The following discussion concerns modelling of fracture in steel plates during an impact test, in which both target and striker are manufactured from the same material, high-strength high-hardness armour steel – Mars® 300. The test conditions (3 mm thick targets, projectiles with different nose shapes at impact velocity lower than 400 m/s) result in severely damaged components, which results in an analysis of stress states showing material failure. Numerical analyses are performed using two material models: the Johnson-Cook approach, as traditionally used in impact simulations, accounting for the effect of stress triaxiality, strain rate and temperature and for comparison, a simulation by means of the stress triaxiality and Lode angle parameter-dependent Hosford-Coulomb model, also incorporating the effect of the strain rate on a fracture initiation. The aim of the study is to analyse the mechanisms of penetration and perforation observed in the armour steel plates and validation of the modelling approaches.

The aim of the paper is to formulate physically well founded yield condition for initially anisotropic solids revealing the asymmetry of elastic range. The initial anisotropy occurs in material primarily due to thermo-mechanical pre-processing and plastic deformation during the manufacturing processes. Therefore, materials in the “as-received” state become usually anisotropic. After short account of the known limit criteria for anisotropic solids and discussion of mathematical preliminaries the energy-based criterion for orthotropic materials was formulated and confronted with experimental data and numerical predictions of other theories. Finally, possible simplifications are discussed and certain model of isotropic material with yield condition accounting for a correction of shear strength due to initial anisotropy is presented. The experimental verification is provided and the comparison with existing approach based on the transformed-tensor method is discussed.