Showing papers on "Fracture mechanics published in 1994"
TL;DR: In this article, a model of dynamic crack growth is presented for a plane strain block with an initial central crack subject to tensile loading, where crack branching emerges as a natural outcome of the initial-boundary value problem solution, without any ad hoc assumption regarding branching criteria.
Abstract: Dynamic crack growth is analysed numerically for a plane strain block with an initial central crack subject to tensile loading. The continuum is characterized by a material constitutive law that relates stress and strain, and by a relation between the tractions and displacement jumps across a specified set of cohesive surfaces. The material constitutive relation is that of an isotropic hyperelastic solid. The cohesive surface constitutive relation allows for the creation of new free surface and dimensional considerations introduce a characteristic length into the formulation. Full transient analyses are carried out. Crack branching emerges as a natural outcome of the initial-boundary value problem solution, without any ad hoc assumption regarding branching criteria. Coarse mesh calculations are used to explore various qualitative features such as the effect of impact velocity on crack branching, and the effect of an inhomogeneity in strength, as in crack growth along or up to an interface. The effect of cohesive surface orientation on crack path is also explored, and for a range of orientations zigzag crack growth precedes crack branching. Finer mesh calculations are carried out where crack growth is confined to the initial crack plane. The crack accelerates and then grows at a constant speed that, for high impact velocities, can exceed the Rayleigh wave speed. This is due to the finite strength of the cohesive surfaces. A fine mesh calculation is also carried out where the path of crack growth is not constrained. The crack speed reaches about 45% of the Rayleigh wave speed, then the crack speed begins to oscillate and crack branching at an angle of about 29° from the initial crack plane occurs. The numerical results are at least qualitatively in accord with a wide variety of experimental observations on fast crack growth in brittle solids.
2,233 citations
Book•
01 Jan 1994
TL;DR: In this paper, the authors present an analysis of the properties of a continuous fiber-reinforced Lamina and its effect on the strength of the composite components, including the elasticity and robustness of the components.
Abstract: Introduction Basic Concepts Constituent Materials for Composites Structural Applications of Composites Multifunctional Applications of Composites Fabrication Processes Elements of Mechanical Behavior of Composites Review of Basic Mechanics of Materials Equations Lamina Stress-Strain Relationships Introduction Effective Moduli in Stress-Strain Relationships Symmetry in Stress-Strain Relationships Orthotropic and Isotropic Engineering Constants The Specially Orthotropic Lamina The Generally Orthotropic Lamina Effective Moduli of a Continuous Fiber-Reinforced Lamina Introduction Elementary Mechanics of Materials Models Improved Mechanics of Materials Models Elasticity Models Semiempirical Models Strength of a Continuous Fiber-Reinforced Lamina Introduction Multiaxial Strength Criteria Micromechanics Models for Lamina Strength Analysis of Lamina Hygrothermal Behavior Introduction Hygrothermal Degradation of Properties Lamina Stress-Strain Relationships Including Hygrothermal Effects Micromechanics Models for Hygrothermal Properties Analysis of a Discontinuously Reinforced Lamina Introduction Aligned Discontinuous Fibers Off-Axis-Aligned Discontinuous Fibers Randomly Oriented Discontinuous Fibers Nanofibers and Nanotubes Particulates Hybrid Multiscale Reinforcements Analysis of Laminates Introduction Theory of Laminated Beams Theory of Laminated Plates with Coupling Stiffness Characteristics of Selected Laminate Configurations Derivation and Use of Laminate Compliances Hygrothermal Effects in Laminates Interlaminar Stresses Laminate Strength Analysis Deflection and Buckling of Laminates Selection of Laminate Designs Application of Laminate Analysis to Composite Structures Analysis of Viscoelastic and Dynamic Behavior Introduction Linear Viscoelastic Behavior of Composites Dynamic Behavior of Composites Nanoenhancement of Viscoelastic and Dynamic Properties Analysis of Fracture Introduction Fracture Mechanics Analysis of Through-Thickness Cracks Stress Fracture Criteria for Through-Thickness Notches Interlaminar Fracture Nanoenhancement of Fracture Toughness Mechanical Testing of Composites and Their Constituents Introduction Measurement of Constituent Material Properties Measurement of Basic Composite Properties Measurement of Viscoelastic and Dynamic Properties Measurement of Hygrothermal Properties Appendix A: Matrix Concepts and Operations Appendix B: Stress Equilibrium Equations Appendix C: Strain-Displacement Equations Index Problems and References appear at the end of each chapter.
