Measurement of retardation in digital photoelasticity by load stepping using a sinusoidal least-squares fitting

Abstract

The use of digital photoelasticity permits us to determine the distribution of principal stress difference by means of the analysis of a photoelastic fringe pattern using a phase measurement method. However, conventional phase measurement methods for fringe pattern analysis require the application of an unwrapping process which commonly fails in the presence of discontinuities. To alleviate this problem, load-stepping methods have been developed. We present an alternative load-stepping algorithm that is based on a nonlinear sinusoidal least-squares fitting. The description of this technique together with its verification on simulated and real experiments are presented in this work. © 2002 Elsevier Science Ltd. All rights reserved.