Modeling the Dynamic Load/Unload Behavior of Ceramics under Impact Loading

Abstract : The RDA ceramic failure model was used to model the behavior SiC and B4C during plate impact loading. The experiments modeled were performed at Sandia National Laboratory. The simulations were performed with a version of the Sandia WONDY-V hydrocode that was modified to run on a PC and to include the RDA ceramic failure model. The model adequately characterizes the two ceramic materials although B4C and SiC exhibit distinctly different degrees of work hardening, strain rate hardening, and damage sensitivity. Both materials experienced damaged (micro-making) on load which was predicated by the model. The experimental unloading data exhibits a reduced magnitude elastic unload wave which suggests that further damage has accumulated after the ceramic reaches peak stress. A strength reducing mechanism such as fatigue, or melting at grain boundaries are suspected as the cause of this unpredicted strength loss. No spall was evident in the measured signals and the model predicts spall will not occur. The predicted axial stress levels were significantly above the estimated spall strengths of the two ceramics. Failure was prevented by positive (compressive) mean stress levels that were maintained throughout the ceramic specimen during the experimental measurement. Therefore, a suggested conclusion is that for tensile failure to occur in these ceramics, the mean stress must be negative (tensile).