1,636 citations
TL;DR: In this article, the effects of defects, inclusions and inhomogeneities on the fatigue strength of metals are reviewed, from the Isibasi model and the Frost model to recent models based on fracture mechanics.
789 citations
Book•
31 May 1994TL;DR: In this article, it is argued that the fracture problem can be distilled into three separate parts: the contact problem itself in full or partial slip, the initiation of a crack from a surface suffering severe distress, and the propagation of a fracture under combined contact and bulk loading.
Abstract: Several aspects of the mechanics of cracks originating at sites of fretting are considered. It is argued that the problem may be distilled into three separate parts: the contact problem itself in full or partial slip, the initiation of a crack from a surface suffering severe distress, and the propagation of a crack under combined contact and bulk loading. The first of these may be solved by either a classical or numerical means, whilst the last merely requires the careful use of fracture mechanics. However, it is the second element which remains elusive to quantify, and the influence of the intrinsic length scales in the problem, including contact length, surface roughness and amplitude of relative tangential displacement on initiation conditions, is discussed and explored.
589 citations
TL;DR: In this article, it was shown that the sum of the dimensional decrement (for material ligament) and the dimensional increment (for fracture surface) must be lower than unity.
422 citations
TL;DR: In this paper, a brittle fracture criterion for structures with sharp notches is proposed based on Irwin's and Novozhilov's criteria and states that a crack will propagate from a tip of a notch when the actual value of the stress intensity factor KI,II,III reaches a critical value.
389 citations
TL;DR: In this paper, a new electric boundary condition was proposed, in which the electric permeability of air in a crack gap was considered, and an exact solution to this problem was given and some numerical results were obtained.
389 citations
TL;DR: In this paper, the authors defined an adhesive fracture energy Ga for the peel testing of flexible laminates, which is considered to be a geometry-independent parameter which reflects the energy to break the interfacial bonding forces and the energy dissipated locally ahead of the peel front in the plastic or viscoelastic zone.
Abstract: The present work has defined an adhesive fracture energy Ga for the peel testing of flexible laminates. The value of Ga characterises the fracture of the laminate and is considered to be a ‘geometry-independent’ parameter which reflects (i) the energy to break the interfacial bonding forces and (ii) the energy dissipated locally ahead of the peel front in the plastic or viscoelastic zone. We have shown that in order to determine this true adhesive fracture energy Ga that the following energy terms must be considered: (i) the stored strain-energy in the peeling arm, (ii) the energy dissipated during tensile deformation of the peeling arm, and (iii) the energy dissipated due to bending of the peeling arm. The analysis proposed yields quantitative expressions for these various energy dissipation terms and, in particular, considers the energy dissipated due to bending of the peeling arm. Another important feature of the analysis is the modelling of the region below the peel front as an elastic beam on an elastic foundation; such that the peeling arm does not act as a truly built-in beam and root rotation at the peel front is allowed. The analysis described in the present paper has been employed for four different laminates. The values of the local angle θ0 at the peel front from the theoretical calculations have been shown to be in excellent agreement with the experimentally measured values; a small-scale peel test rig having been built so that the peel test, as a function of applied peel angle θ, thickness h of peeling arm and rate of test, could be observed and photographed using a stereo-optical microscope. The value of the adhesive fracture energy Ga (i.e the ‘fully corrected’ value) for each laminate is indeed shown to be a ‘material parameter’.
384 citations
TL;DR: In this paper, the problem of the size effects on tensile strength and fracture energy of brittle and disordered materials (concrete, rocks, ceramics, etc.) is reconsidered under a new and unifying light cast on by fractal geometry.
