Effects of hidden welding and overlap ratios on the fatigue life of partially overlapped tubular joints

Abstract

Offshore wind turbine support structures endure significant cyclic fatigue loads, causing peak stresses at welded joints, which can lead to crack initiation and structural failure. The fatigue performance of welded tubular joints is therefore critical in ensuring safety and extending service life. Challenges arise in assessing joints with varying overlap ratios and with or without hidden welds, as traditional methods often fail to capture the complexities of residual stress and welding deformations that influence fatigue behavior. In this study, fatigue analysis of tubular joints with or without hidden weld and with different overlap ratios was conducted to estimate the fatigue life and predict the crack initiation positions. The 3D fatigue FE analysis is based on constitutive equations, thermal elastoplastic analysis, and continuum damage mechanics. Residual stresses and welding deformations were modeled to simulate the weld’s initial state, providing realistic input for cyclic loading in the FE analysis. The study aims to estimate fatigue life and identify likely crack initiation sites in various tubular joint configurations under cyclic fatigue loads. S–N curves obtained through this analysis were compared with Eurocode 3 standards, validating the approach. The study offers refined insights into fatigue behavior across joint types, supporting safer, more reliable offshore wind turbine designs.