Visco-Elasto-Plastic Characterization of PVC Foams

Polyvinyl chloride (PVC) foams are widely used in crashworthiness and energy absorption applications due to their low density combined to the capability of crushing up to large deformations with limited loads; the latter property is due to the particular constitutive behavior of such foams. Indeed, the stress–strain curve is characterized, after an initial yield or peak stress, by a relevant plateau region, followed by a steep increase due to foam densification. Furthermore, the mechanical response of PVC foam is strongly influenced by the rate of load or strain application. In this work, compression tests have been carried out at different speeds on PVC foam samples having different relative density. Quasi-static and intermediate strain rate tests have been performed by pneumatic machine, while high strain rate tests have been conducted by means of a Split Hopkinson Pressure Bar. The tests highlighted a strong compressibility of foam, with negligible lateral expansion; the energy absorption efficiency as well as the densification strain has been evaluated. Finally, the uniaxial stress–strain curves have been used to calibrate a combined visco-elastic and visco-plastic constitutive model, based on a 2-layer scheme borrowed from the literature. In the model, the material behavior is divided into two parallel branches, the former showing an elasto-plastic behavior, the latter showing a visco-elastic behavior; a multiplicative term, accounting for the strain rate sensitivity of the base material, is included into the plastic branch.