354 citations
TL;DR: In this article, the damage mechanisms of four short-glass-fibre-reinforced polypropylenes are investigated in tensile, tensile fatigue and crack propagation tests.
TL;DR: In this article, the effects of microstructure (namely, particulate volume fraction and particulate size) and the counterface materials on the dry-sliding wear resistance of the aluminum matrix composites 2014A1-SiC and 6061Al-Al2O3 were studied.
Abstract: The effects of microstructure (namely, particulate volume fraction and particulate size) and the counterface materials on the dry-sliding wear resistance of the aluminum matrix composites 2014A1-SiC and 6061Al-Al2O3 were studied. Experiments were performed within a load range of 0.9 to 350 N at a constant sliding velocity of 0.2 ms-1. Two types of counterface materials, SAE 52100 bearing steel and mullite, were used. At low loads, where particles act as loadbearing constituents, the wear resistance of the 2014A1 reinforced with 15.8 µm diameter SiC was superior to that of the alloy with the same volume fraction of SiC but with 2.4 µm diameter. The wear rates of the composites worn against a steel slider were lower compared with those worn against a mullite slider because of the formation of iron-rich layers that act asin situ solid lubricants in the former case. With increasing the applied load, SiC and A12O3 particles fractured and the wear rates of the composites increased to levels comparable to those of unreinforced matrix alloys. The transition to this regime was delayed to higher loads in the composites with a higher volume percentage of particles. Concurrent with particle fracture, large strains and strain gradients were generated within the aluminum layers adjacent to contact surfaces. This led to the subsurface crack growth and delamination. Because the particles and interfaces provided preferential sites for subsurface crack initiation and growth and because of the propensity of the broken particles to act as third-body abrasive elements at the contact surfaces, no improvement of the wear resistance was observed in the composites in this regime relative to unreinforced aluminum alloys. A second transition, to severe wear, occurred at higher loads when the contact surface temperature exceeded a critical value. The transition loads (and temperatures) were higher in the composites. The alloys with higher volume fraction of reinforcement provided better resistance to severe wear. Wearing the materials against a mullite counterface, which has a smaller thermal conductivity than a counterface made of steel, led to the occurrence of severe wear at lower loads.
TL;DR: In this article, a semi-circular specimen under three-point bending (SCB) technique was employed to determine the Mode I fracture toughness of a water-saturated synthetic mudstone.
TL;DR: In this paper, the authors present analytical tip region solutions for fracture width and pressure when a power law fluid drives a plane strain fracture in an impermeable linear elastic solid, where the tip region stress is dominated by a singularity which is particular to the hydraulic fracturing problem.
Abstract: We present analytical tip region solutions for fracture width and pressure when a power law fluid drives a plane strain fracture in an impermeable linear elastic solid. Our main result is an intermediate asymptotic solution in which the tip region stress is dominated by a singularity which is particular to the hydraulic fracturing problem. Moreover this singularity is weaker than the inverse square root singularity of linear elastic fracture mechanics. We also show how the solution for a semi-infinite crack may be exploited to obtain a useful approximation for the finite case.
TL;DR: In this article, the effects of crack face boundary conditions on the fracture mechanics of piezoelectric solids are studied, and the results illustrate that the impermeable assumption can lead to significant errors regarding the effect of the electric fields on crack propagation based on an energy release rate criterion.
TL;DR: In this article, a nonhomogeneous elastic medium containing a crack arbitrarily oriented with respect to the direction of property gradient is considered, and the problem is solved under plane strain or generalized plane stress conditions.
TL;DR: In this paper, a new mode of electric-field-induced fatigue crack growth was identified, and fracture mechanics concepts were applied to interpret the observed cracking, and an experimental procedure for characterizing crack extension from preexisting flaws in such materials subject to high-amplitude, alternating electric fields was described.
Abstract: When subjected to large alternating electric fields, ferroelectric ceramics may experience cracking and mechanical degradation. This article describes an experimental procedure for characterizing crack extension from preexisting flaws in such materials subject to high-amplitude, alternating electric fields. A new mode of electric-field-induced fatigue crack growth is identified. Fracture mechanics concepts are applied to interpret the observed cracking.
