Evaluation of the three-dimensional welding residual stresses based on the eigenstran methodology via x-ray measurements

In order to predict the lifetime of welded structures, it is important to evaluate three-dimensional residual stresses nondestructively. However, X-ray diffraction is useful for measuring residual stresses only on the surface. Neutron diffraction is known to be an effective nondestructive method for measuring residual stresses till a depth of several tens of millimeters. Nevertheless, it is not a technique useful for on-site measurements. This is because neutron diffraction is achievable only within special irradiation facilities. In this paper, the authors have proposed a non-destructive method to estimate three-dimensional residual stresses by using X-ray measurements. In this method, the residual stresses for an entire structure are calculated from eigenstrains by using an elastic FEM (Finite Element Method) analysis. Eigenstrains can be estimated from elastic strains measured through X-ray diffraction using inverse analysis. The relationship between the three-dimensional eigenstrains and the surface elastic strains can be obtained if the Young's modulus, Poisson's ratio, and dimensions of the structure are known. This study aims to demonstrate the effectiveness of the proposed method on an actual butt-welded plate made of stainless steel SUS430. To evaluate the accuracy of this method, the residual stresses estimated using the method was compared with that measured using X-ray diffraction. In order to maximize the estimation accuracy of this inverse analysis, we considered the eigenstrain distributions along both the welding and thickness directions, as well elastic strains measured on the weld metal were used to estimate. (author)