Photoelastic Observation an Stress Distribution in Single Crystals of Alumina

Abstract

Residual stress of the synthetic white sapphire cut perpendicular to the optic axis was observed photoelastically, and magnitude of stress was shown by retardation per unit path of light. Stress distribution in a single crystal was estimated from the distribution of the retardation.It was found that crystals splitted into two parts after growth had complex stress distribution in which tensile and compressive stresses lay alternately. Maximum retardation in the splitted crystals was 1200mμ/cm. The retardation could be decreased below 400mμ/cm by holding the crystals at 1900°-1950°C for several hours and then slowly cooling.On the other hand, the stress distribution in single crystal boules was simpler than that in splitted crystals. In boules, maximum stress lay in the plane that was determined by the growth axis and the crystallographic axis c, and the direction of tensile stress was perpendicular to that plane while that of compressive stress was parallel.The complex stress distribution in splitted crystals was explained on the assumption that bending moment which lay in the splitted parts, was released by the splitting and the splitted plane turned into convex.