Residual Stress Characteristics in Spot Weld Joints of High-Strength Steel: Influence of Welding Parameters

This study examines the residual stress characteristics of spot welding in newly developed high-strength steel for automotive body construction through experimental and numerical methods. The effects of sheet thickness, nugget size, and the presence or absence of spacers on residual stress distribution and fracture stability were evaluated. Measurements using XRD and HDR revealed tensile residual stress below the yield strength at the nugget center. A numerical analysis system corroborated experimental findings, demonstrating that larger nugget sizes reduce tensile residual stress at the nugget center, enhancing fracture stability. However, for nugget sizes of 3$\sqrt{t}$ (t: thickness), high tensile stress at the nugget edge compromised stability, while sizes of 3.5$\sqrt{t}$ or larger improved fracture resistance. The study also found that thicker sheets increased fracture safety with larger nugget sizes, and the presence of spacers induced tensile stress through spring-back effects, which shifted to compressive stress as the nugget size increased. These results provide critical insights into optimizing welding parameters to improve the structural integrity of automotive components.