Effects of Defects on the Strength of Nanotubes:   Experimental-Computational Comparisons
  The failure stresses and strains of nanotubes given by theoretical or numerical predictions are much higher than observed in experiments. We show that defects can explain part of this discrepancy: for an n-atom defect with 2<=n<=8, the range of failure stresses for a molecular mechanics calculation is found to be 36GPa to 64GPa. This compares quite well with upper end of the experimental failure stresses, 11GPa to 63GPa. The computed failure strains are 4% to 8%, whereas the experimental values are 2% to 13%. The underprediction of failure strains can be explained by the slippage that occurred in the experiments. The failure processes of nanotubes are clearly brittle in both the experiments and our calculations. 
T. Belytschko, S. P. Xiao and R. Ruoff