Browsing by Subject "Nanotubes"
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Item Multiscale modeling of carbon nanotube materials with distinct element method(2014-05) Ostanin, Igor AleksandrovichMesoscale simulation techniques are becoming increasingly important due to the interest in complex mechanical problems involving nanoscale structures and materials. This work is devoted to the development of a novel mesoscopic modeling technique based on an extension of the distinct element method and its application to the problem of mechanical modeling of carbon nanotube materials. Starting from an atomistic description, the important interactions between segments of the tubes are encapsulated into two types of contact models. The nanomechanics of intratube bonds is characterized by the parallel bond contact model. Intertube interactions are accounted for by an anisotropic vdW contact model. Energy dissipation is formulated in a top-down manner, based on the macroscopic mechanical properties of carbon nanotube materials. The developed model is applied to the analysis of various mesoscopic structures and materials - self-folded nanotube configurations, nanotube bundles and ropes, nanotube papers and films. The results of mesoscopic simulations not only are in good agreement with experimental observations, but they also provide interesting insights on the roles of effects of morphology, vdW adhesion and registry, cross-linking and energy dissipation on the nanomechanics of carbon nanotube based materials.Item A study of bending deformations in carbon nanotubes using the objective molecular dynamics method.(2010-09) Nikiforov, Ilia A.Bending of carbon nanotubes is a topic which has applications in several areas of nanotechnology, including nanotoxicology and NEMS. Atomistic simulations are necessary to understand in detail the fundamentals and the phenomena observed in experiments. Objective molecular dynamics allows the imposition of angular boundary conditions on atomistic systems. Coupled with the Tersoff potential, objective MD is used to systematically investigate reversible elastic bending in carbon nanotubes up to 4:2 nm in diameter. A contrasting behavior is revealed. Single-wall tubes buckle in a gradual way, with a clear intermediate regime before they fully buckle and significant hysteresis between bending and unbending cycles, in agreement with previous studies. Multi-walled tubes with closed cores, not commonly studied using direct atomistic methods, exhibit a hysteresis-free, rate- and size-independent direct transition to an unusual wavelike mode with a 1 nm characteristic length. This rippling mode has a nearly-linear bending response and causes a #24; 35% reduction in the stiffiness of the thickest multi-walled tubes.