The response of dry and wet silica sand to high velocity impact

Abstract

Understanding the mechanisms governing the interaction of high-velocity projectiles and sand targets is important for numerous applications and industries. The high-velocity penetration of sand targets is known to be controlled by micromechanical phenomena; however, our quantification of these phenomena and our understanding of water saturation effects on target response is presently limited. To help improve our understanding of these phenomena, we performed impact experiments on wet and dry sand with in-situ and post-mortem analysis in a two-stage gas gun with varying impact chamber pressures. For in-situ analysis, we developed and used a novel experimental method for measuring projectile depth and three-dimensional displacement fields from orthogonal flash X-ray images acquired during the penetration process. We also employed in-situ high-speed imaging of ejecta. For post-mortem analysis, we examined final depths of penetration, particle size distributions, and permanent penetrator deformation. We found that impacts into wet sand targets featured enhanced sand displacements around projectiles, enhanced ejecta, and enhanced intermediate and final depths of penetration as compared to impacts into dry targets. We also found that impacts into wet targets led to less particle breakage than impacts into dry targets. Target chamber pressure was found to significantly influence final depth of penetration, likely through a fluidization process as air and fluid escaped the sample’s pores to equilibrate with the surrounding chamber pressure after initial impact. We discuss our findings in the context of existing literature and discuss the hypothesized origin of several of our observations with support from modeling efforts described elsewhere.