Numerical simulation and experimental study on constant amplitude fatigue behavior of welded cross plate-hollow sphere joints

In order to reveal the constant-fatigue fracture form and mechanism of the welded cross plate-hollow sphere joints (WCPHSJs) and establish its formula, the WCPHSJs were fatigue tested. A total of 19 specimens were tested under constant amplitude fatigue loads using a specially designed test rig. The joint was analyzed statically by the finite element analysis (FEA), and metallographic analysis of fatigue fracture was done by the electron scanning microscope. Numerical simulation and experimental results show that the hot-spot of WCPHSJ lies at the weld toe location where severe stress is concentrated. Fatigue cracks initiate at the weld toe and then propagate circumferentially around the sphere with a diameter equivalent to the width of the cross plate up to the fatigue fracture. The initial welding defects and constructional detail constitute the main factor of fatigue failure. The S-N curves for the joints were developed through a linear regression analysis of fatigue data. A formula for calculating constant amplitude fatigue, based on the concept of the hot spot stress amplitude, is proposed.