TL;DR: In this paper, the role of length scales in determining ductility, notch sensitivity, and whether failure is catastrophic or noncatastrophic is discussed, as well as the roles of length scale in determining notch sensitivity and ductility.
Abstract: Some recent work on length scales in bridged crack problems is reviewed and enlarged upon. Fundamental differences are highlighted between the solutions obtainable from bridged crack models (nonvanishing crack tip stress intensity factor, Ktip) and traditional cohesive zone models (vanishing Ktip); and from models for which the bridging tractions are nonincreasing (softening) and increasing (hardening) functions of the crack opening displacement. The roles of length scales in determining ductility, notch sensitivity, and whether failure is catastrophic or noncatastrophic are discussed. Length scales for monotonic loading are extended to cyclic loading.
TL;DR: In this paper, conditions under which single or double parameter controlled onset of fracture initiation occur are discussed based on the asymptotic stress fields including higher order terms at the crack tip of a non-linear material.
Abstract: Based on the asymptotic stress fields including higher order terms at the crack tip of a non-linear material, conditions under which single or double parameter controlled onset of fracture initiation occur are discussed. A set of experimental data under cleavage fracture was analysed. It is shown that under Mode I plane strain conditions two parameters J and A2 can be utilized to predict the onset of fracture with J setting the loading level and A2 relating to the constraint. Theoretical meanings of fracture toughness values corresponding to conditions of small scale yielding and the HRR stress distribution are discussed. A procedure of applying this concept to the evaluation of flawed structures is outlined.
Book•
01 Jan 1994
TL;DR: Theoretical models and numerical methods for fracture parameters calculation for fatigue crack propagation in metals have been proposed in this paper, where the three-dimensional boundary element method has been applied to quasistatic and fatigue cracks propagation.
Abstract: Volume 1. Introductory Section. Failure criteria for anisotropic bodies (P.S. Theocaris). Introduction to fracture mechanics of fatigue (H. Kitagawa). Numerical methods for fracture parameters calculation (G.J. Tsamasphyros). Fatigue Behaviour of Metallic Materials. Fatigue of steels for concrete reinforcement and cables (M. Elices et al). Fatigue crack growth and crack shielding in a Fe-C-Cu sintered steel (Y-W. Mai et al). Fatigue and fracture properties of aerospace aluminium alloys (R.J.H. Wanhill). Fatigue crack propagation in titanium alloys (J.K. Gregory). Theoretical Models and Numerical Methods. Mechanical model for fatigue crack propagation in metals (X.-L. Zheng). Application of the three-dimensional boundary element method to quasistatic and fatigue crack propagation (M.H. Aliabadi, Y. Mi). Method of damage mechanics for prediction of structure member fatigue lives (X. Zhang et al.). Stochastic fatigue crack propagation (J.H. Yoon, Y.S. Yang). A fracture mechanics approach to the optimum design of cracked structures under cyclic loading (Z. Knesl). Fundamental Aspects of Fatigue Crack Propagation Phenomenon. Stable and unstable fatigue crack propagation in metals (V.T. Troshchenko). Fatigue crack growth from stress concentrations and fatigue life prediction in notched components (C.S. Shin). Propagation of surface cracks under cyclic loading (A. Carpinteri). Growth behaviour of small fatigue cracks and relating problems (H. Nisitani et al). Analytical and experimental study of crack closure behaviour (D.-h. Chen). Studies of fatigue crack closure (D. Francois). Fatigue threshold of metallic materials - a review (A. Hadrboletz et al). Mechanics of fatigue crack growth as a synthesis of micro-and macro-mechanics of fracture (V.V. Bolotin). Random material non-homogeneity effects on fatigue crack growth (K. Dolinski). Volume 2. Influence of Loading Conditions. Fatigue crack growth under variable amplitude loading (J. Dominguez). Mixed mode fatigue crack propagation (L.P. Pook). Numerical and. experimental study of mixed mode fatigue crack propagation (A.S. Kobayashi, M. Ramulu). Crack growth behaviour under repeated impact load conditions (T. Tanaka et al). Influence of Environmental Conditions. Influence of ambient atmosphere on fatigue crack growth behaviour of metals (J. Petit et al). Influence of hydrogen-containing environments on fatigue crack extension resistance of metals (V.V Panasyuk et al.). Fatigue crack propagation in aqueous environments (Y. Nakai). Application of fatigue crack growth data to low cycle fatigue at high temperature (L. Remy). Creep-fatigue interaction under high-temperature conditions (R. Ohtani, T. Kitamura). Fatigue crack propagation in metals at low temperatures (X.-L. Zheng, B.-T. Lu). (Part contents).
