Finite-size effects in thin-film composites

Abstract Many formulations of the mechanical response of thin-film composites consider the film layers to extend to infinity in the surface plane of the composite. These layers are also assumed to be much thinner than the substrate. Under these assumptions the stress in the substrate becomes negligibly small and the stress transfer between layers does not depend on the elastic moduli of the interfaces. Consequently, in most studies of blanket thin films these terms have received little attention. For thin-film composites with finite dimensions, these terms may be important and they can be calculated from the traditional shear lag model and its extensions. In this paper we show that these models provide widely divergent results when applied to the same structure. These differences arise from the initial stress state and geometry assumptions implicitly contained in such models. Comparison with experimental observations shows that further work is required before these models can be applied to patterned thin-film structures.