Cavity Dynamics for Long Rod Penetration.

Two analytical models for the crater size due to long rod penetrations are presented. The energy method is the first which, in a steady state penetration, relates the kinetic energy loss of a penetrator to the total energy deposited in the target. An equation of cavity dynamics is set up by assuming a radial motion in the target. This approach appears to provide an upper bound of the crater size due to the neglect of energy losses in the penetrator. The second method is based on the observations that two mechanisms are involved in cavity growth due to long rod penetrators: flow of penetrator erosion products, which exerts radial stress on the target and opens a cavity, and axial inertia of the target as it flows around the penetrator nose. The analysis includes the centrifugal force exerted by the penetrator, radial inertia of the target, and the strength of the target. Thus, the extent of cavity growth due to penetrator mushrooming, which cannot be predicted by other analyses, can be estimated. The analytical models are compared with existing formulas and empirical equations and found to be more accurate than other analyses in the literature. Numerical calculations using AUTODYN-2D are also conducted and these confirm the phenomenological assumptions in the models.