Quantum mechanical calculations, using density functional theory and semi-empirical methods and molecular mechanics calculations with a Tersoff-Brenner potential, were used to explore the role played by vacancy defects in the fracture of carbon nanotubes under axial tension. These methods gave reasonable agreement, although the molecular mechanics scheme systematically underestimated fracture strengths. One- and two-atom vacancy defects were observed to reduce failure stresses by as much as some 26%, and markedly reduced failure strains. Large holes - such as those that might be introduced by oxidative purification processes - greatly reduced the strength. This provided an explanation for existing theory versus experiment discrepancies.

The Role of Vacancy Defects and Holes in the Fracture of Carbon Nanotubes. S.L.Mielke, D.Troya, S.Zhang, J.L.Li, S.Xiao, R.Car, R.S.Ruoff, G.C.Schatz, T.Belytschko: Chemical Physics Letters, 2004, 390[4-6], 413-20