Critical Carbon Nanotube Length in Fibers

The excellent mechanical properties of carbon nanotubes (CNTs), such as low density, high stiffness, and great strength make them ideal candidates for reinforcement material in a wide range of high performance materials applications. The strength-to-weight ratio of CNT fibers are anticipated to exceed any materials currently available, yet theoretical calculations indicate that they still do not take full advantage of the superior mechanical properties of the constituent CNTs. The maximum theoretical strength of CNT fibers is obtained when the shear force is equal to the intrinsic breaking strength of the constituent CNTs. Load transfer is an important factor in determining the mechanical properties of the fibers. In this paper, quenched molecular dynamics is used to study the CNT-CNT interactions in a bundle of CNTs under strain. The bundles consist of parallel (5, 5) CNTs arranged in a hexagonal closest packed (HCP) configuration with one central CNT surrounded by six CNTs on its perimeter. The simulations explore the evolution of load transfer and local strain for slipping between CNTs during the extraction of a single CNT from a bundle. The results provide insight into the role contact length plays in determining the shear stress, yield stress, and contact length needed to achieve maximum fiber strength.