Strength and fracture behaviors of ultralong carbon nanotubes with defects

Abstract

The presence of structural defects can result in large discrepancies between theoretical and experimental values of the strength of CNTs. To reveal the relationship between the strength and defects of CNTs, experiments accompanied with an experiment-based molecular dynamics simulation were conducted in this paper, where defects were introduced using oxygen plasma irradiation and the strength of the defective CNTs was measured by uniaxial tensile experiments. It was found that the strength of CNTs was controlled by the feature length of defects and the introduction of the single adatom, C–C bond breaking, and vacancy defect could decrease the strength by 8.2%, 23.2%, and 18.5%, respectively. Especially, when these defects synergized, the strength of CNTs ranged from 0 to 76.8% of the theoretical strength, which was confirmed by the experiments. Moreover, by defining cracks based on the atomic stress distributions around defects, the fracture of CNTs obeyed the Griffith's brittle fracture criterion and the atomic stress distributions along the crack plane obeyed the classical fracture mechanics theory except for some deviation near the crack tip. This work gives a perspective on reasons for the theory-experiment discrepancies on the strength of CNTs over the years, obtains the quantitative relationship between the size of defects and the strength of CNTs and provides a research paradigm for verifying the validity of fracture mechanics theories at nanoscale. • The adatom, C–C bond breaking, and vacancy defects are introduced to CNT by oxygen plasma irradiation. • The feature length of defects controls the strength of CNTs when these defects synergize. • The fracture of CNTs obeys the Griffith's brittle fracture criterion by regarding defects as cracks. • Atomic stress distributions obeys the classical fracture mechanics theory except for some deviation near the crack tip. • The characteristic length in GES is to separate two atoms from the maximum interaction to the interaction can be ignored.