Stress Measurements in Alumina by Optical Fluorescence: Revisited

Stress measurements in single-crystal and polycrystalline alumina are revisited using a recently developed optical fluorescence energy shift method. The method simultaneously utilizes the R₁ and R₂ Cr-related ruby line shifts in alumina to determine two components of the stress tensor in crystallographic coordinates, independent of the intended or assumed stress state. Measurements from a range of experimental conditions, including high-pressure, shock, quasi-static, and bulk polycrystals containing thermal expansion anisotropy effects, are analyzed. In many cases, the new analysis suggests stress states and stress magnitudes significantly different from those inferred previously, particularly for shock experiments. An implication is that atomistic models relating stress state to fluorescence shift require significant refinement for use in materials-based residual stress distribution analyses. Conversely, the earliest measurements of fluorescence in polycrystalline alumina are shown to be consistent with recent detailed measurements of stress equilibrium and dispersion.