Stiffness characteristics for bi-directional tunable thermal expansion metamaterial based on bi-material triangular unit

Abstract

The stiffness and coefficient of thermal expansion (CTE) are of great significance for lightweight metamaterials that adapt to variations in temperature. Toward this goal, bi-directional tunable thermal expansion metamaterial based on bi-material triangular unit is reported and fabricated using multi-layer assembly strategy. The CTE and stiffness of the designed metamaterial can be programmed in two directions, which provides a method for existing metamaterials can only be regulated in a single direction. To describe the mechanical properties, theories of the effective CTE and stiffness are established considering bending, tensile, and shear deformations and verified by numerical analysis. The mechanical response, especially stiffness, of the multi-material metamaterial is experimentally verified. By rationally modulating the cell architectures, the high relative stiffness and tunable CTE can be realized. In particular, the proposed metamaterial achieves a wide range of tunable CTEs from -31.16 ppm/°C to 56.43 ppm/°C. The exclusive integrated functions of the metamaterials including low density, considerable stiffness, and tunable CTE are superior compared with common materials. The coupling design of the CTE, stiffness, and relative density further demonstrates that this work has a positive effect on the development of metamaterials in aerospace applications and other fields.