PHOTOELASTIC TESTING USING A BIREFRINGENCE-SENSITIVE INTERFEROMETER

An interferometric technique for photoelastic testing of small and tra nsparent samples is proposed. By the introduction of two properly orie nted polarisers in the two arms of a Twyman-Green interferometer, it h as been shown that the modified interferometer is rendered sensitive t o birefringent samples placed in the path of a plane polarised paralle l beam of light entering the interferometer. Since the sample is place d in the common arm, unequal phases either inherent in the sample or d ue to deformation under stress will not be reflected in the output. Du ring the testing procedure, the two arms of the interferometer can be left totally undisturbed. Information on the stress distribution over the sample area can be obtained from the recorded interferometric patt ern - since the recorded fringe shifts are proportional to the develop ed stresses. The principle of the technique is discussed and experimen tal results are provided.