High-temperature sensing performance of fiber Bragg grating sensors embedded in composite structures

Abstract This study presents the design, calibration, and performance evaluation of Fiber Bragg Grating (FBG) sensors embedded in phenolic resin-based glass fiber composites for simultaneous temperature and strain monitoring up to 600 °C. A custom high-temperature tensile testing system was developed to perform (i) static tensile tests at room temperature (RT) and after carbonization at 200 °C, 400 °C, and 600 °C, and (ii) dynamic thermal strain tests under controlled heating–cooling cycles. The results demonstrated that the FBG sensors can effectively measure the internal strain within the temperature range of 27 °C to 600 °C. Prior to carbonization of the composite, the elastic modulus at room temperature was approximately 17.5 GPa. After carbonization, the elastic modulus at 600 °C, 400 °C, and 200 °C was 4.1 GPa, 3.5 GPa, and 3.4 GPa, respectively, aligning well with independent high-temperature modulus measurements. The dynamic tests showed that the FBG sensors were able to accurately detect transient strain changes induced by load variations at different temperatures, which was consistent with thermal expansion data. This study provides crucial empirical evidence for the design and optimization of the thermal protection of composite materials, confirming the effectiveness of embedded FBG sensors for monitoring mechanical behavior in high-temperature environments.