Self-calibration of fractional fringe order lines obtained in photoelastic frozen-stress slices by controlled density techniques

Abstract

Controlled density techniques for the photographic evaluation of fractional fringe orders in isochromatic patterns of two-dimensional models or of slices from stress-frozen three-dimensional models normally require calibration by separate models or slices. Where these are not available, certain self-calibrating methods may yield comparative results such as stress concentration factors. The paper describes three purely graphical methods and a method requiring conventional compensation for only a single point or along a single line in the isochromatic pattern of the model or slice in the polariscope. Examples of application and practical indications are given. The methods described can be applied to a large variety of techniques based on observation of periodic phenomena by optical interference methods.