Electrothermally actuated lattice metamaterials with remarkable shear deformation

Active metamaterials with specific deformation responses present great promise in fields such as multifunctional antennas, stretchable electronic devices and reconfigurable soft robots, due to their ability to switch between different operational states within a single system. However, the previous researches on active metamaterials with shear deformation responses exhibit two issues: inability to further enhance the shear deformation magnitude of the active metamaterials and inability to achieve precise customized design of the metamaterials, such as realizing simple shear deformation. Moreover, the inverse design of active metamaterials is challenging because theoretical models describing the finite deformation of active metamaterials under external-field actuation are lacking. To address the aforementioned issues, this study reports a design strategy for the electrothermally actuated lattice metamaterials to realize remarkable shear deformation with the maximum shear angle exceeding 26° and the capability to precisely achieve desired mechanical responses of the active metamaterials. The shear angle of the electrothermally actuated lattice metamaterials reported in this paper has increased by approximately 82 % compared to that achieved in previous studies. Theoretical models for the electrothermally actuated metamaterials are established to describe the shear deformation behaviors. The theoretical models are demonstrated through both qualitative and quantitative comparisons with finite element analyses (FEAs) and experimental results. Theoretical models provide detailed predictions of the configuration after electric heating and offer analytical solutions for crucial mechanical quantities, such as the effective strains and shear angle for the electrothermally actuated lattice metamaterials exhibiting shear deformations. Moreover, experimental results and FEA calculations show that the simple shear deformation mode can be realized in the active metamaterials through the design strategies proposed in this paper, while it cannot be achieved in previous researches. This demonstrates the capability of the design strategies proposed in this paper to precisely realize required mechanical responses of the active metamaterials.