Thin and Thermally Stable Periodic Metastructures

We design, fabricate, and test thin thermally stable metastructures consisting of bi-metallic unit cells and show how the coefficient of thermal expansion (CTE) of these metastructures can be finely and coarsely tuned by varying the CTE of the constituent materials and the unit cell geometry. Planar and threedimensional finite element method modeling (FEM) is used to drive our design and inform experiments, and predict the response of these metastructures. We develop a robust experimental fabrication procedure in order to fabricate thermally stable samples with high aspect ratios. We use digital image correlation (DIC) and an infrared camera to experimentally measure displacement and temperature during testing and compute the CTE of our samples. The samples, composed of an aluminum core and an external titanium frame, exhibit a CTE of 2.6 ppm/°C, which is significantly lower than either constituent. These unit cells can be assembled over a large area to create thin low-CTE foils. Finally, we demonstrate how the approach developed in this work can be used to fabricate metastructures with CTE’s ranging from −3.6 ppm/°C to 8.4 ppm/°C.