Hydrodynamic theory of glancing impact

Abstract

Penetration of high-speed targets, such as missiles or satellites, involves a glancing impact resulting from the velocities of the target and the projectile not necessarily being parallel to one another. Glancing is different from oblique impact in that here the target is in lateral motion relative to the projectile (at speeds that may be comparable).The effect of the transverse motion of the target on the penetration performance is analysed by means of a hydrodynamic model. As is usually done, both the projectile and target materials are taken to behave as ideal fluids, owing to the large stresses obtained upon impact. A complete description of the flow field is obtained for the planar case, making use of a transformation to the hodograph plane. Owing to the lack of symmetry, the solution is obtained indirectly from the known solution for asymmetrically impinging jets, obtaining a determinate solution by a limit process where the jet representing the target fluid becomes infinitely wide.The variations of the rate of penetration and the streamline pattern with the respective ratios of target to projectile speeds and densities are studied. It is found that the relative lateral motion of the target causes a decrease in the rate of penetration (in comparison to normal impact). The analysis is utilized to obtain an estimate for the total depth of penetration (relative to the projectile width). Comparison with experimental data of yawed impact available in the open literature shows good agreement with the theoretical predictions when the latter are modified to account for the deceleration of a finite-length projectile.