A Special User Shell Element for Coarse Mesh and High-Fidelity Fatigue Modeling of Spot-Welded Structures

A special spot weld element (SWE) is presented for simplified representation of spot joints in complex structures for structural durability evaluation using the mesh-insensitive structural stress method. The SWE is formulated using rigorous linear four-node Mindlin shell elements with consideration of weld region kinematic constraints and force/moments equilibrium conditions. The SWEs are capable of capturing all major deformation modes around weld region such that rather coarse finite element mesh can be used in durability modeling of complex vehicle structures without losing any accuracy. With the SWEs, all relevant traction structural stress components around a spot weld nugget can be fully captured in a mesh-insensitive manner for evaluation of multiaxial fatigue failure. For validation purposes, a set of spot-welded lab test specimens has been analyzed for demonstrating the mesh-sensitivity of structural stress computation and fatigue test data transferability, e.g., from lap-shear to coach-peel. Excellent results have been obtained.