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1

Elasto-plastic fracture mechanics of crack growth in soil  

NASA Astrophysics Data System (ADS)

A predominant variable in soil structure formation and degradation is crack propagation. Empirical models exist to predict fracture but these do not describe the underlying physical processes. Theoretical fracture mechanics models have been applied to soil, but most are not applicable when soil is in a wet, plastic state. Since the onset of crack formation in soil tends to occur in this condition, physically sound elasto-plastic fracture mechanics approaches are long overdue. We address this weakness by applying a new elasto-plastic fracture mechanics approach to describe crack formation in plastic soil. Samples are fractured using a deep-notch (modified 4-point) bend test, with data on load transmission, sample bending, crack growth, and crack mouth opening collected to assess the crack opening angle (COA), the crack tip opening angle (CTOA) and the plastic energy dissipation rate (Dpl). These are all material properties that can be used directly to predict and describe crack propagation. CTOA will be used to discuss the results here, although a full description of the other parameters will be provided in the conference presentation. It provides a powerful parameter for describing soil cracking since CTOA is induced by soil shrinkage (an easily measured parameter) and can be used to describe elasto-plastic fracture in finite element modelling packages. The test variables we have studied to date are clay platelet orientation, soil texture, clay mineralogy, and pore water salinity. All samples were formed by consolidating a soil slurry with a 120 kPa vertical stress. Tests on pure kaolinite showed that platelet orientation did not affect CTOA which was 0.23 ± 0.02 for both conditions. Soil texture did have a marked influence, however, with silica sand:kaolinite mixes of 20:80 and 40:60 reducing CTOA to 0.14 ± 0.02 and 0.12 ± 0.01 respectively. These lower values of CTOA indicate that less strain is required to induce fracture when the amount of clay is lowered. Replacing kaolinite with smectite in the 40:60 sample caused CTOA to increase significantly to 0.63 ± 0.01, indicating that higher strain levels are required to fracture smectite rich soils. CTOA had a positive correlation with the plastic and liquid consistency limits for all samples. Other mechanical properties were correlated to CTOA if the kaolinite samples were examined independently of smectite. Salinity (3% NaCl) caused a reduction in the CTOA of pure kaolinite from 0.23 ± 0.02 to 0.17 ± 0.03. Finite element analysis showed good agreement between modelled and measured crack opening morphology, and predicted the stress distribution in the vicinity of an advancing crack. The approach describes elasto-plastic fracture in soil well, and is being extended to consider the influence of biological exudates, plant roots and fungal hyphae. CTOA analysis has already been applied to finite element modelling of soil crack formation.

Hallett, P. D.; Newson, T. A.

2003-04-01

2

The applications of 2D elasto-plastic stochastic finite element method in the field of fracture mechanics  

Microsoft Academic Search

In this paper the stochastic finite element method (SFEM) is applied to the field of fracture mechanics and cracked structures are analysed by using an elasto-plastic methodology. The main random variables considered are Young's modulus, Poisson's ratio and the crack size. The formulae of the mean and variance value of the J-integral for elasto-plastic deformation are discussed and an effective

Jian-Ping Zhao; Wen-Long Huang; Shu-Ho Dai

1998-01-01

3

Fracture Prediction in Plane Elasto-Plastic Problems by the Finite Element Method.  

National Technical Information Service (NTIS)

A finite element program based on the plane stress assumption is developed and applied to elasto-plastic fracture problems involving monotonically increasing loads. The program directly predicts the initiation and propagation of fracture in the structure....

R. G. Belie

1978-01-01

4

Fracture Model of Bimaterial under Delamination of Elasto-Plastic Structured Media  

NASA Astrophysics Data System (ADS)

Delamination of bimaterial composed of two structured materials is considered. A crack is located at the interface between two media. Under tension applied at infinity, I mode fracture is implemented. The improved Leonov-Panasyuk-Dugdale model (LPD model) is proposed to be applied in combination with the Neuber-Novozhilov approach. The case when elastic material characteristics are identical and strength ones essentially differ is analyzed in detail. Analytical description of plotting the fracture diagram of quasi-brittle bimaterial for the plane stress state is given. Numerical modeling of the plasticity zone in bimaterial under quasi-static loading has been performed. The updated Lagrange formulation of solid-state mechanics equations is used in a numerical model. This formulation is most preferable for modeling of bodies made from elasto-plastic material subjected to large strain. Using the finite element method, a plastic zone in the vicinity of a crack tip has been described. It is shown that the shape of the plastic zone in bimetal essentially differs from that in a homogenous medium. Numerical experiments are in good agreement with the proposed analytical model of the pre-fracture zone in the weakest material.

Kornev, V. M.; Kurguzov, V. D.; Astapov, N. S.

2013-04-01

5

Robust characteristics method for modelling multiphase visco-elasto-plastic thermo-mechanical problems  

NASA Astrophysics Data System (ADS)

We have extended our previous 2D method [Gerya, T.V., Yuen, D.A., 2003. Characteristics-based marker-in-cell method with conservative finite-differences schemes for modeling geological flows with strongly variable transport properties. Phys. Earth Planet. Interiors 140, 295 320], which is a combination of conservative finite-differences with marker-in-cell techniques to include the effects of visco-elasto-plastic rheology, self-gravitation and a self-consistently derived evolving curvilinear planetary surface. This code is called I2ELVIS and can solve a new class of computationally challenging problems in geodynamics, such as shear localization with large strains, crustal intrusion emplacement of magmas, bending of realistic visco-elasto-plastic plates and core-formation by vigorous shell tectonics activities related to a global Rayleigh Taylor instability of a metal layer formed around silicate-rich lower density (primordial) core during planetary accretion. We discuss in detail the computational strategy required the rheological constraints to be satisfied at each time step and spatial location. We show analytical benchmarks and examples drawn from comparing between numerical and analogue experiments in structural geology, subducting slab bending with a visco-elasto-plastic rheology and equilibrium spherical configurations from self-gravitation. We have also tested possibilities of future applications by addressing 3D geometries based on multigrid method and including inertial effects in the momentum equation with tracers in order to simulate meteoritic impact events and eventually earthquake instabilities.

Gerya, Taras V.; Yuen, David A.

2007-08-01

6

Robust characteristics method for modelling multiphase visco-elasto-plastic thermo-mechanical problems  

Microsoft Academic Search

We have extended our previous 2D method [Gerya, T.V., Yuen, D.A., 2003. Characteristics-based marker-in-cell method with conservative finite-differences schemes for modeling geological flows with strongly variable transport properties. Phys. Earth Planet. Interiors 140, 295–320], which is a combination of conservative finite-differences with marker-in-cell techniques to include the effects of visco-elasto-plastic rheology, self-gravitation and a self-consistently derived evolving curvilinear planetary surface.

Taras V. Gerya; David A. Yuen

2007-01-01

7

A possible mechanism for the initiation of the Yinggehai Basin: A visco-elasto-plastic model  

NASA Astrophysics Data System (ADS)

The Yinggehai Basin, lying along the trace of the Red River fault zone in the South China Sea, has been related to the movements of the Red River fault zone and the rotation of the Indochina block. However, the tectonic origin of the Yinggehai Basin remains unclear. This paper explores the initiation of the Yinggehai Basin using a visco-elasto-plastic model. This model concentrates on two main aspects: lateral viscosity variations (mainly controlled by temperature) in the lithosphere and internal friction angles of the pre-existing fault zone. Modeling results show that: (1) for a layered viscosity, en echelon faults would likely form when there is no pre-existing strike–slip fault; whereas, the basin would be narrow and deep, if any, when there is a pre-existing fault; (2) for moderate lateral viscosity variations, a large basin forms, even without a pre-existing fault zone; and (3) for strong lateral viscosity variations, a major rift could form over geologic time. Our results indicate that the initiation of the Yinggehai Basin requires moderate lateral viscosity variations (i.e., a pre-existing gentle upwelling of the Mohorovicic discontinuity) but no pre-existing fault. In addition, the initial extension predicted is NE–SW and is generated by the rotation of the Indochina block. This differs from the NW–SE extension that resulted from the movements of the Red River fault zone. This indicates that the left-lateral displacements of the Red River fault zone and the spreading of the South China Sea only influence the basin evolution after its initiation.

Wang, Xinguo; He, Jiankun; Ding, Lin; Gao, Risheng

2013-09-01

8

Electromagnetic Elasto-Plastic Dynamic Response of Conductive Plate  

NASA Astrophysics Data System (ADS)

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

Gao, Yuanwen

2010-05-01

9

Elasto-plastic modeling of volcano ground deformation  

NASA Astrophysics Data System (ADS)

Elasto-plastic models for pressure sources in heterogeneous domain were constructed to describe, assess, and interpret observed deformation in volcanic regions. We used the Finite Element Method (FEM) to simulate the deformation in a 3D domain partitioned to account for the volcano topography and the heterogeneous material properties distribution. Firstly, we evaluated the extent of a heated zone surrounding the magmatic source calculating the temperature distribution by a thermo-mechanical numerical model. Secondly, we included around the pressurized magma source an elasto-plastic zone, whose dimension is related to the temperature distribution. This elasto-plastic model gave rise to deformation comparable with that obtained from elastic and viscoelastic models, but requiring a geologically satisfactory pressure. We successfully applied the method to review the ground deformation accompanying the 1993-1997 inflation period on Mt Etna. The model considerably reduces the pressure of a magma chamber to a few tens of MPa to produce the observed surface deformation. Results suggest that the approach presented here can lead to more accurate interpretations and inferences in future modeling-based assessments of volcano deformation.

Currenti, Gilda; Bonaccorso, Alessandro; Del Negro, Ciro; Scandura, Danila; Boschi, Enzo

2010-08-01

10

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

Microsoft Academic Search

Efforts made over the last three decades to understand the fracture behaviour of structural materials in elastic and elasto-plastic\\u000a fracture mechanics are numerous, whereas investigations related to fracture behaviour of materials in thin sheets or general\\u000a yielding fracture regimes are limited in number. Engineering simulative tests are being used to characterize formability and\\u000a drawability of sheet metals. However, these tests

D. M. Kulkarni; Ravi Prakash; A. N. Kumar

2002-01-01

11

An elasto-plastic damage constitutive model with double yield surfaces for saturated soft rock  

Microsoft Academic Search

An elasto-plastic damage constitutive model with double yield surfaces is developed based on irreversible thermodynamics theory and damage mechanics theory. Two kinds of plastic deformation mechanisms, including plastic friction and plastic pore deformation mechanisms, are considered. The plastic friction yield criterion is established by a parabolic open function that incorporates the volumetric deformation effect, and the motion of yield function

C. Y. Zhou; F. X. Zhu

2010-01-01

12

Limit cycles in an elasto-plastic oscillator  

Microsoft Academic Search

A simple supported elasto-plastic beam is modeled as a single degree of freedom oscillator with bilinear hysteresis. Kinematic hardening is used as a problem parameter and an explicit map is obtained for plastic cycles under free vibrations. This map is analyzed and a bifurcation of the hardening parameter is discussed. An elasto-plastic limit cycle is shown to exist in a

Rudra Pratap; Subrata Mukherjee; Francis C. Moon

1992-01-01

13

Micropillar Compression Technique Applied to Micron-Scale Mudstone ElastoPlastic Deformation  

Microsoft Academic Search

Mudstone mechanical testing is often limited by poor core recovery and sample size, preservation and preparation issues, which can lead to sampling bias, damage, and time-dependent effects. A micropillar compression technique, originally developed by Uchic et al. 2004, here is applied to elasto-plastic deformation of small volumes of mudstone, in the range of cubic microns. This study examines behavior of

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

2010-01-01

14

Simulation of the rock microfracturing process under uniaxial compression using an elasto-plastic cellular automaton  

Microsoft Academic Search

In this paper, an elasto-plastic cellular automaton (EPCA) with the associated code was developed to simulate the non-linear fracturing process of rocks under uniaxial compression. It is a useful method for simulating the process of self-organization of the complex system using simple rules. It has the advantages of localization, parallelization, and being able to consider the heterogeneity of rocks. By

Xia-Ting Feng; Peng-Zhi Pan; Hui Zhou

2006-01-01

15

Explicit finite element method for calculation and analysis to the elasto-plastic dynamic response of fluid-saturated porous media  

Microsoft Academic Search

In order to describe the elasto-plastic dynamic response of fluid-saturated porous media, the incremental elasto-plastic wave\\u000a propagation equations of fluid-saturated porous media are developed by the fundamental theory of continuum mechanics and appointing\\u000a to the characteristic of fluid-saturated porous media. Then, the space discretization of these equations is performed to get\\u000a their Galerkin formula. At last, the time discretization of

Liang Li; Xiuli Du; Liyun Li; Chenggang Zhao

2007-01-01

16

Nonlinear elasto-plastic analysis of wire bond reliability for optical LQFP package  

Microsoft Academic Search

Nonlinear thermo-mechanical simulation is performed on optical low-profile quad flat package (OLQFP) to understand the root cause of the failure and to optimize the package design for improved wire bond reliability. 3D finite element model is established. Gold wire is considered as elasto-plastic material, which the properties are derived from the stress-strain curves measured at different temperatures. It is found

Xueren Zhang; Tong Yan Tee; Conrad Cachia

2004-01-01

17

Analysis and Research on Elasto-Plastic Response Spectra  

NASA Astrophysics Data System (ADS)

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

Ding, Jianguo; Chen, Wei

2010-05-01

18

Numerical verification of solutions for elasto-plastic torsion problems  

Microsoft Academic Search

In this paper, we consider a numerical technique which enables us to verify the existence of solutions for the elasto-plastic torsion problems governed by the variational inequality. Based upon the finite element approximations and the explicit a priori error estimates for a simple problem, we present an effective verification procedure that through numerical computation generates a set which includes the

S. H. Lee; Cheon Seoung Ryoo

2000-01-01

19

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

20

Elasto-plastic model with second order defect density tensor  

NASA Astrophysics Data System (ADS)

The paper deals with a second order finite elasto-plastic model, which involves the defect density tensor, as a measure of the extra material defects existing in the damaged microstructure. The material behaviour is described with respect to an anholonomic configuration, which is introduced through the second order plastic deformation, consisting in plastic distortion and plastic connection. The defect density tensor enters the expression of the plastic connection through its gradient and represents a measure of non-metricity. The constitutive and evolution equations are derived to be compatible with the free energy imbalance. The evolution equation for the defect density tensor is non-local and coupled with the plastic distortion.

Cleja-?igoiu, Sanda

2011-05-01

21

Orthotropic Model For Metallic Sheets In Finite Elasto-Plasticity  

SciTech Connect

In this paper we develop a model, with internal variables, small elastic strains, large elastic rotations and plastic deformations, within the constitutive framework of finite (multiplicative) elasto-plasticity, in Eulerian description. The Orthotropic initial anisotropy for sheets and evolving anisotropy are involved in the model. We pay attention to the full description of the model, not only on the anisotropic yield criteria. The boundary value problems, which describe at every time t the metal forming processes for sheets, lead to solve an appropriate variational inequality, for the velocity field and the plastic multiplier considered to be unknowns of the quasi-static problem.

Cleja-Tigoiu, Sanda [Faculty of Mathematics and Computer Science, University of Bucharest, str.Academiei 14, 010014 Bucharest (Romania)

2007-04-07

22

Visco-elasto-plastic rheology effects on free subduction dynamics  

NASA Astrophysics Data System (ADS)

Subduction dynamics on Earth is a typical three dimensional problem. Complex mantle flow can develop around and above the slabs. In addition, the 3D geometry of slabs (curvature, dip angle) evolves with time and can often be quite complicated. This last aspect strongly depends on their rheological properties and on the force balance in the bending region. Therefore understanding how bending processes, in a lithosphere with Earth-like rheology, affect the dynamics of subduction is key to compare numerical results with Earth subduction geometries. Scaling analysis based on 2D visco-elasto-plastic models has shown that one needs to take into account both the elastic and viscous strengths in order to correctly capture the bending effects on sinking velocities and dip angles. But most 3D numerical models developed so far use a visco-plastic rheology for slabs neglecting the role of elasticity in bending. We developed a new technique to model lithosphere-mantle interaction in 3D where lithosphere is a visco-elasto-plastic solid and mantle is a linear viscous fluid. At each iteration, a finite element solver is used to solve for creep in the oceanic plate and compute plate displacements. These displacements are then used as input in a boundary element software to calculate the full mantle circulation. New mantle tractions are then re-injected in the finite element software via a set of dashpots positioned around the oceanic plate. This technique has the advantage to calculate the full mantle drag only on the plate outer surface thus reducing considerably the computational time. We use this coupled approach to investigate the role of plate width and buoyancy on subduction behaviour.

Fourel, L.; Morra, G.; Goes, S.

2012-04-01

23

Normal and tangential force–displacement relations for frictional elasto-plastic contact of spheres  

Microsoft Academic Search

In this paper, we present the data obtained from numerical experiments that are at the foundation of our successful elasto-plastic force–displacement (FD) models in both the normal direction and tangential direction of spheres in collision. We also present in detail how these data were obtained. Our numerical experiments are in the form of frictional elasto-plastic finite-element analysis of spherical particles

Loc Vu-Quoc; Xiang Zhang; Lee Lesburg

2001-01-01

24

The solution of an axisymmetric inverse elasto-plastic problem using penetration diagrams  

Microsoft Academic Search

In this paper, we propose a mathematical model of a problem related to the determination of elasto-plastic properties of a deformable axisymmetric isotropic material using an experimentally given penetration diagram. The considered physical model is based on elasto-plastic deformation theory. The problem leads to an inverse coefficient problem for the non-linear system of equilibrium equations with an additional condition (experimentally

Alemdar Hasanov; Zahir Seyidmamedov

1995-01-01

25

A gap element for three-dimensional elasto-plastic contact problems  

Microsoft Academic Search

A simple yet efficient contact algorithm with gap elements is developed to solve three-dimensional elasto-plastic contact problems without friction. A special gap element is presented, together with a stress invariance principle, to model the contact process. The solution is achieved through an iterative procedure which adjusts the modulus of the gap elements. The elasto-plastic solid element with variable nodes and

Chang-Koon Choi; Gi Taek Chung

1996-01-01

26

An Elasto-Plastic Analysis of Solids by the Local Meshless Method Based on Mls  

NASA Astrophysics Data System (ADS)

A pseudo-elastic local meshless formulation is developed in this paper for elasto-plastic analysis of solids. The moving least square (MLS) is used to construct the meshless shape functions, and the weighted local weak-form is employed to derive the system of equations. Hencky's total deformation theory is applied to define the effective Young's modulus and Poisson's ratio in the nonlinear analysis, which are obtained in an iterative manner using the strain controlled projection method. Numerical studies are presented for the elasto-plastic analysis of solids by the newly developed meshless formulation. It has demonstrated that the present pseudo-elastic local meshless approach is very effective for the elasto-plastic analysis of solids.

Gu, Y. T.

27

Influence of interphase layer on the overall elasto-plastic behaviors of HA/PEEK biocomposite.  

PubMed

A three-dimensional finite element unit cell model has been designed and constructed for studying mechanical properties of hydroxyapatite (HA) reinforced polyetheretherketone (PEEK) biocomposite. The model consists of an elastic-brittle HA spherical particle, an elasto-plastic matrix and an interphase layer between the particle and the matrix. The interphase layers with four different kinds of material behaviors have been taken into consideration to examine their effects on the overall properties of the composite. The damage evolution in the matrix and the interphase layer, and the interface failure, were also taken into account. Some other factors, such as mesh sensitivity, loading velocity and mass scale scheme, were also discussed in this investigation. A general-purpose finite element software package, ABAQUS, incorporated with a user-defined material subroutine, was used to perform the analysis. The predicted results were compared with the experimental data obtained from existing literatures. The results predicted by using the cell model with consideration of the matrix degradation and the effects of the damage and failure on the interphase layer are in good agreement with the experimental ones. Hence, the suitability of our proposed cell model incorporated with an appropriate type of the interphase layer for modeling the mechanical properties of the particulate biocomposite could be verified. PMID:15130721

Fan, J P; Tsui, C P; Tang, C Y; Chow, C L

2004-10-01

28

Elasto-plasticity model in structural optimization of composite materials with periodic microstructures  

Microsoft Academic Search

The paper deals with a structural optimization of composite materials with periodic microstructures invoking an elasto-plasticity model with the von Mises yield criterion. Closest-point return mapping algorithms within the incremental finite element method are applied for the numerical solution of the problem. The latter iterative schemes are computationally effective, robust and stable, and have recently become the most popular means

Ronald H. W. Hoppe; Svetozara I. Petrova

29

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

SciTech Connect

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.

1991-06-01

30

A finite element analysis of elasto-plastic contact problems in metal forming  

Microsoft Academic Search

A contact finite element has been developed to solve elasto-plastic contact problems frequently encountered in metal forming processes. The element developed is based on the methodology originally used for solving elastic contact problems. It employs an interface spring algorithm that yields a symmetric type of elemental stiffness matrix and that can be conveniently handled by most exiting finite element solvers.

F. H. Lin; A. A. Tseng

1998-01-01

31

A posteriori error estimation for elasto-plastic problems based on duality theory  

Microsoft Academic Search

In this paper we introduce a new approach to a posteriori error estimation for elasto-plastic problems based on the duality theory of the calculus of variations. We show that, in spite of the prevailing view, duality methods provide a viable way for obtaining computable a posteriori error estimates for nonlinear boundary value problems without directly solving the dual problem. Rigorous

Sergey I. Repin; Leonidas S. Xanthis

1996-01-01

32

Complete polynomial expansion of domain variables at boundary for two-dimensional elasto-plastic problems  

Microsoft Academic Search

Domain variables were fully represented by complete series of polynomial expansions at the boundary via the intrinsic correlation among the integral kernels, all of them being derived fundamental solutions, in order to obtain the solution of elasto-plastic problems using the boundary element method without domain integrals in the two-dimensional case. The numerical example of curved surface fitting was performed using

Hang Ma; Norio Kamiya; Song Qing Xu

1998-01-01

33

A semi-smooth Newton method for elasto-plastic contact problems  

Microsoft Academic Search

In this paper we reformulate the frictional contact problem for elasto-plastic bodies as a set of unconstrained, non-smooth equations. The equations are semi-smooth so that Pang's Newton method for B-differentiable equations can be applied. An algorithm based on this method is described in detail. An example demonstrating the efficiency of the algorithm is presented.

Peter W. Christensen

2002-01-01

34

Convergence of Newton-type methods in incremental return mapping analysis of elasto-plastic problems  

Microsoft Academic Search

The incremental finite element algorithm with return mapping stress computation is considered for the solution of problems of elasto-plasticity. This algorithm, performed in load steps, leads to the necessity of solving large scale nonlinear systems. The properties of these systems are investigated in the presented paper together with two iterative techniques for their solution. The main results of the paper

Radim Blaheta

1997-01-01

35

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

36

A meshfree method and its applications to elasto-plastic problems  

Microsoft Academic Search

Standard finite element approaches are still ineffective in handling extreme material deformation, such as cases of large deformations and moving discontinuities due to severe mesh distortion. Among meshfree methods developed to overcome the ineffectiveness, Reproducing Kernel Particle Method (RKPM) has demonstrated its great suitability for structural analysis. This paper presents applications of RKPM in elasto-plastic problems after a review of

ZHANG Ji-fa; ZHANG Wen-pu; ZHENG Yao

2005-01-01

37

On the Use of a Special Nonassociated Flow Rule for Problems of Elasto-Plastic Wave Propagation.  

National Technical Information Service (NTIS)

Computational work to determine wave propagation in soils has been undertaken by various groups, using elasto-plastic materials with nonassociated flow rules. Theoretical objections against such computations have been raised, because in static problems no...

H. H. Bleich

1971-01-01

38

Numerical implementation of pressure-dependent elasto-plastic cosserat continuum model in ABAQUS  

Microsoft Academic Search

Abstact: The subroutine UEL embedded in commercial FEM software ABAQUS is utilized to develop a user element based on the material of pressure-dependent elasto-plastic cosserat continuum model. The user element adopt plane eight-node isoparametric unit which include three degree of freedom(two translation and one rotation) at each node, the Drucker-Prager material model with associate flow rule is used, the stress

Congwen Peng; Xiangguo Kong; Chengxiang Xu

2011-01-01

39

Finite element modelling of anisotropic elasto-plastic timber composite beams with openings  

Microsoft Academic Search

In this paper, constitutive equations to model anisotropic elasto-plastic timber composite beams with openings were formulated and implemented into the finite element (FE) package ABAQUS, via a user-defined subroutine. The Tsai–Hill criterion was applied to judge failure of Oriented Strand Board (OSB) and timber in tension. Both OSB and timber in tension were modelled as linear orthotropic elastic materials, and

Z. W. Guan; E. C. Zhu

2009-01-01

40

Conditions for locking-free elasto-plastic analyses in the Element-Free Galerkin method  

Microsoft Academic Search

The use of finite elements with linear displacement fields in volume-preserving elasto-plastic problems can lead to volumetric locking. Due to the inability of the shape functions to describe certain displacement modes, a response of the structure can be obtained which is much too stiff. The Element-Free Galerkin (EFG) method can provide shape functions that have an intrinsic richer nature and

Harm Askes; René de Borst; Otto Heeres

1999-01-01

41

A finite-strain cam-clay model in the framework of multiplicative elasto-plasticity  

Microsoft Academic Search

The present work discusses a finite-strain plasticity model for soft clays. To motivate such a model, the infinitesimal-strain assumption is shown to be inadequate for the constitutive description of soft clays. Hence, assuming the multiplicative elasto-plastic decomposition of the deformation gradient, a finite-strain Cam-clay model is presented. In particular, with respect to the original Cam-clay formulation, this model improves the

C. Callari; F. Auricchio; E. Sacco

1998-01-01

42

A meshfree method and its applications to elasto-plastic problems  

Microsoft Academic Search

Standard finite element approaches are still ineffective in handling extreme material deformation, such as cases of large\\u000a deformations and moving discontinuities due to severe mesh distortion. Among meshfree methods developed to overcome the ineffectiveness,\\u000a Reproducing Kernel Particle Method (RKPM) has demonstrated its great suitability for structural analysis. This paper presents\\u000a applications of RKPM in elasto-plastic problems after a review of

Zhang Ji-fa; Zhang Wen-pu; Zheng Yao

2005-01-01

43

An ElastoPlastic Analysis of Solids by the Local Meshless Method Based on Mls  

Microsoft Academic Search

A pseudo-elastic local meshless formulation is developed in this paper for elasto-plastic analysis of solids. The moving least square (MLS) is used to construct the meshless shape functions, and the weighted local weak-form is employed to derive the system of equations. Hencky's total deformation theory is applied to define the effective Young's modulus and Poisson's ratio in the nonlinear analysis,

Y. T. Gu

2008-01-01

44

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

Microsoft Academic Search

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

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

2010-01-01

45

Fracture mechanics  

SciTech Connect

The papers presented at the symposium are grouped under the following headings: elastoplastic analyses, linear elastic analyses, temperature and environmental effects, elastoplastic experiments, fatigue crack growth, applications, dynamic fracture mechanics, and basic considerations. Papers are presented on an evaluation of analytical solutions for corner cracks at holes; a model for creep/fatigue interactions in Alloy 718; analysis of bending parameters for bending-type specimens; and characterization of crack closure. Papers are also included on the crack arrest behavior of a high-strength aluminum alloy; observations of a fracture mechanics approach to fatigue crack initiation in Ti-6Al-4V; and elastic-plastic failure analysis of pressure vessel tests.

Kanninen, M.F.; Hopper, A.T.

1985-01-01

46

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

47

Fracture mechanics  

Microsoft Academic Search

The papers presented at the symposium are grouped under the following headings: elastoplastic analyses, linear elastic analyses, temperature and environmental effects, elastoplastic experiments, fatigue crack growth, applications, dynamic fracture mechanics, and basic considerations. Papers are presented on an evaluation of analytical solutions for corner cracks at holes; a model for creep\\/fatigue interactions in Alloy 718; analysis of bending parameters for

M. F. Kanninen; A. T. Hopper

1985-01-01

48

Mesomechanical analysis of the ELASTO-PLASTIC behavior of a 3D composite-structure under tension  

NASA Astrophysics Data System (ADS)

In this contribution, a mesomechanical approach to simulate the mechanical behavior with explicit consideration of the three-dimensional structure is applied to study the elasto-plastic response of a metal matrix composite material under tension. A procedure of a step-by-step packing (SSP) of a finite volume with structural elements has been used to design the composite structure consisting of an Al(6061)-matrix with Al2O3-inclusions. A three-dimensional mechanical problem of the structure behavior under tension has been solved numerically, using both an implicit finite-element method and an explicit finite-difference code. Special attention is given to the comparison of quasistatic and dynamic calculations. Evolution of plastic deformation in the matrix during tensile loading has been investigated. Qualitative and quantitative analysis of different components of stress and strain tensors is provided on the basis of mesomechanical concepts. Basing on the 3D-analysis, some conclusions regarding an applicability of a 2D approximation when considering deformation behavior on meso and macro scale levels have been done.

Romanova, V. A.; Soppa, E.; Schmauder, S.; Balokhonov, R. R.

2005-11-01

49

Application of the Sinc method to a dynamic elasto-plastic problem  

NASA Astrophysics Data System (ADS)

This paper presents the application of Sinc bases to simulate numerically the dynamic behavior of a one-dimensional elastoplastic problem. The numerical methods that are traditionally employed to solve elastoplastic problems include finite difference, finite element and spectral methods. However, more recently, biorthogonal wavelet bases have been used to study the dynamic response of a uniaxial elasto-plastic rod [Giovanni F. Naldi, Karsten Urban, Paolo Venini, A wavelet-Galerkin method for elastoplasticity problems, Report 181, RWTH Aachen IGPM, and Math. Modelling and Scient. Computing, vol. 10, 2000]. In this paper the Sinc-Galerkin method is used to solve the straight elasto-plastic rod problem. Due to their exponential convergence rates and their need for a relatively fewer nodal points, Sinc based methods can significantly outperform traditional numerical methods [J. Lund, K.L. Bowers, Sinc Methods for Quadrature and Differential Equations, SIAM, Philadelphia, 1992]. However, the potential of Sinc-based methods for solving elastoplasticity problems has not yet been explored. The aim of this paper is to demonstrate the possible application of Sinc methods through the numerical investigation of the unsteady one dimensional elastic-plastic rod problem.

Abdella, K.; Yu, X.; Kucuk, I.

2009-01-01

50

Convergence of inexact Newton-like iterations in incremental finite element analysis of elasto-plastic problems  

Microsoft Academic Search

Convergence of two inexact Newton-like methods suitable for application in incremental finite element analysis of problems of elasto-plasticity is investigated by a new technique based on a certain approximation condition. It is shown that the convergence can be controlled by the size of load increments. A numerical example illustrates the developed theoretical results.

