Assessment of the protective properties of two different UHA steels based on material testing and numerical simulation

The present contribution aims to assess the properties of ultra-high-hardness (UHA) armor steels. Characteristic of those steels are yield and tensile strengths reaching 1.6 and 2.0 GPa, respectively, and a hardness of around 600 Brinell or above. Accordingly, they are promising candidates for protective solutions. However, UHA steels are relatively new products and not yet frequently applied. Their potential for armor protection is not fully explored today and has to be investigated further. Ballistic testing of the protective properties of UHA steels is however limited by the commercially available material thicknesses. In the context of present applications, the available sheet thickness for UHA steel is typically below 15 mm, thus ballistic tests for some threat levels are possible only under overmatch conditions where failure mechanisms under shear and low confinement play strong roles. In order to be able to analyze the deep penetration into UHA materials - whether thick plates are today producible or not - we chose an approach based on material characterization and numerical simulation. Two different UHA steels were compared against a reference material from the high-hardness-armor (HHA) steel class. One of the UHA steels was a quenched and tempered steel, while the other was a maraging steel. Based on material testing, parameters for a non-linear equation of state, the Johnson-Cook plasticity model, as well as failure criteria for strain accumulation and wave induced spall rupture were derived and applied in hydrocode simulations of the perforation of thick steel plates by projectiles. From this numerical analysis, a consistent picture emerged. According to the simulations, the protective properties of the UHA steels are increased for thick targets compared to HHA, which was not directly inferable from ballistic tests.