Stress Separation in Digital Photoelasticity Part B - Whole Field Evaluation of Stress Components

Abstract

In photoelasticity, the method of obtaining the individual values of principal stresses/normal stresses separately is referred to as stress separation. For stress separation, one needs the value of fringe order and the isoclinic angle free of noise over the domain. With improved data acquisition and smoothing methodologies, it has now become possible to get accurate and smooth variation of the fringe order and the isoclinic value over the domain. This has been discussed in detail in Part-A of this article. Shear difference is one of the widely used techniques for stress separation in photoelasticity. Though it is a line byline technique, a whole field evaluation of stress separation using this technique and its representation is shown in this paper. It is observed that spikes in isoclinic values lead to streak formation in the whole field representation of separated stress components. The use of outlier algorithm for smoothing isoclinic and isochromatic data has removed these streaks and has also greatly improved the accuracy of the separated stress components. The various issues related to digital implementation such as boundary pixel identification, grids for accommodating the various boundaries etc. are given in the Appendix. Performance of the methodology is verified for simply and multiply connected objects. The models are subjected to moderate loads to have sufficient isochromatic-isoclinic interaction. The stress components obtained are smoothed with the outlier algorithm for improved accuracy. Whole field separated stress values are obtained for the domains considered.