Stress wave propagation and mitigation in two polymeric foams

This paper investigates the ability of a syntactic epoxy foam and an expanded polyurethane foam to mitigate intense (several GPa) and short duration (T < 1 µs) stress waves. Plate impact and electron beam irradiation experiments have been conducted to study their dynamic mechanical responses. Interferometer Doppler Laser method is used to record the target rear surface velocity. A two-wave structure associated with the propagation of an elastic precursor and the compaction of the pores has been observed. The compaction stress level deduced from the velocity measurement is a good indicator of mitigation capability of the foams. Quasi-static tests and dynamic soft recovery experiments have also been performed to determine the compaction mechanisms of these polymeric foams. In the polyurethane foam, the pores were closed by elastic buckling of the matrix and damage of the cellular structure. In the epoxy foam, the compaction is due to the crushing of glass microspheres. A strain rate dependent compaction model successfully represents the macroscopic response of these polymeric foams.