Showing papers on "Fracture mechanics published in 2002"
01 Jun 2002
TL;DR: In this article, a decohesion element with mixed-mode capability is proposed and demonstrated at the interface between solid finite elements to model the initiation and non-self-similar growth of delaminations.
Abstract: A new decohesion element with mixed-mode capability is proposed and demonstrated. The element is used at the interface between solid finite elements to model the initiation and non-self-similar growth of delaminations. A single relative displacement-based damage parameter is applied in a softening law to track the damage state of the interface and to prevent the restoration of the cohesive state during unloading. The softening law for mixed-mode delamination propagation can be applied to any mode interaction criterion such as the two-parameter power law or the three-parameter Benzeggagh-Kenane criterion. To demonstrate the accuracy of the predictions and the irreversibility capability of the constitutive law, steady-state delamination growth is simulated for quasistatic loading-unloading cycles of various single mode and mixed-mode delamination test specimens.
909 citations
TL;DR: There are more than 200 different methods for measuring thin film adhesion, suggesting it to be material, geometry and even industry specific as discussed by the authors, suggesting that the major extrinsic variables are film stress, extent of delamination, thickness and temperature while the major intrinsic ones are modulus, yield strength, the thermodynamic work of adhesion and one or more length scales.
600 citations
TL;DR: In this paper, a self-healing polymeric composite material that can recover as much as 90 percent of its virgin fracture toughness has been developed, based on biological systems in which damage triggers an autonomic healing response.
Abstract: Inspired by biological systems in which damage triggers an autonomic healing response, a polymer composite material that can heal itself when cracked has been developed. In this paper we summarize the self-healing concept for polymeric composite materials and we investigate fracture mechanics issues consequential to the development and optimization of this new class of material. The self-healing material under investigation is an epoxy matrix composite, which incorporates a microencapsulated healing agent that is released upon crack intrusion. Polymerization of the healing agent is triggered by contact with an embedded catalyst. The effects of size and concentration of the catalyst and microcapsules on fracture toughness and healing efficiency are investigated. In all cases, the addition of microcapsules significantly toughens the neat epoxy. Once healed, the self-healing polymer exhibits the ability to recover as much as 90 percent of its virgin fracture toughness.
549 citations
TL;DR: In this article, the authors reviewed the existing fracture models for concrete and the testing methods for fracture energy and other fracture characteristics and some new results on the relationship between fracture testing and size effect are presented.
451 citations
TL;DR: In this article, the fracture energy of concrete, as well as other fracture parameters such as the effective length of the fracture process zone, critical crack-tip opening displacement and the fracture toughness, can be approximately predicted from the standard compression strength, maximum aggregate size, water-cement ratio, and aggregate type (river or crushed).
371 citations
TL;DR: In this article, an analysis of the propagation of a penny-shaped hydraulic fracture in an impermeable elastic rock is presented, where the fracture is driven by an incompressible Newtonian fluid injected from a source at the center of the fracture.
349 citations
TL;DR: In this paper, the effect of inclusions on crack initiation and propagation in gigacycle fatigue was investigated experimentally and analytically in six high strength low alloy steels.
348 citations
TL;DR: In this paper, the straight-through-cracks assumption was applied to the cracked chevron-notched Brazilian disc (CCNBD) specimen and the semicircular bend (SCB) specimen.
323 citations
TL;DR: In this article, two kinds of nonlinear interfacial constitutive laws describing the pre-and post-interfacial microdebonding behavior are introduced to solve the non linear interfacial stress transfer and fracture propagation problems for different kinds of adhesive joints in FRP/steel-strengthened concrete or steel structures.
Abstract: To effectively and efficiently utilize fiber-reinforced plastic (FRP) laminates in strengthening civil infrastructure, a design strategy integrating the properties of FRP reinforcement and composite structural behavior must be adopted. The interfacial stress transfer behavior including debonding should be considered to be one of the most important effects on composite structural behavior. In this paper, 2 kinds of nonlinear interfacial constitutive laws describing the pre- and postinterfacial microdebonding behavior are introduced to solve the nonlinear interfacial stress transfer and fracture propagation problems for different kinds of adhesive joints in FRP/steel-strengthened concrete or steel structures. Expressions for the maximum transferable load, interfacial shear stress distribution, and initiation and propagation of interfacial cracks are derived analytically. In addition, numerical simulations are performed to discuss the factors influencing the interfacial behavior, and the theoretical derivations are validated by finite element analysis.
