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3 May 2010Accuracy improvement of self-reference lock-in thermography method and its application to detection of fatigue cracks in steel bridges
A new remote nondestructive inspection technique, based on thermoelastic temperature measurement by infrared
thermography was developed for evaluation of fatigue cracks propagated from welded joints in steel bridges. Fatigue
cracks were detected from localized high thermoelastic temperature change observed at crack tips due to stress
singularity under variable loading by traffics on the bridge. Self-reference lock-in data processing technique was
developed for improvement of signal/noise ratio of the thermal images in the crack detection process. The technique
makes it possible to perform correlation processing without an external reference signal under the random loading. In
this paper, remote and nondestructive crack detections by the self-reference lock-in thermography were performed for
fatigue cracks in actual steel bridge in service. Accuracy improvement of self-reference lock-in thermography method
was made by motion compensation technique based on the two-dimensional SSD (Square Sum of Differences) parabola
fitting method.
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Yui Izumi, Takahide Sakagami, Shiro Kubo, "Accuracy improvement of self-reference lock-in thermography method and its application to detection of fatigue cracks in steel bridges," Proc. SPIE 7661, Thermosense XXXII, 76610D (3 May 2010); https://doi.org/10.1117/12.852961