Effects of head shape of projectiles on hypervelocity impact cratering on aluminum 5052 alloy targets at 7 km/s

A series of experiments was conducted to investigate the effect of projectile head shape on hypervelocity impact cratering. Aluminum 5052-H112 alloy thick targets were impacted by projectiles which had different heads at velocities of approximately 7.1 km/s. The head shape was classified into five types of head shape, i.e. flat-head and, two types of concave-head and two-types of convex-head. The effect of the head shape was evaluated by final morphology of craters, i.e. variables of the penetration depth, the crater diameter and the crater volume. The concave-head and convex-head projectiles produced shallow-shaped craters and deep-ones, respectively. The ratio of the crater penetration-to-diameter P/D increased as the head shape became more convex, and vice versa. The P/D ratio varied from 0.41 to 0.77. However, the penetration depth and the crater diameter had different dependencies based on the head shape. 'Flat-head conversion', in which the concave-head and the convex-head projectiles were imaginarily regarded as flat-head projectiles with a converted diameter, gave the consistent effect on the crater variables to the concave-head and the convex-head projectiles. A new coupling parameter of the point source solution was defined as a function of impact variables. The crater variables scaled by this coupling parameter was expressed as power laws of impact variables. The coefficient and the exponents of obtained relations were determined by using multiple regression analysis. Regression equations closely estimated the experimental results.