Molecular simulations of pristine and defective carbon nanotubes under monotonic and combined loading

In this paper, mechanical behavior of single-walled pristine and defective carbon nanotubes (CNTs) under monotonic tension, compression, torsion and combined Torsion–Axial loadings has been studied using the molecular dynamics (MD) method. Molecular simulations have been carried out using the classical MD method, in which the Newtonian equations of motion have been solved numerically for a set of atoms. The velocity-Verlet algorithm has been used for solving the Newtonian equations of motion while temperature is controlled by velocity scaling. The Brenner potential has been used for carbon–carbon interaction in the CNT. For defective CNTs, vacancy and Stone–Wales (SW) defects have been considered. Stress–strain behaviors and failure envelopes under combined loading have revealed that the mechanical response of CNT is dependent on the loading sequence of the combined loading and stress stiffening occurs in Axial–Torsional load cases. Moreover, simulation results show that the presence of defects alters the mechanical behavior and failure mode of CNTs. Vacancy defects are found to degrade CNT to a greater extent than SW defects.

► Mechanical behavior of CNTs is studied under monotonic and combined loading.
► Defect affects the failure damage mode and failure envelope.
► Vacancy defect deteriorates the CNTs strength more as compared to the SW defect.
► Under combined loading, mechanical behavior of CNTs is loading sequence dependent.
► Stress stiffening occurs when torsion is followed by axial tension or compression.