Hypervelocity impact tests on a Whipple shield using a flyer plate in the velocity range from 4 km/s to 12 km/s

Abstract

A Mylar flyer plate, being launched by an electric gun, has been applied to explore the ballistic performance of a 2024 alloy Whipple shield consisting of a 1.0-mm-thick bumper and a 3.2-mm-thick rear wall with a standoff of 70 mm between them. In comparison with a spherical projectile, experimental results show that the polymer plate, having about one-fourth mass of an aluminum sphere, can penetrate the same Whipple at impact velocities of 3 km/s and 5 km/s. The ballistic limit curves (BLCs) of the Whipple are obtained in the velocity range from 3 km/s to 12 km/s using 0.25-mm-thick and 0.5-mm-thick Mylar flyers at normal and/or oblique impacts. Different from spherical projectile, the BLCs obtained by a flyer plate oscillate abruptly with impact velocity. The development of the BLC depends on both the spreading feature of the fragmented bumper sheet and the kinetic energy it carries. In normal impact condition, the BLC turns to go upward at the flyer/bumper shock pressures of 41 GPa, 71 GPa and 121 GPa, exactly corresponding to the occurrence of melting in bumper materials under the interactions among rebounded stress pulses, under the first releasing wave propagating through shock-compressed state, and under direct shock compression, respectively. Among the three melting mechanisms, the shock-induced melting produces the most widely spread debris cloud with the finest fragments.