Discussion on fatigue evaluation models of steel welded joints treated by HFMI

High frequency mechanical impact (HFMI) is widely used in the field as a reliable and efficient repost-weld treatment. In order to evaluate the fatigue life of steel welded joints treated by HFMI under different stress ratio R and material yield strength f_y, extensive fatigue test data were re-analyzed using the notch stress approach combined with SWT (smith-watson-topper) and Walker models. The results reveal that the relationship between the fatigue grades FAT, R and f_y of the joints under nominal stress system can be expressed by FAT = 0.1 f_y + M(R). Under the notched stress system, for joints made of the same material loaded under different R values, both models can be used to predict fatigue life, but the Walker model has higher accuracy. For joints of various materials with different R values, SWT model has a fixed form and can comprehensively consider the influence of R and f_y. Based on this, the survival rate P_S = 97.7% of the S-N curve with FAT = 325 MPa and slope m = 6.5 is obtained. The research will directly support the fatigue assessment and anti-fatigue design of engineering structures.