309 citations
TL;DR: In this article, the fatigue properties of a bearing steel in the long-life region were experimentally examined under cyclic axial loading and the complicated S-N behavior was well explained as a combination of s-N curves for surface-induced fracture and interior inclusion-induced fractures.
Abstract: Owing to difficult economical conditions, machines and structures often have to be used beyond the design lifetime. In this study, fatigue properties of a bearing steel in the long-life region were experimentally examined under cyclic axial loading. The complicated S-N behaviour was well explained as a combination of S-N curves for surface-induced fracture and interior inclusion-induced fracture. Fish-eye marks were always observed on the fracture surfaces of specimens, which failed in the latter fracture mode, and an inclusion was found at the center of the fish-eye. Finally, it was found that the fatigue fracture of this steel in the long-life region occurred through the following three processes: (i) formation of the characteristic area as a fine granular area (FGA), (ii) crack propagation to form the fish-eye and (iii) rapid crack propagation to cause the catastrophic fracture.
303 citations
TL;DR: In this article, a vector level set method for modeling propagating cracks in the element-free Galerkin (EFG) method is presented, where only nodal data are used to describe the crack; no geometrical entity is introduced for the crack trajectory, and no partial differential equations need to be solved to update the level sets.
Abstract: A new vector level set method for modelling propagating cracks in the element-free Galerkin (EFG) method is presented. With this approach only nodal data are used to describe the crack; no geometrical entity is introduced for the crack trajectory, and no partial differential equations need to be solved to update the level sets. The nodal description is updated as the crack propagates by geometric equations. The advantages of this approach, here introduced and analysed for the two-dimensional case, are particularly promising in three-dimensional applications, where the geometrical description and evolution of an arbitrary crack surface in a complex solid is very awkward. In addition, new methods for crack approximations in EFG are introduced, using a jump function accounting for the displacement discontinuity along the crack faces and the Westergard's solution enrichment near the crack tip. These enrichments, being extrinsic, can be limited only to the nodes surrounding the crack and are naturally coupled to the level set crack representation. Copyright © 2002 John Wiley & Sons, Ltd.
TL;DR: In this article, the authors deal with the strong discontinuity approach and show the links with the decohesive fracture mechanics provided by that approach, on the basis of 1D continuum damage models.
TL;DR: In this paper, the authors developed preliminary answers to such questions as follows: If a rupturing fault is intersected by another, providing a possible bend in the failure path, when will stressing be consistent with rupture along the bend? What secondary fault locations and orientations, in a damaged region bordering a major fault, will be stressed to failure by the main rupture?
Abstract: [1] On the basis of elastodynamic stress fields for singular crack and nonsingular slip-weakening models of propagating rupture, we develop preliminary answers to such questions as follows: If a rupturing fault is intersected by another, providing a possible bend in the failure path, when will stressing be consistent with rupture along the bend? What secondary fault locations and orientations, in a damaged region bordering a major fault, will be stressed to failure by the main rupture? Stresses that could initiate rupture on a bend are shown to increase dramatically with crack speed, especially near the limiting speed (Rayleigh for mode II, shear for mode III). Whether a bend path, once begun, can be continued to larger scales depends on principal stress directions and ratios in the prestress field. Conditions should often be met in mode II for which bend paths encouraged by stressing very near the rupture tip are discouraged by the larger-scale stressing, a basis for intermittent rupture propagation and spontaneous arrest. Secondary failure in the damage zone likewise increases markedly as the limiting speed is approached. Such may make the fracture energy much greater than for slip on a single surface. The extent of secondary faulting is strongly affected by prestress directions and the ratio of residual to peak strength. For mode II, prestress controls whether activation occurs primarily on the extensional side, which we show to be the typical case, or on the compressional side too. Natural examples are consistent with the concepts developed.
