Multiscale modeling of carbon nanotubes under axial tension and compression

In this paper, we study the elastic and plastic properties of single-walled carbon nanotubes (SWCNTs) under axial compression and tension. The present work employs molecular dynamics (MD) as well as a multiscale technique where a handshaking region between MD and tight-binding (TB) is described and implemented. The interaction forces between the carbon atoms are calculated based on the second-generation reactive empirical bond-order potential, TB derived forces, as well as long-range Lennard-Jones potential. A smooth cutoff Lennard-Jones with switch function is also explored. The detection of sideway buckling due to the asymmetrical axial compression is reported and discussed. This sideway buckling phenomenon is observed when using both pure MD and MD/TB multiscale models. The viability of the presently developed handshaking region between MD and TB in CNTs under axial compression and tension is thus validated.

Figure 1

(Color online) Terminology for regions used in the presently developed multiscale model.

Figure 2

Nearest distances $a$ and $b$.

Figure 3

Comparison of strain energy curve of SWCNT (8,0) under axial compression.

Figure 4

Comparison of stress-strain curve of a SWCNT (12,12) under axial tension.

Figure 5

Strain energy using original Lennard-Jones for SWCNT (8,0) in axial compression.

Figure 6

Strain energy using Lennard-Jones with switch function for SWCNT (8,0) in axial compression.

Figure 7

Nearest distance of SWCNT (8,0) in axial compression using original Lennard-Jones potential.

Figure 8

Nearest distance of SWCNT (8,0) in axial compression using Lennard-Jones with switch function.

Figure 9

Strain energy per atom using MD for SWCNT (7,7) under axial tension.

Figure 10

Stress-strain curve of SWCNT (7,7) under axial tension using MD.

Figure 11

Nearest distance of SWCNT (7,7) under axial tension using MD.

Figure 12

Strain energy per atom using multiscale method for SWCNT (7,7) under axial tension.

Figure 13

Stress-strain curve of SWCNT (7,7) under axial tension using multiscale method.

Figure 14

Nearest distance of SWCNT (7,7) under axial tension using multiscale method.

Figure 15

Multiscale model showing the pure MD, handshaking TB far, and TB near regions in SWCNT: (a) before collapse and (b) after collapse.

Figure 16

Strain energy per atom using MD for SWCNT (7,7) under axial compression.

Figure 17

Stress-strain curve of SWCNT (7,7) under axial compression using MD.

Figure 18

Nearest distance of SWCNT (7,7) under axial compression using MD.

Figure 19

Strain energy per atom using multiscale method for SWCNT (7,7) under axial compression.

Figure 20

Stress-strain curve of SWCNT (7,7) under axial compression using multiscale method.

Figure 21

Nearest distance of SWCNT (7,7) under axial compression using multiscale method.

Figure 22

MD results for sideway buckling at strain values of (a) $\epsilon =0.0569$, (b) $\epsilon =0.0683$, and (c) $\epsilon =0.078$.

Figure 23

Multiscale results for sideway buckling at strain values of (a) $\epsilon =0.0569$, (b) $\epsilon =0.0683$, and (c) $\epsilon =0.078$.

Figure 24

Smoothness of stress-strain curve when using truncated-Newton minimization.

Figure 25

Smoothness of stress-strain curve when using conjugate-gradient minimization.