Finite Element Analysis of Interfacial Fracture in Polyurethane Foam–Steel Composites at Micro-Scale

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 behavior at the interface region at micro-scale. The foam–metal composite consisted of polyurethane (PU) foam directly adhered to a galvanized steel face sheet. Optical, scanning electron and atomic force microscopies 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 the mechanical interlocking and modes of failure, which are directly related to the interfacial strength. A set of FE models of idealized surface pairs of different geometries and dimensions were developed based on the microscopic observations at the foam–metal interface. The FE modeling 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 influence the modes (cohesive or adhesive) of failure.