Time-dependent fracture behavior of single-walled carbon nanotubes with and without Stone-Wales defects

Based on a concept of molecular-level strain energy concentration and a kinetic fracture model, the time-dependent fracture behavior of three different types of single-walled carbon nanotubes (zigzag, armchair, chiral) with or without Stone-Wales (SW) defects were studied. It is found that the SW defects have influences on the site of crack initiation but the path of crack propagation is closely related to the chirality of the nanotube. Defect-free armchair and chiral tubes exhibit higher static fatigue strength than the zigzag tube of similar size. All of the single-walled carbon nanotubes with SW defect are predicted to have a shorter static fatigue life compared with the defect-free tubes. Moreover, geometric form of the defects is found to influence the time-dependent behavior. Predictions with the present model agree reasonably well with experimental stress-life data of single-walled carbon nanotube rope in epoxy.

Figure 1

Stress-life curves of a defect-free zigzag SWNT, (18,0). Filled circles are S-N data from cyclic fatigue experiments of SWNT ropes embedded in epoxy composites.

Figure 2

Stress-life curves of an armchair SWNT, $(10,10)A$ with SW defects of $A$ mode. Filled circles are S-N data from cyclic fatigue experiments of SWNT ropes embedded in epoxy composites.

Figure 3

Stress-life curves of a chiral SWNT, $(10,5)B$, with SW defects of $B$ mode. Filled circles are S-N data from cyclic fatigue experiments of SWNT ropes embedded in epoxy composites.

Figure 4

Comparison of S-N curves of zigzag, armchair, and chiral SWNTs with or without SW defects of $A$ or $B$ mode.