Polymeric foam deformation under dynamic loading by the use of the microtomographic technique

Abstract

The mechanical behaviour of polymeric foams depends on several parameters such as temperature, material density and strain rate. This last point implies that compression tests on conventional testing machines are not sufficient. Study of the behaviour in practical situations requires special apparatus like fly wheels, drop towers or Hopkinson bars, allowing high compression speeds. The polypropylene foams studied are multi-scale materials; agglomerated beads (2–3 mm in diameter), visible to the naked eye, are composed of microscopic closed cells (a few tens of microns). The response of the material to a shock consists of three regions: an elastic phase, a plastic phase and densification. The plastic phase is of prime interest since a great part of the shock energy is dissipated there. Microtomography was used in order to better understand damage mechanisms during the stress plateau of the plastic phase. The final objective of this work is to determine the strain field of porous materials at several levels of shock. As tomography is not fast enough to directly follow the impact deformation, interrupted impact tests were carried out by controlling the levels of sample deformation. Between each impact step, a microtomographic analysis offers insight on the progressive deformation of the sample. The results of these impact tests completed by a microtomographic visualisation in 2D are presented and commented in this paper.