Research on Static Fatigue Failure and Life Prediction of High Temperature Resistant Fiber Bragg Grating Sensors

This study used fracture morphology methods to reveal the static fatigue failure mechanism of polyimide high-temperature resistant fiber Bragg grating sensors under constant amplitude loading. The mirror district, mist district, and sawtooth district presented in the local area of the fiber optic cross-section confirm that it follows the fracture law of hard and brittle materials. Static fatigue failure under constant amplitude load is caused by the gradual accumulation of internal stress and slow propagation of cracks in fiber Bragg gratings under long-term constant amplitude load. After reaching the critical number and size, brittle fiber Bragg gratings experience crystal bond fracture and structural instability, ultimately leading to sensor failure. Through experimental research, a static fatigue S-N curve function model of a high-temperature resistant fiber Bragg grating sensor was established under a constant temperature environment of 300°C. The results showed that its fatigue strength limit was about 330MPa. This provides a basis for scientifically predicting the static fatigue life of high-temperature resistant fiber Bragg grating sensors in practical applications.