TL;DR: In this article, the fracture and failure modes of α-and β-phase polypropylene homopolymers (PP-H, block- and random-type copolymers with ethylene) with high speed flexural tests and compared.
TL;DR: In this paper, the authors investigated the fatigue fracture surfaces of specimens of heat treated hard steels which failed in the regime of N =10 5 to 5 x 10 8 cycles by optical microscopy and SEM.
Abstract: The fatigue fracture surfaces of specimens of heat treated hard steels which failed in the regime of N =10 5 to 5 x 10 8 cycles , were investigated by optical microscopy and SEM. Specimens having a longer fatigue life had a particular morphology beside the inclusion at the fracture origin. The particular morphology looked optically dark and in the previous paper it was named the Optically Dark Area, ODA. The roughness inside ODA is larger than outside ODA. The relative size of the ODA to the size of the inclusion at the fracture origin increases with increase in fatigue life. Thus, the ODA is considered to have a crucial role in the mechanism of ultra long life fatigue failure. Direct evidences of existence of hydrogen at the inclusion at fracture origin are presented. It is presumed that the ODA is made by the cyclic stress coupled with the hydrogen which is trapped by the inclusion at the fracture origin. To verify the influence of hydrogen, specimens containing different levels of hydrogen were prepared by different heat treatments. The results obtained by fatigue tests of these specimens suggest that the hydrogen trapped by inclusions is a crucial factor which causes the ultra long fatigue failure of high strength steels. Aspects of the double S-N curve are also discussed in terms of experimental methods, specimen size and statistical distribution of inclusions sizes.
TL;DR: In this article, a mechanistic model of impact attrition of particulate solids, having a semi-brittle failure mode, has been developed, where the material loss from the particle is due to the formation of the subsurface lateral cracks.
TL;DR: In this article, a review of the mechanics of lap-shear joints is followed by a detailed analysis of the problem using a cohesive-zone approach, which allows not only the influence of geometry to be considered, but also allows the cohesive properties of the interface and plastic deformation of the adherends to be included in the analysis.
Book•
29 Mar 2002
TL;DR: In this paper, the authors present a comprehensive overview of brittle fracture mechanics and their application in the design of fracture-tolerant materials.Most chapters include an Introduction, Summary, References and Exercises.
Abstract: Most chapters include an Introduction, Summary, References and Exercises. 1. Introduction to Fracture Mechanics. Historical Overview of Brittle Fracture. Elementary Brittle-Fracture Theories. Crack Extension Behavior. 2. Elements of Solid Mechanics. Concepts of Stress and Strain. Equations of Elasticity in Cartesian Coordinates. Equations of Elasticity in Polar Coordinates. Solution of the Biharmonic Equation. The Problem of the Elliptical Hole. 3. Elasticity of Singular Stress Fields. Overview. The Williams Problems. The Generalized Westergaard Approach. The Central Crack Problem. Single-Ended Crack Problems. The Effect of Finite Boundaries. Determining the Geometric Stress Intensity Factor. The Three-Dimensional Crack Problem. 4. Numerical Methods for K Determination. Boundary Collocation. The Finite Element Method. 5. Experimental Methods for K Determination. Overview. Classical Photoelesatic Methods. The Method of Caustics. Strain Gages. Multi-Parameter Full-Field Methods: Local Collocation. Interference Patterns. Moire Patterns. Photoelasticity. 6. A Stress Field Theory of Fracture. The Critical Stress-State Criterion. Crack-Tip Plasticity. The Effect of Variables on Fracture Toughness. R-Curves. 7. The Energy of Fracture. Griffith's Theory of Brittle Fracture. A Unified Theory of Fracture. Compliance. 8. Fracture Toughness Testing. Fracture Toughness Standards. Nonstandard Fracture-Toughness Tests. 9. Fatigue. Stages of Fatigue Crack Growth. Mathematical Analysis of Stage II Crack Growth. The Effects of Residual Stress on Crack Growth Rates. Life Prediction Computer Programs. Measuring Fatigue Properties: ASTM. 10. Designing against Fracture. Fracture Mechanics in Conventional Design. The Role of NDE in Design. U.S. Air Force Damage-tolerant Design Methodology. Designing by Hindsight: Case Studies. 11. Elastoplastic Fracture. Nonlinear Elastic Behavior. Characterizing Elastoplastic Behavior. Comments on the J-Integral in Elastoplastic Fracture Mechanics. Appendix A: Comprehensive Exercises. General Comments. Appendix B: Complex Variable Method in Elasticity. Complex Numbers. Complex Functions. Appendix C: An Abbreviated Compendium of Westergaard Stress Functions. Appendix D: Fracture Properties of Engineering Materials. Appendix E: NASGRO 3.0 Material Constants for Selected Materials. Index.
