tibial component based on geometrical measurement from a retrieved knee prosthesis.  

PubMed

The wear phenomenon of ultra-high molecular weight polyethylene (UHMWPE) in knee and hip prostheses is one of the major restriction factors on the longevity of these implants. Especially in retrieved knee prostheses with anatomical design, the predominant types of wear on UHMWPE tibial components are delamination and pitting. These fatigue wear patterns of UHMWPE are believed to result from repeated plastic deformation owing to high contact stresses. In this study, the elasto-plastic contact analysis of the UHWMPE tibial insert, based on geometrical measurement for retrieved knee prosthesis, was performed using the finite element method (FEM) to investigate the plastic deformation behaviour in the UHMWPE tibial component. The results suggest that the maximum plastic strain below the surface is closely related to subsurface crack initiation and delamination of the retrieved UHMWPE tibial component. The worn surface whose macroscopic geometrical congruity had been improved due to wear after joint replacement showed lower contact stress at macroscopic level. PMID:15376727

Cho, C H; Murakami, T; Sawae, Y; Sakai, N; Miura, H; Kawano, T; Iwamoto, Y

2004-01-01

45

Inverse Analyses in Fracture Mechanics  

Microsoft Academic Search

.  The present purpose is a survey of some engineering-oriented research results which may be representative of the main issues\\u000a in the title subject. Some recent or current developments are pointed out in the growing area of fracture mechanics centered\\u000a on the calibration of cohesive fracture models for quasi-brittle materials, by approaches which combine experimentation, experiment\\u000a simulation and minimisation of the

G. Maier; M. Bocciarelli; G. Bolzon; R. Fedele

2006-01-01

46

Modelling the graphite fracture mechanisms  

SciTech Connect

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)

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

2012-07-01

47

Fracture mechanics of cellular glass  

NASA Technical Reports Server (NTRS)

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.

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

1981-01-01

48

Fracture mechanics and corrosion fatigue.  

NASA Technical Reports Server (NTRS)

Review of the current state-of-the-art in fracture mechanics, particularly in relation to the study of problems in environment-enhanced fatigue crack growth. The usefulness of this approach in developing understanding of the mechanisms for environmental embrittlement and its engineering utility are discussed. After a brief review of the evolution of the fracture mechanics approach and the study of environmental effects on the fatigue behavior of materials, a study is made of the response of materials to fatigue and corrosion fatigue, the modeling of the mechanisms of the fatigue process is considered, and the application of knowledge of fatigue crack growth to the prediction of the high cycle life of unnotched specimens is illustrated.

Mcevily, A. J.; Wei, R. P.

1972-01-01

49

Theory of fracture mechanics based upon plasticity  

NASA Technical Reports Server (NTRS)

A theory of fracture mechanics is formulated on the foundation of continuum mechanics. Fracture surface is introduced as an unknown quantity and is incorporated into boundary and initial conditions. Surface energy is included in the global form of energy conservation law and the dissipative mechanism is formulated into constitutive equations which indicate the thermodynamic irreversibility and the irreversibility of fracture process as well.

Lee, J. D.

1976-01-01

50

(Fracture mechanics of inhomogeneous materials)  

SciTech Connect

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.

Bass, B.R.

1990-10-01

51

Fracture mechanics of cellular glass  

SciTech Connect

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

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

1981-02-01

52

Mechanical Coal-Face Fracturer  

NASA Technical Reports Server (NTRS)

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.

Collins, E. R., Jr.

1984-01-01

53

Effect of reinforcement connectivity on the elasto-plastic behavior of aluminum composites containing sub-micron alumina particles  

Microsoft Academic Search

The mechanical properties of composites consisting of an aluminum matrix with 34 and 37 vol.% sub-micron Al2O3 particles were studied in compression for two reinforcement architectures: interconnected and discontinuous. Both the elastic and plastic behaviors of these composites are successfully modeled using a self-consistent approach: the classical self-consistent and the three-phase self-consistent models for the interconnected and discontinuous architectures, respectively.

M. Kouzeli; D. C. Dunand

2003-01-01

54

Contact mechanics at nanometric scale using nanoindentation technique for brittle and ductile materials.  

PubMed

In the last years, Nanoindentation or Instrumented Indentation Technique has become a powerful tool to study the mechanical properties at micro/nanometric scale (commonly known as hardness, elastic modulus and the stress-strain curve). In this review, the different contact mechanisms (elastic and elasto-plastic) are discussed, the recent patents for each mechanism (elastic and elasto-plastic) are summarized in detail, and the basic equations employed to know the mechanical behaviour for brittle and ductile materials are described. PMID:22455731

Roa, J J; Rayon, E; Morales, M; Segarra, M

2012-06-01

55

Efficient probabilistic fracture mechanics analysis  

NASA Technical Reports Server (NTRS)

A systematic and efficient method for probabilistic fracture mechanics analysis is proposed. The method is based on a most-probable-point-locus concept. The locus is obtained iteratively where the initial locus is determined using the linear approximation of the service life N(X) function about the mean values of the random variables X. Linear and quadratic approximations of N(X) are established locally at the most probable points, and the reliability analysis methods are used to compute the cumulative probabilities. By using two examples, the proposed method is demonstrated to be efficient and accurate. One example involved a random loading and N(X) was computed using cycle-by-cycle integration. The method is general and can be applied to other performance functions. It is particularly suitable when the computation of the performance function is time consuming such that Monte Carlo simulation is prohibitively costly.

Wu, Y.-T.; Burnside, O. H.; Dominguez, J.

1987-01-01

56

A semi-analytical integration method for the numerical simulation of nonlinear visco-elasto-plastic materials  

NASA Astrophysics Data System (ADS)

A semi-analytic integration method is proposed, which can be used in numerical simulation of the mechanical behavior of nonlinear viscoelastic and viscoplastic materials with arbitrary stress nonlinearity. The method is based upon the formalism of Prony series expansion of the creep response function and accepts arbitrary stress protocols as input data. An iterative inversion technique is presented, which allows for application of the method in routines that provide strain and require stress as output. The advantage with respect to standard numerical integration methods such as the Runge-Kutta method is that it remains numerically stable even for integration over very long time steps during which strain may change considerably due to creep or recovery effects. The method is particularly suited for materials, whose viscoelastic and viscoplastic processes cover a very wide range of retardation times. In the case of simulation protocols with phases of slowly varying stress, computation time is significantly reduced compared to the standard integration methods of commercial finite element codes. An example is given that shows how the method can be used in three dimensional (3D) constitutive equations. Implemented into a Finite Element (FE) code, the method significantly improves convergence of the implicit time integration, allowing longer time increments and reducing drastically computing time. This is shown in the case of a single element exposed to a creep and recovery cycle. Some simulations of non-homogeneous boundary value problems are shown in order to illustrate the applicability of the method in 3D FE modeling.

Hirsekorn, Martin; Petitjean, Frank; Deramecourt, Arnaud

2011-05-01

57

The fracture mechanics of finite crack extension  

Microsoft Academic Search

This paper describes a modification to the traditional Griffith energy balance as used in linear elastic fracture mechanics (LEFM). The modification involves using a finite amount of crack extension (?a) instead of an infinitesimal extension (da) when calculating the energy release rate. We propose to call this method finite fracture mechanics (FFM). This leads to a change in the Griffith

David Taylor; Pietro Cornetti; Nicola Pugno

2005-01-01

58

Equations For Selected Fracture-Mechanics Parameters  

NASA Technical Reports Server (NTRS)

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.

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

1994-01-01

59

Mechanical properties of pyrolysed wood: a nanoindentation study  

Microsoft Academic Search

The present work focuses on changes of mechanical properties in pyrolysed spruce wood as a function of temperature up to 2400°C. Nanoindentation tests are used for the determination of mechanical properties at the scale of single wood cell walls. Hardness, indentation modulus and elasto-plastic\\/brittle behaviour of the carbonaceous residues are derived as function of pyrolysis temperature. Hardness values increase continuously

G. A. Zickler; T. Schöberl

2006-01-01

60

Fracture mechanics evaluation of GaAs  

NASA Technical Reports Server (NTRS)

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.

Chen, C. P.

1984-01-01

61

4 K fracture toughness investigations of 316 LN stainless steel plate and forging materials  

NASA Astrophysics Data System (ADS)

This report deals with the 4 K elasto-plastic fracture toughness measurements of different cryogenic 316 LN stainless steel materials. Compact tension type specimens with different front shapes and thicknesses between 25 and 15 mm were investigated. The test results reveal that a simplified specimen configuration could be applied, which is considered to be equivalent to that of usual recommended specimen type and thickness. In addition, besides the load-displacement record, the bending of the specimens was detected by placing strain gauges on top and on the back face of the specimens. The significance of the unstable crack advance in elasto-plastic regime was pointed out. The onset of the recorded instabilities are capable of characterizing materials' engineering fracture toughness level. Based on these experimental results a simplified method was proposed to determine the critical load at the crack initiation.

Nyilas, A.; Yanagi, H.

62

Section 3: Damage and fracture mechanics 1 Section 3: Damage and fracture mechanics  

E-print Network

­ effect of distributed crazing Abstract S3.2: Continuum damage mechanics and phase field models Tue, 16Section 3: Damage and fracture mechanics 1 Section 3: Damage and fracture mechanics Organizers-Essen), Michael Ortiz (Caltech): Relaxed Incremental Variational Formulation for Damage in Fiber

Kohlenbach, Ulrich

63

A Hierarchical Approach to Fracture Mechanics  

NASA Technical Reports Server (NTRS)

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.

Saether, Erik; Taasan, Shlomo

2004-01-01

64

Computational Solid Mechanics using a Vertex-based Finite Volume Method  

E-print Network

Computational Solid Mechanics using a Vertex-based Finite Volume Method G. A. Taylor, C. Bailey to be equivalent and in some cases superior to their nite element (FE) counterparts. In this paper we will describe will be given. Key Words: Vertex-based, Finite Volume, Solid Mechanics, Elasto-plastic. 1. Introduction Over

Taylor, Gary

65

Fracture mechanism maps in unirradiated and irradiated metals and alloys  

NASA Astrophysics Data System (ADS)

This paper presents a methodology for computing a fracture mechanism map in two-dimensional space of tensile stress and temperature using physically-based constitutive equations. Four principal fracture mechanisms were considered: cleavage fracture, low temperature ductile fracture, transgranular creep fracture, and intergranular creep fracture. The methodology was applied to calculate fracture mechanism maps for several selected reactor materials, CuCrZr, 316 type stainless steel, F82H ferritic-martensitic steel, V4Cr4Ti and Mo. The calculated fracture maps are in good agreement with empirical maps obtained from experimental observations. The fracture mechanism maps of unirradiated metals and alloys were modified to include radiation hardening effects on cleavage fracture and high temperature helium embrittlement. Future refinement of fracture mechanism maps is discussed.

Li, Meimei; Zinkle, S. J.

2007-04-01

66

Fracture Mechanism Maps in Unirradiated and Irradiated Metals  

SciTech Connect

This paper presents a methodology for computing a fracture mechanism map in two-dimensional space of tensile stress and temperature using physically-based constitutive equations. Four principal fracture mechanisms were considered: cleavage fracture, low temperature ductile fracture, transgranular creep fracture, and intergranular creep fracture. The methodology was applied to calculate fracture mechanism maps for several selected reactor materials, CuCrZr, 316 type stainless steel, F82H ferritic-martensitic steel, V4Cr4Ti and Mo. The calculated fracture maps are in good agreement with empirical maps obtained from experimental observations. The fracture mechanism maps of unirradiated metals and alloys were modified to include radiation hardening effects on cleavage fracture and high temperature helium embrittlement. Future refinement of fracture mechanism maps is discussed.

Li, Meimei [ORNL; Zinkle, Steven J [ORNL

2007-01-01

67

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

SciTech Connect

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.

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

2004-08-30

68

A review of fracture mechanics life technology  

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

69

Fracture Toughness of Metallic Glasses: Ductile-to-Brittle Transition?  

E-print Network

Quantitative understanding of the fracture toughness of metallic glasses, including the associated ductile-to-brittle transitions, is not yet available. Here we use a simple model of plastic deformation in glasses, coupled to an advanced Eulerian level set formulation for solving complex free boundary problems, to calculate the fracture toughness of metallic glasses as a function of the degree of structural relaxation corresponding to different annealing times near the glass temperature. Our main result indicates the existence of an elasto-plastic crack tip instability for sufficiently relaxed glasses, resulting in a marked drop in the toughness, which we interpret as a ductile-to-brittle transition similar to experimental observations.

Rycroft, Chris H

2012-01-01

70

Some Fundamental Mechanisms of Hydraulic Fracturing.  

E-print Network

??This dissertation focuses mainly on three topics: (1) mixed-mode branching and segmentation of hydraulic fractures in brittle materials, (2) hydraulic fracture propagation in particulate materials,… (more)

Wu, Ruiting

2006-01-01

71

Scaling law for the blue cheese model of damage  

NASA Astrophysics Data System (ADS)

This paper presents the derivation of the scaling law for the stiffness of slit weakened two-dimensional continua. The derivation is based on fracture mechanics at the slit scale and is valid for elastic and elasto-plastic materials.

Krajcinovic, Dusan

1993-02-01

72

A chemo-mechanical model of lithiation in silicon  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

73

Fracture mechanics parameters for small fatigue cracks  

NASA Technical Reports Server (NTRS)

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.

Newman, J. C., Jr.

1992-01-01

74

Mechanics of fracture - Fundamentals and some recent developments  

NASA Technical Reports Server (NTRS)

An overview is presented of the fundamental aspects of and recent developments in fracture mechanics. Reference is made to linear elastic fracture mechanics including the state of stresses and displacements in the vicinity of cracks, effects of crack geometry and orientation on stress intensity factors, energy balance of Griffith, Irwin's stress intensity concept, and linear elastic fracture mechanics testing for fracture toughness. Other aspects of this paper include the non-linear behavior of materials and their influence on fracture mechanics parameters, consideration of viscoelasticity and plasticity, non-linear fracture toughness parameters as C.O.D., R-curve and J-integral, and a non-linear energy method, proposed by Liebowitz. Finite element methods applied to fracture mechanics problems are indicated. Also, consideration has been given to slow crack growth, dynamic effects on K(IC), Sih's criterion for fracture, Lee and Liebowitz's criterion relating crack growth with plastic energy, and applications of fracture mechanics to aircraft design. Suggestions are offered for future research efforts to be undertaken in fracture mechanics.

Liebowitz, H.; Subramonian, N.; Lee, J. D.

1979-01-01

75

Patterns and perspectives in applied fracture mechanics  

SciTech Connect

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

Merkle, J.G.

1994-12-31

76

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

Microsoft Academic Search

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.

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

2009-01-01

77

A mesh-free approach to numerical rock mechanics simulations  

NASA Astrophysics Data System (ADS)

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.

Jansen, Gunnar; Galvan, Boris; Miller, Stephen

2014-05-01

78

Solution-adaptive finite element method in computational fracture mechanics  

NASA Technical Reports Server (NTRS)

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.

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

1993-01-01

79

Analysis of layered wooden shells using an orthotropic elasto-plastic model for multi-axial loading of clear spruce wood  

Microsoft Academic Search

The analysis of layered wooden shells requires a suitable constitutive model for multi-axially loaded wood. This paper presents a sophisticated model for softwood suitable for the description of inelastic deformations both in-plane and transverse to the shell surface. It incorporates micromechanical failure mechanisms in an orthotropic single-surface formulation by means of a non-associative hardening\\/softening law. The latter permits identification of

Peter Mackenzie-Helnwein; Herbert W. Müllner; Josef Eberhardsteiner; Herbert A. Mang

2005-01-01

80

Finite element analysis of grain-matrix micro-cracking in shale within the context of a multiscale modeling approach for fracture (Invited)  

NASA Astrophysics Data System (ADS)

The paper models grain-scale micro-cracking in shale at grain-matrix interfaces, assuming constituents are composed of quart silt grains and compacted clay matrix for a typical shale. The influence of grain-matrix-grain interaction on micro-crack patterns is investigated. Elasto-plastic pressure-sensitive cohesive-surface models are inserted at grain-matrix interfaces and intra-clay-matrix finite element facets, while a bulk elasto-plasticity model with bifurcation is employed for the clay matrix to compare to the intra-clay-matrix cohesive-surface model. Numerical examples are presented under two-dimensional plane strain condition at small strains. A procedure is proposed to upscale grain-scale micro-cracking to predict macro-fracture nucleation and propagation in shale and other bound particulate materials. It is shown that using cohesive surface elements (CSEs) at all finite element facets in the clay matrix mesh to simulate micro-cracking in the clay matrix leads to mesh-dependent results. Using CSEs at grain-clay-matrix interfaces is physical and not mesh dependent. We also considered using bulk pressure-sensitive elasto-plasticity with bifurcation condition within the clay matrix to attempt to predict onset of localization around grains in the simulations. It was encouraging to see that for both the single grain and multiple grain simulations, the finite element region in the clay matrix meshes where bifurcation was first detected around the grains was nearly the same. This gives us confidence that once a proper post-bifurcation constitutive model is implemented within an embedded discontinuity formulation, micro-cracking nucleation and propagation at the grain-scale in shale can be properly simulated, which will provide the basis for up-scaling to macro-cracks within a multiscale method for fracture in shale. Other items to address in future research are: (i) include transverse isotropy (elastic and plastic) for the bulk clay matrix elasto-plasticity model, (ii) include influence of moisture content on elasto-plasticity and fracture properties, (iii) extend to three-dimensions, and (iii) coordinate with an experimental effort to calibrate parameters and validate the multiscale modeling approach.

Regueiro, R. A.; Yu, S.

2010-12-01

81

Application of fracture mechanics on the Space Shuttle  

NASA Technical Reports Server (NTRS)

During the design stages of the shuttle orbiter, fracture-mechanics concepts were applied extensively to the highly stressed areas of the structure. This was the first space program to require a comprehensive fracture mechanics approach to prevent structural failures from crack or crack-like defects. As anticipated, some difficult problems were encountered. This paper briefly describes some of them together with the procedure used for fracture control on the orbiter. It is believed that the principles and methods as presented herein can serve as an example of fracture control for aerospace and other industries.

Forman, R. G.; Hu, T.

1984-01-01

82

Integration of NDE Reliability and Fracture Mechanics  

SciTech Connect

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.

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

83

Linear electro-elastic fracture mechanics of piezoelectric materials  

Microsoft Academic Search

The concepts of linear elastic fracture mechanics, generalized to treat piezoelectric effects, are employed to study the influence of the electrical fields on the fracture behavior of piezoelectric materials. The method of distributed dislocations and electric dipoles, already existing in the literature, is used to calculate the electro-elastic fields and the energy-release rate for a finite crack embedded in an

Y. E. Pak

1992-01-01

84

Adaptive Finite-Element Computation In Fracture Mechanics  

NASA Technical Reports Server (NTRS)

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.

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

1995-01-01

85

A nonlinear high temperature fracture mechanics basis for strainrange partitioning  

NASA Technical Reports Server (NTRS)

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.

Kitamura, Takayuki; Halford, Gary R.

1989-01-01

86

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

E-print Network

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

Chiang, Yet-Ming

87

Experimental unsaturated soil mechanics  

E-print Network

In this general report, experimental systems and procedures of investigating the hydro-mechanical behaviour of unsaturated soils are presented. The water retention properties of unsaturated soils are commented and linked to various physical parameters and properties of the soils. Techniques of controlling suction are described together with their adaptation in various laboratory testing devices. Some typical features of the mechanical behaviour of unsaturated soils are presented within an elasto-plastic framework. An attempt to describe the numerous and significant recent advances in the investigation of the behaviour of unsaturated soils, including the contributions to this Conference, is proposed.

Delage, Pierre

2008-01-01

88

Fracture mechanics for delamination problems in composite materials  

NASA Technical Reports Server (NTRS)

A fracture mechanics approach to the well-known delamination problem in composite materials is presented. Based on the theory of anisotropic laminate elasticity and interlaminar fracture mechanics concepts, the composite delamination problem is formulated and solved. The exact order of the delamination crack-tip stress singularity is determined. Asymptotic stress and displacement fields for an interlaminar crack are obtained. Fracture mechanics parameters such as mixed-mode stress intensity factors, KI, KII, KIII, and the energy release rate, G, for composite delamination problems are defined. To illustrate the fundamental nature of the delamination crack behavior, solutions for edge-delaminated graphite-epoxy composites under uniform axial extension are presented. Effects of fiber orientation, ply thickness, and delamination length on the interlaminar fracture are examined.

Wang, S. S.

1983-01-01

89

Reply to Davies: Hydraulic fracturing remains a possible mechanism for  

E-print Network

LETTER Reply to Davies: Hydraulic fracturing remains a possible mechanism for observed methane frac- turing (2). We respond briefly, noting that we carefully avoided ascribing any mechanism the mechanism of contamination better. Comments about sampling procedures and methane seeps are in refs. 3 and 4

Jackson, Robert B.

90

Material properties and fracture mechanics in relation to ceramic machining  

SciTech Connect

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.

Griffith, L.V.

1993-12-02

91

Work of fracture of a composite resin: fracture-toughening mechanisms.  

PubMed

The aim of this work was to investigate those mechanical parameters able to describe the fracture behavior of dental composite resins. A commercially available fine-particle micro-hybrid resin composite was used. Classical parameters as Young's modulus, strength distribution, and critical stress intensity factor were considered. Strength values were determined using the diametrical compression of discs test and for the critical stress intensity factor both unstable and controlled fracture tests were used. Controlled fracture tests allowed determining the work of fracture. Microstructure was studied by optical and field emission scanning electron microscopy. The obtained properties have been Young's modulus, 17.7 +/- 0.6 GPa; Weibull modulus, m = 14 (upper and lower limits for 90% confidence: 17 and 10); characteristic strength 51 MPa (upper and lower limits for 90% confidence: 53 and 49 MPa); critical stress intensity factor in mode I, K(IC) = 1.3 +/- 0.1 and work of fracture, gamma(wof) = 8-9 J/m(2). Pores and bubbles formed during the packing of the composite were identified as critical defects in the tested specimens. Crack deflection and branching have been identified as toughening mechanisms. Classical mechanical parameters (Young's modulus, hardness...) are not able to efficiently predict the major clinical failure mode of composite resins by fatigue. Work of fracture analysis, which is dependant on microstructural parameters such as particle size and shape, have to be included when testing mechanical properties of dental composite resins in future research studies. PMID:18465813

Baudin, Carmen; Osorio, Raquel; Toledano, Manuel; de Aza, Salvador

2009-06-01

92

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

SciTech Connect

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

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

2004-08-18

93

Elastic-plastic fracture mechanics of compact bone  

NASA Astrophysics Data System (ADS)

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.

Yan, Jiahau

94

How do material properties influence wear and fracture mechanisms?  

PubMed

The wear and fracture mechanisms of ultra-high-molecular-weight polyethylene (UHMWPE) hip and knee implant components are of great interest. The material properties of UHMWPE are affected by ionizing radiation as used for sterilization and cross-linking. Cross-linking with high-dose irradiation has been shown to improve the wear resistance of UHMWPE. However, cross-linking leads to a loss in properties such as ductility and resistance to fatigue crack propagation. Highly cross-linked UHMWPE may be more susceptible than conventional UHMWPE to fracture under severe clinical conditions (eg, impingement). Contemporary hip and knee simulator studies provide good information with which new UHMWPE formulations can be screened for clinical wear performance. However, comparable methodologies are lacking for screening UHMWPEs for fracture resistance. Mechanical tests as well as computational material and structural models should be developed to evaluate the combined effect of material and geometry (structure) on fracture resistance under clinically relevant loading conditions. PMID:18612023

Rimnac, Clare; Pruitt, Lisa

2008-01-01

95

RSRM nozzle actuator bracket/lug fracture mechanics qualification test  

NASA Technical Reports Server (NTRS)

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.

Kelley, Peggy

1993-01-01

96

RSRM nozzle actuator bracket/lug fracture mechanics qualification test  

NASA Astrophysics Data System (ADS)

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.

