Influence of combined loading on the structural stability of carbon nanotubes

• Different geometrical modified carbon nanotubes are numerically simulated.
• The stiffness change is evaluated for different modifications.
• Results are compared to perfect CNTs.
• Combined loadings lead to reduced stiffness values for single- and multi-walled CNTs.
• Twisting is the most critical form of geometrical modifications.

Numerous armchair and zigzag carbon nanotubes (CNTs) in their perfect and geometrically modified form were simulated and their buckling behavior was investigated through performing computational tests with different boundary conditions. Both computational and analytical results were compared in the case of perfect tubes. Then, three kinds of geometrical modifications, i.e. twisting angle, z-distortion along the longitudinal axis, and xy-distortion along the radial axis, were introduced to the configuration of perfect CNTs and the buckling behavior of geometrically modified CNTs was numerically evaluated and compared with the behavior of the perfect ones. It was shown that the first critical buckling load of both perfect armchair and zigzag CNTs increases by increasing the chiral number. In addition, it was also concluded that the existence of any type of geometrical modifications in the configuration of CNTs leads to a lower critical load and as a result, lower buckling properties. Finally, it was revealed that by increasing the length of the tubes, the critical buckling load of the CNTs reduces significantly while addition of further walls increases significantly the critical buckling load.