TL;DR: In this paper, the concept of fracture energy is introduced for tensile and compressive loadings and also elaborated for reinforced concrete, and a concise summary is given of recent finite element concepts for cohesive-zone models (fracture energy models).
TL;DR: In this article, the authors used a numerical method to simulate the fragmentation process induced by single and double indenters in a truncated indenter and showed that the simulated forcepenetration curve is an indication of the propagation of cracks, the crushing of microstructural grains and the formation of chips.
TL;DR: In this article, the authors derived the crack propagation law from the S-N data in the very high cycle fatigue of a bearing steel and divided the cracks into stages I and II.
Abstract: The crack propagation law was derived from the S-N data in the very high cycle fatigue of a bearing steel. The propagation rate, da/dN (m/cycle), of surface cracks was estimated to be a power function of the stress intensity range, ΔK (MPa√m) with the coefficient C s = 5.87 x 10- 13 and the exponent m s = 4.78. The threshold stress intensity range was 2.6MPa√m. The crack propagation from internal inclusions was divided into Stages I and II. For Stage I, the coefficient of the power law was C o = 3.44 x 10 -21 and the exponent m o = 14.2. The transition from Stage I to II took place at ΔK = 4.0 MPa√m. For Stage II, the coefficient was C i = 2.08 x 10 -14 and the exponent m i = 4.78. The specimen size and loading mode did not influence the surface fatigue life, while the internal fatigue life was shortened in larger specimens and under tension-compression loading. For ground specimens, the surface fatigue life was raised by the compressive residual stress, while reduced by the surface roughness introduced by grinding. For shot-peened specimens, fatigue fracture did not take place from the surface because of a high surface compressive residual stress. The internal fatigue life was reduced by the tensile residual stress existing in the interior of the specimens.
TL;DR: In this article, a hydraulically driven fracture propagating in an impermeable, linear elastic medium is analyzed, where the fracture is driven by injection of an incompressible, viscous fluid with power-law rheology and behaviour index n⩾ 0.
Abstract: This paper analyses the problem of a hydraulically driven fracture, propagating in an impermeable, linear elastic medium. The fracture is driven by injection of an incompressible, viscous fluid with power-law rheology and behaviour index n⩾0. The opening of the fracture and the internal fluid pressure are related through the elastic singular integral equation, and the flow of fluid inside the crack is modelled using the lubrication theory. Under the additional assumptions of negligible toughness and no lag between the fluid front and the crack tip, the problem is reduced to self-similar form. A solution that describes the crack length evolution, the fracture opening, the net fluid pressure and the fluid flow rate inside the crack is presented. This self-similar solution is obtained by expanding the fracture opening in a series of Gegenbauer polynomials, with the series coefficients calculated using a numerical minimization procedure. The influence of the fluid index n in the crack propagation is also analysed. Copyright © 2002 John Wiley & Sons, Ltd.
TL;DR: In this paper, the change in the modulus of elasticity due to fatigue damage is studied for uni-axial bending, and a coupled approach of residual stiffness and strength is capable of simulating the three stages of stiffness degradation: initial decline, gradual reduction and final failure.
TL;DR: In this paper, a biaxial compression test was performed on a sandstone specimen with a circular opening to simulate a loading-type failure around an underground excavation in brittle rock.
TL;DR: In this article, the authors investigated the mixed mode delamination behavior of reinforced carbon-epoxy laminates using two different test specimens, a T-stiffener and a mixed-mode bending (MMB) specimen.
