Numerical study on crack propagation in high velocity perforation

Perforation response of a target under high velocity projectile impact is controlled by a number of factors such as the thickness of a target, the mass and geometrical shape of a projectile, etc. In this paper, through-thickness crack propagation in perforation problems is studied numerically on the basis of a newly constructed fracture locus formulated in terms of the effective plastic strain and the stress triaxiality. Through a series of numerical simulations using ABAQUS/Explicit, an expression relating crack length to indentation depth is developed. This expression is very general and applicable to both a beam and a circular plate over a wide range of the impact velocity, the mass ratio, and the thickness, provided that the target fails by shear plugging. It is found that the critical indentation depth for the formation and ejection of a plug is about 20-30% of the target thickness for 2024-T351 aluminum alloy, which can be used as an elementary fracture criterion. The average crack tip speed was found to be of order of 1000 m/s, which is one-third of the elastic shear wave speed of 2024-T351 aluminum alloy.