A Two-Stage Global-Local Finite Element Simulation Strategy for Fatigue Life Assessment of Wind Energy Rotor Blades

Kurzfassung

Traditional thermoset resins used in wind turbine rotor blades present significant recycling challenges, often ending up in landfills. The EU-funded ECORES WIND project aims to develop next-generation resin systems tailored for composite rotor blades that enables efficient recovery of both fibre and resin materials, potentially saving approximately 44,000 tonnes of composite waste and reducing CO2 emissions by 1500 kilotons annually [1]. Due to the rotor blades long service life of 20-25 years [2], composites made with this new-generation resin system must exhibit high fatigue performance. To computationally verify the fatigue performance of rotor blades fabricated from these new sustainable composites under realistic loadings, methods to predict their service life are developed.

The fatigue life assessment of wind rotor blades faces two main challenges: (1) Structural modelling, as fatigue simulations on large rotor blade structures are computationally expensive, and (2) Material modelling, as the complex fatigue damage behaviour of fibre reinforced plastics (FRP) needs to be captured based on test data that is usually limited.

To overcome the first challenge, a two-stage global-local simulation strategy is adopted. First, a global Finite Element (FE) model of the rotor blade is used to analyse its overall structural-mechanical behaviour. From these results, load-path-critical regions (hotspots) that are most susceptible to (fatigue) damage are identified. Second, a local sub-component model of the associated hotspot is developed, whereby appropriate boundary conditions are derived from the global model’s load and deformation field. This local sub-component model enables more detailed analyses, paving the way towards an efficient yet accurate computation of a large number of load cases.

To address the second challenge, the fatigue models by M. Kawai et al. [3] and C. Lüders et al. [4] are benchmarked against experimental SN test data on a specimen level. The model by Lüders has already been proven to provide reasonable fatigue predictions for specific FRP materials [4], however Kawai’s model needs significant less experimental data for calibration. The benchmark evaluates each model’s predictive capabilities relative to the experimental calibration effort required. Finally, it is demonstrated how both the fatigue models can be incorporated into the two-stage global-local modelling strategy to predict the fatigue life of the ETA 24m wind rotor blade [5] fabricated from the new sustainable resins.

References: [1] ECORES WIND: NOVEL CIRCULAR RESIN DEVELOPMENT FOR WIND BLADE COMPOSITES (2025). Retrieved 10 February, 2026, from https://www.ecoreswind.eu/wpcontent/uploads/2025/05/ECORES_WIND_brochure_final.pdf [2] P. Majewski, N. Florin, J. Jit and R. A. Stewart: End-of-life policy considerations for wind turbine blades. In: Renewable and Sustainable Energy Reviews 164 (2022), p. 112538. ISSN: 1364-0321. DOI: https://doi.org/10.1016/j.rser.2022.112538 [3] M. Kawai and M. Koizumi: Nonlinear constant fatigue life diagrams for carbon/epoxy laminates at room temperature. In: Composites Part A: Applied Science and Manufacturing 38.11 (2007), p. 2342- 2353. ISSN: 1359-835X. DOI: https://doi.org/10.1016/j.compositesa.2007.01.016 [4] C. Lüders, D. Krause, J. Kreikemeier: Fatigue damage model for fibre-reinforced polymers at different temperatures considering stress ratio effects. In: Journal of Composite Materials 52.29 (2018), p. 4023-4050. DOI:10.1177/0021998318773466 [5] M. Moschini: Requirements and Spec for New Materials in the Wind Turbine Sector. ECORES WIND Deliverable 1.1. (2025) Available from www.ecoreswind.eu