Micro- and Macro-Mechanical Testing of Transparent MgAl$_{2}$O$_{4}$ Spinel

The mechanical properties and reliability aspects of advanced transparent fineandcoarse-grained MgAl$_{2}$O$_[4}$ spinel have been characterized at ambient and hightemperature. The studies were based on a combination of micro- and macro-mechanicalmethods to assess Young’s modulus, hardness, fracture toughness, strength and crackgrowth kinetics. The results and reliability aspects are discussed in terms of linear elasticfracture mechanics. Strength was analyzed using two- and three-parameter Weibullstatistics. The experimental limits of Young’s modulus determination using standard ringon-ring testing are highlighted, and an approach is outlined to correct the measuredapparent values. Experimentally obtained strength data as a function of loading rate areused to assess the potential effect of subcritical crack growth, yielding the failure timeunder static loading, via a strength/probability/time plot for a lifetime prediction.Furthermore, the Brinell indentation showed potential for local strength measurement and the data supported a strength-loaded area relationship that was based on the ring-on-ringtest data. Novel experimental methods were implemented for fracture determination andstrain detection. Particular attention was directed to the effect of defects and associatedlocal strain fields, as assessed using polarized light in photoelastic measurements. Complementary fractography by optical, confocal and scanning electron microscopy provided a correlation between failure initiating defect size and fracture stress