The fracture toughness of thin metal films, confined between elastic layers, was found to depend strongly upon the metal-film thickness and upon the residual stress. Here, a 2-dimensional discrete dislocation model was used to predict the dependence of fracture toughness upon both the residual stress and the film thickness. The fracture toughness was found to be almost independent of the cohesive strength when the cohesive strength exceeded about 900MPa. The predictions for systems with almost zero residual stress agreed well with experiment. The fracture toughness was found to decrease significantly with increasing residual stress, and the predictions were again in qualitative agreement with experiment. The discrete dislocation model predicted that the effect of residual stresses was independent of the sign of the stress, tension versus compression, in contrast to continuum plasticity models. The results demonstrated the ability of dislocation-based modelling to handle multiple-scale dependent plasticity phenomena simultaneously.

Effect of Residual Stress on Fracture in Confined Thin Films - a Discrete Dislocation Study. A.C.Chng, W.A.Curtin, A.A.O.Tay, K.M.Lim: Modelling and Simulation in Materials Science and Engineering, 2008, 16[1], 015002 (19pp)