Sand Penetration: A Near Nose Investigation of a Sand Penetration Event

摘要

This paper presents experimental and computational results relative to a long-rod penetrating dry granular sand at velocities near 100 m/s. The objective of this work is to develop a fundamental understanding of the formation and transmission of dynamic force chains, and the motion and fracture of the individual sand grains as the projectile passes. This is accomplished by several very different experiments including: characterization of the elastic properties of sand, fracture characteristics of individual sand grains and launching a projectile along a view window, backed by sand, in order to directly view and photograph the projectile/sand interactions. Within the sand system, a two-wave structure was observed, composed of a compaction wave (bow shock) that detaches from the dart and moves through the sand at a wave speed near 100 m/s and a damage wave, which remains near the leading edge of the dart. The compaction wave removes porosity and the damage wave fractures grains in the region near the projectile nose. Grain fracture is not observed at dart speeds below 35 m/s.