The work examines fracture behavior of carbon nanotubes (CNTs) under bending and tension. Expanded graphite (EG) was made by intercalating and exfoliating natural graphite flakes. The EG was deposited with nickel particles, from which CNTs were grown by chemical vapor deposition. The CNTs are tip-grown, and their roots are connected to the graphite nanosheets in the EG. The CNT-grown EG were compressed, and many CNTs on the surface were fragmented due to either bending or tension induced by the compression. High-resolution electron microscopes have been used for examining the crack growth within the graphene layers. For both bending and stretching cases, the fracture is characterized by two-region crack growth: outer-tube and inner-tube. An opening crack first appears around the outer-tube. The crack is then branched to grow along the graphene layers, causing pullout of the inner-tube. The tension-induced pullout was in the form of sword-and-sheath. The onset and development of the crack in these two regions are discussed.
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