Novel Star–Ellipse Honeycomb Metamaterials for Achieving Optimal Trade-Offs Between Stiffness and Energy Absorption

To address the trade-off between stiffness and auxeticity in conventional star-shaped honeycombs (SH), this study introduces a novel star-ellipse honeycomb (SEH) design, incorporating elliptical stiffeners that enhance both load-bearing capacity and energy absorption. The mechanical performance of SEH was comprehensively evaluated using FE simulations, theoretical modeling, and quasi-static tests on 3D-printed multi-cell specimens. An equivalent Cauchy model using the Variational Asymptotic Method (VAM) was established and validated against experiment and finite element results, demonstrating high predictive accuracy in elastic behavior analysis while significantly reducing computational costs. Based on the collapse mechanism of a representative unit cell, a theoretical model was proposed to estimate the plateau stress. Comparative analyses show that the elliptical stiffener mitigates the classic stiffness–auxeticity trade-off by enabling cooperative deformation, which results in a simultaneous increase in elastic modulus and a stronger negative Poisson’s ratio compared to conventional star-shaped honeycombs. Additionally, the SEH exhibited a unique progressive folding mode under compression, delivering enhanced stiffness and energy dissipation, albeit with reduced ductility. The elliptical aspect ratio of 1.3, length ratio of 2.1, thickness ratio of 1.0, and star angle of 45–50° offer the best compromise between stiffness, energy dissipation, and auxetic performance, providing clear guidelines for tailoring SEH structures toward specific lightweight protective applications.