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Smart Structures and Systems Volume 19, Number 3, March 2017 , pages 335-340 DOI: https://doi.org/10.12989/sss.2017.19.3.335 |
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Mechanical strength of FBG sensor exposed to cyclic thermal load for structural health monitoring |
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Heonyoung Kim, Donghoon Kang and Dae-Hyun Kim
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| Abstract | ||
| Fiber Bragg grating (FBG) sensors are applied to structural health monitoring (SHM) in many areas due to their unique advantages such as ease of multiplexing and capability of absolute measurement. However, they are exposed to cyclic thermal load, generally in the temperature range of -20°C to 60°C, in railways during a long-term SHM and the cyclic thermal load can affect the mechanical strength of FBGs. In this paper, the effects of both cyclic thermal load and the reflectivity of FBGs on the mechanical strength are investigated though tension tests of FBG specimens after they are aged in a thermal chamber with temperature changes in a range from -20°C to 60°C for 300 cycles. Results from tension tests reveal that the mechanical strength of FBGs decreases about 8% as the thermal cycle increases to 100 cycles; the mechanical strength then remains steady until 300 cycles. Otherwise, the mechanical strength of FBGs with reflectivity of 6dB (70%) and 10dB (90%) exhibits degradation values of about 6% and 12%, respectively, compared to that with reflectivity of 3dB (50%) at 300 cycles. SEM photos of the Bragg grating parts also show defects that cause their strength degradation. Consequently, it should be considered that mechanical strength of FBGs can be degraded by both thermal cycles and the reflectivity if the FBGs are exposed to repetitive thermal load during a long-term SHM. | ||
| Key Words | ||
| structural health monitoring; fiber Bragg grating; thermal load; mechanical strength | ||
| Address | ||
| Heonyoung Kim, Donghoon Kang: Advanced Materials Research Team, Korea Railroad Research Institute, 176 Cheoldo bangmulgwan-ro, Uiwang-si, Gyeonggi-do, 16105, Republic of Korea Heonyoung Kim: School of Mechanical Engineering, Yonsei University, 50 Yonsei-ro, Seodaemum-gu, Seoul, 03722, Republic of Korea. Dae-Hyun Kim: Department of Mechanical and Automotive Engineering, Seoul National University of Science and Technology, 232 Gongneung-ro, Nowon-gu, Seoul, 01811, Republic of Korea | ||