On exploration of directional extreme mechanical attributes and energy absorption of bending-dominated and buckling-induced negative Poisson's ratio metamaterials

This work numerically explores the directional mechanical characteristics, including the effective anisotropy, multiaxial yield surface, long-frequency stress phase wave propagation, buckling resistance, and energy absorption of bending-dominated (BE) and buckling-induced (BU) auxetic metamaterials, considering the influence of the relative density and negative Poisson's ratio, for the first time. The accuracy of numerical homogenization in determining the effective Young's modulus and wave analytical model calculating the wave velocity is confirmed by compared with experimental and numerical data, respectively, with a maximum percent difference of 14.6% for all comparisons found. The results show that BU auxetic structures possess unique mechanical properties, displaying their potential use for fabrication of metamaterials of zero-Poisson's ratio and tunable strength allowing high strength-to-weight ratios. The anisotropy of BE structures is found to be more extreme compared to their BU counterparts. Interestingly, alignment of multiaxial yield surface of auxetic metamaterials is observed to be opposite to that of nonauxetic metamaterials, resulting in poor fitting against extended Hill's criterion. The BU auxetic structure demonstrates a better impact wave resistance, but lower buckling resistance in y-direction compared with BE auxetic structure, and more. This work provides in-depth useful mechanical information on the structures before employing them in practical applications.