Dynamics of sand response to rapid penetration by rigid projectiles

Abstract

The response of dry sand to rapid penetration by a rigid projectile is investigated through a series of high-speed penetration experiments. A ballistic range is used to vertically launch cylindrical projectiles and a scaled version of a 155 mm M107 projectile at impact velocities of approximately 200 m/s into sand targets. A photon Doppler velocimeter is used to track projectiles from impact to rest in the soil target. Data collected from the experiments include the evolution of the cavity crown along with displacement, velocity, and acceleration time history. Analysis of the results reveal that the soil bulk density has a major role in penetration resistance at high relative densities. The role of bulk density diminishes at lower relative densities. Furthermore, the shape of the projectile nose has limited influence on the penetration response, due to the formation of a kernel of crushed sand at high velocities. The crushed sand kernel, known as the false nose, has a curved surface, and it can be approximated as a cone with a 60° apex angle. Only projectiles with a nose sharper than this value affect penetration resistance, while blunter noses effectively behave as 60° cones due to the formation of the false nose. A phenomenological equation of penetration resistance comprising inertial and frictional bearing resistance is used to describe the penetration response and predict the depth of burial (DoB) of the projectile in the soil target with reasonable accuracy.

Graphical Abstract