Fig. 1. Flow chart of surface topography feature extraction in fatigue damage process

Fig. 2. ‍Schematic diagram of 2-layer decomposition of surface topography

Fig. 3. Specimen size

Fig. 4. Experimental system

Fig. 5. Diagram of specimen surface pretreatment area

Fig. 6. 3D topography of each fatigue damage stage^[18]

Fig. 7. Decomposition of gray images of each fatigue damage stage. (a) Fatigue cycle: 0; (b) fatigue cycles: 2000; (c) fatigue cycles: 4000; (d) fatigue cycles: 6000; (e) fatigue cycles 8000; (f) fatigue cycles 10000

Fig. 8. Contrast curves at the highest layer

Fig. 9. Correlation curves at the highest layer

Fig. 10. Characteristic parameter curves at the highest layer. (a) Energy; (b) homogeneity

Fig. 11. Mean value curves of contrast at the highest layer

Fig. 12. Mean value curves of correlation at the highest layer

Fig. 13. Mean value curves of energy at the highest layer

Fig. 14. Mean value curves of homogeneity at the highest layer

Fig. 15. Damage prediction results