Investigation Of CNT Or Graphene And Their Nanostructures By Molecular Dynamics Method

Nanomaterials usually have a size of1-100nm (at least in one dimension) andexhibit unusual mechanical and physical properties. Carbon nanotube and graphene,are typical one-dimensional and two dimensional nanomaterials. They are expected tobe used in composite reinforcement, drug delivery, nano-electronics and nano-devicesfor their outstanding features like small size, low density and excellent mechanicalproperties.Molecular dynamics could be used to examine the atomic-level phenomenathatcannot be observed directly in macroscale of the materials. In this thesis, moleculardynamics simulation was used to study the mechanical properties of carbon nanotube,graphene and their nanostructures. The main contents and results are as follows.(1) Multistability of armchair single-walled carbon nanotubes (SWCNTs) withdifferent diameters was studied. It is proposed that the armchair SWCNTs have fourmetastables/stables as the diameters above a threshold value. The transformationbetween different states of the SWCNTs can be realized by applying external loadingor temperature, which implies a great potential application of SWCNTs in nanoelectromechanical system (NEMS) and relative fields.(2) Two kinds of novel3D nanostructures were constructed by representativeelements of CNTs, which are expected to have potential applications in alignedreinforcement of composites with desired interfacial adhesion and in hydrogen storage.The existence and stability of the nanostructures were examined by the first principle.The present assemble strategy can be extended into the construction of other similarnanostructures of CNTs. Then mechanical properties of the nanostructures wereevaluated using molecular dynamics simulation. The Young’s moduli, critical strainsand strengths were obtained and the deformation and failure modes of the3Dnanostructures assembled by different representative elements of CNTs weredemonstrated.(3) Novel bistable nanosystem based on collapsed double-or multi-walledcarbon nanotubes was proposed. The bistability of the nanosystem is induced by thecoupling of the stiffness of the outer tube and Van der Waals interaction between theinner and outer tubes. Thus, this bistable system can be used as Random accessmemory (RAM) devices. (4) Self-folding of graphene ribbons and the multilayer graphene with open andclosed edges induced by Van der Waals force was investigated. The results show onceone end of the graphene ribbons are folded together, the successive folding of theneighboring portions would generate a domino wave until the whole graphene foldstogether. The edge situation has a great influence to the folded configuration of themultilayer graphene.(5) Interfacial cracking in copper-graphite composites was investigated usingmolecular dynamics simulation and cohesive finite element method. This study isfocused on understanding the mechanism of crack propagation of interface incopper-graphite composites under two different boundary conditions. The cohesivetraction-separation law of copper-graphite interface can be obtained by moleculardynamics method. Both molecular dynamics simulation and cohesive finite elementmethod modeling show that there is an obvious stress concentration, but nosingularity of the stress at the crack tip in the interface. The numerical results indicatethat stress near the crack tip obtained from molecular dynamics simulation andcohesive finite element method are consistent with the solution of classical fracturemechanics.