Interpretation of Moire Patterns

TLDR: In this article, a description of the basic properties of moire patterns used in strain analysis is presented, and the uniqueness and continuity of displacements are noted, compared with topological elevations.

Abstract: A description of several of the basic properties of moire patterns used in strain analysis is presented. The uniqueness and continuity of displacements are noted, compared with topological elevations, and the ordering of fringes is demonstrated to follow. The meaning of lines of zero slope in the pattern is shown to be an aid in strain analysis. Singular points of the elliptical, hyperblic, and double-tangent type are described. Singular lines are noted as an extension of singular points. The effect on the moire pattern of rotation of the master and model grid systems is presented in terms of Mohr’s circle. The use of symmetry in order to obtain additional information from the pattern is demonstrated, including an example of a complete analysis from one pattern, wherein the proper regard is given to symmetry. The description is illustrated with patterns from a ring and a disk under diametral load, a strip with a hole subjected to uniaxial tension, a plate with two concentrated loads on one edge, and a disk subjected to four-point loading.