Failure above and below the elastic limit in AD995

There is an ongoing interest in identifying inexpensive armour materials for use in protection of personnel and vehicles. The response of AD995 under shock loading is one of the materials most extensively investigated. Over recent years, workers have reported failure occurring in various polycrystalline ceramics behind the shock front. This phenomenon has been investigated using embedded stress sensors and a recovery technique that has allowed observation of the microstructure above and below the HEL and these results are brought together here to explain the observed behaviour. The failure front velocity is found to change with the applied stress, in particular it slows markedly as the HEL is exceeded. The evidence in the microstructure shows the response below HEL is dominated by intergranular failure whilst above HEL the response dominated by plasticity in grains (including twinning), which alters failure characteristics.