Ductility of thin metal films on polymer substrates modulated by interfacial adhesion

When a laminate of a thin metal film on a tough polymer substrate is stretched, the metal film may rupture at strains ranging from a few percent to a few tens of percent. This variation in the ductility of the metal film is modulated by the adhesion of the metal/polymer interface. To study this modulation, here we use the finite element method to simulate the co-evolution of two processes: debonding along the interface and necking in the metal film. We model the interface as an array of nonlinear springs, and model the metal and the polymer as elastic-plastic solids. The simulation shows that necking of the film is accommodated mainly by interfacial sliding, rather than interfacial opening. Depending on the resistance of the interface to sliding, the metal film can exhibit three types of tensile behavior: the film slides and ruptures at a small strain by forming a single neck, the film slides and deforms to a large strain by forming multiple necks, and the film deforms uniformly to a very large strain without sliding and necking.