Atomistic simulation of the torsion deformation of carbon nanotubes

A significant amount of work has been done in the past decade to reveal the unique structural and mechanical properties of carbon nanotubes and to explore what might be the key applications of these novel materials. Due to the difficulty in developing experimental techniques, there is still no report on the measured values of shear modulus of carbon nanotubes. In this paper, the mechanical behaviour characteristic of carbon nanotubes (CNTs) under torsion is simulated with a molecular dynamics method. The results show that the shear modulus of a CNT increases as the radius of the CNT enlarges. The value of the shear modulus of the CNT changes from 370 to 500 GPa. The shear modulus of a zigzag CNT is higher than that of an arm-chair CNT. The micro-mechanism of the nanotube buckling under torsion is explained from the viewpoints of energy and structure distortion. It is clearly observed that the atoms in the section move with coplanar displacements before the structure buckles. After the buckling of the CNT, the whole section collapses like a dumbbell and the atoms move with off-plane displacements. This deformation behaviour is similar to the torsion deformation of a thin shell in continuum mechanics. The asymmetric distribution of the system energy induces the buckling of the structure.