Microstructured tunable media with giant negative and positive thermal expansion

This work introduces a microstructured medium designed to achieve a highly tunable effective coefficient of thermal expansion (CTE), capable of being either positive or negative. Remarkably, the effective CTE can exceed that of the constituent phases by more than one order of magnitude. The proposed microstructure consists of a periodic arrangement of thin beams with different thermomechanical properties. Owing to its simplicity, the structure can be studied analytically, allowing the key parameters governing the effective response to be readily identified and tuned. In particular, an asymptotic analysis highlights the dominant role of the internal flexural deformation modes. The analytical predictions are validated by three-dimensional numerical simulations and corroborated by experimental testing, where the simplicity of the architecture facilitates specimen fabrication. With suitable tuning, the medium can not only control longitudinal thermal expansion but also exhibit a non-zero rotational coefficient of thermal expansion, enhancing its functional versatility. These results demonstrate the potential of the proposed design for applications requiring tailored thermal expansion behavior.