Towards space application of a tunable thermal expansion metamaterial fabricated via bi-metallic additive manufacturing to guarantee dimensional accuracy

Dimensional accuracy and structural stability are critical for space applications such as optical benches. This study investigates metamaterials with a tunable coefficient of thermal expansion (CTE) to achieve athermalization in satellite structures without compromising their mechanical integrity. The metamaterial consists of triangular unit cells made of Invar and Inconel 718, fabricated via bi-material laser-based powder bed fusion (PBF-LB). Dimensional accuracy should be achieved by both passive and active stabilization strategies. Experimental measurements using dilatometry and digital image correlation show good agreement with finite element method (FEM) simulations of the metamaterial's CTE. CTE values can be tuned from -20x10 -6 /K to +31x10 -6 /K by changing the unit cell geometry, switching material assignments, and combining different unit cells. Compared with metamaterials with only positive-or negative-CTE unit cells, a more stable CTE can be obtained by combining negativeand positive-CTE unit cells. Adding a trapezoidal geometry for active heating does not affect the CTE. Mechanical tensile tests suggest a strong bi-material bond, with failure occurring in the weaker material -Invar. Although FEM simulations predict interfacial stresses exceeding Invar's ultimate tensile strength under temperature changes, no damage or plastic deformation was observed after 500 cycles across a 270°C span. These findings confirm the metamaterial's reliability and provide a basis for developing more advanced tunable CTE structures for space applications.