High temperature impact response of 998 alumina

The dynamic compressive strength (amplitude of the elastic precursor wave) of alumina of 99.8% purity has been studied in a series of planar impact experiments with the 0.25 to 3-mm thick alumina samples, preheated to 1300 K. The dependence of the dynamic tensile (spall) strength of alumina on the ultimate compressive strength was studied with 2-mm thick samples at 300 and 1300 K. The compressive strength of alumina was found to decline by some 30%-35% between 300 and 1300 K, while the absolute values of the spall strength and its dependence on the peak stress were found to stay almost unchanged between 300 and 1300 K. Over the studied temperature interval, the elastic precursor waves in alumina decayed with propagation distance with the decay parameters almost independent of temperature. The availability of decay parameters made it possible to determine the strain rate function τ (γ , T) of alumina and to derive some conclusions regarding the onset of inelastic deformation in this ceramic.