Low strain rate compressive failure mechanism of coarse grain alumina

The present work reports the dynamic compressive strength (σc) of a dense (~95%) coarse grain (~20 μm) alumina measured at ~30 °C as a function of strain rates (ε)̇ ranging from 10−5 to 5×10−1 s−1. The results showed a unique 40% enhancement of (σc) with the increase in (ε)̇. Extensive post mortem examination of fracture fragments obtained from the compressive failure tests by FESEM, TEM and HRTEM confirmed the formation of micro-cracks, shear bands, nanoscale cleavages and dislocations whose recurrence had increased with strain rate. Both shear induced microplasticity and nanoscale cleavages as well as dislocations had occurred concurrently yet independently during compressive fracture of coarse grain alumina even at very low strain rates. Based on these evidences a new compressive failure mechanism of alumina was proposed.