On phase-shifting integrated photoelasticity

The development of phase-shifting photoelasticity of plane specimens began 21 years ago. Meanwhile, the method was also applied to bodies with three-dimensional stresses, where the secondary principal stresses and their directions generally vary along the path of a probing light beam. In the theory of integrated photoelasticity, a three-dimensional body is represented by an equivalent model with three characteristic parameters, which are the characteristic retardation or phase, and the primary and secondary characteristic directions. Results are commonly tested in plainly stressed specimens at oblique incidence or in a cylindrical body composed of three discs under diametral compression, where the load axes vary from disc to disc. In this study, I verify the applicability of some polariscope arrangements in integrated photoelasticity by means of a bent-beam specimen which exhibits rotating principal directions along the light path. This device enables continuous variation of the stress field. Furthermore, an approximate analytical solution of the characteristic parameters is available. The following three major arrangements of optical elements were investigated: (i) linear polariscope in white light; (ii) linear polariscope in monochromatic light; and (iii) circular polariscope in monochromatic light in the dark- and bright-field arrangement as well as in the half-tone or grey-field arrangement. Results are discussed and compared with the literature of two- and three-dimensional digital photoelasticity.