Computer Aided Nondestructive Evaluation Method of Welding Residual Stresses by Removing Reinforcement of Weld : A Proposal of New Concept and Its Application to Butt Welded Plate

Based on previous works, a new concept of a nondestructive stress measuring system for welded structures was proposed. Firstly, reinforcement of weld is removed. From strain changes on the surface due to removal, distributions of eigenstrain are determined by the inverse analysis. Then, residual stresses are estimated by the elastic FEM (Finite Element Method) analysis by using the determined eigenstrain distributions as anihnitial condition. Toward realization of this concept, applicability of this method was examined by simulations for a butt welded plate with anisotropic eigenstrains along and near a welding line. In a preliminary analysis on an effect of each eigenstrain component on welding residual stresses, it was found that an eigenstrain component in bead direction has a significant influence on producing residual stresses perpendicular and parallel to the welding line. Thus, by separating this dominating component from other two, an accuracy in the inverse analysis can be considerably improved. Further attempt to reduce unknown parameters in the inverse analysis was to approximate eigenstrain distributions by using a series of logistic functions, which proved to have a wide applicability as a curve fitting function form to actual eigenstrain distributions under various welding conditions. Finally, it was shown that welding residual stresses along and perpendicular to welding line in any location of the plate can be evaluated by using the proposed method.