Enhanced local fatigue approach for welded tubular joints using 3D digital scans and implicit gradient model

The design of jacket structures in offshore wind turbines (OWTs) is driven by fatigue, crucial due to dynamic loads from operational movements, waves, and wind. This study aims to develop a digital framework for fatigue analysis of tubular welded joints in jacket OWT, incorporating real 3D scanned geometries and imperfections through their digital images. Numerical analysis has been conducted using finite element method to predict the experimental results, in which the effect of micro-support has been taken into account using an implicit gradient model (IGM). Furthermore, 4R method has been used to account for mean stress corrections due to residual stresses and imperfections. Digital Image Correlation (DIC) was employed during the high-cycle fatigue experiments to detect the initiation and progression of a technical crack, providing precise measurements of strain distribution and crack size development. The results have shown that the proposed numerical framework based on the IGM can successfully determine the lifetime and location of crack initiation in the 3D scanned welded details. The proposed framework significantly improves the accuracy of high-cycle fatigue life predictions and offers a scalable solution for structural health monitoring, facilitating lifetime extension across a wide range of industries, including construction, automotive, aerospace, and renewable energy.