Abstract:
After the discovery, carbon nanotubes (CNTs) have received tremendous scientific
and industrial interests. This is due to their exceptional mechanical, electrical, and
thermal properties. CNTs having perfect structure (i.e., structure without any defect)
hold very high ~echanical properties. However, CNTs suffer from defects which can
appear at production stage, purification stage or be deliberately introduced by
irradiation with energetic particles or by chemical treatment. In this work mechanical
properties of CNTs with defects are studied under both compressive and tensile loads
using molecular dynamics (MD) simulations.
In this work both single-walled and double-walled carbon nanotubes (SWNTs and
DWNTs) with perfect structure, vacancy defects and Stone-Wales defects are
simulated with MD. Five armchair SWNTs having indexes of (3,3), (4,4), (5,5), (6,6)
and (7,7) and one armchair DWNT having index of «3,3),(8,8)) are considered. To
create Stone-Wales defect, four neighboring hexagons are converted into two
pentagons and two heptagons with a 90° rotation of the horizontal bond of the
hexagonal structure of the CNT whereas to create vacancy defects carbon atoms are
removed from the perfect hexagonal structure of the CNTs. Molecular simulations are
carried out using the classical MD method, in which the Newtonian equations of
motion are solved numerically for a set of atoms. The velocity- Verlet algorithm is
used for solving the Newtonian equations of motion. The Brenner potential is used for
carbon-carbon interaction in the CNT and non-bonded interaction between the CNTs
in DWCNTs is modeled with the Lennard-Jones potential. Temperature of the system
is controlled by velocity scaling. In the simulation, tensile and compressive loads are
applied by moving the end atoms of the CNTs rigidly outward and inward directions,
respectively.
Simulation results show that the defects have negligible effect on the modulus of
elasticity of CNTs and defect density influences the compressive and tensile strength
of CNTs insignificantly. The results obtained from the. compressive test by MD
simulations are in well agreement with the results obtained from theoretical Euler
equation.
