Free-Edge Stress Intensity Factors for Edge-Loaded Bimaterial Layers

Abstract

Abstract Structures composed of bonded layers of dissimilar materials are common in a variety of applications. Designing such structures to resist debonding at free edges is often of critical importance. In this work, the problem of initiation of free-edge debonding is considered for use in designing debond-resistant layered structures. It is well known that the local elastic stress fields near the free edge of bonded dissimilar quarter planes can exhibit singular behavior, with the power of the stress singularity determined by the material mismatch. A fracture mechanics-type approach is adopted here which assumes that the local interface tractions governing initiation of debonding can be characterized by the power of the stress singularity and a suitably defined stress intensity factor. The global problem considered in this study is that of a bimaterial strip composed of isotropic layers with a uniform edge pressure applied to the top layer. A dimensionless free-edge stress intensity factor is introduced from which stress intensity factors can be derived for either uniform edge or thermal loadings applied to either or both of the layers. Finite element results are presented for the dimensionless free-edge stress intensity factor over a wide range of material mismatches and relative layer thicknesses. Trends in the dimensionless stress intensity factor are used to identify strategies for designing debond-resistant bimaterials. Finally, the trends are shown to be well approximated by the analytically calculated stress resultants transmitted across the interface, which suggests a simplified approach for designing debond-resistant multilayer structures.