Application of fourier analysis to the laser based interferometric strain/displacement gage |
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Authors: | Marc Zupan K J Hemker |
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Institution: | (1) Dept of Mech. Eng., The Johns Hopkins University, 21218 Baltimore, MD;(2) Dept. of Engineering, University of Cambridge, CB2 IPZ Cambridge, U.K. |
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Abstract: | The laser based interferometric Strain/Displacement Gage (ISDG) measures the in-plane surface deformation between two small
reflecting surface markers. When illuminated with a coherent beam of light, the reflected beams from the two markers form
an interference pattern, and monitoring the shift of the fringe pattern allows strain in the gage section of a specimen to
be directly measured. A minimum on the fringe pattern can be isolated and tracked as the test proceeds, but this technique
utilizes only a small part of the optical signal and often requires a complex programming scheme. This paper presents the
application of Fourier transform and phase shifting techniques to the use of the ISDG during microsample tensile testing.
The Fourier transform samples the entire fringe pattern and greatly improves the optical signal to noise ratio, and the phase
shifting fringe pattern analysis has proven to be more robust and less affected by speckle or optical noise than fringe pattern
minimum tracking. This results in the ability to measure larger deformations with a system resolution of ∼5 microstrain and
an uncertainty of ±15.5 microstrain. An example involving the microsample tensile testing of a MEMS related LIGA Ni specimen
is included to demonstrate the utility of these new techniques. |
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Keywords: | Strain measurement microsample tensile testing ISDG |
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