Optical EngineeringHigher sensitivity moire interferometry for micromechanics studies
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A whole-field in-plane displacement measurement method was developed for micromechanics studies. The method increased the sensitivity of conventional moiré interferometry by an order of magnitude. The increased sensitivity was achieved by a two-step process. Microscopic moiré interferometry, used for step 1 to map an original displacement field, provided a basic sensitivity of 4.8 fringes/μm displacement, which exceeds the previously conceived theoretical limit. Optical/digital fringe multiplication method (ODFMM) was implemented for step 2 to achieve further enhancement of sensitivity. The ODFMM consists of optical fringe shifting and a digital process to sharpen and combine the shifted fringes. The result is a map with p times as many fringe contours as the original map of step 1. A factor of β = 12 was achieved, providing a sensitivity of 57.6 fringes/μm displacement, which corresponds to that of moiré with 57,600 lines per mm (1,463,000 lines per in.). The optical, mechanical, and electronic systems implemented here are remarkably robust and quick. The method is demonstrated by three practical applications: fiber/matrix deformation of a metal/matrix composite, interface strains in a thick 0/90-deg graphite/epoxy composite, and thermal deformation around a solder joint in a microelectronic subassembly.