Investigation of hole formation by steel sphere impacting on thin plate at hypervelocity

Protective structures against hypervelocity impact of fragments consists of a thin skin (bumper plate) followed by air gap and main structure. The bumper causes shattering of the fragment and reduces fragment penetration capability to the main structure. Hole formed in the bumper plate is indicative of damage extent to the main structure and is a direct measure of exposure to new impacts. An extensive study for characterization of hole in thin aluminium plates due to hypervelocity impacts of aluminium projectiles has been reported in literature. Empirical equations are generally used to estimate the hole size which depends on non-dimensional parameters related to the target and projectile geometry, material and impact conditions, and constants of the equation needs to be determined for a given problem. The authors have investigated the hole formation for steel sphere impacting thin steel target with velocity ranging from 2 to 4 km/s and obliquity between 0° and 70°. The constants for a prototype non-dimensional empirical equation for hole formation have been determined using hydro-code simulation and a few experiments have been conducted to validate the predictions.