Mode-dependent toughness and the delamination of compressed thin films

We consider the buckle-driven delamination of compressed thin films. For a wide class of patterns of delamination, it is shown that the loading on the delamination front progressively goes from mode I to mode II during growth of the blister. As a result, the mode dependence of the film/substrate interface excludes widespread delamination. This explains the observations of blisters of finite extent, which are otherwise difficult to interpret. We also study a model of interfacial fracture with friction. It reveals that a severe mode dependence can be induced by interfacial friction. This permits us to account for the mode dependence using only simple ingredients: friction and linear elasticity.