Study on fatigue characteristics of girth welded joints based on equivalent stress intensity factor

[Objective] When designing the fatigue resistance of girth welded joints, it is necessary to measure the fatigue life of girth welded joints with different geometric parameters, which wastes a lot of time and labor costs. [Methods] In this paper, the shear fatigue tests of stainless steel girth welded specimen with different geometric parameters are carried out. The fatigue loading-life (ΔF_a-N) data are obtained. The fatigue characteristics of girth welded joints are analyzed based on the fracture mechanics method with the stress intensity factor under the mixed fracture mode used as the fatigue strength evaluation parameter. The Δk_eq-N_f curve independent of the girth welded geometric parameters is calculated by analytical method and finite element method. The influence of plate thickness and hole size on the fatigue strength of girth welded joints under the same load is studied. [Results] The goodness of fit of the fitting curve by the analytical method is 0.873, while the goodness of fit of the fitting curve by the finite element method is 0.940. [Conclusion] The results show that although the analytical method is simple and efficient, it cannot consider the different thicknesses of the upper and lower plates of the specimen. The finite element method is more general than the analytical method, and it can obtain Δk_eq-N_f with a better normalization effect. Under the same load, Δk_eq decreases with the plate thickness ratio and pore size increase. Consequently, the fatigue strength increases with the plate thickness ratio and hole size. The equivalent stress intensity factor as the fatigue strength evaluation parameter can provide a reference for the structural optimization design of girth welding joints.