Estimation of the critical configuration of a crack arrested at the interface between two materials

Surface crack propagation in a thin soft protective layer on a massive stiffer substrate is analysed using generalised linear elastic fracture mechanics. The growth of the initial crack is considered in both forward and sideways directions and the influence of the interface between the protective layer and massive substrate on the final crack configuration is investigated. It is shown that, depending on the elastic mismatch, the part of the crack front can be arrested at the interface protective layer/substrate and the rest of the crack grows continuously sideways only. The effective value of a stress intensity factor is used in order to predict the conditions under which the crack will propagate through the interface into the second material. Corresponding calculations have been made by finite elements.