R. Blaheta; O. Axelsson

1997-01-01

51

Hardness profile analysis of elasto-plastic heat-treated steels with a gradient in yield strength  

Microsoft Academic Search

An elasto-plastic indentation study on materials with a yield strength gradient like steels which have undergone thermal hardening such as nitriding, is carried out using experimental and finite element methods. The analysis of the normalized mean contact pressure as a function of a dimensionless strain parameter for graded materials shows that the mean contact pressure presents the same tendency as

A. Nayebi; R. El Abdi; O. Bartier; G. Mauvoisin

2002-01-01

52

A Smooth, Three-Surface ElastoPlastic Cap Model: Rate Formulation, Integration Algorithm and Tangent Operators  

Microsoft Academic Search

One of the primary strengths of elasto-plastic cap models is their ability to capture the gross inelastic coupling between deviatoric and volumetric behaviors of many porous media. While numerical integration algorithms for these models have been presented in the literature, performing implicit analysis of earthen systems using cap models remains a challenging endeavor. One of the difficulties associated with most

Colby C. Swan

53

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

NASA Astrophysics Data System (ADS)

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

Zhang, Xiang; Vu-Quoc, Loc

2007-07-01

54

A fast elasto-plastic formulation with hierarchical matrices and the boundary element method  

NASA Astrophysics Data System (ADS)

Boundary element methods offer some advantages for the simulation of tunnel excavation since the radiation condition is implicitly fulfilled and only the excavation and ground surfaces have to be discretized. Hence, large meshes and mesh truncation, as required in the finite element method, are avoided. Recently, capabilities for efficiently dealing with inelastic behavior and ground support have been developed, paving the way for the use of the method to simulate tunneling. However, for large scale three dimensional problems one drawback of the boundary element method becomes prominent: the computational effort increases quadratically with the problem size. To reduce the computational effort several fast methods have been proposed. Here a fast boundary element solution procedure for small strain elasto-plasticity based on a collocation scheme and hierarchical matrices is presented. The method allows the solution of problems with the computational effort and sparse storage increasing almost linearly with respect to the problem size.

Zechner, Jürgen; Beer, Gernot

2013-04-01

55

Degenerate Dirichlet Problems Related to the Invariant Measure of Elasto-Plastic Oscillators  

SciTech Connect

A stochastic variational inequality is proposed to model a white noise excited elasto-plastic oscillator. The solution of this inequality is essentially a continuous diffusion process for which a governing diffusion equation is obtained to study the evolution in time of its probability distribution. The diffusion equation is degenerate, but using the fact that the degeneracy occurs on a bounded region we are able to show the existence of a unique solution satisfying the desired properties. We prove the ergodic properties of the process and characterize the invariant measure. Our approach relies on extending Khasminskii's method (Stochastic Stability of Differential Equations, Sijthoff and Noordhoff, 1980), which in the present context leads to the study of degenerate Dirichlet problems with nonlocal boundary conditions.

Bensoussan, Alain [University of Texas at Dallas, International Center for Decision and Risk Analysis, ICDRiA, School of Management (United States)], E-mail: Alain.Bensoussan@utdallas.edu; Turi, Janos [University of Texas at Dallas, Programs in Mathematical Sciences (United States)], E-mail: turi@utdallas.edu

2008-08-15

56

Dual boundary element formulation for elastoplastic fracture mechanics  

NASA Astrophysics Data System (ADS)

In this paper the extension of the dual boundary element method (DBEM) to the analysis of elastoplastic fracture mechanics (EPFM) problems is presented. The dual equations of the method are the displacement and the traction boundary integral equations. When the displacement equation is applied on one of the crack surfaces and the traction equation on the other, general mixed-mode crack problems can be solved with a single-region formulation. In order to avoid collocation at crack tips, crack kinks and crack-edge corners, both crack surfaces are discretized with discontinuous quadratic boundary elements. The elasto-plastic behavior is modelled through the use of an approximation for the plastic component of the strain tensor on the region expected to yield. This region is discretized with internal quadratic, quadrilateral and/or triangular cells. This formulation was implemented for two-dimensional domains only, although there is no theoretical or numerical limitation to its application to three-dimensional ones. A center-cracked plate and a slant edge-cracked plate subjected to tensile load are analysed and the results are compared with others available in the literature. J-type integrals are calculated.

Leitao, V.; Aliabadi, M. H.; Rooke, D. P.

1995-01-01

57

Mathematical model of phase transformations and elasto-plastic stress in the water spray quenching of steel bars  

SciTech Connect

A mathematical model, based on the finite-element technique and incorporating thermo-elasto-plastic behavior during the water spray quenching of steel, has been developed. In the model, the kinetics of diffusion-dependent phase transformation and martensitic transformation have been coupled with the transient heat flow to predict the microstructural evolution of the steel. Furthermore, an elasto-plastic constitutive relation has been applied to calculate internal stresses resulting from phase changes as well as temperature variation. The computer code has been verified for internal consistency with previously published results for pure iron bars. The model has been applied to the water spray quenching of two grades of steel bars, 1035 carbon and nickel-chromium alloyed steel; the calculated temperature, hardness, distortion, and residual stresses in the bars agreed well with experimental measurements. The results show that the phase changes occurring during this process affect the internal stresses significantly and must be included in the thermomechanical model.

Nagasaka, Y. (Komatsu Ltd., Osaka (Japan)); Brimacombe, J.K. (Alcan International Ltd., Montreal, Quebec (Canada)); Hawbolt, E.B.; Samarasekera, I.V.; Hernandez-Morales, B. (Univ. of British Columbia, Vancouver (Canada)); Chidiac, S.E. (National Research Council of Canada, Ottawa, Ontario (Canada))

1993-04-01

58

Thermal elasto-plastic finite element modelling of the deformation behaviour of metal matrix composites considering interfacial strength  

Microsoft Academic Search

A suggestion of the strength analysis technique considering the interfacial bonding strength is very important for the design\\u000a of parts and the estimation of fatigue behavior. In this paper three dimensional finite element analysis was performed during\\u000a the elasto-plastic deformation of particulate reinforced metal matrix composites. Bonding strength, interface separation and\\u000a matrix void growth between the matrix and reinforcements were

Y. H. Seo; C. G. Kang

1998-01-01

59

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

Microsoft Academic Search

We present in this paper the displacement-driven version of a tangential force–displacement (TFD) model that accounts for both elastic and plastic deformations together with interfacial friction occurring in collisions of spherical particles. This elasto-plastic frictional TFD model, with its force-driven version presented in [L. Vu-Quoc, L. Lesburg, X. Zhang. An accurate tangential force–displacement model for granular-flow simulations: contacting spheres with

Xiang Zhang; Loc Vu-Quoc

2007-01-01

60

A thermo-elasto-plastic constitutive law for inhomogeneous materials based on an incremental Mori–Tanaka approach  

Microsoft Academic Search

The behavior of a composite consisting of aligned thermo-elastic reinforcements embedded in a thermo-elasto-plastic matrix is described by an incremental Mori–Tanaka mean field approach. The matrix phase behavior is described by incremental J2 plasticity and the breakdown of isotropy of the matrix phase upon yielding is accounted for. The proposed method is implemented as a constitutive material model for a

H. E. Pettermann; A. F. Plankensteiner; H. J. Böhm; F. G. Rammerstorfer

1999-01-01

61

Modeling the dependence of the coefficient of restitution on the impact velocity in elasto-plastic collisions  

Microsoft Academic Search

We discuss the modeling of the coefficient of restitution as a function of the incoming velocity in elasto-plastic collisions with normal frictionless impact, and compare the results from nonlinear finite-element analysis to those of two recent normal force displacement models: One by Thornton (ASME J. Appl. Mech. 64 (1997) 383) and one by Vu-Quoc and Zhang (Proc. R. Soc. London,

Xiang Zhang; Loc Vu-Quoc

2002-01-01

62

Evaluation of Fatigue Crack Growth Behavior in FSW Joint by Experiment, Analysis and ElastoPlastic FEM  

Microsoft Academic Search

\\u000a Elasto-plastic FEM is used to examine the crack opening stress of a 2024-T3 Aluminum alloy sheet and a friction stir welded\\u000a (FSW) panel. To investigate the effect of plastic deformation around the crack on the crack opening stress, the effects of\\u000a the following two parameters, the distance between the weld line and the center of the crack starter, and the

T. Okada; K. Kuwayama; M. Asakawa; T. Nakamura; S. Machida; S. Fujita; H. Terada

63

Finite element simulations of elasto-plastic processes in Nb3Sn strands  

NASA Astrophysics Data System (ADS)

The manufacturing of Nb3Sn strands, with drawing and annealing of multifilamentary strands followed by a heat treatment at about 900 K to form the Nb3Sn by reaction of tin and niobium, has the potential to create a complex internal stress system. The strain sensitivity of the Nb3Sn superconducting properties makes prediction of the internal stresses a necessary step to understanding the performance of Nb3Sn conductors under the magnetic load conditions experienced in a coil. An elasto-plastic one dimensional finite element model, including temperature dependent stress strain curves, annealing and manufacturing process stresses, is used to derive the internal stresses of Nb3Sn strands. The model is benchmarked against a range of experimental data, including stress strain tensile tests, superconducting critical current strain tests, and length changes through heat treatment and through a 4 K thermal cycle. The model can predict all the experimental features and shows a number of unexpected conclusions regarding the origin of the Nb3Sn stresses.

Mitchell, N.

2005-07-01

64

Size effects in the conical indentation of an elasto-plastic solid  

NASA Astrophysics Data System (ADS)

The size effect in conical indentation of an elasto-plastic solid is predicted via the Fleck and Willis formulation of strain gradient plasticity (Fleck, N.A. and Willis, J.R., 2009, A mathematical basis for strain gradient plasticity theory. Part II: tensorial plastic multiplier, J. Mech. Phys. Solids, 57, 1045-1057). The rate-dependent formulation is implemented numerically and the full-field indentation problem is analyzed via finite element calculations, for both ideally plastic behavior and dissipative hardening. The isotropic strain-gradient theory involves three material length scales, and the relative significance of these length scales upon the degree of size effect is assessed. Indentation maps are generated to summarize the sensitivity of indentation hardness to indent size, indenter geometry and material properties (such as yield strain and strain hardening index). The finite element model is also used to evaluate the pertinence of the Johnson cavity expansion model and of the Nix-Gao model, which have been extensively used to predict size effects in indentation hardness.

Danas, K.; Deshpande, V. S.; Fleck, N. A.

2012-09-01

65

An analysis for the elasto-plastic problem of the moderately thick plate using the meshless local Petrov–Galerkin method  

Microsoft Academic Search

A meshless local Petrov–Galerkin method for the analysis of the elasto-plastic problem of the moderately thick plate is presented. The discretized system equations of the moderately thick plate are obtained using a locally weighted residual method. It uses a radial basis function (RBF) coupled with a polynomial basis function as a trial function, and uses the quartic spline function as

P. Xia; S. Y. Long; K. X. Wei

2011-01-01

66

The Effective Fracture Toughness in Hydraulic Fracturing  

Microsoft Academic Search

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

Panos Papanastasiou

1999-01-01

67

Modified Integration Algorithm in the Strain Space for Rate and Temperature Dependent Elasto-Plastic Constitutive Model  

NASA Astrophysics Data System (ADS)

This paper is concerned with modified integration algorithm in the strain space for rate and temperature dependent elasto-plastic constitutive relations in order to obtain more accurate results in numerical implementation. The proposed algorithm adopts both the 2-stage Lobatto IIIA with second-order accuracy and the iteration procedure using the Newton-Raphson method to enfoce consistency at the end of the step. The algorithm enables to consider the convective stress rates on the yield surface in the strain space in the numerical integration of the constitutive model. Accuracy assessment using the isoerror maps and FEM analysis of the adiabatic shear band is carried out in order to demonstrate the accuracy of the proposed algorithm.

Cho, Sang-Soon; Huh, Hoon

68

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

69

Micromechanical modeling of open cell structures with application in finite element analysis of vertebral body mechanics  

NASA Astrophysics Data System (ADS)

A nonlinear micromechanical model for two-dimensional irregular hexagonal foams has been developed that allows for anisotropy in morphology and/or material. Based upon the orientation, cross-section, length, and material properties of each strut, the resulting micro-level beam behavior within the unit cell determines its structural properties. Nonlinearity is introduced as coupled elasto-plastic beam behavior, where the elasto-plastic behavior of each beam is considered. The analytical formulation for the stiffness matrix of the general elasto-plastic unit cell is found by considering compatibility and equilibrium of the unit cell. The structural properties of the elasto-plastic unit cell are embedded in a continuum finite element model as material properties, thus capturing the microstructure of the foam in an accurate and efficient model. Structural nonlinearity is therefore directly linked to localized plasticity and its evolution at the micro-level. Elastic analyses investigated the degree of anisotropy in structural properties that was induced by various morphological changes. Plastic analyses showed how structural nonlinearity could be explained by localized microstructural behavior. The formulation for the three-dimensional regular hexagonal foam was then developed as an extension of the two-dimensional formulation. Sensitivity of the constitutive properties to the microstructure and its orientation was studied. The model was then validated for application as an idealized model of the porous trabecular bone material of the human vertebra. The mechanical behavior of the model was shown to capture the basic characteristics of actual bone, where changes in behavior associated with age-related changes in bone architecture (increasing porosity with age) were also considered. Nonlinearity in the load-displacement behavior of trabecular bone specimens was directly linked to localized microstructural nonlinearity and its evolution. Validation was followed by applications in static compression of a whole vertebra. Elastic finite element analyses showed that the relative contribution of the shell to the load-bearing ability of the vertebra decreases with increasing age and lateral wall curvature. Nonlinear elasto-plastic analyses showed regions of failure concentrated in the upper posterior region of the vertebra in both the shell and core components. The model has provided a clearer understanding of the relative role of the core and shell in vertebral body mechanics and has shed light on the mechanism of vertebral burst fracture.

Overaker, David Wolfgang

1997-12-01

70

Introduction into Fracture Mechanics.  

National Technical Information Service (NTIS)

The present report gives an introduction to the basic principles of fracture mechanics. First the behaviour of a linear elastic body containing a crack is described. This is followed by a survey of experimental methods for the determination of fracture me...

K. H. Schwalbe

1981-01-01

71

Linear Elastic Fracture Mechanics Primer.  

National Technical Information Service (NTIS)

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 m...

C. D. Wilson

1992-01-01

72

Fracture mechanics applied to rock  

Microsoft Academic Search

The fracture of rock and theories to predict fracture loads are reviewed in light of the observed mechanisms of fracture in rock. A zone of microcracking precedes the formation of a fracture. In this zone, considerable energy is absorbed by the material. Hence the specific work of fracture (the energy to form a unit of projected fracture surface) is much

1973-01-01

73

Scale Independent Fracture Mechanics  

Microsoft Academic Search

\\u000a Fracture mechanics is considered from the viewpoint of a field theoretical approach based on the physical principle known\\u000a as gauge invariance. The advantage of this approach is scale independent and universal. All stages of deformation, from the\\u000a elastic stage to fracturing stage can be treated on the same theoretical foundation. A quantity identified as the deformation\\u000a charge is found to

Sanichiro Yoshida; Diwas Bhattarai; Tatsuo Okiyama; Kensuke Ichinose

74

Short Course on Fracture and Fracture Mechanics of Metallic Materials.  

National Technical Information Service (NTIS)

The visual presentation sheets of a course on fracture and fracture mechanics in metallic materials are reproduced. The course includes an introduction to fracture mechanics; fracture mechanisms in metallic materials; and the influence of material behavio...

R. J. H. Wanhill

1984-01-01

75

Fracture Mechanics of Inelastic Polymers.  

National Technical Information Service (NTIS)

The author's Generalized Theory of Fracture Mechanics has been applied to several quite different polymeric materials which have in common a nonlinear and inelastic deformation behaviour. Thus the normal Linear Elastic Fracture Mechanics cannot be applied...

E. H. Andrews

1979-01-01

76

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

77

Modeling of the thermal elasto-plastic behavior for composite materials using the homogenization method  

Microsoft Academic Search

In this dissertation, the homogenization method is used to investigate the thermo-mechanical behavior of composite materials. Assuming the characteristic microstructure in a composite material is spatially repeating, the equivalent material properties in one unit cell are calculated. These equivalent material properties represent the microscopic information. Using this approach, three research topics, in particular, stationary heat conduction, thermoelasticity and thermal elastoplasticity

Chaohsien

1992-01-01

78

Damage coupled elasto-plastic finite element analysis of a Timoshenko layered beam  

Microsoft Academic Search

Based on continuum damage mechanics (CDM), the paper presents a non-linear finite element formulation for a Timoshenko beam. A layered approach has been adopted to simulate the progressive growth of damage and plasticity from extreme fibers towards the neutral axis. An isotropic continuum damage 1-D model has been derived for damage evolution for material like Al 2024-T3. Coupling damage with

S. Chandrakanth; P. C. Pandey

1998-01-01

79

Fracture mechanics: Perspectives and directions  

SciTech Connect

The present work includes twelve invited review papers with comprehensive descriptions of the challenges in six topical areas: analytical fracture mechanics, nonlinear and time-dependent fracture mechanics, microstructure and micromechanical modeling, fatigue crack propagation, environmentally assisted cracking, and fracture mechanics of nonmetals and new frontiers. Specific challenge areas include the analytical front, advanced heterogeneous materials, subcritical crack growth for both fatigue and sustained-load crack growth in deleterious environments at elevated temperatures, and problems of education. The book demonstrates that the existing fracture mechanics foundation is well positioned to meet these challenges over the next decades.

Wei, R.P.; Gangloff, R.P.

1989-01-01

80

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

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

81

Mechanics of Ductile Fracture.  

National Technical Information Service (NTIS)

The phenomenon of ductile fracture in plate specimens is described by a finite element stress analysis coupled with the strain energy density fracture criterion. The last ligament of failure tends to curve developing a cup-and-cone type of fracture in ten...

G. C. Sih

1977-01-01

82

Fracture mechanics of composite materials  

Microsoft Academic Search

The above circumstances lead to models based on a discussion of the structure of a composite being used most frequently in the fracture mechanics of composite materials. In view of the stochastic properties of the elements in the structure, especially the dispersion in the strength of the fibers, stochastic fracture models are widely used [4-7]. Nevertheless, there has been no

V. V. Bolotin

1981-01-01

83

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

84

Electronics reliability fracture mechanics. Volume 2: Fracture mechanics  

NASA Astrophysics Data System (ADS)

This is the second of two volumes. The other volume (WL-TR-92-3015) is 'Causes of Failures of Shop Replaceable Units and Hybrid Microcircuits.' The objective of the Electronics Reliability Fracture Mechanics (ERFM) program was to develop and demonstrate a life prediction technique for electronic assemblies, when subjected to environmental stresses of vibration and thermal cycling, based upon the mechanical properties of the materials and packaging configurations which make up an electronic system. The application of fracture mechanics to microscale phenomena in electronic assemblies was a pioneering research effort. The small scale made the experiments very difficult; for example, the 1-mil-diameter bond wires in microelectronic devices are 1/3 the diameter of a human hair. A number of issues had to be resolved to determine whether a fracture mechanics modelling approach is correct for the selected failures; specifically, the following two issues had to be resolved: What fraction of the lifetime is spent in crack initiation? Are macro fracture mechanics techniques, used in large structures such as bridges, applicable to the tiny structures in electronic equipment? The following structural failure mechanisms were selected for modelling: bondwire fracture from mechanical cycling; bondwire fracture from thermal (power) cycling; plated through hole (PTH) fracture from thermal cycling. The bondwire fracture test specimens were A1-1 percent Si wires, representative of wires used in the parts in the modules selected for detailed investigation in this program (see Vol. 1 of this report); 1-mil-diameter wires were tested in this program. The PTH test specimens were sections of 14-layer printed wiring boards of the type used.

Kallis, J.; Duncan, L.; Buechler, D.; Backes, P.; Sandkulla, D.

1992-05-01

85

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

86

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

87

(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

88

Influence of volumetric–deviatoric coupling on crack prediction in concrete fracture tests  

Microsoft Academic Search

The influence of volumetric–deviatoric coupling on the prediction of curved crack patterns in concrete fracture tests is analyzed by using an elasto-plastic-damage model, for which the amount of volumetric–deviatoric coupling is controlled by the hardening modulus of the plasticity model. First, the tangent stiffness matrix and the total stress–strain response for simple shear are investigated. Then, two fracture tests reported

P. Grassl; R. Rempling

2007-01-01

89

Error estimates for stresses in the finite element analysis of the two-dimensional elasto-plastic problems  

Microsoft Academic Search

In the present paper an error estimate for finite element approximations based on the Haar-Karman variational principle is given. To satisfy exactly equilibrium equations in stresses equilibrium finite elements are used while yield condition is satisfied approximately by means of the penalty function having clear mechanical sense. It is shown that there is some relation between parameters of discretization and

G. Seregin

1995-01-01

90

An elasto-plastic model for non-isothermal analysis of flow and deformation in unsaturated porous media: formulation  

Microsoft Academic Search

A rigorous and unified treatment of the theory of non-isothermal flow and deformation in unsaturated porous media is presented. The governing equations based on the equations of equilibrium, the effective stress concept, Darcy's law, Fourier's law and the conservation equations of mass and energy are derived using a systematic macroscopic approach. The thermo-hydro-mechanical coupling processes taken into account include: thermal

N. Khalili; B. Loret

2001-01-01

91

Fracture mechanics of ferroelectric ceramics  

NASA Astrophysics Data System (ADS)

The reliable operation of smart devices and structures depends on the integrity of the materials chosen for sensor and actuator components. Though piezoelectric ceramics rank among the most common transducer materials, their mechanical reliability has yet to be characterized adequately. The difficulty stems from a basic discrepancy between theoretical predictions and empirical observations of their fracture behavior. For instance, experiments conducted on transversely isotropic piezoceramics with cracks normal to the poling axis show an odd functional dependence between the failure load and the applied electric field, but the linear fracture analysis indicates an even relation. In tests performed on unpoled ferroelectric ceramics, an applied voltage appears to promote cracking, while the linear theory predicts no such effect. In an effort to reconcile theory with experience, we present two physics-based models for the polarization switching and saturation that dominate material nonlinearity in these ceramics. In the first, we separate the length scales of the electrical yielding zone and the fracture process zone, and represent the electrical nonlinearity using discrete dipoles superimposed on a homogeneous piezoelectric medium. The multiscale framework reveals a singularity conversion, from apparent electromechanical intensities at the global level to purely mechanical effective opening forces in the local view. By restricting the nonlinearity to a plane passing through the crack front, we derive a closed-form expression for the driving force in terms of the local stress intensities. The resulting fracture criterion is independent of the microstructural parameters, and it predicts a dependence of critical stress on electric field that qualitatively matches the empirically observed trends. In the second model, we remove the geometrical restrictions on the nonlinear region, and include the effects of the transformation strains induced by polarization switching. Local domain interactions are simulated using combinations of electric dipoles and force couples affixed to an isotropic background medium, and domain orientations are changed when an electromechanical energy threshold is exceeded. The model successfully reproduces the hysteresis and butterfly loops typically measured in ferroelectric ceramics. Furthermore, our simulations predict an influence of near-tip domains on crack-opening stresses that explains the effect of voltage on apparent strength reported in experiments.

Fulton, Chandler Chang-Il

92

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

93

A review of the J and I integrals and their implications for crack growth resistance and toughness in ductile fracture  

Microsoft Academic Search

The application of the J and the I-integrals to ductile fracture are discussed. It is shown that, because of the finite size of the fracture process zone (FPZ), the initiation value of the J-integral is specimen dependent even if the plastic constraint conditions are constant. The paradox that the I-integral for steady state elasto-plastic crack growth is apparently zero is

B. Cotterell; A. G. Atkins

1996-01-01

94

Application of fracture mechanics in geological materials  

Microsoft Academic Search

Application of conventional fracture mechanics concepts to treat crack growth and failure problems in geological media is discussed in this paper. Conventional fracture mechanics methods were developed mainly for metallic materials which exhibit nonlinearity associated mainly with plasticity type responses. Thus, these are not directly applicable to geological materials whose inelastic responses originate from inherent large-scale heterogenities, microcracking, strain softening,

1991-01-01

95

Nonlinear fracture mechanics. Volume 1. Time-dependent fracture  

SciTech Connect

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

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

1989-01-01

96

Fracture mechanisms and fracture control in composite structures  

NASA Astrophysics Data System (ADS)

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

Kim, Wone-Chul

97

HFIR vessel probabilistic fracture mechanics analysis  

Microsoft Academic Search

The life of the High Flux Isotope Reactor (HFIR) pressure vessel is limited by a radiation induced reduction in the material`s fracture toughness. Hydrostatic proof testing and probabilistic fracture mechanics analyses are being used to meet the intent of the ASME Code, while extending the life of the vessel well beyond its original design value. The most recent probabilistic evaluation

R. D. Cheverton; T. L. Dickson

1997-01-01

98

Fracture Mechanics for Structural Adhesive Bonds.  

National Technical Information Service (NTIS)

Tests and analyses were conducted to develop and demonstrate the fracture mechanics methodology to predict the growth of bondline flaws in adhesively bonded primary aircraft structure. The development and use of a new baseline specimen for testing bondlin...

T. R. Brussat S. T. Chiu S. Mostovoy

1977-01-01

99

Fracture Mechanics Applications in Rock-Mechanics Problems.  

National Technical Information Service (NTIS)

The application of fracture mechanics principles to the solution of rock-mechanics problems is discussed. Specifically, two examples relating to high-energy gas fracturing and oil-shale blasting are presented to illustrate the point. In high-energy gas fr...

E. P. Chen

1983-01-01

100

The effects of deformations by rolling and uniaxial tension on the structure and the magnetic and mechanical properties of armco iron, steel 12X18H10T, and a steel 12X18H10T-Armco Iron-Steel 12X18H10T composite material  

Microsoft Academic Search

The effects of elasto-plastic deformations by rolling and uniaxial tension on the structure and the magnetic and mechanical\\u000a properties of Armco Iron, 12X18H10T steel, and a three-layer Steel 12X18H10T-Armco Iron-Steel 12X18H10T model composite material\\u000a are investigated. The magnetic characteristics, which vary uniquely during elasto-plastic deformations, thus allowing their\\u000a use as parameters for estimating mechanical properties and the degree of deformation

E. S. Gorkunov; S. M. Zadvorkin; E. A. Kokovikhin; E. A. Tueva; Yu. V. Subachev; L. S. Goruleva; A. V. Podkopytova

2011-01-01

101

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

102

Fracture mechanisms and fracture control in composite structures  

Microsoft Academic Search

Four basic failure modes--delamination, delamination buckling of composite sandwich panels, first-ply failure in cross-ply laminates, and compression failure--are analyzed using linear elastic fracture mechanics (LEFM) and the J-integral method. Structural failures, including those at the micromechanical level, are investigated with the aid of the models developed, and the critical strains for crack propagation for each mode are obtained. In the

Wone-Chul Kim

1991-01-01

103

Fracture mechanics approaches to coating strength evaluation  

Microsoft Academic Search

The incidence of mechanical failure of flame sprayed molybdenum coating on piston rings prompted development of reliable methods of characterising and improving bond strengths. A method of using the ASTM specimen with a small modification, to estimate fracture toughness properties of the coating is proposed. Flame spraying process parameters are optimised to produce coatings of high adhesive strength using Taguchi

N. Gowri Shankar

1996-01-01

104

Fracture mechanics parameters of autoclaved aerated concrete  

Microsoft Academic Search

The influence of the expanding direction of Autoclaved Aerated Concrete (AAC) on the nonlinear fracture mechanics parameters is determined on three different types of AAC. The nonlinear fictitious crack model introduced by Hillerborg et al. [1] is used. Based on the RILEM recommendation AAC 13.1 [2], wedge-splitting tests have been carried out on three different types of AAC. For each

B. Trunk; G. Schober; A. K. Helbling; F. H. Wittmann

1999-01-01

105

HFIR vessel probabilistic fracture mechanics analysis  

SciTech Connect

The life of the High Flux Isotope Reactor (HFIR) pressure vessel is limited by a radiation induced reduction in the material`s fracture toughness. Hydrostatic proof testing and probabilistic fracture mechanics analyses are being used to meet the intent of the ASME Code, while extending the life of the vessel well beyond its original design value. The most recent probabilistic evaluation is more precise and accounts for the effects of gamma as well as neutron radiation embrittlement. This analysis confirms the earlier estimates of a permissible vessel lifetime of at least 50 EFPY (100 MW).

Cheverton, R.D. [Delta-21 Resources, Inc., Oak Ridge, TN (United States); Dickson, T.L. [Oak Ridge National Lab., TN (United States)

1997-01-01

106

Damage and fracture mechanics of composite materials  

NASA Astrophysics Data System (ADS)

The design of structural systems in the aerospace industry has been characterized by a continuing search for strong, yet lightweight, materials to achieve maximum payload capability for minimum weight. In recent years, this search has led to a wide use of fiber reinforced composites, such as carbon, glass and kevelar based composites. Comparison of these new materials with the traditional ones (metals) according to the basic properties, such as density, elastic modulus and also long-time and short-time strength, shows their superiority over traditional materials, when weight is a major design factor, like in the aerospace industry. Most composite materials of interest to aerospace applications have been adequately characterized under static loading conditions. Related work to study their fracture behaviour has been limited. Since most failure mechanisms involve crack growth and/or delamination, design of such components requires knowledge and understanding of their fracture properties. This thesis includes an experimental and analytical investigation of fracture characteristics of composite materials. The post-peak response of notched specimens subjected to uniaxial cyclic loading is established to evaluate the fracture energy associated with progressive matrix damage and subsequent crack growth. A total of 75 uniaxial tension specimens were tested. The experimental work consisted of first testing several un-notched specimens with different thickness (number of layers) to determine the initial and secondary elastic modulus as well as the tensile strength. The investigation studied the effect of the various fracture parameters, including thickness, fiber orientation, and crack width ratio (a/w) on the behaviour of crack propagation, peak load, and post-peak response. The specimens used in this research were prepared using the vacuum bagging technique, with a chosen number of fiber glass cloth layers and fiber orientation. The experimental results provided information regarding the peak load, post-peak response, fracture energy and stress intensity factor of the notched composite materials specimen under repeated loading/unloading cyclicity. The load versus crack opening displacement as well as crack length, fracture toughness and fracture energy versus number of loading cycles are produced for different specimens. Based on the experimental results, concepts of fracture mechanics are applied to evaluate stiffness degradation, fracture toughness and fracture energy evolution associated with crack growth. In addition, a linear elastic fracture mechanics approach combined with continuum damage representation is used to predict the response of specimens (peak load and crack opening displacement). This effort has also generated a new crack band model for computational purposes. A new formula is derived to compute delamination and interlaminar buckling loads using the finite element method. By matching the analytical near crack tip displacement field with the finite element approximation, the crack-axial stress magnitude is established, and therefore an accurate assessment of the buckling load responsible for delamination of composites is accurately evaluated. A comprehensive derivation of the fracture inelastic zone size and shape in anisotropic solids is presented. An adaptation of Hill's failure criterion is used to derive the shape of the inelastic zone. The findings explain the "banded" shape of the damage zone observed during crack growth.

