Delayed failure in shocked silicon carbide

Plate impact and split Hopkinson pressure bar (SHPB) experiments have been conducted on three grades of silicon carbide produced by different routes. Data are presented which indicate that the failure of the materials was delayed for some time after the maximum stress had been achieved, In particular, the measured lateral component of the stress in plate impact was found to increase across a front which traveled behind the shock. This phenomenon is akin to the failure wave which has been observed to occur in glasses but has not previously been reported in polycrystalline materials. Hopkinson bar experiments have revealed significant differences in the behaviors between the three materials. These may be related to the effects observed in the plate impact experiments. These results explain the anomalous ballistic phenomena that have been reported for the penetration behavior of SiC. Additionally the Hugoniot elastic limit (HEL) and shear strength were found to vary with the production route used. (C) 1997 American Institute of Physics.