A new moireinterferometer for determining 3-D displacement field of a slightly strained body is proposed. In this interferometer, the specimen grating not only diffracts the incoming beam into several beams but also rediffracts the diffracted beams, each of them is reflected from a mirror back to the path of the incoming beam. The rediffracted beams are then directed to a camera to generate three interference pat- terns, which are sufficient to determine the 3-D displacement field. The governing equations corresponding to these interference patterns are derived, and the advantages of using this interferometer are described. Some experiments were carried out to verify the governing equations and advantages. © 2001 Society of Photo-Optical Instrumentation Engineers.

Three-dimensional displacement measurement using a newly designed moire´ interferometer

A simple setup for simultaneous measurement of in-plane and out-of-plane displacement components is demonstrated. Since the in-plane and out-of-plane components are recorded at separate positions, no additional processing of the patterns is required. Suggestions are made for further simplification by proper choice of specimen and reference gratings.

Moiré interferometry for simultaneous measurement of U, V W

Moiré interferometry for deformation measurement

Surface topography can be conveniently investigated by a well-known shadow-moire technique. It is relatively free from stringent requirements on stability of instrumentation and quality of the light source. The main unresolved problem of the shadow moire is its relatively low resolution. The digital-image-analysis enhanced shadow-moire technique described here is based on the marriage of two well-known and developed methods: classical shadow moire and contemporary digital image analysis. This combination allows a significant increase of the sensitivity of the classical shadow moire by utilizing the ability of the digital-image-analysis system to acquire wholefield light-intensity information and process this information to yield the related displacement field. The suggested approach was utilized for a three-dimensional curved surface. The obtained topography of the three-dimensional specimen was compared to the one measured by a high precision dial gage and the differences were on average less than three percent between the two sets of data. The described combination of the shadow moire and digital image analysis may prove as a useful tool for on-line quality control in a variety of manufacturing processes.

Enhancement of the shadow-moiré method through digital image processing

Moiré of moiré interferometry

A high sensitivity technique for out-of-plane displacement is demonstrated. A 600 lines mm phase grating is used in conjunction with a specularly reflecting (in some cases mirrored) object, to obtain contours of out-of-plane displacement. Initial patterns due to low quality optics are eliminated by a double exposure technique employing carrier (or mismatch) fringes. Beams with cracks are used to experimentally demonstrate this technique.

http://journals.sagepub.com/doi/pdf/10.1243/03093247V211051

M T Cheung

Papers

Moire interferometry for out-of-plane displacement measurement