Damage Mechanism on Aircraft Coatings of Different Thicknesses under High-speed Water Jet Impact

As a critical component on the leading edge of an aircraft's airframe, the composite radar dome is susceptible to multiple types of damage to its skin when the aircraft passes through rain showers at high speed, resulting in a significant decline in the dome's performance and posing a threat to flight safety. Therefore, a rain-erosion-resistant coating is typically applied to its surface to ensure that the dome meets performance protection requirements. To elucidate the mechanism of rain erosion damage to the radar dome skin coating and to investigate the factors affecting coating damage and their mechanisms of action under different conditions, this work used T300 carbon fiber as the substrate and applied a coating consisting of an epoxy primer and a polyurethane topcoat as test specimens. The rain erosion damage behavior of specimens coated with different types and thicknesses of aerospace polyurethane coatings was evaluated at various impact velocities. Three thickness configurations were established: with a uniform primer thickness of 200 μm and topcoat thicknesses of 200, 250, and 350 μm, with a uniform topcoat thickness of 300 μm and primer thicknesses of 100, 150, and 250 μm and with a total coating thickness of 500 μm and primer-to-topcoat ratios of 1 : 4, 3 : 7, 1 : 1, and 3 : 2. The test setup consisted of a single-jet test platform based on a 10-mm light gas gun, providing jet velocities ranging from 360 to 617 m/s for this experiment. The results indicated that the typical morphology of rain erosion damage was annular, consisting of a damaged region surrounding a central undamaged area. As the damage severity increased, it gradually evolved into circular delamination damage. The severity of damage to the three coating specimens was quantitatively characterized. Data fitting revealed that both the damaged area and volume increased as the jet impact velocity rose. At a 15° impact angle, the velocity threshold at which visible damage began to appear on the coating surface was approximately 360 m/s. Among the factors affecting rain erosion damage to the coating, surface roughness played a more significant role than mechanical parameters such as hardness and modulus of elasticity. When the primer thickness is constant, the area of rain erosion damage gradually decreases as the topcoat thickness increases. A thicker topcoat can mitigate the effects of stress waves and water hammer pressure at the topcoat-primer interface, thereby reducing damage. When the topcoat thickness remains constant, the area of rain-erosion damage gradually increases as the primer thickness increases from 100 μm to 150 μm. However, when the primer thickness reaches 250 μm, the area of rain-erosion damage actually decreases. This phenomenon is attributed to reduced reflection and transmission of stress waves once the primer thickness exceeds the critical protective thickness. When the total coating thickness remains constant, the extent of damage initially increases and then decreases as the ratio of primer to topcoat increases. This indicates that, within the specified thickness range, rain erosion damage to radar dome skin coatings can be reduced by increasing the proportion of topcoat.