DETERMINATION OF PHOTOELASTIC PARAMETERS WITH TWO-WAVELENGTH AND PHASE SHIFTING METHODS

The application of two-wavelength method and phase shifting for automatic analysis of fringe patterns resulted from photoelasticity was investigated. With the aid of two coherent light sources, the fringe orders of isochromatics have been determined through comparing the fractional quantities of the corresponding fringe patterns. In addition, a unique technique has been proposed to identify the orientation of the first principal stress. This technique allows extension of the phase value of the isoclinics from (0, /2) to (– /2, /2) to extinguish the ambiguity of determining which orientation the first principal stress is in, which is extremely helpful for postal stress separation with shear stress differential method. With this technique, the isochromatics are the phase shifted in 8 discrete directions and then a full phase map of isochromatics has been constructed. An epoxy resin disk under diametric loading was tested with these two methods. The advantage and disadvantage of these two methods were discussed and conclusion was drawn that the proposed phase shifting method has potential to achieve automatic analysis for photoelasticity.