3-DIMENSIONAL EFFECTS IN THIN-FILM FRACTURE-MECHANICS

This paper presents the results of a three-dimensional finite element analysis of the mechanics of crack growth and decohesion in a highly c ompliant thin film bonded to a rigid substrate. Essential features of the model are a surface-breaking initial crack which has penetrated to the film-substrate interface, and a remote biaxial residual stress fi eld in the film. Computational analyses show that, in the absence of d ecohesion, the stress intensity factor along the leading edge of the c rack reaches a steady state value when the crack is about twice the fi lm thickness. This steady state condition gives rise to a nearly parab olic crack front along the leading edge. The computed results also con firm the existence of high interface stresses that are the driving for ce for film decohesion. When decohesion is permitted, the stress inten sity factor is observed to increase with debond opening angle. The equ ilibrium state between crack propagation and decohesion may be determi ned from the respective stress intensity factors and fracture toughnes s of the film and the interface.