Papers by Keyword: Atomistic Simulation

Abstract: The strain rate exerts a profound influence on the mechanical characteristics of nanomaterials. To investigate this phenomenon, the molecular dynamics approach was employed to examine the impact of uniaxial compression along the [100] crystallographic direction in monocrystalline Al. The purpose of this research was to determine the differences in reactions observed during the elastic and plastic phases. It employed the Embedded Atom Method (EAM) as well as the Modified Embedded Atom Method (MEAM) potentials at 300 K. A comparative analysis of the outcomes from these potentials demonstrated considerable disparities. The results encompassed the percentage distribution of crystal structures (fcc, hcp, bcc, and others) as well as their atomic configurations. Several analytical factors were examined, including the strain-stress curve, the radial distribution function (RDF), the common neighbor analysis (CAN). The applied MEAM potential represents a subsequent occurrence of transitions following EAM, encompassing both increasing and decreasing phase transitions.

Abstract: The atomic stress tensor at a given continuum point is a spatial average value of some volume near the point. Recent progresses in multiscale modeling include the dealing of the optimal number and the size of these volumes. In this paper, we motivate the application of Iterative self-organizing data analysis technique algorithm to estimate volume numbers. The size of these space averaging volumes then could be got using Gaussian mixture model. Reduced computation complexity is offered by this method. Atomistic simulations are conducted to analyze the stress of a stone-wales defect graphene sheet to validate the method. Other multiscale values could also be determined using this method.

Abstract: We compare the performance of three interatomic interaction potentials for describing the evolution of plasticity and phase transformations in Si: the well established Stillinger-Weber potential, a recent modification used in the description of Al/Si composites, and a modification of the well known Tersoff potential. We show that the generation of dislocations and the evolution of plasticity are well described by the Stillinger-Weber potential and its modification, while the phase transformation to the high-pressure bct5 modification and the subsequent amorphization are better included in the modified Tersoff potential.

Abstract: The effects of [001] uniaxial strain on the stable structures and structural evolution of vacancy clusters in fcc metals, Cu, Ni, Al and Fe, have been studied and compared. Under uniaxial strain, the clusters in all these metals tend to align parallel or perpendicular to the strain axis under tensile or compressive strain. Moreover, both the body cluster and the {001} planar cluster become the dominant types. In addition, the stacking fault tetrahedron cluster becomes another dominant type in Al under compressive strain. The cluster structures in Fe are disordered under strain possibly because the pure fcc Fe is thermodynamically unstable under the current simulation condition.

Abstract: The preferential sites for vacancies on a series of symmetric tilt grain boundaries in copper have been investigated by molecular dynamics simulation. The regularity of preferential sites for vacancies on these boundaries can be described by the structural unit model. This is essential because of the correspondence between the geometries of the structural units and the local stress field. The vacancies are energetically preferred at the sites with relatively large tensile stress, and these sites are the corner sites of the structural units. Moreover, these preferential sites are mainly related to the structural unit types irrespective of which grain boundary that the structure units locate in. Therefore, the preferential sites for vacancies on various grain boundaries formed by combinations of certain structural units can be readily described and predicted by the structural unit model.

Abstract: The elastic-plastic finite element and atomistic models for the frictionless contact of a deformable sphere pressed by a rigid flat is presented. The evolution of the elastic-plastic contact with increasing interference is analyzed using two different analysis tools. The simulation results show that deformation mechanisms revealed in the two different analysis tools are quite different from each other. The physical phenomena “jump-to-contact” and “force drops during dislocation emission” are observed in our atomistic simulations which can not be seen in the continuum analysis.

Abstract: Indenter size effect on the reversible incipient plasticity of Al (001) surface is studied by quasicontinuum simulations. Two cylindrical indenters with the radii 2.5nm and 17.5nm are used to penetrate the surface respectively, in displacement-control in steps of 0.02 nm. Results show that the plasticity under the small indenter is reversible, since it is dominated by the nucleation of a thin deformation twin, which can be fully removed after withdrawal of the indenter, due to the imaging force and stacking fault energy. Under the large indenter, multiple slip systems are activated simultaneously when incipient plasticity occurs, a few twin, dislocation and stacking fault ribbons still remain under the surface when the indenter has been completely retracted, thus the plasticity is irreversible.

Abstract: Dislocation core structures in Au and Cu crystals are investigated by means of quasicontinuum simulations combined with the embedded atom method potentials. A dislocation pair in a graphene sheet, which is observed by Warner et al. experimentally, is also analyzed in the present work. The strain fields around these dislocations in Au, Cu, and graphene crystals are calculated by analyzing the coordinates of discrete atoms, which is a strain tensor calculation method proposed by Zimmerman et al., and compared with theoretical predictions based on Foreman dislocation model. It is shown that the strain fields given by Zimmerman theory are completely suitable for describing the dislocation core structures of Au, Cu and graphene crystals. However, compared with the results of Au and Cu, the Zimmerman strain field in the vicinity of graphene dislocation core is a little less accurate, possibly due to the effect of lattice symmetry of graphene, which needs to be clarified in the future study.

Abstract: The buckling behavior of monolayer graphene sheets with simple-supported, clamped-free and clamped-clamped boundary conditions is investigated by the atomic-scale finite method (AFEM). The initial static equilibrium state of monolayer graphene sheet is obtained in the simulation as a waved configuration which is close to the real graphene observed in experiments. With the increase of compressive displacement, the force displays three stages: linear increasing, nonlinear increasing and decreasing slowly after a sudden drop. Different from the prediction by classical theory, the critical buckling loads of graphene sheets with different boundary conditions are similar, which is attributed to the initial waved configuration of the monolayer graphene sheets.

Abstract: The pull-in behavior of carbon nanotubes (CNTs), which is the sudden increase in the deflection of two interacting CNTs, affects the properties of CNT networks significantly, and thus becomes an important subject in applications. In this paper, an energy-based analysis is carried out to predict the pull-in behavior as well as the critical pull-in distance between two interacting CNTs, and the results agree well with the subsequent atomistic simulations. Furthermore, the factors that affect the critical pull-in distance are also investigated. It is found that the length and diameter of CNTs and space angle between CNTs affect the critical pull-in distance significantly: the critical pull-in distance increases almost linearly with the increasing CNT length and decreasing CNT diameter, and the parallel CNTs have a much higher critical pull-in distance than the non-parallel CNTs. Besides, the chirality of CNTs has a little influence, and when the two CNTs are both zigzag and armchair, the critical pull-in distance is higher than the CNTs with other chiralities due to their stronger commensurability effect. The method and results in this paper will provide nanoscale reference for the design and optimization of CNT-based nanomaterials and nanodevices.