Finite element simulation of multi-layer repair welding and experimental investigation of the residual stress fields in steel welded components

In this work, the effect of multi-pass repair welding for removing a fatigue crack on the residual stress fields of GMA-welded S355J2 + N and S960QL structural steel T-joints was investigated. Two scenarios were considered, a fatigue crack smaller than half of the plate thickness, and a fatigue crack larger than half of the plate thickness. Samples were first welded in a T-joint structure; then, cracks were created on their weld toes by cyclic loading; after that, the cracks were machined at one or two sides of the plate, depending on the crack length, and finally, the sample was repaired by two-pass welding on each machined area. Longitudinal and transverse residual stresses were measured by the X-ray diffraction method. A 2D thermo-metallurgical-mechanical finite element model was developed for each sample to estimate the residual stress fields through the weldments. The results show that, regardless of the alloy or repairing in one or two sides, the repair welding increases the magnitude of the residual stresses compared to the initial weld, but the alloys show different behaviors during the process. In S960QL samples, during repair welding of one weld toe, the residual stress evolutions in previously welded areas that are not subjected to the repair welding occur due to the morphological changes in the phases and expansions and contractions, while for S355J2N samples, the expansions and contractions are mainly responsible for these changes.