Molecular Dynamics And Multiscale Simulation Of Contact And Friction On The Nanoscale

With the development of nanotechnology, nanodevices have been widely used in many fields. Surface force and surface effect resulting from small size and ratio of area to volume play a dominant role in determining the performance and lifespan of nanodevices.Therefore, investigating the mechanism of contact and friction on the nanoscale is vital for the improvement of performance and durability of nanodevices. In this study, we model the system of tip and substrate in Atomic Force Microscopy(AFM) experiments to explore the underlying mechanism of single-asperity nanotribology.First, molecular dynamics (MD) simulations are performed to investigate the effect of a void on the nanoindentation of nickel thin film.In order to elucidate the law of friction and wear, MD simulations are performed to study the process of a diamond tip scratching on the single crystal copper substrate. The effects of tip geometry, scratching depth, scratching velocity and temperature are investigated. The ploughing component and adhesion component of friction on the nanoscratching process are distinguished using MD simulations. The contribution of chip to friction is also evaluated.MD simulations are conducted to study the wearless sliding of the tip on the substrate with incommensurate contact to explore the mechanism of stick-slip on the nanoscale. The stick-slip friction during sliding of a diamond tip on the silver substrate is caused by the transition from incommensurate interface configuration to the locally commensurate one in the contact area. The process of stick-slip is accompanied by the accumulation and release of elastic deformation energy.Finally,a hybrid model based on coupling between MD simulation and finite element method is applied to study two-dimensional nanoindentation process. The two-dimensional multiscale method is extended to study the three-dimensional nanoindentation and nanoscratching process showing that the multiscale method can be used to model system with large size. Nanoindentation experiment of copper thin film is performed using Nanoindentation Tester. The pile-up is observed around the indentation site through AFM, which is consistent with the multiscale simulation results.