Measurement of residual stresses around Vickers indentations in a ruby crystal using a Raman luminescence microscope

A Raman luminescence microscope has been used to determine the residual stresses around Vickers diamond indentations in a relatively large, well-polished, R-cut (10 (1) over bar2) ruby single crystal. The principle of the method is based on the fact that the frequencies of the luminescence R lines of the ruby shift in a systematic manner with applied stress. It is shown that the hydrostatic component of the residual stress around a 25 N Vickers indentation can be as high as about 2 GPa, and that its magnitude decreases as A/r(3), where r is the distance from the centre of indentation and A is a constant. These measurements are shown to be in qualitative agreement with the predictions of the current analytical models, although the magnitudes of the measured residual stresses are an order of magnitude smaller than those predicted by theory. Possible reasons for these differences are discussed.