Fig. 1. Flow chart of fatigue crack prediction based on FBG

Fig. 2. Component size diagram

Fig. 3. Strain field nephograms at different stages of crack propagation. (a) Crack initiation; (b) initial crack propagation; (c) steady crack propagation; (d) crack approaching failure

Fig. 4. Fatigue crack growth monitoring experimental system based on FBG

Fig. 5. Overall schematic diagram of FBG demodulation system

Fig. 6. Fatigue tensile results of samples 1--4

Fig. 7. Schematic diagram of FBG sensor array

Fig. 8. Actual pasting position of FBG sensor array

Fig. 9. Fitting result of fatigue extension a-N curve

Fig. 10. Wavelength change measured by sensor FBG1

Fig. 11. Relationship between peak-to-peak wavelength and cyclic loading times

Fig. 12. Relationship between peak-to-peak wavelength and crack length

Fig. 13. Tensile results of aluminum alloy sample 5

Fig. 14. Principle diagram of GBRT

Fig. 15. Principle of 5-fold cross-verification

Fig. 16. Prediction result of GBRT algorithm