Journal of the Korean Society for Nondestructive Testing (비파괴검사학회지)

The Korean Society for Nondestructive Testing (한국비파괴검사학회)
권호 표지
DOI QR코드

DOI QR Code

Reliability Evaluation of Fiber Optic Sensors Exposed to Cyclic Thermal Load

주기적인 반복 열하중에 노출된 광섬유 센서의 신뢰성 평가

  • 김헌영 (연세대학교 기계공학과) ;
  • 강동훈 (한국철도기술연구원 첨단소재연구팀) ;
  • 김대현 (서울과학기술대학교 기계.자동차공학과)
  • Received : 2016.05.27
  • Accepted : 2016.06.13
  • Published : 2016.06.30
Download PDF
⟨ Previous Next ⟩

Abstract

Fiber Bragg grating (FBG) sensors are currently the most prevalent sensors because of their unique advantages such as ease of multiplexing and capability of performing absolute measurements. They are applied to various structures for structural health monitoring (SHM). The signal characteristics of FBG sensors under thermal loading should be investigated to enhance the reliability of these sensors, because they are exposed to certain cyclic thermal loads due to temperature changes resulting from change of seasons, when they are applied to structures for SHM. In this study, tests on specimens are conducted in a thermal chamber with temperature changes from -$20^{\circ}C$ to $60^{\circ}C$ for 300 cycles. For the specimens, two types of base materials and adhesives that are normally used in the manufacture of packaged FBG sensors are selected. From the test results, it is confirmed that the FBG sensors undergo some degree of compressive strain under cyclic thermal load; this can lead to measurement errors. Hence, a pre-calibration is necessary before applying these sensors to structures for long-term SHM.

광섬유 브래그 격자센서(FBG)는 다중화가 용이하고 절대측정이 가능한 고유의 장점으로 다양한 구조물의 구조건전성 모니터링(SHM)에 활용도를 넓혀가고 있다. 하지만, 구조건전성 모니터링을 위해 FBG 센서를 온도 변화 환경에서 장기간 사용할 경우 FBG 센서는 계절적 요인에 의한 큰 폭의 주기적 온도 변화 환경에 노출되므로 센서의 신뢰성 확보를 위해 신호 특성에 대한 검토가 필요하다. 본 연구에서는 패키징된 FBG 센서의 제작에 많이 활용되는 각각 2가지의 모재 및 접착제를 대상으로 시편을 제작한 후 항온항습기 내에서 -$20^{\circ}C{\sim}60^{\circ}C$의 온도 조건에서 300사이클의 반복 열하중시험을 수행하였다. 시험 결과, FBG 센서에 주기적인 반복 열하중이 가해질 경우 일정량의 압축변형이 작용하며 이는 센서로 사용 시 측정 오차로 작용하므로 장기 구조건전성 모니터링을 위해 FBG 센서의 사용 전 안정화 과정을 통한 사전보정이 필요함을 확인하였다.

Keywords

References

  1. W. Chung and D. Kang, "Full-scale test of a concrete box girder using FBG sensing system," Engineering Structures, Vol. 30, No. 3, pp. 643-652 (2008) https://doi.org/10.1016/j.engstruct.2007.05.003
  2. J. H. Lee, D. H. Kim and I. K. Park, "Application of a fiber Fabry-Perot interferometer sensor for receiving SH-EMAT signals," Journal of the Korean Society for Nondestructive Testing, Vol. 34, No. 2, pp. 165-170 (2014) https://doi.org/10.7779/JKSNT.2014.34.2.165
  3. K. A. Kwon, M. Y. Choi, H. S. Park, J. H. Park, Y. H. Huh and W. J. Choi, "Quantitative defects detection in wind turbine blade using optical infrared thermography," Journal of the Korean Society for Nondestructive Testing, Vol. 35, No. 1, pp. 25-30 (2015) https://doi.org/10.7779/JKSNT.2015.35.1.25
  4. J. B. Ihn and F. K. Chang, "Pitch-catch active sensing methods in structural health monitoring for aircraft structures," Structural Health Monitoring, Vol. 7, No. 1, pp. 5-19 (2008) https://doi.org/10.1177/1475921707081979
  5. K. H. Lee and D. H. Kim. "Shape monitoring of composite cantilever beam by using fiber Bragg grating sensors," Trans. Korean Soc. Mech. Eng. A, Vol. 37, No. 7, pp. 833-839 (2013) https://doi.org/10.3795/KSME-A.2013.37.7.833
  6. D. Kang, D. H. Kim and S. Jang, "Design and development of structural health monitoring system for smart railroad-gauge-facility using FBG sensors," Experimental Techniques, Vol. 38, No. 5, pp. 39-47 (2014) https://doi.org/10.1111/j.1747-1567.2012.00844.x
  7. Y. J. Rao, D. J. Webb, D. A. Jackson, L. Zhang and I. Bennion, "In-fiber Bragg-grating temperature sensor system for medical applications," Journal of Lightwave Technology, Vol. 15, No. 5, pp. 779-785 (1997) https://doi.org/10.1109/50.580812
  8. D. H. Kim and M. Q. Feng, "Real-time structural health monitoring using a novel fiber-optic accelerometer system," IEEE Sensors Journal, Vol. 7, No 4, pp. 536-543 (2007) https://doi.org/10.1109/JSEN.2007.891988
  9. A. Grillet, D. Kinet, J. Witt, M. Schukar, K. Krebber, F. Pirotte and A. Depre, "Optical fiber sensors embedded into medical textiles for healthcare monitoring," IEEE Sensors Journal, Vol. 8, No. 7, pp. 1215-1222 (2008) https://doi.org/10.1109/JSEN.2008.926518
  10. H. Y. Kim and D. H. Kim, "Sensor system for multi-point monitoring using bending loss of single mode optical fiber," Journal of the Korean Society for Nondestructive Testing, Vol. 35, No. 1, pp. 39-45 (2015) https://doi.org/10.7779/JKSNT.2015.35.1.39
  11. D. Kang, H. Y. Kim and D. H. Kim, "Enhancing thermal reliability of fiber-optic sensors for bio-inspired applications at ultra-high temperatures," Smart Materials and Structures, Vol. 23, No. 7, pp. 074012 (2014) https://doi.org/10.1088/0964-1726/23/7/074012
  12. D. Kang, H. Y. Kim, D. H. Kim and S. Park, "Thermal characteristics of FBG sensors at cryogenic temperatures for structural health monitoring," International Journal of Precision Engineering and Manufacturing, Vol. 17, No. 1, pp. 5-9 (2016) https://doi.org/10.1007/s12541-016-0001-4
  13. D. Kang, S. O. Park, C. S. Hong and C. G. Kim, "The signal characteristics of reflected spectra of fiber Bragg grating sensors with strain gradients and grating lengths," NDT & E International, Vol. 38, No. 8, pp. 712-718 (2005) https://doi.org/10.1016/j.ndteint.2005.04.006
  14. W. Chung and D. Kang, "Application of FBG sensors for monitoring of railroad bridge," Journal of the Korea Concrete Institute, Vol. 24, No. 3, pp. 25-28 (2012) https://doi.org/10.4334/JKCI.2012.24.1.025