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Title: Modeling and Simulation of Buckling of Pristine and Defective Carbon Nanotubes
Keywords: continuum modeling, molecular dynamics, buckling, nanotubes
Issue Date: 14-Sep-2011
Source: D.D.THANUJA KRISHANTHI KULATHUNGA (2011-09-14). Modeling and Simulation of Buckling of Pristine and Defective Carbon Nanotubes. ScholarBank@NUS Repository.
Abstract: Carbon nanotube (CNT) is one of several nanomaterials that has attracted enormous attention of researchers within the last two decades. Among the research focuses of CNTs, the buckling behavior of CNT has taken an important place in view that buckling is a major mode of structural instability of CNTs owing to their hollow tubular nature and high aspect ratio. Despite the high number of studies conducted on the buckling of CNTs, there are still several issues that are not addressed sufficiently in the literature. For example, there appear to be little work carried out in investigating the buckling of embedded CNTs and defective CNTs. Moreover, there exist discrepancies between the results obtained from various modeling techniques and these discrepancies have not been subjected to sufficient discussion. The objective of this thesis is therefore to investigate the buckling of freestanding pristine and defective CNTs as well as embedded pristine CNTs. Molecular dynamics simulation (MDS) technique is employed as the main modeling tool while analytical method based on continuum mechanics is also employed wherever possible. The scope of work carried out in this study can be divided mainly into three parts. In the first part of the study, improved analytical formulae are proposed for the buckling strain of single and double-walled carbon nanotubes based on Sanders and first-order shell theories. It is noticed that the buckling strain values computed from existing formula in the literature based on the Donnell shell theory do not show sensitivity to aspect ratio (length/diameter ratio) of CNT. The lack of sensitivity is contrary to the results obtained from MDS where buckling strains actually show considerable sensitivity to the aspect ratio of CNT. The proposed formulae appear to generate results with improved accuracy compared to the widely employed formula existing in the literature. The second part of the thesis is focused on the buckling of embedded CNTs. MDS based studies on buckling of embedded CNTs are found to be lacking in the literature. As a result, the accuracy of the continuum mechanics models employed in analyzing buckling of embedded CNTs is not sufficiently verified. Detailed molecular dynamics study is thus carried out in this thesis to investigate the buckling of pristine embedded CNTs. In addition, the accuracy of the continuum mechanics based analytical models in predicting buckling properties of embedded CNTs is discussed. The analytical models employed in this study are based on Euler beam, Donnell shell and first-order shell theories. Of the three formulae considered in this study, the proposed formula based on first-order shell theory is found to produce the most accurate results irrespective of the buckling mode. However, even the results obtained from the proposed formula appear to deviate considerably from the results obtained from molecular dynamics simulations. It appears from a review of the literature that the buckling of defective CNTs is also not sufficiently examined. Therefore, the third part of this thesis presents the investigation on the buckling properties of defective freestanding SWNTs and DWNTs using MDS. Several types of defects have been identified in CNTs. Among them, non-reconstructed vacancy defects are the type of defects that cause the highest degradation of buckling properties. Therefore in this study, various configurations of non-reconstructed vacancy defects are investigated to identify the severity of degradation of buckling properties expected in defective CNTs. The effect of defects on buckling properties under various thermal environments is also examined.
Appears in Collections:Ph.D Theses (Open)

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