Effects of Plasticity and Residual Stress for Cracks near Interfaces

Abstract

Cracks situated parallel to, and very near, the interface in layered, ductile-brittle composite specimens were investigated with finite element analysis. Elastic, plastic and thermal properties of Cu-W composites previously obtained from experiments were utilized in the model. A finiteelement model for simulating mixed-mode crack propagation in linear elastic materials was modified to incorporate yielding. A routine for automatic crack extension and remeshing enabled simulation of incremental crack propagation. Particular issues, including calculation of fracture parameters, crack propagation direction under mixed-mode loading and retention of plastic strain history, are addressed. The geometry and an example mesh close-up are shown in Fig. 1. Crack propagation was simulated in homogeneous and layered Cu-W composites, employing thermal and mechanical properties previously obtained from experiments. Two effects of plasticity on crack-tip stresses are predicted: (i) compliance mismatch leads to stress intensity factor amplification or ‘anti-shielding’, and (ii) accumulation of plastic strains leads to increases in effective toughness. Competition between these determines the structural reliability of the interface region.