A maximum allowable flaw size for debond-resistant bimaterial layers

Free-edge debonding and subsequent interface crack extension are common modes of failure in a variety of engineering applications in which bonded layers of dissimilar materials are subject to differential expansion stresses. In this study, the susceptibility to debonding of short interface edge cracks is investigated for the global plane elasticity problem of a bimaterial strip with a uniform edge load applied to the top layer (a general model of differential expansion). The goal of this study is to determine the maximum crack length L for which interface crack extension is inhibited, or more specifically, for which the singular interface normal stresses are compressive. This is equivalent to a maximum allowable flaw size, which is of interest to both designers and inspectors of bimaterial systems. The critical crack length L has been extracted from parametric finite element analyses over a wide range of bimaterial configurations using the commercial software package ABAQUS. Results indicate that the critical crack length L increases with both the relative stiffness and thickness of the contracting layer, and may represent a significant inspectable flaw size for a variety of practical bimaterial configurations.