Penetration of Hypervelocity Projectile into Foamed Polystyrene

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Abstract
Spherical nylon projectiles 7 mm in diameter and 0.213 g in mass penetrated into foamed polystyrene targets of nominal densities of 11 kg/m3 (L-type), 37 kg/m3 (M-type), and 74 kg/m3 (H-type), at velocities of up to 4.3 km/s. The hole depth takes a broad maximum around the impact velocity of approximately 3.9, 1.8 and 1.5 km/s for L-type, M-type, and H-type targets, respectively, above which the fragmentation of the projectile occurs. Using L-type targets, more than 86% of the projectile mass at the impact velocity of 3.88 km/s is recovered without fragmentation. Maximum penetration depth, maximum cross-sectional area of the hole, and the target mass removed in the penetration are given as a function of the impact velocity V i and target density ρt and expressed as ∼ρt -1.2, ∼V i +2.2, and ∼E +1.1 (E: Kinetic energy of the projectile), respectively. The latter relationship suggests that a constant proportion of the initial energy is expended to create the hole.