On the Formation of a False Nose During High Speed Penetration of Sand

When a rigid projectile penetrates sand it is possible for a false nose to attach to the nose. Recently, Yankelevksy et al [1] derived an optimum nose shape that results in the greatest penetration into sand for a given nose length and base diameter. They further hypothesized that false noses tend to conform to the optimum shape. We performed experiments with cylindrical projectiles made from 6061T6 aluminum having conical nose shapes with interior apex angles of 180 (flat), 120, 90, 60, and 30 degrees. Impact velocities were 200 m/s within 2%. The material was quartz sand at 1820 kg/m³, which is very near maximum relative density. False noses formed for the blunter three shapes, but not for the sharper two. False nose height was nearly independent of cone angle, being 0.61-0.69 calibers long. All false nose contours were between the predictions of [1] and an ogive. The 90^o false nose shape was closest to the predicted optimum. Penetration depth depended only slightly on nose shape, except for the sharpest nose, which went significantly deeper. However, maximum penetration resistance, quantified as a stress determined from PDV measurements, decreased monotonically with increasing sharpness. The transition in nose formation between 60 and 90 degrees corresponds to a peak stress of 125-145 MPa, which explains how false nose particles become comminuted. The aluminum substrates under false noses were badly pitted.

1. [1] D.Z.Yankelevsky, V.R.Feldgun, Y.S.Karinski, Int’l J. Impact Eng’ing, 177 (2023)