Two-wavelength method for full-field automated photoelasticity

A new method for the whole-field determination of the isoclinic angle alpha and the isochromatic parameter phi is presented. The problems appearing during the calculation of these two parameters are solved with the use of two different wavelengths. Indeed, when a monochromatic light is used as an incident light, alpha is not measurable at the points where phi is equal to 2k pi. In this method, each monochromatic light can compensate for the influence of phi, to obtain the isoclinic angle for the entire model. Also, most of the methods calculate the fractional fringe order that is unwrapped afterward to obtain the isochromatic parameter. This unwrapping process needs an initialization, which cannot be automatic with only one isochromatic fringe pattern. The use of two wavelengths permits a complete automatic unwrapping of the isochromatic parameter, even for the initialization of the process.