Large programmable coefficient of thermal expansion in additively manufactured bi-material mechanical metamaterial

The current metamaterials with the programmable coefficient of thermal expansion (CTE) usually present the unexpected anisotropy, and the experimentally measured CTEs are quite narrower. Here, a bi-material metamaterial was constructed. The material extrusion process was established to fabricate the metamaterial. The measured CTEs in various in-plane directions are in good consistency to each other, experimentally verifying the identical CTE in various in-plane directions. The relative deviation between the experimental measurements and theoretical predictions is within -13.0% to +11.0%. The positive programmable CTEs are as high as 204 and 258 ppm/degrees C, which are larger than those of the basic polymers nylon and polyvinyl alcohol (PVA). Otherwise, the negative CTEs of -25 and -77 ppm/degrees C are obtained, even though both the nylon and PVA have positive CTEs. The programmable CTEs are expanded to be [-77, +258] ppm/degrees C, far beyond the literature results, supplementing the additive manufacturing and experimental basis to the engineering applications.

Automated summary

A bi-material metamaterial was constructed using a material extrusion process to fabricate a material with consistent CTE in various in-plane directions, with experimental results confirming identical CTE values. The programmable CTE values obtained were higher than those of basic polymers, expanding the range to [-77, +258] ppm/degrees C and providing a basis for engineering applications in additive manufacturing.