Dynamically propagating shear bands in impact-loaded prenotched plates—II. Numerical simulations

Abstract

The experimental observations of dynamic failure in the form of propagating shear bands and of the transition in failure mode presented in Part I of this investigation is analyzed. Finite element simulations are carried out for the initiation and propagation of shear-dominated failure in prenotched plates subjected to asymmetric impact loading. Coupled thermomechanical simulations are carried out under the assumption of plane strain. The simulations take into account finite deformations, inertia, heat conduction, thermal softening, strain hardening and strain-rate hardening. The propagation of shear bands is assumed to be governed by a critical plastic strain criterion. The results demonstrate a strong dependence of band propagation speed on impact velocity, in accordance with experimental observations. The calculations reveal an active plastic zone in front of the tip of the propagating shear bands. The size of this zone and the level of the shear stresses inside it do not change significantly with the impact velocity or the speed of shear band propagation. Shear stresses are uniform inside this zone except near the band tip where higher rates of strain prevail. The shear band behind the propagating tip exhibits highly localized deformations and intense heating. Temperature rises are relatively small in the active plastic zone compared with those inside the well-developed shear band behind the propagating tip. The calculations also show shear band speeds and temperature rises that are in good agreement with experimental observations. Computed temperature fields confirm the experimental observation that dissipation continues behind the propagating shear band tip. In addition, the numerical results capture the arrest of the shear band. The arrested shear band is first subjected to reverse shear. Subsequently, the arrested band is subjected to mixed-mode loading which eventually leads to tensile failure at an angle about 30 ° to the band.