Mechanical Behavior Of Graphene/Carbon Nanotubes Under Complex Large Deformation Based On Cauchy-born Rule

Due to its excellent mechanical,thermal,electrical,magnetic and acoustic properties,graphene has been widely used in high-performance nanoelectronic devices,composite materials,field emission materials,gas sensors,energy storage and other fields.Therefore,a comprehensive grasp and in-depth understanding of the mechanical properties of graphene play an irreplaceable role in the development and application of new twodimensional materials represented by graphene.For the study of its properties,the use of molecular dynamics simulation calculation methods requires a lot of resources.The continuous medium mechanics method based on the Cauchy-Born rule can effectively reduce the calculation time,so that graphene can be better put into engineering applications.This postgraduate’s Thesis is first based on the theory of continuum at the atomic level.This type of method directly introduces the potential function between atoms,and the bond energy between atoms is equivalent to the strain energy.Based on the modified Cauchy-Born criterion,it considers the influence of Poisson’s ratio on the stretching process,and establishes a relationship between macro and micro deformations.Kinematics relationship,and compared with the calculation results of molecular dynamics simulation:1.In order to study the finite deformation of graphene in plane,the Poisson’s ratio of graphene during continuous stretching in Armchair direction and saw tooth direction was studied by adjusting the calculation method and minimizing the energy dependence.The relationship between bond length and bond angle of graphene was studied.2.Based on the uniaxial tension of graphene,the critical boundary of graphene under biaxial tension is studied.The stress-strain relationship and Poisson’s ratio are calculated,and the failure boundary of graphene under biaxial loading is determined.3.The relationship between stress and strain and Poisson’s ratio of graphene with different temperature under loading are studied by using the molecular dynamics simulation software LAMMPS.Based on the modified Cauchy-Born rule and Continuum mechanics,the tensile mechanical properties of graphene are predicted and studied,and the obtained graphene stress-strain,Young’s modulus relationship meets expectations well.The feasibility of this method is confirmed;and based on the study of the continuum mechanics method,the calculated Poisson’s ratio is a range value,rather than the fixed value considered by the traditional continuum mechanics.Through the method of continuum mechanics,it occupies fewer computing resources and has low requirements for computing conditions,which can better promote the engineering application of graphene.