Phenomenology of rapid projectile penetration into granular soils

Eighty subscale penetration tests were performed to investigate penetration phenomenology in granular media, with impact velocities in the range of 70-300 m/s. The parameter space consisted of (1) four natural and synthetic granular materials, including Ottawa sand, crushed fused quartz, aragonite, and crushed coral, (2) loose and dense packings, (3) dry and wet targets, and (4) four different projectiles, including spheres and long rods with conical, hemispherical and blunt nose shapes. Two techniques were employed to obtain penetration time histories, including photonic Doppler velocimetry for high velocity impact tests, and high speed imaging for low velocity impact tests. Penetration time histories were differentiated to obtain velocity and acceleration time histories. Analysis of the time histories revealed that the role of nose shape, packing density, and saturation is material dependent. Silica sands and calcareous sands showed contrasting behavior across the parameter space considered. These observations point to the significance of particle crushing in rapid penetration into granular media.