Mechanical analysis of sandwich composite beams manufactured by additive manufacturing

In this thesis, the effect of core geometry on the mechanical properties of composite sandwich structures was experimentally investigated. The main objective of the study was to comparatively evaluate the influence of different core geometries (solid, square, slender, triangular, honeycomb, re-entrant, arc re-entrant, and star-shaped) on bending and impact performance. For this purpose, hybrid sandwich structures were fabricated using carbon fiber-reinforced epoxy skins and thermoplastic polyurethane (TPU) cores. The skins were produced by the Vacuum-Assisted Resin Infusion Method (VARIM), while the cores were fabricated by Additive Manufacturing (Fused Deposition Modeling, FDM), and both components were bonded using an adhesive process. Mechanical performance was assessed through three-point bending tests (ASTM D790) and un-notched Charpy impact tests (ASTM D6110). The results revealed that the triangular core exhibited the highest overall performance with a bending strength of 50.8 MPa, a flexural modulus of 1.60 GPa, and an impact toughness of 25.1 kJ/m². The honeycomb structure offered high specific strength despite its low mass, while the auxetic re-entrant and arc re-entrant geometries showed controlled deformation and energy absorption behavior at medium-high stiffness levels. Star-shaped and slender geometries displayed lower strength and higher deformation tendencies. This research stands out as one of the few systematic experimental comparisons of different core geometries produced under identical manufacturing and testing conditions, demonstrating the potential of hybrid production (VARIM + FDM) for advanced composite design. The findings provide valuable engineering insights for aerospace, automotive, and structural applications where a balance between lightweight, stiffness, and toughness is essential. Ultimately, the decisive role of core geometry in mechanical performance has been experimentally validated, offering a new design perspective for optimizing composite sandwich structures.