Nonlinear analysis of coiled carbon nanotubes using the molecular dynamics finite element method

The mechanical response of single-walled helically coiled carbon nanotubes (CCNTs) under large axial deformations is examined using a molecular dynamics finite element method. The 3D reference configuration of CCNTs is determined based on a 2D graphene layer using conformal mapping. Three sets of analyses are performed to fully describe the mechanical response of (n,n) CCNTs under elongation up to the bond breaking point and compression down to the solid length or the onset of buckling instability. First, the strain dependency of the mechanical properties of individual CCNTs during deformation is investigated by calculating the stress-strain curve and the spring constant of the CCNTs for the entire load range. Significant responses including brittle fracture under tension and buckling instability under compression are observed. Second, to examine the size dependence of the mechanical properties, several CCNTs with different geometric parameters are constructed, and their spring constant, fracture strain, fracture load, and energy storage density are determined. All CCNTs exhibit a superelasticity of 50–66%. A comparison between the mechanical properties of CCNTs and those of carbon nanotubes (CNTs) reveals that the fracture load and energy storage per atom of CCNTs is lower than that of the corresponding armchair CNTs.