Dislocation Onset and Glide in Carbon Nanotubes under Torsion

The torsional plastic response of carbon nanotubes is comprehensively described in the objective molecular dynamics framework~[1-3]. It is shown that an (n,m) tube is prone to slip along a nearly-axial helical path, which introduces a distinct (+1,-1) change in the wrapping index. The low energy realization occurs without loss of mass, via nucleation of a 5-7-7-5 dislocation dipole, followed by a nearly-axial glide of the 5-7 dislocation. The onset of plasticity depends not only on chirality but also on handedness. For a given handedness of the applied twist, chiral tubes of opposed handedness are most susceptible to yield. A right-handed applied twist on an armchair (zig-zag) tube leads to a right- (left-) handed tube. \\[4pt] [1] T. Dumitric\u{a} and R.D. James, {\it Objective Molecular Dynamics}, Journal of the Mechanics and Physics of Solids {\bf 55}, 2206 (2007). \\[0pt] [2] D.-B. Zhang, M. Hua, and T. Dumitric\u{a}, {\it Stability of Polycrystalline and Wurtzite Si Nanowires via Symmetry-Adapted Tight-Binding Objective Molecular Dynamics}, Journal of Chemical Physics {\bf 128}, 084104 (2008). \\[0pt] [3] D.-B. Zhang and T. Dumitric\u{a}, {\it Elasticity of Ideal Single-Walled Carbon Nanotubes via Symmetry-Adapted Tight-Binding Objective Modeling}, Applied Physics Letters {\bf 93}, 031919 (2008).