Strain-rate-dependent dynamic compression-shear response of alumina

This research article investigated the stress-state and strain-rate-dependent mechanical properties and failure of alumina ceramic. Compression-shear testing was carried out using a split-Hopkinson pressure bar under equivalent strain rates ranging from 101 s-1 to 103 s-1. Ultra-high-speed images coupled with digital image correlation were used to investigate the in situ time-evolving strain field and the failure process (e.g., crack growth). Experimental results showed equivalent strength reduced from 4.27 +/- 0.23 GPa for the uniaxial compression tests to 3.75 GPa and 2.00 GPa for compression-shear tests across the strain rates and shear angles (5 degrees to 25 degrees), with the strength decreasing with an increasing shear angle. The crack speed ranged from 908 m/s to 3208 m/s across the range of strain rates and shear angles, with a positive correlation noted for crack speeds with strain rate and increasing sensitivity with an increasing shear angle. The extent of localization of shear strain in alumina under compression-shear deformation was observed to be strain-rate-dependent, and it increased with an increasing strain rate of deformation. Furthermore, axial and shear strain localization increased with the increasing shear angle, contributing to local shear failure before the complete failure of the specimen. Overall, this paper provides new insights and measurements of the strain-rate-dependent and shear-dependent strength and crack speeds of alumina under compression-shear loading, and these serve as vital inputs for future computational model development and validation.