Study of the influence of material and welding modeling on the residual stresses in longitudinal stiffeners

Accurate prediction of the magnitude and spatial variation of post-weld residual stresses in fillet welds is of great importance for the prediction and control of fatigue crack growth in welded structures. This is because the residual stresses associated with the welding process generally determine the location of crack initiation as well as influence the fatigue crack growth rate. However, predictions of residual stresses close to the weld toe are greatly complicated by the presence of local stress concentrations and material phase transformations. In this study, the residual stresses for an austenitic stainless steel and structural carbon steel are numerically computed to ascertain how the residual stresses at the critical weld toe locations depend on geometric stress concentrations, material properties, boundary conditions, and welding parameters. Because of the highly nonlinear nature of the material properties associated with the high-temperature elastic-plastic behavior during welding, it is important to determine the sensitivity of the numerical computations to changes in boundary conditions, mesh density, and material property variations. The results in this study focus on the state of stress close to the weld toe, where it is particularly difficult to obtain converged numerical solutions. The results show that the residual stresses at the weld toe depend strongly on phase change effects (in the case of carbon steel) and also the mechanical (clamping) boundary conditions. It is also shown that by verifying the extent traction-free boundary conditions are satisfied, it can be estimated that the numerical results generated in this study should be valid to within 1 mm of the weld toe for the idealized geometry considered in this study.