Showing papers on "Crack closure published in 2003"
TL;DR: In this article, the effects of weld residual stress and heat affected zone on the fatigue propagation of cracks parallel and orthogonal to the weld direction in friction stir welded (FSW) 2024-T351 joints were investigated.
385 citations
TL;DR: In this article, the monitoring of fatigue crack propagation in steel and welded steel compact tension and T-section girder test specimens, using an advanced acoustic emission system with accurate source location, is described.
328 citations
TL;DR: In this article, the role of constrained microplasticity around debonded particles or shrinkage pores in forming and growing microstructurally small fatigue cracks and is based on the cyclic crack tip displacement rather than linear elastic fracture mechanics stress intensity factor.
322 citations
TL;DR: In this article, an additive decomposition of the total strain into elastic and inelastic parts is adopted, where the elastic part is further decomposed into two portions due to the elastic distortion of the material grains and the other is due to crack closure and void contraction.
259 citations
TL;DR: In this article, a study on near-threshold fatigue crack growth in friction stir welded aluminum alloy 7050-T7451 and a titanium alloy Ti-6Al-4V is presented.
250 citations
TL;DR: In this article, it was shown that when a material is so soft that the cohesive strength (or adhesive strength, in the case of interfacial fracture) exceeds the elastic modulus of the material, a crack will blunt instead of propagating.
Abstract: When a material is so soft that the cohesive strength (or adhesive strength, in the case of interfacial fracture) exceeds the elastic modulus of the material, we show that a crack will blunt instead of propagating. Large–deformation finite–element model (FEM) simulations of crack initiation, in which the debonding processes are quantified using a cohesive zone model, are used to support this hypothesis. An approximate analytic solution, which agrees well with the FEM simulation, gives additional insight into the blunting process. The consequence of this result on the strength of soft, rubbery materials is the main topic of this paper. We propose two mechanisms by which crack growth can occur in such blunted regions. We have also performed experiments on two different elastomers to demonstrate elastic blunting. In one system, we present some details on a void growth mechanism for ultimate failure, post–blunting. Finally, we demonstrate how crack blunting can shed light on some long–standing problems in the area of adhesion and fracture of elastomers.
227 citations
TL;DR: In this paper, the authors studied the 3D growth of wing cracks produced by a single pre-existing crack in uniaxial compression and found that there were intrinsic limits on 3-D wing cracks due to the wrapping of emerging wings around the initial crack.
219 citations
TL;DR: In this article, a cohesive model is used for the prediction of the crack path during stable crack extension in ductile materials and the problem of crackpath deviation is investigated by means of simulation of crack propagation in a round tensile bar.
215 citations
TL;DR: In this article, the authors gave a brief account of the well-known solution for a line crack in a magnetoelectroelastic medium and derived the asymptotic form of the strain energy density function that was first given for the piezoelectric BaTiO 3 -CoFe 2 O 4 composite.
184 citations
TL;DR: In this paper, a threshold for fatigue crack propagation as a function of crack length is defined from a depth given by the position d of the strongest microstructural barrier to crack propagation, which defines the plain fatigue limit.
175 citations
TL;DR: In this paper, two different types (exponential and bilinear) of cohesive zone models (CZMs) have been used to represent the mechanical behavior of the cohesive zones, and it is suggested that different forms of CZMs are the manifestations of different micromechanisms-based inelastic processes that participate in dissipating energy during the fracture process.
TL;DR: In this article, Fatigue crack propagation tests with single tensile peak overloads have been performed in 6082-T6 aluminium alloy at several baseline Δ K levels and stress ratios of 0.05 and 0.25.
TL;DR: In this article, microcracks in the same surface area of interest around and below the notch, and crack growth resistance and crack propagation velocity were analyzed, showing that the formation of micro-cracks continued after the initiation of a fracture crack.
TL;DR: In this paper, two-dimensional, elastic-perfectly plastic finite element analyses of middle-crack tension (MT) and compact tension (CT) geometries were conducted to study fatigue crack closure and to calculate the crack-opening values under plane-strain and plane-stress conditions.
