A new method to increase the sensitivity of photoelasticity

A method is proposed to read the isochromatic-fringe order continuously as a function of position. It utilizes the fact that the fringe order is a continuous function of the light intensity, which is converted into the density of a photographic negative and then traced out either by a microdensitometer or isodensitracer. Explicit relationship between the fringe order and the film density is obtained. Hundreds of points can be read between a half and an adjacent integral order. The method is whole field in nature and offers the possiblity of direct computer processing of photoelastic information.