MODELING INTERFACE DEFEAT AND DWELL IN LONG ROD PENETRATION INTO CERAMIC TARGETS

When a long rod projectile hits a ceramic target, the projectile may sometimes dwell at the target boundary and flow radially. This dwell or interface defeat phenomenon has to do with the dynamic failure process of the ceramic target material. As ceramics are brittle materials, what is needed to model dwell, is a realistic model for dynamic failure of brittle materials. A "standard" such model is the so called JH model (which has several versions). According to JH the material accumulates damage as a function of the effective plastic strain, which is a ductile response feature. Brittle materials are not supposed to accumulate plastic strain before they're fully failed. To model dwell we therefore propose here a different failure model. We call it BSF (= Brittle Shear Failure), and it is based on the Overstress (or overload) principle. Our BSF model is rather simple, has a small number of adjustable parameters, and is readily calibrated. We implement the model in a hydro-code and demonstrate how it works for a typical example of dwell situation. In the example, a long steel rod impacts an AD995 alumina target with and without a copper buffer.