Kelley, Peggy

1993-07-01

97

Fracture mechanism of amorphous polymers at strain fields.  

PubMed

Owing to the wide application of polymeric materials, understanding the fracture mechanism of amorphous polymers at strain fields is a fundamentally important challenge. In this work, we use molecular dynamics simulations to investigate the uniaxial deformation of amorphous polyethylene and further monitor the polyethylene fracture process induced by stretching. Results indicate that the polyethylene systems with chain lengths of 600-800 united atoms exhibit the fracture behavior at a temperature T < 200 K and the strain of 1.0. Further study shows that in the stretching process, the disentanglement and orientation of chains lead to the formation of small cavities in the middle region of the system, and the small cavities subsequently form a large hole, causing the fracture of the whole system. Definitely, the fracture is determined by the two factors of mobility and entanglement of chains. The polyethylene systems with a high chain mobility or a high chain entanglement do not fracture. Finally, a schematic diagram is put forward to illustrate the fracture behavior. PMID:25322468

Huang, Lan; Yang, Xiaoping; Jia, Xiaolong; Cao, Dapeng

2014-10-22

98

Probabilistic fracture mechanics analysis of APT blanket tubes  

SciTech Connect

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

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

2001-01-01

99

Fracture mechanics criteria for turbine engine hot section components  

NASA Technical Reports Server (NTRS)

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.

Meyers, G. J.

1982-01-01

100

Relating Cohesive Zone Model to Linear Elastic Fracture Mechanics  

NASA Technical Reports Server (NTRS)

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.

Wang, John T.

2010-01-01

101

Mechanical transport in two-dimensional networks of fractures  

SciTech Connect

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

Endo, H.K.

1984-04-01

102

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

NASA Astrophysics Data System (ADS)

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.

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

2011-01-01

103

Mechanical stability of propped hydraulic fractures: A numerical study  

SciTech Connect

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

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

1995-03-01

104

A study on mechanical and microstructure characteristics of the STS304L butt joints using hybrid CO 2 laser-gas metal arc welding  

Microsoft Academic Search

In order to examine mechanical characteristics of the stainless steel (STS304L) hybrid welded butt joints, two-dimensional thermal elasto-plastic analysis has been carried out. To this end, a 2D simulation model has been developed considering hybrid welding features. Based on thermal history data obtained from this heat source model, the residual stress distribution in weld metal (WM), heat affected zone (HAZ)

Hee Seon Bang; Han Sur Bang; You Chul Kim; Ik Hyun Oh

2011-01-01

105

Fracture mechanics evaluation for at typical PWR primary coolant pipe  

SciTech Connect

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.

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

1997-04-01

106

Measurements of residual stress in fracture mechanics coupons  

SciTech Connect

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.

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

2010-01-01

107

Investigation of the fracture mechanics of boride composites  

NASA Technical Reports Server (NTRS)

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.

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

1972-01-01

108

Ris-R-1411(EN) Fracture mechanics characterisation of  

E-print Network

, aircrafts and wind turbine blades are made of composite structures that are joined by adhesive bonds. It is therefore of interest to establish approaches for safe design of adhesively bonded compos- ite structuresRisø-R-1411(EN) Fracture mechanics characterisation of medium-size adhesive joint specimens Bent F

109

Finite fracture mechanics: A coupled stress and energy failure criterion  

Microsoft Academic Search

The aim of the present paper is to introduce a new failure criterion in the framework of Finite Fracture Mechanics. Criteria assuming that failure of quasi-brittle materials is affected by stress or energy flux acting on a finite distance in front of the crack tip are widely used inside the scientific community. Generally, this distance is assumed to be small

Pietro Cornetti; Nicola Pugno; Alberto Carpinteri; David Taylor

2006-01-01

110

Mechanical deformation and fracture mode of polycrystalline graphene: Atomistic simulations  

NASA Astrophysics Data System (ADS)

Mechanics of polycrystalline graphene are studied through molecular dynamics simulations. Local buckling forms the ridge or funnel centering on pentagon, and fluctuating stress occurs under small tensile strain due to out-of-plane distortion. In addition, brittle breaking is initialized from heptagons and ends with fracture of pentagons.

Hao, Feng; Fang, Daining

2012-05-01

111

Fracture mechanics applied to the machining of brittle materials  

SciTech Connect

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.

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

1988-12-01

112

Unique mechanism of chance fracture in a young adult male.  

PubMed

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

Birch, Aaron; Walsh, Ryan; Devita, Diane

2013-03-01

113

Structure, mechanical properties, and fracture of 20GL cast steel  

NASA Astrophysics Data System (ADS)

The structure and mechanical properties of 20GL steel are studied. It is shown that a significant decrease in the ductility and impact toughness of the steel is caused by intercrystalline fracture, which is induced by a weakening of the intercrystallite bonds due to the existence of coarse lamellar pearlite and nonmetallic inclusions, namely, film inclusions and eutectic-type oxysulfides, at the boundaries of primary crystals. Annealing from a temperature in the intercritical range is found to improve the mechanical properties.

Schastlivtsev, V. M.; Tabatchikova, T. I.; Yakovleva, I. L.; Klyueva, S. Yu.

2014-04-01

114

Fracture mechanics analysis of composite microcracking - Experimental results in fatigue  

NASA Technical Reports Server (NTRS)

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.

Nairn, J. A.; Liu, S.

1990-01-01

115

A NEW FRACTURE ASSESSMENT APPROACH COUPLING HR-pQCT IMAGING AND FRACTURE MECHANICS-BASED FINITE ELEMENT MODELING  

PubMed Central

A new fracture assessment approach that combines HR-pQCT imaging with fracture mechanics-based finite element modeling was developed to evaluate distal radius fracture load. Twenty distal radius images obtained from postmenopausal women (fracture, n = 10; nonfracture, n = 10) were processed to obtain a cortical and a whole bone model for each subject. The geometrical properties of each model were evaluated and the corresponding fracture load was determined under realistic fall conditions using cohesive finite element modeling. The results showed that the whole bone fracture load can be estimated based on the cortical fracture load for nonfracture (R2 = 0.58, p = 0.01) and pooled data (R2 = 0.48, p < 0.001) but not for the fracture group. The portion of the whole bone fracture load carried by the cortical bone increased with increasing cortical fracture load (R2 ? 0.5, p < 0.05) indicating that a more robust cortical bone carries a larger percentage of whole bone fracture load. Cortical thickness was found to be the best predictor of both cortical and whole bone fracture load for all groups (R2 range: 0.49–0.96, p < 0.02) with the exception of fracture group whole bone fracture load showing the predictive capability of cortical geometrical properties in determining whole bone fracture load. Fracture group whole bone fracture load was correlated with trabecular thickness (R2 = 0.4, p < 0.05) whereas the nonfracture and the pooled group did not show any correlation with the trabecular parameters. In summary, this study introduced a new modeling approach that coupled HR-pQCT imaging with fracture mechanics-based finite element simulations, incorporated fracture toughness and realistic fall loading conditions in the models, and showed the significant contribution of the cortical compartment to the overall fracture load of bone. Our results provide more insight into the fracture process in bone and may lead to improved fracture load predictions. PMID:23497802

Ural, Ani; Bruno, Peter; Zhou, Bin; Shi, X. Tony; Guo, X. Edward

2013-01-01

116

Mechanics of fluid-driven fracture growth in naturally fractured reservoirs with simple network geometries  

Microsoft Academic Search

A numerical model has been developed for fluid-driven opening mode fracture growth in a naturally fractured formation. The rock formation contains discrete deformable fractures, which are initially closed but conductive because of their preexisting apertures. Fluid flow that develops along fractures depends on fracture geometry defined by preexisting aperture distribution, offsets along a fracture path, and intersections of two or

Xi Zhang; Robert G. Jeffrey; Marc Thiercelin

2009-01-01

117

Quantitative Integration of Ndt with Probabilistic Fracture Mechanics for the Assessment of Fracture Risk in Pipelines  

NASA Astrophysics Data System (ADS)

In the context of probabilistic paradigm of fracture risk assessment in structural components a computer simulation rationale is presented which has at the base the integration of Quantitative Non-destructive Inspection and Probabilistic Fracture Mechanics. In this study the static failure under static loading is assessed in the format known as Failure Assessment Diagram (FAD). The fracture risk is evaluated in probabilistic terms. The superposed probabilistic pattern over the deterministic one is implemented via Monte-Carlo sampling. The probabilistic fracture simulation yields a more informative analysis in terms of probability of failure. The ability to simulate the influence of the quality and reliability of non-destructive inspection (NDI) is an important feature of this approach. It is achieved by integrating, algorithmically, probabilistic FAD analysis and the Probability of Detection (POD). The POD information can only be applied in a probabilistic analysis and leads to a refinement of the assessment. By this means, it can be ascertained the decrease of probability of failure when POD-characterized NDI is applied. Therefore, this procedure can be used as a tool for inspection based life time conceptions. In this paper results of sensitivity analyses are presented with the aim to outline, in terms of non-failure probabilities, the benefits of applying NDI, in various qualities, in comparison with the situation when NDI is lacking. A better substantiation is enabled of both the component reliability management and the costs-effectiveness of NDI timing.

Kurz, J. H.; Cioclov, D.; Dobmann, G.; Boller, C.

2010-02-01

118

Mechanical properties and fracture dynamics of silicene membranes.  

PubMed

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

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

2014-09-28

119

Mechanical Properties and Fracture Dynamics of Silicene Membranes  

E-print Network

As graphene became one of the most important materials today, there is a renewed interest on others similar structures. One example is silicene, the silicon analogue of graphene. It share some 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.

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

2014-01-01

120

Combining damage and fracture mechanics to model calving  

NASA Astrophysics Data System (ADS)

Calving of icebergs is a major negative component of polar ice-sheet mass balance. We present a new calving modeling framework relying on both continuum damage mechanics and linear elastic fracture mechanics. This combination accounts for both the slow sub-critical surface crevassing and fast propagation of crevasses when calving occurs. First, damage of the ice occurs over long timescales and enhances the viscous flow of ice. Then brittle fracture propagation happens downward, over very short timescales, in ice considered as an elastic medium. The model is validated on Helheim Glacier, South-West Greenland, one of the most monitored fast-flowing outlet glacier. This allows to identify sets of model parameters giving a consistent response of the model and producing a dynamic equilibrium in agreement with observed stable position of the Helheim ice front between 1930 and today.

Krug, J.; Weiss, J.; Gagliardini, O.; Durand, G.

2014-03-01

121

Combining damage and fracture mechanics to model calving  

NASA Astrophysics Data System (ADS)

Calving of icebergs is a major negative component of polar ice-sheet mass balance. We present a new calving modeling framework relying on both continuum damage mechanics and linear elastic fracture mechanics. This combination accounts for both the slow sub-critical surface crevassing and fast propagation of crevasses when calving occurs. First, damage of the ice occurs over long timescales and enhances the viscous flow of ice. Then brittle fracture propagation happens downward, over very short timescales, in ice considered as an elastic medium. The model is validated on Helheim Glacier, South-West Greenland, one of the most monitored fast-flowing outlet glacier. This allows to identify sets of model parameters giving a consistent response of the model and producing a dynamic equilibrium in agreement with observed stable position of the Helheim ice front between 1930 and today.

Krug, J.; Weiss, J.; Gagliardini, O.; Durand, G.

2014-02-01

122

Discrete fracture patterns of virus shells reveal mechanical building blocks  

NASA Astrophysics Data System (ADS)

Viral shells are self-assembled protein nanocontainers with remarkable material properties. They combine simplicity of construction with toughness and complex functionality. To date we know little about how virus structure determines assembly pathways and shell mechanics. We have used atomic force microscopy to study structural failure of the shells of the bacteriophage ?29. We observed rigidity patterns following the symmetry of the capsid proteins and under prolonged force exertion, we see fractures along well-defined lines of the 2D crystal lattice. We found the mechanically most stable building block of the shells was a trimer. Our approach of ``reverse engineering'' the virus shells thus made it possible to identify stable structural intermediates. Such stable intermediates point to a hierarchy of interactions among equal building blocks correlated with distinct next-neighbor interactions. The results also demonstrate that concepts from macroscopic materials science, such as fracture, can be usefully employed in molecular engineering.

Ivanovska, Irena L.; Miranda, Roberto; Carrascosa, José. L.; Wuite, Gijs J. L.; Schmidt, Christoph F.

2012-02-01

123

Mechanics of materials: Top-down approaches to fracture  

SciTech Connect

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

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

2000-01-01

124

Transverse cracking of orthotropic composite laminates: a fracture mechanics approach  

Microsoft Academic Search

This research is concerned with the fracture mechanics of a laminated composite medium, which contains a central layer sandwiched\\u000a by two outer layers. There is a periodic array of cracks in the central layer along the central axis of the medium. Fourier\\u000a transform is used to reduce the problem to the solution of a system of dual integral equations, which

B. L. Wang; J. C. Han

2010-01-01

125

A Coupled Stress and Energy Criterion within Finite Fracture Mechanics  

Microsoft Academic Search

Aim of the present paper is to introduce a new failure criterion in the framework of Finite Fracture Mechanics. Criteria assuming\\u000a that failure of quasi-brittle materials is affected by the stresses acting at a finite distance from the crack tip are widely\\u000a used inside the Scientific Community. These approaches, in addition to some others, can be grouped together under the

Pietro Cornetti; Nicola Pugno; Alberto Carpinteri; David Taylor

126

Results of fracture mechanics tests on PNC SUS 304 plate  

SciTech Connect

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

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

1985-08-01

127

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

E-print Network

the fracture of cortical bone based on fracture mechanics concepts [4-7]. Fracture mechanics approach combines if if PREDICTION OF PROXIMAL FEMORAL FRACTURE BY USING MECHANICAL QUASI-BRITTLE DAMAGE COUPLED WITH ANISOTROPIC : abettamer2003@yahoo.com Introduction A femoral fracture caused by the osteoporosis becomes increasingly

Boyer, Edmond

128

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

NASA Technical Reports Server (NTRS)

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.

Kattenhorn, Simon

2004-01-01

129

Mechanics of fluid-driven fracture growth in naturally fractured reservoirs with simple network geometries  

NASA Astrophysics Data System (ADS)

A numerical model has been developed for fluid-driven opening mode fracture growth in a naturally fractured formation. The rock formation contains discrete deformable fractures, which are initially closed but conductive because of their preexisting apertures. Fluid flow that develops along fractures depends on fracture geometry defined by preexisting aperture distribution, offsets along a fracture path, and intersections of two or more fractures. The model couples fluid flow, elastic deformation, and frictional sliding to obtain the solution, which depends on the competition between fractures for permeability enhancement. The fractures can be opened by fluid pressure that exceeds the normal stress acting on them and by interactions with intersecting closed fractures experiencing Coulomb-type frictional slip. The Newtonian fluid is assumed to flow through the conductive fractures according to a lubrication equation that relates the cube of an equivalent hydraulic aperture to fracture conductivity. The rock material is assumed to be impermeable and elastic. This paper provides the governing equations for the multiple fracture systems and the solution methods used. Flow distribution and fracture growth in conductive fracture sets are simulated for a range of geometric arrangements and hydraulic properties. Numerical results show that elastic interaction between fracture branches plays a controlling role in fluid migration, although initial apertures can give rise to a preferential fluid flow direction during the early stage. In the presence of offsets, fracture segments subject to strong compression are difficult to open hydraulically, and their resulting smaller permeability can increase overall upstream fracture pressure and opening. The patterns of fluid flow become more complicated if fractures intersect each other. A portion of injected fluid is lost into closed empty fractures that cut across the main hydraulic fracture, and this delays the pressure increases required for fracture growth past the crosscutting fracture. The nonlinear fluid loss rate depends on the geometric complexities of the fracture sets and on the fluid viscosity. Sometimes fracture growth can be accelerated by the fast fluid transport along an intersected, relatively conductive natural fracture.

Zhang, Xi; Jeffrey, Robert G.; Thiercelin, Marc

2009-12-01

130

Measurement of residual stresses using fracture mechanics weight functions  

SciTech Connect

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

Fan, Y.

2000-10-01

131

CHARACTERIZATION, ANALYSIS AND PREDICTION OF DELAMINATION IN COMPOSITES USING FRACTURE MECHANICS  

Microsoft Academic Search

The state-of-the-art for characterizing, analyzing, and predicting delamination growth in composite materials and structures using a fracture mechanics approach will be reviewed. Techniques for measuring delamination fracture toughness and fatigue delamination onset data will be highlighted. The use of these data in finite element analyses utilizing fracture mechanics will be examined. The virtual crack closure technique for calculating strain energy

T. Kevin O'Brien

132

Biomechanical mechanisms of orbital wall fractures - a transient finite element analysis.  

PubMed

As the biomechanical mechanisms of orbital wall fractures are still under research, three different fracture mechanisms were tested in a finite element based investigation. In contrast to earlier studies, a finer skeletal model and a transient dynamic simulation were used to test pure hydraulic, pure buckling and a mixed force transmission. Results showed that each set-up led to different orbital fracture patterns, which correlate well with clinical findings. Therefore the conclusion is that different mechanisms may act together explaining the variety of clinical fracture situations. Biomechanical testing has proven to be appropriate in answering questions regarding fracture mechanisms. PMID:22417768

Schaller, Andreas; Huempfner-Hierl, Heike; Hemprich, Alexander; Hierl, Thomas

2013-12-01

133

Analysis of Fracture Mechanics Tests on Opalinus Clay  

NASA Astrophysics Data System (ADS)

Many studies have recently been conducted to evaluate various mechanical characteristics of the Opalinus Clay (OPA) formation in view of its potential use as the hosting rock for the Swiss nuclear waste repositories. Its sedimentary bedding makes OPA a transversely isotropic rock and its directional mechanical properties need to be measured. This paper reports on an experimental and computational approach that was adopted to define the parallel-to-bedding fracture mechanics (FM) parameters of OPA in Mode-I. OPA cores from Mont Terri Underground Research Laboratory (URL) were submitted to laboratory tests on notched semi-circular specimens under three-point bending (SCB). In these tests, crack propagation is forced along the notch direction. However, the 45° bedding inclination of the specimen axis frequently deviated the crack from the expected direction. An analysis of the SCB tests was performed by means of non-linear FM techniques and the pertinent Mode-I parameters along the bedding were estimated.

Valente, S.; Fidelibus, C.; Loew, S.; Cravero, M.; Iabichino, G.; Barpi, F.

2012-09-01

134

Fracture mechanics analyses for skin-stiffener debonding  

NASA Technical Reports Server (NTRS)

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.

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

1993-01-01

135

Coupled Flow and Mechanics in Porous and Fractured Media*  

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

136

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

E-print Network

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

Cai, Wei

137

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

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

138

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

NASA Technical Reports Server (NTRS)

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.

Herring, H. W.

1972-01-01

139

Elastic plastic fracture mechanics methodology for surface cracks  

NASA Technical Reports Server (NTRS)

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.

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

1993-01-01

140

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

NASA Astrophysics Data System (ADS)

Deep geothermal reservoirs are rock units at depths greater than 400 m from which the internal heat can be extracted using water as a transport means in an economically efficient manner. In many geothermal reservoirs, fluid flow is largely, and may be almost entirely, controlled by the permeability of the fracture network. No flow, however, takes place along a particular fracture network unless the fractures are interconnected. For fluid flow to occur from one site to another there must be at least one interconnected cluster of fractures that links these sites, that is, the percolation threshold must be reached. In "hydrothermal systems", only the natural fracture system (extension and shear fractures) creates the rock or reservoir permeability that commonly exceeds the matrix permeability by far; in "petrothermal systems", by contrast, interconnected fracture systems are formed by creating hydraulic fractures and massive hydraulic stimulation of the existing fracture system in the host rock. Propagation (or termination, that is, arrest) of both natural extension and shear fractures as well as man-made hydraulic fractures is mainly controlled by the mechanical rock properties, particularly rock toughness, stiffness and strengths, of the host rock. Most reservoir rocks are heterogeneous and anisotropic, in particular they are layered. For many layered rocks, the mechanical properties, particularly their Young's moduli (stiffnesses), change between layers, that is, the rocks are mechanically layered. Mechanical layering may coincide with changes in grain size, mineral content, fracture frequencies, or facies. For example, in sedimentary rocks, stiff limestone or sandstone layers commonly alternate with soft shale layers. In geothermal reservoirs fracture termination is important because non-stratabound fractures, that is, fractures not affected by layering, are more likely to form an interconnected fracture network than stratabound fractures, confined to single rock layers. Thus, to minimise exploration risks and for effective stimulation, the geometry of the fracture system and the mechanical properties of the host rock must be known. Here we present first results of structural geological field studies of fracture systems in outcrop analogues studies of rocks that could be used to host man-made geothermal reservoirs in sedimentary rocks in the North German Basin. As examples, we show data from different lithologies, including Buntsandstein (Lower Triassic), a sandstone-shale succession and Muschelkalk (Middle Triassic), a limestone-marl succession. We analyse natural fracture systems and the effects of rock heterogeneities, particularly stiffness variations between layers (mechanical layering) on the propagation of natural fractures. Important fracture parameters include attitude, aperture and interconnectivity to fracture systems. The field studies are supplemented by laboratory measurements of the above mentioned rock mechanical properties. Our field studies indicate that many fractures become arrested at layer contacts, particularly at contacts between layers with contrasting mechanical properties. Measurements of thousands of fractures indicate that even very thin layers (mm to cm-scale thicknesses) of shale or marl may be responsible for the arrest of many fractures. Our results suggest that the propagation and aperture variation of fractures are important parameters in the permeability development of deep geothermal reservoirs. These studies provide a basis for models of fracture networks and fluid transport in future man-made reservoirs. We conclude that the likely permeability of a man-made geothermal reservoir can be inferred from field data from outcrop analogues, laboratory measurements, and numerical models.

Leonie Philipp, Sonja; Reyer, Dorothea

2010-05-01

141

Numerical simulation of thermal-hydrologic-mechanical-chemical processes in deformable, fractured porous media  

Microsoft Academic Search

A method is introduced to couple the thermal (T), hydrologic (H), and chemical precipitation\\/dissolution (C) capabilities of TOUGHREACT with the mechanical (M) framework of FLAC3D to examine THMC processes in deformable, fractured porous media. The combined influence of stress-driven asperity dissolution, thermal-hydro-mechanical asperity compaction\\/dilation, and mineral precipitation\\/dissolution alter the permeability of fractures during thermal, hydraulic, and chemical stimulation. Fracture and

Joshua Taron; Derek Elsworth; Ki-Bok Min

2009-01-01

142

Life assessment for a gas turbine blade under creep conditions based on continuum fracture mechanics  

Microsoft Academic Search

Based on the semi-analytic finite element method and relationships of the continuum fracture mechanics, a numerical investigation\\u000a on the creep and extension of the continuum fracture zone in a gas turbine blade is performed. The value of life prior to\\u000a the formation of a crack-like defect and applicability limits of the relationships of continuum fracture mechanics are determined.

V. A. Bazhenov; A. I. Gulyar; S. O. Piskunov; A. A. Shkryl’

2006-01-01

143

FRACTURE MECHANISM OF A BAINITE STEEL IN PRECRACKED AND NOTCHED SPECIMENS  

E-print Network

Charpy V-notch test from ­100o C to 20o C. To investigate the fracture mechanism in both the precrackedICF10044OR FRACTURE MECHANISM OF A BAINITE STEEL IN PRECRACKED AND NOTCHED SPECIMENS AT LOW of Materials Engineering, Gansu University of Technology, Lanzhou, Gansu, P.R. China ABSTRACT Precracked

Qin, Qinghua

144

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

E-print Network

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

Pan, Ernie

145

Computational Fracture Mechanics of Concrete Structures: A Retrospective through Multiple Lenses  

Microsoft Academic Search

The history of the application of computational fracture mechanics to concrete structures, now 5 decades old, is interesting from many perspectives. In this paper, a retrospective of computational fracture mechanics in concrete structures (ComFraMCoS) is presented through five lenses. These lenses clarify research trends through an historical overview. We intend to interlace the views through these lenses to sometimes offer

J. M. Emery; A. R. Ingraffea

146

Fracture mechanics analysis for various fiber/matrix interface loadings  

NASA Technical Reports Server (NTRS)

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.