Abstract: The mixed mode delamination behavior of through-thickness reinforced carbon–epoxy laminates was investigated using two different test specimens, a T-stiffener and a mixed-mode bending (MMB) specimen. Small quantities of titanium or carbon z-fibers (short rods) substantially improve delamination resistance in both types of specimen. Reinforcement raises the ultimate strength of the MMB specimen by a factor of three. However, the failure sequence and therefore the ultimate load in the T-stiffeners depend strongly on the test configuration. No change in ultimate load is seen in some cases but up to 40% improvement is observed in others. Improved delamination resistance results from crack bridging by the z-fibers, which reduces the driving force for crack growth. Mode I crack displacement is suppressed more effectively than mode II displacement, resulting in purely mode II cracking in what without z-fibers would be a mixed mode or primarily mode I loading situation. This important consequence of so-called large scale bridging effects confirms recent theoretical results for delamination specimens. The mechanisms of bridging and crack propagation are described here in detail.
TL;DR: In this paper, a new criterion for 3D crack growth under multiaxial loading, that means superposition of the fracture modes Mode I, II and III, is described.
Abstract: In many cases the lifetime of technical structures and components is depending on the behaviour of cracks. Due to the complex geometry and loading situation in real-world structures cracks are often subjected to a superposition of normal, in-plane and out-of-plane loading. In this paper a new criterion for 3D crack growth under multiaxial loading, that means superposition of the fracture modes Mode I, II and III, is described. The criterion allows the prediction of three-dimensional crack surfaces advancing from arbitrary 3D crack fronts with the help of the two deflection angles φ0 and ψ0. The underlying theory for the development of this new criterion is described in detail.
TL;DR: In this paper, a review of atomistic aspects of dynamic fracture in a variety of brittle crystalline, amorphous, nanophase, and nanocomposite materials are reviewed.
Abstract: ▪ Abstract Atomistic aspects of dynamic fracture in a variety of brittle crystalline, amorphous, nanophase, and nanocomposite materials are reviewed. Molecular dynamics (MD) simulations, ranging from a million to 1.5 billion atoms, are performed on massively parallel computers using highly efficient multiresolution algorithms. These simulations shed new light on (a) branching, deflection, and arrest of cracks; (b) growth of nanoscale pores ahead of the crack and how pores coalesce with the crack to cause fracture; and (c) the influence of these mechanisms on the morphology of fracture surfaces. Recent advances in novel multiscale simulation schemes combining quantum mechanical, molecular dynamics, and finite-element approaches and the use of these hybrid approaches in the study of crack propagation are also discussed.
TL;DR: In this paper, the authors examined the relationship between elastic strain energy, inelastic strain energy and cohesive energy, the latter encompassing the work of fracture and other energy consuming mechanisms within the fracture process zone, and showed that the plastic energy in the material surrounding the crack is not accounted in the cohesive energy.
Abstract: Cohesive Zone Models (CZMs) are being increasingly used to simulate fracture and fragmentation processes in metallic, polymeric, and ceramic materials and their composites. Instead of an infinitely sharp crack envisaged in fracture mechanics, CZM presupposes the presence of a fracture process zone where the energy is transferred from external work both in the forward and the wake regions of the propagating crack. In this paper, we examine horn the external work flows as recoverable elastic strain energy, inelastic strain energy, and cohesive energy, the latter encompassing the work of fracture and other energy consuming mechanisms within the fracture process zone. It is clearly shown that the plastic energy in the material surrounding the crack is not accounted in the cohesive energy. Thus cohesive zone energy encompasses all the inelastic energy e.g., energy required for grainbridging, cavitation, internal sliding, surface energy but excludes any form of inelastic strain energy in the bounding material.
TL;DR: In this paper, the authors provide a formulation and numerical analysis of a two-dimensional plane strain model with multiple discrete voids located ahead of a pre-existing crack tip, and demonstrate that improvements to be expected in fracture toughness by reducing the population of second phase particles responsible for nucleating voids cannot be understood in terms of trends of one mechanism alone.