Numerical evaluation of surface welding residual stress behavior under multiaxial mechanical loading and experimental validations
Welding residual stresses have been always seen as a threat to the integrity of structures and components during service loadings. However residual stresses could partially or even totally relax under thermal or mechanical external loads if the sum of residual stresses and load stresses exceeds the material yield strength. If the stable portion of residual stresses after relaxation is still significant, care must be taken that residual stresses, similar to mean stresses, could shift the applied stress range. Accordingly, for a reliable structural integrity assessment an accurate insight into the stable residual stress field is essential. A three-dimensional FE model was implemented in software ABAQUS in order to study the relaxation and redistribution of welding residual stresses in a bead on tube weld under multiaxial mechanical loading. The predefined field of residual stress was initially calculated through a welding simulation in software SYSWELD. To verify the numerical simulations, a couple of tubular samples made of steel S355J2H were TIG welded and then mechanically loaded at different applied load levels. The surface residual stresses were measured by means of x-ray diffraction (XRD) in the as-welded condition and also after applying the mechanical loads for further comparisons. Pure torsion and multiaxial tension-torsion loading conditions in the form of quasi-static loading-unloading were investigated experimentally. The predicted welding residual stress relaxation conforms well the measurement results. The accordance between the numerical and experimental relaxation results confirmed the validity of the FE model. The validated model was then used to evaluate numerically the behavior of residual stresses under cyclic torsion loading with regard to the influence of the used material model. Based on the results, for such a material, the major relaxation occurs during the first cycle due to the monotonic yielding but further relaxation may take place in the upcoming cycles due to the accumulation of plastic strains.