A method for directly determining surface strain fields using diffraction gratings

This paper describes a new method for determining the strain distribution at the surface of solid bodies. The method is purely optical; it uses the diffraction phenomena generated by a copy of a grating that is applied to the specimen. A suitable mask performs filtering of the diffraction pattern; the image that is reconstructed from this filtered pattern shows light and dark areas; it is shown that the boundary line of those areas is the locus of points exhibiting the same value of strain, measured along a certain direction.The magnitude of the strain can be easily calculated; it can be adjusted by a simple translation of the filter. A theoretical description of the system and some experimental results are presented.