Fatigue Assessment of Repair-Welded Cast Iron for Sustainable Energy Structures

As the demand for sustainable infrastructure intensifies, repair welding has become a critical solution for
extending the service life of large-scale cast iron components. This is especially true in applications such as
wind turbine hubs [1], where complete replacement is often economically impractical. However, the brittle
nature of cast iron, combined with its susceptibility to thermal and mechanical fatigue, calls for advanced
strategies to evaluate and improve its performance after repair. This study presents a novel integrated
experimental and numerical approach to characterise fatigue crack growth (FCG) in repair-welded ductile cast
iron, with a specific focus on the influence of residual stresses (RS) and weld bead geometry. Fatigue tests
were carried out on compact tension specimens extracted from the weld metal (WM), heat-affected zone
(HAZ), and base metal (BM), revealing significant variation in fatigue thresholds across the different regions.
To complement the experimental work, a validated coupled thermo-mechanical finite element model was
developed to simulate RS fields induced by various welding strategies, including multi-pass welding, inter-
pass temperature control, and weld bead removal. These RS fields were incorporated into 3D FCG simulations
involving semi-elliptical surface and embedded cracks. The results demonstrate that tensile RS significantly
accelerates surface crack propagation at weld toes, while compressive RS can impede embedded crack growth
[2]. Furthermore, removing the weld bead was shown to enhance fatigue life by reducing geometric stress
concentrations. The proposed methodology was applied to a full-scale wind turbine hub repair scenario. The
results showed that RS can reduce fatigue life by over 50 percent. This integrated framework offers a predictive
and cost-effective tool for optimising repair welding procedures in safety-critical cast iron structures, bridging
the gap between laboratory findings and real-world industrial applications.