Shielding performances of a Whipple shield enhanced by Al/Mg impedance-graded materials

Abstract

It is believed that the gradient material bumper shows some positive for shielding performance of Whipple shield. The purpose of this paper is to study the hypervelocity impact characteristic of an new Al/Mg impedance-graded materials (area density is equivalent to 1.5 mm thick aluminum alloy) enhanced Whipple shield at 5.0 km/s, and to investigate the main factors in performance improvement, except higher shock pressures and temperature rise in the projectiles caused by the high-acoustic-impedance coating of bumpers. The hypervelocity impact performances of a shield enhanced by Al/Mg impedance-graded materials and an aluminum Whipple shield are investigated experimentally, using a two-stage light gas gun at velocities of 5.0 km/s. The characteristics of perforation on bumper, debris clouds and damage patterns on the rear wall have been studied. The characteristics of the shielding performance produced by Al/Mg shields include four major features: petal-shaped curling in bumper, slight damage of the rear wall, wider expanded area of debris cloud and smaller impact craters. Some theoretical analysis and calculations are performed. Coupling process of shock energy and thermodynamic states are calculated, and wave propagation in the projectile and bumper is discussed. It is found that the shockwave propagation is affected by the shock impedance mismatch in various area density impedance-graded materials bumpers, it can break the projectile into smaller parts and increase the internal energy conversion in the bumpers. It plays an important role in contributing to kinetic energy attenuation. Thus, the preliminary results show that the shielding capability of an Al/Mg shield is greater than that of an aluminum Whipple shield where the bumper has the same areal density.