Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Mechanical and Materials Engineering

Supervisor

Dr. Liying Jiang

2nd Supervisor

Dr. Xueliang Sun

Joint Supervisor

Abstract

Nanostructured materials with superior physical properties hold promise for the development of novel nanodevices. Full potential applications of such advanced materials require accurate characterization of their physical properties, which in turn necessitates the development of computer-based simulations along with novel experimental techniques. Since controlled experiments are difficult for nanoscale materials and atomic studies are computationally expensive, continuum mechanics-based simulations of nanomaterials and nanostructures have become the focal points of computational nano-science and materials modelling.

In this study, emphasis is given to predicting the mechanical behaviour of carbon nanotube (CNT), graphene, nanowire (NW), and nanowire encapsulated in carbon nanotube (NW@CNT), which are important nanostructures in a variety of real-world applications such as aerospace, automotive, MEMS/NEMS, and electronics. Using elastic continuum models, nonlinear transverse vibration and postbuckling behaviour of CNTs and graphenes embedded in polymer medium is studied. The source of nonlinearity comes from the van der Waals (vdW) interactions between adjacent layers as well as between surrounding polymer medium and carbon-based nanostructure, in which the latter is investigated for the first time in literature. Euler-Bernoulli and Timoshenko beam theories are employed to model CNTs while classic Kirchhoff plate theory is used to model graphene sheets (GSs). A nonlinear function in terms of the graphene or CNT deflection is derived from the interfacial cohesive law to describe the interfacial interactions preserving true nonlinear nature of the vdW forces. Harmonic balance method is successfully employed to solve the nonlinear governing equations and provide parametric and explicit equations for predicting nonlinear resonant frequencies and postbuckling equilibrium path of the embedded CNTs and GSs. Unlike linear analysis results, the resonant frequencies and postbuckling loads are deflection dependent. The surrounding medium effect on the vibrational and buckling behaviour of these embedded carbon-based nanostructures have been studied systematically. Regarding NWs and NW@CNTs, the effects of surface elasticity and residual surface stress on the stiffness, vibration and buckling of these nano structured materials are investigated using Euler-Bernoulli and Timoshenko beam models to reveal their size-dependent properties. The vdW interactions between the NW and CNT at the interface of NW@CNT are accurately described by using the cohesive Law. Effects of axial load, size, boundary conditions and mode shape number on the vibration and buckling of above mentioned nanostructures are discussed in detail.

The quantitative and parametric analysis in this study may contribute to a better understanding on the mechanical behaviour of these nanostructures, thus leading to a better design in real applications.

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