Quasi-continuous Media In Multi-scale Simulation

As the development of Micro-electronics and Microsystems, researchers pay much attention on the micro-mechanical properties of materials. Because micro-components always show different characteristics from components in macro-situations, the microcosmic mechanism of deformation is important to study the properties of material in micro-situations. However, traditional methods based on continuum theories do not work in investigating the mechanism of micro-deformation. Microcosmic methods such as Molecular Dynamics can not be used to simulate the deformation of a large region in common PCs for its large computation amount caused by large degrees of freedom. In this situation, the multi-scale methods coupling atomistic degree and continuum degree are widely applied in computer simulations.The Quasi-continuum Method is developed as a typical multi-scale method which couples atomic scale and continuum scale by selecting "repatoms". In the areas around the defect core, atomic scale is selected, while continuum scale is selected far away from the defect. The selecting of "repatoms" helps reduce the degree of the system. In this thesis, the effect of size, crystal direction, and grain boundary in micro-deformation are investigated using Quasi-continuum Method. The work of this thesis is as follows:First, Quasi-continuum Method is used to simulate the process of nanoindention of 4 FCC metals (Al, Ag, Ni, and Pd) under 4 indenters with various widths. Load-displacement curves, strain energy-displacement curves, as well as nano-rigidity are obtained. The simulated values of the critical load are in good agreement with theoretical values. The relation between rigidity and indenter width is discussed. The widths of extended dislocation obtained in simulation are in agreement with theoretical values. To study the deformation mechanism, the dislocation pictures are plotted and the relation between load-displacement curves and dislocations are discussed.Second, Quasi-continuum Method is used to simulate the nanoindention of Al film in 4 crystal orientations(x[111], y[-110], z[11-2]; x[-1-12], y[111], z[-110]; x[1-10], y[001], z[-1-10]). Load-displacement curves and atomistic arrangements pictures are obtained. Dislocations and deformation twining are observed in the simulation. The differences between different crystal orientations are analyzed by dislocation theory. Third, Quasi-continuum Method is used to simulate the nanoindentation on an Al film with a grain boundary. The load-displacement curves and micro-structures under the indenter with a grain boundary are compared with no grain boundary. The interaction between dislocations and grain boundary is analyzed.At last, Quasi-continuum Method is used to simulate the deformation of crack tips in FCC Cu under modeⅡload, which is a shearing deformation. Dislocations and deformation twining are observed in the simulation. The deformation mechanisms in two crystal orientations are discussed.