Study on the influence mechanism of high-dynamic droplet impact on delamination damage of aircraft coatings

When an aircraft flies through clouds or rainfields at high speed, the extremely high relative velocity between the aircraft and raindrops can cause damage or even detachment of the coating on windward structural surfaces, thereby shortening aircraft service life. Polyurethane coatings offer excellent wear resistance, weather resistance, chemical corrosion resistance, strong adhesion, and good flexibility, and are therefore widely used in aerospace applications. However, research on their rain erosion resistance remains limited. Therefore, this paper investigates the delamination damage  mechanism under high-speed raindrop impact to improve rain erosion resistance.T800 carbon fiber composite laminates were used as the substrate, onto which polyurethane coatings of different interlaminar bond strengths were applied. Based on single-jet and pulsed multi-jet impact test platforms, the influence of interlaminar bond strength between the coating and the substrate on rain erosion damage characteristics and the occurrence mechanism of delamination failure were systematically examined.Under single-jet impact, coatings with low interlaminar bond strength first experience interfacial adhesion failure at the impact center, leading to localized delamination. The reflected stress waves cause significant interfacial stress concentration, resulting in uneven stress transfer and crack propagation along the interface. The characteristic damage morphology includes coating spallation at the impact point, peripheral uplift, and circumferential cracking. By contrast, coatings with higher interlaminar strength better dissipate the impact load and suppress the initiation and growth of microcracks, maintaining coating integrity.Under multiple-jet impacts, the interface is subjected to long-term cyclic loading, making it prone to stress fatigue and the formation of microcracks, which gradually evolve into pronounced delamination. The typical damage morphology appears as elongated delamination bands extending along the carbon fiber orientation, with significant uplift and circumferential cracking at the boundaries, and local carbon fiber fracture may also be observed. Weaker interlaminar bond leads to shorter time to delamination and more severe damage. Based on the experimental results and numerical stress‑response analysis, the delamination mechanism under raindrop impact is clarified: shear waves generated during droplet impact nucleate interfacial microcracks, which continue to propagate and lead to interlaminar cracking and delamination. The stress waves generated by impact reflect at the coating–substrate interface, and under pulsed droplet loading, stress superposition generates high tensile stress. Continuous lateral jet loading further acts on the interface, causing coatings with low interlaminar bond strength to experience delamination after fewer impacts.