Experimental Mechanics @ Michigan State University
		EM Basics: Photoelasticity
Basic principles: At any point in a loaded component there is a stress acting in every direction. The directions in which the stresses have maximum and minimum value for the point are known as principal directions. The corresponding stresses are known as maximum and minimum principal stresses. When polarised light enters a loaded transparent component it is split into two beams. Both beams travel along the same path, but each vibrates along a principal direction and travels at a speed proportional to the associated principal stress. Consequently the light emerges as two beams vibrating out of phase with one another which when combined produce an interference pattern. The polarised light is produced by the polariser in the polariscope and the analyser performs the combination. The interference pattern is observed in the polariscope , and the fringes are contours of principal stress difference which are known as isochromatics. When plane polarised light is used black fringes known as isoclinics are superimposed on the isochromatic pattern. Isoclinics indicate points at which the principal directions are aligned to the polarising axes of the polariser and analyser.
More about:				Two-dimensional photoelasticity
				Three-dimensional photoelasticity
				Reflection Photoelasticity
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