On the path of a crack near a graded interface under large scale yielding

The trajectory of a crack lying parallel to a thin graded layer between two plastically dissimilar materials is studied using the exclusion region (ER) theory of fracture. The ER theory is a theoretical framework for surface separation within which a broad range of fracture phenomenologies can be represented. In the present study, the direction of crack advance is determined by maximizing the resolved normal-opening force on the near-tip region, whereas separation itself is governed by the intensity of plastic deformation near the tip. A computational study was undertaken using the ER theory. The special-purpose finite element analysis platform accommodates arbitrary-and a priori unknown-crack trajectories. The model problem considered herein involves two plastically dissimilar, but elastically identical, materials joined by a thin, graded interface layer. The initial crack lies parallel to the interface layer, and crack advance occurs under conditions of extensive plastic flow. It is found that the position of the initial crack relative to the interface layer has a strong influence on the fracture behavior. In general, the crack trajectories tend to curve toward the less-ductile material. Also, the presence of the interface layer leads to fracture toughnesses that significantly exceed those of either material individually for the configurations studied. (C) 2003 Elsevier Science Ltd. All rights reserved.