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  • Open AccessOpen Access

    REVIEW

    The Emerging Role of Multiscale Modeling in Nano- and Micro-mechanics of Materials

    Nasr M. Ghoniem1, Kyeongjae Cho2
    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.2, pp. 147-174, 2002, DOI:10.3970/cmes.2002.003.147
    Abstract As a result of surging interest in finding fundamental descriptions for the strength and failure properties of materials, and the exciting prospects of designing materials from their atomic level, an international symposium on Multiscale Modeling was convened at ICES'2K in Los Angeles during August 23 - 25, 2000. In this symposium, 23 speakers with research interests spanning fields as diverse as traditional mechanics, physics, chemistry and materials science have given talks at this symposium. The topics of discussion were focused on sub-continuum modeling of the mechanics of materials, taking into account the atomic structure of solid materials. The main motivation… More >

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    1283

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    1143

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    ARTICLE

    A Variational Multiscale Method to Embed Micromechanical Surface Laws in the Macromechanical Continuum Formulation

    K. Garikipati1
    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.2, pp. 175-184, 2002, DOI:10.3970/cmes.2002.003.175
    Abstract The embedding of micromechanical models in the macromechanical formulation of continuum solid mechanics can be treated by a variational multiscale method. A scale separation is introduced on the displacement field into coarse and fine scale components. The fine scale displacement is governed by the desired micromechanical model. Working within the variational framework, the fine scale displacement field is eliminated by expressing it in terms of the coarse scale displacement and the remaining fields in the problem. The resulting macromechanical formulation is posed solely in terms of the coarse scale displacements, but is influenced by the fine scale; thereby it has… More >

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    1237

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    1030

  • Open AccessOpen Access

    ARTICLE

    Initial Dislocation Structure and Dynamic Dislocation Multiplication In Mo Single Crystals

    L. M. Hsiung, D. H. Lassila1
    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.2, pp. 185-191, 2002, DOI:10.3970/cmes.2002.003.185
    Abstract Initial dislocation structures in as-annealed high-purity Mo single crystals, and deformation substructures of the crystals compressed at room temperature under different strain rates have been examined and studied in order to elucidate the physical mechanisms of dislocation multiplication and motion in the early stages of plastic deformation. The initial dislocation density was measured to be in a range of 106 ~ 107 cm−2. More importantly numerous grown-in superjogs were observed along screw dislocation lines. After testing in compression, dislocation density (mainly screw dislocations) increased to 107 ~ 108 cm−2. Besides, the formation of dislocation dipoles (debris) due to the nonconservative… More >

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    1099

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    901

  • Open AccessOpen Access

    ARTICLE

    Computer Simulation of Fundamental Behaviors of Point Defects, Clusters and Interaction with Dislocations in Fe and Ni

    E. Kuramoto, K. Ohsawa, T. Tsutsumi1
    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.2, pp. 193-200, 2002, DOI:10.3970/cmes.2002.003.193
    Abstract In order to investigate the interaction of point defects with a dislocation, an interstitial cluster or a SFT (stacking fault tetrahedron), computer simulation has been carried out in model Fe and Ni crystals. The capture zone (the region where the interaction energy is larger than kT) was determined for various interactions. Calculated capture zone for T =500°C for SIAs (crowdion and dumbbell) around a straight edge dislocation is larger than that for a vacancy in both Fe and Ni. Capture zones for Ni are larger than those for Fe, suggesting that Ni (fcc) has a larger dislocation bias factor than… More >

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    1231

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    892

  • Open AccessOpen Access

    ARTICLE

    The Core Structure and Energy of the 90° Partial Dislocation in Si

    Karin Lin1, D. C. Chrzan2
    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.2, pp. 201-212, 2002, DOI:10.3970/cmes.2002.003.201
    Abstract The 90° partial dislocation in Si is studied using a combination of Tersoff potentials and isotropic elasticity theory. Both periodic supercells and cylindrical cells are employed and the results compared. The dislocation core radius is extracted by fitting the results of atomic scale calculations to an expression for the elastic energy of the dislocation. The energy differences between two proposed reconstructions of the dislocation core are computed and found to depend systematically on the stress field imposed on the dislocation. It is suggested that hydrostatic stresses may introduce a core transformation. More >

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    1263

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    953

  • Open AccessOpen Access

    ARTICLE

    Dislocation Nucleation and Propagation During Thin Film Deposition Under Tension

    W. C. Liu, S. Q. Shi, C. H. Woo, Hanchen Huang1
    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.2, pp. 213-218, 2002, DOI:10.3970/cmes.2002.003.213
    Abstract Using molecular dynamics method, we study the nucleation of dislocations and their subsequent propagation during the deposition of tungsten thin films under tension. Aiming to reveal the generic mechanisms of dislocation nucleation during the deposition of polycrystalline thin films, the case of tungsten on a substrate of the same material is considered. The substrate is under uniaxial tension along the [111] direction, with the thermodynamically favored (01ˉˉ1) surface being horizontal. The simulation results indicate that the nucleation starts with a surface step, where a surface atom is pressed into the film along the [111ˉˉ] direction. This process leads… More >

