Improved determination of retardation in digital photoelasticity by load stepping

Use of phase shifting has revolutionized the acquisition of photoelastic data. Even since its introduction, various researchers have improved the methodology. In phase shifting the problem of ambiguity exists in the sign of fractional retardation in some zones of the model. This has been overcome with the development of load stepping. However, the conventional approach to data processing in load stepping introduces several noise points in the phase map. In this paper a new methodology for data reduction in load stepping, which removes the noise points in the domain is presented. Results from four- and six-step algorithms are analyzed. A normalization scheme to improve the results has been proposed. A comparative study has also been carried out on the evaluation of phase map by phase shifting, load stepping and the new methodology.