Analysis of failure modes in impulsively loaded pre-notched steel plates

We analyze transient plane strain thermomechanical deformations of a pre-notched 4340 steel plate impacted by a 4340 steel projectile in the direction of two parallel notches, and study the influence of the impact speed and notch tip radius on the localization of the deformation. The plate configuration is identical to that in Kalthoffs experiments (1987, 1988). There is no failure or fracture criterion included in our work. However, the computed evolution of stress and plastic strain fields strongly suggest that with an increase of impact speed and decrease in notch tip radius, there is a failure mode transition from a tensile crack opening al approximately 70 degrees to the notch ligament to an adiabatic shear band propagating at -5 degrees to -15 degrees to the notch ligament. This is in qualitative agreement with Kalthoffs findings. (C) 1997 Elsevier Science Ltd.