Influence of the impedance gradient on the debris cloud produced by hypervelocity impact

The protective performance of a Whipple shield to hypervelocity impact could be improved by using an impedance-graded plate. Transmission and reflection of the shock wave on the impedance interface affect the pressure state in the projectile and its fragmentation, and further change the characteristics of the debris cloud. Models of the shock waves and reflection waves in the materials were built in this paper, which describes the geometric characteristics and the pressure states of wave fronts in the impedance-gradient-plate impact. The models predicted theoretically that a smaller central fragment with a series of larger circumferential fragments would be produced by high/low impedance-graded plate. Based on the models, various front plate combinations of aluminum, magnesium and steel (Al/Mg, Al, Mg/Al, Al/steel) were analyzed experimentally and numerically. The pulse attenuation, material spalling, debris cloud characteristics and witness plate damage were analyzed. The results show that the impedance-gradient structure would eventually change the debris cloud characteristics and witness plate damage, and affect the performance of the shield. The plate of Al/Mg (high/low impedance) has a better performance than that of Al, Mg/Al (low/high impedance) and Al/steel (low/high impedance) with the same areal density. The discussion and analysis are also suitable to impedance-gradient plates made up with other materials.