A three-dimensionally tunable mechanical metamaterial enabled by a coupled concave–chiral architecture

Abstract

This paper proposes a three-dimensionally tunable concave–chiral re-entrant auxetic lattice (CCRAL) that couples re-entrant deformation with chiral torsion to achieve multidirectional auxetic responses and tunable mechanical performance. The proposed architecture enables different but coordinated deformation mechanisms to be activated under different loading directions. Under y-direction compression, the auxetic response is mainly governed by bending and rotation of the re-entrant ligaments, whereas under z-direction compression, coordinated chiral torsional rotation and folding dominate the transverse deformation. Quasi-static compression experiments and finite-element simulations show good agreement and validate the deformation characteristics of the proposed structure. The CCRAL maintains negative Poisson’s ratio responses under both loading directions, with the Poisson’s ratio reaching approximately −1.2 under z-direction compression. Parametric analyses further demonstrate that the concavity angle, connecting-rod length, and cell width effectively regulate the stiffness, load-bearing capacity, auxetic response, and specific energy absorption. Within the investigated parameter range, the specific energy absorption reaches approximately 70 J kg−1 at a nominal strain of 0.7. These results demonstrate that coupling concave and chiral deformation mechanisms provides an effective approach for balancing multidirectional auxeticity, load-bearing capacity, and energy absorption, offering a directly fabricable and geometrically tunable platform for lightweight protective and energy-absorbing applications.