Nanomechanics of Twisted Mono- and Few-Layer Graphene Nanoribbons

Enabled by the technique of objective molecular dynamics, we reveal the unusual mechanics exhibited by nanoscale twisted graphene nanoribbons containing up to seven layers. Unlike in a linear-elastic plate, we find that the deformation practically does not contain contributions associated with in-plane shearing but largely with inhomogeneous stretching and compression of the constituent layers. The whole twisted structure undergoes shortening when no axial force is applied, while the constituent layers store various strain energies, depending on their location. We capture this behavior with a simple model and show that the deviations from the plate model are increasing with the number of layers and width of the ribbon. Our results are especially relevant for the experimental efforts of measuring graphene's shear modulus.