Showing papers by "Jeffrey W. Kysar published in 2001"
TL;DR: In this paper, a series of finite element analyses of the bicrystal specimen were performed and two different constitutive hardening models for single crystals were discussed, and it was shown that, depending on the hardening model, regions of single slip around the crack tip may degenerate into regions of triple slip.
Abstract: Cracks that exhibit relative amounts of ductility along a copper/sapphire bicrystal interface are simulated within the context of continuum mechanics. The specimen in question exhibits a directional dependence of fracture; that is a crack oriented in one direction along the copper/sapphire interface propagates much more during a given load increment than does the crack oriented to propagate in the opposite direction along the interface. This phenomenon had previously been explained on the basis of an energetic competition between dislocation nucleation and cleavage failure at the two crack tips using both the Rice and Thomson (Philos. Mag. 29 (1974) 73) model as well as the more recent type of dislocation nucleation analysis by Rice (J. Mech. Phys. Solids 40 (1992) 239) based on a Peierls-like stress vs. displacement relationship on the slip plane. However, recent experiments by Kysar (Acta Mater. 48 (2000) 3509) have shown that the orientation of the directional dependence of fracture in the copper/sapphire bicrystal is opposite to that predicted on the basis of dislocation nucleation arguments. The goal of the present work is to attempt to explain the directional dependence of fracture solely on the basis of continuum mechanics. In Part I of this pair of papers we review the main results of the experiments and then set the stage for a series of finite element analyses of the bicrystal specimen by reviewing the fundamentals of single crystal plasticity and the general features of crack tip fields in single crystals. We then discuss two different constitutive hardening models for single crystals and predict that, depending on the hardening model, regions of single-slip around the crack tip may degenerate into regions of triple slip. This leads to a discussion of how the near-tip displacement field can change dramatically with constitutive models. Next the constitutive properties used in the simulations are fit to experimental data. Finally we describe the finite element meshes and procedures for simulating the stationary and quasistatically growing cracks. The simulation results are reported in Part II.
65 citations
TL;DR: In this paper, the authors investigated the directional dependence of fracture of interfacial cracks in a copper/sapphire bicrystal in terms of continuum stress and deformation fields.
Abstract: The goal of this work is to explain the directional dependence of fracture of interfacial cracks in a copper/sapphire bicrystal in terms of continuum stress and deformation fields. In Part I of this pair of papers, we briefly review the main results of experiments by Kysar (Acta Mater. 48 (2000) 3509) and discuss how the orientation of the directional dependence of fracture is contrary to predictions made on the basis of crack tip dislocation nucleation concepts. We then set the stage for a series of finite element analyses of the bicrystal specimen. In Part II the simulation results are presented. We first conclude that the assumptions which enter into the crack tip dislocation nucleation analyses are valid. Therefore, the orientation of the directional dependence is opposite that of the dislocation nucleation analyses, in spite of the fact that crack tip dislocation nucleation may occur as predicted. We then show that the directional dependence of fracture, at least for the copper/sapphire bicrystal specimen, can be explained by the fact that the quasistatically growing brittle crack has the propensity to generate a significantly higher normal opening stress along its prolongation than does the ductile crack. This conclusion is valid for a wide range of crack growth criteria as well as material constitutive models and parameters. We also present results of the simulated crack opening displacement profiles of the two crack and compare them to experimental measurements. The results do not satisfactorily explain the qualitative features of the normal crack opening displacement profile; however we discuss some possible reasons why the finite element method may not be able to accurately model the crack opening displacement profile.
33 citations
TL;DR: In this article, the theory governing the propagation of light in the region near a plane strain crack tip is extended to optically anisotropic media, where an incident wavefront of light is split into two independent wavefronts.
4 citations
TL;DR: In this paper, the authors extend the technique to situations in which the crack lies along the interface between a stransparent material and a highly reflective metal and discuss how the intensity distribution and the placement of the fringes vary with reflectivity of the metal.
Abstract: Crack-opening interferometry is a technique whereby one can directly measure the normal opening displacement of a crack that exists in a transparent material. Here, wer extend the techique to situations in which the crack lies along the interface between a stransparent material and a highly reflective metal. We discuss how the intensity distribution and the placement of the fringes vary with reflectivity of the metal. However, because the fringe spacing is not affected, the fringes can still be interpreted in terms of normal crack-opening displacement profile. The paper reports experimental measurements of crack-opening displacement profile of an interface crack in a copper-sapphire bircystal. The results show the crack-opening displacement profile to be that of a constant opening angle.
2 citations