Fracture of high-strength armor steel under impact loading

- Material and impact properties of a high-strength and high-hardness armour steel (Mars®300) are discussed.
- The dependence between impact positions and fracture of perforated plates is proven experimentally and numerically.
- The proposed plasticity and fracture model are validated proving their applicability in numerical simulations of impact events.
- Complexity of impact conditions and their influence on the steel fracture is presented.

Mars® 300 is an ultrahigh hard armor (UHHA) martensitic steel designed for ballistic protection. It is available in sheets of different thicknesses and also as perforated plates with a periodic pattern of cylindrical holes. Installed as an add-on layer in front of a main armor, its aim is to cause deflection or fragmentation of small-caliber projectiles. In the present study, the impact process is investigated with a hybrid experimental-numerical approach. Ductile fracture experiments are carried out at different stress states, strain rates and temperatures on a range of flat Mars® 300 steel specimens to identify the plasticity and fracture response. The plasticity model is composed of von Mises yield surface, a non-associated anisotropic flow rule, a combined Swift-Voce strain hardening law and a Johnson-Cook type of rate and temperature-dependency. To predict the onset of fracture, a stress state and strain rate-dependent Hosford-Coulomb fracture initiation model is used. Impact experiments are performed on targets of homogenous and perforated Mars® 300 plates by accelerating cylindrical Mars® 300 projectiles in a single-stage gas gun. Depending on the impact location, three different failure mechanisms are identified for the perforated plate. Subsequently, finite element simulations using the calibrated material model are carried out to thoroughly analyze the impact experiments. A very good prediction of the different impact cases and their fracture patterns is obtained, validating the applicability of the plasticity and the fracture model for impact loadings.