Computer Aided Nondestructive Evaluation Method of Welding Residual Stresses by Removing Reinforcement of Weld : Introduction of Regularization Method and Optimization of Strain Measuring Location

In a previous work, a new method was proposed to estimate 3-D welding residual stresses nondestructively. Firstly, 3-D eigenstrain distributions are estimated by the inverse analysis from surface strain changes due to removal of reinforcement of the weld. Then, residual stresses are easily determined by an FEM analysis using estimated eigenstrains as boundary conditions. Under an existence of possible experimental errors. however, a solution of the eigenstrain distribution becomes unstable due to the ill-posedness of the problem, which is not acceptable as an actual evaluation method. To overcome above ill-posedness, a regularization method based on the singular value decomposition was incorporated. It is confirmed that 3-D residual stress distributions can be obtained in good accuracy. Then, a new optimizing method determining strain measuring locations under reasonably small number, was proposed based on the experimental design theory using the Doptimality criterion and its utility is shown.