Improvements in Photoelastic Technique Obtained by the Use of a Photometric Method

Abstract

A photoelectric photometer has been adapted for use in photoelasticity. The sensitivity of the instrument is such that a photoelastic stress pattern can be measured to within ± 1/500 fringe. The resultant improvements in technique are; (1) the use of materials having less susceptibility to edge effects than those generally used, but with too low a stress-optical coefficient for examination by normal methods; (2) the use of lower stresses which should be of particular advantage in three-dimensional stress analysis by the frozen stress method, where lower stresses would reduce the strains which are often excessive in this method; and (3) greater ease in tracing isoclinics because the photometer enables a distinction to be made between isoclinics and isochromatics. The apparatus is described, examples of its use are given and factors limiting its accuracy are discussed.