Three Dimensional Photoelastic Model Study by Scattered Speckle Light Analysis and Fringe Shifting

Abstract

We show a non-destructive experimental method, which gives the isochromatics, isoclinics and isostatics patterns of slices optically isolated in a three-dimensional photoelastic model. The basic idea is to delimit a slice between two plane laser beams. In the direction perpendicular to the plane of the two illuminated sections, we observe a speckle pattern due to the interferences of the scattered light beams of each section. By Introducing speckle pattern properties, the analysis of the scattered light gives fringes equivalent to those obtained in a plane polariscope. In order to separate the isochromatic and the isoclinic fringes, we record several images for different polarisation orientations. Using the Fourier transform, we separate the isoclinic and isochromatic fringes. Our method can be used with specimens realised by moulding or by stereo lithography technique.