TL;DR: In this article, the atomic structures that form at the tips of atomically sharp cracks in aluminum single crystals under loading were modeled using the quasicontinuum method, and it was found that deformation twinning does occur at aluminum crack tips in agreement with experimental observation.
TL;DR: In this article, the effects of surface roughness on crack initiation mechanism and associated step-wise S-N characteristics were studied, and a fish-eye was always observed in subsurface crack initiation.
TL;DR: In this paper, the authors proposed a new theory of fatigue crack growth in ductile solids based on the total plastic energy dissipation per cycle ahead of the crack, and the fundamental hypothesis of the theory proposes a unified criterion for crack extension under monotonic and fatigue loading.
TL;DR: In this article, the authors present a numerical study of creep crack growth in a fracture mechanics specimen using elastic-creep and elastic-plastic-decreep analyses to predict crack extension under plane stress and plane strain conditions.
TL;DR: In this paper, a fatigue crack growth threshold test procedure is experimentally validated that does not produce load history effects and can be conducted at a specified stress ratio, R. da/dN.
TL;DR: In this article, the authors examined the deflection/penetration behavior of dynamic mode-I cracks propagating at various speeds towards inclined weak planes/interfaces of various strengths in otherwise homogeneous isotropic plates.
Abstract: We examine the deflection/penetration behavior of dynamic mode-I cracks propagating at various speeds towards inclined weak planes/interfaces of various strengths in otherwise homogeneous isotropic plates. A dynamic wedge-loading mechanism is used to control the incoming crack speeds, and high-speed photography and dynamic photoelasticity are used to observe, in real-time, the failure mode transition mechanism at the interfaces. Simple dynamic fracture mechanics concepts used in conjunction with a postulated energy criterion are applied to examine the crack deflection/penetration behavior and, for the case of interfacial deflection, to predict the crack tip speed of the deflected crack. It is found that if the interfacial angle and strength are such as to trap an incident dynamic mode-I crack within the interface, a failure mode transition occurs. This transition is characterized by a distinct, observable and predicted speed jump as well as a dramatic crack speed increase as the crack transitions from a purely mode-I crack to an unstable mixed-mode interfacial crack.
TL;DR: In this paper, a detailed numerical study of the mode I interlaminar fracture of carbon/epoxy composite laminates with z-fibre reinforcement was performed using a double cantilever beam configuration.
20 Jan 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the effect of heat-treatment on the fatigue crack growth and fracture paths in lost foam sand cast B319 and A356 Al has been examined by in situ testing in a scanning electron microscope.
Abstract: The effect of heat-treatment on the fatigue crack growth and fracture paths in lost foam sand cast B319 and A356 Al has been examined by in situ testing in a scanning electron microscope. Fatigue crack growth and fracture toughness experiments were performed at ambient temperature on B319 Al in T5, T6, and T7 conditions and on A356 in the T6 condition to characterize the crack path and the interaction of the crack-tip with the microstructure. High-resolution micrographs of the near-tip region were analyzed using a machined-vision-based stereoimaging technique, known as DISMAP, to determine the crack-tip displacement and strain fields. Selected-area energy dispersive spectroscopy was used to identify the particles in the wake of the fatigue cracks, as well as the alloy content of the Al-matrix ahead of the crack-tip. Microhardness tests revealed the presence of hard and soft zones in B319-T6 that the fatigue cracks tended to follow. The fatigue crack growth rate was reduced and the crack path altered when the crack-tip interacted with (1) localized shear bands, (2) interdendritic boundaries, (3) particle/matrix interface, (4) shrinkage pores, and (5) fractured particles. The decrease in the fatigue crack growth rate can be attributed to increasing crack-tip shielding due to crack branching and deflection. The fracture toughness of A356-T6 is higher than the B319 materials because of the absence of shear localization in the matrix.
TL;DR: In this article, the influence of weld tool travel speed on the occurrence of "onion-skin" forging-type defects in single pass friction stir (SP FS) welds was investigated.
