Review of Progress in Quantitative Nondestructive Evaluation

Nondestructive Evaluation Using Shearing Interferometry

Brunswick, ME

Coherent shearing interferometry involves the interference of a coherent optical wavefront with a spatially shifted version of itself. The resulting interference pattern carries information which for small shears (spatial shifts) can be related to the gradients of the phase of the wavefront. The primary advantage of this optical technique is that it is relatively insensitive to rigid body motion. A coherent wavefront that is transmitted through a body or is reflected from the surface of a body will carry information about the resulting stress state or deformation of the body. This information can be used for nondestructive evaluation applications using optical shearing methods in order to identify defects such as cracks and disbonds. In this paper, we will first give a brief review of various shearing methods, and then describe in detail the use of Coherent Gradient Sensing, a diffraction grating shearing technique that was developed by Tippur, Krishnaswamy and Rosakis [1,2,3], for the optical detection of cracks in bodies.