Development of interior strain measurement techniques using random speckle patterns

Experimental stress analysis is a well established mechanics discipline dealing with measuring stress/strain in solids under load. Most techniques can only be applied to measuring strain of the surface. In this paper we review the development of techniques of using a random speckle patterns as a quantitative tool to mapping interior strain field of solids. After some elementary treatment of the basic principles of the speckle photography technique we describe three approaches that can probe the interior strain field of a transparent object. They are followed by a newly developed 3D strain measurement technique called digital volumetric speckle photography which can probe the interior of opaque materials as well.