Nonlinear fracture analysis of carbon nanotubes with stone-wales defects

In this paper, a molecular mechanic based finite element model is employed to investigate the effects of Stone-Wales defects on mechanical properties of armchair and zigzag carbon nanotubes by considering large deformation and nonlinear geometric effects. Nonlinear characteristic of the covalent bonds are obtained by using the modified Morse potential and effects of the large deformation and geometric nonlinearities are considered by updating the atomistic coordinates of the original nanotube structure at each load step. The results show that the fractures of all types of carbon nanotubes are brittle, but armchair nanotubes are stiffer than zigzag nanotubes and these defects significantly affect the mechanical performance of nanotubes. Fracture initiation and crack propagation direction issues are also studied. It is shown that the direction of crack propagation in armchair nanotube is in the maximum shear directions having an angle of ±45° along its circumference. Comparisons are made with the failure stress and strain results reported in literature that show good agreement with our results.