Finite Element Analysis of Welded Joints Under Variable Loading Conditions

Load histories of welded joints used in marine and offshore structures show high levels of complexity of variable amplitude (VA) loading histories which are different significantly from the constant amplitude loading usually considered in conventional design. In the paper, an FEA-based approach for evaluation of stress state and critical areas of fillet-welded structural joints operating under variable amplitude loading is proposed. Thermal-mechanical sequentially coupled simulation is used for determination of welding residual stresses and then transient dynamic analysis is carried out using artificially generated load histories. Hot-spot stress extrapolation method is applied for determination of structural stress concentrations at weld toes, while peak stress method can be used to calculate mesh-insensitive notch stress intensity factors. Comparison of stress ranges calculated for two joint details: non-load-carrying longitudinal and transverse stiffeners, shows the impact of mean stress level and load sequence on obtained stress range values. The findings of the work show that mesh-sensitive stress extraction method based on FEA allows determination of fatigue-critical zones reliably enough under VA loading conditions.