Nanomechanics of carbon nanotubes creep, inter-tubular friction, and their interactions with graphene oxide.
Date of Issue2012
School of Chemical and Biomedical Engineering
Carbon nanotubes (CNTs) are of great interest for load-bearing applications because of their excellent mechanical properties. While much effort has been made in the last decade in order to address problems that obscure the applications of CNTs with their remarkable properties fully exploited from both experimental and theoretical perspectives, some fundamental issues regarding the nanomechanical behavior of individual CNTs at noncritical stress, the interaction between CNTs in their assembled forms and, along with the development of a method for effectively dispersing CNTs in aqueous and polymer media with their intrinsic properties retained are far from being settled. In this study, we first focus on probing the fracture mechanisms of CNTs creep using classical molecular dynamics (MD) and nudged elastic band (NEB) methods. The long-timescale microstructural evolution of CNTs at relatively low external stress is modeled by dividing the continuous process into a series of successive discrete transitions between metastable states. Our results indicate that there exist bifurcation states of the failure mechanism in armchair CNT: brittle-type fracture dominates the fracture if external stress exceeds 42.2 GPa for a (8, 8) CNT; alternatively, plastic deformation caused by the nucleation and diffusion of a specific type of defects, 5|7 dislocations, takes place, leads to the necking of the CNT before eventual fracture. Since the time-dependent behavior in CNT is only meaningfully characterized in engineering applications by deformation rate, and the relevant quantities that require sampling over a time dimension too large for atomistic simulation to reach, we adopt the concept from kinetic fracture theory.