Dynamic Compressive Failure of Alumina under High-Velocity Impact

摘要

Failure modes in ceramics range from brittle to ductile depending on the deformation conditions. The micro-mechanisms of their compression failure have been examined over a wide range of deformation rates from quasi-static to ballistic strain rates. Data on damage initiation and evolution in ceramic armor materials are used to decipher the essential features of failure phenomena. Under moderate confining pressures and at moderate deformation rates, brittle failure involves initiation of micro-cracks at dominant micro-flaws and pre-existing micro-cracks, and their subsequent interactive growth, leading to axial splitting, faulting or a mixture of brittle-ductile failure. Under great confining pressures, common in ballistic impact, ceramics pulverize into fine powder. Classical crack-growth models seem inadequate for representing the actual failure initiation and evolution. Transmission electron microscopy of recovered Al_2O_3 powder of impact-penetrated ceramics shows extensive twinning with sub-micron spacing. Dynamic compression of ceramics has also shown extensive dislocation activities. These observations have further improved the understanding of potential mechanisms of pulverization of ceramics under extreme compression.