Molecular mechanics calculations, together with coupling methods bridging molecular mechanics and finite crystal elasticity, were used to simulate the fracture of defected carbon nanotubes and to compare it with experimental results. The modified second generation Brenner potential was adopted. The molecular mechanics calculations gave fair agreement with quantum mechanical benchmarks, and indicated that one- and two-atom vacancies reduced the fracture strength of carbon nanotubes by 20 to 33%, whereas the quantum mechanical calculations predicted 14 to 27%. These fracture strengths were still much higher than the experimental ones. It was demonstrated that this experiment versus theory discrepancy could be attributed to the presence of large-scale defects, such as those that could arise from oxidative purification processes. Simulations of multi-walled carbon nanotubes and tubes, twisted prior to tensile loading, revealed negligible effects upon the fracture strength. This indicated 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