철도시스템의 구조건전성 모니터링을 위한 광섬유 센서의 장기 온도특성 평가

초록

Fiber optics sensors that have many merits compared to the other sensors are expanding their application areas from researches on signal characteristics at the beginning to researches on many other fields including railway systems. Various sensors and sensor systems on fiber optic sensors are successfully developed and applied to industrial areas and this leads fiber optic sensors to the initial level of commercialization. However, successful commercialization of fiber optic sensors needs more studies on effects of longtime exposure to environments with temperature changes. In detail, sensors that are under environments with temperature changes for longtime require longtime stability of sensor signals during the operation. Generally, fiber optic sensors for structural health monitoring are used as a package enclosed with metals through epoxy bonding. For the reason, fiber optic sensors can experience signal drift if they are exposed to longtime cyclic thermal loading and consequently it can lead to decrease of measurement reliability. In this study, longtime thermal characteristics of fiber optics sensors, FBG sensors in particular, are investigated through thermal cyclic tests for 300 cycles at temperatures ranging from -20C to 60C, which is equal to the temperature change for four seasons in Korea. Also, the test is conducted in a thermal chamber with respect to changes of both base materials for package and adhesive types. From the test results, gradual compressive strain occurs to the cycles of 50 from the beginning with maximum value of hundreds of micro strains and it maintains to the end of total cycles. In addition, the amount of compressive strain is related to both base material of package and adhesive type.