Photoelastic analysis using automated polariscopes

Two methods of automating photoelastic analysis are described. The first technique is based on phase stepping. A CCD camera and digitizer are used to record six images of intensity corresponding to six orientations of output quarter waveplate and polariser. These are combined mathematically to give full field images of the isochomatic and isoclinic paramaters of the specimen under study. The full field image is composed of 256x256 pixel points, each with an isochromatic fringe value. An alternative technique is proposed based on the point-by-point method of spectral contents analysis. The method used the CCD camera as a 256x256 pixel diode array and eight narrow band filters for the isolation of wavelengths in the range 450 to 750nm. Normalised intensity values from a circular polariscope are used to represent the spectrum of light for each pixel and comparison with the theoretical spectrum using a minimisation procedure produces the absolute retardation. Combination of the retardation and the normalised intensity spectra from the plan polariscope yields the isoclinic parameter. Both simple and complex components are analysed using both automated systems. Results compared well with both manual and theoretical analyses of the components.