Chirality-Dependent and Intrinsic Auxeticity for Single-Walled Carbon Nanotubes

Abstract

Single-walled carbon nanotubes (SWCNTs) have superior mechanical properties which originate from a strong C-C covalent bond and unique nanostructure. Chirality, one of the helical structural parameters of SWCNTs, leads to differences in mechanical performance. In this work, molecular dynamics (MD) simulation was performed to analyze engineering Poisson’s ratio (EPR) and incremental Poisson’s ratio (IPR) of SWCNTs with different chiral angles, respectively, under tensile and compressive load, as well as the chiral effect on rigidity. We reported the minimum EPR for (4, 1) SWCNT and obtained the distribution and trend of EPR which is dependent on chiral index m. In addition, a new observation showed two exactly opposite trends of EPR existing not only in tension and compression but also in the longitudinal and radial directions. Furthermore, we found that the critical strain, over which SWCNT would be auxetic, ranged from 6% to 18% and was also chirality-dependent. Three representative SWCNTs with chiral angle of 0° (zigzag), 10.89° (chiral), and 30° (armchair) were selected for the mechanism study of auxeticity. Finally, a method of the contribution to radial strain for two main deformation modes proposed in this paper could well explain the negative IPR phenomenon.

Prediction of Temperature-Dependent Mechanical Properties for SWCNT/Cu Nanocomposite Metamaterials: A Molecular Dynamics Study

“…However, E 11 of nanocomposite with 10.5 wt.% (28, 8) SWCNT is only 267.8 GPa, about 60% E 11 of nanocomposite with 11.3 wt.% (7, 2). The reason is that SWCNTs of small diameter possess higher modulus [ 39 ] and thus greater enhancement effects. As for the case of nanocomposites with the same weight fraction, all three moduli have been slightly reduced.…”

“…This phenomenon is also observed from the SWCNT/Cu nanocomposites. Furthermore, we find that the increase in SWCNT content may diminish the auxetic nature of SWCNT/Cu nanocomposites, although the Poisson’s ratio of SWCNT is positive but relatively small [ 39 ]. As listed in Table 3 , the presence of nano-hole leads to NPRs υ 12 and υ 21 decreases by −19.4% and −37.0%, respectively.…”

“…The chiral angle θ and diameter d of (7, 2) SWCNT are 12.22° and 6.41 Å, respectively. According to our previous work [ 39 ], Poisson’s ratios for some chiral SWCNTs with variable chiral indices are listed in Table 1 .…”

“…Generally, there are two ways to present content of CNT in nanocomposites: volume fraction (vol.%) and weight fraction (wt.%). However, it might be inaccurate to measure SWCNT content by using volume fraction because determination of effective wall thickness of SWCNT is inevitable in this method but controversy truly exists [ 39 ]. Alternatively, the weight fraction of SWCNTs is adopted, which is obtained directly from the calculation based on the number of Cu and C atoms and their atomic mass.…”

Mechanical Performance of Advanced Composite Materials and Structures

“…Carbon nanotubes (CNTs), as one of the ideal potential fillers for nanocomposites [11], exhibit superior excellent mechanical properties compared to carbon fiber. In the paper "Chirality-Dependent and Intrinsic Auxeticity for Single-Walled Carbon Nanotubes", Zhang et al [12] discovered the auxetic nature of CNTs. They employed the molecular dynamics (MD) method to analyze the effect of chiral indices on the mechanical behavior, especially Poisson's ratio, of CNTs.…”