Where do polymer adhesives fail?

We use molecular-dynamics simulations of a polymer film confined between two walls to isolate the factors that control where an adhesive bond breaks. Failure occurs either at the wall/film interface (adhesive failure) or within the film (cohesive failure). Most theories relate the location of failure to equilibrium interfacial free energies. However, we find that the location of failure coincides with the region of lowest initial yield stress and cannot be predicted from equilibrium interfacial free energies.