Peculiar elastic behavior of mechanical metamaterials with various minimal surfaces

Molecular dynamics simulations were performed on nanostructured metamaterials (NMs) with gyroid, diamond, and primitive structures to evaluate their mechanical behavior, especially elastic properties. Unlike the constant nature of Young's (E) and shear (μ) moduli of bulk materials, the values of both E and μ of NMs change with relative density and cell size but at different rates depending on the morphologies of the structure. This is particularly the case for μ; for a given relative density and cell size of NMs, the μ values differ greatly, depending on the types of structure, causing the NMs to display differing μ/E values and thus resistance to shear deformation. The mechanistic origin of this observation was analyzed by resolving the morphologies of the NMs in terms of the numbers and orientations of the fundamental structural motifs for constructing metamaterials.