Flexural behaviors of asymmetric Re-entrant auxetic honeycombs

A family of negative Poisson's ratio honeycombs with asymmetric base units and potential applications in civil and marine industries are introduced by introducing asymmetricities to the geometry of regular re-entrant unit cell. These structures, namely the single symmetry-broken re-entrant (SSR), double symmetry-broken re-entrant (DSR), and hybrid symmetry-broken re-entrant (HSR) honeycomb lattices, are fabricated through fused filament fabrication and subjected to experimental three-point bending (TPB) experiments and simulations. The novel designs showcase exceptional specific energy absorption (SEA) attributes compared to the regular metamaterial, with the SSR structure exhibiting a remarkable 147.2% higher SEA. The asymmetric metamaterials also demonstrate higher flexural modulus (E_f) compared to the benchmark design, with the SSR and DSR models boasting approximately 29% and 19% higher E_f, respectively. Studies on design parameters show that internal angle of unit cells that creates the asymmetricity affects the flexural performance of the unique auxetic honeycombs, significantly. Finally, parametric investigation on out-of-plane bending of the honeycombs showed the dominance of all asymmetric-unit honeycombs over the benchmark due to having organized self-contact regions. The SSR and DSR structures own about 51% and 39% higher SEA than the benchmark honeycomb under out-of-plane TPB, respectively.