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

1991-01-01

147

Fracture mechanics analysis for various fiber/matrix interface loadings  

NASA Technical Reports Server (NTRS)

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.

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

1991-01-01

148

Fracture mechanics analysis for various fiber/matrix interface loadings  

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

149

Fracture mechanisms of thin amorphous carbon films in nanoindentation  

Microsoft Academic Search

The nanoindentation fracture of amorphous carbon films on silicon substrate was studied. Load-displacement curves were obtained during indentation in conjunction with the scanning electron microscope (SEM) observations of fractured surfaces at different loads. The fracture process was found to progress in three stages: (1) first ring-like through-thickness cracks form around the indenter by high stresses in the contact area; (2)

Xiaodong Li; Dongfeng Diao; Bharat Bhushan

1997-01-01

150

[Assessment of mechanical complications of intramedullary osteosynthesis in trochanteric fractures of the femur in elderly people].  

PubMed

Operational treatment of trochanteric fractures of the femur, independently of the applied connecting implant, carries the risk of various types of complications. In this paper the incidence of mechanical complications in performed osteosynthesis of trochanteric fractures of the femur was analyzed as well as the risk factors influencing them and their extent were assessed. The results showed statistically significant influence of the type of implant, the type of fracture and the patients' age. It has been proven that the use of Gamma nail decreases the risk of mechanical complications almost twofold in comparison with the Ender's posts, disregarding the type of trochanteric fracture of the femur. PMID:21751513

H?adki, Waldemar; Bednarenko, Marcin; Kotela, Ireneusz

2011-01-01

151

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

SciTech Connect

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.

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

2009-02-01

152

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

NASA Technical Reports Server (NTRS)

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.

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

153

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

SciTech Connect

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.

Ernst, H.A.; Saxena, A.; Mcdowell, D.L.; Atluri, S.N.; Newman, J.C. Jr.; Raju, I.S.; Epstein, J.S.

1992-01-01

154

Surface integral and finite element hybrid method for two- and three-dimensional fracture mechanics analysis  

Microsoft Academic Search

This paper summarizes the development of the surface integral and finite element hybrid method for two and three dimensional fracture mechanics analysis. The fracture, which is a discontinuity in the displacement field, is modeled explicitly and efficiently by use of dislocations for two dimensional analysis and by dipoles of point forces for three dimensional applications. The boundary value problem of

W. D. Keat; B. S. Annigeri; M. P. Cleary

1988-01-01

155

Mechanisms for Fracture and Fatigue-Crack Propagation in a Bulk Metallic Glass  

E-print Network

Mechanisms for Fracture and Fatigue-Crack Propagation in a Bulk Metallic Glass C.J. GILBERT, V. SCHROEDER, and R.O. RITCHIE The fracture and fatigue properties of a newly developed bulk metallic glass exhibited a vein morphology typical of metallic glasses, and, in some cases, evidence for local melting

Ritchie, Robert

156

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

PubMed Central

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

Abe, Hiroyuki

2009-01-01

157

Fracture-mechanisms in pure iron, two austenitic steels, and one ferritic steel  

NASA Astrophysics Data System (ADS)

The mechanisms of fracture of round tensile specimens of pure iron, two austenitic stainless steels (types 304 and 316) and one ferritic steel (2¼ Cr-1 Mo) have been studied. These new observations have been combined with published information to construct two types of fracture mechanism diagram which show the regions of dominance of each mechanism, and summarize the fracture observations between absolute zero and melting point. These diagrams may help in distinguishing between creep-brittle and creep-ductile batches of steel, and in the rational extrapolation of creep-rupture data.

Fields, R. J.; Weerasooriya, T.; Ashby, M. F.

1980-02-01

158

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

SciTech Connect

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.

Bower, K.M.

1996-06-01

159

Mechanical design considerations for fracture-treating down casing strings  

SciTech Connect

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

Clark, H.C.

1987-06-01

160

Porosity Dependence and Mechanism of Brittle Fracture in Sandstones  

Microsoft Academic Search

Brittle fracture tests of 105 fine-grained quartz arenites were conducted at 25øC, 1.0-kb confining pressure, a constant strain rate of 6.5. X 10-5\\/set, and pore pressure ranging from 0 to 750 bars. Orientation of planar anisotropy (bedding or cross-bedding) with respect to principal stresses has little influence on the fracture strength. The Donath orientation effect depends on rock type. Strong

David E. Dunn; Lester J. Lafountain; Robert E. Jackson

1973-01-01

161

Mechanical properties of two canine iliac fracture fixation systems  

E-print Network

. Computer generated plots of force versus displace- ment were made for determination of the stiffness and failure strength of the specimen. Failure was defined as exceedance of ultimate strength or fracture gap propaga- tion of greater than 2 mm. Failed.... Either situation is considered exceedance of ultimate strength. In all plated specimens in all testing modes failure was defined in terms of fracture gap propagation greater than 2 mm. In torsional testing the bone plate fixation system usually...

VanGundy, Thomas Eugene

2012-06-07

162

Injection-Sensitive Mechanics of Hydraulic Fracture Interaction with Discontinuities  

NASA Astrophysics Data System (ADS)

We develop a new analytical model, called OpenT, that solves the elasticity problem of a hydraulic fracture (HF) contact with a pre-existing discontinuity natural fracture (NF) and the condition for HF re-initiation at the NF. The model also accounts for fluid penetration into the permeable NFs. For any angle of fracture intersection, the elastic problem of a blunted dislocation discontinuity is solved for the opening and sliding generated at the discontinuity. The sites and orientations of a new tensile crack nucleation are determined based on a mixed stress- and energy-criterion. In the case of tilted fracture intersection, the finite offset of the new crack initiation point along the discontinuity is computed. We show that aside from known controlling parameters such stress contrast, cohesional and frictional properties of the NFs and angle of intersection, the fluid injection parameters such as the injection rate and the fluid viscosity are of first-order in the crossing behavior. The model is compared to three independent laboratory experiments, analytical criteria of Blanton, extended Renshaw-Pollard, as well as fully coupled numerical simulations. The relative computational efficiency of OpenT model (compared to the numerical models) makes the model attractive for implementation in modern engineering tools simulating hydraulic fracture propagation in naturally fractured environments.

Chuprakov, D.; Melchaeva, O.; Prioul, R.

2014-09-01

163

Fractures  

MedlinePLUS

A fracture is a break, usually in a bone. If the broken bone punctures the skin, it is called an open ... falls or sports injuries. Other causes are low bone density and osteoporosis, which cause weakening of the ...

164

Scaling law for the blue cheese model of damage  

Microsoft Academic Search

This paper presents the derivation of the scaling law for the stiffness of slit weakened two-dimensional continua. The derivation is based on fracture mechanics at the slit scale and is valid for elastic and elasto-plastic materials. Member of the Institute for Theoretical Physics, University of California, Santa Barbara, Santa Barbara, USA.

Dusan Krajcinovic

1993-01-01

165

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

NASA Technical Reports Server (NTRS)

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

Swanson, P. L.

1984-01-01

166

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

E-print Network

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...

Zhou, Minjian

2012-06-07

167

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

E-print Network

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...

Safariforoshani, Mohammadreza

2013-08-09

168

FFTF Irradiation of Fracture Mechanics Specimens for out-of-Core Structures.  

National Technical Information Service (NTIS)

The National Program Plan has established data requirements for out-of-core structures for FBRs. Significant FFTF irradiation space with moderate gamma heating levels is required to irradiate relatively large fracture mechanics specimens to total neutron ...

D. C. King

1978-01-01

169

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

NASA Technical Reports Server (NTRS)

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.

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

2011-01-01

170

An Experimental Study of Fracture of LIGA Ni Micro-Electro-Mechanical Systems Thin Films  

Microsoft Academic Search

This article presents the results of an experimental study of fracture in LIGA Ni micro-electro-mechanical systems (MEMS)\\u000a thin films. Microtesting techniques are developed for the study of the J-resistance curve (J-?a) behavior in compact tension (CT) thin film specimens. In-situ measurements of crack-tip strain are presented together with in-situ and ex-situ microscopic images of crack-tip deformation and fracture mechanisms. Fractographic

Y. Yang; S. Allameh; B. Boyce; K. S. Chan; W. O. Soboyejo

2007-01-01

171

Relationships between fracture patterns, geodynamics and mechanical stratigraphy in Carbonates (South-East Basin, France)  

NASA Astrophysics Data System (ADS)

This study aims at improving the understanding of fracture genesis in layered carbonate sedimentary sequences, focusing on field analysis of Jurassic to Maastrichtian age carbonates of Provence (France). Fracture patterns of 9 outcrops were characterized in 3D: 6 of Urgonian, 1 of Tithonian and 2 of Campanian-Late Maastrichtian ages. Seven sites are located in relatively weakly deformed areas away from larges fault and fold zones where strain partitioning and stress localization effects may take place. Two sites are located in fold flanks for the purpose of relative dating and for comparison with the sites in the weakly deformed areas. Patterns and detailed fracture attributes were compared to host rock sedimentary facies, porosity and P-wave velocities. Fracture chronology was determined with cross-cutting relationships and compared to burial/uplift history reconstructed from subsidence curves and from a regional structural analysis. Our results show that fractures are clustered in two perpendicular joint sets whatever the host rock age. We observe an average spacing of 20 cm and no control of strike, age, facies, or bed thickness on fracture size. There is no mechanical stratigraphy. The fracture sequence compared to subsidence curves indicates that fractures occurred before tectonic inversion, during early and rapid burial, whatever the host rock age and facies. The abundance of burial stylolites does not correlate with maximum burial depth but with fracture frequency, host rock porosity and P-wave velocity. We conclude that the studied carbonates had early brittle properties controlled by their geographic position rather than by depositional facies types and undergone early diagenesis. The porosity loss/gain and the mechanical differentiation in carbonates of Provence could have been acquired during very early burial and diagenesis and have preserved through time. This study also demonstrates that regional fracturing is not necessarily driven by large scale structural events as it is often assumed in fractured reservoir modelling.

Lamarche, Juliette; Lavenu, Arthur P. C.; Gauthier, Bertrand D. M.; Guglielmi, Yves; Jayet, Océane

2012-12-01

172

Elasto-plasticity in wrinkled polymerized lipid membranes  

PubMed Central

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

Chaieb, Sahraoui

2014-01-01

173

Contributions to the anisotropic elasto-plastic analysis of shells  

E-print Network

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

Kim, Do-Nyun

2009-01-01

174

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

E-print Network

Fracture of disordered solids in compression as a critical phenomenon. I. Statistical mechanics as a critical phenomenon. This first article establishes a statistical mechanics based on ensemble averages when articles that develops a statistical mechanics that allows the possible phase transitions in a cracking

Toussaint, Renaud

175

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

SciTech Connect

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.

Stephen L. Karner, Ph.D

2006-02-01

176

Mechanical and hydraulic behavior of a rock fracture under shear deformation  

NASA Astrophysics Data System (ADS)

With regard to crystalline rock that constitutes deep geology, attempts have been made to explore its hydraulic characteristics by focusing on the network of numerous fractures within. As the hydraulic characteristics of a rock are the accumulation of hydraulic characteristics of each fracture, it is necessary to develop the hydraulic model of a single fracture to predict the large-scale hydraulic behavior. To this end, a simultaneous permeability and shear test device is developed, and shear-flow coupling tests are conducted on specimens having fractures with varied levels of surface roughness in the constant normal stiffness conditions. The results show that the permeability characteristics in the relation between shear displacement and transmissivity change greatly at the point where the stress path reaches the Mohr-Coulomb failure curve. It is also found that there exists a range in which transmissivity is not proportional to the cube of mechanical aperture width, which seems to be because of the occurrence of channeling phenomenon at small mechanical aperture widths. This channeling flow disappears with increasing shear and is transformed into a uniform flow. We develop a simulation technique to evaluate the macroscopic permeability characteristics by the lattice gas cellular automaton method, considering the microstructure of fracture, namely the fracture surface roughness. With this technique, it is shown that the formation of the Hagen-Poiseuille flow is affected by the fracture microstructure under shear, which as a result determines the relationship between the mechanical aperture width and transmissivity.

Nishiyama, Satoshi; Ohnishi, Yuzo; Ito, Hisao; Yano, Takao

2014-12-01

177

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

NASA Technical Reports Server (NTRS)

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.

Goree, James G.; Richardson, David E.

1991-01-01

178

E. coli RS2GFP Retention Mechanisms in Laboratory-Scale Fractured Rocks: A Statistical Model  

NASA Astrophysics Data System (ADS)

With billions of gallons of groundwater being withdrawn every day in the US and Canada, it is imperative to understand the mechanisms which jeopardize this resource and the health of those who rely on it. Porous media aquifers have typically been considered to provide significant filtration of particulate matter (e.g. microorganisms), while the fractures in fractured rock aquifers and aquitards are considered to act as contaminant highways allowing a large fraction of pathogens to travel deep into an aquifer relatively quickly. Recent research results indicate that fractured rocks filter out more particulates than typically believed. The goal of the research presented here is to quantify the number of E. coli RS2GFP retained in a single, saturated, laboratory-scale fracture, and to relate the retention of E. coli RS2GFP to the aperture field characteristics and groundwater flow rate. To achieve this goal, physical experiments were conducted at the laboratory-scale to quantify the retention of E. coli RS2GFP through several single, saturated, dolomitic limestone fractures under a range of flow rates. These fractures were also cast with a transparent epoxy in order to visualize the transport mechanisms in the various different aperture fields. The E. coli RS2GFP is tagged with a green-fluorescent protein (GFP) that is used to obtain visualization data when excited by ultraviolet light. A series of experiments was conducted, each of which involved the release of a known number of E. coli RS2GFP at the upstream end of the fracture and measuring the effluent concentration profile. These experiments were conducted using both the natural rock and transparent cast of several different aperture fields, under a range of flow rates. The effects of different aperture field characteristics and flow rates on the retention of E. coli RS2GFP will be determined by conducting a statistical analysis of the retention data under different experimental conditions. The images captured during the visualization experiments will help to draw conclusions regarding the retention mechanisms at play in the fractures. This paper will present a statistical model for the retention of E. coli RS2GFP in fractures as a function of aperture field characteristics and flow rate. The images of the E. coli RS2GFP travelling through the casts, in combination with direct aperture field measurements, will provide insight into the different mechanisms instrumental to particulate retention within the fractures. The results of these experiments will partially bridge the knowledge gap in fractured aquifers by furthering the understanding of transport and retention mechanisms of microorganisms within fractured rocks.

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

2011-12-01

179

Mechanisms of orbital floor fractures: a clinical, experimental, and theoretical study.  

PubMed Central

PURPOSE: The purpose of this study was to investigate the two accepted mechanisms of the orbital blow-out fracture (the hydraulic and the buckling theories) from a clinical, experimental, and theoretical standpoint. METHODS: Clinical cases in which blow-out fractures resulted from both a pure hydraulic mechanism and a pure buckling mechanism are presented. Twenty-one intact orbital floors were obtained from human cadavers. A metal rod was dropped, experimentally, onto each specimen until a fracture was produced, and the energy required in each instance was calculated. A biomathematical model of the human bony orbit, depicted as a thin-walled truncated conical shell, was devised. Two previously published (by the National Aeronautics Space Administration) theoretical structural engineering formulas for the fracture of thin-walled truncated conical shells were used to predict the energy required to fracture the bone of the orbital floor via the hydraulic and buckling mechanisms. RESULTS: Experimentally, the mean energy required to fracture the bone of the human cadaver orbital floor directly was 78 millijoules (mj) (range, 29-127 mj). Using the engineering formula for the hydraulic theory, the predicted theoretical energy is 71 mj (range, 38-120 mj); for the buckling theory, the predicted theoretical energy is 68 mj (range, 40-106 mj). CONCLUSION: Through this study, we have experimentally determined the amount of energy required to fracture the bone of the human orbital floor directly and have provided support for each mechanism of the orbital blow-out fracture from a clinical and theoretical basis. Images FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5A FIGURE 5B FIGURE 5E FIGURE 5F PMID:10703119

Bullock, J D; Warwar, R E; Ballal, D R; Ballal, R D

1999-01-01

180

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

181

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

NASA Astrophysics Data System (ADS)

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.

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

2012-05-01

182

Fast water infiltration: a mechanism for fracture formation during land subsidence  

NASA Astrophysics Data System (ADS)

A mechanism for fracture generation and for triggering land subsidence is presented. Infiltration through a pre-existing fracture zone into a two-layered system, as well as the deformation of unconsolidated sediments on the land surface, was numerically investigated. The numerical simulation of infiltration is based on a two-phase flow-model concept for porous media, and for the deformation, it is based on a Mohr-Coulomb model concept. Different studies with variations of the fracture parameter and infiltration conditions have been carried out. The infiltration results show that fast infiltration in a partially saturated aquifer leads to land subsidence, extension of pre-existing fractured zones and the generation of new cracks. If the water column is only on the fracture, the clay layer acts like a barrier and inhibits the infiltration through the fracture. If the water column covers the entire surface, the barrier effect is overcome; the infiltration intensity depends on the height of the water column, the fracture permeability and the fracture width. The deformation results show that a strong rainfall event of 2 h leads to deformations that are about 30 % of the vertical and 70 % of the horizontal annual land-subsidence rates.

Martinez, Isaac; Hinkelmann, Reinhard; Savidis, Stavros

2013-06-01

183

Fracture Permeability Alteration due to Chemical and Mechanical Processes: A Coupled High-Resolution Model  

NASA Astrophysics Data System (ADS)

Reactive fluid-flow experiments in fractures subjected to normal stress suggest the potential for either increased or decreased permeability resulting from fracture-surface dissolution. We present a computational model that couples mechanical deformation and chemical alteration of fractures subjected to constant normal stress and reactive fluid flow. The model explicitly represents micro-scale roughness of the fracture surfaces and calculates elastic deformation of the rough surfaces using a semi-analytical approach that ensures the surfaces remain in static equilibrium. A depth-averaged reactive transport model calculates chemical alteration of the surfaces, which leads to alteration of the contacting fracture surfaces. The mechanical deformation and chemical alteration calculations are explicitly coupled, which is justified by the disparate timescales required for equilibration of mechanical stresses and reactive transport processes. An idealized analytical representation of dissolution from a single contacting asperity shows that under reaction-limited conditions, contacting asperities can dissolve faster than the open regions of the fracture. Computational simulations in fractures with hundreds of contacting asperities show that the transition from transport-limited conditions (low flow rates) to reaction-rate-limited conditions (high flow rates) causes a shift from monotonically increasing permeability to a more complicated process in which permeability initially decreases and then increases as contacting asperities begin to dissolve. These results are qualitatively consistent with a number of experimental observations reported in the literature and suggest the potential importance of the relative magnitude of mass transport and reaction kinetics on the evolution of fracture permeability in fractures subjected to combined normal stress and reactive fluid flow.

Ameli, Pasha; Elkhoury, Jean E.; Morris, Joseph P.; Detwiler, Russell L.

2014-09-01

184

Hydro-mechanical modelling of geological CO2 storage and the study of possible caprock fracture mechanisms  

E-print Network

and effective stresses in the reservoir and its surronding layers through pore pressure increase (e.g., RutqvistHydro-mechanical modelling of geological CO2 storage and the study of possible caprock fracture mechanisms N. Guy,1-2 D.M. Seyedi,1 F. Hild2 BRGM, Natural Risks & CO2 Storage Safety Division, 3 av. Claude

185

Fracture mechanics and crack propagation in fragile matter  

NASA Astrophysics Data System (ADS)

Using simulations and theory, we investigate fracture processes and the formation of cracks in near-isostatic networks derived from jammed packings in both the quasi-static limit and with molecular dynamics. We study how localized cracks in networks with high coordination number become randomly distributed and isolated bond breakages near the isostatic point and suggest that this may be related to the scaling of the size of the process zone with characteristic lengths from jamming.

Chen, Bryan; Ulrich, Stephan; Upadhyaya, Nitin; Vitelli, Vincenzo

2013-03-01

186

Mechanical properties and fracture behavior of ? particle irradiated type 316 stainless steel at high temperature  

NASA Astrophysics Data System (ADS)

The effect of helium on the mechanical properties and fracture behaviors of a type 316 austenitic steel is presented. Helium implantation was performed by 30-MeV ?-particle injection on very small, thin specimens, using a cyclotron accelerator. Average helium content in the He-deposited region was 50 to 2000 appm He. These specimens showed the transition of fracture mode from transgranular to intergranular fracture in elevated temperature tests. The transition temperature decreased with increase in the amount of implanted helium. For example, in the case of 2000 appm and 500 appm He implantation, the transition temperatures were between 773 and 873 K and between 873 and 973 K, respectively.

Miyahara, K.; Itoh, A.; Sakamoto, Y.; Kayano, H.; Hosoi, Y.

1992-09-01

187

Fracture mechanisms of retrieved titanium screw thread in dental implant.  

PubMed

Titanium and its alloy are increasingly attracting attention for use as biomaterials. However, delayed fracture of titanium dental implants has been reported, and factors affecting the acceleration of corrosion and fatigue have to be determined. The fractured surface of a retrieved titanium screw and metallurgical structures of a dental implant system were analyzed. The outer surface of the retrieved screw had a structure different from that of the as-received screw. It was confirmed that a shear crack initiated at the root of the thread and propagated into the inner section of the screw. Gas chromatography revealed that the retrieved screw had absorbed a higher amount of hydrogen than the as-received sample. The grain structure of a titanium screw, immersed in a solution known to induce hydrogen absorption, showed features similar to those of the retrieved screw. It was concluded that titanium in a biological environment absorbs hydrogen and this may be the reason for delayed fracture of a titanium implant. PMID:12033593

Yokoyama, Ken'ichi; Ichikawa, Tetsuo; Murakami, Hiroki; Miyamoto, Youji; Asaoka, Kenzo

2002-06-01

188

Investigation of the fracture mechanics of boride composites  

NASA Technical Reports Server (NTRS)

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.

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

1971-01-01

189

Dynamic damage and fracture mechanism of three-dimensional braided carbon fiber\\/epoxy resin composites  

Microsoft Academic Search

Three-dimensional braided carbon fiber\\/epoxy resin composites are significant structural materials in the fields of astronauts and aeronautics. The effect of the process and test parameters on the mechanical properties was studied in this paper. Optical microscope and field emission gun scanning electron microscope (SEM) were used to analyze the macro- and micro-fracture morphology. The fracture morphology of the three-dimensional braided

Guoyi Tang; Yunjie Yan; Xihua Chen; Jin Zhang; Bin Xu; Zhihai Feng

2001-01-01

190

Fracture mechanics of fiber-reinforced brittle-matrix composite materials  

Microsoft Academic Search

The fracture mechanics model of matrix cracking in uniaxially fiber-reinforced brittle matrix composites depends significantly on the load transfer mechanism between the fiber and the matrix. A model is developed theoretically under uniform tension in the direction parallel to the fibers and normal to the crack plane. It is assumed that the fibers are strong enough to remain intact when

Gu Lixing

1991-01-01

191

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

E-print Network

Fracture Mechanisms of Bone: A Comparative Study between Antler and Bovine Femur P.Y. Chen1 , F fracture [1,2]. Antlers have a similar microstructure as mammalian long bones, composed primarily of type, University of California, San Diego, La Jolla, CA 92093-0411, U.S.A. ABSTRACT In this study, fracture

McKittrick, Joanna

192

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

PubMed

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

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

2014-11-01

193

Updated Fatigue-Crack-Growth And Fracture-Mechanics Software  

NASA Technical Reports Server (NTRS)

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.

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

1995-01-01

194

Brittleness of twig bases in the genus Salix: fracture mechanics and ecological relevance.  

