Abstract
<jats:p>Hybrid composite lattice structures have emerged as a promising approach for improving the impact resistance of lightweight aerospace components. This study investigates the influence of density-gradient direction in metallic Body-Centred Cubic (BCC) lattice reinforcement on the bird-strike response of a composite UAV leading-edge (L.E) structure. Three lattice architectures uniform, backward graded, and forward graded were parametrically generated using Rhino/Grasshopper and integrated within a carbon-fibre-reinforced polyamide L.E. The hybrid structures were analysed using Abaqus/Explicit with a validated Smooth Particle Hydrodynamics (SPH) bird model (1 kg, 95 m/s). All configurations maintained nearly identical structural mass, enabling the influence of lattice density distribution on structural response to be isolated. The backward graded configuration promoted progressive plastic collapse, resulting in the highest lattice energy absorption but also increased deformation and load transfer to the spar. In contrast, the forward graded configuration suppressed progressive collapse, confined deformation near the impact interface, and significantly reduced stress transmission to critical structural components. Peak displacement and spar energy transfer were reduced by approximately 95% and 90%, respectively, compared with the backward graded configuration. The results demonstrate that density-gradient tailoring of metallic lattice reinforcement enhances the structural performance of hybrid composite-lattice L.E structures by improving load sharing, deformation control, and impact resistance without increasing structural mass.</jats:p>