Research On Separate Quasi-Particle Method And Multiscale Simulation Of Nanoindentation

In recent decades, the very large-scale integrated circuits (VLSI) technology and nanotechnology have developed rapidly. Especially when the characteristic width of VLSI reduces to nanometer level, the study on indentation, which reveals the nano-scale mechanical properties in various types of electronic components, has become one focus of application researches. Furthermore, some new material properties, such as gold may become liquid at room temperature; insulator silicon may become the conductor, also strongly arouses the enthusiasm of scholars in exploring the surprising nano-scale phenomena. Yet the solving of the all problems is not separable in the development and perfection of multiscale methods. In especial, the multiscale method of cross atoms and continuum plays an important role in the multiscale analysis. However, the usual multiscale methods employ the finite element method for simulation in continuum region. The approach could easily produce some false phenomena (e.g. ghost force) at the boundary between atomic model and finite element model. It may case that the physical quantities do not pass through boundary smoothly. Meanwhile, the treatment that the distance of finite element nodes is equal to the one of adjacent atoms would consume a large amount of storage space and computation time. In the last years, researchers have made the model discretization in continuum scale, replaced the finite element system with particle system, and developed a new method, which is called as atomic/particle multiscale method. The kind of method that has its unique geometric construction and clear physical concept attracts researchers to develop and improve it continuously. In the present work, based on previous atomic/particle multiscale analysis methods, the calculation for quasi-particle position and quasi-particle interaction would be the basic breakthrough point. And the following aspects, focused on the establishment and applications of atomic/quasi-particle method, have been researched in detail.1. According to the basic principles of atom/particle model, the new three-dimensional geometric model of second-scale quasi-particles has been established in the correspondence of face-centered cubic crystal lattice of atom system so that the spatial distribution of quasi-particles could be more in line with the actual characteristics of the material. The quantitative relationship between quasi-particle geometry model and face-centered cubic crystal lattice has been proposed. Meanwhile, the construction of virtual quasi-particle and virtual atomic regions at both sides of atomic system and quasi-particle system introduces natural boundary conditions into the separate quasi-particle multiscale method to ensure the displacement, stress or other physical quantities could pass thought freely between atomic area and quasi-particle area.2. In the quasi-particle system, the parameters of potential function, which are solved by average acceleration method, are applied to calculate the quasi-particle acceleration, velocity and position. Furthermore, the parameters of other potential function are obtained by the law of conservation of energy. And they are used to calculate the interaction of quasi-particles. In above process, the position and force of quasi-particle system keep in step with actual physical information of atom system by avoiding introducing Newton's second law directly,3. To take the single-crystal copper nanowire for example, the simulation results of the separate quasi-particle method, generalized particle method and molecular dynamics method under different loading rates have been compared and analyzed to validate the correct for the separate quasi-particle method.4. The single crystal copper thin films with surface defects have been simulated by using the separate quasi-particle method. The variations between the load on thin film and the displacement of indenter are discussed when the distance between defect and indenter takes four different values. Meanwhile, by comparing to the x-direction displacement distribution and Mises local shear strain invariant distribution, the effects of defect on the material atomic system microstructure have been systematically revealed. And the influence of surface defect on the Peierls stress has been calculated and discussed.5. The size effect of copper, aluminum and silver nanoindentation has been studied by adopting the new multiscale method. According to the analysis and comparison of load-displacement cures for the three materials under the four specimens and four indenter widths, the effects of various physical parameters on the dislocation nucleation have been discussed. The Mises local shear strain invariant distribution and x-direction displacement distribution have been plotted to directly reflect the material details in the process of loading. Comparing the hardness values of the three materials with the result of the literature, the multiscale method has been proved correct. As an example, the nanoindentation at aluminum film is simulated in the discussion of relationship between critical load of dislocation nucleation and indenter width. The separate quasi-particle multiscale method is further proved to be correct with the comparison of results between the separate quasi-particle multiscale method, theoretical method and the QC method.In conclusion, a new multiscale method cross atom/particle have been proposed and studied systematically. The geometric model and dynamic equations for this method have been obtained and applied in the analysis of nanoindentation of some metal films, which hopefully would provide useful reference to the nanotechnology research and engineering problems.