Numerical analysis of fatigue crack growth in welded joints with multiple defects

In the case of welded steel structures (such as pressure equipment), welded joints are often critical location for stress concentrations, due to different mechanical properties and chemical composition compared to the parent material, and due to changes in geometry. In addition, the presence of imperfections (defects) in welded joints can contribute to the increase in local stress, resulting in crack initiation. Recently, standards that are related to acceptable dimensions of various types of defects in welded joints started taking fatigue loading into account as well. For the purpose of this research, a 3D numerical model was made, of a welded joint with different types of defects (linear misalignment and a crack in the weld metal), based on the previous work, which involved static loading of the same specimen. In this case, fatigue was taken into account, and the simulation was performed using ABAQUS software, as well as Morfeo, an add-on used for determining the fatigue behaviour of structures via XFEM (extended finite element method). The welded joint was made using steel P460NL1 as the parent material, and EPP2NiMo2 wire was used for the weld metal. An additional model was made, whose defects included a crack and an overhang. Fatigue crack growth analysis was performed for this model as well, and the results for stress intensity factors and stress/strain distribution were compared in order to obtain information about how different defects can affect the integrity of a welded joint