Design of integrally 3D-printed sandwich structures with functionally graded honeycomb and continuous carbon fibre-reinforced grid hybrid cores

A B S T R A C T Sandwich structures are critical for lightweight engineering yet preventing face-core interface failure remains a significant challenge.Additive manufacturing offers a solution by enabling complex, integrally reinforced designs, though optimising these for mechanical performance requires advanced strategies.To address this, this study demonstrates the feasibility of manufacturing fully 3D-printed sandwich panels using material extrusion, featuring a tree-leaf-inspired honeycomb-grid hybrid core.The proposed multi-scale design approach involved three steps: (i) topology optimisation to generate a material distribution map; (ii) construction of a cellular structure with varying trabecular cell sizes; and (iii) integration of a curved grip mesh at domain boundaries to ensure geometric and mechanical continuity.Incorporating the grid into the functionally graded core improved strength by 4%, while embedding continuous carbon fibres further increased strength by 52%.The benefits of fabricating the sandwich panel in a single printing step using polyamide for both face sheets and cores include larger adhesion areas and reduced stiffness mismatch.Failure analysis revealed a shift in failure mode from the core-face interface to the face sheets themselves, indicating enhanced structural integrity.These findings highlight the potential of hybrid 3D-printed sandwich structures for lightweight, high-performance applications.