Effect of randomly occurring Stone–Wales defects on mechanical properties of carbon nanotubes using atomistic simulation

Abstract

The remarkable mechanical properties of carbon nanotubes (CNTs) have generated a lot of interest in recent years. While CNTs are found to have ultra-high stiffness and strength, an enormous scatter is also observed in available laboratory results. This randomness is partly due to the presence of nanoscale defects, heterogeneities etc., and this paper studies the effects of randomly distributed Stone-Wales (SW or 5-7-7-5) defects on the mechanical properties of single-walled nanotubes (SWNTs) using the technique of atomistic simulation (AS). A Matern hard-core random field applied on a finite cylindrical surface is used to describe the spatial distribution of the Stone-Wales defects. We simulate a set of displacement controlled tensile loading up to fracture of SWNTs with (6,6) armchair and (10, 0) zigzag configurations and aspect ratio around 6. A modified Morse potential is adopted to model the interatomic forces. We found that fracture invariably initiates from a defect if one is present; for a defect-free tube the crack initiates at quite random locations. The force-displacement curve typically behaves almost linearly up to about half way, although there is no obvious yield point. Three mechanical properties -stiffness, ultimate strength and ultimate strain  are calculated from the simulated force and displacement time histories. The randomness in mechanical behavior resulting only from initial velocity distribution was found to be insignificant at room temperature. The mean values of stiffness, ultimate strength and ultimate strain of the tube decrease as the average number of defects increases although the coefficients of variation do not show such monotonic trend. The introduction of an additional defect has the most pronounced effect on the randomness in mechanical properties when the tube is originally defect free. We also found that, for a given mean number of defects in the tube, the zigzag configuration has less strength and less ultimate strain on the average, but more uncertainty in its stiffness and ultimate strain, compared with the armchair tube.

Mesoscale modeling of mechanics of carbon nanotubes: Self-assembly, self-folding, and fracture

“…9,[24][25][26] Several other studies using molecular dynamics have been carried out to develop a molecular level understanding of the failure processes, using a variety of atomistic modeling techniques. 9,10,[27][28][29][30][31] …”

“…9,10,[27][28][29][30][31] However, such models are limited to very short time-and length-scales so that a direct comparison with experimental scales is often extremely difficult or impossible.…”

Using theory and computation to model nanoscale properties

“…This dramatic variation of results points to the importance of defects. A number of theory studies have been performed to help sort this out (49,55,(57)(58)(59)(60)(61)(62), but developing a quantitative theory of the effect of defects on nanotube fracture has been challenging. Fig.…”

Analysis of Randomness in Mechanical Properties of Carbon Nanotubes Through Atomistic Simulation

“…CNT is found to be among the most robust materials: it has high elastic modulus (order of 1 TPa), high strength (up to 150 GPa), good ductility (up to 15% max strain), flexibility to bending and buckling and robustness under high pressure A survey of recent studies on the elastic modulus and strength of single-walled and multi-walled carbon nanotube (SWNT and MWNT) has been reported in Ref. 14. The collected data clearly show a few features: (i) the Young's modulus of SWNT is found to range from 0.31~1.25TPa, the Young's modulus of MWNT ranges from 0.1 to 1.6 TPa; (ii) the Young's modulus may depend on chiralities, but the elastic modulus measured from tubes with similar diameters varies quite significantly; (iii) experiments roughly show a trend that Young's modulus drops quickly as the diameter of tubes increases; (iv) the strength varies a lot from about 5GPa to 150Gpa; (v) last but not the least important, these mechanical properties (elastic modulus, strength and failure strain) reported from experiments and analysis show significant variation.…”