Abdussalam, Saleh Ramadan

107

Polypropylene–rubber blends: 5. Deformation mechanism during fracture  

Microsoft Academic Search

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

A van der Wal; R. J. Gaymans

1999-01-01

108

Pseudopillow fracture systems: Insights into cooling mechanisms and environments from lava flow fractures  

NASA Astrophysics Data System (ADS)

We present field observations of lava flow structures within the remarkably well-exposed flow front of a flow-banded trachyandesite lava at Djúpalón on the coast of the Snæfellsnes peninsula, west Iceland. New discoveries from this lava flow reveal additional scales of complexity in pseudopillow fractures and give an enhanced understanding of these fracture systems and their association with particular environments containing water, ice or snow. The flow interior is characterised by large curviplanar master fractures with many smaller subsidiary fractures perpendicular to them. Such structures have previously been called pseudopillows or pseudopillow fractures. They have been recognised in a range of lava compositions from basalt to rhyolite. We propose the term pseudopillow fracture systems to emphasise the consistent package of different fracture types that occur together. All documented occurrences of these fracture systems are in lavas that have interacted with some type of an additional coolant (i.e. water, ice, snow). Thusfar little has been understood about the formation mechanisms of these fractures and the reason for their association with particular environments. We identify three distinct types of master fracture on the basis of their fracture surface texture (fractography) and orientation in relation to flow banding; and two different types of subsidiary fractures based on their shape. Surface features used to identify fracture mechanisms include straight and curved chisel marks (or striae), cavitation dimples, river lines and rough and smooth fracture surface textures. Using these fracture surface features we infer that master fractures can form by both brittle and ductile fracture, whereas subsidiary fractures only form by brittle fracture. Glass very commonly occurs in association with pseudopillow fracture systems in the Djúpalón lava flow, providing evidence of rapid cooling during their formation.

Forbes, A.; Blake, S.; McGarvie, D.; Tuffen, H.

2012-04-01

109

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

110

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

National Technical Information Service (NTIS)

This report contains a state-of-the-art summary of past and current research activities in the application of fracture mechanics methodologies to cracking and fracture of concrete as well as contains recommendations of a fracture model to determine the fr...

S. E. Swartz

1986-01-01

111

Fracture-toughening mechanisms responsible for differences in work to fracture of hydrated and dehydrated dentine  

Microsoft Academic Search

This study investigates the nature of deformation and differences in the mechanisms of fracture and properties of dentine where there has been a loss of moisture, as may occur with removal of the pulp in the endodontic treatment of teeth. Controlled fracture toughness testing was conducted on bovine teeth to determine the influence of hydration on the work of fracture

Bill Kahler; Michael V. Swain; Alex Moule

2003-01-01

112

Fracture mechanisms in wood fibre reinforced polyethylene  

Microsoft Academic Search

The fracture toughness of wood fibre reinforced polyethylene has been studied and several methods of improving this important property have been developed. A mechanistic fracture model which incorporates the features of wood fibres and the fibre\\/matrix interface was also developed. The modeling revealed that the key to enhancing the fracture toughness is to promote fibre pull-out during composite fracture. Based

Chengjie Zhang

1997-01-01

113

Ship Fracture Mechanisms Investigation. Part 1.  

National Technical Information Service (NTIS)

The report presents the results of a three year investigation conducted to review past research on fractures and existing fracture case studies, and to inspect new ship fractures in an effort to determine the modes of serious fractures in ship structure; ...

K. A. Stambaugh W. A. Wood

1990-01-01

114

Fracture mechanics considerations in the Charpy impact test  

Microsoft Academic Search

Instrumentation of the Charpy impact test permits an analysis of the data in terms of linear elastic fraeture mechanics. Measurements of time to fracture are converted to estimated crack opening displacements at fracture and thus to values of the fracture toughness parameter KC. The variation of these values with temperature shows a transition which is interpreted as a change from

G. D. Fearnehough; R. W. Nichols

1968-01-01

115

Computational methods for creep fracture analysis by damage mechanics  

Microsoft Academic Search

Some mechanical problems of the computational method of creep fracture analysis based on continuum damage mechanics are discussed. After brief review of the local approach to creep crack growth analysis by means of finite element analysis and continuum damage mechanics, intrinsic feature of the fracture analysis in the framework of continuum theory and the causes of mesh-dependence of the numerical

S. Murakami; Y. Liu; M. Mizuno

2000-01-01

116

Fatigue fracture mechanism maps for a type 304 stainless steel  

NASA Astrophysics Data System (ADS)

Fatigue fracture mechanism maps at room temperature and 573 K for a type 304 stainless steel were constructed by correlating the crack propagation rate with information obtained on the fracture surface. Depending on the crack propagation rate, ranging from 1 × 10-6 to 1 × 10-11 m/cycle, three types of fracture surfaces were observed. One was a striation region; the second was a “featureless” fracture region, which appeared rough under scanning electron microscope (SEM) observation; and the third was crystallographic fracture region, which appeared smooth under SEM observation. The area fractions and the indexes of the fracture surfaces were quantified and identified by the etch-pit method. From the results, crack initiation and propagation mechanisms were cleared and fatigue fracture mechanism maps were constructed. The maps may be useful for investigating the cause of the fatigue failure accident of structures made of type 304 steels.

Kimura, M.; Yamaguchi, K.; Hayakawa, M.; Kobayashi, K.; Takeuchi, E.; Matsuoka, S.

2004-04-01

117

Mechanisms for fast flow in unsaturated fractured rock  

SciTech Connect

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

Tokunaga, Tetsu K.; Wan, Jiamin

1998-03-01

118

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

119

A Convergence Analysis of an H-Version Finite-Element Method with High-Order Elements for Two-Dimensional Elasto-Plasticity Problems  

Microsoft Academic Search

Abstract: We investigate how the non-analytic solitary wave solutions --- peakons andcompactons --- of an integrable biHamiltonian system arising in fluid mechanics, can berecovered as limits of classical solitary wave solutions forming analytic homoclinic orbits forthe reduced dynamical system. This phenomenon is examined to understand the importanteffect of linear dispersion terms on the analyticity of such homoclinic orbits.

Yiwei Li; Ivo Babuvska

1997-01-01

120

A Damage Evolution Approach in Fracture Mechanics of Pipelines  

Microsoft Academic Search

\\u000a The paper concentrates on perspectives of the damage evolution approach in fracture mechanics of oil and gas pipelines. This\\u000a approach is based on the generalised concept of damage. It is postulated that deformation and fracture processes in solids\\u000a are determined by some general functional law related to the accumulation of damage. Fracture mechanics parameters are accepted\\u000a as the controlling parameters

Yu. G. Matvienko

121

Modeling shallow slip deficit in large strike-slip earthquakes using simulations of spontaneous earthquake sequences in elasto-plastic media  

NASA Astrophysics Data System (ADS)

Slip inversions of several large strike-slip earthquakes point to coseismic slip deficit at shallow depths (< 3-5 km), i.e., the amount of coseismic slip sharply decreases towards the Earth surface (e.g., Fialko et al., 2005; Bilham, 2010). Examples include the 1992 M7.3 Landers earthquake, the 1999 M7.1 Hector Mine earthquake, the 2005 M6.5 Bam earthquake, the 2010 M7.0 Haiti earthquake, and the M7.2 Sierra El Mayor (Mexico) earthquake. Determining the origin of shallow slip deficit is important both for understanding physics of earthquakes and for estimating seismic hazard, as suppression of shallow rupture could greatly influence strong ground motion in the vicinity of active faults. Several mechanisms may be invoked to explain the deficit. A widely accepted interpretation is the presence of velocity-strengthening fault friction at shallow depths where the coseismic slip deficit is compensated by afterslip and interseismic creep. However, geodetic observations indicate that the occurrence of interseismic creep and afterslip at shallow depths is rather uncommon, except for certain locations near major creeping segments of mature faults and/or in areas with thick sedimentary covers with overpressurized pore fluids (e.g., Wei et al., 2009). Fialko et al. (2005) proposed that extensive inelastic failure of the shallow crust in the interseismic period or during earthquakes may result in coseismic slip deficit at shallow depths. In this work, we investigate whether inelastic failure of the shallow crust can lead to shallow coseismic slip deficit using simulations of spontaneous earthquake sequences on vertical planar strike-slip faults. To account for inelastic deformation, we incorporate off-fault plasticity into 2-D models of earthquake sequences on faults governed by laboratory-derived rate and state friction (Kaneko et al., 2010). Our preliminary results suggest that coseismic slip deficit could occur in a wide range of parameters that characterize inelastic material properties. We will report on our current efforts on identifying key parameters of fault friction and bulk rheology that link to the degree of coseismic slip deficit over multiple earthquake cycles.

Kaneko, Y.; Fialko, Y.

2010-12-01

122

Mixed-mode Mechanism of Hydraulic Fracture Segmentation  

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

123

The mechanical properties of composites reinforced with woven and braided fabrics  

Microsoft Academic Search

This paper addresses an application of a versatile yet user-friendly micromechanics model, the bridging model, to simulate the mechanical properties of composites reinforced with woven and braided fabrics. The application is elaborated with a 2-D 1×1 woven and braided fabric geometry. The elastic, elasto-plastic, and ultimate strength behavior of the fabric composites under any arbitrary load condition can be easily

Zheng ming Huang

2000-01-01

124

Numerical prediction of slant fracture with continuum damage mechanics  

Microsoft Academic Search

Ductile specimens always exhibit an inclined fracture surface with an angle relative to the loading axis. This paper reports a numerical study on the cup–cone fracture mode in round bar tensile tests and the slant fracture in plane-strain specimens based on continuum damage mechanics. A combined implicit–explicit numerical scheme is first developed within ABAQUS through user defined material subroutines, in

X. Teng

2008-01-01

125

Fracture mechanism of cross-ply carbon\\/carbon composites  

Microsoft Academic Search

Mode I fracture toughness tests were carried out on (0\\/90) cross-ply carbon\\/carbon composite laminates in order to investigate the applicability of the concept of the fracture toughness based on linear elastic fracture mechanics. Tests were carried out by using both compact tension (CT) and single edge notched beam (SENB) specimens. Effect of the root radius of the starter notch was

Masaki Hojo; Shojiro Ochiai; Nobuhiro Joyama; Jun Takahashi

1996-01-01

126

Fracture Mechanics and the Time Dependent Strength of Adhesive Joints  

Microsoft Academic Search

The strength of technical joints formed with (soft) polymeric ad hesives is discussed from the detailed viewpoint of fracture mechanics. A new approach to the analysis of technical joints has been attempted by considering the variety of complex modes by which fracture can progress in such joints. Particular attention has been given to separat ing the geometric and loading factors

W. G. Knauss

1971-01-01

127

MECHANISMS OF DEFORMATION AND FRACTURE IN PYROLYTIC GRAPHITE  

Microsoft Academic Search

Mechanisms of deformation and fracture at room temperature are studied ; by testing deposits in flexure and compression as a function of specimen ; orientation. Values of Young's modulus parallel and perpendicular to the planes, ; flexure strength, and strength in shear across the layers are determined. Shear ; between layers by kinking, which may be reversible, and by fracture

1961-01-01

128

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

129

Elastoplastic fracture mechanics of crack growth in soil  

Microsoft Academic Search

A predominant variable in soil structure formation and degradation is crack propagation. Empirical models exist to predict fracture but these do not describe the underlying physical processes. Theoretical fracture mechanics models have been applied to soil, but most are not applicable when soil is in a wet, plastic state. Since the onset of crack formation in soil tends to occur

P. D. Hallett; T. A. Newson

2003-01-01

130

Comparison of Fracture Initiation and Propagation in Untreated and Thermally Damaged Westerly granites Using a Geophysical Imaging Cell  

NASA Astrophysics Data System (ADS)

By performing controlled thermal cracking experiments, we compare quantitatively the influence of microcracks on strength, deformation, elastic wave velocities (compressional and shear waves) and acoustic emission activity of a pre-heated (850C) specimen with that of an unheated (room temperature, RT) specimen of Westerly granite. Comparison shows a distinctive difference as they undergo a similar stress path during the experiment. The RT specimen shows a failure strength of 420 MPa and axial strain of 0.013, characterized by an elasto-plastic stress-strain curve exhibiting class-2 unstable post-failure behaviour. The 850C specimen fails at 360 MPa with an axial strain of 0.022, characterized by a plasto-elasto-plastic stress-strain curve showing class-1 stable post-failure fracture propagation behaviour. VP measured in the axial direction for the 850C specimen increases steadily from ~4.6 to 5.7 km/s up to the failure point and then decrease to 5.4 km/s at post-failure. VP measured in both horizontal directions increases from 4.6 km/s to a maximum of 5.25 km/s, then decreases to 4.9 km/s during the 33 minutes period prior to failure and settles at 4.3 km/s after the full development of fracture planes. Propagation of axial fractures parallel to sigma1 cause the reduction of VP measured normal to the axial planes which is concomitant to the change in the pre-failure nature of the stress-strain curve shown by the 850C specimen when it experiences increased plasticity at the beginning of dilation. Fracture clustering, coalescence and propagation happened at three distinct stages, as demonstrated from analysis of the AE hit count, AE source location and stress-time curve for a period of 3 to 4 minutes during the pre to post-failure regime of the 850C specimen. AE sensors show a peak number of AE hits/s roughly 25 seconds prior to each stress drop. Induced AE source location analysis demonstrates the evolution of fracture propagation corresponding to each stress drop. Source mechanisms were computed for events that occurred in a 15 minute window covering both the pre and post failure regimes of the 850C specimen. Prior to failure the observed events are close to a +Dipole type event appearing outside the significantly deviatoric region on the source type plot and showing a 20-30% volumetric component. At each of the subsequent three stress drops the source mechanisms migrate into the significantly deviatoric region on the source type plot and cluster around a Double Couple shear type event. Between the second and third stress drops a cluster of compressive events resembling -Dipole and +Crack type events appear. Evolution of the stress-strain curve for the RT specimen shows only one stress drop during the pre-failure to post-failure regime, which is accompanied by only one peak for AE hits/s prior to sudden brittle failure. Evolution of AE for RT specimen shows fracture initiation taking place at the middle of the specimen, propagating rapidly towards the outer edges of the specimen along an inclined fault plane. This study aims at comparing the evolution of strength, deformation, seismic wave velocities and AE response for two different media representing intact and highly damaged rocks under a similar stress regime.

Nasseri, M. B.; Goodfellow, S.; Young, R.

2011-12-01

131

Application of fracture mechanics to geophysical problems  

NASA Astrophysics Data System (ADS)

This study is a contribution to the understanding of fracture processes in the upper crust. Theoretical, computational and observational approaches are combined to address various questions related to the mechanics of active faults and magma filled cracks. The results of a theoretical study that aimed to investigate the conditions under which magmatic intrusions are able to-propagate along active faults are presented in Chapter 2. Addressing this question required analysis of the stress field ahead of the propagating intrusion. This is particularly difficult, because the stress field in that region is sensitive to non-elastic deformation and to the response of the pore fluid. In addition to improving the understanding of the mechanical aspects of dike intrusions into faults in the upper crust, the results of this study have implications on the ability to infer paleostresses from "frozen" dike orientations, and the interpretation of seismicity induced by some dikes and hydrofractures. Several studies of stress transfer between mainshocks and aftershocks found that the correlation between stress change and seismicity rate change disappears below some small stress, typically about 0.1 bar. This result may be interpreted either as a detection limit, or as mechanical threshold for triggering. Because according to the available friction models (both Coulomb and the rate-and-state) there is no physical reason why lower threshold should exist, resolving this issue is important. In Chapter 3 we present the results of a study that aimed to address this question. In this study we reported that lower threshold for earthquake triggering in central California has not been found. An inherently discrete model of an earthquake fault is presented in Chapter 4. We show that this model produces earthquake catalogs that display many features that are observed in natural seismicity, including foreshocks, aftershocks and close to power law earthquake size distribution. In Chapter 5 we show that this type of computer simulation is useful for the interpretation of aftershock sequences. A comparison of seismicity rate response to a stress change along the Sargent fault, the Calaveras fault and a section of the San Andreas fault is presented in Chapter 5. This comparison reveals great variability in fault behavior. Comparison between observed and simulated spatio-temporal clustering suggests that these differences may be attributed to differences in fault constitutive properties.

Ziv, Alon

2001-12-01

132

[Quantitative trauma mechanics in pelvic fracture].  

PubMed

Quasistatic loading of the isolated pelvis and of the pelvis in situ is reported; dynamic loading with an impactor and on 90 degrees car/car side impact are then considered. The isolated pelvis was loaded laterally at the ala of the ilium and the pelvis in situ in the anterior-posterior direction in the area of the symphysis with universal dynamometer; the loading profile was a rigid disk 150 mm in diameter. Some dynamic tests were performed with an impactor with rigid disk 80 mm in diameter as impact surface; the impact was applied against the trochanter major area at a velocity of 30-35 km/h. Otherwise, the pelvic area was stressed by impact through the intrusion of the car side or by impaction of the pelvis against a rigid wall. In the tests conducted with isolated pelves, forces of 850-4850 N were measured; pelvic fractures were observed, specifically fractures of the acetabular margin, pubic bone, and ischium, and comminuted fractures of the symphysis and the iliosacral. In the impactor tests, forces of 6.5-11 kN were enough to cause, pelvic fracture except in one case, and fractures of the femoral neck were found in some cases in addition. With quasistatic anterior-posterior loading of the pelvis in situ, forces of 4,700-10,000 N were measured in cases in which fractures were found. PMID:7676253

Fleischer, G; Kallieris, D; Käppner, R; Schmidt, G

1995-07-01

133

On Mechanisms of Hydraulic Fracturing in Cohesionless Materials  

NASA Astrophysics Data System (ADS)

Based on the developed experimental techniques, hydraulic fracturing in particulate materials has been directly observed in the laboratory. We have conducted an experimental series by varying such controlling parameters as the properties of particulate materials and fracturing fluids, boundary conditions, initial stress states, and injection volumes and rates. As a result, we suggested some (hopefully, fundamental) mechanisms of hydraulic fracturing in particulate materials and determined some (hopefully, relevant) scaling relationships (e.g., the interplay between elastic and plastic processes). While the ongoing work is likely to change at least some conclusions, it is important that the results reported in this paper appear to form the framework for modeling and, perhaps, even for (qualitative) interpretation of some field data. The main conclusion of our work is that hydraulic fracturing in particulate materials is not only possible, but even probable if the fluid leakoff is minimized (e.g., high flow rate, high viscosity, or low permeability). The observed fracture geometry and the measured pressure injection curves suggest that hydraulic fracturing occurs in soft sediments in the following sequence: (i) cavity expansion before the injection pressure reaches its peak; (ii) fracture front initiation from the expanding cavity near the pressure peak; and (iii) propagation of the developed fracture after the peak. Another important conclusion of our work is that all parts of the particulate material (including the tip zone of hydraulic fracture) are likely to be in compression. The compressive stress state is an important characteristic of hydraulic fracturing in particulate materials with low, or no, cohesion (such as were used in our experiments). For the fracture initiation at the peak pressure (i.e., following the initial cavity expansion), there exists a threshold value of cohesion that results in compressive stresses everywhere in the particulate material. For less cohesion, the cohesive materials can be considered to be effectively cohesionless. Three main types of fracture fronts were observed in our laboratory experiments: round, beveled and fingered. Accordingly, three physical mechanisms of fracture propagation corresponding to the three observed front types were suggested. These are ``pile driving'' or cavity expansion, shear banding, and induced cohesion, which appear to be consistent with round, beveled, and fingered fracture fronts, respectively. It is important to emphasize the importance of leakoff effect on hydraulic fractures in particulate materials. In our experiments, fractures appear rather different compared to those in the no-leakoff case. The fluid leakoff region manifests itself as a (bubbly) layer around the fracture, which thins towards the fracture tip, which is similar to brittle fractures. Furthermore, even the tip details of these fractures remarkably resemble cracks in brittle materials. Therefore, currently available experimental observations suggest that even small leakoff may change the fracture pattern rather dramatically. For example, while at the stage of fracture initiation, the cavity expansion mechanism may still be important, the mechanism of induced cohesion may prevail at the developed stage of fracture growth.

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

2005-12-01

134

COMPUTATIONAL FRACTURE MECHANICS: A SURVEY OF THE FIELD  

Microsoft Academic Search

This paper surveys examples of historical and state-of-the-art approaches of computational fracture mechanics. A global taxonomy of these approaches is first defined. The two main branches of this taxonomy are approaches based on geometrical representation and numerical representation of cracks. Approaches are briefly described and compared for their use in both the traditional role of computational fracture mechanics—calculation of crack

Anthony R. Ingraffea; Paul A. Wawrzynek

2004-01-01

135

Meshfree simulations of thermo-mechanical ductile fracture  

Microsoft Academic Search

In this work, a meshfree method is used to simulate thermo-mechanical ductile fracture under finite deformation. A Galerkin meshfree formulation incorporating the Johnson-Cook damage model is implemented in numerical computations. We are interested in the simulation of thermo-mechanical effects on ductile fracture under large scale yielding. A rate form adiabatic split is proposed in the constitutive update. Meshfree techniques, such

D. C. Simkins; S. Li

2006-01-01

136

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

Microsoft Academic Search

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

P. L. Swanson

1984-01-01

137

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

138

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

139

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

140

Snowboarder's Talus FractureMechanism of Injury  

Microsoft Academic Search

Fracture of the lateral process of the talus is an injury unique to snowboarders and is of particular clinical relevance because it masquerades as an anterolateral ankle sprain and is difficult to detect on standard radiographic views. Misdiagnosis can lead to long-term morbidity in a young and active population, with ensuing severe degeneration of the subtalar joint. To date, the

Andrea J. Boon; Jay Smith; Mark E. Zobitz; Kimberly M. Amrami

2001-01-01

141

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

142

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

143

Critical Review of the State-of-the-Art of Fracture Mechanics with Emphasis on Layered Rocks.  

National Technical Information Service (NTIS)

Results are presented of a literature survey of over 70 pertinent publications and critical reviews of fracture mechanics emphasizing the fracture behavior of layered rocks. Historical perspective, fracture mechanisms, linear and nonlinear fracture mechan...

M. D. Kuruppu K. P. Cheng J. N. Edl

1983-01-01

144

Investigation of fracture toughness and fracture mechanisms using acoustic emission measurements  

SciTech Connect

This report is the FINAL PROGRESS REPORT'' for the research program Investigation of Fracture Toughness and Fracture Mechanisms using Acoustic Emission Measurements.'' The time period covered by this report is from 1 March 1988 through August 1991. The research program consisted of three separate but closely related investigations: (1) An Investigation of the Acoustic Emission Generated during the Deformation and Fracture of Premium Grade 4340 Steel as a function of Mechanical Properties. (2) An Investigation of the Acoustic Emission Generated during the Deformation and Fracture of Ti-641-4V Alloys as a Function of Microstructure. (3) An Investigation of the Acoustic Emission Generated from Second Phase Particles in Aluminum-Silicon Alloys as a Function of Second Phase Particle Size and Density. A synopsis of each of the individual investigations including pertinent data and meaningful results will be given in the report. A listing of graduate student involvement, publications and presentations will also be provided.

Carpenter, S.H.

1991-01-01

145

Investigation of Fracture Toughness and Fracture Mechanisms Using Acoustic Emission Measurements: Progress Report, 1 March 1988-28 February 1989.  

National Technical Information Service (NTIS)

This report provides a brief discussion and presentation of the progress accomplished on the research program ''Investigation of Fracture Toughness and Fracture Mechanisms using Acoustic Emission Measurements'' for the time period of 1 March 1988 through ...

S. H. Carpenter

1988-01-01

146

Mechanical Properties for Fracture Analysis of Mild Steel Storage Tanks.  

National Technical Information Service (NTIS)

Mechanical properties of 1950's vintage, A285 Grade B carbon steels have been compiled for elastic-plastic fracture mechanics analysis of storage tanks (Lam and Sindelar, 1999). The properties are from standard Charpy V-notch (CVN), 0.4T planform Compact ...

R. L. Sindelar P. S. Lam G. R. Caskey L. Y. Woo

1999-01-01

147

A Fracture Mechanics Approach to Structural Reliability of Ceramic Capacitors  

Microsoft Academic Search

Physical defects, such as cracks, spa!Is, and delaminations, may be associated with a significant percentage of the multilayered capacitors produced for high reliability applications. These defects may lead to severe cracking of the capacitors and eventually to their electrical failure. This paper presents a fracture mechanics approach to the reliability assessment of physically defective capacitors used under high mechanical stress

MICHAEL J. COZZOLINO; GARY J. EWELL

1980-01-01

148

Fracture mechanics analysis of vertical root fracture from condensation of gutta-percha.  

PubMed

A two-dimensional fracture mechanics analysis of vertical root fracture (VRF) in single-canal roots from apical condensation of gutta-percha (gp) is developed. The resulting analytic relation for apical load causing VRF agrees with major trends reported in in-vitro tests on roots subjected to either continuous or, the more clinically relevant, repeating vertical condensation of gp. The model explicitly exposes the role of root canal morphology and dentin fracture toughness on VRF. Ovoid and irregular canals are prone to fracture while the effect of mean root canal radius is modest. Canal taper and instrumentation details may affect VRF only marginally and indirectly. The model predicts dentinal cracks to occur following root canal instrumentation and obturation, which may pose long-term threats to tooth integrity. PMID:22503579

Chai, Herzl; Tamse, Aviad

2012-04-13

149

Modeling fracture of random media via stochastic molecular mechanics  

NASA Astrophysics Data System (ADS)

Inspired by recent experimental results suggesting that the heterogeneous distribution of the elastic modulus in bone tissue leads to increased toughness, we determine the toughness modulus of a flawed discrete particle system with stochastic elastic properties. We consider an elastic solid in plane strain conditions in uniaxial tension with a Young's modulus distribution modeled as a 2-d Gaussian process with covariance modeled as an exponential kernel. We solve the problem from a continuum perspective, both employing spectral methods with stochastic finite elements and Monte Carlo methods with conventional finite elements. We also analyze an equivalent discrete particle system, modeled as a spring bead network of FCC-lattices. Our results validate the persistence of the Cauchy Born rule in a stochastic system. We then analyze a flawed discrete particle system to assess the effect of heterogeneity on fracture properties. By studying the fracture mechanics of this system with a range of variance and correlation length parameters in the exponential kernel we gain fundamental insights in to the essential length scales of heterogeneity critical to enhanced fracture properties. This validated stochastic molecular mechanics framework further supports the inverse computation of local elastic properties, not accessible with continuum mechanics, to tailor global mechanical properties such as the fracture toughness. Specifically, Markov Chain Monte Carlo can be used to infer the elastic and geometric parameters. Our work sets the foundation for stochastic modeling in a micromechanical environment and unveils mechanisms by which mechanical behavior can be tailored due to increasingly heterogeneous mechanical properties.

Dimas, Leon; Giesa, Tristan; Buehler, Markus

2013-03-01

150

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

151

Meshfree simulations of thermo-mechanical ductile fracture  

NASA Astrophysics Data System (ADS)

In this work, a meshfree method is used to simulate thermo-mechanical ductile fracture under finite deformation. A Galerkin meshfree formulation incorporating the Johnson-Cook damage model is implemented in numerical computations. We are interested in the simulation of thermo-mechanical effects on ductile fracture under large scale yielding. A rate form adiabatic split is proposed in the constitutive update. Meshfree techniques, such as the visibility criterion, are used to modify the particle connectivity based on evolving crack surface morphology. The numerical results have shown that the proposed meshfree algorithm works well, the meshfree crack adaptivity and re-interpolation procedure is versatile in numerical simulations, and it enables us to predict thermo-mechanical effects on ductile fracture.

Simkins, D. C.; Li, S.

2006-08-01

152

Probabilistic fracture mechanics of 2D carbon-carbon composites  

NASA Astrophysics Data System (ADS)

The fracture toughness of two types of carbon-fabric-reinforced carbon composite (KKARB, Types A and C) is evaluated, the mechanisms of crack propagation resistance are identified, and both are related to microstructural differences. The two composites have the same constituents (i.e., fibers, yarns, fabric weaving and matrix precursor). However, different processing cycles result in apparent differences in microstructure (e.g., different number and length distribution of microcracks, crimp angle) and toughness. The crack diffusion model (CDM) is invoked to parameterize the fluctuating strength field of the composite in terms of an average fracture energy gamma a minimum fracture energy gamma(min) and a shape parameter alpha. The values of gamma(min) are in direct correlation with the average size of microcracks in each composite, and alpha is found to correlate with the scatter in fracture toughness.

Moet, A.; Mostafa, I.; Chudnovsky, A.; Kunin, B.

1992-05-01

153

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

154

Critical Review of the State-of-the-ART of Fracture Mechanics with Emphasis on Layered Rocks.  

National Technical Information Service (NTIS)

This paper presents results of a literature survey of over 70 pertinent publications and critical reviews of fracture mechanics emphasizing the fracture behavior of layered rocks. Historical perspective, fracture mechanisms, linear and nonlinear fracture ...

M. D. Kuruppu K. P. Chong J. N. Edl

1983-01-01

155

Fracture and toughening mechanisms in an ?2 titanium aluminide alloy  

NASA Astrophysics Data System (ADS)

The deformation and fracture behaviors of the Ti-24Al-11Nb alloy with an equiaxed ?2 + ? microstructure have been characterized as a function of temperature by performing uniaxial tension and J IC fracture toughness tests. The micromechanisms of crack initiation and growth have been studied by post mortem fractographic and metallographic examinations of fractured specimens, as well as by in situ observation of the fracture events in a scanning electron microscope (SEM) equipped with a high-temperature loading stage. The results indicate that quasistatic crack growth in the Ti-24Al-11Nb alloy occurs by nucleation and linkage of the microcracks with the main crack, with the latter frequently bridged by ductile ? ligaments. Three microcrack initiation mechanisms have been identified: (1) decohesion of planar slipbands in the ?2 matrix, (2) formation of voids and microcracks in ?, and (3) cracking at or near the ?2 + ? interface due to strain incompatibility resulting from impinging planar slip originated in ?2. The sources of fracture toughness in the 25 °C to 450 °C range have been attributed to crack tip blunting, crack deflection, and a bridging mechanism provided by the ductile ? phase. At 600 °C, a change of toughening mechanisms leads to a lowering of the initiation toughness (the K IC value) but a drastic increase in the crack growth toughness and the tearing modulus.

Chan, K. S.

1990-10-01

156

Equine cortical bone exhibits rising R-curve fracture mechanics.  

