Transition of failure modes in round-nosed mass-to-beam impact

The deformation and failure response of a long metal beam impacted by a rigid, round-nosed projectile is investigated numerically using a newly developed ductile fracture locus. Attention is focused on the transition of failure modes from the tensile dominated to shear dominated mechanism with increasing impact velocities. Effects of material ductility are highlighted by introducing two metals: 2024-T351 aluminum alloy and Weldox 460 E steel, which represent a less and a more ductile material, respectively. It is revealed that tensile tearing is a favorable failure mode for both materials at a velocity near the ballistic limit. The steel beam tends to break by tensile tearing while the aluminum beam fails by shear plugging at an impact velocity well above the ballistic limit. The energy dissipated in the target increases with the impact velocity, reaches a maximum value at or near the ballistic limit, and suddenly decreases just beyond the ballistic limit. The numerical findings are consistent with experimental observations given in the literature. The present paper provides an insight into the mechanics and mechanisms of ductile fracture in rigid mass impact on beam. At the same time, it is clearly demonstrated that the new fracture criterion is capable of capturing crack formation and distinct failure modes.