Variation of crater geometry with projectile L/D for L/D ≤ 1

A series of hydrocode calculations and terminal ballistics experiments were performed to investigate the penetration mechanics of projectiles with L/D ≤ 1. Projectile L/D ranged from 132 to 1; impact velocity ranged from 1.5 to 5 km/s. Projectiles were tungsten or tungsten alloy, targets were RHA. The paper concentrates on the effect of projectile L/D on the size and geometry of the target crater. Normalized crater depth (or penetration) increases with decreasing projectile L/D and achieves a maximum at about LD=18 for 1.5 km/s and 116 for 3 km/s, and then decreases with further decrease in L/D. For 5 km/s, PL increases with decreasing L/D over the entire range studied. PL scales with impact velocity as PL ∼ Vf(LD) where, we believe, f(LD) approaches 2 as L/D 0. The ratio of crater to projectile diameter DcD decreases with decreasing L/D and approaches a value of 1 as L/D approaches zero for all velocities studied. The crater shape measured by PDc decreases with decreasing L/D; i.e., as L/D decreases, the crater changes from approximately hemispherical for LD = 1 to a very shallow disk shape. The kinetic energy required per unit crater volume, KEVc, increases with decreasing L/D for LD < 14. That is, cratering efficiency decreases with decreasing projectile L/D. For the impacts studied, KEVc increases from about 5 kJ/cm3 to 12 kJ/cm3 as projectile L/D is reduced from 1 to 132.