Quantum mechanical calculations were made using density functional theory and semi-empirical methods, and molecular mechanics calculations with a Tersoff–Brenner potential that explored the role of vacancy defects in the fracture of C nanotubes under axial tension. The methods exhibited reasonable agreement, although the molecular mechanics scheme systematically underestimated fracture strengths. One- and 2-atom vacancy defects were observed to reduce failure stresses by as much as ~26%, and markedly reduced failure strains. Large holes greatly reduced the strength, and provided an explanation for the theoretical–experimental discrepancies.

The Roles 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