Studies On The Mechanical Properties Of Graphene By Molecular Structural Mechanics Based On Finite Element Method

Graphene is another new low-dimensional carbon nanomaterial after thediscovery of fullerene and carbon nanotube in recent years, whose structure is a singleplanar sheet of sp2-bonded carbon atoms that are densely packed in a honeycombcrystal lattice. Theoretical analysis and experiments have showed that grapheneexhibits high strength and rigidity as well as excellent electrical, thermal, and opticalproperties. It is considered to be the most promising materials because of itsextremely broad potential applications in many fields. The studies on mechanicalproperties and microscopic deformation mechanism of graphene have attracted moreand more attentions of researchers. In this thesis, theoretical researches on mechanicalproperties and deformation behavior of perfect and defective graphene are made usingmolecular structural mechanics based on finite element method.Via the linkage between the interatomic potential energy in molecular mechanicsand the strain energy in classical structural mechanics, the models of space framestructures are developed to simulate perfect graphene and graphene with Stone-Walesdefects, and the geometric and physical parameters of the models are obtainedaccording to the force constants in molecular mechanics. The finite element analysesof graphene are made via ANSYS code, and the size-and chirality-dependentmechanical properties of perfect graphene nanoribbons as well as the influence ofStone-Wales defects on the elastic properties of monolayer and multilayer graphenenanofilms are studied.For perfect monolayer graphene, the Young’s moduli and Poisson’s ratios of botharmchair and zigzag graphene nanoribbons are investigated with increasing length andwidth of graphene, and the elastic constants of monolayer graphene nanofilms areproved to be size-and chirality-dependent. With the nonlinear effect of the C-C bondspotential energy function taken into account, tensile fracture behavior of graphene arestudied and tensile stress-strain curves and fracture strength of graphene are given.Besides, Young’s moduli and Poisson’s ratios of multilayer graphene nanoribbons aresimulated with surface relaxation taken into account to explore the relation betweenthe elastic constants and relaxation coefficient as well as the thickness of graphene.For graphene with Stone-Wales defects, the influences of several factors, includingthe types and number of Stone-Wales defects, the distance between two defects and the position of defects in the graphene, on Young’s modulus and Poisson’s ratios ofboth chirality monolayer graphene are investigated, respectively. The size-dependentmechanical properties of multilayer graphene nanofilms with surface Stone-Walesdefects are also analyzed.