title: 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 chemical vapor 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 to the compression-induced bending. Two major modes of the bending fracture were observed: cone-shaped and shear-cut. High-resolution scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the crack growth within the graphene layers. The bending fracture is characterized by two-region crack growth. An opening crack first appears around the outer-tube due to the bending-induced tensile stress. The crack then branches to grow along an inclined direction toward the inner-tube due to the presence of the shear stress in between graphene layers. An inner-tube pullout with inclined side surface is formed. The onset and development of the crack in these two regions are discussed.
authors: Department of Aerospace and Systems Engineering, Feng-Chia University, Taichung 407, Taiwan, Republic of China.
authors: Wen-Shyong
authors: WS
authors: Kuo
authors: Hsin-Fang
authors: HF
authors: Lu