TL;DR: In this paper, the use of the acoustic emission technique to monitor fatigue crack propagation in steel compact tension specimens and T-section girders is described, based on correlations between crack propagation rates, acoustic emission count rates and stress intensity factor range procedures are suggested for predicting remaining fatigue life.
TL;DR: Roychowdhury et al. as discussed by the authors proposed a finite element study of plasticity-induced crack closure in the 3D small-scale yielding (SSY) model under mode I, constant amplitude cyclic loading with a ratio R=Kmin/Kmax.
TL;DR: In this article, a fatigue model based on the crack growth was developed and validated with experiments to develop a model for life prediction of foam core sandwich beams in a three-point flexure mode.
15 Jan 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the effect of microstructural characteristics on high-cycle fatigue properties and fatigue crack propagation behavior of welded regions of an investment cast Ti-6Al-4V were investigated.
Abstract: The effect of microstructural characteristics on high-cycle fatigue properties and fatigue crack propagation behavior of welded regions of an investment cast Ti-6Al-4V were investigated. High-cycle fatigue and fatigue crack propagation tests were conducted on the welded regions, which were processed by two different welding methods: tungsten inert gas (TIG) and electron beam (EB) welding. Test data were analyzed in relation to microstructure, tensile properties, and fatigue fracture mode. The base metal was composed of an alpha plate colony structure transformed to a basket-weave structure with thin α platelets after welding and annealing. High-cycle fatigue results indicated that fatigue strength of the EB weld was lower than that of the base metal or the TIG weld because of the existence of large micropores formed during welding, although it had the highest yield strength. In the case of the fatigue crack propagation, the EB weld composed of thinner α platelets had a faster crack propagation rate than the base metal or the TIG weld. The effective microstructural feature determining the fatigue crack propagation rate was found to be the width of α platelets because it was well matched with the reversed cyclic plastic zone size calculated in the threshold Δ K regime.
TL;DR: In this paper, the authors examined the crack growth behavior of structural steels by using the Unified Approach developed by the authors in this approach, fatigue requires two load parameters involving maximum stress intensity, Kmax, and stress intensity amplitude, △K For a fatigue crack to grow, both Kmax and △ K must exceed their respective threshold values Similarly, for any other crack growth rate, two limiting values, KMAX∗ and K�K∗ are required to enforce the growth rate The variation of these two critical values forms the crack trajectory map, which is defined by plotting
TL;DR: In this article, the fracture mechanism of laser cutting with controlled fracture is studied and the relationship between laser power cutting speed, diameter of laser spot, and specimen geometry are obtained from the experimental analysis, and the phenomena are also explained from the results of stress analysis.
Abstract: Laser cutting using the controlled fracture technique has great potential to be used for the machining of brittle materials. In this technique, the applied laser energy produces a mechanical stress that causes the material to separate along the moving path of the laser beam. The material separation is similar to a crack extension and the fracture growth is controllable. The fracture mechanism of laser cutting with controlled fracture is studied in this paper. The temperature and stress distributions are obtained by using the finite element software ANSYS. The laser heat first induces compressive stress around the laser spot. After the passage of the laser beam, the compressive stress is relaxed, and then a residual tensile stress is induced, which makes the fracture grow from upper surface to lower surface of the substrate. The stable separation of the brittle material is due to the local residual tensile stress. However, if the tensile stress is distributed throughout the thickness around the crack tip, the crack will extend unstably. The experimental materials in this study are alumina ceramic and the laser source is CO 2 laser. It is found that the crack propagation is non-uniform and the speed is variable during the cutting process. The relationships between laser power cutting speed, diameter of laser spot, and specimen geometry are obtained from the experimental analysis, and the phenomena are also explained from the results of stress analysis.
TL;DR: In this article, an indentation crack in a poled PZT ceramic subjected to an electric field was investigated using AFM and KFM to determine the crack opening displacement and the electrical potential difference across the crack.