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The Research on Interfacial Stress Transfer of Carbon Nanotube Reinforced Composites and Elastic Properties of a Monolayer Graphene Nanosheet

Author: ZhouLiJun
Tutor: KangYiLan
School: Tianjin University
Course: Solid Mechanics
Keywords: carbon nanotube reinforced composites stress transfer van der Waalsforce residual stress graphene elastic properties
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Type: PhD thesis
Year: 2012
Downloads: 43
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Abstract


Carbon nanotubes and graphene are regarded as the promising reinforcingphase in the advanced composites, due to their superior physical and mechanicalproperties. The interfacial mechanical behavior between the CNTs/graphene andmatrix has great influence on the mechanical properties of composites, and hasattracted much attention of researchers in recent years. In the thesis, theoreticalresearches on the interfacial stress transfer in the carbon nanotubes reinforcedcomposites and elastic properties of a graphene nanosheet have been made.A three-dimensional axisymmetric two-cylinder model is presented toinvestigate interfacial stress transfer in the double-walled carbon nanotube (DWCNT)reinforced composites when the interface between the DWCNT and the matrix isperfect bonding and debonding, respectively. In the model, the Poisson’s effects ofDWCNT and matrix as well as the effects of the van der Waals (vdW) interactionbetween two layers of DWCNT and the residual stress induced by thermal expansioncoefficient (TEC) mismatch of DWCNT and matrix are taken into account. Based onthe equilibrium relation and the interfacial continuous condition of displacement andstress, the differential equations of DWCNT axial stress are derived, and theanalytical expressions of the interfacial shear stress and the axial stresses of DWCNTand matrix are obtained and nondimensionalized, respectively. Then via numericalcalculation, the influence of DWCNT aspect ratio, DWCNT volume fraction, relativemodulus between the DWCNT and the matrix, temperature variation, interfacialfriction coefficient and vdW force are analyzed, respectively. Furthermore, numericalsimulations based on finite element methods are presented to in the thesis toinvestigate the interfacial debonding as well as stress transfer and pullout force in thesingle-walled carbon nanotubes (SWCNTs) reinforced polymer composites. Anaxisymmetric three-cylinder model is presented, and a cohesive element in theABAQUS code is applied to simulate the interfacial layer between the SWCNTs andpolymer matrix. The influence aspect ratio of SWCNTs, interfacial strength andthermal residual stress on the interfacial shear stress as well as axial stress ofSWCNTs and pullout force are analyzed and discussed.In addition, an analytical approach is presented in the thesis to predict the elasticproperties of a monolayer graphene nanosheet based on interatomic potential energy and continuum mechanics. The elastic extension and torsional springs are utilized tosimulate the stretching and angle variation of carbon-carbon bond, respectively. Theconstitutive equation of the graphene nanosheet is derived by using the strain energydensity, and the analytical expressions of five nonzero elastic constants are obtained.The in-plane elastic properties of the monolayer graphene nanosheet are proved to beanisotropic. The effective Young’s moduli, Poisson’s ratios and shear modulus of themonolayer graphene nanosheet are calculated according to the force constants derivedfrom Morse potential and AMBER force field, respectively, and they were proved tobe chirality-dependent.

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