Fatigue crack propagation characteristics of segmented egg-shaped pressure shells

This study focused on the fatigue crack propagation and fatigue life of an egg-shaped pressure shell fabricated by welding and hydroforming a six-segment frustum. First, the segmented egg-shaped pressure shell was designed, and the hydroforming was analysed by the finite element method (FEM). Moreover, the numerical simulation of the egg-shaped shell under uniform external pressure and welding residual stress was carried out, and the stress distribution at the weld was obtained. Second, the equivalent specimens were designed to have structures with maximum stress in the weld. Equivalent specimens with different initial crack shape ratios were tested, and the unified crack propagation rate model of 18Ni (250) was obtained by fitting the data. The fatigue life of the equivalent specimen was calculated by ABAQUS and FRANC3D software and compared with the test results. Finally, the crack propagation rate model was used to predict the fatigue life of the egg-shaped pressure shell. The results of this study provide a reference for prediction of fatigue damage and assessment of the safe operation of egg-shaped pressure shells. •The equivalent specimen was designed to have a structure with the maximum stress of the segmented egg-shaped shell weld.•Equivalent specimens with different initial crack shape ratios were tested, and the unified crack growth rate of 18Ni (250) was obtained.•The numerical results of fatigue life of equivalent specimens agree well with experimental results, the deviation is 0.59%–12.56%.•The optimum pressure for the hydraulic forming of the segmented egg-shaped was obtained.