Papers by Keyword: Atomistic Simulation

Abstract: Experimental studies proved that structures and properties of misfit dislocations and their intersections (nodes) in semi-coherent interfaces strongly affect thermal and mechanical stability of interface. Employing atomistic simulations, we reveal that misfit dislocation lines can exhibit a spiral pattern (SP) or remain straight in association with dislocation character at nodes. By analyzing nodes formation processes in terms of kinetics and energetics, we found that the variation is ascribed to the competition between core energy of misfit dislocation and interface stacking fault energy with respect to coherent interface.

Abstract: The mechanisms of low-temperature deformation around a crack tip in a hexagonally closed-packed (hcp) magnesium single crystal have been studied by molecular dynamics simulations. In our simulation a {1010} < 12 10 > model I (opening model) crack is selected. The results indicate that slip on the basal plane is activated due to the shear stress at the crack tip. Thus shear banding caused by a successive slip of the basal planes is the main deformation way for this type of crack.

Abstract: The present study deals with diffusion behavior of adsorbed atoms on stepped crystal surfaces. In volume-immiscible systems, two-dimensional (2D) atomic intermixing at epitaxial interface could be completely blocked on step-free surface domains. This is a result of high diffusion barrier for direct atomic exchange between adsorbed layer and substrate. In that case, diffusion takes place exclusively across the steps of atomic terraces. In such systems, dynamic competition between energy gain by mixing and substrate strain energy results in diffusion scenario where adsorbed atoms form alloyed stripes in the vicinity of terrace edges. At high temperatures, the stripe width increases and finally completely destroys the terraces. This process leads to formation of alloyed 2D atomic islands on top of pure substrate layer. The atomistic Monte Carlo simulations reveal vacancy-mediated mechanism of diffusion inside atomic terraces as a result of spontaneous generation of vacancies at high temperature. Being in agreement with recent experimental findings, the observed surface-confined alloying opens up a way various surface pattern to be configured at different atomic levels on the crystal surface.

Abstract: Using joined super-lattice Kinetic Monte Carlo simulations, continuous modelling and recent experimental data on the homoepitaxial growth of 4H Silicon Carbide we study the transition between monocrystalline and polycrystalline growth in terms of misorientation cut, growth rate and temperature. We compare these optimally calibrated results both with previous continuous models and literature data. We demonstrate that this study was, indeed, necessary to correctly reformulate the phase diagram of the transition.

Abstract: Nanostructured composites inspired by structural biomaterials such as bone and nacre form intriguing design templates for biomimetic materials. Here we use large scale molecular dynamics to study the shock response of nanocomposites with similar nanoscopic structural features as bone, to determine whether bioinspired nanostructures provide an improved shock mitigating performance. The utilization of these nanostructures is motivated by the toughness of bone under tensile load, which is far greater than its constituent phases and greater than most synthetic materials. To facilitate the computational experiments, we develop a modified version of an Embedded Atom Method (EAM) alloy multi-body interatomic potential to model the mechanical and physical properties of dissimilar phases of the biomimetic bone nanostructure. We find that the geometric arrangement and the specific length scales of design elements at nanoscale does not have a significant effect on shock dissipation, in contrast to the case of tensile loading where the nanostructural length scales strongly influence the mechanical properties. We find that interfacial sliding between the composite’s constituents is a major source of plasticity under shock loading. Based on this finding, we conclude that controlling the interfacial strength can be used to design a material with larger shock absorption. These observations provide valuable insight towards improving the design of nanostructures in shock-absorbing applications, and suggest that by tuning the interfacial properties in the nanocomposite may provide a path to design materials with enhanced shock absorbing capability.

Abstract: Crack propagation in bcc iron at different strains under low temperature (30K) has been studied using the atomistic simulation. We show that cracks display a brittle character of extension at low strains, and at relative higher strains cracks extend with a periodic series of twins(or SF) bursts. These bursts decrease the crack speed and produce velocity oscillations with an increase in energy dissipation that increases the toughness. Here we also develop a new form of dynamic fracture energy. Using our form of dynamic fracture energy, the results therefore are in quantitative agreement with the theoretical single-crack equation of motion.

Abstract: Junction disclinations are important elements of the structure of nanostructured metals produced by severe plastic deformation (SPD). Effect of these defects on the formation energy of vacancies in grain boundaries (GBs) is studied by means of atomistic computer simulations. Estimates based on the calculations of vacancy formation energies suggest that at least two orders of magnitude increase of the GB diffusion coefficient can be expected due to junction disclinations in nanostructured metals.

Abstract: To enhance the high-temperature stability of zirconate pyrochlore structures, one has to focus on their transformation to the disordered state, fluorite. An atomistic simulation calculation is presented in this paper to predict the propensity of rare earth zirconate pyrochlores to transform to fluorite at high temperature. By detailed calculation of defect formation energy of cation antisites and Frenkel pair, as well as their interactions, the mechanisms of disorder transformation are ascertained. The results show that the tendency of cation disorder is less than the anion’s and disorder transformation will accelerate in advanced stage. The calculation of defect energy in pyrozirconates with different cation on the A site have proved helpful in unraveling their different order-disorder transformation tendency.

Abstract: The diamond structure of single crystal silicon transforms to other structures under mechanical stress. We investigate the structural transformation of diamond cubic structure to betatin structure in silicon
under uniaxial stress using atomistic simulation on the basis of the Tersoff potential. As a result, under extensive compressive strain, the structural transformation from Si-I to Si-II is found.

Abstract: Carbon nanotubes (CNTs) have been attracting attention because of their prominent mechanical and electronic properties. In this study, we investigate the deformation of a single-walled carbon nanotube (SWCNT) with a bend junction using atomistic modeling with Brenner potential to analyze strain concentration caused by macroscopic tube shape and microscopic interatomic bond structure. The simulation model consists of (8,8) and (14,0) CNTs connected with a flexion angle of 30 degrees. For geometric reasons five and seven-membered rings are introduced at the inside and outside of the bend junction. After the structure under no external load is determined, tensile load is applied to the model. Then, we analyze the strain concentration at the bend junction, and high tensile strain is observed at the inside of the bend junction. The strain at the seven-membered ring at the inside of the bend junction has higher strain compared to the neighboring rings due to the microscopic effect.