A novel mechanical metamaterial with tailorable Poisson's ratio and thermal expansion based on a chiral torsion unit

Auxetic and negative thermal expansion metamaterials have a wide range of applications in flexible electronics, aerospace, biomedicine. Based on the compression/thermal-torsion coupling effects, and combining the special deformation mechanism of the planar anti-tetrachiral structure, this work proposed a novel 3D mechanical metamaterial with negative Poisson's ratio (PR) and negative coefficient of thermal expansion. The mechanical design method of the metamaterial is demonstrated, and the coordinated deformation theory between its in-plane and out-of-plane deformations is established. By numerical simulation, the torsional deformation response of torsion unit of the metamaterials is explored, and Poisson's characteristics and thermal expansion effect of the metamaterials are analyzed. The results show that the PR and thermal expansion effect of the metamaterial can be adjusted and switched, and its deformation behavior can be programmed. The coupling design method for metamaterials provides a good design strategy for engineering applications such as intelligent actuators, flexible robots, and biomedical sensors.