PubMed

The twig bases within the genus Salix were investigated. Brittleness of twig bases as defined in the literature neither correlates with Young's modulus nor with growth strains, which were measured for S. alba, S. fragilis and S. x rubens. For the species S. alba, S. appendiculata, S. eleagnos, S. fragilis, S. purpurea, S. triandra, S. viminalis, and S. x rubens, fracture surfaces of broken twigs were investigated and semiquantitatively described in terms of 'relative roughness' (ratio of rough area of fracture surface over whole area of fracture surface). The relative roughness clearly corresponds with the classification into brittle and nonbrittle species given in the literature. An attempt was made to quantify brittleness with mechanical tests. The absolute values of stress and strain do not correlate with the brittleness of the twig bases as defined by the relative roughness. However, the 'index stress' (ratio of stress at yield over stress at fracture) or the 'index strain' (ratio of strain at yield over strain at fracture), correlate well with the relative roughness. The graphic analysis of index stress against index strain reveals a straight line on which the eight species are ordered according to their brittleness. Depending on growth form and habitat, brittle twig bases of willows may function ecologically as mechanical safety mechanisms and, additionally, as a propagation mechanism. PMID:10938818

Beismann, H; Wilhelmi, H; Baillères, H; Spatz, H C; Bogenrieder, A; Speck, T

2000-03-01

195

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

USGS Publications Warehouse

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

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

2009-01-01

196

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

SciTech Connect

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.

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

1987-01-01

197

6. Fracture mechanics lead author: J, R. Rice  

E-print Network

of solid mechanics and materials science holds promise for understanding the atomistics of brittle vs duc. Irwin's ap- proach in particular brought progress in theoretical solid mechanics, especially on elastic

198

The Mechanical Benefit of Medial Support Screws in Locking Plating of Proximal Humerus Fractures  

PubMed Central

Background The purpose of this study was to evaluate the biomechanical advantages of medial support screws (MSSs) in the locking proximal humeral plate for treating proximal humerus fractures. Methods Thirty synthetic left humeri were randomly divided into 3 subgroups to establish two-part surgical neck fracture models of proximal humerus. All fractures were fixed with a locking proximal humerus plate. Group A was fixed with medial cortical support and no MSSs; Group B was fixed with 3 MSSs but without medial cortical support; Group C was fixed with neither medial cortical support nor MSSs. Axial compression, torsional stiffness, shear stiffness, and failure tests were performed. Results Constructs with medial support from cortical bone showed statistically higher axial and shear stiffness than other subgroups examined (P<0.0001). When the proximal humerus was not supported by medial cortical bone, locking plating with medial support screws exhibited higher axial and torsional stiffness than locking plating without medial support screws (P?0.0207). Specimens with medial cortical bone failed primarily by fracture of the humeral shaft or humeral head. Specimens without medial cortical bone support failed primarily by significant plate bending at the fracture site followed by humeral head collapse or humeral head fracture. Conclusions Anatomic reduction with medial cortical support was the stiffest construct after a simulated two-part fracture. Significant biomechanical benefits of MSSs in locking plating of proximal humerus fractures were identified. The reconstruction of the medial column support for proximal humerus fractures helps to enhance mechanical stability of the humeral head and prevent implant failure. PMID:25084520

Liu, Yanjie; Pan, Yao; Zhang, Wei; Zhang, Changqing; Zeng, Bingfang; Chen, Yunfeng

2014-01-01

199

Atomistic mechanisms of moisture-induced fracture at copper-silica interfaces  

NASA Astrophysics Data System (ADS)

Tailoring the chemo-mechanical properties of metal-dielectric interfaces is crucial for many applications including nanodevice wiring, packaging, composites, and catalysis. Here, we combine moisture-induced fracture tests, electron spectroscopy, and density functional theory calculations to reveal fracture toughness partitioning and atomistic delamination mechanisms at copper-silica interfaces. Copper plasticity is supported above a threshold work of adhesion and delamination occurs by moisture-induced Cu-O bond scission in Cu-O-Si bridges. These results provide insights into the effects of the nature of metal-oxygen bonding on moisture-induced delamination of metal-dielectric interfaces.

Vijayashankar, Dandapani; Zhu, Hong; Garg, Saurabh; Teki, Ranganath; Ramprasad, R.; Lane, Michael W.; Ramanath, Ganpati

2011-09-01

200

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

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

201

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

PubMed Central

Objective To evaluate the impact of the type of root canal preparation, intraradicular post and mechanical cycling on the fracture strength of roots. Material and Methods eighty human single rooted teeth were divided into 8 groups according to the instruments used for root canal preparation (manual or rotary instruments), the type of intraradicular post (fiber posts- FRC and cast post and core- CPC) and the use of mechanical cycling (MC) as follows: Manual and FRC; Manual, FRC and MC; Manual and CPC; Manual, CPC and MC; Rotary and FRC; Rotary, FRC and MC; Rotary and CPC; Rotary, CPC and MC. The filling was performed by lateral compactation. All root canals were prepared for a post with a 10 mm length, using the custom #2 bur of the glass fiber post system. For mechanical cycling, the protocol was applied as follows: an angle of incidence of 45°, 37°C, 88 N, 4 Hz, 2 million pulses. All groups were submitted to fracture strength test in a 45° device with 1 mm/ min cross-head speed until failure occurred. Results The 3-way ANOVA showed that the root canal preparation strategy (p<0.03) and post type (p<0.0001) affected the fracture strength results, while mechanical cycling (p=0.29) did not. Conclusion The root canal preparation strategy only influenced the root fracture strength when restoring with a fiber post and mechanical cycling, so it does not seem to be an important factor in this scenario. PMID:25025556

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

2014-01-01

202

Mechanical properties of highly defective graphene: from brittle rupture to ductile fracture.  

PubMed

Defects are generally believed to deteriorate the superlative performance of graphene-based devices but may also be useful when carefully engineered to tailor the local properties and achieve new functionalities. Central to most defect-associated applications is the defect coverage and arrangement. In this work, we investigate, by molecular dynamics simulations, the mechanical properties and fracture dynamics of graphene sheets with randomly distributed vacancies or Stone-Wales defects under tensile deformations over a wide defect coverage range. With defects presented, an sp-sp(2) bonding network and an sp-sp(2)-sp(3) bonding network are observed in vacancy-defected and Stone-Wales-defected graphene, respectively. The ultimate strength degrades gradually with increasing defect coverage and saturates in the high-ratio regime, whereas the fracture strain presents an unusual descending-saturating-improving trend. In the dense vacancy defect situation, the fracture becomes more plastic and super-ductility is observed. Further fracture dynamics analysis reveals that the crack trapping by sp-sp(2) and sp-sp(2)-sp(3) rings and the crack-tip blunting account for the ductile fracture, whereas geometric rearrangement on the entire sheet for vacancy defects and geometric rearrangement on the specific defect sites for Stone-Wales defects account for their distinctive rules of the evolution of the fracture strain. PMID:24270887

Xu, Lanqing; Wei, Ning; Zheng, Yongping

2013-12-20

203

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

SciTech Connect

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}.

Nakai, Yoshikazu [Kobe Univ., Hyogo (Japan). Dept. of Mechanical Engineering

1995-11-01

204

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

Microsoft Academic Search

The mechanical and fracture properties of austenitic stainless steels (SSs) alloyed with gallium require assessment in order to determine the likelihood of premature storage-container failure following Ga uptake. AISI 304 L SS was cast with 1, 3, 6, 9, and 12 wt pct Ga. Increased Ga concentration promoted duplex microstructure formation with the ferritic phase having a nearly identical composition

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

2004-01-01

205

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

Microsoft Academic Search

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

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

1998-01-01

206

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

Microsoft Academic Search

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

Y. B. Park; Jin Yu

1997-01-01

207

A fracture mechanics approach to the failure of graphite in laboratory tests  

Microsoft Academic Search

Laboratory tests show that for some graphites the calculated stress at failure exceeds the tensile strength in uniform tension by an amount which depends on the test considered and increases with the severity of the stress gradient. Fracture mechanics has been applied to bend, internal pressure and diametral compression tests to investigate whether it can provide a consistent failure criterion

M. I. Darby

1976-01-01

208

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

NASA Technical Reports Server (NTRS)

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.

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

1994-01-01

209

Fatigue reliability-based assessment of welded joints applying consistent fracture mechanics formulations  

Microsoft Academic Search

Design of welded structures for fatigue limit state is normally carried out by means of either single- or two-sloped SN curves. To properly assess the effect of an inspection and repair strategy of structures degrading due to crack growth, fracture mechanics (FM) models need to be applied to describe crack propagation. To provide a proper tool for making decisions regarding

Efren Ayala-Uraga; Torgeir Moan

2007-01-01

210

The use of fracture mechanics in failure analysis in the offshore diamond mining industry  

Microsoft Academic Search

This paper considers two major failures of offshore diamond mining equipment, which should not have occurred had both fracture mechanics aspects and materials behaviour been more fully understood. The two case studies include (a) failure of a wire rope swivel, and (b) failure of a load cell (used for monitoring rope load). In case (a) the swivel shank had failed

R. B. Tait; C. Emslie

2005-01-01

211

A simple mechanical model to predict fracture and yield strengths of particulate two-phase materials  

Microsoft Academic Search

A simple mechanical model is developed and the following basic characteristics of fracture and yield strengths of particulate two-phase materials are predicted based on this model: (1) The rule of mixture can be approximately used in the particulate two-phase materials with fine particles; (2) For a material of a soft (hard) matrix with hard (soft) particles, the mixture law is

Zhonghua Li; S. Schmauder; M. Dong

1999-01-01

212

Enhanced fatigue endurance of metallic glasses through a staircase-like fracture mechanism  

E-print Network

Enhanced fatigue endurance of metallic glasses through a staircase-like fracture mechanism Bernd, 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

Ritchie, Robert

213

Fracture activity: A possible triggering mechanism for slope instabilities in the Eastern Atlantic?  

Microsoft Academic Search

The largest known submarine slope instabilities occur on gently inclined slopes or in the deep sea. The sedimentation rates are mostly too low to induce an excess pore-water pressure sufficient to create failure. A possible triggering mechanism for these instabilities is additional horizontal ground acceleration caused by earthquakes. Old zones of weakness, represented by fracture zones, can be reactivated by

Peter Holler

1986-01-01

214

Remaining life analysis for a pressure vessel subjected to cyclic loads based on fracture mechanics  

Microsoft Academic Search

Fracture mechanics has evolved into an engineering tool able to solve problems related to the safety of structures containing defects. In practice, however, a wide choice of parallel methods as well as unsolved discrepancies in the theory requires engineering judgement and pragmatism. In this paper a practical case study is presented, concerning a maintenance strategy assessment performed on a welded

G. Duvenhage; J. Wannenburg

1995-01-01

215

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

Microsoft Academic Search

In this review, some of the technical developments that have occurred during the past 40 years are presented which have led to the merger of fatigue and fracture mechanics concepts. This review is made from the viewpoint of “crack propagation”. As methods to observe the “fatigue” process have improved, the formation of fatigue micro-cracks have been observed earlier in life

J. Newmanjr

1998-01-01

216

Notch fatigue behaviour in cast irons explained using a fracture mechanics approach  

Microsoft Academic Search

Many aspects of the fatigue behaviour of cast iron materials are difficult to explain. For example, they display a very low notch sensitivity, and notched specimens are subject to a strong size effect. These effects can be explained if a fracture mechanics approach is adopted, which has two elements. First, the notch itself is modelled as a crack: this approach

D. Taylor; M. Hughes; D. Allen

1996-01-01

217

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

SciTech Connect

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.

Reinhold H. Dauskardt

2005-08-01

218

Fatigue behaviour and fracture mechanism of a 316 stainless steel hardened by carburizing  

Microsoft Academic Search

Fatigue behaviour and fracture mechanism of a carburized 316 stainless steel were studied under rotary bending in laboratory air and in 3% NaCl aqueous solution using materials with two different case depths. In laboratory air, the carburized materials showed considerably higher fatigue strength compared with the untreated material, and the fatigue lives of the material with thick case were longer

Keiro Tokaji; Kei Kohyama; Masayuki Akita

2004-01-01

219

Mechanisms of deformation localization at the tips of shear fractures: Findings from analogue experiments and field evidence  

Microsoft Academic Search

Using analogue experiments on polymethylmethaacrylate (PMMA) models, we investigated the process of deformation localization at the tips of preexisting planar shear cracks. Experiments show that this can take place in any of the following four principal mechanisms. Mechanism A: Brittle deformation is the dominant process and forms a pair of long tensile fractures at the crack tips. The tensile fractures

Santanu Misra; Nibir Mandal; Rajib Dhar; Chandan Chakraborty

2009-01-01

220

Identification of Fracture Toughness for Discrete Damage Mechanics Analysis of Glass-Epoxy Laminates  

NASA Astrophysics Data System (ADS)

A methodology for determination of the intralaminar fracture toughness is presented, based on fitting discrete damage mechanics (DDM) model predictions to available experimental data. DDM is constitutive model that, when incorporated into commercial finite element software via user material subroutines, is able to predict intralaminar transverse and shear damage initiation and evolution in terms of the fracture toughness of the composite. The applicability of the DDM model is studied by comparison to available experimental data for Glass-Epoxy laminates. Sensitivity of the DDM model to h- and p-refinement is studied. Also, the effect of in-situ correction of strength is highlighted.

Barbero, E. J.; Cosso, F. A.; Martinez, X.

2014-08-01

221

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

SciTech Connect

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

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

1984-07-01

222

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

Microsoft Academic Search

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

J. Toribio

223

Fracture toughness, adhesion and mechanical properties of low- K dielectric thin films measured by nanoindentation  

Microsoft Academic Search

The semiconductor industry is gradually moving from well-established Al\\/SiO2 technology to the new Cu\\/low-k interconnects, which brings a challenge in terms of poor thermal and\\/or mechanical properties of low-K dielectric films. Extensive nanoindentation studies have been undertaken on organo-silicate glass (OSG) low-K films to explore their mechanical and fracture properties. A cube corner indentation method was used to measure the

Alex A. Volinsky; Joseph B. Vella; William W. Gerberich

2003-01-01

224

Deformation and Fracture Mechanisms of Bone and Nacre  

NASA Astrophysics Data System (ADS)

Bone and nacre are the most-known biological hard tissues to materials researchers. Although highly mineralized, both bone and nacre are amazingly tough and exhibit remarkable inelasticity, properties that are still beyond the reach of many modern ceramic materials. Very interestingly, the two hard tissues seem to have adopted totally different structural strategies for achieving mechanical robustness. Starting from a true nanocomposite of the mineralized collagen fibril and following up to seven levels of hierarchical organization, bone is built on a structure with extreme complexity. In contrast, nacre possesses a structure of surprising simplicity. Polygonal mineral tablets of micrometer size are carefully cemented together into a macroscopic wonder. A comparative analysis of the structure-property relations in bone and nacre helps us to unveil the underlying mechanisms of this puzzling phenomenon. In this review, we critically compare the various levels of structures and their mechanical contributions between bone and nacre, with a focus on inelasticity and the toughening process. We demonstrate that, although nacre and bone differ from each other in many aspects, they have adopted very similar deformation and toughening mechanisms.

Wang, Rizhi; Gupta, Himadri S.

2011-08-01

225

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

SciTech Connect

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.

Derek Elsworth; Abraham Grader; Susan Brantley

2007-04-25

226

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

NASA Technical Reports Server (NTRS)

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).

Fu, L. S. W.

1982-01-01

227

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

228

Mechanics model for the multi-fracture processes in ceramic composites  

SciTech Connect

This article concerns the mechanical response of fiber reinforced ceramic composites. When these materials are subjected to tension parallel to the fiber direction they develop a multitude of internal cracks and fiber/matrix interfacial slips which induce three major kinds of energy absorption mechanisms within the otherwise brittle ceramic matrix. These mechanisms, namely matrix cracking, interfacial slipping and fiber breakage extend the ultimate strain of the composite and enable it to fail in a ductile-like manner. The present work provides a mechanics model to predict the multi-fracture response which occurs under the above circumstances.

Zhu, H. [Univ. of Tennessee, Knoxville, TN (United States); Weitsman, Y.J. [Univ. of Tennessee, Knoxville (United States); [Oak Ridge National Lab., TN (United States)

1993-12-31

229

Nontraumatic Fracture of the Femoral Condylar Prosthesis in a Total Knee Arthroplasty Leading to Mechanical Failure  

PubMed Central

This paper reports a case of fatigue fracture of the femoral component in a cruciate-retaining cemented total knee arthroplasty (TKA). A 64-year-old man had undergone a primary TKA for osteoarthritis 10 years previously at another institution using the PFC-Sigma prosthesis. The patient recovered fully and was back to his regular activities. He presented with a history of sudden onset pain and locking of the left knee since the preceding three months. There was no history of trauma, and the patient was mobilizing with difficulty using crutches. Radiographs revealed fracture of the posterior condyle of the femoral prosthesis. Revision surgery was performed as an elective procedure revealing the broken prosthesis. The TC3RP-PFC revision prosthesis was used with a medial parapatellar approach. The patient recovered fully without any squeal. Mechanical failure of the knee arthroplasty prosthesis is rare, and nontraumatic fracture of the femoral metallic component has not been reported before. PMID:24587928

Swamy, Girish N.; Quah, Conal; Bagouri, Elmunzar; Badhe, Nitin P.

2014-01-01

230

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

NASA Astrophysics Data System (ADS)

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.

Milenkovic, Srdjan; Caram, Rubens

2014-07-01

231

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

NASA Technical Reports Server (NTRS)

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.

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

2011-01-01

232

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

NASA Astrophysics Data System (ADS)

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

Newman, J. C.

1998-07-01

233

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

SciTech Connect

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

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

1997-12-31

234

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

NASA Technical Reports Server (NTRS)

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.

Newman, James C., Jr.

1997-01-01

235

A damage-mechanics model for fracture nucleation and propagation  

E-print Network

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.

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

2010-01-01

236

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

237

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

E-print Network

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...

Deng, Jiayao

2011-02-22

238

The mechanics of delamination in fiber-reinforced composite materials. II - The delamination behavior and fracture mechanics parameters  

NASA Technical Reports Server (NTRS)

Based on theories of laminate anisotropic elasticity and interlaminar fracture, the complete solution structure associated with a composite delamination is determined. Fracture mechanics parameters characterizing the interlaminar crack behavior are defined from asymptotic stress solutions for delaminations with different crack-tip deformation configurations. A numerical method employing singular finite elements is developed to study delaminations in fiber composites with any arbitrary combinations of lamination, material, geometric, and crack variables. The special finite elements include the exact delamination stress singularity in its formulation. The method is shown to be computationally accurate and efficient, and operationally simple. To illustrate the basic nature of composite delamination, solutions are shown for edge-delaminated (0/-0/-0/0) and (+ or - 0/+ or - 0/90/90 deg) graphite-epoxy systems under uniform axial extension. Three-dimensional crack-tip stress intensity factors, associated energy release rates, and delamination crack-closure are determined for each individual case. The basic mechanics and mechanisms of composite delamination are studied, and fundamental characteristics unique to recently proposed tests for interlaminar fracture toughness of fiber composite laminates are examined. Previously announced in STAR as N84-13222

Wang, S. S.; Choi, I.

1983-01-01

239

The mechanics of delamination in fiber-reinforced composite materials. Part 2: Delamination behavior and fracture mechanics parameters  

NASA Technical Reports Server (NTRS)

Based on theories of laminate anisotropic elasticity and interlaminar fracture, the complete solution structure associated with a composite delamination is determined. Fracture mechanics parameters characterizing the interlaminar crack behavior are defined from asymptotic stress solutions for delaminations with different crack-tip deformation configurations. A numerical method employing singular finite elements is developed to study delaminations in fiber composites with any arbitrary combinations of lamination, material, geometric, and crack variables. The special finite elements include the exact delamination stress singularity in its formulation. The method is shown to be computationally accurate and efficient, and operationally simple. To illustrate the basic nature of composite delamination, solutions are shown for edge-delaminated (0/-0/-0/0) and (+ or - 0/+ or - 0/90/90 deg) graphite-epoxy systems under uniform axial extenstion. Three-dimensional crack-tip stress intensity factors, associated energy release rates, and delamination crack-closure are determined for each individual case. The basic mechanics and mechanisms of composite delamination are studied, and fundamental characteristics unique to recently proposed tests for interlaminar fracture toughness of fiber composite laminates are examined.

Wang, S. S.; Choi, I.

1983-01-01

240

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

NASA Technical Reports Server (NTRS)

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.

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

2010-01-01

241

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

SciTech Connect

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.

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

2007-05-31

242

Fracture characterization of C\\/C composites under various stress modes by monitoring both mechanical and acoustic responses  

Microsoft Academic Search

C\\/C composites with different porosities, produced by chemical vapor infiltration have been mechanically tested under quasi-static loading in bending modes using uniform and notched specimens. The acoustic emission (AE) method was used to monitor the damage accumulation profile during loading up to fracture, supported by optical and scanning electron microscope characterization. Three stages in the damage buildup up to fracture

A. Bussiba; M. Kupiec; R. Piat; T. Böhlke

2008-01-01

243

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

Microsoft Academic Search

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

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

1989-01-01

244

Mechanisms of hydrogen-assisted fracture in austenitic stainless steel welds.  

SciTech Connect

The objective of this study was to quantify the hydrogen-assisted fracture susceptibility of gas-tungsten arc (GTA) welds in the nitrogen-strengthened, austenitic stainless steels 21Cr-6Ni-9Mn (21-6-9) and 22Cr-13Ni-5Mn (22-13-5). In addition, mechanisms of hydrogen-assisted fracture in the welds were identified using electron microscopy and finite-element modeling. Elastic-plastic fracture mechanics experiments were conducted on hydrogen-charged GTA welds at 25 C. Results showed that hydrogen dramatically lowered the fracture toughness from 412 kJ/m{sup 2} to 57 kJ/m{sup 2} in 21-6-9 welds and from 91 kJ/m{sup 2} to 26 kJ/m{sup 2} in 22-13-5 welds. Microscopy results suggested that hydrogen served two roles in the fracture of welds: it promoted the nucleation of microcracks along the dendritic structure and accelerated the link-up of microcracks by facilitating localized deformation. A continuum finite-element model was formulated to test the notion that hydrogen could facilitate localized deformation in the ligament between microcracks. On the assumption that hydrogen decreased local flow stress in accordance with the hydrogen-enhanced dislocation mobility argument, the finite-element results showed that deformation was localized in a narrow band between two parallel, overlapping microcracks. In contrast, in the absence of hydrogen, the finite-element results showed that deformation between microcracks was more uniformly distributed.

Balch, Dorian K.; Sofronis, Petros (University of Illinois, Urbana, IL); Somerday, Brian P.; Novak, Paul (University of Illinois, Urbana, IL)

2005-03-01

245

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

Microsoft Academic Search

The mechanical and fracture properties of austenitic stainless steels (SSs) alloyed with gallium require assessment in order\\u000a to determine the likelihood of premature storage-container failure following Ga uptake. AISI 304 L SS was cast with 1, 3,\\u000a 6, 9, and 12 wt pct Ga. Increased Ga concentration promoted duplex microstructure formation with the ferritic phase having\\u000a a nearly identical composition

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

2004-01-01

246

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

Microsoft Academic Search

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

J. K. Jethwa; A. J. Kinloch

1997-01-01

247

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

Microsoft Academic Search

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

Huajian Gao

2006-01-01

248

Functionality of a Novel Percutaneous Aortic Valve Stent – A Fracture Mechanics Study  

Microsoft Academic Search

\\u000a To design against mechanical failure, most implants such as valve stents are assessed on the basis of survival on a long term.\\u000a However, accurate investigation of the stress\\/ strain distributions in such valve stents, which govern their deformation and\\u000a fracture behavior, is essential for their prolonged, and safe use. Nitinol, a shape-memory alloy, can “remember” a previous\\u000a shape and can

Gideon Praveen Kumar; Lazar Mathew

249

Fracture toughness testing and toughening mechanisms of some commercial cobalt-free hardfacing alloys  

SciTech Connect

Hardfacing alloys are weld deposited to provide a wear resistant surface for structural base materials. Commercial low cobalt hardfacing alloys are being evaluated to reduce plant activation levels. Since hardfacing alloys typically must be resistant to cracking to assure adequate in service performance, fracture toughness is a critical material property. Fracture toughness (K{sub IC}) measurements of Fe base, Ni-base, and Co-base hardfacing were performed in accordance with ASTM E399-90 procedure in an effort to identify a tough cobalt-free alternative. Reduced scatter in K{sub IC} data was observed for the Fe base hardfacing, and the 95% lower bound K{sub IC} values were generally higher than the Ni-base Hardfacing alloys. Preliminary crack growth data obtained during precracking indicate that the Ni-base hardfacing possess better fatigue crack growth resistance. However, none of the Fe-base or Ni-base hardfacing have K{sub IC} values that are comparable to the reference Co-base hard facing. The test specimens were machined from thick (0.5 inches) weld deposits, and the microstructures of the test specimens are compared with the more prototypic, thinner deposits. Microstructural and fractographic examinations are used to characterize the fracture mechanisms and delineate the operative toughening mechanisms. Crack deflection and crack bridging toughening mechanisms are shown to be relevant for most of the commercial hardfacing.

