The residual stress in one-groove welding using an ellipsoidal heat source is analysed. The results show that it can ameliorate the residual stress distribution and greatly decrease the peak value of residual stress after welding if the converse welding method is adopted between adjacent layers in a multi-layer weld, or between adjacent beads in every layer. Moreover, the numerical simulation results of the double V-groove thick plate welding model show that the residual tensile stress appears on the weld and nearby, the residual compressive stress appears on the area far away from the weld and the peak value of tensile stress appears on the surface of the weld. Differences in the welding sequence influence the value and the distribution of the welding residual stress greatly, and a more suitable welding sequence can be deduced. The reliability of the numerical simulation results is proved by the experimental results.

In order to improve the fracture resistance of undermatched butt joint, the influence of joint shape parameters on the stress intensity factor (SIF) of undermatched butt joint with mode I centre crack was studied, and the solution of SIF was obtained by combining the analytical method with the finite element method as well. The results are useful to guide the shape design of undermatched butt joint with mode I centre crack under both static load and fatigue load conditions.