The Mechanics of Layered Foam

This thesis contributes to the understanding of the mechanical response of layered and hybrid foam structures, such as the sandwich beam, and protective plates comprising foamed and solid materials. These materials may find applications ranging from critical structural members in aircraft wings and hulls of ships, to the packaging industry as well as protective components in bike helmets or dashboards of cars. The thesis may be broadly split in two parts. Part I considers the influence of residual stress on the elastic indentation mode of collapse of a sandwich beam whilst the effect of residual stress on the elastic limit is also explored. Both are explored by the formulation of analytical models and subsequent numerical models and experiments. The elastic indentation collapse mode increases or decreases in the presence of a tensile or compressive residual stress. The elastic limit of a sandwich beam in bending is dictated by the occurrence of three competing mechanisms and the presence of residual stress, compressive or tensile, is found to negatively affect the load carrying capacity due to earlier yielding of the sandwich beam. In Part II, the plane strain indentation response of a polycarbonate (PC) face sheet adhered to a polyvinyl chloride (PVC) foam substrate is measured. The deformation response is modelled by finite element simulations and, together with experimental observations, an analytical model is synthesised. The model assumes elastic membrane stretching of a face sheet on an elastic, perfectly-plastic foam foundation, and includes the role of shear-lag between face sheet and foam substrate. Finally, a parametric finite element study is performed on the indentation of a PC plate attached to a foam foundation consisting of a high-density PVC foam foundation which is in turn attached to a foundation of low-density foam. The purpose of such a hybrid material is to protect a structure underneath the foam foundation, whilst also providing similar indentation resistance at reduced weight.Engineering and Physical Sciences Research Council, award number 1463953, SABI