Fiber-optic sensor for simultaneous strain and temperature monitoring in composite materials at cryogenic condition

Low thermal sensitivity and cross sensitivity of Fiber Bragg Grating (FBG) towards the applied strain, temperature make FBG implementation complicated in composite materials at cryogenic conditions. In order to alleviate this problem, our work focuses on simultaneous strain and temperature monitoring inside the composite material at cryogenic temperatures. The temperature sensitive polymer coating on an FBG sensor makes it a suitable candidate for cryogenic temperature measurement. The average temperature sensitivity of 48 pm °C−1 was obtained in −1180 ∼ 25 °C. In addition, the cross sensitivity problem has been adjusted by introducing a glass capillary tube to encapsulate the FBG. The thermal expansion of capillary material was compensated by cleaving the one end of FBG free and the other end with the temperature resistant epoxy resins. Experiments results validate that the proposed method can successfully monitor the strain and temperature factors that can be applied to composite material at cryogenic temperatures.