Abstract
Lightweight welded steel structures with high fatigue strength are demanded in various industrial applications such as wind farms, offshore structures, ships, and bridges. High-frequency mechanical impact (HFMI) treatment is an effective tool for this demand. Applying the HFMI treatment introduces compressive residual stress in the weld toe and material hardening in the surface layer, improving the local weld geometry and removing typical weld defects. A matter of concern in real situations is the alteration in compressive residual stress layer by high-peak loads, which may suppress the benefit of HFMI treatment. Since the crack initiation and propagation periods within short crack lengths significantly contribute to the total fatigue life for the HFMI-treated welds, a deep understanding of local evolution and relaxation of residual stress at a potential crack initiation site is needed. Thus, this study aims to clarify the local relaxation of residual stress in HFMI-treated high-strength steel welded joints subjected to high-peak loads. First, experimental measurements characterize residual stress, local notch geometry, and material properties for the HFMI-treated welds. Then, the weld joint behaviour is simulated with FE analyses incorporating those experimental measurements and load cycles, including high tensile and compressive peak loads. This simulation considers two types of HFMI geometry models: with or without roughness effect on the HFMI groove surface. Finally, the changes in residual stress due to the applied loads at different crack initiation potential sites and the influence of the model definition of HFMI geometry on residual stress relaxation are discussed. Session
