Mechanics of Hybrid Square Lattices with Tunable Thermal Expansion Coefficient

New hybrid square lattices are designed, which are composed of hard cells or inclusions connected via specially designed soft components, such as soft networks, soft hinges, or bilayer joints. Upon external stimuli, the curvature of the joints will change due to the stimuli-induced mismatch. Also, the square cells will rotate due to the chiral arrangement of the cells connected by the stimuli-responsive joints. Both deformation mechanisms will contribute to the overall volume change of the material and lead to the change in both mechanical properties and functionality related to the material structure. To further prove the concept, prototypes of selected designs are fabricated via a multi-material 3D printer. Uni-axial tension experiments are performed in a thermal chamber. By varying the temperature, due to the mismatch in thermal expansion of the bi-layer and the chiral design of the hybrid square lattices, the material experiences dramatic volume change. By varying the design parameters, including material combination and geometry, both overall positive and negative thermal expansion coefficients can be achieved. The mechanical property, structure, temperature relationships are quantified. In addition, numerical simulations are performed to support mechanical experiments.