TL;DR: In this article, a new form of the maximum strain energy release rate (G-criterion) was proposed for predicting the mixed mode crack propagation, which can predict the shear failure but not the tensile failure, and the capacity of the F-Criterion in predicting both mode I and mode II propagation was demonstrated for two models subjected to uniaxial compression for a single crack and a set of two cracks.
TL;DR: In this paper, the authors used three independent jacks orthogonally disposed, making it possible to apply a purely tensile force, so that the secondary flexural stresses, if kept under control, constitute a degree of error comparable with the values allowed for normal testing apparatus.
Abstract: Tests were carried out using three independent jacks orthogonally disposed, making it possible to apply a purely tensile force, so that the secondary flexural stresses, if kept under control, constitute a degree of error comparable with the values allowed for normal testing apparatus. The method enables a stress versus strain curve to be plotted with the descending (softening) branch up to the point where the cross-section of the tensile specimen breaks away. The principal purpose is to avoid any spurious effect that might provide a fallacious explanation of the recurring size effects on apparent tensile strength and fictitious fracture energy. Once the secondary effects have been excluded, only the disorder and fractality of the concrete microstructure remain to explain such fundamental trends. In the case of tensile strength, the dimensional decrement represents self-similar weakening of the material ligament, due to pores, voids, defects, cracks, aggregates, inclusions, etc. Analogously, in the case of fracture energy, the dimensional increment represents self-similar tortuosity of the fracture surface, as well as self-similar overlapping and distribution of microcracks in the direction orthogonal to that of the forming macrocrack.
TL;DR: In this article, a testing technique has been developed capable of measuring the interfacial fracture resistance, Γi, of thin ductile films on substrates, where the thin film on the substrate is stressed by depositing onto the film a second superlayer of material, having a large intrinsic stress, such as Cr. The strain energy available for driving the debond crack is modulated by varying the thickness of the Cr superlayer.
Abstract: A novel testing technique has been developed capable of measuring the interfacial fracture resistance, Γi, of thin ductile films on substrates. In this technique, the thin film on the substrate is stressed by depositing onto the film a second superlayer of material, having a large intrinsic stress, such as Cr. Subsequent processing defines a precrack at the interface between the film and the substrate. The strain energy available for driving the debond crack is modulated by varying the thickness of the Cr superlayer. Spontaneous decohesion occurs for superlayers exceeding a critical thickness. The latter is used to obtain Γi from elasticity solutions for residually stressed thin films. The technique has been demonstrated for Cu thin films on silica substrates.
TL;DR: In this paper, a 3D crack propagation in transparent rock-like brittle materials under uniaxial compression is studied. But the results show that a single 3D fracture cannot propagate any appreciable distance and the loading results in dynamic, burst-like failure of the sample.
