Tight-binding molecular dynamics studies were made of single-walled carbon nanotubes, with and without a variety of defects, in order to study their effect upon the nanotube modulus and failure by bond rupture. For a pristine (5,5) nanotube, the Young’s modulus was calculated to be ∼1.1TPa, and brittle rupture occurred at a strain of 17% under quasi-static loading. The predicted modulus was consistent with experimentally determined values of thermal vibration and with tensile test measurements. The defects resulted from moving or removing one or two carbon atoms, and correspond to a 1.4% defect density. The occurrence of a Stone-Wales defect did not significantly affect the Young’s modulus, but failure occurred at 15% strain. The presence of a pair of separated vacancy defects lowered the Young’s modulus by ∼160GPa, and decreased the critical or rupture strain to 13%. These defects apparently acted independently, since one of the defects alone was shown to lower the Young’s modulus by ∼90GPa; again with a critical strain of 13%. When the pair of vacancy defects was adjacent, the Young’s modulus was lowered by only ∼100GPa; but with a lower critical strain (11%). In each case, there was noticeable strain softening leading, for instance, to a ∼250GPa drop in the apparent secant modulus at 10% strain. When a chiral (10,5) nanotube with a vacancy defect was subjected to tensile strain, failure occurred via a continuous spiral-tearing mechanism that maintained a high level of stress (2.5GPa) even as the nanotube unraveled. Because the statistical likelihood of defects occurring near to each other increased with nanotube length, the results were expected to have important implications for interpreting experimental distributions of moduli and critical strain.

Tight-Binding Molecular Dynamics Study of the Role of Defects on Carbon Nanotube Moduli and Failure. R.W.Haskins, R.S.Maier, R.M.Ebeling, C.P.Marsh, D.L.Majure, A.J.Bednar, C.R.Welch, B.C.Barker, D.T.Wu: Journal of Chemical Physics, 2007, 127[7], 074708