Mechanical characterization of novel lightweight bio and bio-inspired sandwich composites: Investigating the impact of geometrical parameters and reinforcement techniques

This study examines the mechanical performance of bio- and bio-inspired composite sandwich panels under out-of-plane compressive loading. Using balsa wood face sheets and natural oak tree cupules for core reinforcement, the research aims to develop lightweight, sustainable structures. Three different cupule arrangements and geometries were tested, with and without polyurethane (PU) foam infill, to compare natural and commercial cores. The results show that cupule geometry significantly influences mechanical behaviour, demonstrating notable load-bearing and energy absorption capabilities, though with a tendency towards brittle fracture. Reinforcement techniques, such as cupule duplication and the integration of commercial PU foam, were explored to enhance load-bearing capacity and energy absorption while mitigating sudden failure. Panels reinforced with oak tree cupule-filled PU foam cores exhibited superior mechanical properties compared to non-reinforced cores. This study highlights the potential of using oak tree cupules to improve mechanical performance and sustainability in sandwich panel design. Furthermore, bio-inspired structures were fabricated via Multi Jet Fusion additive manufacturing, harnessing the unique properties of cupules to achieve superior mechanical performance in printed structures, emphasising their potential in structural engineering applications.