PubMed

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

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

2003-02-01

157

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

158

Elementary mechanisms of brittle and semi-brittle fracture  

NASA Astrophysics Data System (ADS)

Advances in Our understanding of the mechanisms of brittle and semi-brittle fracture processes are often made by direct comparison of microscopic modeling and carefully designed experiments. In this paper, examples are taken from ab-initio simulations and empirical atomistic modeling of brittle fracture which show that the production of metastable fracture surfaces or directional cleavage anisotropy are readily anticipated consequences of the discrete nature of the bond breaking at the crack tip. Both phenomena have been reported from fracture experiments on Silicon single crystals.Dislocation simulations are helpful in analyzing the dependence of fracture toughness on predeformation, temperature or loading rate in semi-brittle materials below the brittle-to-ductile transition. By comparison of fracture experiments on tungsten single crystals with simulations it is shown that dislocation nucleation is the limiting factor at low tem- peratures, while the dependence on loading rate at intermediate temperatures requires that dislocation mobility takes control. Furthermore it is shown that the intermediate temperature regime up to the brittle-to-ductile transition temperature can be scaled onto a master curve with one unique activation energy.

Gumbsch, P.

2003-03-01

159

Mechanics of materials: top-down approaches to fracture  

Microsoft Academic Search

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

J. W. Hutchinson; A. G. Evans

2000-01-01

160

Fracture mechanics approach to penetration of bottom crevasses on glaciers  

Microsoft Academic Search

A simple model, based on linear elastic fracture mechanics, is used to investigate conditions allowing the existence of bottom crevasses. On grounded glaciers, these crevasses can only occur if the basal water pressure is close to the ice overburden pressure. If the piezometric head drops more than ?10 m below the flotation level, very large stretching rates are required for

C. J van der Veen

1998-01-01

161

Relating Cohesive Zone Model to Linear Elastic Fracture Mechanics.  

National Technical Information Service (NTIS)

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 differen...

J. T. Wang

2010-01-01

162

Fracture Mechanics of Sublaminate Cracks in Composite Laminates.  

National Technical Information Service (NTIS)

This paper presents an overview of a fracture mechanics approach to some of the most frequently encountered matrix-dominated, sub-laminate cracks in epoxy-based composite laminates. By 'sub-laminate', it is meant that the cracks are internal to the lamina...

A. S. D. Wang

1983-01-01

163

Fracture Mechanics Evaluation of B-1 Materials. Volume I. Text.  

National Technical Information Service (NTIS)

A total of 1764 fracture mechanics tests were conducted on fourteen alloys to develop property data for use in the B-1 design. Tests were performed on aluminum alloys 2024, 2124, 2219, 7049, 7050, 7075 and 7175; titanium alloy Ti-6Al-4v; steel alloys 9Ni-...

R. C. Berryman R. R. Ferguson

1976-01-01

164

Fracture Modeling of Concrete Using Two Different Microstructural Mechanics Approaches  

Microsoft Academic Search

Here we present two microstructural mechanics approaches to model the development and propagation of fracture in concrete. One of the two approaches is the Delft Lattice Model (14) where the microstructure of concrete can be projected on a lattice and corresponding properties are assigned to relevant elements in the lattice. Another approach is the Microstructural Micropolar Model (7). In this

T. K. Wang; C. S. Chang; J. G. M. van Mier; L. J. Sluys; T. N. Bittencourt

165

Section-and-Etch Study of Hertzian Fracture Mechanics  

Microsoft Academic Search

A section-and-etch technique is used to study the mechanics of Hertzian cone-crack growth in glass. With a suitable choice of test environment the cone cracks propagate at a convenient rate through successive phases of stability at constant indenter load. Systematic measurements of the etched-crack lengths as a function of indentation time permit a detailed description of the fracture mechanics. Within

A. G. Mikosza; B. R. Lawn

1971-01-01

166

Atomic-scale friction and its connection to fracture mechanics  

NASA Astrophysics Data System (ADS)

This paper present a study of contact, adhesion, and friction for nanoasperities using atomic-force microscopy. Proportionality was observed between friction and true contact area, as well as agreement with continuum mechanics models at the nanometer scale, although several features unique to the nanoscale were also observed. The continuum models can be understood in the framework of fracture mechanics and are used to determine the fundamental tribological parameters of nanoscale interfaces: the interfacial shear strength and the work of adhesion.

Carpick, R. W.; Flater, E. E.; Sridharan, K.; Ogletree, D. F.; Salmeron, M.

2004-10-01

167

Critical review of the state-of-the-art of fracture mechanics with emphasis on layered rocks  

SciTech Connect

Results are presented of a literature survey of over 70 pertinent publications and critical reviews of fracture mechanics emphasizing the fracture behavior of layered rocks. Historical perspective, fracture mechanisms, linear and nonlinear fracture mechanics, energy theories, ductile and brittle fractures, process regions, specific work of fracture, J-integrals, failure theories, static and dynamic fractures, rock fracture mechanics, fracture toughness of layered rocks (e.g., oil shale), experimental and numerical methods are reviewed and discussed. Innovative and promising methods tailored for the fracture mechanics of layered rocks are recommended.

Kuruppu, M.D.; Cheng, K.P.; Edl, J.N. Jr.

1983-07-01

168

Fracture Mechanics and Crack Propagation Approach to the Study of Overconsolidated Clays.  

National Technical Information Service (NTIS)

Fracture and crack propagation is over consolidated clays have been part of geotechnical engineering thinking for years. The mechanical behavior of stiff clays is studied and analyzed through the discipline of fracture mechanics. A test is developed to de...

A. S. Saada A. Chudnovsky M. Kennedy M. Sharaf

1985-01-01

169

A new fracture assessment approach coupling HR-pQCT imaging and fracture mechanics-based finite element modeling.  

PubMed

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 (R(2)=0.58, p=0.01) and pooled data (R(2)=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 (R(2)?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 (R(2) 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 (R(2)=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

2013-03-13

170

Application of dynamic fracture mechanics to the investigation of catastrophic failure in aircraft structures  

Microsoft Academic Search

A dynamic fracture mechanics approach to the estimation of the residual strength of aircraft structures is presented. The dependence of the dynamic crack initiation toughness of aluminum 2024-T3 on loading rate is first studied experimentally. Based on the experimental results and on established dynamic fracture mechanic concepts, a fracture mechanics based failure model is established and is used to estimate

Benjamin Bin Chow

2001-01-01

171

Modeling naturally fractured reservoirs: From experimental rock mechanics to flow simulation  

Microsoft Academic Search

Fractures have a big impact on reservoir production but are inherently difficult to quantify. This study gives a robust and practical workflow to obtain a mechanically consistent naturally fractured reservoir model without direct sampling of the fracture network. The three tiers of the workflow are: (1) subcritical testing, (2) geomechanical modeling, and (3) flow modeling. Subcritical fracture index, a rock

Margaretha Catharina Maria Rijken

2005-01-01

172

Extrinsic fracture mechanisms in two laminated metal composites  

SciTech Connect

The crack growth behavior and fracture toughness of two laminated metal composites (6090/SiC/25p laminated with 5182 and ultrahigh-carbon steel laminated with brass) have been studied in both ``crack arrester`` and ``crack divider`` orientations. The mechanisms of crack growth were analyzed and extrinsic toughening mechanisms were found to contribute significantly to the toughness. The influence of laminate architecture (layer thickness and component volume function), component material properties and residual stress on these mechanisms and the resulting crack growth resistance are discussed.

Lesuer, D.; Syn, C.; Riddle, R.; Sherby, O.

1994-11-29

173

Mechanism-based approach for prediction of ductile fracture  

NASA Astrophysics Data System (ADS)

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

Kim, Jin Kook

174

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

175

The mechanics of thoracolumbar fractures stabilized by segmental fixation.  

PubMed

Patients with unstable thoracolumbar spine fractures greatly benefit from the rapid mobilization made possible by surgical reduction and secure internal fixation. The Harrington distraction method provides excellent hook fixation to the spine but is attached only to the proximal and distal ends of the instrumental segment and is dependent on an intact anterior longitudinal ligament. Because the spine is multisegmented and viscoelastic, a distraction method alone may not provide persistent tension on the anterior longitudinal ligament. Segmental spinal instrumentation (Luque) is less efficient in obtaining reduction because it has no built in distractive mechanism. In addition, the lack of laminar hook attachments is a significant disadvantage in maintaining a distractive force. A combined system consisting of Harrington distraction rods segmentally attached to all available motion segments improves the currently available mechanical construct for obtaining and maintaining reduction in unstable thoracolumbar fractures. PMID:6478707

Wenger, D R; Carollo, J J

1984-10-01

176

Discrete fracture patterns of virus shells reveal mechanical building blocks  

PubMed Central

Viral shells are self-assembled protein nanocontainers with remarkable material properties. They combine simplicity of construction with toughness and complex functionality. These properties make them interesting for bionanotechnology. To date we know little about how virus structure determines assembly pathways and shell mechanics. We have here 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. Under prolonged force exertion, we observed fracture along well-defined lines of the 2D crystal lattice. 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, Jose L.; Wuite, Gijs J. L.; Schmidt, Christoph F.

2011-01-01

177

Fracture mechanism of aluminium friction stir welded blanks  

Microsoft Academic Search

The fracture mechanism of friction stir welded blanks is studied in this paper. An extensive test matrix comprising ten different\\u000a weld configurations is designed for the study. The welds are produced with ten combinations of different alloys and thicknesses.\\u000a The selected alloys are 2024-T3 and 7075-T6 and the thickness ratio varies between 1 and 1.7. Welding parameters are optimized\\u000a for

Amir Abbas Zadpoor; Jos Sinke; Rinze Benedictus

2009-01-01

178

Fracture mechanics assessment of railway axles: Experimental characterization and computation  

Microsoft Academic Search

The results of a joint research project aiming at developing validated fracture mechanics assessment procedures for railway axles are presented. Experimentally determined fatigue crack growth parameters for the commonly used axle steel 25CrMo4 (A4T) and the high strength steel 34CrNiMo6 are included in the range of stable crack propagation and near threshold. The results are employed for predicting fatigue crack

M. Luke; I. Varfolomeev; K. Lütkepohl; A. Esderts

2010-01-01

179

Mechanical Properties for Fracture Analysis of Mild Steel Storage Tasks  

SciTech Connect

Mechanical properties of 1950's vintage, A285 Grade B carbon steels have been compiled for elastic-plastic fracture mechanics analysis of storage tanks (Lam and Sindelar, 1999). The properties are from standard Charpy V-notch (CVN), 0.4T planform Compact Tension (C(T)), and Tensile (T) specimens machined from archival steel from large water piping. The piping and storage tanks were constructed in the 1950s from semi-killed, hot-rolled carbon steel plate specified as A285 Grade B. Evaluation of potential aging mechanisms at both service conditions shows no loss in fracture resistance of the steel in either case.Site and literature data show that the A285, Grade B steel, at and above approximately 70 degrees Fahrenheit, is in the upper transition to upper shelf region for absorbed energy and is not subject to cleavage cracking or a brittle fracture mode. Furthermore, the tank sidewalls are 1/2 or 5/8-inch thick, and therefore, the J-resistance (JR) curve that characterizes material resistance to stable crack extension under elastic-plastic deformation best defines the material fracture toughness. The JR curves for several heats of A285, Grade B steel tested at 40 degrees Fahrenheit, a temperature near the average ductile-to-brittle (DBTT) transition temperature (CVN {at} 15 ft-lb), are presented. This data is applicable to evaluate flaw stability of the storage tanks that are operated above 70 degrees Fahrenheit since, even at 40 degrees Fahrenheit, crack advance is observed to proceed by ductile tearing.

Sindelar, R.L.

1999-03-03

180

Investigation of fracture toughness and fracture mechanisms using acoustic emission measurements  

NASA Astrophysics Data System (ADS)

The research program consisted of three separate but closely related investigations: (1) an investigation of the acoustic emission generated during the deformation and fracture of premium grade 4340 steel as a function of mechanical properties; (2) an investigation of the acoustic emission generated during the deformation and fracture of Ti-641-4V alloys as a function of microstructure; (3) an investigation of the acoustic emission generated from second phase particles in aluminum-silicon alloys as a function of second phase particle size and density. A synopsis of each of the individual investigations is presented, including pertinent data and meaningful results. A listing of graduate student involvement, publications, and presentations is also provided.

Carpenter, S. H.

181

Brittle - ductile transition and scatter in fracture toughness of ferritic steels  

NASA Astrophysics Data System (ADS)

Here we analyze a dislocation simulation model for the brittle-to-ductile transition of Ferritic Steels, a typical multiphase material. The crack tip plastic zones are simulated as arrays of discrete dislocations emitted from crack-tip sources and equilibrated against the friction stress due to lattice and obstacles. The crack-tip gets blunted and the emitted dislocation arrays modify the elastic field of the crack. The combined stress field of the crack and the emitted dislocations describe an elasto-plastic crack field. The simulated crack system involves microcracks embedded in the plastic zone of a macrocrack. The inherent scatter in fracture toughness measurements are studied by using a size distribution for microcracks, distributed on the plane of the macrocrack. The scatter in fracture toughness measurements is found to be an effect of the size distribution of microcracks rather than their spatial distribution on the matrix ahead of the crack plane.

Noronha, Silvester

2006-11-01

182

Fracture mechanics based design of a railway wheel made of austempered ductile iron  

Microsoft Academic Search

In the present contribution numerical stress analyses are presented at static and cyclic loads for the fracture mechanical assessment of railway wheels made of austempered ductile iron (ADI) with graphite nodules. The emphasis is placed on the safe dimensioning of the ADI wheel against fracture and fatigue crack growth. Therefore a linear elastic fracture mechanical analysis is carried out assuming

M. Kuna; M. Springmann; K. Mädler; P. Hübner; G. Pusch

2005-01-01

183

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

184

Fracture mechanics of a postulated crack in ITER vacuum vessel  

SciTech Connect

A vacuum vessel wall with a postulated crack is modeled by using the two-dimensional solid finite elements. The J-integral value, a criterion of fracture mechanics, is calculated to estimate the integrity of the vacuum vessel wall with a postulated crack. The analytical results show that the J-integral value of a crack having a quarter depth of the wall width is considerably less than the fracture toughness J{sub IC} when the membrane stress is less than the 0.2% proof stress of the unirradiated material, even if the vacuum vessel is irradiated to 3 dpa. This means that a shallow crack in the vacuum vessel wall does not become critical in the design load. 4 refs., 7 figs., 1 tab.

Kurihara, Ryoichi; Ueda, Shuzo; Tada, Eisuke [Japan Atomic Energy Research Inst., Ibaraki (Japan)

1996-12-31

185

An Unrecognised Case of a Scapula Fracture Sustained through an Unusual Indirect Mechanism  

PubMed Central

Scapula fractures following low-velocity injuries are extremely rare but can be a missed associated fracture of other upper limb injuries. We describe the case of a patient who sustained a fracture of the scapula through an unusual and hitherto unreported indirect mechanism. The injury was associated with a radial head fracture and initially missed on presentation. This case highlights the need for increased vigilance when diagnosing injuries with unusual mechanisms.

Rajpura, Asim; Shahid, Mohammad; Sandher, Dilraj

2013-01-01

186

Failure mechanisms and surface roughness statistics of fractured Fontainebleau sandstone.  

PubMed

In an effort to investigate the link between failure mechanisms and the geometry of fractures of compacted grains materials, a detailed statistical analysis of the surfaces of fractured Fontainebleau sandstones has been achieved. The roughness of samples of different widths W is shown to be self-affine with an exponent zeta=0.46+/-0.05 over a range of length scales ranging from the grain size d up to an upper cutoff length xi approximately =0.15 W. This low zeta value is in agreement with measurements on other sandstones and on sintered materials. The probability distributions pi delta z(delta h) of the variations of height over different distances delta z>d can be collapsed onto a single Gaussian distribution with a suitable normalization and do not display multiscaling features. The roughness amplitude, as characterized by the height-height correlation over fixed distances delta z, does not depend on the sample width, implying that no anomalous scaling of the type reported for other materials is present. It is suggested, in agreement with recent theoretical work, to explain these results by the occurrence of brittle fracture (instead of damage failure in materials displaying a higher value of zeta approximately =0.8 ). PMID:17930307

Ponson, L; Auradou, H; Pessel, M; Lazarus, V; Hulin, J P

2007-09-12

187

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

SciTech Connect

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

Gray, L.J.

1990-11-09

188

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

Microsoft Academic Search

The papers contained in this volume provide an overview of current theoretical and experimental research in the field of fracture mechanics. Topics discussed include three-dimensional issues, computational and analytical issues, damage tolerance and fatigue, elastoplastic fracture, dynamic inelastic fracture, and crack arrest theory and applications. Papers are presented on approximate methods for analysis of dynamic crack growth and arrest, constraint-loss

Cruse

1988-01-01

189

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

Microsoft Academic Search

A zone of distributed microcracking is often suggested to accompany tensile macrocrack propagation in rocks and ceramics. The microcracking is said to be largely responsible for (1) high values of fracture energy (2) increasing resistance to fracture with crack extension and (3) the dependence of fracture mechanics data on the experimental setup. In the present paper, the material breakdown processes

Peter L. Swanson

1987-01-01

190

Studies of fracture mechanics of coal. Final technical report, 1 June 1979-30 November 1980  

Microsoft Academic Search

The purpose of the research project was to gain more knowledge of the basic fracture mechanics behavior of coal and of its response to hydraulic fracturing. The work concentrated on experimental measurements; theoretical explanations and analytical modeling were secondary. Eighty successful fracture toughness tests were performed on notched beam specimens (using modified ASTM E-399 Standard Test Method). The results indicate

1980-01-01

191

Application of probabilistic fracture mechanics to the PTS issue  

SciTech Connect

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

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

1985-01-01

192

Effects of hydrogen on mechanical properties and fracture mechanism of 8090 Al-Li alloy  

Microsoft Academic Search

The effects of hydrogen and strain rate on the mechanical properties and fracture mechanism of 8090 Al-Li alloy under electrochemical\\u000a charging conditions have been studied. Experimental results demonstrate that the tensile strength [ultimate tensile strength\\u000a (UTS) and yield strength (YS)] and plasticity [reduction of area (RA) and elongation (EL)] drop linearly with the decrease\\u000a of strain rate. The charged hydrogen

Lian Chen; Wenxiu Chen; Zhonghao Liu; Yuxia Shao; Zhuangqi Hu

1993-01-01

193

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

Microsoft Academic Search

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

Alexander N. Guz

2009-01-01

194

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

PubMed

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

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

2013-02-21

195

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

Microsoft Academic Search

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

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

196

Fracture mechanics of hydroxyapatite single crystals under geometric confinement.  

PubMed

Geometric confinement to the nanoscale, a concept that refers to the characteristic dimensions of structural features of materials at this length scale, has been shown to control the mechanical behavior of many biological materials or their building blocks, and such effects have also been suggested to play a crucial role in enhancing the strength and toughness of bone. Here we study the effect of geometric confinement on the fracture mechanism of hydroxyapatite (HAP) crystals that form the mineralized phase in bone. We report a series of molecular simulations of HAP crystals with an edge crack on the (001) plane under tensile loading, and we systematically vary the sample height whilst keeping the sample and the crack length constant. We find that by decreasing the sample height the stress concentration at the tip of the crack disappears for samples with a height smaller than 4.15nm, below which the material shows a different failure mode characterized by a more ductile mechanism with much larger failure strains, and the strength approaching that of a flaw-less crystal. This study directly confirms an earlier suggestion of a flaw-tolerant state that appears under geometric confinement and may explain the mechanical stability of the reinforcing HAP platelets in bone. PMID:23500480

Libonati, Flavia; Nair, Arun K; Vergani, Laura; Buehler, Markus J

2013-01-01

197

Special fracture mechanics specimens for multilayer plastic pipes testing  

Microsoft Academic Search

Pipes consisting of layers of different materials (multilayer pipes) are considered. The fracture toughness value of the main pipe is taken into account as a parameter relevant to fracture assessment connected with the resistance of pipe material against slow crack growth. With the aim of simplifying estimation of main pipe material fracture toughness, non-homogeneous test specimens cut directly from multi-layer

P. Huta?; L. Šestáková; Z. Knésl; E. Nezbedová; L. Náhlík

2009-01-01

198

Diameter of basalt columns derived from fracture mechanics bifurcation analysis.  

PubMed

The diameter of columnar joints forming in cooling basalt and drying starch increases with decreasing growth rate. This observation can be reproduced with a linear-elastic three-dimensional fracture mechanics bifurcation analysis, which has been done for a periodic array of hexagonal columnar joints by considering a bifurcation mode compatible with observations on drying starch. In order to be applicable to basalt columns, the analysis has been carried out with simplified stationary temperature fields. The critical diameter differs from the one derived with a two-dimensional model by a mere factor of 1/2. By taking into account the latent heat released at the solidification front, the results agree fairly well with observed column diameters. PMID:19518517

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

2009-05-05

199

Fracture processes and mechanisms of crack growth resistance in human enamel  

Microsoft Academic Search

Human enamel has a complex micro-structure that varies with distance from the tooth’s outer surface. But contributions from\\u000a the microstructure to the fracture toughness and the mechanisms of crack growth resistance have not been explored in detail.\\u000a In this investigation the apparent fracture toughness of human enamel and the mechanisms of crack growth resistance were evaluated\\u000a using the indentation fracture

Devendra Bajaj; George D. Quinn; Dwayne Arola

2010-01-01

200

Ductile Fracture Simulation in the Taylor Rod Impact Test Using Continuum Damage Mechanics  

Microsoft Academic Search

Taylor rod impact tests are used as experimental and numerical tests for determining the mechanical behavior of materials subjected to high strain rates. At sufficiently high velocities, a significant plastic deformation leading to fracture is observed. In this article, fracture in Taylor rod made of AISI1045 steel is simulated using a continuum damage mechanics model. The simulation is performed in

Sachin S. Gautam; Raman Babu; P. M. Dixit

2011-01-01

201

PVrisk: an approach integrating non-destructive testing an d probabilistic fracture mechanics  

Microsoft Academic Search

The integration of non-destructive testing and probabil istic fracture mechanics offers the possibility to gain realistic fracture mechanical assessment results considering nearly all uncertainties of the input values. Therefore, a probabilistic analysis has to be performed using distributions instead of discrete values as input parameters. This concept was realized wi th the developed software PVrisk which allows deterministic, parametric and

Jochen H. Kurz; Dragos D. Cioclov; Gerd Dobmann

2007-01-01

202

Fracture mechanism of NCG reinforced MMC fabricated by the squeeze casting method  

Microsoft Academic Search

When carbon fiber is coated by metal in order to increase the wettability of carbon fiber and metal matrix, the coating layer is affected by the processing conditions. The fracture mechanism of the composite depends on how the coating layers are affected with the processing conditions. In order to investigate the fracture mechanism of composites with the processing conditions, we

Y. M. Ryu; E. P. Yoon; M. H. Rhee

2000-01-01

203

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

Microsoft Academic Search

Fracture repair, which aims at regaining the functional competence of a bone, is a complex and multifactorial process. For the success of fracture repair biology and mechanics are of immense importance. The biological and mechanical environments must be compatible with the processes of cell and tissue proliferation and differentiation. The biological environment is characterized by the vascular supply and by

Peter Augat; Ulrich Simon; Astrid Liedert; Lutz Claes

2005-01-01

204

Characterisation of Fracture Behaviour of Starch Gels Using Conventional Fracture Mechanics and Wire Cutting Tests  

NASA Astrophysics Data System (ADS)

The fracture behaviour of starch gels is investigated through experimental tests and finite element simulations. Both conventional fracture and wire cutting experiments were performed. The results from these two tests were consistent with the fracture toughness increasing with loading rate. In the FE analysis, a non-linear elastic constitutive relationship was used to model the starch gels and frictionless condition was assumed between the wire-starch gel contact interface. A failure criterion based on critical fracture strain was assumed. Predictions of the steady-state cutting force at various wire diameters were found to be in good agreement with the wire cutting data.

Gamonpilas, C.; Charalambides, M. N.; Williams, J. G.; Dooling, P. J.; Gibbon, S. R.

2008-07-01

205

Fracture mechanics of the cell wall of Chara corallina.  

PubMed

Previous mechanical studies using algae have concentrated on cell extension and growth using creep-type experiments, but there appears to be no published study of their failure properties. The mechanical strength of single large internode cell walls (up to 2 mm diameter and 100 mm in length) of the charophyte (giant alga) Chara corallina was determined by dissecting cells to give sheets of cell wall, which were then notched and fractured under tension. Tensile tests, using a range of notch sizes, were conducted on cell walls of varying age and maturity to establish their notch sensitivity and to investigate the propagation of cracks in plant cell walls. The thickness and stiffness of the walls increased with age whereas their strength was little affected. The strength of unnotched walls was estimated as 47+/-13 MPa, comparable to that of some grasses but an order of magnitude higher than that published for model bacterial cellulose composite walls. The strength was notch-sensitive and the critical stress intensity factor K1c was estimated to be 0.63+/-0.19 MNm(-3/2), comparable to published values for grasses. PMID:11525518

Toole, G A; Gunning, P A; Parker, M L; Smith, A C; Waldron, K W

2001-03-01

206

Fracture and toughening mechanisms in an ? 2 titanium aluminide alloy  

Microsoft Academic Search

The deformation and fracture behaviors of the Ti-24Al-11Nb alloy with an equiaxed ?2 + ? microstructure have been characterized as a function of temperature by performing uniaxial tension andJ\\u000a \\u000a IC\\u000a fracture toughness tests. The micromechanisms of crack initiation and growth have been studied bypost mortem fractographic and metallographic examinations of fractured specimens, as well as byin situ observation of the

K. S. Chan

1990-01-01

207

Mechanics of landslide initiation as a shear fracture phenomenon  

Microsoft Academic Search

A 3-D model of shear fracture in an elastic half-space provides insight into the initiation of sliding along weak pre-existing surfaces in rock or consolidated sediments. An elastic model is justified physically if regions of non-elastic deformation associated with sliding are small relative to the size of the shear fracture. A subsurface elliptical shear fracture parallel to the surface simulates

S. J. Martel

2004-01-01

208

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

209

Combined effect of electric and mechanical loading on fracture of the PZT5 ferroelectric ceramics  

Microsoft Academic Search

The combined effect of electric and mechanical loading on fracture of the PZT-5 ferroelectric ceramics in silicon oil has been investigated using single-edge notched specimens. The results show that the fracture toughness and the threshold stress intensity factor of delayed fracture in silicon oil, i.e., stress corrosion cracking, decreases linearly with increasing the applied electric field, either positive or negative.

Y. J Su; Y Wang; W. Y Chu; K. W Gao; L. J Qiao

2004-01-01

210

Optimizing the vacuum heat treatment of hot-work tool steels by linear elastic fracture mechanics  

Microsoft Academic Search

Linear elastic fracture mechanics was used to optimize the vacuum heat treatment procedures for conventional hot-work AISI\\u000a H11 tool steel. The fracture toughness was determined with nonstandard, circumferentially notched and fatigue-precracked tensile\\u000a test specimens. The fracture testing method is sensitive to changes caused by variations in the microstructure resulting from\\u000a the austenitizing and tempering temperatures as well as the homogeneity

V. Leskovšek; B. Šuštarši?; G. Jutriša; D. Baksa; J. Kopa?

2006-01-01

211

Fracture behaviour of polypropylene films at different temperatures: fractography and deformation mechanisms studied by SEM  

Microsoft Academic Search

The fracture surfaces and the deformation micro-mechanisms of one polypropylene homopolymer and three ethylene–propylene block copolymers (EPBC) have been studied by scanning electron microscopy. The results are compared to the essential work of fracture parameters obtained in a previous study with deeply double-edge-notched-tension samples of films fractured between ?40 and 70°C. The homopolymer shows shear-yielding at T??20°C, but at lower

Didac Ferrer-Balas; Yiu-Wing Mai

2002-01-01

212

Fracture criterion for conductive cracks in soda-lime glass under combined mechanical and electrical loading  

Microsoft Academic Search

Fracture tests of electrically conductive cracks on pre-notched four-point bending soda-lime glass samples were conducted\\u000a under combined mechanical and electrical loading. The experimental results show that the critical stress intensity factor\\u000a at fracture is reduced if an electric field is applied, thereby indicating that the electric field makes contributions to\\u000a the fracture of conductive cracks. Base on the charge-free zone

Dong-Jun Yan; Hai-You Huang; Chi-Wai Cheung; Tong-Yi Zhang

2010-01-01

213

The mechanical behavior of porous metal fiber sintered sheets  

NASA Astrophysics Data System (ADS)

Porous metal fiber sintered sheets (MFSSs) are a type of low density cellular materials promising for functional and structural applications. A micromechanics random beam model is proposed to investigate the elasto-plastic behavior of MFSSs. The relative density dependence of the elastic constants and yield strength of MFSSs is predicted and found to agree well with available experimental results. Fiber stretching is identified as the dominant deformation mechanism under uniaxial and multiaxial loading. When compared with two-dimensional Voronoi foams and honeycombs, the stretching deformation dominated MFSSs exhibit higher stiffness and tensile strength, but lower compressive strength due to long fiber buckling. With the developed micromechanics model, the multiaxial elasto-plastic responses of MFSSs are simulated. A macroscopic phenomenological constitutive model with a segmented yield function is proposed to describe the predicted multiaxial responses. The yield function and its evolution can be fully calibrated in terms of the uniaxial tension and compression responses rather than complex multiaxial loading responses, which can greatly facilitate practical applications of the model. This constitutive model is also expected to be applicable to other fiber sintered materials with hydrostatic pressure sensitive and asymmetric tension-compression yielding behaviors.

Jin, M. Z.; Chen, C. Q.; Lu, T. J.

2013-01-01

214

Borehole Breakouts in Berea Sandstone Reveal a New Fracture Mechanism  

NASA Astrophysics Data System (ADS)

- Vertical drilling experiments in high-porosity (22% and 25%) Berea sandstone subjected to critical true triaxial far-field stresses, in which ?H (maximum horizontal stress) >?v (vertical stress) >?h (least horizontal stress), revealed a new and non-dilatant failure mechanism that results in thin and very long tabular borehole breakouts that have the appearance of fractures, and which counterintuitively develop orthogonally to ?H. These breakouts are fundamentally different from those induced in crystalline rocks, as well as limestones and medium-porosity Berea sandstone. Breakouts in these rocks are typically dog-eared in shape, a result of dilatant multi-cracking tangential to the hole and subparallel to the maximum far-field horizontal stress ?H, followed by progressive buckling and shearing of detached rock flakes created by the cracks. In the high-porosity sandstone a narrow layer of grains compacted normal to ?H is observed just ahead of the breakout tip. This layer is nearly identical to ``compaction bands'' observed in the field. It is suggested that when a critical tangential stress concentration is reached along the ?h spring line at the borehole wall, grain bonding breaks down and a compaction band is formed normal to ?H. Debonded loose grains are expelled into the borehole, assisted by the circulating drilling fluid. As the breakout tip advances, the stress concentration ahead of it persists or may even increase, extending the compaction band, which in turn leads to breakout lengthening.

