Study of ageing of laminates and its effects on wind turbine blade deflection

Some wind turbines have exceeded their nominal design service life and are continuing their operation with periodic inspections and maintenance. In the case of rotor blades, the reliability of the inspection is very limited because of the blade structure that comprises laminates and sandwich structures, which are very difficult to monitor. For this reason, wind farm owners are searching for technologies or approaches that will guarantee a safe operation of their wind turbines after the design life has elapsed. The main objective of this paper was to investigate whether detection of ageing of wind turbine blades using deflection as key parameter is feasible using commercial equipment. The paper is divided in three phases. In phase 1, the effect of ageing on a new UD‐0° glass fibre with high moduli was obtained. Using these results and bibliography data, a theoretical study was performed in phase 2 to determine the magnitude of blade deflection along its lifetime due to material ageing. Finally, in phase 3, in‐field deflection measurements where performed on a wind turbine blade to evaluate the utility and limitations of commercial equipment for the detection of blade ageing. It was concluded that material ageing could result in an increase in blade deflection under self‐weight that can be detected using commercial measurement equipment. These results can be used by wind farm owners in their O&M strategies to monitor blades over time and decide whether they should be repaired or replaced.