Measurement uncertainty of fatigue properties and its effect on the wind turbine blade reliability level

Wind turbine rotor blades are large composite structures performing most of their design life under random cycle loading patterns. Material properties of the building ply exhibit also inherent variability. In order to assure a safe and cost effective design, uncertainty related to the basic variables (material properties, loads, etc.) should be quantified and taken into account in design calculations. Herein, for the first time, measurement uncertainty for the fatigue properties of the composite material is quantified based on detailed experimental data and following principles of metrology. The effect of considering measurement uncertainty directly on the blade failure probability is investigated by enhancing probabilistic analysis tools developed for use on wind turbine blade design. The application is performed on the INNWIND.EU reference 10MW rotor blade of 90m length. Sensitivity analysis with respect to the final reliability estimation is further performed on the fatigue analysis details, such as the selection of constant life diagram and the discretization strategy followed in the rainflow counting method.