An improved oblique-incidence technique for principal-strain separation in photoelastic coatings

This paper presents a generalized theory for oblique-incidence measurement of relative retardation in photoelastic coatings. Using this theory, measurements can be performed from a fixed observation point and do not require rotating the test object. Thus, this technique greatly reduces the time and labor involved in oblique-incidence measurements. Furthermore, the technique is potentially applicable to the separation of dynamic principal strains.