Fast x-ray radiography to study the dynamic compaction mechanisms in a rigid polyurethane foam under plate impact

This article presents results of plate impact experiments coupled to in situ X-ray radiography, performed on a polyurethane foam, to visualize its deformations during the propagation of a stress wave. A two-wave structure associated with the propagation of an elastic precursor and pores compaction has been observed. A phenomenological compaction model, implemented in a dynamic explicit one-dimensional hydrocode, was used to simulate the dynamic macroscopic response of the foam. By using this model, which has previously been calibrated and validated by performing dedicated dynamic experiments, it is possible to compare calculated and experimental waves velocities and improve interpretations. Quasi-static tests coupled to in situ X-ray tomography have also been performed to study the mechanical behavior under low strain rates. Experimental results show that the compaction is due to bending and buckling of cell edges, and then matrix failure. Strain rate dependence of the foam behavior has been observed.