Simulation of ellipsoidal projectile impact on whipple shields

Abstract

From terminal ballistics it is evident and well known that a projectiles aspect ratio influences it's penetration performance. Most investigations of hypervelocity impact deal with spherical or rod shape cylindrical projectiles. This is due to the relative low launch effort and good reproducibility of impact tests with these projectile types. However, space debris not necessarily is spherical. Moreover non spherical projectiles under oblique impact angles are the statistically regular case. Therefore, several studies have been performed in the past investigating the influence of projectile shape, e.g. Denardo [1], Morrison [2], Bjerke et al. [3], Konrad et al. [4] and Orphal et al. [5]. An enhanced knowledge base about the combined influence of shape and obliquity is being investigated at EMI. Both experimental and numerical studies were performed. Simulation turned out to be an important tool to understand these influences because the range of experimentally feasible impact and shape conditions is limited. In this paper numerical simulation of ellipsoidal projectiles' impact on Whipple shields using AUTODYN-2D and -3D are presented. Only some of the simulated cases are investigated by experiments with EMI two-stage light gas guns. Thus simulation is performed as a predictor with only few existing experimental validation. Future experiments will show how predictive these calculations are. Both projectiles and targets are made from aluminum alloys. Three different types of projectile shapes are being considered: ellipsoids with oblate, spherical, and prolate shape. The projectile mass was kept constant at 0.183 grams. The Whipple shield is similar to typical single bumper shield configurations on the modules of the international space station: It consists of a 1.0 [mm] thick bumper, having a stand-off of 200 [mm] from the 3.0 [mm] thick back wall. The impact velocities range between 0.85 [km/s] and 10 [km/s].