The false nose shape in a high velocity projectile penetration into dry sand

Abstract

The present article deals with a particularly interesting phenomenon of a false nose that is formed during the high velocity penetration of a projectile into a granular soil like sand. The false nose is composed of compacted, fractured, and comminuted sand particles. It is formed as a cap in front of flat nose projectile and accompanies the projectile during its penetration. Only limited sparse experimental evidence exists on the false nose shape that is mostly observed after the penetration event. So far, no theoretical study was carried out to assess the false nose shape and its effect on penetration. The present paper conjectures that the shape of the false nose is equal to the optimal shape formed from the target soil material that yields the minimal resistance during its penetration in the soil. This nose together with the original flat nose projectile behind, yield a stable deep penetration that is comparable to projectiles with shaped noses. The present study extends the approach of a full false nose in front of a flat nose projectile, to a partially added false nose in front of a hemispherical, spherical, or other short noses. Analysis of experimental images of false noses verifies the above conjecture and prove that the shape of the false nose is very close to the optimal shape of a projectile nose that is made of compacted soil. These findings enable implementation of the well-proven DISCS approach (which was originally developed for penetration of projectiles with slender noses into various compressible media) and extend it for flat, spherical and hemispherical projectiles penetration into a granular soil. The efficiency of the proposed approach is demonstrated through numerous examples for the above types of projectiles, at various impact velocities, showing very good agreement with experimental data.