Cockeram, B.V.

1998-04-27

250

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

PubMed

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

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

2014-10-31

251

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

NASA Astrophysics Data System (ADS)

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.

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

252

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

SciTech Connect

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.

Kida, Sotoaki; Suzuki, Megumu [Kanazawa Inst. of Tech., Ishikawa (Japan). Dept. of Mechanical Engineering

1995-11-01

253

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

E-print Network

Fluid flow mechanisms in a large naturally fractured heterogeneous carbonate reservoir were investigated in this manuscript. A very thin layer with high permeability that produces the majority of production from specific wells and is deemed...

Abu-Hassoun, Amer H.

2009-05-15

254

Linear elastic fracture mechanics predicts the propagation distance of frictional slip  

E-print Network

When a frictional interface is subject to a localized shear load, it is often (experimentally) observed that local slip events initiate at the stress concentration and propagate over parts of the interface by arresting naturally before reaching the edge. We develop a theoretical model based on linear elastic fracture mechanics to describe the propagation of such precursory slip. The model's prediction of precursor lengths as a function of external load is in good quantitative agreement with laboratory experiments as well as with dynamic simulations, and provides thereby evidence to recognize frictional slip as a fracture phenomenon. We show that predicted precursor lengths depend, within given uncertainty ranges, mainly on the kinetic friction coefficient, and only weakly on other interface and material parameters. By simplifying the fracture mechanics model we also reveal sources for the observed non-linearity in the growth of precursor lengths as a function of the applied force. The discrete nature of precursors as well as the shear tractions caused by frustrated Poisson's expansion are found to be the dominant factors. Finally, we apply our model to a different, symmetric set-up and provide a prediction of the propagation distance of frictional slip for future experiments.

David S. Kammer; Mathilde Radiguet; Jean-Paul Ampuero; Jean-François Molinari

2014-08-18

255

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

PubMed

The fracture resistance (R-curve behaviour) of two commercial dental composites (Filtek Z350(®) and Concept Advanced(®)) were studied using Double Cantilever Beam sandwich specimens loaded with pure bending moments to obtain stable crack growth. The experiments were conducted in an environmental scanning electron microscope to (a) accurately measure the applied energy-release rate for crack initiation, (b) measure the early (rising) part of the R-curve, and (c) provide direct microscopic evidence of the toughening mechanisms ahead of and/or in the wake of the crack tip. The two tested composites displayed distinctly different R-curve behaviours. The difference was related to different toughening mechanisms as the two composites had markedly different microstructures. Contrary to common experience, the composite with the finer microstructure (smaller particles), the Concept Advanced(®), showed significantly higher fracture resistance than the composite with the coarser microstructure. The fracture properties were related to the flexural strength of the dental composites. The method, thus, can provide useful insight into how the microstructure enhances toughness, which is necessary for the future development of such materials. PMID:21396605

De Souza, J A; Goutianos, S; Skovgaard, M; Sørensen, B F

2011-05-01

256

Transformation of creep stresses in ice shelves for fracture mechanical analyses  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

257

The Relationship Between DP, Fracture Degree and Mechanical Strength of Cellulose I? in Insulation Paper by Molecular Dynamic Simulations  

NASA Astrophysics Data System (ADS)

The degree of polymerization (DP) has been regarded as an important symbol of mechanical strength, reflecting the aging condition of transformer insulation paper. In this article, a new concept called fracture degree is proposed on the basis of DP. First, nine cellulose I? crystal models with different fracture degrees were built. Then relevant mechanical parameters and hydrogen bond numbers were calculated by molecular dynamics (MD) simulation. Results showed that during the aging process of insulation paper with fracture of cellulose chain, the elastic constant C33 produces appreciable impact on the Young's modulus (E). With the decrease of DP and increase of fracture degree, the Young's modulus step decreases. To the 50% and 100% fracture degree models respectively, the relationship between their different degrees of polymerization and Young's modulus is subjected to similar exponential distributions. With the increase of the fracture degree, the average hydrogen bond number drops, and the change rules apply to the Young's modulus. Since hydrogen bond is the main factor of mechanical strength, it can be inferred that the fracture degree influences mechanical strength seriously.

Wang, You-Yuan; Yang, Tao; Tian, Miao; Liao, Rui-Jin

2013-09-01

258

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

SciTech Connect

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.

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

2012-01-01

259

Study on Shear Fatigue Fracture and Delamination Mechanism of Thermal Barrier Coatings After Thermal Loading  

NASA Astrophysics Data System (ADS)

In this study, it is investigated experimentally and analytically that fracture process and fatigue behavior of Thermal Barrier Coatings (TBCs) used in a high temperature component in a land based gas turbine. The effects of the thermal load on TBCs are investigated by measuring residual stress of top coat, finite element method and torsion test. It is found that delamination of top coat under thermal load occurs at a peak of undulation in top coat and bond coat interface. Around the peak, a tearing stress is generated. Fracture and fatigue tests under torsion are carried out by using cylindrical butted specimens. It is found that the mechanical property of bond coat changes after thermal aging and the shear fatigue behavior of TBCs is affected by bond coat strength.

Kaneko, Kenji; Takatou, Satoshi; Enomoto, Kazuki

260

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

NASA Technical Reports Server (NTRS)

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.

Forman, R. G.

1985-01-01

261

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

E-print Network

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.

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

2014-01-01

262

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

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

263

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

SciTech Connect

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.

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

2011-01-01

264

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Dynamic Response and Fracture Mechanism of a Novel Structural Radar Absorbing Material  

NASA Astrophysics Data System (ADS)

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

Cao, Mao-Sheng; Zhou, Wei; Qu, Gui-Min; Rong, Ji-Li

2008-08-01

265

Anomalous surface states modify the size-dependent mechanical properties and fracture of silica nanowires.  

PubMed

Molecular dynamics simulations of amorphous silica nanowires under tension were analyzed for size and surface stress effects on mechanical properties and for structural modifications via bond angle distributions. Their fracture behavior was also investigated beyond the elastic limit. The Young's moduli of silica nanowires were predicted to be about 75-100 GPa, depending on the nanowire size. The ultimate strength was calculated to be ?10 GPa, depending on the diameter, which is in excellent agreement with the experiments. The dependence of the Young's modulus on nanowire diameter is explained in terms of surface compressive stress effects. The fracture behavior of nanowires was also found to be influenced by surface compressive stresses. Bond angle distribution analysis of various nanowires reveals significant compressive surface states, as evidenced by the appearance of a secondary peak in the Si-O-Si bond angle distribution at ?97°, which is absent in bulk silica. The strain rate was found to have a negligible effect on the Young's modulus of the silica nanowires, but it has a critical role in determining their fracture mode. PMID:25298024

Tang, Chun; Dávila, Lilian P

2014-10-31

266

Anomalous surface states modify the size-dependent mechanical properties and fracture of silica nanowires  

NASA Astrophysics Data System (ADS)

Molecular dynamics simulations of amorphous silica nanowires under tension were analyzed for size and surface stress effects on mechanical properties and for structural modifications via bond angle distributions. Their fracture behavior was also investigated beyond the elastic limit. The Young’s moduli of silica nanowires were predicted to be about 75–100 GPa, depending on the nanowire size. The ultimate strength was calculated to be ?10 GPa, depending on the diameter, which is in excellent agreement with the experiments. The dependence of the Young’s modulus on nanowire diameter is explained in terms of surface compressive stress effects. The fracture behavior of nanowires was also found to be influenced by surface compressive stresses. Bond angle distribution analysis of various nanowires reveals significant compressive surface states, as evidenced by the appearance of a secondary peak in the Si-O-Si bond angle distribution at ?97°, which is absent in bulk silica. The strain rate was found to have a negligible effect on the Young’s modulus of the silica nanowires, but it has a critical role in determining their fracture mode.

Tang, Chun; Dávila, Lilian P.

2014-10-01

267

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

PubMed

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

Daxini, S D; Prajapati, J M

2014-01-01

268

A fracture mechanics study of stress corrosion cracking of type-316 austenitic steel  

Microsoft Academic Search

A new test specimen configuration, designated the T-notch double cantilever beam (TNDCB), was developed, calibrated and employed\\u000a for a fracture mechanics study of stress corrosion cracking (SCC) of cold worked Type-316 austenitic stainless steel exposed\\u000a to hot aqueous solutions of 44.7 wt pct MgCl2. The effects of stress intensity (K\\u000a \\u000a I\\u000a ), temperature (T) and electrochemical potential (E) upon the

Alan J. Russell; Desmond Tromans

1979-01-01

269

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

NASA Technical Reports Server (NTRS)

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.

Hardrath, H. F.

1974-01-01

270

Use of holographic optical elements in speckle metrology. Part 3: application to fracture mechanics.  

PubMed

In this work a two-hololens imaging system has been used to measure crack-mouth opening displacement and crack-tip opening displacement to determine the stress intensity factor K(1), the crack-tip plastic zone size r(p)(*) and the rotational factor r in a beam specimen having the central edge crack subjected to three-point bending using focused plane speckle photography. Experimental results are in good agreement with theoretical predictions. Current experimental investigations establish that low-cost holographic optics can be advantageously used in speckle metrology to solve complex problems of fracture mechanics. PMID:20706433

Shakher, C; Yadav, H L

1991-09-01

271

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

NASA Astrophysics Data System (ADS)

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

Ameli, Pasha

272

Simulation of the behavior of the cutting force during ultrasonic rotary machining of materials using structure-time fracture mechanics  

NASA Astrophysics Data System (ADS)

An analytical model is developed for the behavior of the cutting force during ultrasonic rotary polishing, and it is based on the concepts of dynamic fracture mechanics and the solution to the problem of impact surface fracture. The dependence of the threshold fracture energy obtained in the problem of erosion using a structure-time approach is used to construct the cutting force model. The dependences of the cutting force on the material feed rate and the rate of tool rotation are obtained, and the developed model is shown to be efficient to explain the effects observed in experiments.

Gorbushin, N. A.; Volkov, G. A.; Petrov, Yu. V.

2014-06-01

273

Fracture of hard thin films using nanoindentation and nanoscratch techniques: A materials and mechanics approach  

SciTech Connect

Thin films are used in many applications where special properties are needed to insure performance and reliability. Of particular interest are thin tantalum nitride films. They are used extensively in microelectronic applications because of their long term stability and low thermal coefficient of resistance. They are sputter deposited which produces films with a high structural defect content and high compressive residual stresses both of which can alter the physical and mechanical properties of microelectronic thin films. Although these films are strong heat generators, they exhibit no changes in structure or composition of the interface with aluminum oxide substrates that degrade performance or reliability. However, the use of high power density components is driving a move to replace aluminum oxide with aluminum nitride for greater heat transfer. 6 This replacement substrate creates concern as residual stresses and long-term operation could induce detrimental changes along the thin film interface not observed in aluminum oxide devices. As a result, the authors employed nanoindentation and continuous nanoscratch testing to determine the effects of the intrinsic compressive residual stresses on the properties and fracture resistance of the thin tantalum nitride films. These techniques sample small volumes of material while preserving the production configuration of a free surface. Although nanoscratch tests lack a rigorous derivation of stress distributions and strain energy release rates, good approximations for strain energy release rates can be obtained using mechanics-based models for blister formation where residual stresses dominate interfacial fracture behavior. When combined with scanning and transmission electron microscopy, the results define structure-property relationships and resistance to fracture of these hard films.

Moody, N.R.; Medlin, D.; Hwang, R.Q.; Boehme, D. [Sandia National Labs., Livermore, CA (United States); Venkataraman, S. [Applied Materials, Santa Clara, CA (United States); Gerberich, W.W. [Univ. of Minnesota, Minneapolis, MN (United States)

1998-03-19

274

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

SciTech Connect

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.

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

1982-06-01

275

Standard guide for evaluating data acquisition systems used in cyclic fatigue and fracture mechanics testing  

E-print Network

1.1 This guide covers how to understand and minimize the errors associated with data acquisition in fatigue and fracture mechanics testing equipment. This guide is not intended to be used instead of certified traceable calibration or verification of data acquisition systems when such certification is required. It does not cover static load verification, for which the user is referred to the current revision of Practices E 4, or static extensometer verification, for which the user is referred to the current revision of Practice E 83. The user is also referred to Practice E 467. 1.2 The output of the fatigue and fracture mechanics data acquisition systems described in this guide is essentially a stream of digital data. Such digital data may be considered to be divided into two types- Basic Data, which are a sequence of digital samples of an equivalent analog waveform representing the output of transducers connected to the specimen under test, and Derived Data, which are digital values obtained from the Basic D...

American Society for Testing and Materials. Philadelphia

1998-01-01

276

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

SciTech Connect

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.

Smith, J.A.; Salzbrenner, D.; Sorenson, K.; McConnell, P.

1998-04-01

277

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

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

278

Lakes, R. S., Nakamura, S., Behiri, J. C. and Bonfield, W., "Fracture mechanics of bone with short cracks", Journal of Biomechanics, 23, 967-975 (1990).  

E-print Network

1 Lakes, R. S., Nakamura, S., Behiri, J. C. and Bonfield, W., "Fracture mechanics of bone prior to failure. Studies of fracture toughness in bone have been performed by Bonfield and Datta (1976 investigation, fracture experiments have been performed on bone specimens with short, controlled notches

Lakes, Roderic

279

Early detection of delayed union in lower leg fractures using a computerised analysis of mechanical vibration reactions of bone for assessing the state of fracture healing.  

PubMed

Standard X-ray techniques are used to follow up the healing process of bone fractures. However, these methods allow only indirect conclusions about the stability of the healing bone, depending on the experience of the clinician. In addition, by radiologic means, delayed union or non-union can only be diagnosed on the basis of the absence of specific changes such as callus formation. Therefore, efforts have been made to develop alternative methods for monitoring the healing process. The measuring principle of a non-invasive method is based on evaluation of changes in mechanical vibration reactions. The measuring system is composed of two sound transducers, an amplifier module and an AD converter attached to a PC. The assessment of 150 healthy individuals as well as an initial measuring series after treatment of tibial fractures with an external fixator system revealed highly significant differences between intact and fractured tibias. Thus, computerised sonometry is capable of supplying quantitatively recordable information about the stability of a fractured bone at any time in the healing process. Furthermore, this non-invasive technique allows early diagnosis of disorders in the repair process by the absence of change in the parameters. PMID:8186056

Fellinger, M; Leitgeb, N; Szyszkowitz, R; Peicha, G; Passler, J; Seggl, W; Schanner, A

1994-01-01

280

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

281

Analysis of mechanical strength to fixing the femoral neck fracture in synthetic bone type Asnis  

PubMed Central

OBJECTIVE: To analyze the results of biomechanical assays of fixation of Pauwels type III femoral neck fracture in synthetic bone, using 7.5mm cannulated screws in inverted triangle formation, in relation to the control group. METHODS: Ten synthetic bones were used, from a domestic brand, divided into two groups: test and control. In the test group, a 70° tilt osteotomy of the femoral neck was fixated using three cannulated screws in inverted triangle formation. The resistance of this fixation and its rotational deviation were analyzed at 5mm displacement (phase 1) and 10mm displacement (phase 2). The control group was tested in its integrity until the fracture of the femoral neck occurred. The Mann-Whitney test was used for group analysis and comparison. RESULTS: The values in the test group in phase 1, in samples 1-5, showed a mean of 579N and SD =77N. Rotational deviations showed a mean of 3.33°, SD = 2.63°. In phase 2, the mean was 696N and SD =106N. The values of the maximum load in the control group had a mean of 1329N and SD=177N. CONCLUSION: The analysis of mechanical strength between the groups determined a statistically significant lower value in the test group. Level of Evidence III, Control Case.

Freitas, Anderson; Lula, Welder Fernandes; de Oliveira, Jonathan Sampaio; Maciel, Rafael Almeida; Souto, Diogo Ranier de Macedo; Godinho, Patrick Fernandes

2014-01-01

282

Influences of process parameters and microstructure on the fracture mechanisms of ODS steels  

NASA Astrophysics Data System (ADS)

The present work investigates the impact response of three ODS steels containing 9%Cr and 14%Cr. These steels were produced by hot extrusion in the shapes of a rod and a plate. The 9%Cr ODS steel has a quasi-isotropic microstructure and is given as a reference material. In comparison, the 14%Cr ODS steel has a strong morphological and crystallographic texture given by the process route. The impact behaviour is anisotropic and the fracture energies are higher when the material is tested in the longitudinal direction compared to the transverse direction. Moreover, the 14%Cr ODS steel has a better impact behaviour when it is extruded in the shape of a rod rather than in the shape of a plate. This work focuses on the fracture mechanisms involved in the ductile to brittle transition regime and in the brittle regime of these materials. In the case of the 14%Cr ODS steel, the cleavage facets observed at very low temperature are much larger than the actual size of the grains. Packets of grains with less than 15° of internal misorientation were defined as effective grains for cleavage. In the transition range, the texture enhances intergranular delamination on the 14%Cr rod material. The occurrence of delamination consumes a lot of energy and tends to enhance scattering in impact energies.

Rouffié, A. L.; Wident, P.; Ziolek, L.; Delabrouille, F.; Tanguy, B.; Crépin, J.; Pineau, A.; Garat, V.; Fournier, B.

2013-02-01

283

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

SciTech Connect

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.

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

1998-12-31

284

Stability-based classification for ankle fracture management and the syndesmosis injury in ankle fractures due to a supination external rotation mechanism of injury.  

PubMed

The aim of this thesis was to confirm the utility of stability-based ankle fracture classification in choosing between non-operative and operative treatment of ankle fractures, to determine how many ankle fractures are amenable to non-operative treatment, to assess the roles of the exploration and anatomical repair of the AITFL in the outcome of patients with SER ankle fractures, to establish the sensitivities, specificities and interobserver reliabilities of the hook and intraoperative stress tests for diagnosing syndesmosis instability in SER ankle fractures, and to determine whether transfixation of unstable syndesmosis is necessary in SER ankle fractures. The utility of stability based fracture classification to choose between non-operative and operative treatment was assessed in a retrospective study (1) of 253 ankle fractures in skeletally mature patients, 160 of whom were included in the study to obtain an epidemiological profile in a population of 130,000. Outcome was assessed after a minimum follow-up of two years. The role of AITFL repairs was assessed in a retrospective study (2) of 288 patients with Lauge-Hansen SE4 ankle fractures; the AITFL was explored and repaired in one group (n=165), and a similar operative method was used but the AITFL was not explored in another group (n=123). Outcome was measured with a minimum follow-up of two years. Interobserver reliability of clinical syndesomosis tests (study 3) and the role of syndesmosis transfixation (study 4) were assessed in a prospective study of 140 patients with Lauge-Hansen SE4 ankle fractures. The stability of the distal tibiofibular joint was evaluated by the hook and ER stress tests. Clinical tests were carried out by the main surgeon and assistant, separately, after which a 7.5-Nm standardized ER stress test for both ankles was performed; if it was positive, the patient was randomized to either syndesmosis transfixation (13 patients) or no fixation (11 patients) treatment groups. The sensitivity and specificity of both clinical tests were calculated using the standard 7.5-Nm external rotation stress test as reference. Outcome was assessed after a minimum of one year of follow-up. Olerud-Molander (OM) scoring system, RAND 36-Item Health Survey, and VAS to measure pain and function were used as outcome measures in all studies. In study 1, 85 (53%) fractures were treated operatively using the stability based fracture classification. Non-operatively treated patients reported less pain and better OM (good or excellent 89% vs. 71%) and VAS functional scores compared to operatively treated patients although they experienced more displacement of the distal fibula (0 mm 30% vs. 69%; 0-2 mm 65% vs. 25%) after treatment. No non-operatively treated patients required operative fracture fixation during follow-up. In study 2, AITFL exploration and suture lead to equal functional outcome (OM mean, 77 vs. 73) to no exploration or fixation. In study 3, the hook test had a sensitivity of 0.25 and a specificity of 0.98. The external rotation stress test had a sensitivity of 0.58 and a specificity of 0.9. Both tests had excellent interobserver reliability; the agreement was 99% for the hook test and 98% for the stress test. There was no statistically significant difference in functional scores (OM mean, 79.6 vs. 83.6) or pain between syndesmosis transfixation and no fixation groups (Study 4). Our results suggest that a simple stability-based fracture classification is useful in choosing between non-operative and operative treatment of ankle fractures; approximately half of the ankle fractures can be treated non-operatively with success. Our observations also suggest that relevant syndesmosis injuries are rare in ankle fractures due to an SER mechanism of injury. According to our research, syndesmotic repair or fixation in SER ankle fracture has no influence on functional outcome or pain after minimum one year compared with no fixation. PMID:23205893

Pakarinen, Harri

2012-12-01

285

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)

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.

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

2012-12-01

286

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)

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.

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

2013-04-01

287

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

E-print Network

stress at the fracture surface and shear failure around the main fracture. Finally, a hybrid BEFEM model is developed to analyze stress redistribution in the overburden and within the reservoir during fluid injection and production. Numerical results show...

Rawal, Chakra

2012-07-16

288

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

NASA Technical Reports Server (NTRS)

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.

Herring, H. W.

1971-01-01

289

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

E-print Network

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

Peirce, Anthony

290

Fracture of glass bead\\/epoxy composites: on micro-mechanical deformations  

Microsoft Academic Search

To understand the fracture behavior of inorganic particle filled polymers, glass bead filled epoxies having different glass bead contents and sizes were prepared as model systems. Although their macroscopic fracture behavior was brittle, diffuse matrix shear yielding and micro-shear banding were found to occur around crack paths. Besides these plastic deformations, debonding of glass beads, step formation on fracture surface,

J. Lee; A. F. Yee

2000-01-01

291

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

NASA Technical Reports Server (NTRS)

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.

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

2003-01-01

292

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

NASA Technical Reports Server (NTRS)

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

Poe, C. C., Jr.

1985-01-01

293

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

NASA Technical Reports Server (NTRS)

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.

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

1976-01-01

294

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

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

295

Integrated nondestructive evaluation, materials, and fracture mechanics approach to life extension of steam turbine rotors  

NASA Astrophysics Data System (ADS)

The aging hollow forged steel rotors of steam turbine and generator units typical to utility power plants are a major area of concern for the future safety and integrity of the overall power plant. These components are also critical in determining future inspection intervals for the turbine unit and its remaining life. Over the past five years a number of lifetime extension projects have been conducted using an integrated nondestructive evaluation (NDE), materials and fracture mechanics approach to determining inspection intervals and remaining life. These projects have resulted in extending inspection intervals, predicting remaining life, and restoring original equipment manufacturer (OEM) retired rotors to operation. Key aspects of the integrated program will be covered using the results of a recently completed project.

Leon-Salamanca, Teodoro; Reinhart, Eugene R.

