The influence of microstructure on the static and dynamic strength of transparent Magnesium Aluminate Spinel (MgAl2O4)

The dynamic flexural strength of transparent ceramics is an important property for demanding applications. Therefore, this work reports a systematic study of the grain size influence on the dynamic and static flexural strength of Magnesium Aluminate Spinel (MgAl2O4), utilizing a modified split Hopkinson (Kolsky) apparatus. An ultra-high-speed camera (8 × 106 frames/sec), was extensively used and provided precious insight of the dynamic crack initiation and propagation. It was found that fine microstructure Spinel exhibits slightly higher static flexural strength than coarser microstructure. However, in the dynamic regime, no significant difference was found. Moreover, the fracture timing method, i.e. fracture gauge or high-speed camera, influences significantly the dynamic strength results. While the fracture gauges indicate complete fracture, the high-speed camera captures the onset of the fracture as a true material property. Consequently, Spinel's dynamic flexural strength is not rate sensitive, based on high-speed imaging.