The ballistic performance of an ultra-high hardness armour steel: An experimental investigation

Abstract

The ballistic performance of an ultra-high hardness armour steel (UHA) has been evaluated for a range of thicknesses and obliquities against armour piercing (AP) and fragment simulating projectiles (FSPs). Together with published literature, these results enable the effect of plate hardness on performance against both AP and FSP threats to be characterized over a range of plate hardnesses from ~ 300 to 600 HB. For AP projectiles, a complex relationship was observed that corresponded well with historical phenomenological curves describing the effect of varying projectile and armour failure mechanisms. In the ultra-high hardness regime (> 570 HB), against AP projectiles with core hardnesses of 610–745 HB (i.e. 7.62 mm APM2 and 12.7 mm APM2 projectiles), projectile shatter was demonstrated to be the controlling mechanism of armour performance. Against much softer FSPs (281 HB), where projectile shatter is not a relevant mechanism, the armour performance was found to initially decrease with increasing plate hardness up to ~ 450 HB due to increased susceptibility to adiabatic shear plugging. Above ~ 450 HB the performance was observed to plateau. The observed performance plateau appears to relate to a critical threshold for adiabatic shear failure beyond which further increases in plate hardness will not result in a decrease in performance. A number of common empirical and analytical models were applied to reproduce the experimentally-determined relationship between hardness and penetration resistance, none of which were able to qualitatively or quantitatively reproduce the observed relationships for either projectile class.