Shearography: A New Optical Method For Strain Measurement And Nondestructive Testing

Abstract

This paper presents a new optical method referred to as shearography. Shearography is an interferometric method which employs an image-shearing camera. It permits full-field measurement of derivatives of surface displacements. The object under study is illuminated by laser light, and it is imaged by an image-shearing camera. The image-shearing camera produces two laterally sheared images in the image plane. When a photographic film in the image plane is doubly exposed with the object being deformed between the exposures, the processed photograph yields a fringe pattern which depicts the surface displacement gradients. Theory of the method as well as its applications to strain meausrements and nondestructive testing are presented.