Design and quasi-static compression responses of auxetic metamaterials based on re-entrant hexagonal structure with two-step deformation mode

A novel, multi-step deformation auxetic metamaterial is proposed. Through an extensive study of unit cells, designed by overlapping two re-entrant hexagonal cells and optimizing the distribution of transverse rods, we identified a double re-entrant hexagon with a vertical strut (DRHVS) as the optimal configuration. This configuration exhibits a distinct two-step deformation mode and dual-plateau stress characteristics. A theoretical model was developed to predict plateau stress based on energy conservation and plastic hinge dissipation for the proposed DRHVS structure. Numerical simulations were conducted to analyze the quasi-static response and deformation mechanisms of a honeycomb structure composed of DRHVS unit cells. A parametric study was performed on the key dimensions, and the mechanical properties under different impact velocities were evaluated. Finally, the mechanical properties of DRHVS were compared with those of other re-entrant auxetic structures. The results indicate that DRHVS exhibits outstanding energy absorption capacity and impact resistance. This study expands the design framework of auxetic metamaterials for high-performance, multi-step deformation structures in impact-resistant applications.