Haimson, B. C.

215

The dual boundary element formulation for elastoplastic fracture mechanics  

NASA Astrophysics Data System (ADS)

The extension of the dual boundary element method (DBEM) to the analysis of elastoplastic fracture mechanics (EPFM) problems is presented. The dual equations of the method are the displacement and the traction boundary integral equations. When the displacement equation is applied to one of the crack surfaces and the traction equation on the other, general mixed-mode crack problems can be solved with a single-region formulation. In order to avoid collocation at crack tips, crack kinks, and crack-edge corners, both crack surfaces are discretized with discontinuous quadratic boundary elements. The elastoplastic behavior is modeled through the use of an approximation for the plastic component of the strain tensor on the region expected to yield. This region is discretized with internal quadratic, quadrilateral, and/or triangular cells. A center-cracked plate and a slant edge-cracked plate subjected to tensile load are analyzed and the results are compared with others available in the literature. J-type integrals are calculated.

Leitao, V.; Aliabadi, M. H.; Rooke, D. P.

1993-08-01

216

Calculations to Benchmark Probabilistic Fracture Mechanics Computer Codes  

SciTech Connect

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

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

2007-07-22

217

Evaluation of Fracture in a Three Stage Forging Process Using Continuum Damage Mechanics  

Microsoft Academic Search

In forging process, formability is limited by ductile fracture. In many cases forgeability is determined by the occurrence of ductile fracture and therefore limitations are set by the appearance of surface or internal cracks within regions that are highly strained due to extensive material flow. In this paper, the continuum damage mechanics framework for ductile materials developed by Lemaitre has

M. Mashayekhi; S. Ziaei-Rad; J. Parvizian; H. Hadavinia

2007-01-01

218

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

219

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

PubMed

ABSTRACT: Bisphosphonates are highly effective agents for reducing osteoporotic fractures in women and men, decreasing fracture incidence at the hip and spine up to 50%. In a small subset of patients, however, these agents have recently been associated with 'atypical femoral fractures' (AFFs) in the subtrochanteric region or the diaphysis. These fractures have several atypical characteristics, including occurrence with minimal trauma; younger age than typical osteoporotic fractures; occurrence at cortical, rather than cancellous sites; early radiographic appearance similar to that of a stress fracture; transverse fracture pattern rather than the familiar spiral or transverse-oblique morphologies; initiation on the lateral cortex; and high risk of fracture on the contralateral side, at the same location as the initial fracture. Fracture is a mechanical phenomenon that occurs when the loads applied to a structure such as a long bone exceed its load-bearing capacity, either due to a single catastrophic overload (traumatic failure) or as a result of accumulated damage and crack propagation at sub-failure loads (fatigue failure). The association of AFFs with no or minimal trauma suggests a fatigue-based mechanism that depends on cortical cross-sectional geometry and tissue material properties. In the case of AFFs, bisphosphonate treatment may alter cortical tissue properties, as these agents are known to alter bone remodeling. This review discusses the use of bisphosphonates, their effects on bone remodeling, mechanics and tissue composition, their significance as an effective therapy for osteoporosis, and why these agents may increase fracture risk in a small population of patients. PMID:22958475

van der Meulen, Marjolein Ch; Boskey, Adele L

2012-08-29

220

Fracture Mechanics Based Approach for Quantifying Corrosion Damage, Tri-Service Committee on Corrosion Proceedings.  

National Technical Information Service (NTIS)

A fracture mechanics based approach to quantify the influence of initial corrosion damage on structural integrity is described. This approach assumes that corrosion can be approximated by a geometric structural change consisting of a general thickness red...

M. T. Doerfler A. F. Grandt R. J. Bucci M. Kulak

1994-01-01

221

The Applicability of a Fracture Mechanics-Nondestructive Testing Design Criterion.  

National Technical Information Service (NTIS)

This report describes the work conducted on a program designed to investigate the potential applicability of a combined fracture mechanics-nondestructive inspection procedure as a design approach for aircraft structures. The program consisted of three pha...

P. F. Packman H. S. Pearson J. S. Owens G. B. Marchese

1968-01-01

222

Applications and Limits of Application of Fracture Mechanics Methods in Assessing the Safety of Components.  

National Technical Information Service (NTIS)

On the basis of fracture mechanics calculations and experimental investigations, it is shown how cracks of different shape and location behave under given static and cyclic loads. In particular, component safety with regard to spontaneous failure and crac...

R. Stahlberg

1977-01-01

223

Forced vibrations of an elasto-plastic and deteriorating beam  

Microsoft Academic Search

Summary A solution method for elastoplastic vibrating beams including damage accumulation is shown, where inelastic behavior of the structure is represented by an additional loading due to sources of selfstresses acting upon the linear elastic structure of time-invariant stiffness. Response due to this additional loading is evaluated using proper Green's functions. Thus, integral relations are set up, similar to Maysel's

P. Fotiu; H. Irschik; F. Ziegler

1987-01-01

224

Energetic formulation of multiplicative elasto-plasticity using dissipation distances  

Microsoft Academic Search

We introduce a new energetic formulation for the inelastic rate-independent behavior of standard generalized materials. This formulation is solely based on the classical elastic energy-storage potential $\\\\hat{\\\\psi}$ and a dissipation potential $\\\\hat{\\\\Delta}$, and it replaces the classical variational inequalities which describe the flow rules for the inelastic variables like the plastic deformation and the hardening parameters. The energetic formulation has

A. Mielke

2003-01-01

225

A fracture mechanics-based model for assessing the mechanical failure of nuclear fuel rods due to rock fall  

Microsoft Academic Search

One of the potential failure mechanisms of nuclear fuel rods that will be disposed in the proposed Yucca Mountain repository is mechanical failure of the degraded cladding tubes caused by rock fall impacting on waste packages. In this paper, the development of a fracture mechanics-based model for treating rock fall-induced failure of nuclear fuel cladding tubes is described. The rock

Kwai S. Chan; Yi-der Lee

2000-01-01

226

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

NASA Astrophysics Data System (ADS)

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

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

2010-06-01

227

Modeling Interfaces Through an Extension of Continuum Mechanics to the Nanoscale with Application to Fracture and Debonding of Composites.  

National Technical Information Service (NTIS)

This report summarizes the progress made in developing the theoretical underpinnings for a new theory of brittle fracture based upon an extension of continuum mechanics to the nanoscale. In contrast to classical fracture theories, the new theory predicts ...

J. R. Walton T. Sendova

2008-01-01

228

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

229

Unusual mechanism of Chance fracture in an adult.  

PubMed

Flexion-distraction injuries of the upper lumbar spine typically occur in case of a head-on motor vehicle collision, while wearing a lap seat belt without shoulder strap. According to Smith and Kaufer the axis of flexion is situated at the point of contact of the belt with the abdominal wall. This results in a horizontal separation of the anterior, middle and posterior columns. The lesion is called a Chance fracture when it involves primarily bone, rather than ligaments. However, a Chance fracture can happen in unbelted persons: the present case concerns a 30-year-old man who fell from a height. PMID:16305094

Todkar, Manoj

2005-10-01

230

Fracture mechanics evaluation of reactor piping reliability. II: simulation of pipe fracture probability  

Microsoft Academic Search

An objective of the Load Combination Program at the Lawrence Livermore National Laboratory is to estimate the probability of primary coolant loop pipe fracture caused directly by an earthquake. This probability will be used by the US Nuclear Regulatory Commission (NRC) to help decide whether to decouple LOCA and earthquake. If the probability is small, the US NRC may decouple

L. L. George; E. Y. Lim; S. L. Basin; D. L. Iglehart

1981-01-01

231

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

232

Fracture mechanics in retrospect in contrast to multiscaling in prospect  

Microsoft Academic Search

Failure of man-made structures and machine components becomes eminent when they exceed their useful life. Such incidents, however, can be annoying and costly when they involve substantial financial loss and human lives. The post World War II period was an era when large size structures such as passenger air transports, ships, storage tanks, pipelines, etc, were fracturing unexpectedly for no

G. C. Sih ab

233

Spinal fractures in recreational bobsledders: an unexpected mechanism of injury  

PubMed Central

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

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

2012-01-01

234

Failure mechanisms at the human dentin-resin interface: a fracture mechanics approach.  

PubMed

The present study reports on the failure mechanisms at the human dentin-resin interface, with special reference to two specific questions: (1) does failure at the human dentin-resin interface occur by a cohesive or an adhesive mechanism? (2) is the failure mechanism accompanied by a plastic deformation, and if so how important is it? The experimental design, computational analysis, and fractography were applied to two generically different bonding systems: Scotchbond-2 (SB2) and Scotchbond-multipurpose (SBM). The theoretical basis of the study required a three-dimensional finite element analysis for calibration of the new geometric factor coefficient. A minimum geometric factor coefficient (Ym) of 17.3 was then obtained which was vital for the determination of the interfacial fracture toughness. Accordingly, the dentin-resin interfacial fracture toughness (GIC), for the SB2 and for the SBM were 30.22 +/- 5.61 and 49.56 +/- 7.65 J m-2, respectively, which were significantly different (p < 0.01). Both SB2 and SBM interfaces with dentin displayed significant degrees of plasticity (0.15 and 0.19) which were beneficial to crack resistance. Thus, correcting for the plasticity, the GIC for SB2 and for SBM increased to 42.83 +/- 7.75 and 74.97 +/- 10.47 J m-2, respectively. The fractography of the two systems reflected these numeric differences. SB2 showed largely interfacial adhesive failure, while SBM showed adhesive-cohesive failure with occasional dentin adhesions attached to the composite interface and vice versa. PMID:8089158

Lin, C P; Douglas, W H

1994-08-01

235

Tensile fracture mechanisms of ferritic/martensitic structural materials  

NASA Astrophysics Data System (ADS)

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

Pan, Xiao

236

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

237

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

Microsoft Academic Search

Increasing temperature and decreasing loading rate degrade the plane strain initiation ( K ICifrom the J integral) and growth (tearing modulus, T R) fracture toughnesses of RS\\/PM 8009 (Al-8.5Fe-1.3V-1.7Si, wt pct). K ICidecreases with increasing temperature from 25 ‡C to 175 ‡C (33 to 15 MPa&surd;m for an extrusion and 28 to 11 MPa&surd;m for hot cross-rolled plate) and further

William C. Porr; Richard P. Gangloff

1994-01-01

238

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

SciTech Connect

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

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

1991-01-01

239

Correlation of AO and Lauge-Hansen Classification Systems for Ankle Fractures to the Mechanism of Injury.  

PubMed

BACKGROUND: Our aim was to assess whether the Lauge-Hansen (LH) and the Muller AO classification systems for ankle fractures radiographically correlate with in vivo injuries based on observed mechanism of injury. METHODS: Videos of potential study candidates were reviewed on YouTube.com. Individuals were recruited for participation if the video could be classified by injury mechanism with a high likelihood of sustaining an ankle fracture. Corresponding injury radiographs were obtained. Injury mechanism was classified using the LH system as supination/external rotation (SER), supination/adduction (SAD), pronation/external rotation (PER), or pronation/abduction (PAB). Corresponding radiographs were classified by the LH system and the AO system. RESULTS: Thirty injury videos with their corresponding radiographs were collected. Of the video clips reviewed, 16 had SAD mechanisms and 14 had PER mechanisms. There were 26 ankle fractures, 3 nonfractures, and 1 subtalar dislocation. Twelve fractures with SAD mechanisms had corresponding SAD fracture patterns. Five PER mechanisms had PER fracture patterns. Eight PER mechanisms had SER fracture patterns and 1 had SAD fracture pattern. When the AO classification was used, all 12 SAD type injuries had a 44A type fracture, whereas the 14 PER injuries resulted in nine 44B fractures, two 44C fractures, and three 43A fractures. CONCLUSION: When injury video clips of ankle fractures were matched to their corresponding radiographs, the LH system was 65% (17/26) consistent in predicting fracture patterns from the deforming injury mechanism. When the AO classification system was used, consistency was 81% (21/26). The AO classification, despite its development as a purely radiographic system, correlated with in vivo injuries, as based on observed mechanism of injury, more closely than did the LH system. LEVEL OF EVIDENCE: Level IV, case series. PMID:23729206

Rodriguez, Edward K; Kwon, John Y; Herder, Lindsay M; Appleton, Paul T

2013-05-31

240

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

SciTech Connect

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

Murty, K.L.; Mathew, M.D.; Miraglia, P.Q. [North Carolina State Univ., Raleigh, NC (United States)] [and others

1997-12-01

241

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

NASA Astrophysics Data System (ADS)

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

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

1992-02-01

242

Fracture behavior and mechanism in austempered ductile iron  

Microsoft Academic Search

The fracture behavior of copper-alloyed austempered ductile iron (ADI) was studied using metallography and fractography of\\u000a selected samples. Three different grades of ADI were developed by austenitization at 900 ?C for 60 min, followed by austempering\\u000a for 60 min at either 270, 330, or 380 ?C. The variation in austempered microstructure was determined by scanning electron\\u000a microscopy of metallographically prepared

U. Batra

2005-01-01

243

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

244

Fracture mechanics analysis of the BIMET welded pipe tests  

Microsoft Academic Search

Within the Fourth Euratom Research Framework Programme 1994&1998: Nuclear Fission Safety, the multinational project BIMET was carried out which consisted of bend tests on pre-cracked bi-metallic welds in the form of butt welded pipes and analytical as well as numerical analyses of their fracture behaviour. The present paper reports the application of analytical engineering assessment procedures. The various engineering methods

Karl-Heinz Schwalbe; Alfred Cornec; David Lidbury

2004-01-01

245

Fracture mechanism of FeAl matrix composites with discontinuous ceramic reinforcements  

Microsoft Academic Search

The fracture mechanism of Fe-40at.%Al matrix composites with ceramic particles, whiskers and short fibers fabricated by reactive hot-pressing was investigated in air and in oil bath at ?300 K. The loading rate was varied in the range of 10?2–10 MPa m1\\/2 s?1 to characterize the sensitivity for environmental embrittlement. The fracture resistance of the composites basically depends on the stress

Masahiro Inoue; Katsuaki Suganuma; Koichi Niihara

1999-01-01

246

A three-dimensional edge-crack finite element for fracture mechanics applications  

Microsoft Academic Search

A three-dimensional extension of a previously published two-dimensional cracked finite element [Potirniche, G.P., Hearndon, J., Daniewicz, S.R., Parker, D., Cuevas, P., Wang, P.T., Horstemeyer, M.F., 2008. A two-dimensional damaged finite element for fracture applications. Engineering Fracture Mechanics 17(13), 3895–3908] is presented in this paper. The new element has an embedded edge crack, and was developed to model damage in three-dimensional

Kurt J. Hall; Gabriel P. Potirniche

247

Fatigue strength and fracture mechanism of ceramic-metal joints under cyclic bending  

Microsoft Academic Search

The cyclic fatigue strength and fracture mechanism of the ceramic-metal joint Si3N4-SS304 were investigated under cyclic bending loading. The results show that the fatigue strength at 107 cycles was about half the static bending strength. Different types of failure were observed for the low-cycle fatigue and high-cycle fatigue regions. Fracture surfaces were examined with SEM and EPMA. Three distinctive failure

Soon-Bok Lee; H. Kobayashi; J.-W. Huh

1995-01-01

248

Probabilistic fracture mechanics by Galerkin meshless methods – part II: reliability analysis  

Microsoft Academic Search

This is the second in a series of two papers generated from a study on probabilistic meshless analysis of cracks. In this\\u000a paper, a stochastic meshless method is presented for probabilistic fracture-mechanics analysis of linear-elastic cracked structures.\\u000a The method involves an element-free Galerkin method for calculating fracture response characteristics; statistical models\\u000a of uncertainties in load, material properties, and crack geometry;

S. Rahman; B. N. Rao

2002-01-01

249

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

Microsoft Academic Search

Increasing temperature and decreasing loading rate degrade the plane strain initiation (K\\u000a ICifrom theJ integral) and growth (tearing modulus,T\\u000a R) fracture toughnesses of RS\\/PM 8009 (Al-8.5Fe-1.3V-1.7Si, wt pct).K\\u000a ICidecreases with increasing temperature from 25 ‡C to 175 ‡C (33 to 15 MPa?m for an extrusion and 28 to 11 MPa?m for hot cross-rolled\\u000a plate) and further declines to 10 MPaVm

William C. Porr; Richard P. Gangloff

1994-01-01

250

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

Microsoft Academic Search

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

Markus J. Buehler

2006-01-01

251

The influence of microcrack density on the elastic and fracture mechanical properties of Stripa granite  

Microsoft Academic Search

Microcracks can have a strong influence on the elastic and fracture mechanical properties of rocks if they are numerous, or if they are orientated in unfavourable directions in anisotropic rocks in particular. This paper presents results from a great number of mechanical tests on Stripa granite containing various amounts of microcracks. Variations in the microcrack density were obtained by shock-heating

Ove Alm; Lise-Lotte Jaktlund; Kuo Shaoquan

1985-01-01

252

Modelling the physical properties of cracked rocks using fracture mechanics and statistical physics  

Microsoft Academic Search

Cracks play a major role in most rocks submitted to crustal conditions. Mechanically, cracks make the rock much more compliant. They also make it much easier for fluid to flow through any rock body. Relying on Fracture Mechanics and Statistical Physics, we introduce a few key concepts which allow to understand and quantify how cracks do modify both the elastic

P. Benson; A. Schubnel; S. Vinciguerra; J. Hazzard; R. Young; P. Meredith

2004-01-01

253

Probabilistic fracture mechanics analyses of nuclear pressure vessels under PTS events  

Microsoft Academic Search

This paper describes some recent research activities on probabilistic fracture mechanics (PFM) for nuclear reactor pressure vessels (RPVs) performed by the RC111 research committee of the Japan Society of Mechanical Engineers (JSME) under a subcontract of the Japan Atomic Energy Research Institute (JAERI). To establish standard procedures for evaluating failure probabilities of nuclear RPVs, we have performed PFM analyses for

G Yagawa; S Yoshimura; N Soneda; M Hirano

1997-01-01

254

Probabilistic fracture mechanics analysis of nuclear structural components: a review of recent Japanese activities  

Microsoft Academic Search

This paper describes a review of recent Japanese activities on probabilistic fracture mechanics (PFM) analyses. Japan Atomic Energy Research Institute (JAERI) has sponsored research committees on PFM organized by Japan Society of Mechanical Engineers (JSME) and Japan Welding Engineering Society (JWES) for more than 10 years. The purpose of the continuous activity is to establish standard procedures for evaluating failure

G. Yagawa; Y. Kanto; S. Yoshimura; H. Machida; K. Shibata

2001-01-01

255

Identification of Deformation Mechanisms Responsible for Failure in Incremental Forming using a Damage Based Fracture Model  

Microsoft Academic Search

Single Point Incremental forming (SPIF) has generated significant interest recently due to its increased formability and greater process flexibility. However, the complicated deformation mechanisms involved in SPIF have prevented conclusive identification of the primary mechanisms responsible for failure. This work successfully predicts the forming forces and occurrence of failure in SPIF using explicit FEA with a damage based fracture model

Rajiv Malhotra; Liang Xue; Jian Cao; Ted Belytschko

2011-01-01

256

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

National Technical Information Service (NTIS)

The effects of a decreased static fracture-toughness value from that used in the previous fracture-mechanics analyses of the Ederer cranes in the Device Assembly Facility were examined to see what effects, if any, would be exerted on the fatigue crack gro...

E. Dalder

1996-01-01

257

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

SciTech Connect

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

Dalder, E. N. C.

1996-11-01

258

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

259

Relationship between Microstructure, Material Distribution, and Mechanical Properties of Sheep Tibia during Fracture Healing Process  

PubMed Central

The aim of this study was to investigate the relationship between microstructural parameters, material distribution, and mechanical properties of sheep tibia at the apparent and tissue levels during the fracture healing process. Eighteen sheep underwent tibial osteotomy and were sacrificed at 4, 8, and 12 weeks. Radiographs and micro-computed tomography (micro-CT) scanning were taken for microstructural assessment, material distribution evaluation, and micro-finite element analysis. A displacement of 5% compressive strain on the longitudinal direction was applied to the micro-finite element model, and apparent and tissue-level mechanical properties were calculated. Principle component analysis and linear regression were used to establish the relationship between principle components (PCs) and mechanical parameters. Visible bony callus formation was observed throughout the healing process from radiographic assessment. Apparent mechanical property increased at 8 weeks, but tissue-level mechanical property did not increase significantly until 12 weeks. Three PCs were extracted from microstructural parameters and material distribution, which accounted for 87.592% of the total variation. The regression results showed a significant relationship between PCs and mechanical parameters (R>0.8, P<0.05). Results of this study show that microstructure and material distribution based on micro-CT imaging could efficiently predict bone strength and reflect the bone remodeling process during fracture healing, which provides a basis for exploring the fracture healing mechanism and may be used as an approach for fractured bone strength assessment.

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

2013-01-01

260

Relationship between Microstructure, Material Distribution, and Mechanical Properties of Sheep Tibia during Fracture Healing Process.  

PubMed

The aim of this study was to investigate the relationship between microstructural parameters, material distribution, and mechanical properties of sheep tibia at the apparent and tissue levels during the fracture healing process. Eighteen sheep underwent tibial osteotomy and were sacrificed at 4, 8, and 12 weeks. Radiographs and micro-computed tomography (micro-CT) scanning were taken for microstructural assessment, material distribution evaluation, and micro-finite element analysis. A displacement of 5% compressive strain on the longitudinal direction was applied to the micro-finite element model, and apparent and tissue-level mechanical properties were calculated. Principle component analysis and linear regression were used to establish the relationship between principle components (PCs) and mechanical parameters. Visible bony callus formation was observed throughout the healing process from radiographic assessment. Apparent mechanical property increased at 8 weeks, but tissue-level mechanical property did not increase significantly until 12 weeks. Three PCs were extracted from microstructural parameters and material distribution, which accounted for 87.592% of the total variation. The regression results showed a significant relationship between PCs and mechanical parameters (R>0.8, P<0.05). Results of this study show that microstructure and material distribution based on micro-CT imaging could efficiently predict bone strength and reflect the bone remodeling process during fracture healing, which provides a basis for exploring the fracture healing mechanism and may be used as an approach for fractured bone strength assessment. PMID:24046532

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

2013-09-07

261

1-stage primary arthroplasty of mechanically failed internally fixated of hip fractures with deep wound infection  

PubMed Central

Background and purpose Mechanically failed internal fixation following hip fracture is often treated by salvage arthroplasty. If deep wound infection is present, a 2-stage procedure is often used. We have used a 1-stage procedure in infected cases, and we now report the outcome. Patients and methods We reviewed 16 cases of deep wound infection after mechanically failed hip fracture fixation, treated between 1994 and 2010. In all patients, a joint prosthesis was implanted in a 1-stage procedure. Results After an average follow-up period of 12 (2–18) years, no reinfection was detected. In 4 cases, a hip dislocation occurred and 3 of these needed further surgery. Interpretation A 1-stage procedure for arthroplasty of an infected, mechanically failed hip fracture fixation is feasible and carries a low risk of infection.

Klatte, Till O; O'Loughlin, Padraigh F; Citak, Mustafa; Rueger, Johannes M; Gehrke, Thorsten; Kendoff, Daniel

2013-01-01

262

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

PubMed Central

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

Luo, Jin; Adams, Michael A.; Dolan, Patricia

2010-01-01

263

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

264

Fracture Mechanism in Fatigue of Nickel-Based Superalloy Inconel 718 at Elevated Temperatures  

NASA Astrophysics Data System (ADS)

In order to investigate the fracture mechanism in fatigue of nickel-based superalloy at elevated temperature, rotating bending fatigue tests were carried out for Inconel 718 at 500°C and 600°C up to 108 cycles. At both temperatures, fatigue fracture initiated from the subsurface of specimens in the long life region, though the origin of fracture was on the surface of specimens in the short life region. As a result, S-N curves showed a two-step shape. Although surface cracking was observed even in the long life region at elevated temperatures, similar results as observed at room temperature, surface cracks ceased propagating after extending to approximately 20-30?m at elevated temperatures. Meanwhile, intergranular cracking was observed at the origins of subsurface fracture, which was found to be nucleated in the early stage of fatigue.

Kawagoishi, Norio; Chen, Qiang; Yan, Nu; Goto, Masahiro; Wang, Qingyuan; Ohzono, Yoshihisa

265

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

SciTech Connect

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

Tow, D.M.; Reuter, W.G.

1998-03-01

266

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

267

Roughness and fractality of fracture surfaces as indicators of mechanical quantities of porous solids  

NASA Astrophysics Data System (ADS)

The 3D profile surface parameter H q and fractal dimension D were tested as indicators of mechanical properties inferred from fracture surfaces of porous solids. High porous hydrated cement pastes were used as prototypes of porous materials. Both the profile parameter H q and the fractal dimension D showed capability to assess compressive strength from the fracture surfaces of hydrated pastes. From a practical point of view the 3D profile parameter H q seems to be more convenient as an indicator of mechanical properties, as its values suffer much less from statistical scatter than those of fractal dimensions.

Ficker, Tomáš; Martišek, Dalibor

2011-12-01

268

Permeability Evolution of Fractured Anhydrite Caused by Chemical and Mechanical Alteration  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

269

Accurate in vitro identification of fracture onset in bones: failure mechanism of the proximal human femur.  

PubMed

Bone fractures have extensively been investigated, especially for the proximal femur. While failure load can easily be recorded, and the fracture surface is readily accessible, identification of the point of fracture initiation is difficult. Accurate location of fracture initiation is extremely important to understand the multi-scale determinants of bone fracture. In this study, a recently developed technique based on electro-conductive lines was applied to the proximal femoral metaphysis to elucidate the fracture mechanism. Eight cadaveric femurs were prepared with 15-20 electro-conductive lines (crack-grid) covering the proximal region. The crack-grid was connected to a dedicated data-logger that monitored electrical continuity of each line at 700 kHz. High-speed videos (12,000 frames/s, 0.1-0.2 mm pixel size) of the destructive tests were acquired. Most crack-grid-lines failed in a time-span of 0.08-0.50 ms, which was comparable to that identified in the high-speed videos, and consistent with previous video recordings. However, on all specimens 1-3 crack-grid-lines failed significantly earlier (2-200 ms) than the majority of the crack-grid-lines. The first crack-grid-line to fail was always the closest one to the point of fracture initiation identified in the high-speed videos (superior-lateral neck region). Then the crack propagated simultaneously, at comparable velocity on the anterior and posterior sides of the neck. Such a failure pattern has never been observed before, as spatial resolution of the high-speed videos prevented from observing the initial opening of a crack. This mechanism (fracture onset, time-lag, followed by catastrophic failure) can be explained with a transfer of load to the internal trabecular structure caused by the initial fracture of the thin cortical shell. This study proves the suitability of the crack-grid method to investigate bone fractures associated to tensile stress. The crack-grid method enables significantly faster sampling than high-speed cameras. The present findings elucidate some aspects of the failure mechanism of the proximal human femoral metaphysis. PMID:23218142

Juszczyk, Mateusz Maria; Cristofolini, Luca; Salvà, Marco; Zani, Lorenzo; Schileo, Enrico; Viceconti, Marco

2012-12-04

270

Mechanical property and fracture behavior of squeeze-cast Mg matrix composites  

SciTech Connect

The present study aims to investigate the microstructure and fracture properties of AZ91 Mg matrix composites fabricated by the squeeze-casting technique, with variations in the reinforcement material and applied pressure. Microstructural and fractographic observations, along with in situ fracture tests, were conducted on three different Mg matrix composites to identify the microfracture process. Two of them are reinforced with two different short fibers and the other is a whisker-reinforced composite. From the in situ fracture observation of Kaowool-reinforced composites, the effect of the applied pressure on mechanical properties is explained using a competing mechanism: the detrimental effects of fiber breakage act to impair the beneficial effects of the grain refinement and improved densification as the applied pressure increases. On the other hand, for the composites reinforced with Saffil short fibers, microcracks were initiated mainly at the fiber/matrix interfaces at considerably higher stress intensity factor levels, while the degradation of fibers was not observed even in the case of the highest applied pressure. This finding indicates that the higher applied pressure yields better mechanical properties, attributable to the Saffil short fibers having relatively high resistance to cracking. Although an improved microstructure was obtained by accommodating the appropriate applied pressure in the short fiber-reinforced composites, their mechanical properties were far below those of conventional Al matrix composites. In this regard, the Alborex aluminum borate whisker is suggested as a replacement for the short fibers used in the present investigation, to achieve better mechanical properties and fracture toughness.

Sohn, K.S. [Korea Research Inst. of Chemical Technology, Daejon (Korea, Republic of). Advanced Materials Div.; Euh, K.; Lee, S. [Pohang Univ. of Science and Technology (Korea, Republic of). Center for Advanced Aerospace Materials; Park, I. [Pusan National Univ. (Korea, Republic of). Dept. o Metallurgical Engineering

1998-10-01

271

Size effect law and fracture mechanics of the triggering of dry snow slab avalanches  

NASA Astrophysics Data System (ADS)

A size effect law for fracture triggering in dry snow slabs of high enough length-to-thickness ratio is formulated, based on simplified one-dimensional analysis by equivalent linear elastic fracture mechanics. Viscoelastic effects during fracture are neglected. The derived law, which is analogous to Bažant's energetic size effect law developed for concrete and later for sea ice, fiber composites, rocks, and ceramics, is shown to agree with two-dimensional finite element analysis of mode II cohesive crack model with a finite residual shear stress. Fitting the proposed size effect law to fracture data for various slab thicknesses permits identifying the material fracture parameters. The value of preexisting shear stress in a thin weak zone of finite length is shown to have significant effect. There exists a certain critical snow depth, depending on the preexisting stress value, below which the size effect disappears. Practical applications require considering that the material properties (particularly the mode II fracture toughness or fracture energy) at the snow slab base are not constant but depend strongly on the slab thickness. This means that one must distinguish the material size effect from the structural size effect, and the combined size effect law must be obtained by introducing into the structural size effect law dependence of its parameters on snow thickness. The thickness dependence of these parameters can be obtained by matching the combined law to avalanche observations. Matching Perla's field data on 116 avalanches suggests that the mode II fracture toughness is approximately proportional to 1.8 power of snow thickness.

Bažant, Zden?K. P.; Zi, Goangseup; McClung, David

2003-02-01

272

Fatigue damage-fracture mechanics interaction in cortical bone.  

