Calculation of residual stresses in shaped sapphire single crystals from conoscopic measurement data

The paper deals with the measurement of residual stresses formed in shaped sapphire single crystals grown from the melt. The algorithm for calculating the normal components of the residual stress tensor from the optical conoscopic measurement data is developed for optically uniaxial crystals in the shape of wafers. Examples of measurement of residual stresses and calculation of the normal components are given for a square rod and a basal-faceted sapphire ribbon. It is shown that normal stresses are mainly concentrated in the periphery of wafers and reach 25 MPa in the rod and 70 MPa in the ribbon.