In-plane strain measurement by speckle photography: A practical assessment of the use of Young's fringes

Abstract

A photograph of a laser speckle pattern will diffract light, and a doubly exposed negative, which has been shifted between exposures, will produce a Young's fringe pattern with the fringe spacing inversely proportional to the displacement. This effect is used to detect the in-plane displacements of tensile specimens and cracked specimens, and changes in length of aluminium crystals due to annealing.