Abstract: Fracture of rocks containing a multitude of pre-existing cracks is considered from both theoretical and experimental points of view, paying attention mainly to the underlying mechanisms The competition between a number of mechanisms in producing tear or shear type fractures is discussed in relation to the properties of the rock and the system of pre-existing cracks on the one hand and the type of loading on the other hand First, 2-D theoretical models and experimental results aimed at the explanation and description of brittle fracture under compression are considered Their insufficiency and the necessity to address the 3-D peculiarities of crack growth in rock are shown on the basis of new experimental results on 3-D crack propagation in transparent rock-like brittle materials under uniaxial compression The results show that in contrast to the 2-D case, a single 3-D crack cannot propagate any appreciable distance and the loading results in dynamic, burst-like failure of the sample Possible mechanisms of the routinely observed extensive fracture propagation in rock samples (splitting), as well as the possibility of shear (oblique) fracture in uniaxial compression, are discussed in connection with these experiments
TL;DR: In this paper, a model for a crack lying along one of the interfaces of a thin ductile layer joining two elastic solids is proposed for the joint whose major parameters are the layer thickness, the elastic-plastic properties of material in the layer, and the work of separation and peak separation stress of the local interface fracture process.
Abstract: The contribution of plastic deformation to the effective work of fracture is computed for a crack lying along one of the interfaces of a thin ductile layer joining two elastic solids. A model is proposed for the joint whose major parameters are the layer thickness, the elastic-plastic properties of material in the layer, and the work of separation and peak separation stress of the local interface fracture process. A symmetric mode I loading of the joint is considered under conditions where the thickness of the layer and the extent of the plastic zone are small compared with the crack length. The crack growth resistance behaviour is computed, with special emphasis on the steady-state work of fracture. The role of the layer thickness in the development of the plasticity contribution to toughness is detailed. Plastic dissipation is fully realized for layers above a certain thickness, characteristic of a plastic zone dimension, and is negligible when the layer is thin relative to this dimension. Othe...
TL;DR: In this article, an application of dual boundary element method to the analysis of three-dimensional mixed-mode crack growth is presented, where the crack growth processes are simulated numerically with an incremental crack-extension analysis based on the minimum strain energy density criterion and a fatigue crack growth law.
TL;DR: In this paper, the authors examined the phenomenon of perosvskite-type ceramics deforming under electric fields and fracture in a multilayer actuator and found that, under a given electric field, cracking is suppressed in a multi-layer actuator if the ceramic layers are sufficiently thin.
Abstract: Many perosvskite-type ceramics deform appreciably under electric fields; they make good actuators which deliver motions upon receiving electrical signals. High electric fields are usually applied to induce large strains. Fracture has been observed in the actuators under electrical loading. In this theoretical study, the phenomenon is examined on the basis of electrostriction and fracture mechanics. Attention is focused on a crack emanating from an internal electrode or a conducting damage path. At the edge of the conducting path, the electric field is intense and nonuniform, inducing incompatible electrostrictive strains. Consequently, a stress field is set up in the ceramic, localized around the edge of the conducting path. The condition for the stress to extend a crack is estimated by two models, using either quadratic or step-like electrostriction law. It is found that, under a given electric field, cracking is suppressed in a multilayer actuator if the ceramic layers are sufficiently thin.
TL;DR: In this article, the authors considered the presence of corner point singularities in the vicinity of a corner point where a crack front intersects a free surface and derived the stress intensity factors for three-dimensional mixed mode configurations.
TL;DR: In this paper, a simple shear-lag stress analysis was extended to the laminates containing delaminations at the tips of transverse cracks, and the relationship between the measured material damage and Young's modulus reduction was compared with experimental data.
TL;DR: In this article, a physically based model for the evolution of a single set of planar, parallel fractures subject to constant remote stress is presented, which simulates the mechanical interaction between fractures using a recently developed approximation technique for stress analysis in elastic solids with many fractures.
Abstract: A physically based model for the evolution of a single set of planar, parallel fractures subject to a constant remote stress is presented. The model simulates the mechanical interaction between fractures using a recently developed approximation technique for stress analysis in elastic solids with many fractures. A comparison between experimental and numerical results shows that the model can accurately simulate the development of experimentally generated fracture sets. Once the flaw geometry is specified, only one parameter controls the geometric evolution of the fracture set. This parameter, the velocity exponent, relates fracture propagation velocity to stress concentration at the fracture tip. Monte Carlo sensitivity analyses suggest that this parameter also controls the extent to which fracture growth is concentrated within zones or clusters. Similar analyses suggest that the extent of fracture clustering is less sensitive to the flaw density.