Application of Determination of Principal-Stress Directions by Color Phase Shifting Technique to Model Containing Isotropic Points

This paper presents an application of a new point-wise technique for unwrapping the isoclinic parameter determined by a four-step color phase shifting. The unwrapping technique is based on a largest region in a binary image that corresponds to a largest visible-wrapped period of the computed isoclinic parameter. The largest region is obtained using an intersection operation between the extended ranges of the computed isoclinic parameter. The method uses four raw photoelastic fringe images. The technique is applied to a circular ring containing isotropic points subjected to diametral compression. Results show the method provides the correct isoclinic parameter in the true interval over the entire domain.