Polymeric foam behaviour under static and dynamic loadings – Effect of the gas entrapped in the porous structure

Abstract
Expanded polystyrene foams are commonly used to absorb energy during impact on structures. Previous works studied the influence of density or strain rate on the performance of these foams. The final aim of this study is to evaluate the influence of gas trapped in the foam's closed cells on the macroscopic mechanical behaviour. Static and dynamic compression tests were performed on classical samples and on samples partially emptied of gas before the test. Firstly, the experimental device was validated. It is constituted by a vacuum pump, an instrumented closed chamber usable with a compression electro-mechanical machine or with a flywheel. The fact that a quantity of gas can be evacuated from the sample further in a vacuum environment is established. This assumption can be verified with a high-speed camera by the detection (or not) of bubbles during compression tests in water or alcohol. The influence of gas on the elastic modulus, on the viscoelastic and on the plastic properties, is assessed.