Measurement of Slope Contours by means of moiré Fringes

A moire method is described for measuring partial slope contours of flat surfaces of transparent plates. A reference grating is projected by means of a collimated light beam on the surface of a specimen. The light beam passing through the specimen forms a distorted image of the reference grating on the surface of an identical grating, and produces moire fringes which yield partial slope contours of the specimen.A formula for obtaining the slope contour from the inclination and the spacing of the moire fringe is introduced theoretically. Experiments made with a straight line grating of 0.025 mm spacing show that this method has nearly the same precision as the optical interference method.In this paper few applications are shown. As an example, the slope contours are calculated from moire pattern produced by an acrylyte plate which is supported at both ends and loaded at mid point. And also a moire pattern produced by the fractured surface of acrylyte plate is shown.The method described in this paper is applicable for the transparent materials, but for the reflecting materials their slope contours are derived by the somewhat different moire technique.