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7 March 2006 New generation of optical extensometers based on grating (moire) interferometry
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Current design, analysis and control engineering applications require effective experimental methodologies and tools for determination of displacement and strain fields as well as material characterization. The quality of experimental data obtained at industrial environment has to be sufficient to introduce them into further numerical analysis by FEM (CAE) or use immediately for product quality assessment process. In the paper we present two novel types of full-field laser extensometers based on four-beam, grating (moire) interferometry method. The first type of extensometers is designed for medium size field of view (6 x 4.5 mm ). It is integrated and works directly on a standard loading machine with the possibility to control the load on the base of local on-line strain measurements. It enables the measurements during static, monotonic and cyclic loads and full-field analysis of arbitrary sequence of images, The second type, based on the concept of waveguide interferometer, is designed for small size field of view (min. 0.18 x 0. 12 mm2). It is integrated with a standard optical microscope and it seems to be an excellent tool for local material studies and strain analysis of microcomponents. The waveguide extensometer presented includes miniature Twyman- Green interferometer, which allows to measure out-of-plane displacements. Both extensometers give high contrast and good quality interferograms, are insensitive to vibrations and work with simple, low cost laser diode. The capabilities of the extensometers are presented on the example of low cyclic fatigue testing of a steel specimen and local displacement and strain investigations performed at the ferritic-austenic steel sample and silicon microbeam.
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Malgorzata Kujawinska and Leszek A. Salbut "New generation of optical extensometers based on grating (moire) interferometry", Proc. SPIE 4101, Laser Interferometry X: Techniques and Analysis, (7 March 2006);


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