Distortion mechanisms and control methodology for welding thin-plate panel structures

Welding distortion behavior induced by welding a thin-plate panel structure was studied focusing on its basic mechanisms, buckling and angular bending, and the control methodology necessary to obtain minimum welding distortion. As a tool for numerical analysis, the inherent shrinkage model was proposed to analyze welding residual stresses and distortion. In this study, welding induced distortion in panel structures was characterized as global or local distortion. Global distortion is related to girder bending which may cause the panel plates to buckle, local distortion is angular plate bending and plate buckling induced by in-plane stresses due to weld shrinkage.; To analyze the buckling behavior of the stiffened plates, parametric numerical analysis was performed using a mechanical and thermal model. The changes in residual stresses were characterized in both distribution and magnitude for the stiffened panels with respect to various design variables. From the analysis results, it was found that in-plane residual stresses had little effect on buckling strength of stiffened panels because the compressive residual stress was not sufficient in magnitude and decreases with increasing plate width. From analysis using a mechanical model, large girder displacement can induce large deformation in the panel plates, however, the girder displacement due to the fillet weld shrinkage is too small to cause buckling in the stiffened panel plates.; From numerical analysis of a constrained T-joint panel plate, angular plate bending was found to be dependent on the welding sequence. To obtain an optimum welding sequence, the joint rigidity method (JRM) was developed. The joint rigidity method was based on the continuous evaluation of the changing joint rigidity of the panel structures with the progress of the welding process. The joint rigidity method was then applied to a single panel structure and a complex ship panel structure. The optimum welding sequence was determined by following the maximum joint rigidity of each joint. This optimization procedure resulted in a welding sequence which caused minimum angular plate bending as compared with other welding sequences.