Failure zones in polycrystalline aluminas

We have recently demonstrated that glasses show damage after the arrival of a plane, compressive shock wave. The failure travels, in this case, at a uniform velocity, increasing at higher stresses. The purpose of this paper is to show that a range of polycrystalline aluminas also show failure in a similar manner to glasses. The difference is that the wave in aluminas is slowed and eventually stopped leaving a surface failed zone, whereas the process continues in glasses without reducing speed. These surface failure zones have a marked effect. One of the consequences is that the Hugoniot elastic limit for these materials may have to be taken at a higher point in the stress history than is conventional. A second is that speculation about decays with distance of elastic precursors may refer to the stress at which the failure zone is formed rather than to the stress at which yielding takes place.