Enhancing the structural stiffness and energy absorption of re-entrant auxetic honeycombs using folded stiffeners

Enhancing the stiffness, energy absorption, and load-carrying capacity of conventional re-entrant honeycombs (CRH) is crucial for adapting complex loading conditions. To address this issue, a folded stiffener design is introduced into the CRH structure, known as improved re-entrant honeycomb (IRH). By utilizing the variational asymptotic method, the intricate 3D model is deconstructed into microscopic unit-cell constitutive modeling and macroscopic analysis via 2D equivalent plate model or 3D equivalent Cauchy model. The equivalent models aid in incorporating macroscopic responses into the recovery relationships, thereby facilitating the identification of local field distributions. Quasi-static uniaxial compression tests and numerical simulations on 3D printed multi-cellular structures reveal that the auxetic effect of IRH structures arises from constrained rotation of both folded stiffeners and inclined struts. Parameter analysis highlights the significant impact of slenderness ratio on in-plane and out-of-plane modulus, while adjusting the re-entrant angle affects Poisson’s ratio markedly. Compared to the CRH, the inclusion of folded stiffeners in the IRH results in a fourfold increase in the elastic modulus and reduces the negative Poisson’s ratio to 15%. Furthermore, the IRH demonstrates a more uniform stress distribution and improved energy absorption efficiency. Incorporating folded stiffeners to reduce porosity and enhance structural performance provides valuable insights for re-entrant auxetic honeycomb design. •Folded stiffeners enhance stiffness and energy absorption in re-entrant honeycombs.•Variational asymptotic method aids in modeling and analysis at multiple scales.•The auxetic effect arises from the rotation of the folded stiffener and inclined strut.•Parameter analysis highlights impact of slenderness ratio and re-entrant angle.•IRH outperforms CRH: superior mechanics, stress distribution, porosity reduction.