Bio-Inspired Gradient Coatings Enhance the Leading Edge Erosion Resistance of Wind Blades.

Rain-induced erosion of wind blades is a challenge to wind energy growth. As blade lengths and tip speeds increase, droplet-impact kinetic energy increases, accelerating surface degradation and reducing aerodynamic efficiency. Conventional polyurethane coatings require maintenance and are unable to withstand prolonged exposure to high-frequency impact stresses. Recent approaches have investigated impedance-matched multilayer and particle-reinforced coatings, but these often suffer from abrupt impedance transitions and weak interfacial adhesion. Here, we demonstrate that a bio-inspired, platelet-reinforced polyurethane coating with a graded through-thickness architecture enhances erosion resistance. We reason that minimising the acoustic impedance mismatch between the coating and substrate while maintaining a compliant outer layer reduces interfacial stresses. Compared to monolayer coatings, our system doubles the incubation time under erosion testing, confirming increased durability. Dynamic Mechanical Analysis shows that platelet volume fraction governs the viscoelastic and acoustic impedance behavior, while orientation has negligible influence on viscoelasticity but is critical for wave propagation and damage evolution. We demonstrate that these graded architectures inspired by natural impact-resistant structures offer superior protection. By providing a deeper understanding of the interplay between acoustic impedance, viscoelasticity, and wave propagation, our study lays the groundwork for designing bio-inspired graded coatings that actively mitigate impact damage in renewable energy applications.