Elastic constant and strain measurements using a three beam speckle pattern interferometer

Abstract

The theoretical interpretation of speckle pattern interference fringes produced by small surface displacements is considered. New arrangements for a speckle pattern interferometer are described. Firstly the object is illuminated by plane wavefronts propagating at the same angle to orthogonal axes in the plane of the object. Secondly a 'composite speckle interferogram' is obtained when adjacent regions in the object are illuminated by different configurations of wavefront. Part of the object is illuminated as previously described, the remainder is illuminated by two wavefronts propagated at equal angles to a single axis in the surface. Interferograms made using this system can be employed to determine the components of plane strain tensors. A method for the measurement of elastic constants is experimentally verified and white light projection of frozen speckle pattern interference fringes is briefly discussed.