VARIATION OF CRATER GEOMETRY WITH PROJECTILE L D FOR L/D-LESS-THAN-OR-EQUAL-TO-1/

A series of hydrocode calculations and terminal ballistics experiments were performed to investigate the penetration mechanics of projectile s with L/D less than or equal to 1. Projectile L/D ranged from 1/32 to 1; impact velocity ranged from 1.5 to 5 km/s. Projectiles were tungst en 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 p rojectile L/D and achieves a maximum at about L/D = 1/8 for 1.5 km/s a nd 1/16 for 3 km/s, and then decreases with further decrease in L/D. F or 5 km/s, P/L increases with decreasing L/D over the entire range stu died. P/L scales with impact velocity as P/L similar to v(f(L/D)) wher e, we believe, f(L/D) approaches 2 as L/D approaches 0. The ratio of c rater to projectile diameter D-c/D decreases with decreasing L/D and a pproaches a value of 1 as L/D approaches zero for all velocities studi ed. The crater shape measured by P/D-c decreases with decreasing L/D; i.e., as L/D decreases, the crater changes from approximately hemisphe rical for L/D = 1 to a very shallow disk shape. The kinetic energy req uired per unit crater volume, KE/V-c, increases with decreasing L/D fo r L/D < 1/4. That is, cratering efficiency decreases with decreasing p rojectile L/D. For the impacts studied, KE/V-c increases from about 5 kJ/cm(3) to 12 kJ/cm(3) as projectile L/D is reduced from 1 to 1/32.