Alumina strength degradation in the elastic regime

Measurements of Kanel et. al. [1991] have suggested that deviatoric stresses in glasses shocked to nearly the Hugoniot Elastic limit (HEL) relax over a time span of microseconds after initial loading. Failure (damage) waves have been inferred on the basis of these measurements using time-resolved manganin normal and transverse stress gauges. Additional experiments on glass by other researchers, using time-resolved gauges, high-speed photography and spall strength determinations have also lead to the same conclusions. In the present study the authors have conducted transmitted-wave experiments on high-quality Coors AD995 alumina shocked to roughly 5 and 7 GPa (just below or at the HEL). The material is subsequently reshocked to just above its elastic limit. Results of these experiments do show some evidence of strength degradation in the elastic regime.