Investigation Of A Single-Layer Graphene Under Nanoindentation Based On The Molecular Dynamics Simulation

Molecular dynamics simulations are carried out on the nanoindentation process of monolayer graphene, and the results are illustrated in this paper.Firstly, the thesis describes the development of the new material-graphene and the background of current nanoindentation technology briefly. Secondly, the basic idea of molecular dynamics and the basic steps of simulation are introduced, and the selection of the potential function and algorithm are discussed. Based on the above theories, the numerical nanoindentation model of monolayer graphene is built, with Tersoff potential function to simulate the inter-atom force in the diamond tip and in the monolayer graphene, and Lennerd-Jones potential function is employed to describe the interaction between the indenter and the graphene film. Meanwhile, the Verlet algorithm is utilized to solve the equations of motion. In this article, the microscope mechanism of monolayer graphene during the nanoindentation is investigated, and the rules in load-displacement curve and the deformatation mechanism are discussed. The deformatation mechanism in defect graphene is studied and simulation results with different kinds of defects in graphene are compared.It is shown that there is a close connection between the critical load and the radius of indenter tip. The critical load increases and the corresponding displacement becomes larger as the radius of the tip becomes bigger. As to the intender load of monolayer graphene, it is the radius of indenter, but not that of graphene, that plays a significant role. In a certain data range, the critical load becomes larger and the relevant indentation depth becomes bigger with the the loading rate of indenter increasing. The load-displacement curve has a crucial effect on the loading rate which is bigger than 0.05 nm/ps, while the curve has little change on the other hand. For defect graphene, the smaller distances of both mono-vacancies and multi-vacancies from the center of the film, the smaller of the corresponding limit load; Meanwhile, the load-displacement curves vary with the different types of vacancy defects in graphene. Single Stone-Wales defect has little effect on the mechanical properties of monolayer graphene and the deformation and failure mechanism. Temperature influence in graphene(both the perfect and the defect) is analyzed under the nanoindentation. Temperature has a certain effect on the mechanical properties of the single-layer graphene film.