In situ radiographic and ex situ tomographic investigation of pore collapse in laser shock-loaded polyurethane foam

Abstract

Laser-driven shock experiments were conducted at a synchrotron facility to investigate the dynamic response of polyurethane foam. These experiments were coupled to in situ x-ray imaging to radiograph foam deformations and to determine the propagation velocity of stress waves. To increase the amplitude and the duration of the pressure load generated by the laser-matter interaction, the front surface of the target was covered with a confining layer (water and BK7 glass). Preliminary calibration tests involving time-resolved velocity measurements were performed to calculate the ablation pressure on the front surface of foam samples. The calculated pressure loads were used as input data for hydrodynamic simulations, in which the foam is modeled using a homogeneous porous macroscopic model, and model predictions were compared with experimental results. A fair consistency was found for most experiments, while for the others, an overestimation of the applied pressure is suspected, likely due to a laser breakdown within the confining medium. Finally, post-shot x-ray tomography of the recovered samples showed permanent deformation of the foam, unlike what was observed under quasi-static compression, and revealed heavy damage in the vicinity of the loaded zone.