Optimization research on S-N curve of ring welding structure based on structural stress method

In engineering, oF-N curves are usually used to predict the fatigue life of ring welding, which is time-consuming, laborious, and not universal. To improve the above inadequacies, an S-N curve for evaluating the fatigue life of the ring welded specimen is proposed. The fatigue life of ring welded specimens with different materials, plate thicknesses, and hole diameters is obtained by tensile and shear fatigue tests. Shell elements, CBar beam elements (a kind of beam element in Nastran that can simulate bending), and rigid elements are used to establish the finite element model of ring welding. The stress of the ring welding structure under tensile shear load is calculated according to the structural stress method. The stress range o sigma s of the welding core is taken as the longitudinal coordinate and the experimental life N as the horizontal coordinate, using two-parameter log-log model and the least square method of the fatigue data for linear fitting to obtain the S-N curve equation of fatigue life evaluation. Most of the data are located within five times of the life span, which proves that the predicted life is close to the actual life of the test, and it can provide a certain reference for design and life prediction of the ring welding structures.