High Mechanical Strength Thermally Regenerated Fiber Bragg Gratings for High-Temperature Stress Monitoring

High-temperature resistant fiber Bragg grating (FBG) has a wide application in aerospace, energy, smelting, and other high-temperature sensing fields. However, the general FBG will experience grating thermal decay and fiber thermal embrittlement when working for a long time in high-temperature environments, resulting in the sensors being unable to be applied in stress-strain-related sensing. Therefore, the thermal stability and mechanical properties of FBG in high-temperature environments are crucial for health monitoring of high-temperature or high-pressure equipment. Here, we developed an effective approach of thermal regeneration and annealing for FBG by studying the influence of different annealing conditions on the axial stress and mechanical properties of FBG and then obtained a thermally regenerated fiber Bragg grating (RFBG) with high mechanical properties and high-temperature resistance. Compared with ordinary RFBG, the mechanical strength of RFBG obtained under optimized regeneration and annealing conditions is increased by about four times. Furthermore, six optimized RFBG sensors are utilized to simultaneously and stably monitor the temperature field distribution and local stress-strain state of a high-temperature autoclave. The corresponding mean temperature sensitivity and stress-strain sensitivity are 16.50 pm/°C and 1.25 pm/mu varepsilon , respectively. This work proposes an effective high-temperature and stress-strain sensing technology, which is expected to be used for structural health monitoring in high-temperature environment.