Crack paths in graded and layered structures

Abstract

This chapter reviews the prediction of crack paths in materials with graded, and/or layered, composition, microstructure, and/or properties. The relevant applications span a wide variety of technologies where structural integrity is important and includes composites, layered materials, coatings, and joints. For most cases, the prediction of failure requires a priori knowledge of the crack path. In many cases, the crack path may be sufficiently defined by considering just crack kinking, that is, a small or infinitesimal increment of crack deviation from its plane. For other cases, the full crack path needs to be determined, something usually done with remeshing techniques in numerical simulation. In linear elastic systems, the residual stress that arises from the coefficient of thermal expansion mismatch between constituents generally dominates the behavior, but not if the elastic mismatch is very large or if there are big toughness mismatches. For linear elastic systems where plasticity occurs, but small-scale yielding still applies, the crack is usually drawn toward the softer material which also is generally tougher. For all cases, if the crack stress fields from all the sources are accurately defined, and materials properties known, it is possible to predict the crack path.