Modellering av korrosionsutmattning i armering för dynamiska sjökablar: En SWT-baserad analys av kopplingen mellan punktfrätning och mekanisk utmattning

As the world transitions to sustainable energy, the reliability of floatingoffshore wind farms is critical. A primary challenge lies in the longevity ofdynamic submarine power cables, whose steel armouring is simultaneouslyexposed to aggressive seawater corrosion and continuous cyclic loading fromwaves and platform motion. This coupled action of corrosion and fatigue,particularly the formation of corrosion pits that act as stress raisers, drasticallyreduces the cable’s service life. This complexity, combining electrochemistrywith advanced solid mechanics, justifies a dedicated research effort andexplains why no standardised predictive model currently exists.This thesis addresses this gap by developing a comprehensive computational framework to predict the fatigue life of 316L stainless steel armouring.The methodology integrates several advanced techniques within a FiniteElement (FE) model. Material behaviour under cyclic loading was capturedusing a combined isotropic-kinematic (Voce-Chaboche) hardening model.The progressive growth of a corrosion pit was simulated using a diffusioncontrolled model, implemented by deactivating FE elements over time whilecrucially preserving the accumulated plastic strain in the remaining material.Fatigue life at each pit depth was then calculated using the Smith–Watson–Topper (SWT) critical plane criterion, and Miner’s rule was applied to assesscumulative damage under a realistic annual wave-loading spectrum.The thesis successfully calculates the fatigue life, determined byidentifying the critical point where the rate of fatigue failure surpasses the rateof pit growth. The analysis confirms that as pits deepen, they significantlyamplify local stress and strain, accelerating damage accumulation. Thisthesis delivers a novel, integrated modelling framework that can now beused for virtual testing and comparison of different materials and designs. Itprovides a more cost-effective and time-efficient alternative to purely physicaltesting, enabling engineers to enhance the durability and reliability of criticalinfrastructure for renewable energy.