A novel approach for full-field measurement of principal stress directions in photoelasticity

A novel approach, called min-max scan, is proposed to measure the full-field principal stress directions digitally. By using a light-field plan-polariscope and a PC-based image processing system, the intensities of the, model images under varying loads are scanned and compared in real-time to form images representing the minimum (isoclinics) and maximum intensities at each point on the model. The influence of isochromatics on the isoclinics is eliminated. Using two sets of images obtained at the angle of 0 and pi/8, respectively, the full-field principal stress directions can be determined in the range [0, pi/2]. Relevant theory for the proposed approach is introduced and the experiment results are shown.