Computer aided photoelasticity by an optimum phase stepping method

Abstract

ABSTRACT--In this paper an automated photoelastic method based on the phase stepping technique is described. It provides full-field maps of the isoclinic parameter and the relative retardation. The technique is based on processing six images of a photoelastic specimen acquired using plane and circularly polarized light. The number of acquisitions and the type of polariscope used in this approach have been chosen with the aim at reducing the influence of quarter wave plate errors and obtaining raw photoelastic data in a periodic form suitable for easy applications of automatic unwrapping routines.

RGB photoelasticity applied to the analysis of membrane residual stress in glass

“…Figure 6 shows the isochromatic fringes at the ROI and the section chosen for the measurement of the retardation. Figure 7 shows the retardation δ 0 along the measurement section determined by the RGB method (using both the calibration on polycarbonate and the self-calibration) and, for comparison, by the phase-shifting method based on six acquisitions [19]. Similar results are obtained by the simplified phaseshifting method based on three acquisitions [5] and with the phase-shifting method in white light [16].…”

Review of RGB photoelasticity

“…Barone and Petrucci observed that for light fluctuations less than 10%, the classic error function (6) is applicable, while for higher fluctuations the authors propose the application of the chromatic coordinate r, g and b from Eq. (9)(10)(11). In order to reduce the localised fluctuations they also recommended the application of median filtering techniques to the R, G and B values (separately), in particular in the creation of the look-up table, as described in Section 2.1.…”

“…Because of the periodicity of the tangent function, the above maps are wrapped, it is therefore necessary to apply procedures of unwrapping. Various methods that minimize the influence of the error of quarter-wave plates on isochromatic and isoclines have been proposed [8,9]. For a survey on the phase shifting methods, the reader is referred to the literature [10].…”

Photoelastic Analysis of Edge Residual Stresses in Glass by Automated “Test Fringes” Methods

“…In particular the analysed section is located at the fringe of order 1 in the tensile zone of the carrier. Figure 9(b) shows the retardation along the chosen section as determined by the relationship (16) and by using a six acquisitions phase shifting method [13] for comparison. Almost identical results are obtained by the simplified phase shifting method based on three acquisition [6] and with the phase shifting method in white light [14].…”