Nature-inspired entwined coiled carbon mechanical metamaterials: molecular dynamics simulations

Entwining-induced robust natural biosystems show superior mechanical performances over their counterparts. However, the role played by topological entwinement in the mechanical properties of artificial nanohelixes remains unknown. Here, the tensile characteristics of nano-entwined carbon nanocoil (ECNC) metamaterials are explored by atomistic simulations. The simulation results show that ECNCs exhibit heterogeneous pre-stress distribution along the spiral surfaces. The predicted stretching stress-strain responses correlate with the topological nano-entwining and dimensionality. Topological analysis reveals that the collective stretching of the bond and bond angle on the inner hexagon edge of the coils characterizes both early and final elastic extensions, whereas the intermediate elasticity is exclusively attributed to the inner-edged hexagon-angular deformation. The ECNCs impart pronounced tensile stiffnesses to the native structures, surprisingly with a maximum of over 13-fold higher stiffness for one triple-helix, beyond the scalability of mechanical springs in parallel, originating from the nano-entwining mechanism and increase in bulkiness. However, the reinforcement in strengths is restricted by the elastic strain limits that are degraded in ECNCs owing to the steric hindrance effect. All metastructures show superelongation-at-break due to a successive break-vs.-arrest process. Upon plastic deformation, the localized reduction in the radii of ECNCs leads to the formation of carbyne-based networks.