Metamaterials designed to present a negative thermal expansion are bi-material lattice structures. The influence of their unit cell geometry on the coefficient of thermal expansion (CTE) has been simulated in the last decades and good agreement with experimentally obtained CTEs of metamaterials fabricated via bi-material additive manufacturing has been found. However, up to now, neither a bi-metallic combination that allows a wide range of CTEs to be tuned, nor a thorough understanding of the metamaterial’s behavior, including at cryogenic temperatures, has been presented. In this work, we present simulations and experimentally obtained CTEs of bi-metallic metamaterial unit cells and multi-unit-cell structures. Unit cells with different geometric features are manufactured of Invar and Inconel 718 by laser-based powder bed fusion. Unit cells based on triangles with low angles lead to CTEs of up to –37x10–6/K, but are sensitive to geometric features which influence the hinge stiffness and may significantly increase their CTE, such as strut thickness and offset between base and side. A good match between the simulations and dilatometry measurements was achieved by manufacturing a multi-unit-cell segment of the metamaterial and selecting the corresponding boundary conditions for finite element simulations, allowing the prediction of the expansion behavior of future metamaterials.     «

Metamaterials designed to present a negative thermal expansion are bi-material lattice structures. The influence of their unit cell geometry on the coefficient of thermal expansion (CTE) has been simulated in the last decades and good agreement with experimentally obtained CTEs of metamaterials fabricated via bi-material additive manufacturing has been found. However, up to now, neither a bi-metallic combination that allows a wide range of CTEs to be tuned, nor a thorough understanding of the me...     »