ИСТИНА

The objective of this study was to estimate possible contribution of stress relaxation into the response of hard ceramic materials to high-rate compression and tension. With this goal, the free surface velocity histories have been measured for plane samples of reaction bonded SiC ceramic of 3.07 g/cm3 density subjected to impact by a flyer plate. The sample thickness was varied from 0.5 mm up to 8.3 mm. The peak shock stress was in a range of 17.9 to 21.9 GPa. The Hugoniot elastic limit (HEL) is between 8.34 GPa and 8.72 GPa for this material, the spall strength value is 0.5 to 0.62 GPa. Both the HEL and the spall strength are in reasonable agreement with published data for SiC ceramics of corresponding density. Measurements have not revealed any decay of the elastic precursor wave. Moreover, it has been found the evolution of the compression wave is practically self-similar and is well described by the simple wave approach. In other words, the stress relaxation does not provide significant contribution into the response of hard ceramic materials. The ramped transition from elastic to plastic wave is caused by strain hardening of the material and by successive involving of grains of various orientations into the inelastic deformation process.