Molecular Dynamics Simulation Of Nanoindentation And Scratch Of Multilayer Graphene

Graphene has incomparable excellent mechanical properties than that of bulk materials. Graphene has a very broad application prospects, such as high performance nanoelectronic devices, field emission material, composite materials, biological medicine and nergy storage areas, etc. Owing to graphene has unique two-dimensional plane structure and characteristics, studying the mechanical and friction properties of graphene have being very important significance for its device assembly and preparation.The nanoindentation of bilayer graphene is studied by molecular dynamics simulation, the Lernnard-Jones potential function optimal value of cut-off radius are discussed and typical load-depth curves are obtained. Then, the main examine factors including indenter numbers, temperature and size have effect on the mechanical properties of graphene are analyzed. The Young’s modulus and failure strength of bilayer graphene are obtained to be 0.897 TPa and 197.3 GPa, respectively. The mechanical properties of graphene had a strong dependence on temperature and indenter size.Comparing with pristine graphene, graphene with various defects produced by current technology still has a certain application value. Therefore it is necessary to investigate the influence of defects on graphene properties, so that the defective graphene can be fully utilized, which will promote the industrial application of graphene.Based on pristine graphene model, the effects including Stone-Thrower-Wales(STW)defect, vacancy(single and double vacancy defects) and hole defect with different positions and numbers on the mechanical properties of graphene are studied. The results show that: When defect is in the film’s center, it makes Young’s modulus of graphene decrease slightly, while the failure strength decreases significantly. When vacancydefect is in the region covered by indenter, the critical load increases linearly with the increase of the distance which is from the defect to the film’s center; The more numbers of vacancy defects, the lower Young’s modulus and intensity. The number of hole defects reaching a certain concentration outside the region covered by indenter radius which makes the mechanical properties of graphene decrease apparently. It is concluded that graphene with the stable structure is not sensitive to small defects and defective graphene still has good performance and practical value.Finally the nanoscratch process of four-layer graphene is simulated. In particular,the relationship between the scratch depth, speed, direction and the friction properties of graphene are studied. Friction characteristics of graphene differs with the use of different scratch depth. When scratch depth is small, it lead to the friction curve is very smooth with sinusoidal periodicity, the fluctuation cycle is about 2.45 ?, which is roughly equal to graphene lattice constant 2.46 ?, graphene has a superlow frictional behavior. The increase in the scratch depth lead to the cross-linking begins to come out,this phenomenon is the root cause that led to the coefficient of friction increasing.Besides, for a certain extent of velocity the sliding friction of graphene film does not change with the sliding velocity, but is determined by the lattice constant of the matrix.The amplitude of friction in different direction of scratches is inconsistent, and there is a certain difference between the wave period and period. The friction coefficient showed obvious anisotropy.