An improved two-load method for whole-field complete determination of photoelastic parameters is presented. The dark-field isoclinic images are used to determine the isoclinic angles. Using two isoclinic maps obtained from two different loads effectively compensates the indeterminable points. The use of dark-field and light-field photoelastic images for normalization extends the two-load method to analyze dark-field photoelastic fringe patterns and avoids model movement. Larger errors on the determined fringe orders are further reduced by a least-squares quadric fitting. The results are compared well to the theoretical ones. Further comparison of the improved two-load method and the two-wavelength method are given.

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A new approach for whole-field digital determination of isoclinic angle and total isochromatic fringe order is presented. The method uses a plan polariscope with two different filters to calculate the photoelastic parameters, and to compensate the influence of the isochromatic fringes on the isoclinic pattern. The method allows for the determination of whole-field fringe orders without zero-order fringes.