Fully Foldable Mechanical Metamaterials With Isotropic Auxeticity and Its Generated Multi-Mode Folding Form

Abstract Auxetic materials, a type of mechanical metamaterial with negative Poisson's ratio, are potentially utilized in the realms of energy absorption and engineering structures. However, most of the existing auxetic materials either contain a large amount of rotational motion or still have gaps when fully folded, which is not conducive to lifting loads. Besides, their application is limited to flexible environments due to their single-folding mode. To overcome such limitations, a fully foldable mechanical metamaterial with isotropic auxeticity is proposed by utilizing the Sarrus mechanism, and a derivative multi-mode folding form is obtained in this paper. Then, the degrees-of-freedom (DOF), bistability, and kinematic characterizations are analyzed to show the performance of the proposed structures. Finally, the parameters of the proposed fully foldable mechanical metamaterials are discussed to simplify the structures. Some prototypes are fabricated to validate the effectiveness and performance of the proposed mechanical metamaterials. The proposed mechanical metamaterials have some merits, such as isotropic auxeticity, being fully folded to achieve dense compression, being bistable with load-bearing capacity, multi-mode folding form, and single-DOF, and they have versatile potential applications in complex environments requiring large deformation and flexible adaptation.