Influence of debonding and substrate plasticity on thin film multicracking

Abstract

Multicracking of a thin brittle layer deposited on a substrate with an intermetallic layer is studied using finite fracture mechanics. Nonlinear implementation of the coupled criterion is used to predict the initiation and successive subdivisions of a periodic network of cracks considering intermetallic layer plasticity and interface debonding. Plasticity has a moderate influence on the cracking kinetics whereas debonding length has a strong influence on the saturation crack spacing. The cracking kinetics predicted numerically is more abrupt than in experiments because of the periodicity assumption, however crack spacing at saturation similar to those measured experimentally are obtained. The tensile strength and critical energy release rate of the thin brittle layer are determined by inverse identification based on the crack density variation as a function of the imposed loading. The proposed approach also enables the accurate determination of the interface critical energy release rate based on the experimentally measured debonding lengths.