Full field automated photoelasticity using two-load-step method

A new two-load-step approach to the phase-shifting method is presented for the full field determination of both isoclinic and isochromatic parameters in photoelasticity. The ambiguity that exists in the phase-shifting photoelasticity is overcome by investigating the relationships between the phase retardation introduced by two different steps. The isoclinic angle is automatically determined in the correct range [-pi /2, pi /2] and the isochromatic parameter is therefore obtained unambiguously. The results obtained from a bending test and an irregular specimen subjected to multiple forces demonstrate the effectiveness of this method. Compared with the load-stepped method (Ekman and Nurse, 1998) or the three-load method (Asundi et al., 2000), this new algorithm is a simpler approach and is easier to execute. (C) 2001 society of Photo-Optical Instrumentation Engineers.