Strain-independent auxetic metamaterials inspired from atomic lattice

Metamaterials with strain-independent negative Poisson's ratio (NPR) and Young's modulus are essential for the applications with extreme loading conditions. However, strain-independent auxetic metamaterials are rare, and there is a lack of design inspiration for them. In this paper, we present a novel auxetic metamaterial inspired from the atomic lattice with strain-independent NPR. The novel NPR properties due to the unique atomic lattice keep valid when scaling up by 6 orders of magnitude to macroscopic metamaterials, with the similar deformation mechanism. The NPR and Young's modulus keep constant with increasing loading strain. These strain-independent auxetic effects are robust with various designable geometric parameters in wide ranges. Furthermore, the geometric parameters optimization for the auxetic metamaterial is conducted through developing the matrix displacement method. An optimized metamaterial is achieved with 3 times enhancement of auxeticity and 2 orders of magnitude enhancement of Young's modulus, compared to the initio architectures. This work provides a wealth of inspirations from atomic lattice in nature to design strain-independent macroscale auxetic metamaterials.