Decoupling Poisson's ratio effect from compression-torsion metamaterial

Abstract

Compression-torsion metamaterials are always coupled with the Poisson's ratio effect, leading to some uncontrollable deformation mechanisms, such as premature buckling and failure. Decoupling these two effects and independently regulating them can create various novel lightweight and flexible actuators with displacement mode conversion in narrow working spaces. However, significant challenges still exist in decoupling Poisson's ratio effect from the compression-torsion metamaterial. This paper proposes a kind of cylindrical shell metamaterials composed of inclined X-members, which enables simultaneous and independent regulation of Poisson's ratio and compression-torsion effects. Theoretical models are established to express both the compression-torsion efficiency and the Poisson's ratio with the configurational parameters of X-member, which show good agreement with experiments and simulations. The results reveal that the proposed X-member metamaterial exhibits remarkable compression-torsion efficiency and a controllable Poisson's ratio that spans a wide range, from negative to positive, under uniaxial tension or compression. The designed compression-torsion metamaterial with zero Poisson's ratio can achieve stable rotation-displacement conversion without occupying extra space, thus enabling effective flexible actuation in confined spaces. Moreover, under torsional loading, the metamaterial also demonstrates widely adjustable lateral deformation, including contraction, invariance and expansion, enabling flexible grasping. By introducing a double-layer design of metamaterial, soft actuators and soft graspers are fabricated that effectively protect fragile or precision objects, which work directly through the elastic deformation of the metamaterial, driven by a single motor. Due to the independently and widely adjustable compression-torsion and Poisson's ratio effects, the proposed X-member metamaterial offers a diverse range of lightweight and low-cost flexible transmission solutions, exhibiting tremendous potential in bioengineering and flexible robotics.