Notch tip fields in amorphous films resting on ductile substrates

The architecture consisting of films resting on a ductile substrate is ubiquitous in a wide variety of applications. A typical failure mechanism of such a structure is cracking of the films. In this study, the calculations for the notch tip fields in a metallic glass film deposited on a ductile substrate are carried out to explore the fracture mechanisms of the amorphous films. The amorphous film is characterized by an isotropic elastic-plastic model which captures the pressure sensitive yielding and post-yield strain softening behavior of metallic glasses, and the substrate is taken to be an elastic-plastic solid with the flow rule given by von-Mises flow theory. It is found that the thick amorphous films exhibit high opening stress and small plastic deformation, indicating that brittle cracking of the films tends to be the dominant fracture mode. Whereas, the low opening stress is observed and shear bands develop in the case of thin amorphous films, implying that the cracking caused by shear bands governs the fracture of films. We further revealed that the pressure sensitive yielding plays an important role in the fracture of amorphous films; large degree of pressure sensitivity enables low opening stress and enhanced plastic deformation in the films, increasing the propensity of formation of shear bands. The findings of this study provide plausible explanations for the experimentally observed fracture behavior of amorphous films on ductile substrates, and shed new light on the fracture mechanisms of such a structure.