Development of Numerical Estimation Technique for Production of Welded Structure with High Accuracy

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Most of the construction processes in the welded structures is the thermal working, which is phenomenally a kind of unsteady and nonlinear behavior. An objective of this research was to visualize and reveal such a nonlinear behavior by using various simulation methods based on the computational science. The main results in this study were as follows;(1) The inherent deformation method, in which the inherent deformation is introduced into the elastic finite element method (FEM) as the initial strain, is one of the effective methods to predict the plate panel welded structures such as ships and bridges. Where, the values of the inherent deformations for various weld joints must be known beforehand. So, in this study, a simple and efficient method to estimate inherent deformation of typical weld joints by using inverse analysis was developed and its validity was revealed through the examinations for joint specimens and large structures.(2) FEM is a powerful tool to predict the welding residual stresses and deformations. However, the three-dimensional (3D) thermal-elastic-plastic FE analysis requires very long computational times and most of the previous computations using 3D-FEM were limited to simple problems such as a bead-on plate welding and a butt joint welding. So, in this research, an iterative substructure method was developed as a method to reduce the computational time in 3D analysis based on the understanding that the welding problem is a strong nonlinear transient problem and the nonlinearity in welding is much localized. By using this method, the computing time was accelerated more than 10 times and the welding distortion of a part of the practical structure under a single pass welding can be analyzed. Also, it was succeeded to analyze and quantitatively predict the welding distortion of a part of nuclear reactor after multi pass welding.