A multistable hybrid honeycomb with tunable Poisson's ratio and enhanced energy absorption

Honeycomb structures are promising for ship sandwich panels, marine fenders, and localized protection systems owing to their low weight and high energy-absorption capacity. However, conventional honeycombs remain limited in their ability to tune mechanical properties, maintain deformation stability, and provide multistage energy absorption. This study proposes a multistable hybrid honeycomb (MSHH) integrating hexagonal cells, rhombic cells, and cosine-shaped curved beams. Successive snap-through buckling of the curved beams enables configurational transformations and a multistage mechanical response. PA12 specimens were fabricated by selective laser sintering, and their deformation modes, Poisson's ratio evolution, and energy-absorption performance were investigated through quasi-static compression tests and finite element analysis. The MSHH exhibited distinct multistage deformation behavior. During compression, its Poisson's ratio assumed positive, near-zero, and negative values before returning to positive values. Its experimentally measured specific energy absorption reached 2.94 J/g, 96.0% higher than that of the conventional hexagonal honeycomb (1.50 J/g). By combining multistable configurational transformations with hybrid-cell strengthening, the MSHH provides cushioning with a low reaction force during the initial stage and efficient energy absorption during subsequent stages. This study offers a new design strategy for sandwich structures requiring multistage energy absorption.