On the Method of Measuring Strain by Use of Diffraction at Mis-matched Moire Fringes

Abstract

In the usual moire method and the multiplication method, the sensitivity to deformation is not sufficient at present. Then, how to increase the sensitivity is studied. In the measurement of a usual sheet metal specimen, moire fringes with large mis-match is photographed on a film at first. Such fringes are equivalent to grating lines on the specimen, as thy displace corresponding to strain, and they can be amplified by applying the multiplication method to that film. When strain is expressed by two beam interference fringes, one of the beams is tilted by a small amount, then fine fringes are obtained. They are equivalent to moire fringes with large mis-match and the multiplication method can be applied. Applications in various conditions have been shown. Consequently, concerning a sheet metal, measurement of elastic-plastic strain (ε⋍ 0.001) becomes possible and in the special condition that the surface of a specimen has been finished mirror-like, elastic strain (ε⋍ 0.001) can be measured.