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T Thurner, S. C. Schneider, B. G. Zagar
Laser Speckle Strain Measurement and its Application in Material Science
In this paper we report on the principle, the measurement set-up, and the applicability of two different laser-speckle strain sensor systems and present selected measurement results. The essential difference between both systems is in their optical set-up. The first system images precisely two laser-illuminated surface spots onto a CCD-camera, which has a well defined geometry and determines with high resolution the load-dependent shift of the surface with respect to the illuminated spots. The laser illumination is used to produce a high contrast speckle pattern which is characteristic for the part of the surface under test (fingerprint of the surface). The difference between both calculated shift values of the surface spots divided by the base length, defined by the distance of the two illuminated surface spots, gives the desired strain value. The achievable resolution of the system improves with increasing base length, but strain values also will be more spatially averaged. Many users require a sensor, which gives local strain information. Therefore our research is aimed at improving this sensor in this respect following up an idea of Yamaguchi. We compare and discuss the features and applicability of both systems.
tm – Technisches Messen, Oldenbourg Wissenschaftsverlag
Print ISSN: 0171-8096
Volume: 70, 02/2003
Pages: 071