Absolute determination of the isochromatic parameter by loadstepping photoelasticity

TLDR: In this article, a new approach to full-field automated photoelasticity is presented in which a circular polariscope is used to enable the isochromatic phase value (α) to be determined unambiguously and without input of a known isochrome value obtained using an auxiliary technique.

Abstract: A new approach to full-field automated photoelasticity is presented in which a circular polariscope is used to enable the isochromatic phase value (α) to be determined unambiguously and without input of a known isochromatic value obtained using an auxiliary technique. Values of cosα are obtained from light-field and dark-field images for three loads of small incremental steps. Using a relatively straight-forward procedure, ramped phase maps for α are produced which can be unwrapped using conventional techniques. The resulting distribution of α is then found absolutely using information provided by which δα is the incremental change in the isochromatic phase value between the load steps. The results obtained for disk-in-compression tests presented here in comparison with theoretical solutions demonstrate that the technique is both simple to use and very accurate. A similar approach may be adopted using three wavelengths instead of three load steps.