Stress variations and particle movements during penetration into granular materials

Abstract

Granular materials such as sand are crushed and compacted locally when subjected to projectile penetration. It is necessary to obtain more diagnostic information during the experiment to develop a thorough understanding of the deformation mechanisms inside the target. In this study, we embedded piezoelectric film pressure gages at strategically distributed locations inside cylindrical sand targets. The gages are designed to measure only the pressure normal to the gage plane. The pressure gages are calibrated using a Kolsky bar before being embedded into the targets. The instrumented target is then subject to penetration by a cylindrical steel projectile with a semi-spherical nose. The distributed gages measure the pressure histories at the local gage positions. Flash X-rays installed around the target record the instant images of moving projectile and the gages inside the target. It was found that the penetration-induced pressure concentrates locally around the projectile.