Comparison Of Moire-Mismatch, Moire-Fringe Multiplication And Moire-Interferometry As A Method For Measuring In Plane Displacements

Abstract

Traditional Moire-technique uses two equal bar-and-space gratings to get Moire-fringes by mechanical superposition. In order to measure in plane displacement a very high density of the grating is needed where as a grating frequency of 40 L/mm is usual (in Moire-technique). Mismatch as well as Fringe-Multiplication is used to overcome the difficulties arising from this fact. Sciammarella and Lurowist also introduced a method to determine fractional fringe order by an operation quite similar to Tardy's method in photoelasticity. Laterly a special case of Fringe-Multiplication was introduced by D. Post the so called Moire interferometry. That is a relatively easy technique for producing high frequeny gratings and it extends the Moire-method into a high-sensitivity domain. Moire-Interferometry works in the reflection area, therefore to perform the experimental analysis it is not necessary to use a transparent specimen or a transparent replica of the deformed specimen grating; the observation of the actual workspiece is possible. Of course the multiplicator factor is only 2, however following Post procedure it is easy to get very high frequency grating. Using two Laser-beams a virtual reference grating frequency up to 4000 L/mm have been reached, that means a sensitivity up to. 25 μm/fringe. Examples for these methods can be shown, dealing with our investigations of some repear patch problems.© (1985) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.