On the design of debond-resistant bimaterials - Part I: Free-edge singularity approach

Structures composed of bonded layers of dissimilar materials are common in a variety of applications. In many such structures, residual or applied stresses can lead to initiation of interface debonding near free edges. 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 order of the stress singularity determined by the material mismatch. A fracture mechanics-type approach to the design of debond-resistant bimaterials is adopted herein, which assumes that the local interface tractions governing initiation of debonding can be completely described by the order of the stress singularity and a suitably defined free-edge stress intensity factor. The global plane elasticity 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, which is a general model of differential expansion. Finite element results are presented for dimensionless free-edge stress intensity factors over a wide range of practical material mismatches and relative layer thicknesses. Trends in the dimensionless free-edge stress intensity factors are used to identify strategies for designing debond-resistant bimaterials. The results of this study motivate a comparison between free-edge singularity and interface crack approaches to bimaterial design, which is the focus of Part II. (C) 2000 Elsevier Science Ltd. All rights reserved.