Composite sandwich structures are widely used in unmanned aerial vehicle (UAV) components due to their high stiffness-to-weight ratio; however, their vulnerability to impact-induced damage remains a major limitation for structural reliability. Conventional sandwich panels with uniform foam or honeycomb cores often experience either excessive indentation or brittle collapse under low-velocity impact, leading to significant degradation of post-impact stiffness. Although impact damage mechanisms in sandwich composites are well established, experimental validation of hybrid graded core architectures at full structural scales remains limited. In this study, a combined experimental and numerical investigation is conducted to evaluate the impact response and residual bending performance of hybrid graded sandwich panels for UAV applications. Sandwich panels incorporating carbon-fiber-reinforced polymer (CFRP) face sheets and three core configurations, namely uniform foam, uniform honeycomb, and hybrid graded foam-honeycomb, were subjected to a 25 J low-velocity impact followed by residual three-point bending tests. The results demonstrate that the hybrid graded configuration significantly improves impact tolerance by promoting progressive damage evolution. The graded panels exhibited a sustained force plateau, higher energy absorption (48.6 J), and effective damage confinement (∼4 cm 2 ), compared with lower energy absorption (28.5 J for foam and 35.4 J for honeycomb) and larger delamination areas (8 cm 2 and 12 cm 2 ) in conventional cores. Residual bending tests revealed stiffness retention approximately 90%, substantially higher than that of uniform core configurations. These improvements arise from both core architecture and the controlled interaction of face-sheet damage, core crushing, and limited delamination governing post-impact load transfer. Finite element simulations developed in Abaqus/Explicit accurately reproduced the impact response and damage evolution, with deviations within ∼11%. This study provides a validated full-scale demonstration of hybrid graded sandwich structures for UAV applications and establishes a quantitative correlation between damage morphology and residual structural performance, offering practical design guidance for impact-tolerant lightweight structures.
Settu et al. (Fri,) studied this question.