Unusually high ratio of shear modulus to Young's modulus in a nano-structured gyroid metamaterial.

Unlike the constant nature of elastic coefficients of isotropic bulk materials, the Young's (E) and shear (μ) moduli of nano-structured (NS) gyroid metamaterials change with relative density (ρ), but at different rates depending on the cell size of the structure. These elastic behaviors displayed by E and μ cause crossover/inversion of these two moduli, such that μ of the NS gyroid metamaterials is greater than E for the structures with ρ < 0.23. This peculiar elastic behavior causes NS gyroid metamaterials to display high μ/E values (~1.0), which are more than 250% larger than the typical values of the bulk material (~0.38), indicating that the NS gyroid metamaterial, even if it is light, is resistant to shear deformation. Here, we report the results of molecular dynamics simulations performed to elucidate the reason for unusually high μ/E values in NS gyroid metamaterials.