Fracture SWNT bundles

TEM images of fatigue failure surfaces (a) very tips of pulled-out SWNTs on a fracture surface. The pulled out SWCNT bundles showed a dendrite-like morphology, believed resulted from splitting of SWCNT rope during fatigue, (b) kink-induced failure of a SWNT bundle, (c) brittle-like failure and (d) ductile-like failure of SWNT bundle. 

SWNT fractures are observed at the very tips of pulled-out SWNTs (Fig. 13.13(a)), and within SWNT bundles away from the tips. Some of die SWNT failures are characterized with rather flat fracture surfaces, a characteristic of brittle-like failure (Fig. 13.13(c)). It should be mentioned that die fractured bundle shown in Fig. 13.13(c) may contain many SWNTs. In Fig. 13.13(d), tearing fractures are seen, where SWNT ropes are tom apart, leaving a ductile-like fracture surface. For some SWNT ropes, stepwise, abmpt changes in diameter are seen, indicating that SWNTs within a rope may not be broken at the same time or at the same location. 

FESEM images of SWNT/epoxy fracture surface (a) Pulled out CNT bundles as long as 30-40 can be seen. Plastic deformation of the matrix is obvious. Scale bar is 2fj,m. (b) Fracture surface in lower magnification. The failure modes of the composite portion include SWNT pullout, matrix cracks bridged by SWNT. Scale bar is 10 / m. 

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