Additively manufactured bi-material metamaterial to program a wide range of thermal expansion

Abstract

The current research on bi-material diamond metamaterials, which can be used to program the coefficient of thermal expansion (CTE) over a wide range, mainly focuses on the theoretical design, while the corresponding experimental range of the CTEs is far narrower. In this study, a bi-material diamond metamaterial was additively manufactured using two polymers: nylon and polyvinyl alcohol (PVA). Without any need for extra processes such as bonding, welding, and mechanical fitting, the additively manufactured metamaterial integrated the nylon and PVA, providing an integrated fabrication process to ensure the expected programmable CTE. The experimentally measured CTEs agreed well with the theoretical predictions. When the material layout was selected as MAT-1 = PVA and MAT-2 = nylon, programmable CTEs ranging from 217.72 to 694.00 ppm/°C were obtained, which were larger than the CTEs of the nylon and PVA. When the material layout was MAT-1 = nylon and MAT-2 = PVA, even though both the nylon and the PVA had positive CTEs, a wide range of negative CTEs (varying from −25.02 to −369.01 ppm/°C) was obtained. The foregoing wide ranges of programmable CTEs are remarkably larger than the literature results, indicating the enhanced programmability of the bi-material metamaterial and stabilizing the foundation for the further design of multilevel and hierarchical metamaterials.