A numerical evaluation of the influence of defects on the elastic modulus of single and multi-walled carbon nanotubes

Finite element models of single-walled and multi-walled carbon nanotubes in their perfect and fundamental forms (zigzag and armchair) were constructed. Then, after obtaining the mechanical properties of perfect carbon nanotubes, three types of imperfections, i.e., doping with Si atoms, carbon vacancy and perturbation of the ideal location of the carbon atom were introduced in different amounts to the perfect models to make them imperfect. Finally, the mechanical properties of the imperfect carbon nanotubes were numerically simulated and compared with those of perfect ones. Simple relations which predict the change of Young’s modulus as a function of the imperfection percentage were derived. The results show that the existence of any kind of imperfection in the perfect models leads to lower stiffness values. This study allows to realistically judge any simulation based on perfect structures and gives for the first time a good estimate to which extend the values based on perfect structures must be lowered in order to account for common imperfections to predict the mechanical properties of carbon nanotubes which are nowadays used in the production of advanced nanocomposites and reinforced materials.