Robust isoclinic calculation for automatic analysis of photoelastic fringe patterns

There are two main steps in the analysis of photoelastic fringe patterns: the isoclinics and isochromatics computation. For the isochromatic computation there exist several possibilities but one of the best, from the point of view of reliability and automatization, is the phase shift technique. However all phase shift isochromatic algorithms need a good estimation of the isoclinic direction angle that is a challenging task in presence of low birrefringence, isotropic points and monochromatic illumination. In this work we discuss the application of a novel isoclinic direction calculation method based in a phase shifting technique and a fast direction estimation regularized filter. Experimental results show that the proposed method together with a standard phase shifting isochromatic estimation is a good option for the automatic analysis of photoelastic fringe patterns under different illumination conditions, load levels and sample complexity, making possible further processing steps as full-field stress separation.