Finite element analysis of carbon nanotubes with stone-Wales defects

Like any other geometric structure or building, carbon nanotubes may break down due to either material failure or structural failure. In this paper, it is shown that the failure mechanism of carbon nanotubes not only depends on the type and direction of loading but also on the location and number of defects. For the finite element simulations we use a new 4-node finite element without rotational degrees of freedom based on the force field method. For the examples shown here, mainly a single-walled (10, 10) armchair nanotube with different Stone-Wales defects, the material parameters are directly taken from the DREIDING force field. For carbon nanotubes subject to tension a kind of material failure, i.e. a breaking of bonds, can be observed. For carbon nanotubes subject to bending, an interesting question is whether they fail due to a breaking of bonds in the tension zone, which would be similar to the tension experiment, or due to a snap-through of bonds in the compression zone. From our FE simulations, it can be concluded that neither of these two failure mechanisms, but local buckling in the compression zone can be observed. From a mechanical point of view, however, it is not a pure bifurcation problem because the buckles are formed relatively slowly which corresponds more to a snap-through problem. For carbon nanotubes subject to torsion, we have to distinguish between bifurcation problems which are the case for defect-free nanotubes and snap-through problems which can be observed for those with defects. In all cases the Stone-Wales defects are responsible for a reduction of the maximum load, about 10% for tension and bending, and up to 30% for torsion.