Plane-surface strain examination by speckle-pattern interferometry using electronic processing

Abstract

The characteristic speckle pattern formed when imaging a scattering surface illuminated by laser light retains phase information, which can be used for interferometric measurement of surface displacement. The application of this principle to measuring in-plane strain resolved in one direction is described, together with the novel use of television equipment to detect and process the information contained in the speckle pattern and display the consequent interferogram. This is faster, and more convenient and versatile than customary photographic methods. Sources of practical error are analyzed, and some results are presented from investigations of strain distributions in fibre-composite tensile specimens.