MULTIPLE-IMAGE SHEAROGRAPHY - A DIRECT METHOD TO DETERMINE CURVATURES

We present a modified method of shearography, known herein as multiple -image shearography, whereby the curvatures of an object can be measur ed directly from the resulting fringes. It employs an image-shearing c amera that produces three sheared images simultaneously to interfere w ith each other in the image plane. When film is doubly exposed before and after an object is deformed, three sets of fringes are observed of which one set would depict the second-order derivatives of surface di splacement. The theory of the multiple-image shearography technique an d its application to curvature measurements in plate bending are prese nted.