A debris cloud model for hypervelocity impact of the spherical projectile on reactive material bumper composed of polytetrafluoroethylene and aluminum

In this paper, a debris cloud model is presented for the case of hypervelocity impact of the spherical projectile on the thin PTFE (polytetrafluoroethylene)/Al (aluminum) reactive material bumper at normal incidence. The experiments of projectiles with hypervelocity impact on Whipple shields with PTFE/Al and Al2024 as bumper respectively were carried out by using two-stage light-gas gun, and the movement process of debris cloud was recorded through laser shadow photography system. According to the numerical simulation results and the laser shadow photographs of debris cloud obtained from the experiment of hypervelocity impact, two parts named as internal and external debris cloud are considered in the theoretical model. Several assumptions are made, and the theoretical model of debris cloud is developed by the conservation laws of mass, momentum and energy. Four characteristic velocities of the debris cloud are first calculated, and thus the whole evolution process of the debris cloud is plotted according to those velocities. By comparing the size of the debris cloud shown in the experiment, it can be concluded that the theoretical model agrees well with the experimental results. Moreover, the characteristic velocities of projectile fragments and bumper fragments in the debris cloud are calculated, and the mass areal density and momentum areal density distribution of the debris cloud on the rear wall are also obtained. Additionally, the effects of the detonation reaction of the reactive material bumper on the projectile during the impact are analyzed in contrast with the results on the Al2024 bumper. It is indicated that the detonation reaction of PTFE/Al can reduce the velocity of center of mass of debris cloud and increase the expansion velocity of debris cloud. PTFE/Al bumper can reduce damage caused by debris cloud to rear wall.