Experimental and Numerical Study on Ballistic Testing and Failure Mechanism of Ultra-High Hard and Rolled Homogeneous Armor Steels

<div>The escalating weight of main battle tanks (MBTs) has compelled designers to innovate with Ultra-high hard armor (UHA) steel against the current generation rolled homogenous armor (RHA). This study delves into investigating the experimental and numerical ballistic performance of 15 mm–thick UHA steel and 15 mm–thick RHA steel against a 7.62 mm armor-piercing (AP) small-arm projectile. Finite element (FE) simulations were executed using ANSYS software, incorporating the Johnsons Cook model and shock Rankine–Hugoniot equations. The outcomes highlight that the UHA steel arrests the projectile’s advancement at a depth of penetration (DoP) of 3 mm, where the mode of failure is projectile break-up with cleavage failure. Conversely, the RHA base metal demonstrates perforation accompanied by ductile hole growth as the mode of failure. This perforation is attributed to plastic deformation and material extrusion, aligning well with the FE model. In the second scenario, the ballistic limit of a 7.62 mm AP projectile on RHA plate is explored by increasing the plate thickness to 18 mm. At this thickness, the projectile comes to a halt, creating a smooth bulge. Notably, UHA steels exhibit a projectile break-up mode of failure and an 81.5% reduction in weight compared to RHA steels. An intriguing correlation is identified between hardness and thickness, as elevated hardness and thickness shift the failure mode from ductile hole growth to projectile break-up.</div>