Tight-binding molecular dynamics study of the role of defects on carbon nanotube moduli and failure

Abstract

We performed tight-binding molecular dynamics on single-walled carbon nanotubes with and without a variety of defects to study their effect on the nanotube modulus and failure through bond rupture. For a pristine (5,5) nanotube, Young's modulus was calculated to be approximately 1.1 TPa, and brittle rupture occurred at a strain of 17% under quasistatic loading. The predicted modulus is consistent with values from experimentally derived thermal vibration and pull test measurements. The defects studied consist of moving or removing one or two carbon atoms, and correspond to a 1.4% defect density. The occurrence of a Stone-Wales defect does not significantly affect Young's modulus, but failure occurs at 15% strain. The occurrence of a pair of separated vacancy defects lowers Young's modulus by approximately 160 GPa and the critical or rupture strain to 13%. These defects apparently act independently, since one of these defects alone was independently determined to lower Young's modulus by approximately 90 GPa, also with a critical strain of 13%. When the pair of vacancy defects adjacent, however, Young's modulus is lowered by only approximately 100 GPa, but with a lower critical strain of 11%. In all cases, there is noticeable strain softening, for instance, leading to an approximately 250 GPa 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 through a continuous spiral-tearing mechanism that maintained a high level of stress (2.5 GPa) even as the nanotube unraveled. Since the statistical likelihood of defects occurring near each other increases with nanotube length, these studies may have important implications for interpreting the experimental distribution of moduli and critical strains.

The influence of a compatibilizer on the thermal and dynamic mechanical properties of PEEK/carbon nanotube composites

“…Moreover, the laser process leads to CNTs of the highest purity and quality (few defects, high crystallinity, low amorphous carbon content) and larger aspect ratio (>10 000) when compared with any other synthesis methods; these characteristics make them potentially more efficient for composite reinforcement [49]. Acid treatments, such as that used in this work to purify the arc grown SWCNTs, are known to shorten the CNTs and induce defects on their side walls, thus having detrimental effects on mechanical properties of the SWCNTs [50]. However, further experiments would be required to confirm the reasons for the differences observed among the composites tested.…”

Development and characterization of PEEK/carbon nanotube composites

“…This is not surprising since the purity, quality, aspect ratio and nature of impurities, hence the source of SWCNTs are determining factors in the final properties of CNT based composites. It has recently been shown that defects have detrimental effects on mechanical properties of SWCNTs [49]. The laser process produces CNTs of the highest quality (few defects, high crystallinity) as compared to any other synthesis methods known; it also generates nanotubes with very large aspect ratio (>10,000).…”

Molecular Dynamics Simulation Study on the Mechanical Properties and Fracture Behavior of Single-Wall Carbon Nanotubes

“…They took pristine as well as defective CNTs with one and two atom vacancies. The role of defects on carbon nanotube elastic moduli and failure behavior was studied by tight binding molecular dynamics simulation by Haskins et al (Haskins et al, 2007). Molecular simulation was used by Yang et al (Yang et al, 2007) to determine the fracture strength of single-wall carbon nanotubes containing different concentrations of randomly distributed point defects.…”