SEM Observations of a Metal Foil Laminated with a Polymer Film

Abstract

A thin metal foil laminated on a polymer film usually fracture at higher strains than its corresponding freestanding material layer. On the contrary the polymer film can be observed to fracture at smaller nominal strains when laminated. This is due to the strain localization induced by the created localised neck and plastic deformation in the metal foil. A significant reduction of the “gauge length” of the polymer film is observed locally. This scenario prevails if the adhesion is sufficiently high to prevent delamination to grow between the layers. The newly created gauge length is in the order of two times a metal foil thickness if the adhesion is very strong, leading to local high stress and low strains measured globally. However, this effect is not due to the brittleness of the material or shift of mechanical properties during lamination. During stretching, large deformations are observed in the moderately ductile and strain-hardening polymer film. Tensile failure (boundary conditions and geometrical effects) of polymer laminates has been observed to be governed by two mechanisms demonstrated in Fig. 1. below. In the first case, the polymer film forms a neck and is deformed locally where the metal foil has fractured and ruptures at a small strain (I). In the second case, the delamination is grown and the polymer deforms and delocalizes the strain to a substantial larger area (II). In some cases the laminated material creates multiple necks and the metal film ruptures at several positions and thus deforms at larger strains. All these observations have experimentally been demonstrated by using scanning electron microscopic (SEM) micrographs.