Research on fatigue failure and life of high-temperature resistant fiber Bragg grating sensors

This study adopts the method of fracture morphology to reveal the fatigue failure mechanism of fiber bragg grating sensors under cyclic loading. The mirror district, mist district, and sawtooth district of the fiber optic cross-section confirm that it follows the fracture law of hard and brittle materials. The failure is caused by initial defects on the surface of the optical fiber, which induce cracks during the process of increasing stress. When the crack size reaches the critical value, it leads to fracture. Due to the higher brittleness of the optical fiber compared to the coating layer, the grain boundary friction intensifies during cyclic loading, leading to grain boundary fracture. In addition, cyclic loading accelerates stress corrosion, resulting in additional damage and promoting crack propagation. Through the analysis of experimental data, an S-N curve function model of the fiber bragg grating sensor was established under the conditions of constant temperature at 300℃, 10Hz vibration frequency, and 0.1 stress ratio. The results showed that its fatigue strength limit was about 330MPa. This provides a basis for scientifically predicting the service life of fiber bragg grating sensors in practical applications.