Fatigue experiments and assessment of structural steel unequal thickness butt-welded joints by means of local approaches

This study examines the fatigue failure behavior of Unequal Thickness Butt Welded Joint (UT-BWJ) in structural steel applications for construction machinery. The research combines experimental fatigue testing with Finite Element Analysis (FEA) to evaluate UT-BWJs using both structural and local assessment methodologies. Three distinct configurations of longitudinal load-carrying BWJs were analyzed to quantify their fatigue strength under cyclic tensile loading conditions. The investigation systematically evaluates the fatigue characteristics of UT-BWJs through comprehensive local and structural assessment approaches. The obtained fatigue strength was benchmarked against international standard codes and existing reference data. Additionally, multiple three-dimensional Finite Element (FE) models were established to simulate UT-BWJs with backing bars. The relationship between critical geometric parameters and fatigue performance was identified, and the fatigue loading capacity of these welded joints was evaluated by means of nominal stress, structural, and local approaches. Results indicate that fatigue life can be predicted using Strain Energy Density (SED) theory, and analytical solutions for predicting fatigue characteristics in UT-BWJs were proposed, demonstrating the accuracy of the estimation model. The results provide valuable insights for fatigue strength and design optimization of unequal thickness welded connections in structural applications.