Whole-field digital measurement of principal stress directions in photoelasticity

A method that uses three light-field isoclinic images and the associated light-field unloaded model (or white) images for whole-field digital determination of the principal stress directions in photoelasticity is presented. Relevant theory is derived and explicit conditions for directly determining the directions to the range 0–π/2 are given. Tests of this method on a directly loaded two-dimensional disc and a stress frozen photoelastic slice are demonstrated. The results agree well with the values obtained from the manual method and/or the theory.