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    1439

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    1103

  • Open AccessOpen Access

    ARTICLE

    Atomistic Measures of Materials Strength

    Ju Li1, Sidney Yip1
    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.2, pp. 219-228, 2002, DOI:10.3970/cmes.2002.003.219
    Abstract We examine the role of atomistic simulations in multiscale modeling of mechanical behavior of stressed solids. Theoretical strength is defined through modes of structural instability which, in the long wavelength limit, are specified by criteria involving elastic stiffness coefficients and the applied stress; more generally, strength can be characterized by the onset of soft vibrational modes in the deformed lattice. Alternatively, MD simulation of stress-strain response provides a direct measure of the effects of small-scale microstructure on strength, as illustrated by results on SiC in single crystal, amorphous, and nanocrystalline phases. A Hall-Petch type scaling is introduced to estimate strength… More >

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    1243

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    888

  • Open AccessOpen Access

    ARTICLE

    The Influence of Crystal Surfaces on Dislocation Interactions in Mesoscopic Plasticity: A Combined Dislocation Dynamics- Finite Element Approach

    R. Martinez1, N. M. Ghoniem2
    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.2, pp. 229-244, 2002, DOI:10.3970/cmes.2002.003.229
    Abstract We focus here on the direct coupling of Dislocation Dynamics (DD) computer simulations with the Finite Element Method (FEM) to simulate plastic deformation of micro-scale structures, and investigate the influence of crystal surfaces on dislocation motion. A series of three-dimensional (3-d) DD simulations of BCC single crystals with a single shear loop in the (101)-[111] slip system are first presented. The purpose of these simulations is to explore the relationship between loop force distributions and the proximity of the loop to the crystal boundary. Traction boundary conditions on a single crystal model are satisfied through the superposition of the "image''… More >

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    1232

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    948

  • Open AccessOpen Access

    ARTICLE

    A Multi-Scale Theoretical Scheme for Metal Deformation

    Robb Thomson, Retired1, L. E. Levine1, Y. Shim E. 2, M. F. Savage1, D. E. Kramer1
    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.2, pp. 245-254, 2002, DOI:10.3970/cmes.2002.003.245
    Abstract A conceptual theoretical scheme for single crystal metal deformation is presented consisting of multi-scale models from dislocation dynamics to the continuum constitutive relations. The scheme rests on the fundamental observations that deformation is characterized by partially ordered internal dislocation wall structures, discontinuous strain bursts in time, and strain localization in a surface slip band structure. A percolation strain model corresponds to elementary slip line burst events, with percolation parameters to be supplied from experiments and dislocation dynamics studies of wall structures. A model for localization of the slip lines into bands is proposed (for suitable loadings) which envisions channels for… More >

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    1204

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    934

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    ARTICLE

    Molecular Dynamics Study of Temperature Dependent Plastic Collapse of Carbon Nanotubes under Axial Compression

    Chengyu Wei1, 2, Deepak Srivastava 2, Kyeongjae Cho1
    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.2, pp. 255-262, 2002, DOI:10.3970/cmes.2002.003.255
    Abstract The temperature dependence of the plastic collapse of single-wall carbon nanotubes under axial compression has been studied with classical molecular dynamics simulations using Tersoff-Brenner potential for C-C interactions. At zero temperature, an (8,0) single-wall carbon nanotube under axial compression collapses by forming fins-like structure which remains within the elastic limit of the system, in agreement of previous molecular dynamics study. At finite temperatures, however, we find that temperature dependent fluctuations can activate the formation of sp3 bonds, in agreement with a recently proposed plastic collapse mechanism of the same nanotube with a generalized tight-binding molecular dynamics description. Furthermore, Stone-Wales defects… More >

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    1233

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    906

  • Open AccessOpen Access

    ARTICLE

    Numerical Simulation of Cohesive Fracture by the Virtual-Internal-Bond Model

    P. Zhang1, P. Klein2, Y. Huang1,3, H. Gao4, P. D. Wu5
    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.2, pp. 263-278, 2002, DOI:10.3970/cmes.2002.003.263
    Abstract The recently developed virtual-internal-bond (VIB) model has incorporated a cohesive-type law into the constitutive law of solids such that fracture and failure of solids become a coherent part of the constitutive law and no separate fracture or failure criteria are needed. A numerical algorithm is developed in this study for the VIB model under static loadings. The model is applied to study three examples, namely the crack nucleation and propagation from stress concentration, kinking and subsequent propagation of a mode II crack, and the buckling-driven delamination of a thin film from a substrate. The results have demonstrated that the VIB… More >

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    1178

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    916

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