Through-thickness distributions of the welding residual stresses were studied in the range of 50–100 mm thick plates by using finite-element modeling (FEM) and neutron diffraction measurements. In order to simulate the residual stresses through the thickness of the thick weld joints, this paper proposes a two-dimensional generalized plane strain (GPS) finite-element model coupled with the mixed work hardening model. The residual stress distributions show mostly asymmetric parabola profiles through the thickness of the welds and it is in good correlation with the neutron diffraction results. Both the heat input and plate thickness have little influence on the residual stress distributions due to the relatively large constraints of the thick specimen applied for each welding pass. A general formula has been suggested to evaluate the distributions of the through-thickness residual stresses in thick welds based on FEM and neutron diffraction experimental results.

In this study, the effects of ultrasonic impact treatment (UIT) on the residual stress in a repair welding joint are investigated by experimental and finite element methods. A three-dimensional numerical analysis approach including a thermomechanical-coupled welding simulation and dynamic elastic-plastic UIT simulation is developed, which has been validated by X-ray diffraction measurement and indentation strain method. The results show that longitudinal residual stresses basically turned into the small tensile stress state from the large tensile stress state, and transverse residual stresses have mainly turned into compressive stresses from large tensile stress after the UIT. In the thickness direction, the average decrease of longitudinal residual stress is 259.9 MPa, which is larger than the 149.1 MPa of transverse residual stress. The calculated residual stress distribution after the UIT of the thin plate is compared with that of the thick plate in the literature, with the results showing the stress accumulation layer inside the thick plate. The simulation results show that the elastic strains are decreased slightly and the equivalent plastic strain is increased markedly after UIT, which explains the mechanism of residual stress relaxation.