Molecular mechanics calculations, together with coupling methods bridging molecular mechanics and finite crystal elasticity, were used to simulate the fracture of defected C nanotubes, and compared with available experimental results. The molecular mechanics calculations exhibited a fair agreement with quantum mechanical benchmarks, and indicated that 1- and 2-atom vacancies reduced the fracture strength of C nanotubes by 20 to 33% (whereas quantum mechanical calculations predicted 14 to 27%); but these fracture strengths were still much higher than the experimental values. It was then demonstrated that this discrepancy could be attributed to the presence of large-scale defects, such as those that could arise from oxidation processes. Simulations of multi-walled C nanotubes and tubes twisted before tensile loading revealed negligible effects upon fracture strength; indicating that these were not the causes of the low experimental values.

Mechanics of Defects in Carbon Nanotubes - Atomistic and Multiscale Simulations. S.Zhang, S.L.Mielke, R.Khare, D.Troya, R.S.Ruoff, G.C.Schatz, T.Belytschko: Physical Review B, 2005, 71[11], 115403 (12pp)