Moiré topography of curved surfaces

Abstract

A physical surface presents a macroscopic curvature and a microscopic curvature, associated with roughness, which is superimposed on the former. Moiré techniques developed in this paper deal with the measurement of partial slopes and macroscopic curvatures of cylindrical and conical shells due to loading. Two distinct techniques are presented, capable of measuring both the undeformed shape of the shell, as well as small departures from the initial shape due to loading. The first one yields the deflection-contour pattern of the loaded shell by bringing into interference the lines of a reference grating, placed close to the matt surface of the shell, and their shadows cast on this surface. The second one provides patterns of partial-slope contours by bringing into interference the reflected lines of a reference grating, placed at a distance apart from the specularly reflecting surface of the shell, and a second grating named the specimen grating. For the complete definition of the surface, an orthogonal set of partial-slope contour or curvature patterns is needed.

Either method is sufficient for the evaluation of the moment and strain distribution of the loaded shell, with the second method being more sensitive and accurate. Illustrative examples are given for both methods.