Bending fracture in carbon nanotubes

Abstract

A novel approach was adopted to incur bending fracture in carbon nanotubes (CNTs).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 chemicalvapor deposition. The CNTs were tip-grown, and their roots were fixed on the EG flakes.The EG flakes were compressed, and many CNTs on the surface were fragmented due tothe compression-induced bending. Two major modes of the bending fracture wereobserved: cone-shaped and shear-cut. High-resolution scanning electron microscopy(SEM) and transmission electron microscopy (TEM) were used to examine thecrack growth within the graphene layers. The bending fracture is characterized bytwo-region crack growth. An opening crack first appears around the outer-tube due tothe bending-induced tensile stress. The crack then branches to grow along aninclined direction toward the inner-tube due to the presence of the shear stressin between graphene layers. An inner-tube pullout with inclined side surface isformed. The onset and development of the crack in these two regions are discussed.