Acceleration of the plates of an ERA cassette using a rigid plastic Gurney model

Abstract
An Explosive Reactive Annor (ERA) cassette is a sandwich of an explosive layer between two steel plates. To assess the performance of an ERA cassette against a shaped charge metal jet, we need to estimate the velocity and shape of the moving plates interacting with the jet. This is usually done with the classical Gurney model or by computer simulation. The Gurney model assumes that the accelerated plates are rigid, and is able to predict their final velocity quite accurately. But tests and computer simulations show that because of their plasticity, the plates become curved as they accelerate. In this paper we revisit Gurney's derivation and extend it to include the plasticity of the plates. We assume that the plates are rigid-plastic and we model the symmetric case as well as the asymmetric case. To check the model we perform computer simulations with AUTODYN for the same two problems. We find a fair agreement between the model predictions and the computer simulation results.