PubMed

Fatigue loading causes accumulation of damage that may lead to the initiation of a macrocrack and result in a catastrophic failure of bone. The objective of this study was to examine the influence of fatigue damage on crack growth parameters in bovine cortical bone. Nineteen rectangular beam specimens (4 x 4 x 48 mm) were machined from bovine tibiae. The long axis of the beams was aligned with the long axis of bones. Using a four-point bending fatigue setup, ten specimens were fatigue-damaged to different levels as indicated by stiffness loss. A through-thickness notch was machined at the center of each damaged and undamaged beam. The notched specimens were then monotonically loaded beyond failure using a three-point bending protocol. Critical stress intensity factor, K(I), and work to critical load, W(Q), were significantly lower in the damaged group than in the undamaged group (p < 0.03). When the undamaged specimens were assigned a percent stiffness loss of zero and pooled with the damaged group, significant negative correlations of percent stiffness loss with K(I) (R = 0.58, p < 0.01), W(Q) (R = 0.54, p < 0.02), maximum load, P(max) (R = 0.59, p < 0.008), deflection at maximum load, Delta(max) (R = 0.48, p < 0.04), structural stiffness, S(max) (R = 0.53, p < 0.02), W(max) (R = 0.55, p < 0.02), and load at 1.4 mm deflection (a value beyond failure but without complete fracture), P(1.4) (R = 0.47, p < 0.05), were found. Post hoc analysis revealed that the average load-deflection curve from the damaged group was transformable into that from the undamaged group through a special shift on the load-deflection plane. Fatigue damage reduces bone stiffness and resistance to crack initiation, maximum load-carrying capacity, and deflection before and after failure in cortical bone. The data suggest there is a single rule that governs the overall effect of fatigue damage on the fracture behavior of cortical bone. PMID:11882466

Yeni, Y N; Fyhrie, D P

2002-03-01

273

Fracture mechanism under dynamic loading of elastomer-modified polypropylene  

Microsoft Academic Search

In last decades, rubber-toughened polymer blends have been the object of considerable interest by many investigators, owing to their attractive mechanical as well as physical properties. Polypropylene (PP) is a type of polyolefin which can be toughened using rubber particles. In another paper [J. Appl. Polym. Sci., submitted for publication], the role of ethylene–propylene (EPR) particles on the deformation mechanism

S. M. Zebarjad; A. Lazzeri; R. Bagheri; S. M. Seyed Reihani; M. Frounchi

2003-01-01

274

Fracture-mechanical analysis of the residual service life of the welded main girders of the highway bridges of Ruedersdorf  

Microsoft Academic Search

A fracture mechanics analysis was carried out on a certain type of weld defect contained in the main girders of the Ruedersdorf highway bridges (River Luehlen, Germany). To assess fatigue cracks which start from welding defects of about 10 mm height at the end of the inner cover plates, specimens were taken from the bridges. The fracture mechanical properties of

Karl-Otto Edel

1992-01-01

275

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

Microsoft Academic Search

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

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

1995-01-01

276

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

Microsoft Academic Search

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

Bimalendu Guha

1995-01-01

277

Fracture mechanics of dissimilar material bonded through an orthotropic interfacial zone  

Microsoft Academic Search

The fracture mechanics of orthotropic materials containing collinear interface cracks is considered. The objective is to study the influence of the thickness and the structure of the interfacial regions on the crack driving force. The interfacial region is assumed to be a relatively thin orthotropic elastic layer. The stress intensity factors or the strain energy release rates are assumed to

Fazil Erdogan; Binghua Wu

1992-01-01

278

Fracture Mechanical Studies on High Temperature Alloys Between Room Temperature and 900 deg C.  

National Technical Information Service (NTIS)

As a contribution to the fracture mechanics characterization of the three solid-solution hardened alloys X10NiCrAlTi 32 20, NiCr 22 Co 12 Mo and NiCr 22 W 12 Si, (material No. 1.4876, No. 2.4663 and No. 2.4972) investigations of the J-integral concept in ...

R. J. Kwasny M. Roedig F. Schubert H. Nickel

1987-01-01

279

A fracture mechanics approach to thermal fatigue life prediction of solder joints  

Microsoft Academic Search

A life prediction approach for solder joints under thermal fatigue, based on fracture mechanics and assuming that the thermal fatigue crack propagation in solder joints is primarily controlled by the C* and the J Integrals, is presented. The approach is applied to model experiments in which surface mounted electronic components were mounted on substrates with eutectic Pb\\/Sn solder joints and

Yi-Hsin Pao

1992-01-01

280

Fracture initiation mechanisms of thin hard coatings during the impact test  

Microsoft Academic Search

The impact test can be successfully applied for the characterization of thin and thick coatings fatigue and creep properties, respectively. In the present paper experimental and analytical investigations concerning thin films fracture initiation during this test are introduced. The damage initiation of thin hard coatings deposited on smooth surfaces is mainly induced by fatigue mechanisms and characterized by the removal

K.-D Bouzakis; A Siganos

2004-01-01

281

Life assessment by fracture mechanics analysis and damage monitoring technique on combustion liners  

Microsoft Academic Search

A methodology has been developed and tested including a multi-disciplinary framework towards integrated analysis of gas turbine combustors. The sub-elements consist of combustion dynamics, stress and modal analysis, fracture mechanics and structural health monitoring have been interlinked indicating the damage evaluation to life assessment. The interaction between the interrelated combustion driven flame dynamics, acoustic pressure fluctuations and liner wall vibration

A. Can Altunlu; Hoogt van der Peter; Boer de André

2011-01-01

282

Corrosion Cracking of Zirconium Cladding Tubes (A Review). I. Methods of Study and Mechanisms of Fracture  

Microsoft Academic Search

Methods of study and criteria of evaluation of stress corrosion cracking (SCC) of zirconium alloys are generalized as applied to cladding tubes of nuclear reactors. Mechanisms of SCC in zirconium cladding tubes in iodine-bearing media (iodine vapors, solution of iodine in methanol, etc.) are described. Metallographic and fracture features of damage in these media are analyzed. Data on cracking rates

S. A. Nikulin; A. B. Rozhnov

2005-01-01

283

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

Microsoft Academic Search

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

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

2005-01-01

284

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

285

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

286

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

287

Crack-Propagation Sensitivity Index as a Tool to Promote Concepts of Fracture Mechanics  

Microsoft Academic Search

We consider basic parameters used for the evaluation of the reliability of engineering structures by the methods of fracture mechanics, namely, the geometry and location of cracklike defects, loading conditions, and crack-growth resistance of the material. It is indicated that the results of evaluation of reliability can be efficiently combined with the data of nondestructive diagnostics of structural elements. For

L. Toth

2001-01-01

288

FRACTURE MECHANICS IN THE ANALYSIS OF STEEL PRESSURE BOUNDARY RELIABILITY M. STAAT  

Microsoft Academic Search

It is shown that the difficulty for probabilistic fracture mechanics (PFM) is the general problem of the high reliability of a small population. There is no way around the problem as yet. Therefore what PFM can contribute to the reliability of steel pressure boundaries is demonstrated with the example of a typical reactor pressure vessel and critically discussed. Although no

289

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

Microsoft Academic Search

This paper is concerned with round-robin analyses of probabilistic fracture mechanics (PFM) problems of aged RPV material. Analyzed here is a plate with a semi-elliptical surface crack subjected to various cyclic tensile and bending stresses. A depth and an aspect ratio of the surface crack are assumed to be probabilistic variables. Failure probabilities are calculated using the Monte Carlo methods

G. Yagawa; S. Yoshimura; N. Handa; T. Uno; K. Watashi; T. Fujioka; H. Ueda; M. Uno; K. Hojo; S. Ueda

1995-01-01

290

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

291

A probabilistic fracture mechanics assessment method based on the R6 procedure  

Microsoft Academic Search

The R6 procedure can confidently estimate critical defect size, but due to defect size and material properties, as well as loading, being statistically distributed, a probabilistic approach must be adopted. A probabilistic fracture mechanics assessment method based on the R6 principle has been developed for the integrity of structures. With this method, the probability of failure as an output of

Y. J. Hong

1997-01-01

292

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

Microsoft Academic Search

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

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

1984-01-01

293

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

Microsoft Academic Search

To study the damage and fracture mechanism of 6063 aluminum alloy under different stress states, three kinds of representative triaxial stress states have been adopted, namely smooth tensile, notch tensile, and pure shear. The results of the study indicate the following. During the notch tensile test, a relatively higher stress triaxiality appears in the root of the notch. With the

Hao ZHU; Liang ZHU; Jianhong CHEN

2008-01-01

294

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

NASA Astrophysics Data System (ADS)

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

Hyde, Brian

295

Numerical analysis of fracture mechanisms and failure modes in bi-layered structural components  

Microsoft Academic Search

The problem of crack propagation in bi-layered structural components is addressed. Due to the presence of the bi-material interface and depending on the loading direction, a competition between different crack trajectories (failure modes) can take place. The quantification of the dominant failure mode and of the prevailing fracture mechanism is very often a challenging task, although it is crucial for

Alberto Carpinteri; Marco Paggi

2007-01-01

296

Fracture Mechanics of Advanced Composites (DEPSCoR 92).  

National Technical Information Service (NTIS)

This report document instrumentation obtained under a DEPSCoR grant to support research in the mechanics of advanced composite materials. While the equipment will support a broad range of research topics, it has already spawned studies into micromechanica...

M. C. Larson

1995-01-01

297

Similarity Solutions of Creep — Damage Coupled Problems in Fracture Mechanics  

Microsoft Academic Search

The asymptotic solution to Mode III and Mode I crack problems in a creeping solid in the framework of Continuum Damage Mechanics\\u000a is presented. The kinetic law of damage evolution is the Kachanov — Rabotnov equation [1]. The damage parameter is incorporated into the power-law creep constitutive equations. Thus the coupled system of damage\\u000a mechanics — creep theory equations is

L. V. Stepanova; M. E. Fedina

298

Identification of Deformation Mechanisms Responsible for Failure in Incremental Forming using a Damage Based Fracture Model  

NASA Astrophysics Data System (ADS)

Single Point Incremental forming (SPIF) has generated significant interest recently due to its increased formability and greater process flexibility. However, the complicated deformation mechanisms involved in SPIF have prevented conclusive identification of the primary mechanisms responsible for failure. This work successfully predicts the forming forces and occurrence of failure in SPIF using explicit FEA with a damage based fracture model in which failure envelope depends on the hydrostatic pressure and the Lode angle. Furthermore it is shown that through-the-thickness shear is primarily responsible for failure in SPIF. Simulations are also performed to form the same component using SPIF and using a conventional punch and die, and a comparison is made between the dominant mechanisms of failure in the two processes. Furthermore, it is shown that reduction of tool-sheet friction can delay fracture in SPIF and the mechanism behind this effect is discussed as well.

Malhotra, Rajiv; Xue, Liang; Cao, Jian; Belytschko, Ted

2011-08-01

299

Fracture mechanics associated with non-classical heat conduction in thermoelastic media  

NASA Astrophysics Data System (ADS)

This paper studies the thermoelastic fracture in a solid under non-classical Fourier heat conduction. The temperature field and the associated thermal stresses are solved by the dual integral equation technique. Both thermally insulated crack and heated crack are considered. It is found that the crack tip thermal stress is singular and can be expressed in terms of the thermal stress intensity factor in a closed-form. Numerical results show that the crack considerably amplifies the local thermal stresses, confirming the significance of the effect of non-classical heat conduction on the thermoelastic fracture mechanics of materials.

Wang, BaoLin; Han, JieCai

2012-03-01

300

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

PubMed Central

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

2012-01-01

301

Mechanisms of fatigue crack propagation and fracture toughness behavior in advanced aluminum-lithium alloys  

Microsoft Academic Search

Mechanisms and mechanics influencing the fatigue crack propagation and plain-stain fracture toughness behavior commercial aluminum-lithium alloys are investigated as a function of the microstructure and plate orientation, both at ambient and liquid nitrogen temperatures. With ultra-low density, improved elastic modulus and high strength, in comparison to existing 7XXX and 2XXX alloys, the alloys additionally exhibit superior long (\\/approx gt\\/ 10

Venkateswara Rao

1988-01-01

302

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

Microsoft Academic Search

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

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

2010-01-01

303

Fracture mechanics for a mode III crack in a magnetoelectroelastic solid  

Microsoft Academic Search

In this paper, we developed a Stroh-type formalism for anti-plane deformation and then investigated the fracture mechanics for an elliptical cavity in a magnetoelectroelastic solid under remotely uniform in-plane electromagnetic and\\/or anti-plane mechanical loading, which allowed us to take the electromagnetic field inside the cavity into account. Reducing the cavity into a crack, we had explicit solutions in closed forms

Cun-Fa Gao; Pin Tong; Tong-Yi Zhang

2004-01-01

304

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

305

Mechanical testing and fracture studies of a nickel-alumina functionally graded material system  

NASA Astrophysics Data System (ADS)

Elastic modulus and fracture toughness was determined for a layered nickel-alumina functionally graded material (FGM) system. FGM samples with a linear compositional gradient profile were formed by sequentially stacking different Ni-Al 2O3 cermet compositions and bonding together by solid-state sintering. From these bulk samples tensile and compact-tension (C-T) specimen geometries were used to determine the elastic moduli and fracture response within each specific layer of the FGM structure, respectively. Moire interferometry techniques were used extensively to determine the physical displacement across the entire tensile specimen surface and the surface directly adjacent to the crack tip during testing. Interferometry results were used to verify the accuracy of a series of computer simulations calculating the fracture response through a material interface. While the macroscopic effects of residual stress resulting from the layered gradient structure were anticipated for this study, defects within the microstructure were shown to dominate the mechanical and fracture response in this material system. The level of microdamage was illustrated by much lower elastic modulus values measured for cermet layers possessing an interpenetrating network microstructure. These microstructures had considerable contact between the two constituents, nickel and alumina, providing maximum opportunity for microdamage within these cermet interlayers. Using the measured moduli values the elastic fracture response for a crack propagating from an 80%-Al2O3 layer toward a 60%-Al 2O3 layer was both measured experimentally and calculated using finite element modeling techniques. As expected, the fracture toughness of the FGM increased as a crack propagated within the more ductile layer. Relatively straight, brittle fracture was seen in the 80%-Al2O 3 microstructure while crack bridging, deflection, and bifurcation were all observed within the 60%-Al2O3 layer. A gradual rise in fracture toughness as the crack approached the sharp material interface was calculated from computer simulations illustrating the effect on fracture toughness as the material (and thus elastic modulus) is changed in front of the crack tip. Again, microstructural damage dominated the fracture response in the form of significantly reduced elastic moduli while macroscopic residual stresses had only a minimal effect, due in part to the crack propagation direction.

Windes, William E.

306

Self-induced vomiting as a probable mechanism of an isolated hyoid bone fracture.  

PubMed

Fractures of the laryngeal skeleton (hyoid bone and thyroid horns) are an important finding in a forensic autopsy because they are almost always caused by significant trauma and often are relevant in determining the cause and manner of death. In the forensic setting, these injuries are seen in some hangings and more frequently in manual strangulation. Less common mechanisms include direct blows, "choke holds," and hyperextension of the neck. We present a case of a 37-year-old woman who died of complications of acute ethanol intoxication. The case involves an incidental hyoid bone fracture unrelated to the cause of death as well as facial petechiae. After review of all of the medical records, autopsy findings and scene/police investigations-the key findings of facial petechial hemorrhages and hyoid bone fracture are best attributed to the mechanism of self-induced vomiting. This case emphasizes the importance of synthesizing autopsy findings with the patient's medical and social history to avoid unnecessary investigation or prosecution. This is the second known case of this novel mechanism of hyoid bone fracture in the medical literature and the first in the forensic literature. PMID:20585227

White, Joseph K; Carver, John

2012-06-01

307

Investigation of fracture toughness and fracture mechanisms using acoustic emission measurements. Final progress report, 1 March 1988--31 August 1991  

SciTech Connect

This report is the ``FINAL PROGRESS REPORT`` for the research program ``Investigation of Fracture Toughness and Fracture Mechanisms using Acoustic Emission Measurements.`` The time period covered by this report is from 1 March 1988 through August 1991. The research program consisted of three separate but closely related investigations: (1) An Investigation of the Acoustic Emission Generated during the Deformation and Fracture of Premium Grade 4340 Steel as a function of Mechanical Properties. (2) An Investigation of the Acoustic Emission Generated during the Deformation and Fracture of Ti-641-4V Alloys as a Function of Microstructure. (3) An Investigation of the Acoustic Emission Generated from Second Phase Particles in Aluminum-Silicon Alloys as a Function of Second Phase Particle Size and Density. A synopsis of each of the individual investigations including pertinent data and meaningful results will be given in the report. A listing of graduate student involvement, publications and presentations will also be provided.

Carpenter, S.H.

1991-12-31

308

Continuum mechanics analysis of fracture progression in the vitrified cryoprotective agent DP6  

PubMed Central

As part of an ongoing effort to study the continuum mechanics effects associated with cryopreservation, the current report focuses on the prediction of fracture formation in cryoprotective agents. Fractures had been previously observed in 1 m? samples of the cryoprotective agent cocktail DP6, contained in a standard 15 m? glass vial, and subjected to various cooling rates. These experimental observations were obtained by means of a cryomacroscope, which has been recently presented by the current research team. High and low cooling rates were found to produce very distinct patterns of cracking. The current study seeks to explain the observed patterns on the basis of stresses predicted from finite element analysis, which relies on a simple viscoelastic constitutive model and on estimates of the critical stress for cracking. The current study demonstrates that the stress which results in instantaneous fracture at low cooling rates is consistent with the stress to initiate fracture at high cooling rate. This consistency supports the credibility of the proposed constitutive model and analysis, and the unified criterion for fracturing, that is, a critical stress threshold.

Steif, Paul S.; Palastro, Matthew C.; Rabin, Yoed

2008-01-01

309

Can Deterministic Mechanical Size Effects Contribute to Fracture and Microdamage Accumulation in Trabecular Bone?  

PubMed Central

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

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

2010-01-01

310

Application of a Fracture Methodology for Studying the Mechanics that Govern Failure of Aluminum Structures  

NASA Astrophysics Data System (ADS)

The existence of cracks besides the effect of structural degradation can cause partial or total failure of a structure. Usually, structures are designed to resist yielding, buckling and fatigue, but not fracture due to limited existing data on large scalemodels. As a result, robust methods and procedures to design structures against fracture have not been developed, although the industry is seeking to achieve more efficient concepts and designs with advanced safety and performance using optimized structural design. The rapidly increasing application of lightweight materials and thin-walled structures in several industries requires fundamental understanding of the mechanisms and mechanics of fracture that govern stiffened panels. A methodology consisting of the application of advanced fracture models, material calibration, and validation through component testing is provided that will increase the survivability envelope of new structures. This paper presents its application that will enable designers to evaluate critical areas within a structure with respect to crack initiation, propagation, optimum material usage, and computational cost. It is based on the effect of stiffening configurations on fracture of aluminum marine structures by studying the structural response of various stiffened plates, represented by small-scale compact tension (CT) and intermediate-scale specimens, which are compared with unstiffened plates. It is shown that mapping of crack patterns in stiffened plates is feasible. Numerical modeling and analyses of ductile fracture initiation and propagation on a precracked geometry using a commercial finite element code (ABAQUS), taking into account the behavior of simple uncracked material, has been performed showing a very good agreement with small and intermediate scale tests.

Galanis, Konstantinos Panagiotis; Wierzbicki, Tomasz; Papazoglou, Vassilios John

311

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

PubMed

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

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

2010-04-14

312

Fracture Mechanisms in Carbon Nanotube-Reinforced Composites  

Microsoft Academic Search

Carbon nanotubes have been targeted for potential applications ranging from the next generation of computers and flat-panel\\u000a displays to structural and functional materials. In addition to their wellknown stiffness (> 1 TPa) and strength (?30 GPa)\\u000a properties, carbon nanotubes also possess exceptionally high electrical and thermal conductivities, with the axial thermal\\u000a conductivity near that of crystalline diamond. The unique mechanical

E. T. Thostenson; T.-W. Chou

313

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

SciTech Connect

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

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

1996-09-01

314

Optimizing the Vacuum Heat-Treatment of Hot-Work Tool Steels by Linear Elastic Fracture Mechanics  

Microsoft Academic Search

Linear elastic fracture mechanics was used to optimize the vacuum heat-treatment procedures for conventional hot-work AISI H11 tool steel. The fracture toughness was determined with non-standard, circumferentially notched and fatigue-precracked tensile-test specimens. The fracture-testing method is sensitive to changes caused by variations in the microstructure resulting from the austenitizing and tempering temperatures as well as the homogeneity of the material

Vojteh Leskovšek; Borivoj Šuštarši?

2006-01-01

315

Fracture toughness and failure mechanisms in unreinforced and long-glass-fibre-reinforced PA66\\/PP blends  

Microsoft Academic Search

In this paper unreinforced and long-glass-fibre-reinforced PA66\\/PP blends with different glass-fibre sizing were studied with respect to their fracture toughness determined by the typical Kc method. The fracture surfaces of these blends were studied by scanning electron microscopy in order to characterize the failure mechanisms. For the unreinforced blends a decrease in fracture toughness was observed when 25 wt% of

T. Harmia; K. Friedrich

1995-01-01

316

A study of failure in bonded lap joints using fracture mechanics  

NASA Astrophysics Data System (ADS)

Although adhesively bonded lap joint has already been widely applied in structures, the strength prediction of the joint is still a challenge. Among many parameters which affect the failure load of the lap joint, the adhesive layer thickness is a very important one. In this study, fracture mechanics is used to analyze the failure mechanism of the lap joint and evaluate the thickness effect on strength of the lap joint. Generally, the adhesive material is softer than the substrates and the crack in the adhesive layer is constrained by the rigid boundaries. The stress field is changed due to the effect of the rigid boundaries. For linear elastic material, the K-Dominance zone is highly reduced and the traditional constant stress intensity factor prediction over-predicts the failure load of the specimens. Constant effective fracture toughness is proposed for better strength prediction by considering of the non-singular stress term ahead of the crack tip. For elastic-plastic material, CTOA is proven to be insensitive to the constraining of the rigid boundaries and can be used as the failure criterion for fracture analysis. Both experimental and FEA simulation show that constant CTOA criterion well predicts the adhesive thickness effect on strength of the DCB specimens for mode I fracture failure. The failure initiation mode of single lap joint is analyzed and the constant CTOA criterion is also proven to be capable to prediction the strength of single lap joint.

Qian, Haiyang

317

Deformation, fracture, and mechanical properties of low-temperature-tempered martensite in SAE 43xx steels  

SciTech Connect

Uniaxial tensile tests were performed on 4330, 4340, and 4350 steels in the as-quenched (AQ) condition and after quenching and tempering at 150 C, 175 C, and 200 C for times of 10 minutes, 1 hour, and 10 hours, respectively. Strength parameters decreased and ductility parameters increased continuously with increasing tempering. Mechanical properties are presented as a function of tempering conditions and steel carbon content, and hardness and ultimate strength changes are given as a function of Hollomon-Jaffe tempering parameters. All tempered specimens, except for some lightly tempered 4350 specimens, deformed plastically through necking instability and failed by ductile fracture. The stresses required for the ductile fracture, estimated from an analysis of the interfacial stresses at particles in the neck at fracture, showed no systematic variation with carbon content of tempering conditions despite significant variations in deformation and strain hardening. The AQ specimens of the 4340 and 4350 steels, and some of the lightly tempered 4350 steels, failed by brittle mechanisms. The deformation and fracture of the low-temperature-tempered 43xx steels are discussed in terms of the changes in fine structure, namely, the formation of transition carbides and a rearranged dislocation substructure that evolve from an AQ martensitic substructure consisting of dislocations with and without carbon atom segregation.

Saeglitz, M. [Deutsche Bahn AG, Brandenburg-Kirchmoeser (Germany); Krauss, G. [Colorado School of Mines, Golden, CO (United States). Dept. of Metallurgical and Materials Engineering

1997-02-01

318

Fracture toughening mechanism of cortical bone: an experimental and numerical approach.  

PubMed

In this investigation, the crack propagation mechanisms contributing to the toughness of cortical bone were studied using a combination of experimental and numerical approaches. Compact tension (CT) specimens were prepared from bovine cortical bones to achieve crack propagation in the longitudinal and transverse directions. Stable crack extension experiments were conducted to distinguish the crack growth resistance curves, and virtual multidimensional internal bond (VMIB) modeling was adopted to simulate the fracture responses. Results from experiments indicated that cortical bone exhibited rising resistance curves (R-curves) for crack extension parallel and perpendicular to the bone axis; the transverse fracture toughness was significantly larger, indicating that the fracture properties of cortical bone are substantially anisotropic. Microscopic observations showed that the toughening mechanisms in the longitudinal and transverse directions were different. When the crack grew in the transverse direction, the crack deflected significantly, and crack bifurcations were found at the crack wake, while, in the longitudinal direction, the crack was straight and uncracked ligaments were observed. Numerical simulations also revealed that the fracture resistance in the transverse direction was greater than that in the longitudinal direction. PMID:21783108

An, Bingbing; Liu, Yang; Arola, Dwayne; Zhang, Dongsheng

2011-02-28

319

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

320

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

PubMed Central

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

2012-01-01

321

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

322

Effect of heat treatments on mechanical properties and fracture behavior of a thixocast A356 aluminum alloy  

Microsoft Academic Search

The effect of different heat treatments (T5 and T6) on mechanical properties, fracture behavior and damage evolution of A356 Thixocast aluminum alloy have been examined in detail in the present work. Tensile tests of the material have been performed in the as cast and as treated conditions in order to observe the different fracture behavior in consequence of the heat

P. Cavaliere; E. Cerri; P. Leo

2004-01-01

323

Life extension simulation of aged reactor pressure vessel material using probabilistic fracture mechanics analysis on a massively parallel computer  

Microsoft Academic Search

This paper describes a probabilistic fracture mechanics (PFM) computer program using the parallel Monte Carlo (MC) algorithm. In the stratified MC algorithm, a sampling space of probabilistic variables such as fracture toughness value, the depth and aspect ratio of an initial semi-elliptical surface crack is divided into a number of small cells. Fatigue crack growth simulations and failure judgements of

S. Yoshimura; M.-Y. Zhang; G. Yagawa

1995-01-01

324

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

Microsoft Academic Search

The dissertation focuses on the analysis, through combined analytical and numerical techniques, of the partial differential equations arising from a new approach to modeling brittle fracture, based on extension of continuum mechanics to the nanoscale. The main part of this work deals with the analysis of several fracture models. Integral transform methods are used to reduce the problem to a

Tsvetanka Bozhidarova Sendova

2008-01-01

325

Fracture mechanics evaluation of the static fatigue life of optical fibers in bending  

NASA Astrophysics Data System (ADS)

Methods for predicting the time-dependent strength (static fatigue) of optical fibers using principles of fracture mechanics have been developed over the past few years. Previous fracture mechanics evaluations of optical fibers reported in the literature have generally considered the case of applied uniform tension. In many applications, fibers are in bending. This paper uses stress intensity factors for semi-circular surface flaws in a round bar subjected to tension or bending to generate relations between fiber proof-stress level, applied stress and expected lifetimes. The factors are taken as function of instantaneous crack depth during stress corrosion growth. Application of the results to the design of fiber optic organizer/closures is discussed.

Nelson, D. V.; Fentress, V. A.

326

Effects of mechanical fracturing and experimental trampling on Hawaiian corals.  

PubMed

In situ trampling occurred under experimental conditions to quantify the differences in the responses to anthropogenic trampling in four dominant species of Hawaiian corals, Porites compressa, Porites lobata, Montipora capitata, and Pocillopora meandrina. Trampling was simulated daily for a period of nine days at which time further breakage was minimal. Forty treatment colonies produced 559 fragments. Trampling was followed by an 11-month recovery period. Coral colony and fragment mortality was low. All four species were highly tolerant of inflicted damage, suggesting that some species of corals can withstand limited pulse events that allow time for recovery. Growth rates following trampling were significantly lower in the treatment groups for three of the four species. This study demonstrated that very few trampling events can produce significant changes in growth even after a long recovery period. Survivorship of fragments is clearly size- and species-dependent in M. capitata and P. compressa. Smaller fragments (<5 cm) had higher mortality than larger fragments (>5 cm). High breakage rates for M. capitata and P. compressa are consistent with the near shore, low-energy regions they inhabit-the same environment frequented by skin divers and waders. Mechanical tests were conducted to determine tensile and compressive strengths. Pocillopora meandrina exhibited the strongest skeletal strength, followed in decreasing order by Porites lobata, Porites compressa, and Montipora capitata. The skeletal strength obtained from the experiments correlate with the wave energy present in the environments in the regions they inhabit, suggesting that structural strength of corals is an adaptive response to hydraulic stress. PMID:12592453

Rodgers, Ku'ulei; Cox, Evelyn; Newtson, Craig

2003-03-01

327

Investigation of a Limestone Pillar Failure Part 2: Stress History and Application of Fracture Mechanics Approach  

Microsoft Academic Search

Summary   Observed pillar failure could not be explained by comparing pillar strength with stresses on the pillar induced by mining\\u000a activities. Instead, the effects of the combined stress history of strata and pillar on the deformational response of rock\\u000a mass and rock were assessed. Application of the principles of fracture mechanics, i.e., extension strain and strain energy\\u000a release rate criteria

M. Alber; J. Heiland

2001-01-01

328

Fracture mechanics and surface chemistry studies of subcritical crack growth in AISI 4340 steel  

Microsoft Academic Search

Coordinated fracture mechanics and surface chemistry experiments were carried out to develop further understanding of environment\\u000a enhanced subcritical crack growth in high strength steels. The kinetics of crack growth were determined for an AISI 4340 steel\\u000a (tempered at 204C) in hydrogen and in water, and the kinetics for the reactions of water with the same steel were also determined.\\u000a A

G. W. Simmons; P. S. Pao; R. P. Wei

1978-01-01

329

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

Microsoft Academic Search

The Nuclear Regulatory Commission (NRC) requested Oak Ridge National Laboratory (ORNL) to perform a pressurized-thermal-shock (PTS) probabilistic fracture mechanics (PFM) sensitivity analysis for the Yankee Rowe reactor pressure vessel, for the fluences corresponding to the end of operating cycle 22, using a specific small-break-loss- of-coolant transient as the loading condition. Regions of the vessel with distinguishing features were to be

T. L. Dickson; R. D. Cheverton; J. W. Bryson; B. R. Bass; D. K. M. Shum; J. A. Keeney

1993-01-01

330

Probabilistic assessment of the fracture mechanics behaviour of an HTR-module primary circuit pressure boundary  

Microsoft Academic Search

In this paper the fracture mechanical behaviour of the primary circuit pressure boundary of a planned HTR-module reactor for electricity and steam generation under normal operation is assessed probabilistically. First and second order reliability methods (FORM-SORM) are used to calculate failure probabilities. They also allow a simplified analysis of the leak-before-break (LBB) behaviour. No LBB was probabilistically identified for the

M. Staat

1996-01-01

331

Non-linear fracture mechanics analyses of part circumferential surface cracked pipes  

Microsoft Academic Search

This paper provides engineering estimates of non-linear fracture mechanics parameters for pipes with part circumferential inner surface cracks, subject to internal pressure and global bending. Solutions are given in the form of two different approaches, the GE\\/EPRI approach and the reference stress approach. For the GE\\/EPRI approach, the plastic influence functions for fully plastic J solutions are tabulated based on

Yun-Jae Kim; Jin-Su Kim; Young-Ze Lee; Young-Jin Kim

2002-01-01

332

Application of linear-elastic fracture mechanics concepts to ferritic spent fuel shipping casks  

Microsoft Academic Search

A linear-elastic fracture mechanics analysis is an appropriate methodology for the fail-safe design of spent fuel shipping containers. It provides a quantitative basis by which to assess the margin of safety inherent to a particular cask. Required inputs are the maximum stresses to be expected from a nine-meter drop, the largest flaw size that may be expected to exist in

P. McConnell; R. A. Wullaert; A. Trujillo

1983-01-01

333

Application of s-Version Finite Element Method to Two-Dimensional Fracture Mechanics Problems  

Microsoft Academic Search

S-version finite element method (s-FEM) is applied to two-dimensional linear\\/nonlinear fracture mechanics problems. s-FEM in crack problems is such that local detailed finite element mesh (local mesh) is superposed on cores finite element model (global mesh) representing the global structure. Therefore, the local and the global meshes are generated independently. This methodology is considered to be one of global-local type

Hiroshi Okada; Sayaka Endoh; Masanori Kikuchi

2007-01-01

334

Two-dimensional fracture mechanics problems for solids with sharp and rounded V-notches  

Microsoft Academic Search

The survey of research on the problems of fracture mechanics of solids with V-shaped notches is discussed. The methods of\\u000a solution of plane problems of the elasticity theory for domains with angular points on boundary contours are considered. Special\\u000a attention is paid to the results of the research which authors obtained applying the unified approach to the solution of stress

Mykhaylo P. Savruk; Andrzej Kazberuk

2010-01-01

335

The initial phase of fracture healing is specifically sensitive to mechanical conditions.  

