Mechanical response of hydrogen-filled single-walled carbon nanotubes under torsion

Molecular dynamics simulations are performed to investigate the torsional buckling behavior of single-walled carbon nanotubes (SWCNTs) filled with hydrogen gas. The simulation model accounts for both the mechanical deformation of the SWCNT and the interactions among the hydrogen and carbon atoms. It is found that the critical torsional moment and stiffness of the SWCNT are both significantly dependent on the hydrogen molecule storage density. Importantly, the change in torsional stiffness differs from that of conventional linear elastic materials as a result of the nonlinear oscillatory response due to nonlinear mechanical effects. It is shown that under large deformations, the SWCNT switches reversibly between different morphological patterns. Each change in pattern corresponds to an abrupt release of the strain energy and a singularity in the stress-strain curve. It is shown that at higher hydrogen storage densities, the hydrogen molecules exert a stabilizing effect on the SWCNT. The degree of torsional stability is determined principally by the distribution of the hydrogen molecules within the SWCNT. Finally, it is shown that the torsional deformation of the SWCNT is characterized by a stick-slip phenomenon.