Papers by Keyword: Fracture Mechanic

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Authors: Xing Ai, Zhao Qian Li
Authors: A. Fontana, M. Minotti, Pietro Salvini
Abstract: High speed MODE I crack growth in elastic-plastic materials, involving large scale plasticity and dynamic effects connected to rapid propagation, is faced through a cohesive model to tune force nodal release. The stress resisting to the opening of the edges in the cohesive zone should account of effective stress field ahead crack tip. In this paper a reference value is accounted: it represents the maximum closing stress measured at the crack tip, where the cohesive effects begin. A bi-parametric analytical formulation of stress distribution ahead the crack tip is suggested. The bi-parametric formulation is able to extrapolate the stress at the tip whatever is the T-stress (i.e. the stress acting in the direction of fracture propagation), thus completely defining the cohesive loads.
Authors: Wei Li, Qing Li, Jeffery Loughran, Michael Swain, Ionut Ichim, Naoki Fujisawa
Abstract: Natural human tooth consists of multiple layered quasi-brittle biomaterials, which make dental restorations experience a complex stress state under masticatory contact loading. As such, many restorations are prone to failure and a constant effort is made to improve the mechanical characteristics of the restorative materials. Clinical observations have shown that improved strengths and fracture toughness in ceramic materials do not necessarily lead to an anticipated higher functional longevity of the restoration. While substantial experimental investigations have been carried out to identify the contact induced fracture in such multi-layer material systems, numerical modelling of this event was largely unexplored. This paper presents a new numerical method to account for micro-damage driven fracture in various multi-layered biomaterial structures. In this study, a Rankine constitutive model is adopted and the crack initiation and propagation are automatically implemented in an explicit finite element (FE) framework. The effects of indenter radius, surface curvature and thickness of layered biomaterials on the cracking patterns are investigated. The results show good agreement with the experimental studies in literature.
Authors: Won Beom Kim, Jeom Kee Paik
Abstract: In this research, corrosion fatigue tests using 490MPa TMCP steel were performed in synthetic seawater condition to investigate the corrosion fatigue crack propagation characteristics of TMCP steel plate which is often used for ships and offshore structures from its weldability and weight reduction purpose. In addition, relationships between boundary correlation factor F(α,β) and α(= 2a/W) of the fracture mechanics formula for the test specimen which was exerted by the pin load were calculated for the evaluation of da/dN-.K. To get the boundary correlation factor F(α,β), the calculation of J as a path-independent line integral was carried out. The solutions of J integral showed similar value in spite of the different path. Crack propagation tests for the same steel in air condition was carried out also for comparison. Finally, it was clear from the crack propagation test results that the propagation rate of TMCP steel plate in synthetic seawater condition is faster than that of in air condition at least twice.
Authors: Jing Wang, Xiao Wei Gao, Chuan Zeng Zhang
Abstract: This paper presents an elastostatic crack analysis in three-dimensional (3D), isotropic, functionally graded and linear elastic solids. A boundary element method (BEM) based on boundary-domain integral equations is applied. A multi-domain technique and discontinuous elements at the crack-front are adopted. To show the effects of the materials gradients on the crackopening- displacements (CODs) and the stress intensity factors (SIFs), numerical results for a pennyshaped crack are presented and discussed.
Authors: Leonard M. Rogers
Abstract: This paper addresses the fundamentals of the acoustic emission effect associated with fatigue and stress corrosion cracking in metals. It considers the microstructure of cracks and the magnitude of the different types of physical event that can occur at the crack tip during plastic deformation and stable crack growth. Expressions are given for the threshold plastic zone size ‘Dl’ at which local fracture instability occurs and the stress-wave displacement amplitude as a function of distance ‘ui(r)’ for the different wave types ‘i’ produced during crack extension. Dispersion of the stress-wave and its convolution into an electrical burst signal at the sensor is considered together with the choice of appropriate sensing frequency. A methodology is described for correcting the measured signal amplitude for attenuation in the structure and for determining the maximum sensor spacing for the detection and location of events of a specified magnitude ‘Mae’ similar to the Richter scale. Case studies are presented to illustrate the extensive database now available on acoustic emission from crack growth in metallic structures and the technical and commercial benefits to be gained from an acoustic emission based inspection strategy. The applications considered are: • Fatigue crack growth in the node joints of offshore structures, • Stress corrosion cracking in platform flow lines.
Authors: Karl Maile, Andreas Klenk, J. Granacher, G. Schellenberg, M. Tramer
Authors: Michal Zouhar, Pavel Hutař, Luboš Náhlík, Zdeněk Knésl
Abstract: Failure of layered materials is frequently caused by the existence of interfaces between single layers. In structures loaded by long-term constant stress the damage can be described on micro-scale by material changes due to active creep mechanism and at the macro-level by a corresponding change of the stress and strain field. In the contribution the behavior of a crack propagating through the interface is analyzed. Primary attention is devoted to a crack with its tip at the interface under creep exposition. The step change of material properties at the bi-material interface means that standard fracture mechanics access is not applicable and a modified approach based on generalization of the classical concept has to be used. The approach is illustrated on the damage of a plastic pipe with protective layer.
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