PubMed

Interfragmentary movements affect the quality and quantity of callus formation. The mounting plane of monolateral external fixators may give direction to those movements. Therefore, the aim of this study was to determine the influence of the fixator mounting plane on the process of fracture healing. Identically configured fixators were mounted either medially or anteromedially on the tibiae of sheep. Interfragmentary movements and ground reaction forces were evaluated in vivo during a nine week period. Histomorphological and biomechanical parameters described the bone healing processes. Changing only the mounting plane led to a modification of interfragmentary movements in the initial healing phase. The difference in interfragmentary movements between the groups was only significant during the first post-operative period. However, these initial differences in mechanical conditions influenced callus tissue formation significantly. The group with the anteromedially mounted fixator, initially showing significantly more interfragmentary movements, ended up with a significantly smaller callus diameter and a significantly higher callus stiffness as a result of advanced fracture healing. This demonstrates that the initial phase of healing is sensitive to mechanical conditions and influences the course of healing. Therefore, initial mechanical stability of an osteosynthesis should be considered an important factor in clinical fracture treatment. PMID:12798066

Klein, Petra; Schell, Hanna; Streitparth, Florian; Heller, Markus; Kassi, Jean-Pierre; Kandziora, Frank; Bragulla, Hermann; Haas, Norbert P; Duda, Georg N

2003-07-01

336

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

337

Computational mechanics  

SciTech Connect

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

Raboin, P J

1998-01-01

338

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

339

Mechanical measurements of passive film fracture on an austenitic stainless steel  

NASA Astrophysics Data System (ADS)

The initiation of fracture in passive films formed on a 304 stainless steel has been measured using a nanoindentation technique as well as bulk circumferentially notched tensile bars (CNTBs). The nanoindentation method was coupled with scanning probe microscopy to isolate individual grains that were free of any observable inclusions, so as to probe only the properties of the film upon the base alloy. The mechanical response of the film was measured while being anodically polarized in 0.1 M sulfuric acid with various halide concentrations, as well as with respect to the applied potential. The passive film strengthened as the applied potential increased in the passive regime, possibly due to film-thickness changes. In both the bulk and nanoscale tests, the passive film-fracture strength was found to decrease with increasing salt concentration in solution, which cannot be attributed to the uniform thinning of the passive film. The correlation between the bulk and nanoscale tests demonstrates that both methods are viable options of measuring the fracture of passive films on metals. Nanoindentation results are used to estimate the applied tensile stress at film fracture between 1 and 2 GPa for an anodically grown passive film on 304 stainless steel at 0 V vs that on Ag/AgCl in 0.1 pct NaCl-0.1 M sulfuric acid.

Rodriguez-Marek, D.; Bahr, D. F.; Pang, M.

2003-06-01

340

Analysis of residual stress on AH32 butt joint by hybrid CO 2 laser-GMA welding  

Microsoft Academic Search

This study has focused on the two-dimensional thermal elasto-plastic analysis to understand and clarify the mechanical phenomena of thermal elasto-plastic behavior on the hybrid welded butt joints. For this, the heat source model for simulation has been determined considering the hybrid welding characteristics. From the results obtained by thermal elasto-plastic analysis, thermal, residual stress characteristics and their production mechanism on

Hee Seon Bang; Han Sur Bang; You Chul Kim; Sung Min Joo

2010-01-01

341

Application of dynamic fracture mechanics to the investigation of catastrophic failure in aircraft structures  

NASA Astrophysics Data System (ADS)

A dynamic fracture mechanics approach to the estimation of the residual strength of aircraft structures is presented. The dependence of the dynamic crack initiation toughness of aluminum 2024-T3 on loading rate is first studied experimentally. Based on the experimental results and on established dynamic fracture mechanic concepts, a fracture mechanics based failure model is established and is used to estimate the residual strength of aircraft structures. A methodology to determine residual strength of dynamically loaded structures based on global structural analysis coupled with local finite element analysis is introduced. Local finite element calculations were performed for different loading rates to simulate the conditions encountered in an explosively loaded aircraft fuselage. The results from the analyses were then used in conjunction with the experimental results for the dynamic fracture toughness of a 2024-T3 aluminum alloy as a function of loading rate, KdIC vs. K?d(t), to determine the time to failure, tf, for a given loading rate. A failure envelope, sf vs. ? , based on the failure model and finite element analysis, is presented for the different cases and the implications for the residual strength of aircraft structures is discussed. Mixed mode dynamic crack initiation in aluminum 2024-T3 alloy is investigated by combining experiments with numerical simulations. The optical technique of coherent gradient sensing (CGS) and a strain gage method are employed to study the evolution of the mixed mode stress intensity factors. The dynamic mixed mode failure envelope is obtained using the crack initiation data from the experiments at a nominal loading rate of 7 x 105 MPam/s . Numerical simulations of the experiments are conducted to both help in designing the experiments and to validate the results of the experiments. The numerical simulations show good correlation with the experimental results.

Chow, Benjamin Bin

342

Fracture mechanisms of aluminium cast alloy locally reinforced by SiC particles and Al 2 O 3 whiskers under monotonic and cyclic load  

Microsoft Academic Search

In the present paper, fracture mechanisms and corresponding stress distributions in aluminium cast alloy locally reinforced by SiC particles and Al2O3 whiskers under monotonic and cyclic load are investigated experimentally and numerically. The material is monotonically and cyclically deformed to failure at room temperature. The fracture origin and the fracture path are investigated on the fracture surfaces. The fracture occurs

M. D. Rafiquzzaman; Y. Arai; E. Tsuchida

2008-01-01

343

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

SciTech Connect

The fracture and fatigue properties of a newly developed bulk metallic glass alloy, Zr{sub 41.2}Ti{sub 13.8}Cu{sub 12.5}Ni{sub 10}Be{sub 22.5} (at. pct), have been examined. Experimental measurements using conventional fatigue precracked compact-tension C(T) specimens ({approximately}7-mm thick) indicated that the fully amorphous alloy has a plane-strain fracture toughness comparable to polycrystalline aluminum alloys. However, significant variability was observed and possible sources are identified. The fracture surfaces exhibited a vein morphology typical of metallic glasses, and, in some cases, evidence for local melting was observed. Attempts were made to rationalize the fracture toughness in terms of a previously developed micromechanical model based on the Taylor instability, as well as on the observation of extensive crack branching and deflection. Upon partial or complete crystallization, however, the alloy was severely embrittled, with toughnesses dropping to {approximately}1 MPa {radical}m. Commensurate with this drop in toughness was a marginal increase in hardness and a reduction in ductility (as measured via depth-sensing indentation experiments). Under cyclic loading, crack-propagation behavior in the amorphous structure was similar to that observed in polycrystalline steel and aluminum alloys. Moreover, the crack-advance mechanism was associated with alternating blunting and resharpening of the crack tip. This was evidenced by striations on fatigue fracture surfaces. Conversely, the (unnotched) stress/life (S/N) properties were markedly different. Crack initiation and subsequent growth occurred quite readily, due to the lack of microstructural barriers that would normally provide local crack-arrest points. This resulted in a low fatigue limit of {approximately}4 pct of ultimate tensile strength.

Gilbert, C.J.; Schroeder, V.; Ritchie, R.O. [Univ. of California, Berkeley, CA (United States). Dept. of Materials Science and Mineral Engineering

1999-07-01

344

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

NASA Astrophysics Data System (ADS)

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 (˜7-mm thick) indicated that the fully amorphous alloy has a plane-strain fracture toughness comparable to polycrystalline aluminum alloys. However, significant variability was observed and possible sources are identified. The fracture surfaces exhibited a vein morphology typical of metallic glasses, and, in some cases, evidence for local melting was observed. Attempts were made to rationalize the fracture toughness in terms of a previously developed micromechanical model based on the Taylor instability, as well as on the observation of extensive crack branching and deflection. Upon partial or complete crystallization, however, the alloy was severely embrittled, with toughnesses dropping to ˜1 MPa sqrt m . Commensurate with this drop in toughness was a marginal increase in hardness and a reduction in ductility (as measured via depthsensing indentation experiments). Under cyclic loading, crack-propagation behavior in the amorphous structure was similar to that observed in polycrystalline steel and aluminum alloys. Moreover, the crack-advance mechanism was associated with alternating blunting and resharpening of the crack tip. This was evidenced by striations on fatigue fracture surfaces. Conversely, the (unnotched) stress/life (S/N) properties were markedly different. Crack initiation and subsequent growth occurred quite readily, due to the lack of microstructural barriers that would normally provide local crack-arrest points. This resulted in a low fatigue limit of ˜4 pct of ultimate tensile strength.

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

1999-07-01

345

The effects of prolonged thermal exposure on the mechanical properties and fracture toughness of C458 aluminum–lithium alloy  

Microsoft Academic Search

The effect of thermal exposure at 83, 135 and 177°C up to 1000h on the electrical resistivity, mechanical properties and fracture toughness of a peak aged Al–Li–Cu–Zr alloy, C458-T861 was studied. Good thermal stability in mechanical properties was observed up to 135°C. The fracture toughness dropped both as a function of increasing temperature and times.

D. Ortiz; J. Brown; M. Abdelshehid; P. DeLeon; R. Dalton; L. Mendez; J. Soltero; M. Pereira; M. Hahn; Eui Lee; J. Ogren; R. Clark; J. Foyos; O. S. Es-Said

2006-01-01

346

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

2011-01-26

347

Evaluation of Fracture in a Three Stage Forging Process Using Continuum Damage Mechanics  

NASA Astrophysics Data System (ADS)

In forging process, formability is limited by ductile fracture. In many cases forgeability is determined by the occurrence of ductile fracture and therefore limitations are set by the appearance of surface or internal cracks within regions that are highly strained due to extensive material flow. In this paper, the continuum damage mechanics framework for ductile materials developed by Lemaitre has been utilized numerically. A constitutive elastic-plastic-damage model has been implemented inside the finite element code ABAQUS. In forming process, crack closure effects have a strong influence on damage evolution. Therefore, it is necessary to split the tensile and compression stresses in damage evolution and deal with them separately. A modified version of Lemaitre model has been implemented and utilized through the study. The prediction of the surface cracks in forging is analyzed numerically. The results could correctly predict the location of surface cracks in the forging process.

Mashayekhi, M.; Ziaei-Rad, S.; Parvizian, J.; Hadavinia, H.

2007-05-01

348

Breakdown of linear elastic fracture mechanics near the tip of a rapid crack.  

PubMed

We present high resolution measurements of the displacement and strain fields near the tip of a dynamic (mode I) crack. The experiments are performed on polyacrylamide gels, brittle elastomers whose fracture dynamics mirror those of typical brittle amorphous materials. Over a wide range of propagation velocities (0.2-0.8c(s)), we compare linear elastic fracture mechanics (LEFM) to the measured near-tip fields. We find that, sufficiently near the tip, the measured stress intensity factor appears to be nonunique, the crack tip significantly deviates from its predicted parabolic form, and the strains ahead of the tip are more singular than the r(-1/2) divergence predicted by LEFM. These results show how LEFM breaks down as the crack tip is approached. PMID:19437643

Livne, Ariel; Bouchbinder, Eran; Fineberg, Jay

2008-12-31

349

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

350

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

351

Mechanical properties of SnPb and lead-free solders at high rates of strain  

NASA Astrophysics Data System (ADS)

The mechanical properties of 63% Sn-37% Pb and lead-free solders have been measured at high strain rates (500-3000 s-1) using a split Hopkinson pressure bar. The solders were produced by quenching in water from the melt, to give the phase structure associated with rapid cooling. Measurements were made at -40 °C, room temperature and +60 °C. The Sn-Pb solder was strongly strain rate and temperature dependent, whereas the lead-free solders showed only a weak dependence on these parameters. All of the materials behaved elasto-plastically until a plateau stress of circa 200 MPa. An unexpected, and possibly important, feature of the lead-free solders was the division of the specimens into two groups with different strengths at low temperatures.

Siviour, C. R.; Walley, S. M.; Proud, W. G.; Field, J. E.

2005-11-01

352

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

NASA Astrophysics Data System (ADS)

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

Yeni, Yener Nail

353

Type II odontoid fracture from frontal impact: case report and biomechanical mechanism of injury.  

PubMed

The authors report a case of Type II odontoid fracture from a frontal impact sustained in the crash of a late-model motor vehicle. They discuss the biomechanical mechanisms of injury after considering patient demographic data, type and use of restraint systems including seatbelt and airbags, crash characteristics, and laboratory-based experimental studies. Multiple factors contributed to the Type II odontoid fracture: the patient's tall stature and intoxicated state; lack of manual three-point seat belt use; obliqueness of the frontal impact; and the most likely preflexed position of the head-neck complex at the time of impact, which led to contact of the parietal region with the A-pillar roof-rail area of the vehicle and resulted in the transfer of the dynamic compressive force associated with lateral bending. Odontoid fractures still occur in individuals involved in late-model motor vehicle frontal crashes, and because this injury occurs secondary to head impact, airbags may not play a major role in mitigating this type of trauma to an unrestrained occupant. It may be more important to use seat belts than to depend on the airbag alone for protection from injury. PMID:15871490

Yoganandan, Narayan; Baisden, Jamie L; Maiman, Dennis J; Pintar, Frank A

2005-04-01

354

Results of fracture mechanics analyses of the ederer cranes in the device assembly  

SciTech Connect

Fracture mechanics analyses were conducted on three critical locations on the lower flange of the load-beam of the Ederer 5 ton and 4 ton cranes in the D.A.F. Facility. Based on these results, it appears that: 1. Propagation of a 5 mm long flaw, previously undetected by non-destructive examination (NDE), to a length sufficient to cause structural failure of either flange, should not occur in at least 100 times the postulated operating scenarios for each crane; 2. Should each crane undergo annual inspection, any surface flaw with a length greater that 20 mm should be removed and repaired by qualified and approved repair procedures.

Dalder, E.

1996-08-01

355

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

Microsoft Academic Search

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

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

2009-01-01

356

Vena Tech LGM Filter Retrieval 16 Years after Implantation: Piecemeal Removal by Intentional Mechanical Fracture.  

PubMed

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

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

2013-11-01

357

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

Microsoft Academic Search

The National Program Plan has established data requirements for out-of-core structures for FBRs. Significant FFTF irradiation space with moderate gamma heating levels is required to irradiate relatively large fracture mechanics specimens to total neutron fluences ranging between 5 x 10²¹ and 5 x 10²² n\\/cm² and temperatures which range between 400°C (750°F) and 650°C (1200°F). Priority 1 data on stainless

2010-01-01

358

Fracture mechanics of ceramics. Vol. 10 - Fracture fundamentals, high-temperature deformation, damage, and design; Proceedings of the 5th International Symposium, Nagoya, Japan, July 15-17, 1991  

Microsoft Academic Search

Current research on the mechanical behavior of ceramic materials is addressed. Topics discussed include dissipative processes accompanying fracture, analysis of the precracking parameters for ceramic single-edge-precracked-beam specimens, reliability of ceramics fracture toughness measurements by indentation, the indentation fracture resistance of self-reinforced mullites, the evidence of plastic deformation on slow crack growth of borate glass, creep damage mechanisms in structural ceramics,

R. C. Bradt; D. P. H. Hasselman; D. Munz; M. Sakai; V. I. A. Shevchenko

1992-01-01

359

Effects of heat treatment and testing temperature on fracture mechanics behavior of low-Si CA15 stainless steel  

Microsoft Academic Search

This research studied the effects of heat treatment and testing temperature on fracture mechanics behavior of Si-modified\\u000a CA-15 martensitic stainless steel (MSS), which is similar to AISI 403 grade stainless steel, which has been widely used in\\u000a wall and blanket structures and in the pipe of nuclear power plant reactors, turbine blades, and nozzles. The results indicated\\u000a that fracture toughness

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

2004-01-01

360

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

Microsoft Academic Search

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

T. Auger; Z. Hamouche; L. Medinaalmazan; D. Gorse

2008-01-01

361

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

362

PHOSPHO1 is essential for mechanically competent mineralization and the avoidance of spontaneous fractures  

PubMed Central

Phosphatases are essential for the mineralization of the extracellular matrix within the skeleton. Their precise identities and functions however remain unclear. PHOSPHO1 is a phosphoethanolamine/phosphocholine phosphatase involved in the generation of inorganic phosphate for bone mineralization. It is highly expressed at sites of mineralization in bone and cartilage. The bones of Phospho1?/? mice are hypomineralized, bowed and present with spontaneous greenstick fractures at birth. In this study we show that PHOSPHO1 is essential for mechanically competent mineralization that is able to withstand habitual load. Long bones from Phospho1?/? mice did not fracture during 3- point bending but deformed plastically. With dynamic loading nanoindentation the elastic modulus and hardness of Phospho1?/? tibiae were significantly lower than wild-type tibia. Raman microscopy revealed significantly lower mineral:matrix ratios and lower carbonate substitutions in Phospho1?/? tibia. The altered dihydroxylysinonorleucine/hydroxyllysinonorleucine and pyridoline/deoxypyridinoline collagen crosslink ratios indicated possible changes in lysyl hydroxylase-1 activity and/or bone mineralization status. The bone formation and resorption markers, N-terminal propeptide and C-terminal telopeptide of Type I collagen, were both increased in Phospho1?/? mice and this we associated with increased bone remodelling during fracture repair or an attempt to remodel a mechanically competent bone capable of withstanding physiological load. In summary these data indicate that Phospho1?/? bones are hypomineralized and, consequently, are softer and more flexible. An inability to withstand physiological loading may explain the deformations noted. We hypothesize that this phenotype is due to the reduced availability of inorganic phosphate to form hydroxyapatite during mineralization, creating an undermineralized yet active bone.

Huesa, Carmen; Yadav, Manisha C.; Finnila, Mikko A.J.; Goodyear, Simon R.; Robins, Simon P.; Tanner, K. Elizabeth; Aspden, Richard M.; Millan, Jose Luis; Farquharson, Colin

2011-01-01

363

Mechanoanions produced by mechanical fracture of bacterial cellulose: ionic nature of glycosidic linkage and electrostatic charging.  

PubMed

Mechanoanions were produced by heterogeneous scission of the glycosidic linkages of the main chain of bacterial cellulose (BC); scission was induced by mechanical fracture of the BC in a vacuum in the dark at 77 K. The mechanoanions were detected using electron-spin-trapping methods with tetracyanoethylene. The yield of mechanoanions was positively correlated with the absolute value of the change in the Mulliken atomic charge, which was used as a descriptor of the ionic nature of the glycosidic linkage. Homogeneous scission of the glycosidic linkages induced by mechanical fracture generated mechanoradicals, the electron affinity of which was estimated on the basis of the energy of the lowest unoccupied molecular orbital for the model structure of the mechanoradical. It was concluded that the electrostatic charging of BC is caused by electron transfer from mechanoanions to mechanoradicals, which have high electron affinities. The electrostatic charge density of BC in a vacuum in the dark at 77 K was estimated to be 6.00 × 10(-1) C/g. PMID:22978760

Sakaguchi, Masato; Makino, Masakazu; Ohura, Takeshi; Iwata, Tadahisa

2012-09-27

364

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

Microsoft Academic Search

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

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

1998-01-01

365

Hydrologic mechanisms governing fluid flow in partially saturated, fractured, porous tuff at Yucca Mountain  

SciTech Connect

In contrast to the saturated zone where fluid moves rapidly along fractures, the fractures (with apertures large relative to the size of matrix pores) will desaturate first during drainage process and the bulk of fluid flow would be through interconnected pores in the matrix. Within a partially drained fracture, the presence of a relatively continuous air phase will produce practically an infinite resistance to liquid flow in the direction parallel to the fracture. The residual liquid will be held by capillary force in regions around fracture contact areas where the apertures are small. Normal to the fracture surfaces, the drained portion of the fractures will reduce the effective area for liquid flow from one matrix block to another matrix block. A general statistical theory is constructed for flow along the fracture and for flow between the matrix blocks to the fractures under partially saturated conditions. Results are obtained from an aperture distribution model for fracture saturation, hydraulic conductivity, and effective matrix-fracture flow areas as functions of pressure. Drainage from a fractured tuff column is simulated. The parameters for the simulations are deduced from fracture surface characteristics, spacings and orientations based on core analyses, and from matrix characteristics curve based on laboratory measurements. From the cases simulated for the fractured, porous column with discrete vertical and horizontal fractures and porous matrix blocks explicitly taken into account, it is observed that the highly transient changes from fully saturated conditions to partially saturated conditions are extremely sensitive to the fracture properties. However, the quasi-steady changes of the fluid flow of a partially saturated, fractured, porous system could be approximately simulated without taking the fractures into account. 22 references, 16 figures.

Wang, J.S.Y.; Narasimhan, T.N.

1984-10-01

366

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

367

A Fracture Mechanics Model for Cavitation Damage in Mechanical Heart Valve Prostheses  

Microsoft Academic Search

In the 1994 Replacement Heart Valve Guidance of the Food and Drug Administration (FDA), both cavitation and damage tolerance analyses are required for mechanical heart valves (MHV). Cavitation results from a sequence of events. First, vaporous bubbles are generated in the blood flow. They then collapse to form high-speed micro liquid jets, striking against the solid valve boundary, and subsequently

Changfu Wu; Ned H. C. Hwang; Y. K. Lin

2001-01-01

368

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

SciTech Connect

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

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

1993-08-01

369

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

370

[Bone fracture and the healing mechanisms. A new method for evaluation of fracture healing by echo tracking].  

PubMed

Assessment of bone healing on radiographs is not necessarily objective. A clinical system was developed to quantify the stiffness of healing fractures of the tibia in patients by the echo tracking (ET) method in a manner similar to a three-point bending test. The lower leg was supported. An ultrasound probe was placed on the proximal and distal fragments and a load of 25 N was applied. With a multiple ET system, two probes measured the displacement of five tracking points on each of the proximal and distal fragments of the tibia, thereby detecting the bending of the two fragments generated by the load. ET angle was defined as the sum of the inclinations of the proximal and distal fragments. Patients with tibial fracture treated by a cast or internal fixation were measured over time. In patients with radiographically normal healing, the bending angle decreased exponentially over time. However, in patients with nonunion, the angle remained the same over time. It was demonstrated that the ET method could be clinically applicable to evaluate fracture healing as a versatile, quantitative and noninvasive technique. PMID:19398836

Ohnishi, Isao; Matsuyama, Juntaro

2009-05-01

371

Action of recombinant human BMP-2 on fracture healing in rabbits is dependent on the mechanical environment.  

PubMed

The utility of recombinant human bone morphogenetic protein-2 (rhBMP-2) in inducing bone formation in fractures of bone is well known. However, the influence of the mechanical environment on the actions of rhBMP-2 on fracture healing is not clear. An experimental model of fractures of the tibia in rabbits was developed and utilized to investigate the role of mechanical environment on rhBMP-2 action. A 1 mm osteotomy gap was stabilized by either a low- or high-stiffness fixator (LSF or HSF, respectively), and local treatment with rhBMP-2 in an absorbable collagen sponge (ACS) was evaluated. The results of the investigation were analysed by both histomorphometry and biomechanics. The LSF caused an increase in mineralized periosteal callus compared to HSF, the rhBMP-2 in ACS accelerated fracture healing only in the LSF group but not in the HSF group. The area of mineralized tissue in interfragmentary callus was determined by fixation stiffness and not by BMP treatment. rhBMP-2 caused higher bone resorption in the endosteal callus during the late stages of fracture healing, but these histological differences did not affect the mechanical properties. Biomechanical evaluation showed only differences at 3 weeks between LSF-rhBMP-2 and LSF-ACS. The bending and torsional properties were higher in the rhBMP-2/ACS group compared to ACS alone at 3 weeks. PMID:20209659

Cuenca-López, María D; Peris, José L; García-Roselló, Mireia; Atienza, Carlos; Prat, Jaime; Becerra, José; Andrades, José A

2010-10-01

372

Experimental and numerical study of ball indentation for evaluation of mechanical properties and fracture toughness of structural steel  

Microsoft Academic Search

Determination of mechanical properties of materials using non-conventional techniques has been an active area of research\\u000a for a long time. Among various small specimen techniques to determine mechanical properties of materials, the ball indentation\\u000a technique (BIT) has proved to be advantageous. BIT is used to measure material’s mechanical properties including fracture\\u000a toughness when a tensile test cannot be performed: on

Sabita Ghosh; Mita Tarafder; S. Sivaprasad; Soumitra Tarafder

2010-01-01

373

The possibilities of fracture mechanics as applied to problems of strength, service life, and substantiation of safe operation of heat-generating and mechanical equipment  

NASA Astrophysics Data System (ADS)

The fundamentals of fracture mechanics are briefly outlined, and its possibilities as a tool for estimating the longevity and bearing capacity of equipment components the metal of which contains cracklike flaws are pointed out. Experimentally obtained kinetic crack resistance diagrams lying at the heart of methods for determining the survivability of structures are given for some steels. Practical application of the methods of fracture mechanics is demonstrated on a particular example of substantiating temporary operability of a boiler drum having cracklike flaws near the holes for water downtake pipes.

Grin', E. A.

2013-01-01

374

Simulation of crack growth governed by delayed fracture mechanism under high-cycle loading  

NASA Astrophysics Data System (ADS)

The surface crack growth that results from the delayed fracture mechanism under sliding contact of two solids which gives rise to the formation of a wear particle is computed. The cyclic loading in the form of repetitions of loading and unloading under such conditions is produced by stresses distributed over widely space spots of real contact, which are passing through the site where the crack is positioned. Every passage produces a cycle or event of one loading and one complete unloading. The problem is to find the number of cycles or events from the beginning of the loading process till the critical event. A method suitable to solving the problem for large number of cycles is presented.

Gotlib, V. A.; Salganik, R. L.; Rapoport, L.

1995-10-01

375

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

SciTech Connect

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

Bezalel c. Haimson

2005-06-10

376

Microdamage detection and repair in bone: fracture mechanics, histology, cell biology.  

PubMed

Bone is an elementary component in the human skeleton. It protects vital organs, regulates calcium levels and allows mobility. As a result of daily activities, bones are cyclically strained causing microdamage. This damage, in the form of numerous microcracks, can cause bones to fracture and therefore poses a threat to mechanical integrity. Bone is able to repair the microcracks through a process called remodelling which is tightly regulated by bone forming and resorbing cells. However, the manner by which microcracks are detected, and repair initiated, has not been elucidated until now. Here we show that microcrack accumulation causes damage to the network of cellular processes, resulting in the release of RANKL which stimulates the differentiation of cells specialising in repair. PMID:19478407

Hazenberg, Jan G; Hentunen, Teuvo A; Heino, Terhi J; Kurata, Kosaku; Lee, Thomas C; Taylor, David

2009-01-01

377

Mechanics of slip and fracture along small faults and simple strike-slip fault zones in granitic rock  

SciTech Connect

We exploit quasi-static fracture mechanics models for slip along pre-existing faults to account for the fracture structure observed along small exhumed faults and small segmented fault zones in the Mount Abbot quadrangle of Calfornia and to estimate stress drop and shear fracture energy from geological field measurements. Along small strike-slip faults, cracks that splay from the faults are common only near fault ends. In contrast, many cracks splay from the boundary faults at the edges of a simple fault zone. Except near segment ends, the cracks preferentially splay into a zone. We infer that shear displacement discontinuities (slip patches) along a small fault propagated to near the fault ends and caused fraturing there. Based on elastic stress analyses, we suggest that slip on one boundary fault ends and caused fracturing there. Based on elastic stress analyses, we suggest that slip patches preferentially led to the generation of fractures that splayed into the zones away from segment ends and out of the zones near segment ends. We estimate the average stress drops for slip events along the fault zones as /similar to/1 MPa and the shear fracture energy release rate during slip as 5/times/10/sup 2//minus/2/times/10/sup 4/ J/m/sup 2/. This estimate is similar to those obtained from shear fracture of laboratory samples, but orders of magnitude less than those for large fault zones. These results suggest that the shear fracture energy release rate increases as the structural complexity of fault zones increases. /copyright/ American Geophysical Union 1989

Martel, S. J.; Pollard, D. D.

1989-07-10

378

Fracture mechanics of ceramics. Vol. 10 - Fracture fundamentals, high-temperature deformation, damage, and design; Proceedings of the 5th International Symposium, Nagoya, Japan, July 15-17, 1991  

SciTech Connect

Current research on the mechanical behavior of ceramic materials is addressed. Topics discussed include dissipative processes accompanying fracture, analysis of the precracking parameters for ceramic single-edge-precracked-beam specimens, reliability of ceramics fracture toughness measurements by indentation, the indentation fracture resistance of self-reinforced mullites, the evidence of plastic deformation on slow crack growth of borate glass, creep damage mechanisms in structural ceramics, and a high temperature fracture mechanism of gas-pressure sintered silicon nitride. Also discussed are a generic model for creep rupture lifetime estimation of a fibrous ceramic composite, the role of cracks in the nonlinear deformation and fracture behavior of polycrystalline ceramics, particle impact damage of engineering ceramics, the effect of defects and grain size on strength of mullite ceramics, and a design methodology for manufacturing glass cathode ray tubes.

Bradt, R.C.; Hasselman, D.P.H.; Munz, D.; Sakai, M.; Shevchenko, V.IA.

