Moiré Methods for Engineering and Science — Moiré Interferometry and Shadow Moiré

Abstract

Moiré interferometry and shadow moiré are extraordinarily versatile and effective methods for determining in-plane and out-of-plane displacement fields, respectively. The basic concepts are reviewed for both methods, topics on practice and analysis are addressed, and numerous examples of important applications are presented.

The moiré data are received as whole-field fringe patterns, or contour maps, of displacements. For moiré interferometry with the typical reference grating frequency of 2400 lines/mm, the contour interval is 0.417 μm per fringe order; the sensitivity is 2.4 fringes per μm displacement. Orthogonal U and V displacements are measured, and normal and shear strains are determined from these in-plane displacement fields. For microscopic moiré interferometry, sensitivity corresponding to 17 nm per fringe contour has been achieved by means of the optical/digital fringe multiplication algorithm.

The patterns of moiré interferometry are characterized by excellent fringe contrast and spatial resolution, including patterns from complex applications. The applications reviewed here address laminated composites, including the study of free-edge effects along the cylindrical surface of holes in laminated plates; thermal deformation of microelectronics devices; the damage wake along a crack path; and a micromechanics study of grain deformations in titanium.

The examples of shadow moiré show the out-of-plane displacements W for prebuckling and post-buckling of columns; and W displacements of electronic packages subjected to temperature changes. Phase-stepping analyses were used for the electronic packages to increase sensitivity, providing 12.54 μm per fringe contour. Since W is typically much larger than U and V, the sensitivity of shadow moiré can be adjusted to serve broad categories of engineering applications.