Failure of a steel spherical projectile upon impact on high-porous sheets

The failure of a 2-mm-diameter steel projectile at normal impact with a velocity of 1.5-7.3 km/sec on bumpers 1 mm thick was studied. Two types of bumpers were used: solid sheets of Duralumin and high-porous bumpers of a copper powder. The depth of the largest crater and the positions, areas, and equivalent diameters of all craters were measured on the witness plate. Values of the threshold impact velocities for the beginning of failure of the steel projectile and distributions of the number of craters in size and radius from the impact point were obtained for various impact velocities. It is shown that at identical impact pressures near the failure threshold, the low-density high-porous sheets break tip the steel projectile better than the Duralumin bumpers. This is possibly caused by the thermal explosion of the bumper material in the impact region, which increases the time of interaction of the projectile with the bumper.