1992-01-01

379

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

PubMed

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

Choudhary, Lokesh; Raman, R K Singh

2011-10-31

380

Application of the Probabilistic Mechanics of Fatigue Fracture to the Evaluation of the Reliability of Welded Structures  

Microsoft Academic Search

We propose a method for the evaluation of the reliability of load-carrying elements of welded metallic bridges in the process of long-term operation based on the probabilistic mechanics of fatigue fracture. This method enables one to estimate the risk of failure of a structure as a result of the development of fatigue cracks in the zones of stress concentration near

O. I. Darchuk

2003-01-01

381

HydroMechanical Modelling of underground CO2 Storage and Risk Evaluation through a Probabilistic Fracturing Model  

Microsoft Academic Search

This study provides an analysis of the influence of underground CO2 storage on the effective stress field in a representative geological formation. Large scale finite element models are used to describe the injection process. For high injection rates, different material degradation mechanisms may be activated depending on initial conditions. The case of rock fracturing due to tensile stresses (i.e. mode

N. Guy; M. Seyedi; F. Hild

382

FE-investigation of the stress\\/strain and fracture mechanics properties of intermetallic phase regions in leadfree solder interconnects  

Microsoft Academic Search

This main objective of this paper is to use a finite element analysis of the state of stress and strain within an intermetallic layer at the interface of a lead-free solder joint for an investigation of the comparatively unknown fracture mechanics properties and critical state of stress of intermetallic compounds. For this purpose we discuss the magnitude and sign of

W. H. Miillera; Taoufiq Hannach; H. J. Albrecht

2006-01-01

383

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

Microsoft Academic Search

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

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

2008-01-01

384

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

SciTech Connect

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

Robert Podgorney; Chuan Lu; Hai Huang

2012-01-01

385

Mechanical modeling of tectonic deformations  

SciTech Connect

Finding oil traps is based essentially on interpreting seismic data. The interpretation is often difficult; the geologist generally is faced with several possible solutions because structures are not always clearly defined. Rock mechanics are used to retain only the kinematic solutions that are stable at all times. All the possible evolutions are no longer equally probable. Two different methods were used. Elasto-plastic behaviors (limestones, sandstones, etc.) are satisfactorily taken into account within a finite element code. It must be able to model the great displacement and large deformations that occur on a geological time scale. In an experimental approach, conditions of structural deformation are recreated in laboratories using physical models. Results of the numerical modeling have to be calibrated against these experiments. A sedimentary basin has been modeled in this way. This basin has been numerically modeled. Sedimentation is modeled by a gradual activation of the meshing. The plastic strain is computed at each time step of the deformation. Large values are located along lined zones corresponding to the faults observed on physical models. The creation and propagation of faults are modeled correctly. Moreover, the authors check that the spacing of the faults depends on the thicknesses of the layers. Viscous behaviors of salt domes are better taken into account by a finite differences code. Mushroom diapirs and balloon diapirs have been modeled in this way. Other parameters such as the spacing between salt domes may be studied, too.

Julien, P. (TOTAL C.F.P., Paris (France))

1990-05-01

386

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

387

Posterior fracture-dislocation of the distal part of the fibula. Mechanism and staging of injury.  

PubMed

The Bosworth fracture, a fixed posterior fracture-dislocation of the distal part of the fibula due to external rotation of the supinated foot, is a rare injury. In this report we review the literature, present two new cases, and describe our cadaver studies, showing that the initial stages of the injury are identical to those of a Maisonneuve fracture. The final stages that are unique to this fracture-dislocation are the posterior dislocation and fracture of the fibula and the fracture of the medial malleolus or rupture of the deltoid ligament. The objectives of treatment are reduction of the dislocation, repair and stabilization of the tibiofibular syndesmosis, and restoration of the ankle mortise to its anatomical position. PMID:6630259

Perry, C R; Rice, S; Rao, A; Burdge, R

1983-10-01

388

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

PubMed

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 10(8) cycles is required, testing is performed to ascertain whether the device will survive 10(8) cycles under accelerated in vitro loading conditions. This is a far from satisfactory approach as the safety factors, which essentially tell you how close you are to failure, remain unknown; rather, the probability of fatigue failure should instead be assessed on the basis of testing to failure. In this work, a new damage-tolerant analysis of a cardiovascular stent is presented, where the design life is conservatively evaluated using a fracture mechanics methodology. In addition to enabling estimates of safe in vivo lifetimes to be made, this approach serves to quantify the effect of flaws in terms of their potential effect on device failure, and as such provides a rational basis for quality control. PMID:16260033

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

2005-11-02

389

Fracture mechanisms during fiber pull-out for carbon-fiber-reinforced thermosetting composites  

NASA Astrophysics Data System (ADS)

We have investigated the mechanism of fiber/resin debonding in three untreated and three corresponding plasma-treated carbon-fiber-reinforced thermosetting microcomposites, by examining the fiber/resin fracture surfaces with the aid of wetting force scanning. The wettability of a debonded microdroplet resin site (50-150 microns long) on a fiber was compared with that of the original fiber surface by scanning with ethylene glycol. Wetting force scans show that, for most fiber/resin combinations, the original location of the interface had a distinctly different wetting force as compared with adjacent nonbonded fiber surfaces. This suggested either the removal of a layer of carbon fiber along with the resin or a submicroscopic cohesive failure in the resin leaving a thin residual layer of the resin on the fiber. For only a few specimens, no change in wetting force at the resin site was observed, suggesting adhesive failure of the interface. The different failure mechanisms proposed for various fiber/resin systems are explained on the basis of the morphological structures of the carbon fibers, cohesive shear strengths of the resins, and the measured bond strengths.

Chou, C. T.; Gaur, U.; Miller, B.

390

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

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

391

Fracture mechanics behavior of the T91 martensitic steel in contact with liquid lead-bismuth eutectic for application in an accelerator driven system  

NASA Astrophysics Data System (ADS)

The fracture toughness of the T91 martensitic steel in liquid lead-bismuth eutectic has been measured at 300 °C in plane stress and plane strain conditions. The effect of achieving wetting at the crack tip prior starting mechanical testing is demonstrated to be the key factor for a correct evaluation of the potential effect of LBE on fracture toughness. In plane stress, one observes a serrated fracture mode associated with a reduction of fracture toughness between 20% and 30%. The toughness reduction is higher in plane strain where the cleavage fracture mode prevails. The difference between the two fracture modes is due to the higher plastic deformation level reached at final fracture in plane stress and to the higher crack growth rate in plane strain. These results will be useful for the design of future nuclear systems cooled by LBE planning to use martensitic steels as structural materials.

Auger, T.; Gorse, D.; Hamouche-Hadjem, Z.; van den Bosch, J.; Coen, G.; Almazouzi, A.; Hojna, A.; Dalikova, K.; di Gabriele, F.; Serrano, M.; Gessi, A.; Agostini, P.; Vogt, J.-B.; Serre, I.

2011-08-01

392

A frequency domain analysis to characterize heterogeneity and recharge mechanisms in a fractured crystalline-rock aquifer  

NASA Astrophysics Data System (ADS)

We investigate aquifer behavior and recharge mechanisms in fracture media using a frequency domain approach. Main interest was the quantification of aquifer characteristic time response, storativity and estimation of heterogeneity and connectivity impact on well behavior on a wide range of temporal scales from 1 day to 8 years. Transfer Functions were calculated for a fractured crystalline-rock aquifer system located in Ploemeur (S of Brittany, France). Recharge, first calculated as effective rainfall, and groundwater level fluctuations (tide effects removed) were used as input and output functions, respectively. The Transfer Function quantifies the ratio of amplitudes of the input and output in the frequency domain. The obtained transfer functions are typically constant at low frequency and decay with frequency for mid and high frequencies. Classical behavior models for interpreting transfer functions are the linear and Dupuit models, plus combination with fast flow component. For linear and Dupuit models, the transfer function |H(?)|2 scales respectively as |H(?)|2 ~ ?-2, and |H(?)|2 ~ ?-1 for high frequencies. The transfer functions obtained for the fractured rock aquifer of Ploemeur do not follow these scaling. Instead, they scale as |H(?)|2 ~ ?-?, with ?=0.7. This suggests that the heterogeneity at different scales in this fractured system involves a variety of transfer processes that cannot be represented by classical models. We discuss the relevance of alternative dual-permeability and multi-permeability models for modeling the rainfall-hydraulic head response in this fractured media. We analyze the variability of the response (characteristic time, amplitude and asymptotic log-log slope) for wells intersecting the main fracture zone, intersecting secondary fracture zones or located in weathered rock.

Jimenez-Martinez, J.; Longuevergne, L.; Le Borgne, T.; Davy, P.; Bour, O.; Goderniaux, P.; Russian, A.; Thomas, Z.

2011-12-01

393

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

394

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, ...

395

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

SciTech Connect

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

Chong, K.P.

1984-09-01

396

Effect of temperature on the fracture mechanisms of 8090 Al–Li alloy and 8090 Al–Li\\/SiC composite  

Microsoft Academic Search

The fracture mechanisms in tension were analyzed in a peak-aged 8090 Al–Li alloy and 8090 Al–Li\\/SiC as a function of temperature. Failure in the alloy changed from intergranular fracture at ambient temperature to ductile void growth above 150 °C, leading to a tenfold increase in the elongation to failure. Damage in the composite was always nucleated by particle fracture, and

C. González; A. Mart??n; J. Llorca

2004-01-01

397

Fracture Mechanics in Low-Cycle Loading and in the Presence of High Strain Gradient.  

National Technical Information Service (NTIS)

The fracture criterion for variable low-cycle loading was developed based on the concept of cumulative damage. The study of fracture stability in high strain gradient field is based on the argument that couple-stress becomes significant in such fields. An...

F. D. Ju Y. C. Hsu

1971-01-01

398

Are knee mechanics during early stance related to tibial stress fracture in runners?  

Microsoft Academic Search

BackgroundTibial stress fractures are a serious overuse injury in runners. Greater vertical loading rates and tibial shock have been found in runners with previous tibial stress fracture compared to controls. The timing of these variables occurs very early in the stance phase and suggests that conditions shortly after footstrike may be important in determining injury risk. The purpose of this

Clare E. Milner; Joseph Hamill; Irene Davis

2007-01-01

399

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

Microsoft Academic Search

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

M. Jha; R. Narasimhan

1992-01-01

400

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

401

Study on rock micro-rupture mechanism and macroscopic fracture characteristic of phyllite  

Microsoft Academic Search

The macroscopic fracture s of rock are strongly linked to the presence of microstructures and micro-defects within. And the evidence of deformation is left after fracture process. This paper put the sericite phyllite and siliceous plate phyllite of Middle Devonian series as the research object on upriver of Jinsha River. The micro-rupture properties of rock are judged and the relation

Zheng Da

2011-01-01

402

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

Microsoft Academic Search

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

David M. McClung

1979-01-01

403

Hydraulic Fracture Containment in Sand  

Microsoft Academic Search

The mechanism of hydraulic fracturing in soft, high permeability material is considered fundamentally different from that in hard, low permeability rock, where a tensile fracture is created and conventional linear elastic fracture mechanics (LEFM) applies. The fracturing and associated modeling work is then a relatively new area. Particularly, the fracture containment in layered formations remains unknown. This research is aiming

Y. Dong

2010-01-01

404

Scaling of strength and lifetime probability distributions of quasibrittle structures based on atomistic fracture mechanics.  

PubMed

The failure probability of engineering structures such as aircraft, bridges, dams, nuclear structures, and ships, as well as microelectronic components and medical implants, must be kept extremely low, typically <10(-6). The safety factors needed to ensure it have so far been assessed empirically. For perfectly ductile and perfectly brittle structures, the empirical approach is sufficient because the cumulative distribution function (cdf) of random material strength is known and fixed. However, such an approach is insufficient for structures consisting of quasibrittle materials, which are brittle materials with inhomogeneities that are not negligible compared with the structure size. The reason is that the strength cdf of quasibrittle structure varies from Gaussian to Weibullian as the structure size increases. In this article, a recently proposed theory for the strength cdf of quasibrittle structure is refined by deriving it from fracture mechanics of nanocracks propagating by small, activation-energy-controlled, random jumps through the atomic lattice. This refinement also provides a plausible physical justification of the power law for subcritical creep crack growth, hitherto considered empirical. The theory is further extended to predict the cdf of structural lifetime at constant load, which is shown to be size- and geometry-dependent. The size effects on structure strength and lifetime are shown to be related and the latter to be much stronger. The theory fits previously unexplained deviations of experimental strength and lifetime histograms from the Weibull distribution. Finally, a boundary layer method for numerical calculation of the cdf of structural strength and lifetime is outlined. PMID:19561294

Bazant, Zdenek P; Le, Jia-Liang; Bazant, Martin Z

2009-06-26

405

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

SciTech Connect

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

Z. Ceylan

2002-04-30

406

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

NASA Astrophysics Data System (ADS)

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

Lin, Youbo

407

Fracture-mechanical analysis of the residual service life of the welded main girders of the highway bridges of Ruedersdorf  

NASA Astrophysics Data System (ADS)

A fracture mechanics analysis was carried out on a certain type of weld defect contained in the main girders of the Ruedersdorf highway bridges (River Luehlen, Germany). To assess fatigue cracks which start from welding defects of about 10 mm height at the end of the inner cover plates, specimens were taken from the bridges. The fracture mechanical properties of the 55 years old steel and the stress intensity factors were determined to analyze the unstable and stable crack extension. The essential influence on the residual life is the extending traffic density. The assesssment of the critical crack size and that of the crack growth show a residual service life of some years. Only limited data can be generated from specimens removed from the bridges, and the effect of the service environment of any specific structure must be taken into account.

Edel, Karl-Otto

1992-07-01

408

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

SciTech Connect

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

Takahashi, Hideaki; Watanable, Kimio; Hashida, Toshiyuki

1995-01-26

409

Research paper Thermal-mechanical modeling of cooling history and fracture development in inflationary basalt lava flows  

Microsoft Academic Search

Thermal-mechanical analyses of isotherms in low-volume basalt flows having a range of aspect ratios agree with inferred isotherm patterns deduced from cooling fracture patterns in field examples on the eastern Snake River Plain, Idaho, and highlight the caveats of analytical models of sheet flow cooling when considering low-volume flows. Our field observations show that low-volume lava flows have low aspect

Simon A. Kattenhorn; Conrad J. Schaefer

410

Effect of yttrium on cryogenic mechanical properties and fracture behavior of Al-Li-Cu-Mg-Zr alloy  

Microsoft Academic Search

The effect of various contents (0.07 and 0.23 Wt-%) of rare earth (RE) element yttrium on cryogenic mechanical properties and fracture behavior of an Al-Li-Cu-Mg-Zr alloy has been studied at temperatures from 295 to 4 K. Y increased the yield strength, ultimate tensile strength, elongation, and notched tensile strength of the alloy at ambient and cryogenic temperatures. However, Y had

L. M. Ma; G. J. Liang; Y. Y. Li

1997-01-01

411

Welded Penstock, Produced of High-Strength Steel and Application of Fracture Mechanics Parameters to Structural Integrity Assessment  

Microsoft Academic Search

Application of high-strength steel for welded penstock increased the probability of crack-like defects and in welded joint.\\u000a Structural integrity assessment procedure is presented and applied to welded penstock produced of highstrength steel, comparing\\u000a crack driving force and material crack resistance in terms of J-integral as fracture mechanics parameter. The safety and structural integrity of welded penstock are experimentally verified\\u000a by

Stojan Sedmak; Aleksandar Sedmak

412

The effect of mechanical constraint on the flow and fracture of 63\\/37 Sn\\/Pb eutectic alloy  

Microsoft Academic Search

Copper compact tension specimens containing joints of 63\\/37 Sn\\/Pb eutectic solder alloy are used to study experimentally the flow and fracture behavior of eutectic solder under conditions of monotonic loading and mechanical constraint. Such constraint arises naturally due to the presence of the specimens' copper\\/solder interfaces, and various levels of constraint are achieved by employing joints of various sizes. Concomitant

S. V. Harren; J. Botsis

1995-01-01

413

Study of rib fracture mechanisms based on the rib strain profiles in side and forward oblique impact.  

PubMed

Rib fractures constitute a good indication of severity as there are the most frequent type of AIS3+ chest injuries. In 2008, Trosseille et al. showed a promising methodology to exhibit the rib fracture mechanisms, using strain gauges glued on the ribs of Post-Mortem Human Subjects (PMHS) and developing a specific signal analysis. In 2009, they published the results of static airbag tests performed on 50th percentile male PMHS at different distances and angles (pure lateral and 30 degrees forward oblique direction). To complete these already published data, a set of 8 PMHS lateral and oblique impactor tests were performed with the same methodology. The rib cages were instrumented with more than 100 strain gauges on the ribs, cartilage and sternum. A 23.4 kg impactor was propelled at 4.3 or 6.7 m/s. The forces applied onto the PMHS at 4.3 m/s ranged from 1.6 kN to 1.9 kN and the injuries varied from 4 to 13 rib fractures. At 6.7 m/s, the forces applied onto the PMHS ranged from 2.6 kN to 4 kN and the injuries varied from 9 to 16 rib fractures. The results of 24 tests from Trosseille et al. 2008 and 2009 and from the current study were processed in the same way and analyzed together. The time and location of the fractures were determined for each test and a ribcage fracture scenario was defined for each configuration. Strain profile corridors were built for pure lateral and forward oblique impacts, in the case of a rigid impact (impactor) or for an airbag loading. They can be used to assess the human body model biofidelity and the validation of rib fracture mechanisms in these models. Based on these corridors, the effects of the severity, the impact angle and the loading system on rib strain profiles were analyzed and are presented in this paper. PMID:22869310

Leport, Tiphaine; Baudrit, Pascal; Potier, Pascal; Trosseille, Xavier; Lecuyer, Erwan; Vallancien, Guy

2011-11-01

414

Computational fracture mechanics estimation of the strength of deep-water welded constructions  

NASA Astrophysics Data System (ADS)

The principles of estimating the strength of deep-water engineering constructions using the brittle fracture prevention criterion are presented. They are based on the experimental results and theoretical developments accumulated in our works.

Il'in, A. V.; Filin, V. Yu.

2013-04-01

415

[New experimental insights into the mechanism of blow-out fractures].  

PubMed

Model impact tests on 3-dimensional PMMA eye models with a swing type impact tester (Dynstat) were performed. There are three kinds of impact tests; the impact to the eyeball alone, the impact to the eyeball and infraorbital margin, and the impact to the isolated infraorbital margin. All impact tests of eye models were recorded by high speed camera with 3,000 pictures per second. Analysis of impact tests showed, that the primary factor of blow-out fractures was deformation of the eyeball by kinetic energy of impact. Transmission of impact force by deformed eyeball to orbital walls is causing blow-out fractures on the weakest areas of the orbit without fracturing the orbital rim. Against the present accepted theories of "hydraulic force" und "buckling force" this is a new theory for pathomechanism of blow-out fractures. Our experimental results support the clinical investigations on treated patients. PMID:2528872

Schneider, D

1989-01-01

416

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 MPam 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

417

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

418

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

NASA Astrophysics Data System (ADS)

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

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

2004-02-01

419

Mechanisms of fracture and creep of structural alloys. Annual report, 1 January 1992-28 February 1993  

SciTech Connect

Progress is reviewed for a research which focuses on two aspects which limit the performance of structural alloys. First, in a study generic to a wide range of materials, the authors are determining the mechanisms, as well as local failure criteria, by which voids grow, interact and link during ductile fracture due to damage accumulation. Secondly, in a study focused specifically at high strength titanium alloys, the authors are examining the deformation and fracture behavior of novel beta titanium alloy Ti-23Nb-11Al, which is age-hardenable by the formation of ordered precipates based on Ti3Al. Progress for the period January 1, 1992 to February 28, 1993 is reviewed for the following projects: (1) two-dimensional modeling studies of void linking during ductile, microvoid fracture, (2) a three-dimensional experimental modeling study void growth and linking during ductile fracture, and (3) the influence of temperature on the deformation and oxidation behavior of a new age-hardenable beta titanium alloy.

Koss, D.A.

1993-03-29

420

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

Microsoft Academic Search

The variation of yield strength and fracture toughness was investigated for four different heat treatments attempted on specimens\\u000a of a near-eutectoid steel. The aim of this study was to optimize the microstructure for simultaneous improvements in strength\\u000a and toughness. Further, the fracture toughness deduced through empirical relations from tensile and charpy impact tests was\\u000a compared with those measured directly according

K V Sudhakar; G S Murty

1998-01-01

421

Low-temperature fracture mechanisms in a spheroidised reactor pressure vessel steel  

Microsoft Academic Search

The micromechanisms of fracture of a spheroidised A533B reactor pressure vessel steel over the temperature range of ?190°C\\u000a to + 60°C were investigated by performing uniaxial tensile tests on double-notched cylindrical specimens. Failure was by quasi-cleavage\\u000a at temperatures between ?190°C and ?145°C. Quasi-cleavage fracture surfaces are characterised by clusters of planar facets\\u000a that are separated from other facets either by large

A. Kumar; S. G. Roberts; A. J. Wilkinson

2007-01-01

422

Tensile Deformation and Fracture Mechanism of Bulk Bimodal Ultrafine-Grained Al-Mg Alloy  

Microsoft Academic Search

The tensile fractures of ultrafine-grained (UFG) Al-Mg alloy with a bimodal grain size were investigated at the micro- and\\u000a macroscale using transmission electron microscopy (TEM), scanning electron microscopy (SEM) equipped with focused ion beam\\u000a (FIB), and optical microscopy. The nanoscale voids and crack behaviors near the tensile fracture surfaces were revealed in\\u000a various scale ranges and provided the evidence to

Zonghoon Lee; Velimir Radmilovic; Byungmin Ahn; Enrique J. Lavernia; Steven R. Nutt

2010-01-01

423

Fatigue fracture mechanisms and fractography of short-glassfibre-reinforced polyamide 6  

Microsoft Academic Search

An adaptation to existing failure models for fatigue fracture of short-fibre-reinforced thermoplastics is presented. This\\u000a was based on results using some new experimental methods. These results led to the conclusion that cracks in glassfibre-reinforced\\u000a polyamide 6 (conditioned to equilibrium water content) remain bridged by plastically drawn matrix material and\\/or fibres until\\u000a just prior to final fracture. In this article, emphasis

J. J. HORST; J. L. SPOORMAKER

1997-01-01

424

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.

425

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

426

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

427

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

428

Fracture Mechanics Investigation of Oil Shale to Aid in Understanding the Explosive Fragmentation Process. Final Technical Report, January 1983-July 1984.  

National Technical Information Service (NTIS)

This report summarizes goals and findings achieved in developing technologies to improve the overall efficiency of oil shale recovery processes. The objectives are to (a) develop theoretical fracture mechanics tools that are applicable to transversely iso...

K. P. Chong

1984-01-01

429

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

430

Fine fracture structures in the geothermal region of Hakone volcano, revealed by well-resolved earthquake hypocenters and focal mechanisms  

NASA Astrophysics Data System (ADS)

Occurrence of swarm earthquake in volcanically or geothermally active regions has been thought to be caused by the migration of the magmatic and/or hydrothermal fluid (e.g. Hill, 1977; Sibson, 1996; Spicak and Horalek, 2001; Hensch et al., 2008). It has been suggested that the fault-related fracture systems are responsible for the migration of fluid flow (e.g. Hill, 1977; Sibson, 1987; Sibson, 1996). For example, Sibson (1987) and Curewitz and Karson (1997) supposed that high permeable fracture system is mainly developed by the interaction between active faults at a pull- apart region (dilational fault jogs). However, it has not been shown that the fracture system is actually related to clustering of earthquakes in swarm activities. We investigated precise hypocentral distribution and mechanisms of small earthquakes in the geothermal region of Hakone volcano, near Tokyo Metropolitan Area central Japan, where swarm activities have been frequently observed. Hakone volcano is located in the northern boundary zone of the Izu-Mariana volcanic arc. The surface traces of the Hirayama and Tanna Fault are also located at the northern and southern part of Hakone volcano, respectively. The precise hypocenter determination is decisively important to elucidate occurrence mechanism of swarm earthquakes as well as to mitigate volcanic hazard at a world-famous sight-seeing spot near Tokyo Metropolitan Area, Japan. We first determined initial hypocenters, using the station corrections and one-dimensional velocity structures estimated by the joint hypocenter determination method (Kissling et al., 1994). Then, we applied the double-difference method (Waldhauser and Ellsworth, 2000) to relocate the initial hypocenters using the differential arrival time obtained by both manual picking and waveform cross-correlation analysis. Subsequently, we determined the focal mechanisms from the absolute P- and SH-wave amplitudes by adding the P-wave polarities. We found that most swarm earthquakes are distributed on thin plane-like zones from 100 m to several km. We found that these plane-like hypocentral distributions are mainly oriented to the strike in the EW or NW-SE directions and consistent with one of the nodal planes of focal mechanism. It is likely that most of the swarm earthquakes occur along pre-existing fractures in geothermal region. It is suggested that these fractures are developed by the interaction of active faults: Tanna and Hirayama Faults which cross through the Hakone caldera.

Yukutake, Y.; Tanada, T.; Honda, R.; Harada, M.; Ito, H.; Yoshida, A.

2009-12-01

431

Crustal Rock Fracture Mechanics for Design and Control of Artificial Subsurface Cracks in Geothermal Energy Extraction Engineering ({Gamma}-Project)  

SciTech Connect

Recently a significant role of artificial and/or natural cracks in the geothermal reservoir has been demonstrated in the literatures (Abe, H., et al., 1983, Nielson, D.L. and Hullen, J.B., 1983), where the cracks behave as fluid paths and/or heat exchanging surfaces. Until now, however, there are several problems such as a design procedure of hydraulic fracturing, and a quantitative estimate of fluid and heat transfer for reservoir design. In order to develop a design methodology of geothermal reservoir cracks, a special distinguished research project, named as ''{Lambda}-Project'', started at Tohoku University (5 years project, 1983-1988). In this project a basic fracture mechanics model of geothermal reservoir cracks is being demonstrated and its validation is being discussed both theoretically and experimentally. This paper descibes an outline of ''{Lambda}-Project''.

Abe, Hiroyuki; Takahashi, Hideaki

1983-12-15

432

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

433

Mechanical Properties and Fracture Surfaces of Thixoformed HP9/4/30 Steel  

NASA Astrophysics Data System (ADS)

Most work in semi-solid metal processing has been focused on relatively low-melting temperature materials such as aluminium, magnesium, tin, lead and their composites. Because of the high melting temperatures and related measurement difficulties, there is relatively small amount of experimental data available on the thixoforming of high temperature materials such as steels. This paper discusses the relationships between tensile tests data and the fracture surfaces of HP9/4/30 steel samples, in as-received and as-thixoformed conditions. Some of the as-thixoformed samples were subjected to commercial heat treatments before the tests were carried out. The as-received samples showed a typical ductile fracture of `cup' and `cone' surface appearance. The thixoformed samples, although showing some significant increase in tensile strength values, failed in a brittle manner, with the fracture surfaces showing a `cobbled' surface appearance. The application of the commercial heat treatment to the thixoformed samples has significantly improved their ductility.

Omar, M. Z.; Atkinson, H. V.; Kapranos, P.; Jaharah, A. G.

2007-04-01

434

Fall mechanisms, bone strength, and hip fractures in elderly men and women in Taiwan  

Microsoft Academic Search

Summary  Three modifiable factors of fall direction, poor bone strength, and depression were associated with an increased risk of hip\\u000a fractures for elderly men and women; fall direction was a much stronger predictor than the other two. When a fall occurs,\\u000a changing fall direction may be most effective to prevent hip fractures.\\u000a \\u000a \\u000a \\u000a \\u000a Introduction  A matched case-control study was conducted to identify risk

H.-F. Hwang; H.-D. Lee; H.-H. Huang; C.-Y. Chen; M.-R. Lin

2011-01-01

435

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

NASA Astrophysics Data System (ADS)

We propose in this paper an adaptive reduced order modelling technique based on domain partitioning for parametric problems of fracture. We show that coupling domain decomposition and projection-based model order reduction permits to focus the numerical effort where it is most needed: around the zones where damage propagates. No \\textit{a priori} knowledge of the damage pattern is required, the extraction of the corresponding spatial regions being based solely on algebra. The efficiency of the proposed approach is demonstrated numerically with an example relevant to engineering fracture.

Kerfriden, P.; Goury, O.; Rabczuk, T.; Bordas, S. P. A.

2013-04-01

436

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

PubMed Central

We propose in this paper a reduced order modelling technique based on domain partitioning for parametric problems of fracture. We show that coupling domain decomposition and projection-based model order reduction permits to focus the numerical effort where it is most needed: around the zones where damage propagates. No a priori knowledge of the damage pattern is required, the extraction of the corresponding spatial regions being based solely on algebra. The efficiency of the proposed approach is demonstrated numerically with an example relevant to engineering fracture.

Kerfriden, P.; Goury, O.; Rabczuk, T.; Bordas, S.P.A.

2013-01-01

437

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

PubMed

We propose in this paper a reduced order modelling technique based on domain partitioning for parametric problems of fracture. We show that coupling domain decomposition and projection-based model order reduction permits to focus the numerical effort where it is most needed: around the zones where damage propagates. No a priori knowledge of the damage pattern is required, the extraction of the corresponding spatial regions being based solely on algebra. The efficiency of the proposed approach is demonstrated numerically with an example relevant to engineering fracture. PMID:23750055

Kerfriden, P; Goury, O; Rabczuk, T; Bordas, S P A

2013-04-01

438

Fracture mechanics characterization of welds: Fatigue life analysis of notches at welds: J(sub Ic) fracture toughness tests for weld metal  

NASA Astrophysics Data System (ADS)

In this report two methods of fracture analysis of welds will be emphasized, one addressing fatigue life testing and analysis of notches at welds, and the other addressing the final fracture of the welded component and the fracture toughness tests used to characterize final fracture. These fatigue and fracture methods will be described by referring to recent work from the technical literature and from the U.S. Army Armament Research, Development, and Engineering Center, primarily fracture case study and fracture test method development investigations. A brief general summary will be given of fatigue and fracture methods and concepts that have application to welded structures. Specific fatigue crack initiation tests and analysis methods will be presented, using example results from a welded stainless steel box beam of a cannon carriage. Recent improvements and simplifications in J.integral fracture toughness tests will be described, particularly those related to welds. Fracture toughness measurements for various stainless steel weld metals and heat treatments will also be described.

Underwood, John H.

1995-03-01

439

Variational Formulation of Softening Phenomena in Fracture Mechanics: The One?Dimensional Case  

Microsoft Academic Search

. We show that discrete models of atoms subject to nearest?neighbour non?linear interactions approximate continua allowing\\u000a for softening and fracture. A detailed study of local minima and stationary points is carried out. Scale effects are discussed.

Andrea Braides; Gianni Dal Maso; Adriana Garroni

1999-01-01