In situ mechanical characterization during deformation of PVC polymeric foams using ultrasonics and digital image correlation

Cellular solids such as polymeric foams are finding increasing applications including its use as a core material for sandwich structures. In this study, a novel method is used to measure both the longitudinal and shear wave speeds of a material simultaneously while applying a compressive load in four different densities of polymeric foams made from the same base polymer, polyvinyl chloride (PVC). The study showed that there was a significant difference in evolution of the wave speeds and hence in the apparent modulus during deformation of the lower density foams in comparison to the higher density foams. The non-contact full-field method of digital image correlation (DIC) is used to gain insights into the failure modes during deformation. The lower density foams undergo heterogeneous deformation and failed due to buckling of cell walls. In contrast, the higher density foams undergo nominally homogeneous deformation due to plastic collapse. The failure mode transition is shown to be governed by the relative density of the foams and the mechanical properties of the polymer