Research On Relaxation And Controlling Of Welding Residual Stress In Welded Joint

Welding is one of the key technological processes in the field of ship and naval architecture building. During the shipbuilding process, welding technology is widely used from parts manufacturing to subassemblies joining, even hull blocks erection. But due to the welding residual stress presents in the welded joint, which causes many adverse effects on the performance and reliability of welding structures of ship. Therefore, how to simulate the welding residual stress accurately, analysis its effects to the fatigue life of welding structure and effectively control it see a tremendously importance in practice.Firstly, thermal elasto-plastic finite element method is used to calculate the temperature field and welding residual stresses in dissimilar butt-welded Q235 steel and 304 Stainless Steel plates. The experimental result verifies the reliability of finite element modeling. The calculation and experimental results indicate that differences between physical properties of parent materials caused the asymmetric distribution of the welding temperature field and the residual stress; Peak of the longitudinal residual stress presents on 304 Stainless Steel side. Based on above study, the welding residual stresses in dissimilar butt-welded Q235 steel and 304 Stainless Steel pipes with different welding currents were studied here, the calculation result indicates that residual stresses are asymmetric distribution in both inner and outer surface of the pipes; Axial residual stress in both inner and outer surface keeps balance; Changing in welding current does not have a significant effect on the peaks of stresses.Secondly, longitudinal residual stress relaxation and fatigue life of the butt-welded Q235 steel plate under cyclic load were simulated and calculated. The numerical simulation result indicates that the residual stress relaxation is almost limited to the first cycle under the cyclic load with constant amplitude, and has nothing to do with the load cycles; Magnitude of the residual stress relaxation depends on the peak of the cyclic load, the higher the peak of cyclic load is applied, the more relaxation of residual stress will be. The result of fatigue life shows that the lowest part of fatigue life presents in the weld and the area nearby the weld.At last, through simulating the welding residual stresses in butt-welded Q235 and 304 Stainless Steel plates with different pre-tensile stresses, the result indicates that stress the longitudinal residual stress can be significantly decreased by applying with suitable longitudinal pre-tension(0.4s～0.7s), and the more the pre-loads, the lower the longitudinal residual stresses.