APPLICATION OF A BIREFRINGENT LENS IN PHOTOELASTIC STUDIES USING A COHERENT MOIRE TECHNIQUE

In photoelastic investigations, one uses the property of stress induce d birefringence for stress analysis. Normal polariscopes are used for such studies. However, the accuracy of the methods is low. For better accuracy, interferometric and holographic methods are generally used. Holography, along with a shearing technique, is also used to obtain pa rtial derivatives of displacement with respect to spatial co-ordinates . In these methods, the resultant fringe pattern is obtained from the mutually shifted holograms and the generation of such patterns require s four exposures altogether. The present paper represents a method bas ed on a coherent moire technique for studying the first derivative of a stress pattern using birefringence properties. The analysis seems to be very similar to holographic techniques as both produce second orde r fringes. The advantage of this method is that it requires only one e xposure. The basic principle as well as some experimental results are presented.