Effect of Kinetic Energy due to Hail Impact on Damage Evolution in Gelcoated Glass Fibre Reinforced Polymer Composite
S. John Vaseekaran (TU Delft - Aerospace Engineering)
Julie J.E. Teuwen (Aerospace Manufacturing Technologies)
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Abstract
Leading Edge Erosion is a major concern for the wind energy industry as it affects the aerodynamic efficiency of wind turbine blades and, therefore, the power generated. Hail impact on the leading edge could significantly damage the protective layer and the composite substrate. The focus of this research study is to investigate the effect of kinetic energy on the damage mode in gelcoated glass fibre reinforced composite in terms of the velocity and sizes of the hailstone during hail impact. The gelcoated glass fibre composite samples were tested using a gas cannon using parameters based on conditions experienced in real life but with slight modifications to enable accelerated testing. The gelcoated samples were impacted at various velocities for different hailstone sizes, 15mm hailstone (140 m/s, 150 m/s and 160 m/s), 18mm hailstone (100 m/s, 110 m/s, 120 m/s and 140 m/s) and 20mm hailstone (90 m/s) to determine the Failure Threshold Energy (FTE) for each hailstone size considered. This threshold was determined to be the limit below which no damage would be initiated. The kinetic energy of each hailstone is estimated from the mass of the hailstone, and impact velocity, which is measured using a high-speed camera. Using non-contact profilometry (optical microscopy), cross-sectional damage analysis, and ultrasonic C-scan, the damage on gelcoated fibre-reinforced polymer composite samples were analysed.
The coatings did not exhibit any damage or signs of delamination in the coating-substrate interface. However, the substrate showed signs of impact damage. The damage mode was highly influenced by the kinetic energy imparted by hail impact. The damage mode of matrix cracks in the transverse and longitudinal directions was observed in the substrate for most of the impact parameters. The damage mode remained the same for the different hailstone sizes. The impact tests confirmed that a Failure Threshold Energy existed for each hailstone size. It was observed that FTE was increasing with the hailstone size, and it could be stated that multiple impacts had no effect on damage initiation for a limited number of impacts.