Fcc Crystal Enterprise Molecular Dynamics Study Of Dislocation Loops

With the improvement of calculation speed of computers and the development of calculation methods, more and more people use molecular dynamics method to study properties of materials. Using reasonable interaction potential between atoms, such as EAM potential for metal, Molecular dynamics simulation can give well results on mechanical and thermodynamic properties of metal, comparing to experimental results.Molecular dynamics simulations can track the detailed dynamic evolution of material to provide a clear image of the evolution, so it is useful for analyzing dynamic response characteristics of materials. In this paper, the focus of concern is the mechanical characteristics of evolution of Frank loops and partial dislocation loops in FCC copper.Molecular dynamics program using in this paper is called LAMMPS, taking advantage of the background grid and the bond analysis, a program was prepared to deal with the identification procedures of atom types efficiently. Before the start of simulation, EAM potential parameters of copper providing by LAMMPS was used to the quantitative calculation of balance crystal constant, elastic constants and stacking fault energy of copper, calculated values and experiments values are in good. This shows that the EAM potential parameters of copper in LAMMPS can be a very good description of the interaction between copper atoms.At zero temperature, studies on Frank loop in FCC copper obtain a series of meaningful results: Frank loops of different sizes and shapes can form different final stable configurations, however, they follow a unified law of dislocation decomposition and reaction. All of these configurations are called expanded stacking-fault tetrahedron (SFT); There are two phenomena related to the size of Frank loop during the formation of expanded SFT - critical size and oscillation phenomenon, the critical sizes of Frank loop of various shapes which can not form expand SFT are carefully analyzed, detailed analysis show that the oscillation of large-size Frank loop evolution is due to asynchrony of attractive force and repulsive force between dislocations, caused by the delayed effect of elastic wave propagation.At finite temperature, simulation results about the contraction process of partial dislocation by self-interaction show that: temperature have obvious influence on the migration velocity of dislocation, In general, the higher the temperature is, the greater the dislocation migration velocity will be; different types of dislocation have different change rate of migration velocity caused by temperature. Overall, at a lower temperature, between OK and 50K, change rate of migration velocity of edge dislocation and screw one are nearly the same, so that they have almost same migration velocity. At a higher temperature, between 50K and 100K, change rate of migration velocity of edge dislocation is greater than screw dislocation, edge dislocation migrate faster; When temperature reaches 150K or higher(here is between 150K and 350K), new dislocation will appear and then separate from original one in the process of self-contraction. The appearance and separation of new partial dislocations reveals a new mechanics of dislocation source, different from Frank-Read type. The underlying cause of appearance and separation of new partial dislocation is due to the combined effect of dislocation core broadening and local stress.Text in Chapters II and III, respectively, briefed the fundamental knowledge in crystal dislocation theory and molecular dynamics, contents such as derivation of complex formulas, construction method of dislocation configuration and post-processing methods are listed in the appendix.