1998-03-01

296

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

SciTech Connect

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.

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

2011-01-01

297

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

USGS Publications Warehouse

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.

Pollard, D.D.; Holzhausen, G.

1979-01-01

298

Dynamic tensile response of Zr-based bulk amorphous alloys: Fracture morphologies and mechanisms  

NASA Astrophysics Data System (ADS)

Plate impact experiments were conducted to examine the dynamic tensile response of Zr-based bulk amorphous alloys (BAAs) having a nominal composition of Zr56.7Cu15.3Ni12.5Nb5.0Al10.0Y0.5. The experimental configuration used in our work permitted soft recovery of the samples to allow a careful examination of the fractured samples along with real-time measurements of the sample free-surface velocity (FSV) histories. Tensile loading was preceded by elastic compressive loading to peak stresses in the 3.6 to 6.0 GPa range. Tensile damage in the recovered samples was examined using optical and electron microscopy. The microscopy results showed that the BAA samples exhibit a brittle behavior (as a glass) at the macroscopic level and a ductile behavior (as a metal) at the microscopic level; in addition, corrugations and bumps are observed at the nanoscale. The observed fracture morphologies are related to three key features present in our spall experiments: preceding compressive stress (3.6-6.0 GPa), high tensile loading rate (˜106/s), high mean tensile stress (˜2.3 GPa); and are intrinsically related to the amorphous glassy structure of the BAAs (free volume content). We propose that the compressive stress depletes the free volume content. With increasing compressive stress, the available free volume decreases causing a suppression of shear stresses during tension. Thus, the mean tensile component becomes more dominant at higher stresses. Consequently, the observed surface morphology results from brittle cleavage, causing an increased damage localization in the recovered samples spalled at higher stresses. These observations support the inferences made from measurements of FSV histories. The high tensile loading rate is proposed to be responsible for cracking by multiple shear band propagation and interception, rendering the observed serrated surface morphology. Finally, we proposed that the corrugations are created due to a succession of arrest and propagation of mode I cracks. A subsequent dilatation, due to the effect of the tensile mean stress, caused the corrugations to evolve to bump-type features with sizes in the range of 10-100 nm. Our proposed mechanisms, although qualitative, constitute a systematic attempt to provide an explanation for the fracture morphologies observed in spalled BAA samples.

Escobedo, J. P.; Gupta, Y. M.

2010-06-01

299

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

Microsoft Academic Search

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

Karun Mehta; Anil V. Virkar

1990-01-01

300

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

NASA Technical Reports Server (NTRS)

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.

Gangloff, Richard P.; Kim, Sang-Shik

1993-01-01

301

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

PubMed

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

Hohenwarter, A; Pippan, R

2013-05-01

302

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

NASA Astrophysics Data System (ADS)

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.

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

2014-12-01

303

Modeling Fractures in Thermal Systems: Thermal-Mechanical Feedback and Vein Formation  

NSDL National Science Digital Library

Barb Dutrow, Department of Geology & Geophysics, Louisiana State University Topic: Mineralogy, Petrology, fracture formation Course type: Upper level undergraduate course Description In many geologic systems, ...

304

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

NASA Astrophysics Data System (ADS)

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

Sommer, Silke

2010-06-01

305

Mechanical Properties and Fracture Behavior of Electroless Ni-Plated Short Carbon Fiber Reinforced Geopolymer Matrix Composites  

NASA Astrophysics Data System (ADS)

Electroless Ni-plated short carbon fiber reinforced geopolymer matrix composites with various carbon fiber/matrix interface coating thicknesses have been successfully fabricated. The influences of coating thickness on the mechanical properties and fracture behavior have been investigated by three-point bending test and scanning electron microscopy. The flexural strength and Young's modulus of Ni-plated short carbon fiber reinforced geopolymer composites exhibit maximums as the average fiber coating thickness increases, but the work of fracture has a sharp decrease, and the fracture manner changes from ductile to brittle. This is mainly attributed to the fact that the carbon fibers favor breakage rather than pulling-out during loading because of the higher interface bonding strength of fiber/matrix, and pliability of the carbon fibers decreases with the increase of the coating thickness.

Lin, Tiesong; Jia, Dechang

306

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

NASA Astrophysics Data System (ADS)

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.

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

2008-06-01

307

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

PubMed

Fall from height is a common cause of unintentional injuries in children and accounts for 6% of all trauma-related childhood deaths, usually from head injury. We report a case of a 2-year-old child with multiple fractures of the bilateral lower limbs due to this reason. A child fell from a height of around 15 feet after toppling from a balcony. He developed multiple fractures involving the right femoral shaft, right distal femoral epiphysis (Salter Harris type 2), right distal metaphysis of the tibia and fibula, and undisplaced Salter Harris type 2 epiphyseal injury of the left distal tibia. There were no head, abdominal or spinal injuries. The patient was taken into emergency operation theatre after initial management which consisted of intravenous fluids, blood transfusion, and splintage of both lower limbs. Fracture of the femoral shaft was treated by closed reduction and fixation using two titanium elastic nails. Distal femoral physeal injury required open reduction and fixation with K wires. Distal tibia fractures were closely reduced and managed nonoperatively in both the lower limbs. All the fractures united in four weeks. At the last follow-up, the child had no disability and was able to perform daily activities comfortably. We also proposed the unique mechanism of injury in this report. PMID:25293902

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

2014-10-01

308

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

SciTech Connect

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

Wibowo, J.; Amadei, B.; Sture, S. [Univ. of Colorado, Boulder, CO (United States)] [and others

1995-08-01

309

Fracture Mechanics Analysis of Cracked Discs of Anisotropic Rock Using the  

E-print Network

(SIFs) and the fracture toughness of anisotropic rocks from the results of diametral compression tests compression (Brazilian test) of discs of rock. It is shown how a new formulation of the Boundary Element with the determi- nation of the deformability, tensile strength and fracturing of anisotropic rocks by diametral

Pan, Ernie

310

A mechanism for the production of electromagnetic radiation during fracture of brittle materials  

Microsoft Academic Search

The feasibility of the charge separation model as the source of electromagnetic radiation received from the fracture of brittle materials is demonstrated. An analytical expression and a finite difference method enable the calculation of currents flowing around the tip of a crack. Results from the model compare favourably with fracture events recorded from ice samples. Changes in material conductivity affect

Steven G. O'Keefe; David V. Thiel

1995-01-01

311

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

E-print Network

Hydromechanical interactions in a fractured carbonate reservoir inferred from hydraulic, France Abstract Hydromechanical coupled processes in a shallow fractured carbonate reservoir rock were of hydraulic loading/unloading of a water reservoir in which fluid flow occurs mainly inside a heterogeneous

Paris-Sud XI, Université de

312

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

NASA Technical Reports Server (NTRS)

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,

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

2007-01-01

313

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

NASA Technical Reports Server (NTRS)

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.

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

2010-01-01

314

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

NASA Technical Reports Server (NTRS)

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.

Curbishley, G.

1975-01-01

315

Proximal femoral fractures.  

PubMed

Fractures of the proximal femur include fractures of the head, neck, intertrochanteric, and subtrochanteric regions. Head fractures commonly accompany dislocations. Neck fractures and intertrochanteric fractures occur with greatest frequency in elderly patients with a low bone mineral density and are produced by low-energy mechanisms. Subtrochanteric fractures occur in a predominantly strong cortical osseous region which is exposed to large compressive stresses. Implants used to address these fractures must be able to accommodate significant loads while the fractures consolidate. Complications secondary to these injuries produce significant morbidity and include infection, nonunion, malunion, decubitus ulcers, fat emboli, deep venous thrombosis, pulmonary embolus, pneumonia, myocardial infarction, stroke, and death. PMID:12597064

Webb, Lawrence X

2002-01-01

316

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

NASA Astrophysics Data System (ADS)

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

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

317

Mechanisms for fracture and fatigue-crack propagation in a bulk metallic glass  

Microsoft Academic Search

The fracture and fatigue properties of a newly developed bulk metallic glass alloy, Zr41.2Ti13.8Cu12.5 Ni10Be22.5 (at. pct), have been examined. Experimental measurements using conventional fatigue precracked compact-tension C(T) specimens\\u000a (?7-mm thick) indicated that the fully amorphous alloy has a plane-strain fracture toughness comparable to polycrystalline\\u000a aluminum alloys. However, significant variability was observed and possible sources are identified. The fracture surfaces

C. J. Gilbert; V. Schroeder; R. O. Ritchie

1999-01-01

318

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

NASA Technical Reports Server (NTRS)

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.

Ko, William L.

1989-01-01

319

A case of fracture of posterior margin of lateral tibial plateau by pivot shift mechanism in chronic ACL insufficiency  

Microsoft Academic Search

We present a case of the fracture of the posterior margin of the lateral tibial plateau, probably by pivot shift mechanism\\u000a in a chronic anterior cruciate ligament (ACL) insufficient knee. Multitudes of direct and indirect signs of ACL injury were\\u000a evident on MRI, including anterior translation of the lateral tibial plateau, buckling of the posterior cruciate ligament,\\u000a deep sulcus sign,

Jae Ho Yoo; Bo Kyu Yang; Ho Kwang Ryu

2009-01-01

320

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

NASA Astrophysics Data System (ADS)

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

Rohmer, J.

2014-04-01

321

Aspects of fracture mechanics in cryogenic model design. Part 2: NTF materials  

NASA Technical Reports Server (NTRS)

Results of fatigue crack growth and fracture toughness tests conducted on three candidate materials are presented. Fatigue crack growth and fracture toughness tests were conducted on NITRONIC 40 at room temperature and -275 F. Fracture toughness tests were also conducted on Vascomax 200 and 250 maraging steel from room temperature to -320 F. NITRONIC 40 was used to make the Pathfinder 1 model. The fatigue crack growth rate tests were conducted at room temperature and -275 F on three-point notch bend specimens. The fracture toughness tests on the as received and stress relieved materials at -275 F were conducted on the center crack tension specimens. Toughness tests were also conducted on Vascomax CVM-200 and CVM-250 maraging steel from room temperature to -320 F using round and rectangular compact specimens.

Newman, J. C., Jr.; Lisagor, W. B.

1983-01-01

322

Ductile fracture at intermediate stress triaxialities : experimental investigations and micro-mechanical modeling  

E-print Network

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 ...

Dunand, Matthieu

2013-01-01

323

Mechanical behavior of polycrystalline ceramics: Brittle fracture of SiC-Si3N4 materials  

NASA Technical Reports Server (NTRS)

Research on the fracture behavior of silicon nitride and silicon carbide is reported along with the role of anion impurities in the fabrication and behavior of magnesium oxide. The results of a survey of crack propagation in SiC and Si3N4 are presented. Studies in the following areas are reported: development of a fracture toughness testing technique, constant moment beam, microcrack examination, and etching techniques.

Ceipold, M. H.; Kapadia, C. M.; Kelkar, A. H.

1972-01-01

324

Application of Fracture Mechanics to Specify the Proof Load Factor for Clamp Band Systems of Launch Vehicles  

NASA Astrophysics Data System (ADS)

This article presents a methodology for evaluation of the proof load factor (PLF) for clamp band system (CBS) made of M250 Maraging steel following fracture mechanics principles.CBS is most widely used as a structural element and as a separation system. Using Taguchi's design of experiments and the response surface method (RSM) the compact tension specimens were tested to establish an empirical relation for the failure load ( P max) in terms of the ultimate strength, width, thickness, and initial crack length. The test results of P max closely matched with the developed RSM empirical relation. Crack growth rates of the maraging steel in different environments were examined. Fracture strength (?f) of center surface cracks and through-crack tension specimens are evaluated utilizing the fracture toughness ( K IC). Stress induced in merman band at flight loading conditions is evaluated to estimate the higher load factor and PLF. Statistical safety factor and reliability assessments were made for the specified flaw sizes useful in the development of fracture control plan for CBS of launch vehicles.

Singaravelu, J.; Sundaresan, S.; Nageswara Rao, B.

2013-04-01

325

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

SciTech Connect

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.

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

2010-04-08

326

Fracture Mechanical Measurements with Commercial Stainless Steels at 4 K and with Cp-Titanium at 173 K  

NASA Astrophysics Data System (ADS)

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 MPa?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.

Nyilas, A.; Mitterbacher, H.

2010-04-01

327

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

SciTech Connect

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.

Yuan, Rong

2007-02-06

328

Fracture mechanics analysis of NGV fuel cylinders. Part 1: Steel cylinders  

NASA Astrophysics Data System (ADS)

Compressed natural gas (CNG) cylinders for natural gas vehicles (NGVs) are subject to a combination of pressure cycles, associated with periodic refueling, and a potentially corrosive CNG environment. Under these conditions it has been shown that the life of the cylinder is governed by the corrosion-fatigue crack growth of internal flaws such as voids, pits or folds that may be present after manufacture. For NGV applications, these cylinders are required to operate for at least 15 years and the report, through a detailed fracture mechanics analysis, describes approaches to achieving the desired life. The analysis shows that a 15 year cylinder life can be obtained by using quality control to ensure that no initial defects greater than 0.045 in. X 0.090 in. exist after manufacture. Alternatively, gas drying can be used at the distribution stations to reduce the detrimental effects of the remaining CNG impurities, and thereby, produce long cylinder lives. The analysis also considers the role of in-service inspection/retest and shows that in-service NDE has little advantage, either technically or economically, for ensuring the fitness-for-service of steel NGV cylinders. The analysis also shows that hydrostatic testing of cylinders, either at manufacture or in service, is ineffective for detecting fatigue cracks and therefore should not be implemented as part of a fitness-for-service plan for NGV fuel cylinders. The issue of cylinder geometry was also considered and the analysis shows that improperly designed flat-bottomed CNG cylinders can result in premature fatigue failures originating at the inner wall in the transition region between the cylinder end and sidewall.

Connolly, M. P.; Hudak, S. J.; Roy, S.

1993-02-01

329

The solution of hypersingular integral equations with applications in acoustics and fracture mechanics  

NASA Astrophysics Data System (ADS)

The numerical solution of two classes of hypersingular integral equations is addressed. Both classes are integral equations of the first kind, and are hypersingular due to a kernel containing a Hadamard singularity. The convergence of a Galerkin method and a collocation method is discussed and computationally efficient algorithms are developed for each class of hypersingular integral equation. Interest in these classes of hypersingular integral equations is due to their occurrence in many physical applications. In particular, investigations into the scattering of acoustic waves by moving objects and the study of dynamic Griffith crack problems has necessitated a computationally efficient technique for solving such equations. Fracture mechanic studies are performed using the aforementioned techniques. We focus our studies on problems addressing the Stress Intensity Factors (SIF) of a finite Griffith crack scattering an out of plane shear wave. In addition, we consider the problem of determining the SIF of two parallel Griffith cracks and two perpendicular Griffith cracks. It is shown that the method is very accurate and computationally efficient. In acoustics, we first consider the moving wing problem. For this problem we wish to find the sound produced by the interaction of a moving wing with a known incident sound source. Although this problem is relatively simple, it is a good precursor to the two-dimensional, finite, moving duct problem. The bulk of the research is focused on solving the two- dimensional, finite, moving duct problem. Here we look at sound propagation and radiation from a finite, two- dimensional, moving duct with a variety of inlet configurations. In particular, we conduct studies on the redirection of sound by a so-called scarf inlet design. In said designs, we are able to demonstrate the ability to redirect sound away from sensitive areas.

St.John, Richard S.

330

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

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

331

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

SciTech Connect

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

Sokolov, M.A.; Wallin, K.; McCabe, D.E.

1996-12-31

332

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

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.

Ghoniem, N. M.

2003-07-14

333

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

NASA Astrophysics Data System (ADS)

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.

Afrifah, Kojo Agyapong

334

On the Relationship Between J-Integral and Crack Tip Opening Displacement in Elastic-Plastic Fracture Mechanics  

NASA Astrophysics Data System (ADS)

The relationship between J-integral ( J) and crack tip opening displacement (?), considered fundamental for elastic-plastic fracture mechanics, can be established based on prior knowledge of the constraint factor m, which depends on the work hardening exponent and the material's yield strain. Both J and ? were simultaneously determined at fracture initiation and at different points along the resistance curves for a number of structural steels. The corresponding m values were calculated and then compared with the predictions made by different models. The results indicate that the experimentally determined m values are in fair agreement with the predictions made by ASTM over the whole range of flow parameters considered in this study. The Hutchinson-Rice-Rosengren singularity-based predictions result in overestimating m for steels considered to be of low strength and high strain hardening exponent. Predictions made by other models are predominantly higher in comparison with their experimental counterparts.

Pereira, Marcos Venicius; Darwish, Fathi Aref; Campelo, Eduardo

2013-08-01

335

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

NASA Astrophysics Data System (ADS)

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.

Seggewiss, G.; Dickson, S. E.

2013-12-01

336

Interaction of Age and Mechanical Stability on Bone Defect Healing: An Early Transcriptional Analysis of Fracture Hematoma in Rat  

PubMed Central

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

Ode, Andrea; Duda, Georg N.; Geissler, Sven; Pauly, Stephan; Ode, Jan-Erik; Perka, Carsten; Strube, Patrick

2014-01-01

337

A comparative investigation of the use of laminate-level meso-scale and fracture-mechanics-enriched meso-scale  

E-print Network

-mechanics enriched meso-scale composite- laminate material model, in which the fracture-mechanics character of micro-mechanics-enriched meso-scale composite-material models in ballistic-resistance analyses M. Grujicic · T. He · H. Marvi-scale material models for continuous-fiber reinforced polymer­matrix composites. Suitability of these material

Grujicic, Mica

338

Relationships between tensile and fracture mechanics properties and fatigue properties of large plastic mould steel blocks  

Microsoft Academic Search

Moulds for plastic automotive components such as bumpers and dashboards are usually machined from large pre-hardened steel blocks. Due to their dimensions, the heat treatment produces mixed microstructures, continuously varying with the distance from the quenched surface, at which fracture toughness and fatigue properties are not well known and generally lower than those corresponding to a fully quenched and tempered

Donato Firrao; Paolo Matteis; Giorgio Scavino; Graziano Ubertalli; Maria Giuseppina Ienco; Maria Rosa Pinasco; Enrica Stagno; Riccardo Gerosa; Barbara Rivolta; Antonio Silvestri; Giuseppe Silva; Andrea Ghidini

2007-01-01

339

Mechanical properties and fracture characteristics of high carbon steel after equal channel angular pressing  

E-print Network

was fabricated in a fully pearlitic Fe­0.8 wt% C steel after equal channel angular pressing (ECAP) at 923 K via spheroidized by increasing the number of ECAP passes. After four passes, the cementite lamellae are fully and percentage of reduction in area increase with the number of ECAP passes. The tensile fracture morphology

Volinsky, Alex A.

340

Fracture mechanics analysis of cracked discs of anisotropic rock using the boundary element method  

Microsoft Academic Search

This paper is the second of a series of two papers dealing with the determination of the deformability, tensile strength and fracturing of anisotropic rocks by diametral compression (Brazilian test) of discs of rock. It is shown how a new formulation of the Boundary Element Method (BEM), proposed recently by the authors, can be used to determine the stress intensity

Chao-Shi Chen; Ernian Pan; Bernard Amadei

1998-01-01

341

In vitro simulation of stent fracture mechanisms in ureteric nitinol wire stents.  

PubMed

The ZebraStent is a new-concept lumen-less teflon-coated nitinol double-J wire-stent, designed to facilitate the passage of residual fragments after extracorporeal shock wave lithotripsy. In clinical practice we observed a small number of stent fractures. Hence, an experimental model was designed to simulate the physical forces that may lead to material fatigue of the stent. Flexion force was simulated by "half circular kidney mimicking structures" (HCKMS) into which the upper part of the stent was placed. All experiments were done for a minimum of 5 million cycles representing a stent indwelling time of 9 months, or until stent fracture, and simulating respiratory kidney movement. It was demonstrated that as the diameter of the HCKMS decreases, thus leading to an increased bending of the stent, the likelihood of stent fracture increased proportionally and occurred earlier. From our results it appears that stent fractures can be avoided by observing a maximum indwelling time of 6-8 weeks (which should suffice for the duration of a average SWL treatment), by choosing the correct (and shortest possible) stent length, and perhaps by manufacturer's modifications decreasing the stent's resistance to flexion. The ZebraStent concept remains appealing if it is considered as a short-term stent for post-SWL residual fragments. PMID:18751973

Hajdinjak, Tine; Patel, Mayur; Papatsoris, Athanasios; Masood, Junaid; Buchholz, Noor; Birch, Malcolm

2008-10-01

342

Contact-induced Damage in Ceramic Coatings on Compliant Substrates: Fracture Mechanics and Design  

Microsoft Academic Search

Simple explicit relations are presented for the onset of com- peting fracture modes in ceramic coatings on compliant sub- strates from Hertzian-like contacts. Special attention is given to a deleterious mode of radial cracking that initiates at the lower coating surface beneath the contact, in addition to traditional cone cracking and quasiplasticity in the near- contact area. The critical load

Young-Woo Rhee; Hae-Won Kim; Yan Deng; Brian R. Lawn

2001-01-01

343

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

Microsoft Academic Search

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

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

2004-01-01

344

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

NASA Technical Reports Server (NTRS)

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.

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

2009-01-01

345

Skull fracture  

MedlinePLUS

Basilar skull fracture; Depressed skull fracture; Linear skull fracture ... Skull fractures may occur with head injuries . The skull provides good protection for the brain. However, a severe impact ...

346

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)

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".

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

2012-04-01

347

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

NASA Technical Reports Server (NTRS)

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.

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

2008-01-01

348

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

NASA Technical Reports Server (NTRS)

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.

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

2005-01-01

349

Modeling Shear-Enhanced Permeability as the Mechanism for Fluid Flow in Fractured Reservoirs - A Promising Improvement to Predicting Reservoir Production  

NASA Astrophysics Data System (ADS)

An accurate geomechanical reservoir model including constraints on stress magnitudes and orientations, mechanical rock properties, and the orientations and characteristics of natural fractures is essential to understanding reservoir response to stimulation and production in low permeability reservoirs such as crystalline basement geothermal or oil and gas reservoirs. In these low permeability reservoirs, stimulation response is controlled largely by the properties of natural and induced fracture networks which are in turn controlled by the in situ stresses, the fracture distribution and the hydraulic behavior of the fractures. These hydraulic properties of the fractures, their width, stiffness and strength are often difficult to quantify, leading to large uncertainties in predicted response to stimulation of fractured reservoirs. A well-constrained and calibrated fracture model makes it possible not only to predict reservoir response to stimulation, including the shape and orientation of the stimulated region, but also to predict the required stimulation pressure. Such a model also makes it possible to predict the change in flow properties during production due to depletion, resulting in better predictions of production rate and ultimate recovery. As part of the evaluation process of a compartmentalized fractured basement reservoir, wellbore image and other data were used to develop a 3D geomechanical model of stress and natural fractures through the reservoir volume. Although the results clearly defined the optimal directions in which to drill wells to exploit pre-existing natural fractures, large uncertainties in the models resulted in significant uncertainties in predictions of stimulation response. Because the pre-existing natural fractures were insufficiently permeable and operational constraints precluded the use of hydraulic fracturing to stimulate the reservoir, an innovative approach was taken to determine the extent to which injection at pressures below the least principal stress could enhance natural fracture conductivity. This approach involves injecting small amounts of water at successively higher rates, followed by a period of lower-rate injection, to determine pre- and post-stimulation fracture permeability and the required stimulation pressure. Additional successively higher rate injectivity tests were designed and conducted to verify reservoir permeability. These tests allowed assessment of the likely effects of stimulation on reservoir flow properties and helped to reduce uncertainties in the prediction of the optimal well trajectory for enhanced reservoir production. The approach applied in this basement reservoir is applicable to any field in which fractures provide the primary flow paths but are too impermeable in their natural state to make wells economic.

Barton, C.; Moos, D.

