Engineering Viscoelastic Properties in Polyurethane Coatings to Reduce Erosion Risks in Wind Turbine Blades

The dynamic mechanical response of a commercial prototype Leading Edge Protection (LEP) coating based on polyurethane (PU) chemistry is analysed using Dynamic Mechanical Thermal Analysis (DMTA) as a function of temperature and frequency. The temperature range chosen reflects the operating range used in offshore wind turbines, with the damping characteristics of the coating maximal at 25 °C. The Time Temperature Superposition (TTS) methodology was applied to the DMTA data to predict the viscoelastic behaviour of the PU LEP at frequencies (10-2 - 1010 Hz) consistent with the predicted strain rates induced by the impact of rain droplets on wind turbine blades (106 - 109 Hz). A Young’s modulus is reported for the PU of 2.78 x106 GPa at 108 s-1, compared with 278 MPa at 1 s-1 i.e. the equivalent of quasi-static testing. This method presents a potential for improved understanding of LEP material at high strain rates and a test methodology for generating material properties for coating lifetime prediction.