Ballistic limit equation for the normal impact of unyawed ellipsoid-shaped projectiles on aluminium Whipple Shields
In this study, an approach to cope with the impactor shape in ballistic limit assessment of Whipple shields is presented. A ballistic limit equation (BLE) for impacts of ellipsoid-shaped projectiles on Whipple Shields was derived from existing and thoroughly verified BLEs which were originally developed to yield the critical projectile diameter of spherical projectiles impacting on aluminium Whipple shields. The derived equation was validated by hypervelocity impact tests and numerical simulations. The Whipple Shields had a bumper thickness of 1.0 mm and backwall thicknesses of 3.0 mm and 4.0 mm, respectively, placed at a stand-off of 200 mm and 150 mm, respectively, from the bumper. The total number of impact tests on Whipple Shields performed was 39, covering shape factors of around 0.4, 1.0, and 1.53. Projectile masses amounted to between 0.18 g and 0.32 g. Impact velocities ranged between 0.85 km/s and 6.76 km/s. The numerical simulations of hypervelocity impacts on Whipple Shields with spherical and prolate shaped projectiles (f=1.53) covered the velocity range up to 13 km/s which is not accessible to experimental testing. 8 numerical simulation runs were performed. The BLE can be used to predict the critical projectile mass for a given projectile shape for normal and unyawed impact on aluminium Whipple Shields as a function of impact velocity.