2011-12-01

350

Tensile properties and fracture mechanism of Al–Mg alloy subjected to equal channel angular pressing  

Microsoft Academic Search

Casting Al–2.77wt.% Mg alloy was subjected to equal channel angular pressing (ECAP) and subsequent low-temperature annealing treatment. Tensile properties and fracture modes of as-ECAPed and annealed samples were investigated. It is found that the strength of the Al–Mg alloy increases with increasing the number of ECAP passes, while its elongation decreases. After annealing, the elongation is recovered to a large

D. R. Fang; Q. Q. Duan; N. Q. Zhao; J. J. Li; S. D. Wu; Z. F. Zhang

2007-01-01

351

Thermodynamically consistent constitutive equations for nonisothermal large strain, elasto-plastic, creep behavior  

NASA Technical Reports Server (NTRS)

The paper is concerned with the development of constitutive relations for large nonisothermal elastic-viscoplastic deformations for metals. The kinematics of elastic-plastic deformation, valid for finite strains and rotations, is presented. The resulting elastic-plastic uncoupled equations for the deformation rate combined with use of the incremental elasticity law permits a precise and purely deductive development of elastic-viscoplastic theory. It is shown that a phenomenological thermodynamic theory in which the elastic deformation and the temperature are state variables, including few internal variables, can be utilized to construct elastic-viscoplastic constitutive equations, which are appropriate for metals. The limiting case of inviscid plasticity is examined.

Riff, R.; Carlson, R. L.; Simitses, G. J.

1985-01-01

352

Elasto-plastic stress analysis of thick-walled FGM pipes  

SciTech Connect

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.

Figueiredo, Fabio; Borges, Lavinia; Rochinha, Fernando [LMS -Mechanics of Solids Laboratory, Mechanical Engineering Department-COPPE UFRJ-Federal University of Rio de Janeiro, Box. 68503-CEP 21945-970-Rio de Janeiro, RJ (Brazil)

2008-02-15

353

Elasto-plastic analysis of a right-angle bent bar structure  

SciTech Connect

The limit analysis for a plastic analysis of structures usually employs an interaction curve. The plastic deformation is believed to proceed to the normal direction on the interaction curve (normality rule) in this analysis. It is supposed without doubt that the normality rule, suggested by R. Hill and D.C. Drucker for the conventional plastic flow, can be applied for the generalized plastic deformation. However, the previous studies show that the radiality rule is reasonable rather than the normality rule for the plastic deformation. In this research, the collapse load on the radiality rule and the normality rule is discussed with investigating the deformational behavior of the right-angle bent bar structure introduced by Heyman.

Nishimura, Tetsu; Nemoto, Osamu [Nihon Univ., Tokyo (J); Yanase, Hiroyasu [Hitachi Co., Ltd., Mobara, Chiba (Japan). Production Engineering Dept.

1996-12-01

354

Contact Problems for ElastoPlastic Impact in Multi-Body Systems  

Microsoft Academic Search

Low to moderate speed collision between elastic-plastic bodies results in imperceptible permanent indentation of the contact\\u000a surfaces if the bodies are hard. Nevertheless in these collisions the contact force-indentation relation is irreversible since\\u000a internal energy gained from work done by the contact force during the compression is partially trapped in elastic waves, work\\u000a done in plastic deformation and work done

W. J. Stronge

355

From rock fracture to plate tectonics. Evidence of non extensive statistical mechanics in Earth physics, A review  

NASA Astrophysics Data System (ADS)

The non-extensive statistical mechanics pioneered by the Tsallis group offers a consistent theoretical framework, based on a generalization of entropy, to analyze the behavior of systems with fractal or multi-fractal distribution of their elements. Such systems where long-range interactions or intermittency are important, lead to power law behavior. The question of whether earth systems are described by non-extensive statistical physics, even at the phenomenological level (i.e., without specifying any underlying model), represents a challenge. This is the problem we review here. Our aim is not to present a precise model, but rather to emphasize in simple arguments of physical plausibility. Examples supporting the non-additive behavior of earth system, from rocks fracture (e.g., acoustic emissions) to geodynamic (e.g., plate tectonics, global seismicity) scale are presented. 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".

Vallianatos, F.

2012-04-01

356

High-Temperature Mechanical Behavior and Fracture Analysis of a Low-Carbon Steel Related to Cracking  

NASA Astrophysics Data System (ADS)

Cracking in continuously cast steel slabs has been one of the main problems in casting for decades. In recent years, the use of computational models has led to a significant improvement in caster performance and product quality. However, these models require accurate thermomechanical properties as input data, which are either unreliable or nonexistent for many alloys of commercial interest. A major reason for this lack of reliable data is that high-temperature mechanical properties are difficult to measure. Several methods have been developed to assess the material strength during solidification, especially for light alloys. The tensile strength during solidification of a low carbon aluminum-killed (LCAK; obtained from Tata Steel Mainland Europe cast at the DSP plant in IJmuiden, the Netherlands) has been studied by a technique for high-temperature tensile testing, which was developed at Sumitomo Metal Industries in Japan. The experimental technique enables a sample to melt and solidify without a crucible, making possible the accurate measurement of load over a small solidification temperature range. In the current study, the tensile test results are analyzed and the characteristic zero-ductility and zero-strength temperatures are determined for this particular LCAK steel grade. The fracture surfaces are investigated following tensile testing, which provides an invaluable insight into the fracture mechanism and a better understanding with respect to the behavior of the steel during solidification. The role of minor alloying elements, like sulfur, in hot cracking susceptibility is also discussed.

Santillana, Begoña; Boom, Rob; Eskin, Dmitry; Mizukami, Hideo; Hanao, Masahito; Kawamoto, Masayuki

2012-12-01

357

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

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.

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

1993-06-01

358

Influence of the microstructure on the fracture toughness and fracture mechanisms of forging steels microalloyed with titanium with ferrite-perlite structures  

SciTech Connect

Titanium addition to vanadium microalloyed forging steels is one of the ways proposed to improve fracture toughness. Fine TiN particles inhibit austenite grain growth after recrystallization at the high temperatures used to forge these steels. TiN particles, however, can be formed in the liquid, and as their sizes exceed one micron, they could act as cleavage nucleation sites, impairing the fracture toughness. The present work reports fracture toughness results obtained in Ti treated microalloyed forging steels, showing that in coarse microstructures cleavage is nucleated in coarse TiN particles, but that after refining the microstructure, voids originate at the same particles, resulting in ductile rupture.

Linaza, M.A.; Romero, J.L.; Rodriguez-Ibabe, J.M.; Urcola, J.J. (ESII de San Sebastian and CEIT, Basque Country (Spain))

1993-08-15

359

Nose fracture  

MedlinePLUS

Fracture of the nose; Broken nose; Nasal fracture ... A fractured nose is the most common fracture of the face. It usually occurs after an injury and often occurs with other fractures of the face. Sometimes a blunt injury can ...

360

Fracture Education in Engineering.  

ERIC Educational Resources Information Center

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.…

Sidey, D.; And Others

361

Relative Permeability Through Fractures  

E-print Network

SGP-TR-170 Relative Permeability Through Fractures Gracel P. Diomampo August 2001 Financial support, California #12;#12;v Abstract The mechanism of two-phase flow through fractures is of importance in understanding many geologic processes. Currently, two-phase flow through fractures is still poorly understood

Stanford University

362

Fracture of Bone  

Microsoft Academic Search

Fracture of bone is investigated by measuring the energy required to propagate a crack and by observing, microscopically, the mechanism of fracture. At low strain rates bone displays very high resistance to crack propagation comparable even to some metallic materials. The type of fracture is similar to fiber-reinforced composite materials.

K. Piekarski

1970-01-01

363

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

NASA Technical Reports Server (NTRS)

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.

Goree, James G.; Richardson, David E.

1990-01-01

364

Corrosion fatigue of iron-chromium-nickel alloys: Fracture mechanics, microstructure and chemistry  

SciTech Connect

Phase transformation and cracking during RT aging of charged, high-purity Fe18Cr12Ni alloy and commerical 304 ss were examined; results show that [epsilon]* (hcp) hydride formed on Fe18Cr12Ni upon charging, and it decomposed rapidly to form first [epsilon] and then [alpha]' martensite. Morphology of fracture surfaces of Fe18Cr12Ni produced by corrosion fatigue in NaCl solutions and in hydrogen was found to be identical. Effort was made to examine the approaches and methodologies used in service life predictions and reliability analyses.

Wei, R.P.

1993-01-25

365

Dynamical mechanism for non-locality in dense granular flows  

E-print Network

The dynamical mechanism at the origin of the non-local rheology of dense granular flows is investigated trough discrete element simulations. We show that the influence of a shear band on the mechanical behavior of a distant zone is contained in the spatial variations observed in the network of granular contacts. Using a micro-rheology technique, we establish that the exponential responses hence obtained, do not proof the validity of a mechanical activation process as previously suggested, but stem from the spatial relaxation of the shear rate as a direct consequence of a macroscopic non-local constitutive relation. Finally, by direct visualization of the local relaxation processes, we dismiss the kinetic elasto-plastic picture, where a flow is conceived as a quasi-static sequence of localized plastic events interacting through the stress field. We therefore conclude in favor of the jamming scenario, where geometrical constrains lead to coherent non-affine displacements along floppy modes, inherently non-local.

M. Bouzid; M. Trulsson; P. Claudin; E. Clement; B. Andreotti

2014-05-09

366

Mechanical analysis of femoral neck fracture fixation with dynamic condylar screw in synthetic bone  

PubMed Central

Objective: To analyze statistically results in biomechanical testing of fixation of femoral neck Pauwels type III fractures, on synthetic bone, with dynamic condylar screw (DCS) and control group. Methods: Ten synthetic bones of a national brand were used. Test Group: fixation was performed after osteotomy at 70o tilt using DCS plate with four holes. We analyzed the resistance of this fixation with 5 mm displacement and rotational deviation (Step 1) and with10 mm (Step 2). Control group: the models were tested in their integrity until the femoral neck fracture occurred. Results: The values of the test group in Step 1 showed a mean of 974N and SD = 114N. In Stage 2, we obtained on average 1335N and SD = 98N. The values in the control group were: 1544N, 1110N, 1359N, 1194N, 1437N, respectively. Statistical analysis using the Mann-Whitney test for comparison of the maximum force (N) between the test group and the control, in Step 2, demonstrated that there is no significant difference between the DCS and control plates (p = 0.91). Conclusion: There is no significant difference between the DCS boards and the control group exposed to full resistance. Level of Evidence III, Case Control.

Freitas, Anderson; Maciel, Rafael Almeida; Lima, Renato De Almeida; Souto, Diogo Ranier De Macedo; Ferrer, Marcelo De Almeida

2014-01-01

367

Joint location and source mechanism inversion of microseismic events: benchmarking on seismicity induced by hydraulic fracturing  

NASA Astrophysics Data System (ADS)

Seismic monitoring can greatly benefit from imaging events with a low signal-to-noise ratio (SNR) as the number of the events with a low signal grows exponentially. One way to detect weaker events is improvement of a SNR by migration-type stacking of waveforms from multiple stations. We have developed a new method of location of seismic events that involves stacking of seismic phases and amplitudes along diffraction traveltime curves to suppress noise and detect seismic events with a SNR lower than that on individual receivers. The stacking includes polarity correction based on a simultaneous seismic moment tensor inversion and detection algorithm on the stack function. We applied this method to locate microseismicity induced by hydraulic fracturing. First we calibrated the velocity model by locating perforation shots at known locations. Then we processed 3 d of data from microseismic monitoring of shale stimulation and benchmarked migration-type locations of the largest events that were manually located. The detected and located events induced by hydraulic fracturing in this case study are mostly shear events forming narrow bands along the maximum horizontal stress direction approximately 100 m above the injection intervals. The proposed technique is fully automated and feasible for real-time seismic monitoring.

Anikiev, D.; Valenta, J.; Stan?k, F.; Eisner, L.

2014-07-01

368

Fracture of synthetic diamond  

Microsoft Academic Search

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 of free-standing diamond plates, grown by chemically-vapor deposited (CVD) methods, was measured using Vickers indentations and by the use of disk-shaped compact-tension specimens; the latter method provides an evaluation of the through-thickness fracture properties,

M. D. Drory; R. H. Dauskardt; A. Kant; R. O. Ritchie

1995-01-01

369

Culture-independent pilot study of microbiota colonizing open fractures and association with severity, mechanism, location, and complication from presentation to early outpatient follow-up.  

PubMed

Precise identification of bacteria associated with post-injury infection, co-morbidities, and outcomes could have a tremendous impact in the management and treatment of open fractures. We characterized microbiota colonizing open fractures using culture-independent, high-throughput DNA sequencing of bacterial 16S ribosomal RNA genes, and analyzed those communities with respect to injury mechanism, severity, anatomical site, and infectious complications. Thirty subjects presenting to the Hospital of the University of Pennsylvania for acute care of open fractures were enrolled in a prospective cohort study. Microbiota was collected from wound center and adjacent skin upon presentation to the emergency department, intraoperatively, and at two outpatient follow-up visits at approximately 25 and 50 days following initial presentation. Bacterial community composition and diversity colonizing open fracture wounds became increasingly similar to adjacent skin microbiota with healing. Mechanism of injury, severity, complication, and location were all associated with various aspects of microbiota diversity and composition. The results of this pilot study demonstrate the diversity and dynamism of the open fracture microbiota, and their relationship to clinical variables. Validation of these preliminary findings in larger cohorts may lead to the identification of microbiome-based biomarkers of complication risk and/or to aid in management and treatment of open fractures. PMID:24395335

Hannigan, Geoffrey D; Hodkinson, Brendan P; McGinnis, Kelly; Tyldsley, Amanda S; Anari, Jason B; Horan, Annamarie D; Grice, Elizabeth A; Mehta, Samir

2014-04-01

370

Conditions Under Which Gaseous Methane Will Fracture Ocean Sediments and Penetrate Through the Hydrate Stability Zone: Modeling Multiphase Flow and Sediment Mechanics at the Pore-Scale  

NASA Astrophysics Data System (ADS)

We simulate two competing processes, capillary invasion and fracture opening, by which free methane gas penetrates the Hydrate Stability Zone (HSZ), and we predict the in situ conditions in which the methane propagates fractures and flows all the way through the HSZ and into the ocean, bypassing hydrate formation. In our fully coupled model, we use the discrete element method to simulate the sediment mechanics, and we account for the pore fluid pressures and surface tension between the gas and brine by incorporating additional sets of pressure forces and adhesion forces. We find that given enough capillary pressure, the main factor controlling the mode of gas transport is the grain size, and show that coarse-grain sediments favor capillary invasion and widespread hydrate formation, whereas fracturing dominates in fine-grain sediments. We calculate the fracturing threshold as a function of grain size, capillary pressure, and seafloor depth, and place these results in the context of naturally-occurring hydrate systems.

Jain, A. K.; Juanes, R.

2008-12-01

371

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

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.

Pugh, C.E.; Bass, B.R.; Keeney, J.A. [comps.] [Oak Ridge National Lab., TN (United States)

1993-10-01

372

Finite element method for simulating coupled thermo-hydro-mechanical processes in discretely fractured porous media and application to enhanced geothermal reservoir analysis  

NASA Astrophysics Data System (ADS)

We present our recent development of the finite element method (FEM) for simulating coupled thermo-hydro-mechanical (THM) processes in discretely fractured porous media and an application to geothermal reservoir modeling for the research test site Gross Schoenebeck in Germany operated by the GFZ German Research Centre for Geosciences. Numerical analysis of multi-physics problems in fractured rocks is important for various geotechnical applications. In particular for enhanced geothermal reservoirs where induced fractures and possibly natural fault systems dominate the system behavior, explicit modeling of those characteristic fractures (i.e. discrete fracture models) is essential to get more detailed understanding of in-situ processes and reliable estimations of heat extraction from those deep reservoirs. However, as fractures are mechanical discontinuities, it is difficult to solve the problems using continuity based numerical methods such as the FEM. Currently, equivalent porous medium or multiple continuum model approaches are often only the way to model fractured rocks with the FEM. The authors have recently developed lower-dimensional interface elements (LIEs) for modeling mechanics-involved coupled processes with pre-existing fractures (Watanabe et al. 2012 IJNME). The method does not require any double nodes unlike conventional interface elements. Moreover, for coupled problems, the approach allows for the use of a single mesh for both mechanical and other related processes such as flow and transport. All the code developments have been carried out within the scientific open source project OpenGeoSys (www.opengeosys.net) (Kolditz et al. 2012 EES). Using both traditional and new simulation techniques, a geothermal reservoir model for the research test site Gross Schoenebeck has been developed. Unstructured meshing of the complex faulted reservoir including both rock matrix and fracture elements has been conducted using recently developed automatic preprocessing software MeshIT (Cacace et al. 2012 IGC). This model will be used for lifetime prediction of the geothermal reservoir under different operational conditions (i.e. pressure regimes, injection-production rates). The model is able to describe the complex interaction of THM processes during heat extraction for real conditions in deep georeservoirs. The figure shows the flow regime (pathlines) as well as heat distribution after 15 years operation of the borehole doublet in the fractured rock system. Simulated flow regime (pathlines) as well as heat distribution after 15 years operation of the borehole doublet in the enhanced geothermal system

Watanabe, N.; Wong, L.; Bloecher, G.; Cacace, M.; Kolditz, O.

2012-12-01

373

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

E-print Network

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 ...

Shabelansky, Andrey Hanan

2012-01-01

374

Numerical Modeling of Hydraulic Fracture Propagation Using Thermo-hydro-mechanical Analysis with Brittle Damage Model by Finite Element Method  

E-print Network

Better understanding and control of crack growth direction during hydraulic fracturing are essential for enhancing productivity of geothermal and petroleum reservoirs. Structural analysis of fracture propagation and impact on fluid flow is a...

Min, Kyoung

2013-07-16

375

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

PubMed

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 J IC as a global measure by recording the crack growth resistance curve. Additionally, the initiation toughness in terms of the crack opening displacement (COD i ) 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 J IC . 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

Hohenwarter, A; Pippan, R

2012-04-01

376

Mechanical basis for slip along low-angle normal faults  

NASA Astrophysics Data System (ADS)

The existence of active low-angle normal faults is much debated because (1) the classical theory of fault mechanics implies that normal faults are locked when the dip is less than 30° and (2) shallow-dipping extensional fault planes do not produce large earthquakes (M > 5.5). However, a number of field observations suggest that brittle deformation occurs on low-angle normal faults at very shallow dip. To reconcile observations and theory, we use an alternative model of fault reactivation including a thick elasto-plastic frictional fault gouge, and test it at large strain by the mean of 2D mechanical modeling. We show that plastic compaction allows reducing the effective friction of faults sufficiently for low-angle normal faults to be active at dip of 20°. As the model predicts that these faults must be active in a slip-hardening regime, it prevents the occurrence of large earthquakes. However, we also evidence the neoformation of Riedel-type shear bands within thick fault zone, which, we believe, may be responsible for repeated small earthquakes and we apply the model to the Gulf of Corinth (Greece).

Lecomte, Emmanuel; Le Pourhiet, Laetitia; Lacombe, Olivier

2012-02-01

377

Integrated vapor pressure, hygroswelling, and thermo-mechanical stress modeling of QFN package during reflow with interfacial fracture mechanics analysis  

Microsoft Academic Search

In this paper, a comprehensive and integrated package stress model is established for quad flat non-lead package with detailed considerations of effects of moisture diffusion, heat transfer, thermo-mechanical stress, hygro-mechanical stress and vapor pressure induced during reflow. The critical plastic materials, i.e., moldcompound and die attach are characterized for hygroswelling and moisture properties, which are not easily available from material

Tong Yan Tee; Zhaowei Zhong

2004-01-01

378

Nonlinear fracture mechanics of mode-I and mixed-mode free edge delamination in carbon-epoxy composites  

SciTech Connect

A geometrically and physically nonlinear finite element approach is presented for the analysis of free edge delamination in composite laminates which properly accounts for the effects of initial thermal and hygroscopic stresses. A constitutive model based on nonlinear fracture mechanics is used to describe delamination. An orthotropic plasticity model is used to determine the initiation and propagation of delamination. Although the orthotropic yield surface is based on stresses, it is proven, that in combination with a softening type of post-failure response, the resulting computational strategy converges to a unique and physically realistic solution upon mesh refinement. The results from the nonlinear finite element computations -- including predictive analyses -- are compared with model and mixed-mode free edge delamination experiments. This comparison shows that the numerical predictions are within 10% of the experimental data.

Schellekens, J.C.J.; Borst, R. de [Delft Univ. of Technology (Netherlands)

1993-12-31

379

Fracture mechanics and full scale pipe break testing for the Department of Environment's New Production Reactor-Heavy Water Reactor  

NASA Astrophysics Data System (ADS)

Oak Ridge National Laboratory (ORNL) is completing a major task for the Department of Energy (DOE) in the demonstration that the primary piping of the New Production Heavy Water Reactor (NPR-HWR), with its relatively moderate temperature and pressure, should not suffer an instantaneous Double-Ended-Guillotine-Break (DEGB) under design basis loadings and conditions. The growth of possible small preexisting defects in the piping wall was estimated over a plant life of 60 years. This worst case flaw was then evaluated using fracture mechanics methods. J estimation methods and tearing instability approximations used in this analysis are discussed in this paper. It was established that this worst case flaw would increase in size by at least 14 times before pipe instability during an earthquake would even begin to be possible. The fatigue crack growth analysis is discussed in this paper.

Poole, A. B.

380

A path-independent integral for fracture of solids under combined electrochemical and mechanical loadings  

NASA Astrophysics Data System (ADS)

In this study, we first demonstrate that the J-integral in classical linear elasticity becomes path-dependent when the solid is subjected to combined electrical, chemical and mechanical loadings. We then construct an electro-chemo-mechanical J-integral that is path-independent under such combined multiple driving forces. Further, we show that this electro-chemo-mechanical J-integral represents the rate at which the grand potential releases per unit crack growth. As an example, the path-independent nature of the electro-chemo-mechanical J-integral is demonstrated by solving the problem of a thin elastic film delaminated from a thick elastic substrate.

Haftbaradaran, Hamed; Qu, Jianmin

2014-11-01

381

Mechanical assessment of local bone quality to predict failure of locked plating in a proximal humerus fracture model.  

PubMed

The importance of osteoporosis in proximal humerus fractures is well recognized. However, the local distribution of bone quality in the humeral head may also have a significant effect because it remains unclear in what quality of bone screws of standard implants purchase. The goal of this study was to investigate whether the failure of proximal humerus locked plating can be predicted by the DensiProbe (ARI, Davos, Switzerland). A 2-part fracture with metaphyseal impaction was simulated in 12 fresh-frozen human cadaveric humeri. Using the DensiProbe, local bone quality was determined in the humeral head in the course of 6 proximal screws of a standard locking plate (Philos; Synthes GmbH, Solothurn, Switzerland). Cyclic mechanical testing with increasing axial loading until failure was performed. Bone mineral density (BMD) significantly correlated with cycles until failure. Head migration significantly increased between 1000 and 2000 loading cycles and significantly correlated with BMD after 3000 cycles. DensiProbe peak torque in all screw positions and their respective mean torque correlated significantly with the BMD values. In 3 positions, the peak torque significantly correlated with cycles to failure; here BMD significantly influenced mechanical stability. The validity of the DensiProbe was proven by the correlation between its peak torque measurements and BMD. The correlation between the peak torque and cycles to failure revealed the potential of the DensiProbe to predict the failure of locked plating in vitro. This method provides information about local bone quality, potentially making it suitable for intraoperative use by allowing the surgeon to take measures to improve stability. PMID:24025003

Röderer, Götz; Brianza, Stefano; Schiuma, Damiano; Schwyn, Ronald; Scola, Alexander; Gueorguiev, Boyko; Gebhard, Florian; Tami, Andrea

2013-09-01

382

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

E-print Network

Tvergaard a , John W. Hutchinson b,* a Department of Mechanical Engineering, Technical University of Denmark by Tvergaard and Hutchinson. While both mechanisms are based on void nucleation, growth and coalescence.elsevier.com/locate/ijsolstr * Corresponding author. Fax: +1-617-495-9837. E-mail address: hutchinson@husm.harvard.edu (J.W. Hutchinson). 0020

Hutchinson, John W.

