It was recalled that, although carbon nanotubes had ultra-high stiffness and strength levels, an enormous scatter was observed in available laboratory data. This randomness was due partly to the presence of nanoscale defects and the effects of randomly distributed Stone-Wales (5-7-7-5) defects. The mechanical properties of single-walled nanotubes were studied here using atomistic simulations. A Matern hard-core random field, applied to a finite cylindrical surface, was used to describe the spatial distribution of Stone-Wales defects. A set of displacement-controlled tensile loadings, up to fracture, of single-walled carbon nanotubes with (6,6) armchair and (10,0) zig-zag configurations and an aspect ratio of about six was simulated. A modified Morse potential was used to model the interatomic forces. It was found that fracture invariably initiated from a defect if one was present. In a defect-free tube, the cracks initiated at quite random locations. The force-displacement curve typically behaved almost linearly up to about half way, although there was no obvious yield-point. Mechanical properties - stiffness, ultimate strength and ultimate strain - were calculated from the simulated force and displacement time histories. The randomness in mechanical behavior resulting only from the initial velocity distribution was found to be insignificant at room temperature. The mean values of the stiffness, ultimate strength and ultimate strain of the tube decreased as the average number of defects increased. The coefficients of variation did not exhibit such a monotonic trend. The introduction of an additional defect had the most pronounced effect upon the randomness in mechanical properties when the tube was originally defect-free. It was also found that, for a given mean number of defects in the tube, the zig-zag configuration exhibited lower strength and ultimate strain on average; but more uncertainty in its stiffness and ultimate strain when compared with the armchair tube.

Effect of Randomly Occurring Stone-Wales Defects on Mechanical Properties of Carbon Nanotubes using Atomistic Simulation. Q.Lu, B.Bhattacharya: Nanotechnology, 2005, 16[4], 555-66