Dynamic Mechanical Properties and Failure Mechanisms of PVC Foams

Abstract

Abstract Two closed-cell PVC foams were characterized at strain rates up to 1000 s−1. Experiments in the strain rate range between 10−4 and 1 s−1 were conducted on a servohydraulic testing machine and those in the range between 1 and 103 s−1 were conducted on a modified Split Hopkinson Pressure Bar (SHPB) apparatus. The striker and input/output pressure bars in the latter were made of polycarbonate (Lexan) instead of metal. The polycarbonate material was tested at different strain rates and found to behave linearly for strain rates up to 1000 s−1. All stress-strain curves show typically five deformation stages, initial elastic deformation, nonlinear deformation up to a peak load, softening after the peak, a plateau and finally strain hardening corresponding to material densification. The initial modulus increases slightly with strain rate and both peak and plateau stresses increase with strain rate. The softening stage becomes longer with increasing strain rate, a fact attributed to heat generation during the adiabatic deformation. Failure mechanisms at different stages of deformation were identified by loading specimens to different strain levels and observing them by scanning electron microscopy. The initial elastic behavior corresponds to bending of the cell walls; nonlinear and softening behavior correspond to buckling of the cell walls; and densification results from collapse of the cells.