High-velocity fragment impact on aircraft thin-walled aluminum alloy structures typically induces severe debris cloud generation, which causes widespread secondary damage to internal equipment and greatly impairs structural survivability and post-damage repairability. Polyurea, as a lightweight hyper-elastomeric protective material, shows great potential in mitigating impact-induced damage, while its inhibitory effect and underlying mechanism on post-target debris cloud effects remain to be fully elucidated. In this study, we designed and fabricated polyurea-coated aluminum plate specimens with different coating configurations (rear-face single-sided coating and double-sided sandwich coating) and conducted systematic ballistic impact tests under 1300–1400 m/s fragment impact using a 14.5mm ballistic gun system. The optimized test setup enabled direct and quantitative observation of the regulation effect of polyurea coatings on post-target debris cloud evolution. Experimental results show that polyurea coatings can effectively suppress debris cloud diffusion and reduce secondary damage, and the rear-face coated configuration (Type A) exhibits optimal post-target effect mitigation performance: the debris cloud dispersion angle is reduced from 67.5°1.2° (uncoated plate) to 58.2°1.1°, and the maximum distribution radius of secondary impact craters on the witness plate is reduced by 46.7% compared with the uncoated specimen. Furthermore, a finite element model coupled with the adaptive FEM-SPH method was established and validated against experimental data to reveal the physical mechanism of polyurea’s protective effect. The results demonstrate that the excellent hyperelasticity, high fracture strain, and energy absorption capacity of polyurea are the core factors for debris suppression: the polyurea coating achieves debris entrapment through large deformation and contraction, dissipates impact energy via viscoelastic dissipation, and modulates stress wave propagation to reduce aluminum substrate spalling and debris generation. This study clarifies the inhibitory mechanism of polyurea coatings on post-target secondary effects under highvelocity impact and provides valuable experimental and theoretical guidance for the lightweight protective design of aircraft thinwalled structures using polyurea materials.
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