The growing demand for renewable energy has led to significant developments in wind turbine technology. The ever increasing size of turbine blades and their exposure to a variety of environmental factors can affect their annual energy production and service life. Erosion caused by rainfall and hailstones is identified as two of the most detrimental types of environmental factors to the life of a turbine blade. Hailstone impact in particular is expected to affect the aerodynamic profile of the leading edge as well as cause significant damage to the composite substrate.

The aim of this research study is to investigate the effect of varying hailstone sizes on the damage mode in leading edge polyurethane coated composites subjected to hail impact. The coated glass fibre composite samples were experimentally tested using an impact gas cannon. The impact parameters were determined based on real-life scenarios of blade tip speeds and hailstone sizes. Simulated hail ice (SHI) were manufactured using de-ionized water to form monolithic ice spheres. SHI of 15 mm and 20 mm diameter were used in the research for conducting the hail impact experiments. The coated composite samples were evaluated using non-contact profilometry (optical microscopy) and non-destructive testing (ultrasonic c-scan). Observations revealed that the polyurethane coatings remain largely intact throughout the hail impacts and no visible sign of damage or delamination between the coating and substrate was noticed during damage analysis. The damage mode of matrix cracks in the substrate for the impact parameters used, remained the same for both hailstone sizes. Further, it was seen over the experiments that there exists a failure threshold energy (FTE) for each hailstone size and sample thickness, below which no surface/sub-surface damage is visible. It is hypothesized based on observations in literature that a smaller hailstone will have a lower FTE compared to a larger hailstone and will be more lethal, owing to the concentrated area of contact. Future research to develop further awareness of damage evolution in the coated composites is recommended and discussed.