Hyper-velocity Crater Size and Target Strength

Abstract

IT has been shown^1–3 that at ambient temperature the hyper-velocity force per unit area of crater surface can be related to the engineering ultimate tensile strength of a material by the expression d³ = mv²/4πS where d is the depth (or radius) of a hemispherical crater, m and v are the mass and velocity of the projectile, and S is the measured ultimate tensile strength of the target. Aluminium alloys were divided⁴ into two groups on the basis of their ultimate tensile strength at room temperature; those having a strength of 4 × 10⁹ dynes/cm² or larger were not corrected for relaxation while those with strengths of 3 × 10⁹ dynes/cm² and less were increased by 25 per cent to obtain agreement between the target strength and impact force per unit area. The relaxation correction is an all-embracing term which includes the correction for relaxation of the target material after release of the impact pressure and other effects such as the error in the determination of the strength of very ductile materials caused by necking during loading.