These slides were presented at the NAFEMS World Congress 2025, held in Salzburg, Austria from May 19–22, 2025.

Abstract

Weld cracks play a significant role to fatigue failure, making the accurate modeling of both spot welds and seam welds crucial for structural durability. In the automotive industry, various methods, such as force-based and nominal stress approaches, are recommended by international guidelines for assessing the fatigue life of welded components. However, directly incorporating local stress provides more accurate results. The key geometrical parameters of welds are the notch radius at the weld toe and root, along with the penetration depth at the weld root. Accurately simulating the geometric notch requires extremely fine meshes to capture local stress, which can result in considerable computational demands. To tackle this challenge, an approach with superelements is introduced. In finite element analysis, the superelement method simplifies and accelerates the evaluation of complex structures by dividing them into smaller, manageable components called superelements. Each superelement is treated as an independent substructure with its behavior condensed into a reduced set of equations, which are then integrated into the global analysis. In this case, each spot or seam weld is represented as a separate superelement. The study thoroughly outlines the process of generating superelements to represent welds, accurately positioning them within the complete assembly, recovering stress components at the notch and calculating at the end fatigue life. For various types of seam welds, such as overlap, Y-joint, laser, butt and corner welds, precise placement along the weld line is particularly challenging and requires special attention. A constant weld radius is applied and von-Mises equivalent stress is used as the fatigue criterion. This work involves the comprehensive analysis of components with welds, providing a thorough and detailed description of the entire process and the challenges faced. It includes comparisons of stress results between superelement welds and those modeled with detailed geometry, aiming to critically evaluate the methodology and emphasize its significant practical benefit.