Stiffness-degradation fatigue damage model for probabilistic reliability analysis of wind turbine blade

Composite wind turbine blades are subjected to multiaxial fatigue loading and environmental aging, which progressively degrade structural stiffness and ultimately impair reliability and service life. This study proposes an integrated reliability assessment framework that incorporates a novel fatigue damage model and advanced probabilistic methodologies. A 5 MW offshore wind turbine blade is evaluated using blade element momentum theory and computational fluid dynamics to simulate aerodynamic loading and fluid-structure interactions, with validation against benchmarks established by the National Renewable Energy Laboratory. To reduce computational burden, Kriging surrogate models are employed in place of high-fidelity simulations across a range of wind speeds and material parameters. A new three-parameter arctangent fatigue model is developed to characterize nonlinear stiffness degradation in composite laminates, capturing distinct fatigue stages: micro-crack initiation, stable crack propagation, and rapid failure. The proposed model demonstrates superior performance compared to existing models based on R² values and percentage deviation, with parameter γ identified as a critical factor in damage evolution. The fatigue model is embedded within a system reliability framework that accounts for correlated failure modes via a Gumbel copula. Uncertainty propagation and failure probability estimation are conducted using polynomial chaos expansion and saddlepoint approximation. The findings indicate a continuous decline in reliability over the blade’s operational lifespan. This comprehensive methodology provides a validated analytical toolset for enhancing the structural design and maintenance strategies of wind turbine blades under realistic service conditions.