The interrelation of failure modes observed in the penetration of metallic targets

Abstract

Three of the main modes of failure observed in the penetration of metallic armour are classified as ductile failure, adiabatic shear plugging and discing. It is demonstrated that a change from ductile modes of failure to those which involve adiabatic shearing or discing can be understood in terms of the work done to penetrate a target. Adiabatic shearing is possible if the rate of thermal softening exceeds the rate of work hardening of the target material. In adiabatic shear failure, where several shear bands propagate independently towards the rear of the target, intersection of one band with the rear surface may lead to asymmetry in the deformation. Asymmetric conditions do not favour further propagation of adiabatic shear bands and failure can be completed by discing and/or ductile tearing giving a mixed mode of failure. Discing is accentuated if the target plate shows relatively low toughness particularly in the through thickness orientation. Other studies have shown that the fractures associated with discing may be produced by shearing in the plane of the plate, and it is demonstrated that discing is more likely when fracture occurs on a number of parallel planes.