Polypropylene Foam Behavior UnderCompressive Loading At High Strain Rate

Abstract

Polypropylene foams are widely used in many impact-absorbing applications. To improve their mechanical performances, these structures have to be modelled. This approach requires the characterisation of the foam behavior at high strain rate in order to identify parameters of rheological models commonly implemented in FE code. Tests were achieved on polypropylene foams under high strain rate compression loading. The material behavior has been determined as a function of two parameters, density and strain rate. Foams (at several densities) were tested on two specific machines. First, an electromechanical testing machine has been used which enables to apply an uniaxial compression for initial strain rates up to 0.33 s -1 . These results were completed by those obtained on a new device installed on a flywheel. This device was designed in order to achieve stopped compression tests on foam. It consists in compressing the sample by a hammer fixed on a metallic wheel turning at high speed. With these testing machines, the dynamic compressive behavior has been evaluated in the strain rate range up [6.7.10 -4 s -1 , 100 s -1 ]. From these tests, stress-strain responses of polypropylene foam were defined as a function of density and strain rate. Result curves show three regimes: an elastic behavior followed in a second step by a stress plateau corresponding to yielding. Finally, for high strains, a rising hardening step occurs due to foam densification. Hence, model depending on these two parameters density and strain rate was built from the stress-strain responses.