Interfacial fracture of polymer foam-metal composites at micro-scale using finite element analysis

Foam-metal composites are being increasingly used in a variety of applications. One important aspect in the structural integrity of foam-metal interface is the ability to resist failure around the interface whilst ensuring required load bearing capacity. This study investigated the mechanical and failure behaviour at the interface region at micro scale. The foam-metal composite consisted of polyurethane foam directly adhered to a galvanised steel face sheet. Optical, scanning electron and atomic force microscopy were used to examine the interface geometry and to obtain a realistic surface profile for use in a finite element (FE) model. Finite element analysis (FEA) was used to study the effects of different interfacial roughness profiles on mechanical interlocking and modes of failure, which are directly related to interfacial strength. A set of finite element models of idealised surface pairs of different geometries and dimensions were developed based on the microscopic observations at the foam-metal interface. The finite element modelling results show that the micro- scale roughness profile at the foam-metal interface causes mechanical interlocking and affects the stress field at the scale of the interface surface roughness, which consequently governs the specific failure mode and the relative proportion of the cohesive to adhesive failure in the interface region for a given foam-metal interface. It was found that the aspect ratio (relative width and height) and width ratio (relative spacing) of roughness elements have a significant effect on the stresses and deformations produced at the interface and consequently control the modes (cohesive or adhesive) of failure.