Hybrid Analysis for Stress Separation in Photoelasticity

Photoelasticity is a non-contact and full-field type method of experimental stress analysis. It does not provide individual stress components directly. In this study, a new technique of stress separation is developed, in which this problem is divided into the following three: (1) determination of the difference of the principle stresses based on isochromatic data, (2) estimation of unknown boundary values from the difference of the principal stresses, and (3) computation of individual stress components inside the body based on the estimated boundary values. Problem (1) is solved by using the isochromatic fringe images obtained at incremental loading steps. Fourier transform method and direct method are applied to determine the difference of the principal stresses. Problems (2) and (3) are formulated and solved by BEM. A nonlinear optimization method is employed to solve problem (2) since the relation between the unknown boundary value and the difference of the principal stresses is nonlinear. The effectiveness of this technique is verified through numerical simulation and experimental data analysis.