From this study is concluded that for various crack problems, the Det.-criterion of fracture gives theoretical results which are agreed with the experimental results. The interest in this study is that the distribution of the determinant of the stress tensor is calculated experimentally from isochromatic- and isopachic-fringe patterns and so, the prediction of the direction of crack initiation Can be experimentally calculated. The experimental stress analysis near the crack tip and far from it, is succeed by the combination of the photoelastic, interferometric and caustics methods.