It was shown here that the failure mechanism of carbon nanotubes depended not only upon the type and direction of loading but also upon the location and the number of defects. For finite-element simulations, a new 4-node finite element without rotational degrees of freedom was used. This was based upon the force-field method. For the present examples, mainly a single-walled (10,10) armchair nanotube with various Stone-Wales defects, the material parameters were taken directly from the Dreiding force field. For carbon nanotubes subjected to tension, a form of material failure - breaking of bonds - could be observed. For carbon nanotubes subjected to bending, the question was whether they failed due to a breaking of bonds in the tension zone - similar to a tensile test - or due to a snap-through of bonds in the compression zone. From the finite element simulations, it was deduced that neither of these two failure mechanisms - but local buckling in the compression zone - was observed. From the mechanical point of view, it was not a pure bifurcation problem because buckling formed relatively slowly; corresponding rather to a snap-through problem. For carbon nanotubes subjected to torsion, it was necessary to distinguish between bifurcation problems, as in the case of defect-free nanotubes, and snap-through problems which could be observed for nanotubes with defects. In all cases, the Stone-Wales defects were responsible for a reduction of the maximum load: about 10 % for tension and bending, and up to 30 % for torsion.

Finite Element Analysis of Carbon Nanotubes with Stone-Wales Defects. L.Nasdala, G.Ernst, M.Lengnick, H.Rothert: Laser Physics, 2005, 15[3], 293-304