Absolute determination of the isochromatic parameter by load-stepping photoelasticity

Abstract

ABSTRACT--A new approach to full-field automated photoelasticity is presented in which a circular polariscope is used to enable the isochromatic phase value (c 0 to be determined unambiguously and without input of a known isochromatic value obtained using an auxiliary technique. Values of cosc~ are obtained from light-field and dark-field images for three loads of small incremental steps. Using a relatively straightforward procedure, ramped phase maps for c~ are produced which can be unwrapped using conventional techniques. The resulting distribution of cl is then found absolutely using information provided by which Oct 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.

Data Acquisition Techniques in Photoelasticity

“…Another possibility for obtaining the phase‐shifted images necessary in the “phase shifting” technique was to use different loads (load stepping) 79–85 or different wavelengths (wavelength stepping) 86–90 instead of employing different positions of the filters (phase stepping). These new approaches surmounted the limitations of the unwrapping process in “phase stepping.” Research continues to this day in order to improve all these “phase shifting” techniques, which offer great potential: the use of white light and the combination with other techniques (as will be seen later on) substantially improve the technique.…”

Review of RGB photoelasticity

“…[30][31][32][33] allows to determine the retardation regardless of the isoclinic parameter, eliminating the ambiguities of the PSM. It is also not necessary to know the fringe order at one point.…”

A temporal phase unwrapping algorithm for photoelastic stress analysis

“…Moreover, the extrapolation procedure requires isolating the object from the background. Alternatively either two levels of load [7][8][9] or two or more monochromatic light sources [10][11][12][13][14] can be used. In this way, as shown by Eq.…”