Molecular dynamics simulation of nucleation and growth of defects in the alloy fe-cr in the conditions of high-energy loading

Features of primary radiation damages in the near-surface layers of the Fe-Cr crystallite were investigated. The calculations were based on the molecular dynamics method. It was found that the number of surviving defects at the generation of atomic displacement cascades near the free surfaces is almost twice their number than in case of cascade generation far away from the various interfaces. Besides it the cascades can knock out some atoms from the free surfaces and form some specific structural defects: craters, adatom islands, dislocation loops of vacancy type. The crystallographic orientation of the irradiated surfaces has a significant influence on the features of the material damage. Craters are much more frequently formed at the irradiation of the (111) surface. There is a correlation between the size of the vacancy loops and the number of adatoms on the free surface. The size of the vacancy loops formed by the irradiation of the (111) surface is slightly larger than the number of adatoms. The inverse relationship was found at the irradiation of the (110) surface of Fe-Cr crystallite

Computer simulation of surface modification of al crystallite under high energy treatment

The simulation of structural changes in the surface region of Al crystallite during self-ion bombardment was carried out. The calculations were performed on the base of the molecular dynamics method. A many-body potential calculated in the approximation of the embedded atom method was used to describe the interatomic interactions. It is shown that atomic displacement cascades in the near-surface region were generated under ion irradiation. At relatively low energies the impact of the atomic displacement cascades not only lead to the generation of Frenkel pairs, but also to the nucleation of plastic deformation. That is due to the high-rate heating of the grains, causing their expansion and deformation in the stained conditions with the formation of stacking faults. Melting of surface layers takes place at high energies of irradiation. A crystallization process and a formation of a grain structure of the surface layers will be determined by the characteristics of the propagation of the crystallization front, which shape depends on the relative location, size and orientation of grains on the boundary of the liquid and solid phases

Features of nucleation and evolution of defect structure in vanadium under constrained deformation

Atomic mechanisms of structural transformations leading to fragmentation in vanadium under deformation in constrained conditions without changing its volume are investigated on the basis of the molecular dynamics method. The process of formation of a fragmented structure in a deformed specimen can be divided into two stages. At the first stage, twins nucleate and grow in the crystallite. In the second stage, the orientation of lattice in twins may change due to the intersection of twins leading to their anisotropic deformation. In this case, the directions of stretching and compression of the crystal lattice in the deformed twin quite closely lie in the directions of stretching and compression of the whole crystallite

Latvia's transition to democracy and the challenges of democratic consolidation in Latvia

Diplomová práce "Přechod k demokracii v Lotyšsku a problémy konsolidace lotyšské demokracie" se zabývá analýzou lotyšského přechodu k demokracii a procesů demokratické konsolidace po obnovení nezávislosti v Lotyšsku. Práce se zaměřuje na průběh transformačních procesů na konci osmdesátých a na začátku devadesátých let v této pobaltské republice, stejně jako analyzuje klíčové problematické aspekty vývoje lotyšské demokracie po znovuzískání nezávislosti až do současnosti.The master thesis "Latvia's transition to democracy and the challenges of democratic consolidation in Latvia" deals with the analysis of Latvian transition to democracy and the processes of democratic consolidation after regaining the independence in Latvia. The thesis focuses on the development of transformation processes in the late nineteen eighties and at the beginning of the nineteen nineties in this Baltic republic as well as it analyses the most significant problematic aspects of the development of Latvian democracy after regaining the independence till now.Department of Political ScienceKatedra politologieFaculty of Social SciencesFakulta sociálních vě

Influence of crystallographic orientation on the response of copper crystallites to nanoindentation

Molecular dynamics simulation was performed to study the features of nucleation and development of plastic deformation in copper crystallites in nanoindentation with different crystallographic orientations of their loaded surface: (011), (001), and (111). Atomic interaction was described by a potential constructed in terms of the embedded atom method. It is shown that behavior of the crystallite reaction force correlates well with a change in the fraction of atoms involved in local structural rearrangements. The generation of local structural changes decreases the slope of the crystallite reaction force curve or results in an extremum due to internal stress relaxation. Analysis of structural changes in the material being indented demonstrates that the orientation of its loaded surface greatly affects the features of nucleation and development of plastic deformation

Properties of dusty plasma crystal accounting charge variety of dust particles

Shock wave properties generated by impulse mechanical loading and base state structure of dusty plasma system versus the change of dusty particle charges with height were investigated in the framework of the molecular dynamics method. Spherically symmetric electrostatic confinement was used as the boundary conditions. Interactions between dusty particles were described using Debye-Huckel potential. Particle charges decreased linearly with the increase of height. Shape of dusty plasma crystals with taking into account a variable particle charge was simulated

Investigation of defect nucleation in titanium under mechanical loading

The paper undertakes a study of plastic deformation in a titanium crystallite under mechanical loading (uniaxial tension and indentation) in terms of atomic mechanisms of its generation and development. The molecular dynamics method with many-body interatomic potentials is employed. It is shown that there is a threshold strain, at which a crystal reveals the generation of local structural transformations associated with changes in atomic configurations of the first and second coordination spheres. The onset of plastic deformation in a crystallite is accompanied by a stepwise decrease in potential energy. The effect of free surfaces and grain boundaries on the generation of local structural transformations in a titanium crystallite is investigated

Features of particle synthesis at metal wire dispersion

Features of particle synthesis under simultaneous dispersion of copper and nickel wires were investigated using a molecular dynamics method. The dynamics of wire dispersion, the size and phase composition of synthesized particles depend on the internal structure of dispersed metal wires and the distance between them. The main mechanism of particle synthesis was agglomeration of sputtered clusters, which predominated over the atom deposition from the gas phase on the particle surface. Synthesized particles were characterized by a nonuniform distribution of chemical elements along their cross section. The subsurface region had a higher concentration of copper in comparison with the particle volume. The molecular dynamics simulation of the metal wire dispersion allows finding optimal loading parameters for the synthesis of particles with desirable size and internal structure