Investigation of the photo stimulated luminescence spectroscopy technique for measuring 3-D stresses

Photo-stimulated luminescence spectroscopy (PSLS) is an attractive nondestructive tool to measure stresses in a variety of engineering fields. However, due to a lack of phenomenological relations between applied stress and spectral characteristics, the current scope of this technique has been somewhat narrow. This research investigates additional spectral characteristics of Al2O3:Cr3+, like shifts of vibronic sidebands and changes in linewidths of R-lines with applied stress, in order to broaden the applicability of the PSLS method. Results indicate that like R-lines, vibronic sidebands also exhibit piezo behavior. In addition, at room temperature all spectral characteristics were found to vary linearly with uniaxial compressive stress. Based on piezospectroscopic effects of spectral characteristics, a single crystal model has been developed for measuring 3-D stresses in Al2O3:Cr3+ using PSLS technique. Utilizing the characteristic luminescence properties of optical fluorescence lines (R-lines and vibronic sidebands) of Al2O3:Cr 3+, 36 piezospectroscopic coefficients, have been obtained: 18 associated with principal stress directions and 18 associated with principal shear directions. All spectral characteristics demonstrated linear variations with applied stress. However, values of the shear coefficients indicate that the sensitivity of shear stress measurements will be less than that of principal stress measurements. In addition, off axis compression tests were conducted to experimentally verify the single crystal model can predict 3-D stresses. Finally, a polycrystal model has been derived from the single crystal model for predicting 3-D stresses in polycrystalline materials