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Title: Simulation of carbon nanocones using molecular dynamics
Other Titles: yong fen zi dong li xue mo ni tan na mi zhui
Authors: Wei, Jingxi (魏靖席)
Department: Department of Building and Construction
Degree: Master of Philosophy
Issue Date: 2007
Publisher: City University of Hong Kong
Subjects: Nanostructured materials -- Computer simulation.
Molecular dynamics.
Notes: x, 84 leaves : ill. (some col.) 30 cm.
Thesis (M.Phil.)--City University of Hong Kong, 2007.
Includes bibliographical references (leaves [77]-84)
CityU Call Number: TA418.9.N35 W45 2007
Type: thesis
Abstract: research community has paid much attention to this form of carbon nanostructure because of its exceptional properties. There are several methods for studying CNTs, such as molecular dynamics (MD), quantum mechanics, and continuum theory, all of which have been variously used to determine the properties of CNTs, such as their mechanical properties, thermal properties, and electrical properties. However, another newly synthesized form of carbon nanostructure – the carbon nanocone (CNC) – has attracted less attention. Unlike the well developed theories for CNTs, research work on CNCs is in its infancy. Up to now, researchers have struggled to establish universally accepted approaches for CNC structures and growth mechanisms, and reports on their mechanical properties are even scarcer. In this work, the mechanical behavior of single-walled carbon nanocones (SWCNCs) with an apex angle of 19.2º under compression is investigated. The analysis is performed using molecular dynamics simulation, with two loading directions – axial compression and in-plane compression – being applied to study their influence on the strain energy of CNCs. Empirical formulas are derived for calculating the critical strains of CNCs with various top radii that are subjected to both axial and in-plane compression. The results of the simulation reveal that cones under in-plane compression show a higher energy level than those under axial compression. In the buckling and postbuckling stage, each shape change, accompanied by an abrupt release of energy in the energy-strain curve, is analyzed, and the possible reasons for early plastic failure are examined, taking into account the buckling behavior of CNCs with different geometrical parameters (top radius, bottom radius and height). The computed results show that for a fixed height/bottom radius ratio, CNCs with a smaller top radius tend to be stiffer. The elastic and plastic behavior of SWCNCs under tension is also examined using MD simulation, and the force-strain response of CNCs are obtained and compared with those of CNTs. It is revealed that CNCs with a larger apex angle have a greater failure strength but a smaller maximum strain under tension. Following this law, CNTs exhibit the smallest failure strength but the greatest maximum strain due to their zero conical angle. The mechanical properties of CNCs, such as the Young’s modulus, elastic strain limit, and ultimate force, are determined and discussed. The Young’s modulus of CNCs is to found fall within the range of 0.29Tpa to 0.73Tpa, depending on their conical angles, height, and top radius. Illustrations of the Young’s modulus of CNCs demonstrate the dependency of the stiffness on the height to top radius ratio. The Young’s modulus tends to converge as the top radius of CNCs achieves a certain level for a fixed length to top radius ratio.
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