Projectile nose-length effect on specific cavitation energy and ballistic limit velocity and thickness

The perforation of armour plates by quasi-rigid projectiles in ductile hole growth has been demonstrated to be influenced by the ratio of plate thickness to projectile diameter, referred to as the hole slenderness ratio, $h/D$. Here we propose a new non-dimensional geometric ratio, termed as the target containment ratio, that uses the projectile nose-length in place of the diameter, i.e., $h/L$. We demonstrate that the hole slenderness ratio is a special approximation of the target containment ratio for projectiles with a nose-shape ratio (projectile nose-length normalised by projectile shank radius) on the order of 3. We validate the proposed relationship via a comprehensive numerical study and through comparison with experimental data for the 14.5 mm BS41 armour piercing bullet, for which the nose-shape ratio is about 2. We show that the new target containment ratio dependent formulation of the specific cavitation energy improves the accuracy of the model suggested in Masri and Ryan (2024). This new formulation is also used to update existing formulae for ballistic limit predictions of monolithic and multilayer ductile targets.