Improvement of the Method of Measuring Shear Strain Using Interferometry of Diffraction Beams

Abstract

In measuring in-plane deformation by using diffraction beams, fringes corresponding to contour lines of various strain components can be obtained. Measurement of normal strain (or the first order derivative of displacement) is rather simple, and the authors reported on the method for it already. In this paper a new method of measuring shear strain is proposed, in which a modified Sciammarella's optical system (1967) is used and the double exposure processing is applied. In this method sensitivity in measurement is twice that of the recent moire method using diffraction beams, or 6 times that of the conventional moire method using interference of grating lines. Further, errors in moire fringes due to mis-adjustment of an optical system, non-uniformity of thickness of film (specimen grating), etc. are compensated almost completely.