On impact upon brittle solids

The response of brittle materials to uniaxial compressive shock-loading has been the subject of much recent discussion. The physical interpretation of the yield point of brittle materials, the Hugoniot elastic limit (HEL), the rate-dependence of this threshold, and the effect of polycrystalline microstructure still remain to be comprehensively explained. Evidence of failure occurring in glasses behind a travelling boundary that follows a shock front has been accumulated and verified in several laboratories. Such a boundary has been called a failure wave. The variations in properties across this front include complete loss of tensile strength, partial loss of shear strength, reduction in acoustic impedance, lowered sound speed and opacity to light. Recently we have reported a similar behaviour in gabbro and the polycrystalline ceramics SiC, alumina and titanium diboride. It is the object of this work to present further observations of these phenomena and their relation to ballistic performance.