Propagation of failure front in shock-loaded polycrystalline alumina

The experimental measurement and theoretical analysis were conducted to study dynamic failure behaviors of brittle alumina under shock loadings. Plate impact experiments were carried out on alumina, where the free surface velocity profiles were measured through VISAR and the recovered samples were scanned with SEM. The SEM observation shows that the principal factor controlling the inelastic deformation and failure process is the mesoscopic configuration of ceramics. With the particle free surface velocity history in alumina ceramics under shock-loadings compared with that in glass, the recompression signals in alumina may be obtained, which are similar to those in glass where failure waves have been widely verified. It is shown that the recompression signal appears in advance of the compressive shock unloading whether in alumina or glass. The failure front propagates in the material when the particle velocity history at free surface is checked. Dynamic failure properties of the failure front in alumina are discussed. A dynamic failure model of shock-loaded alumina and the governing equation of failure front propagation along with a respective failure criterion are obtained. Numerical results on the propagation of failure front in terms of longitudinal and transverse stresses in alumina are presented.