As a key pressure-bearing equipment, the degree of fatigue failure of natural gas pressure vessel affects the operational safety. Based on finite element stress analysis and Kwofie-Zhu model, this paper establishes an equivalent driving force model considering crack closure effect. Combined with the Johnson-Cook thermoviscoplastic constitutive equation and the fluid-solid coupling algorithm, the numerical analysis model of explosion crack extension is constructed. The correlation of stress ratio (R) to fatigue threshold (ΔKth) and the effect of yield strength on crack extension rate are revealed through multi-scale modeling analysis. The results showed that ΔKth decreased from 7.32MPa·m1/2 to 5.45MPa·m1/2 when R was increased from 0.05 to 0.35. The crack extension rate increased from 10-9cm/s to 10-8cm/s when the yield strength was increased from 282 MPa to 582 MPa. The multiscale modeling analysis reveals that R has a negative correlation with ΔKth, and the yield strength varies positively with the crack extension rate.
