Planar bi-metallic lattice with tailorable coefficient of thermal expansion

A mechanical metamaterial that has a tailorable coefficient of thermal expansion (CTE) is promising for guaranteeing the reliability of electrical and optical instruments under thermal fluctuations. Despite growing research on the design and manufacturing of metamaterials with extraordinary CTEs, it remains challenging to achieve a nearly isotropic tailorable CTE while ensuring a sufficient load bearing capacity for applications, such as mechanical supporting frames. In this research, we propose a type of bi-metallic lattice whose CTE is artificially programmed from positive (75 ppm/K) to negative (−45 ppm/K), and whose equivalent modulus can be as high as 80 MPa. The bi-metallic lattice with a tailorable CTE in two orthogonal directions can be readily assembled without special modifications to construct large-scale planar structures with desired isotropic CTEs. A theoretical model that considers the actual configuration of the bi-metallic joint is developed; the model precisely captures the thermal deformations of lattice structures with varied geometries and material compositions. Guided by our theoretical design method, planar metallic structures that were manufactured using Al, Ti, and Invar alloy were experimentally characterized; the structures exhibited outstanding performance when compared with typical engineering materials.