Monitoring and instantaneous evaluation of fatigue crack using integrated passive and active laser thermography

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This study proposes an integrated passive and active laser thermography (IPALT) system comprising a continuous wave (CW) laser and an infrared OR) camera for fully noncontact monitoring and instantaneous evaluation of a fatigue crack in a metallic structure. The IPALT system operates in two phases: (1) passive thermography (PT) mode, and (2) active thermography (AT) mode. The PT mode monitors the fatigue crack initiation by measuring the thermoelastic effects on the fatigue crack tip in real time using the IR camera. Once the crack tip is identified, the AT mode is automatically triggered, and the corresponding fatigue crack is precisely quantified using the CW laser and the IR camera. Through this effective crack monitoring system under operating conditions, time dependent crack propagating behavior analysis, as well as early crack detection, can be achieved. The feasibility of the proposed IPALT system is experimentally validated by monitoring a metallic structure under a 10 Hz cyclic loading. The validation tests indicate that fatigue crack initiation is detected at 10,000 cycles by the PT mode, and the fatigue crack length is quantified as 10.45 nun with an accuracy of 99.43% compared to the microscope observed ground truth of 10.51 mm.
Publisher
ELSEVIER SCI LTD
Issue Date
2019-08
Language
English
Article Type
Article
Citation

OPTICS AND LASERS IN ENGINEERING, v.119, pp.9 - 17

ISSN
0143-8166
DOI
10.1016/j.optlaseng.2019.02.001
URI
http://hdl.handle.net/10203/261856
Appears in Collection
CE-Journal Papers(저널논문)
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