383

A fracture mechanics approach for estimating fatigue crack initiation in carbon and low-alloy steels in LWR coolant environments  

SciTech Connect

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.

Park, H. B.; Chopra, O. K.

2000-04-10

384

Experimental and numerical study on the relationship between creep crack growth properties and fracture mechanisms  

NASA Astrophysics Data System (ADS)

Evaluation of creep crack growth properties taking microscopic aspects into account is effective for developing more accurate life prediction of structural components. The present study investigated the relationship between creep crack growth properties and microscopic fracture aspects for austenitic alloy 800H and 316 stainless steel. The growth rate of wedge-type intergranular and transgranular creep crack could be characterized by creep ductility. Creep damages formed ahead of the void-type crack tip accelerated the crack growth rate. Based on these experimental results, a three-dimensional finite element method (FEM) code, which simulates creep crack growth, has been developed. The effect of creep ductility on da/dt vs C* relations could be simulated based on the critical strain criteria. The diffusion of vacancies toward crack tip would accelerate the crack growth under creep conditions. The change of vacancy concentration during creep was computed for a three-dimensional compact-type (CT) specimen model by solving the diffusive equation under multiaxial stress field. The experimental results that crack growth was accelerated by creep damages formed ahead of the crack tip could be successfully simulated.

Tabuchi, Masaaki; Ha, Jechang; Hongo, Hiromichi; Watanabe, Takashi; Yokobori, Toshimitsu

2004-06-01

385

Influence of the microstructure on the fracture toughness and fracture mechanisms of forging steels microalloyed with titanium with ferrite-perlite structures  

Microsoft Academic Search

Titanium addition to vanadium microalloyed forging steels is one of the ways proposed to improve fracture toughness. Fine TiN particles inhibit austenite grain growth after recrystallization at the high temperatures used to forge these steels. TiN particles, however, can be formed in the liquid, and as their sizes exceed one micron, they could act as cleavage nucleation sites, impairing the

M. A. Linaza; J. L. Romero; J. M. Rodriguez-Ibabe; J. J. Urcola

1993-01-01

386

Finite element analysis of grain-matrix micro-cracking in shale within the context of a multiscale modeling approach for fracture (Invited)  

Microsoft Academic Search

The paper models grain-scale micro-cracking in shale at grain-matrix interfaces, assuming constituents are composed of quart silt grains and compacted clay matrix for a typical shale. The influence of grain-matrix-grain interaction on micro-crack patterns is investigated. Elasto-plastic pressure-sensitive cohesive-surface models are inserted at grain-matrix interfaces and intra-clay-matrix finite element facets, while a bulk elasto-plasticity model with bifurcation is employed for

R. A. Regueiro; S. Yu

2010-01-01

387

Fracture Mechanics of Collagen Fibrils: Influence of Natural Cross-Links  

PubMed Central

Tendons are important load-bearing structures, which are frequently injured in both sports and work. Type I collagen fibrils are the primary components of tendons and carry most of the mechanical loads experienced by the tissue, however, knowledge of how load is transmitted between and within fibrils is limited. The presence of covalent enzymatic cross-links between collagen molecules is an important factor that has been shown to influence mechanical behavior of the tendons. To improve our understanding of how molecular bonds translate into tendon mechanics, we used an atomic force microscopy technique to measure the mechanical behavior of individual collagen fibrils loaded to failure. Fibrils from human patellar tendons, rat-tail tendons (RTTs), NaBH4 reduced RTTs, and tail tendons of Zucker diabetic fat rats were tested. We found a characteristic three-phase stress-strain behavior in the human collagen fibrils. There was an initial rise in modulus followed by a plateau with reduced modulus, which was finally followed by an even greater increase in stress and modulus before failure. The RTTs also displayed the initial increase and plateau phase, but the third region was virtually absent and the plateau continued until failure. The importance of cross-link lability was investigated by NaBH4 reduction of the rat-tail fibrils, which did not alter their behavior. These findings shed light on the function of cross-links at the fibril level, but further studies will be required to establish the underlying mechanisms. PMID:23746520

Svensson, Rene B.; Mulder, Hindrik; Kovanen, Vuokko; Magnusson, S. Peter

2013-01-01

388

The Material Behavior and Fracture Mechanism of a Frangible Bullet Composite  

NASA Astrophysics Data System (ADS)

The quasi-static and dynamic compressive mechanical properties of a bullet composite are investigated using the scattered spot technique, an electronic universal testing machine, and a Split—Hopkinson pressure bar. The stress-strain curves under static and dynamic loading are also obtained, and the strain rate effect is analyzed. The rupture structure is observed under a scanning electron microscope, and the microscopic damage mechanism of the bullet composite is examined. Results show that the composite is sensitive to the strain rate, such that the compressive strength of the composite increases with increased strain rate. The relationship of the compressive strength and elastic modulus with the logarithmic strain rate is nonlinear.

Li, Jian; Rong, Ji-Li; Zhang, Yu-Ning; Xu, Tian-Fu; Li, Bin

2013-07-01

389

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

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

390

Ris-R-1394(EN) A general mixed mode fracture mechan-  

E-print Network

), The Wind Energy Department, Risø National Laboratory, The Department of Mechanical Engineering (Solid process zone parameters: Energy release rate and mode mixity 8 2.3 Specimens experiencing large scale.1 Advantages and drawbacks of the experimental approach 26 5.2 On the use of a displacement potential

391

Effect of residual stress around cold worked holes on fracture under superimposed mechanical load  

Microsoft Academic Search

Cold working is one method used to enhance the fatigue life of holes in aerospace structures. The method introduces a compressive stress field in the material around the hole and this reduces the tendency for fatigue cracks to initiate and grow under superimposed cyclic mechanical load. To include the benefit of cold working in design the stress intensity factors must

M. J. Pavier; C. G. C. Poussard; D. J. Smith

1999-01-01

392

Research on fatigue behavior evaluation and fatigue fracture mechanisms of cruciform welded joints  

Microsoft Academic Search

The applications of infrared thermographic method and the relationship between the microstructures and mechanical properties of materials were reviewed. Experimental tests, using the thermographic method, have been carried out in order to evaluate the fatigue behavior of cruciform welded joints subjected to a high mean stress. A good agreement was achieved between the predicted values and those obtained by the

J. L. Fan; X. L. Guo; C. W. Wu; Y. G. Zhao

2011-01-01

393

Fracture mechanics approach to creep growth in welded IN738LC gas turbine blades  

Microsoft Academic Search

Microcracks caused by hot cracking or strain age cracking mechanisms are very likely to be discovered in the weld repair zone of precision-cast IN738LC gas turbine blades. The possibility of crack propagation under the operating conditions of the gas turbine thereby becomes a crucial issue for gas turbine designers. The creep crack growth rate in air of the hipped and

W. P. Foo; R. Castillo

1992-01-01

394

Fatigue and life prediction for cobalt-chromium stents: A fracture mechanics analysis  

Microsoft Academic Search

To design against premature mechanical failure, most implant devices such as coronary and endovascular stents are assessed on the basis of survival, i.e., if a fatigue life of 108 cycles is required, testing is performed to ascertain whether the device will survive 108 cycles under accelerated in vitro loading conditions. This is a far from satisfactory approach as the safety

Ramesh V. Marrey; Robert Burgermeister; Randy B. Grishaber; R. O. Ritchie

2006-01-01

395

Fatigue crack growth of cable steel wires in a suspension bridge: Multiscaling and mesoscopic fracture mechanics  

Microsoft Academic Search

Intrinsically, fatigue failure problem is a typical multiscale problem because a fatigue failure process deals with the fatigue crack growth from microscale to macroscale that passes two different scales. Both the microscopic and macroscopic effects in geometry and material property would affect the fatigue behaviors of structural components. Classical continuum mechanics has inability to treat such a multiscale problem since

C. X. Li; X. S. Tang; G. B. Xiang

2010-01-01

396

Coalescence of fractures under shear stress in experiments  

Microsoft Academic Search

A series of uniaxial compression tests were performed on gypsum specimens with preexisting fractures to study the failure mechanism of fractures and rock bridges in fractured rock masses. The coalescence mechanism of two parallel and offset fractures was investigated by monitoring the process of fracture initiation and propagation with a video camera. The tests showed that two inclined parallel fractures

Baotang Shen; Ove Stephansson; Herbert H. Einstein; Bidjan Ghahreman

1995-01-01

397

In Situ Observations of the Deformation Behavior and Fracture Mechanisms of Ti-45Al-2Nb-2Mn + 0.8 vol pct TiB2  

NASA Astrophysics Data System (ADS)

The deformation and fracture mechanisms of a nearly lamellar Ti-45Al-2Nb-2Mn (at. pct) + 0.8 vol pct TiB2 intermetallic, processed into an actual low-pressure turbine blade, were examined by means of in situ tensile and tensile-creep experiments performed inside a scanning electron microscope (SEM). Low elongation-to-failure and brittle fracture were observed at room temperature, while the larger elongations-to-failure at high temperature facilitated the observation of the onset and propagation of damage. It was found that the dominant damage mechanisms at high temperature depended on the applied stress level. Interlamellar cracking was observed only above 390 MPa, which suggests that there is a threshold below which this mechanism is inhibited. Failure during creep tests at 250 MPa was controlled by intercolony cracking. The in situ observations demonstrated that the colony boundaries are damage nucleation and propagation sites during tensile creep, and they seem to be the weakest link in the microstructure for the tertiary creep stage. Therefore, it is proposed that interlamellar areas are critical zones for fracture at higher stresses, whereas lower stress, high-temperature creep conditions lead to intercolony cracking and fracture.

Muñoz-Moreno, Rocio; Boehlert, Carl J.; Pérez-Prado, M. Teresa; Ruiz-Navas, Elisa M.; Llorca, Javier

2012-04-01

398

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

Microsoft Academic Search

In this paper some experimental results and analyses regarding the behavior of AISI 420 martensitic stainless steel under\\u000a different environmental conditions are presented. That way, mechanical properties like ultimate tensile strength and 0.2 percent\\u000a offset yield strength at lowered and elevated temperatures as well as short-time creep behavior for selected stress levels\\u000a at selected elevated temperatures of mentioned material are

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

399

Mechanical fracture predictions for sensitized stainless steel piping with circumferential cracks. Final report. [SS304 welds  

Microsoft Academic Search

Circumferential intergranular stress corrosion cracks have been discovered in the heat-affected zones of girth welds in the Type 304 stainless steel recirculation bypass piping systems of several boiling water reactor (BWR) plants. To determine the residual strength of the cracked pipe, an integrated program of small-scale laboratory experiments, full-scale pipe tests, finite-element computation, and a mechanical failure analysis was conducted.

Oldberg

1976-01-01

400

Atraumatic sternum fracture.  

PubMed

The spine, pelvic bones and long bones of the lower extremities are common sites for insufficiency fractures. Cases of sternum insufficiency fractures have rarely been reported among elderly patients. Insufficiency fractures tend to occur in bones with decreased mechanical strength especially among elderly patients, in postmenopausal women and patients with underlying diseases. We describe a case of spontaneous sternum insufficiency fracture in a healthy man, with no known risk factors to fracture, or previous history of fractures. Sternum insufficiency fracture is a rare cause of chest pain. This case serves to remind the emergency physician to remain vigilant for other non-cardiac, non-pulmonary and non-traumatic causes of chest pain, especially among patients with known risk factors such as osteoporosis, chronic obstructive pulmonary disease, rheumatoid arthritis, systemic lupus erythematosus and patients on long-term steroid treatment. If diagnosed correctly, these patients can be discharged and treated as outpatients as this case emphasises. PMID:25326566

Abrahamsen, Sebastian Ørskov; Madsen, Christina Friis

2014-01-01

401

Fracture prediction in metal sheets  

E-print Network

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. ...

Lee, Young-Woong

2005-01-01

402

Modelling chemo-hydro-mechanical behaviour of unsaturated clays: a feasibility study  

NASA Astrophysics Data System (ADS)

Effective capabilities of combined chemo-elasto-plastic and unsaturated soil models to simulate chemo-hydro-mechanical (CHM) behaviour of clays are examined in numerical simulations through selected boundary value problems. The objective is to investigate the feasibility of approaching such complex material behaviour numerically by combining two existing models. The chemo-mechanical effects are described using the concept of chemical softening consisting of reduction of the pre-consolidation pressure proposed originally by Hueckel (Can. Geotech. J. 1992; 29:1071-1086; Int. J. Numer. Anal. Methods Geomech. 1997; 21:43-72). An additional chemical softening mechanism is considered, consisting in a decrease of cohesion with an increase in contaminant concentration. The influence of partial saturation on the constitutive behaviour is modelled following Barcelona basic model (BBM) formulation (Géotech. 1990; 40(3):405-430; Can. Geotech. J. 1992; 29:1013-1032).The equilibrium equations combined with the CHM constitutive relations, and the governing equations for flow of fluids and contaminant transport, are solved numerically using finite element. The emphasis is laid on understanding the role that the individual chemical effects such as chemo-elastic swelling, or chemo-plastic consolidation, or finally, chemical loss of cohesion have in the overall response of the soil mass. The numerical problems analysed concern the chemical effects in response to wetting of a clay specimen with an organic liquid in rigid wall consolidometer, during biaxial loading up to failure, and in response to fresh water influx during tunnel excavation in swelling clay.

Liu, Z.; Boukpeti, N.; Li, X.; Collin, F.; Radu, J.-P.; Hueckel, T.; Charlier, R.

2005-08-01

403

Dementia and Hip Fractures  

PubMed Central

Dementia and hip fractures are 2 conditions that are seen primarily in older adults, and both are associated with substantial morbidity and mortality. An individual with dementia is up to 3 times more likely than a cognitively intact older adult to sustain a hip fracture. This may occur via several mechanisms, including (1) risk factors that are common to both outcomes; (2) the presence of dementia increasing hip fracture incidence via intermediate risk factors, such as falls, osteoporosis, and vitamin D; and (3) treatment of dementia causing side effects that increase hip fracture risk. We describe a model that applies these 3 mechanisms to explain the relationship between dementia and hip fractures. Comprehensive understanding of these pathways and their relative influence on the outcome of hip fracture will guide the development of effective interventions and potentially improve prevention efforts. PMID:23569663

Friedman, Susan M.; Menzies, Isaura B.; Bukata, Susan V.; Mendelson, Daniel A.; Kates, Stephen L.

2010-01-01

404

Direct quantification of the mechanical anisotropy and fracture of an individual exoskeleton layer via uniaxial compression of micropillars.  

PubMed

A common feature of the outer layer of protective biological exoskeletons is structural anisotropy. Here, we directly quantify the mechanical anisotropy and fracture of an individual material layer of a hydroxyapatite-based nanocomposite exoskeleton, the outmost ganoine of Polypterus senegalus scale. Uniaxial compression was conducted on cylindrical micropillars of ganoine fabricated via focused ion beam at different orientations relative to the hydroxyapatite rod long axis (? = 0°, 45°, 90°). Engineering stress versus strain curves revealed significant elastic and plastic anisotropy, off-axial strain hardening, and noncatastrophic crack propagation within ganoine. Off-axial compression (? = 45°) showed the lowest elastic modulus, E (36.2 ± 1.6 GPa, n ? 10, mean ± SEM), and yield stress, ?(Y) (0.81 ± 0.02 GPa), while compression at ? = 0° showed the highest E (51.8 ± 1.7 GPa) and ?(Y) (1.08 ± 0.05 GPa). A 3D elastic-plastic composite nanostructural finite element model revealed this anisotropy was correlated to the alignment of the HAP rods and could facilitate energy dissipation and damage localization, thus preventing catastrophic failure upon penetration attacks. PMID:21755939

Han, Lin; Wang, Lifeng; Song, Juha; Boyce, Mary C; Ortiz, Christine

2011-09-14

405

Evaluation of the relationship between fracture conductivity, fracture fluid production, and effective fracture length  

NASA Astrophysics Data System (ADS)

Low-permeability gas wells often produce less than predicted after a fracture treatment. One of the reasons for this is that fracture lengths calculated after stimulation are often less than designed lengths. While actual fracture lengths may be shorter due to fracture growth out of zone, improper proppant settling, or proppant flowback, short calculated fracture lengths can also result from incorrect analysis techniques. It is known that fracturing fluid that remains in the fracture and formation after a hydraulic fracture treatment can decrease the productivity of a gas well by reducing the relative permeability to gas in the region invaded by this fluid. However, the relationships between fracture fluid cleanup, effective fracture length, and well productivity are not fully understood. In this work I used reservoir simulation to determine the relationship between fracture conductivity, fracture fluid production, effective fracture length, and well productivity. I simulated water saturation and pressure profiles around a propped fracture, tracked gas production along the length of the propped fracture, and quantified the effective fracture length (i.e., the fracture length under single-phase flow conditions that gives similar performance as for multiphase flow conditions), the "cleanup" fracture length (i.e., the fracture length corresponding to 90% cumulative gas flow rate into the fracture), and the "apparent" fracture length (i.e., the fracture length where the ratio of multiphase to single-phase gas entry rate profiles is unity). This study shows that the proppant pack is generally cleaned up and the cleanup lengths are close to designed lengths in relatively short times. Although gas is entering along entire fracture, fracturing fluid remains in the formation near the fracture. The water saturation distribution affects the gas entry rate profile, which determines the effective fracture length. Subtle changes in the gas rate entry profile can result in significant changes in effective fracture length. The results I derived from this work are consistent with prior work, namely that greater fracture conductivity results in more effective well cleanup and longer effective fracture lengths versus time. This study provides better explanation of mechanisms that affect fracturing fluid cleanup, effective fracture length, and well productivity than previous work.

Lolon, Elyezer P.

406

Asian Rock Mechanics Symposium, ARMS2012, 15-19 October 2012, Seoul, Korea Determination of equivalent continuum mechanical model for fractured  

E-print Network

Excavation Damaged Zone (EDZ) around deep underground galleries excavated in claystone. The fractures. Introduction The Excavation Damaged Zone (EDZ) around deep underground galleries excavated in claystone around deep galleries in claystone (a): fractures outcropping on the wall (photo), (b): geometrical model

Paris-Sud XI, Université de

407

Evaluation of viscoelastic master curves of filled elastomers and applications to fracture mechanics.  

PubMed

The viscoelastic response of filler-reinforced elastomers has been investigated by dielectric- and dynamic-mechanical spectroscopy. Horizontal and vertical shifting factors are evaluated, which are used for the construction of viscoelastic master curves. They are discussed in the framework of filler network effects and the slowed-down dynamics of a polymer layer close to the filler surface. The observed shifting behaviour is shown to be related to the superposition of two relaxation processes, i.e. that of the polymer matrix and the filler network, leading to a failure of the time-temperature superposition principle. While the matrix transforms according to the Vogel-Fulcher equation, the filler network exhibits an Arrhenius dependence, which results from the thermal activation of filler-filler bonds, i.e. glassy-like polymer bridges between adjacent filler particles. Based on the viscoelastic master curves relaxation time spectra are evaluated. By referring to a recently developed theory of crack propagation in viscoelastic solids it is demonstrated that the behaviour of the scaling exponent of the relaxation time spectra correlates fairly well with that of the crack propagation rates measured under moderate severity conditions. PMID:21817263

Klüppel, M

2009-01-21

408

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

NASA Astrophysics Data System (ADS)

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.

Seo, Minwhan

409

Progressive Fracture of Composite Structures  

NASA Technical Reports Server (NTRS)

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.

Chamis, Christos C.; Minnetyan, Levon

2008-01-01

410

Innovations in the management of hip fractures.  

PubMed

Hip fractures include fractures of the head, neck, intertrochanteric, and subtrochanteric regions. Head fractures commonly accompany dislocations. Neck fractures and intertrochanteric fractures occur with greatest frequency in elderly patients with a low bone mineral density and are produced by low-energy mechanisms. Subtrochanteric fractures occur in a predominantly strong cortical osseous region that is exposed to large compressive stresses. Implants used to address these fractures must accommodate significant loads while the fractures consolidate. Complications secondary to hip fractures produce significant morbidity and include infection, nonunion, malunion, decubitus ulcers, fat emboli, deep venous thrombosis, pulmonary embolus, pneumonia, myocardial infarction, stroke, and death. PMID:12934739

Teasdall, Robert D; Webb, Lawrence X

2003-08-01

411

Enhanced fatigue endurance of metallic glasses through a staircase-like fracture mechanism.  

PubMed

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

Gludovatz, Bernd; Demetriou, Marios D; Floyd, Michael; Hohenwarter, Anton; Johnson, William L; Ritchie, Robert O

2013-11-12

412

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

PubMed Central

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, a.k.a. 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 IC50 ~25 ?M, and inhibited CD40L-dependent cell 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 three-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. PMID:21417339

Silvian, Laura F.; Friedman, Jessica E.; Strauch, Kathy; Cachero, Teresa G.; Day, Eric S.; Qian, Fang; Cunningham, Brian; Fung, Amy; Sun, Lihong; Shipps, Gerald W.; Su, Lihe; Zheng, Zhongli; Kumaravel, Gnanasambandam; Whitty, Adrian

2012-01-01

413

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

SciTech Connect

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.

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

2011-12-31

414

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

E-print Network

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 in the reservoir which...

Ogbechie, Joachim Nwabunwanne

2012-02-14

415

Hydraulic fracturing  

E-print Network

Hydraulic fracturing (also hydrofracturing, hydrofracking, fracking, or fraccing) is a well-stimulation technique in which rock is fractured by a hydraulically pressurized liquid. Some hydraulic fractures form naturally—certain veins or dikes are examp...

416

In-situ Fracture Studies and Modeling of the Toughening Mechanism Present in Wrought LCAC, TZM, and ODS Molybdenum Flat Products  

SciTech Connect

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).

Cockerman, B. V. and Chan, K. S.

2007-07-01

417

Effects of alloying elements on mechanical and fracture properties of base metals and simulated heat-affected zones of SA 508 steels  

Microsoft Academic Search

This study was aimed at developing low-alloy steels for nuclear reactor pressure vessels by investigating the effects of alloying\\u000a elements on mechanical and fracture properties of base metals and heat-affected zones (HAZs). Four steels whose compositions\\u000a were variations of the composition specification for SA 508 steel (class 3) were fabricated by vacuum-induction melting and\\u000a heat treatment, and their tensile properties

Sangho Kim; Sunghak Lee; Young-Roc Im; Hu-Chul Lee; Yong Jun Oh; Jun Hwa Hong

2001-01-01

418

Semi-probabilistic fracture mechanics approach for a quality assurance system for welds of a containment for a 1000 MW nuclear power unit  

Microsoft Academic Search

The paper deals with a quality control system based on: (1) limit stage design for a given level of failure probability (Pf?10?6), and (2) fracture mechanics requirements for welds, the heat-affected zone (HAZ), and parent material (St 355 E). This quality control system was carried out under on-site-conditions when building a steel-sheet\\/reinforced concrete composite construction of a containment for a

Siegfried Butler

1997-01-01

419

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

E-print Network

settlements above deep tunnels in fractured crystalline rock: Part 1--Investigations above the Gotthard and the excavation of the highway tunnel (begun in 1970 and completed in 1977) suggested that the surface deformation

420

Mechanical strength of McLaughlin hip nail-plates manufactured from 316 LVM stainless steel. A biomechanical study of unstable trochanteric fractures. V.  

PubMed

Mechanical testing of McLaughlin hip nail-plates manufactured from 316 LVM stainless steel was performed. The mode of failure is described and the results are compared with previous tests of McLaughlin implants manufactured from Cobalt-Chromium-Molybdenum alloy. As there was no significant difference between these two products as regards the basic mechanical problem of failure of the nail-plate junction, it is recommended that the design be changed to make the implant suitable for internal fixation of unstable trochanteric fractures. PMID:7446023

Jensen, J S

1980-06-01