Elastic torsional responses of carbon nanotube systems

The mechanical responses of several different carbon nanotube systems to applied torsional loading at various temperatures are examined using classical molecular dynamics simulations, and the results are interpreted and compared to the predictions of continuum mechanics theory. The specific materials considered include filled and chemically functionalized, individual single-walled and multiwalled carbon nanotubes, as well as bundled carbon nanotubes. The simulations indicate that the mechanical responses to the torsional loading are buckling and that all the carbon nanotube systems considered are highly elastic. They also indicate that the critical buckling moment can be increased by the presence of filling materials and inner carbon nanotubes, and that the amount of this increase depends on the kind of filling materials and the number of inner tubes. The simulations further show that the critical buckling moment of a single carbon nanotube in a bundle is higher than that of the individual nanotubes alone. In addition, the dependence of the torsional stiffness on the diameters of the nanotubes is found to vary as K similar to D-2.99, where K is the torsional stiffness and D is the nanotube diameter, and the torsional shear modulus is found to be relatively independent of the nanotube diameter and length, in good agreement with predictions from continuum mechanics theory. Lastly, the simulations indicate that the critical buckling moment can be modified by adjusting the system temperature and through chemical functionalization of the carbon nanotube walls.