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  • Open AccessOpen Access

    ARTICLE

    A Micromechanics Analysis of Nanoscale Graphite Platelet-Reinforced Epoxy Using Defect Green's Function

    B. Yang1,2, S.-C. Wong3, S. Qu3
    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 81-94, 2008, DOI:10.3970/cmes.2008.024.081
    Abstract In the modeling of overall property of composites, the effect of particle interaction has been either numerically taken into account within a (representative) volume element of a small number of particles or neglected/ignored in order for efficient solution to a large system of particles. In this study, we apply the point-defect Green's function (GF) to take into account the effect of particle interaction. It is applicable to small volume fractions of particles (within 10 %). The high efficiency of the method enables a simulation of a large system of particles with generally elastic anisotropy, arbitrary shape and composition, and arbitrary… More >

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    858

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    691

  • Open AccessOpen Access

    ARTICLE

    Carbon Nanotube Transmission between Linear and Rotational Motions

    Hanqing Jiang1, Junqiang Lu2, Min-Feng Yu2, Yonggang Huang3
    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 95-102, 2008, DOI:10.3970/cmes.2008.024.095
    Abstract The periodic lattice registry of multi-walled carbon nanotubes (MWCNTs) have been exploited for the possibilities of development of nanodevices. This paper studied the telescoping behaviors of double-walled carbon nanotubes (DWCNTs) by atomic-scale finite element and tight-bind Green function methods. It was found that telescoping a DWCNT (e.g., (6,3)/(12,6)) will induce a rotational motion of the inner CNT that has a chirl angle θ (0° < θ < 30°). This telescoping-induced rotational motion does not exist for armchair and zigzag DWCNTs due to the symmetry of CNTs. The rotational angle is completely determined by the chirality of the inner CNT and… More >

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    830

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    748

  • Open AccessOpen Access

    ARTICLE

    Evaluation of Effective Material Parameters of CNT-reinforced Composites via 3D BEM

    F.C. Araújo1, L.J. Gray2
    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 103-122, 2008, DOI:10.3970/cmes.2008.024.103
    Abstract In recent years, carbon nanotubes (CNTs) have been widely employed to build advanced composites. In this work, a Boundary Element Method (BEM) is applied to 3D representative volume elements (RVEs) to estimate mechanical properties of CNT-based composites. To model the thin-walled nanotubes, special integration procedures for calculating nearly-strongly-singular integrals have been developed. The generic BE substructuring algorithm allows modeling complex CNT-reinforced polymers, containing any number of nanotubes of any shape (straight or curved). The subregion-by-subregion strategy, based on Krylov solvers, makes the independent generation, assembly, and storage of the many parts of the complete BE model possible. Thus, significant memory… More >

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    813

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    751

  • Open AccessOpen Access

    ARTICLE

    Phonon Transport and Thermal Conductivity Percolation in Random Nanoparticle Composites

    Weixue Tian1, Ronggui Yang2
    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 123-142, 2008, DOI:10.3970/cmes.2008.024.123
    Abstract In this paper, we investigated the effective thermal conductivity of three dimensional nanocomposites composed of randomly distributed binary nanoparticles with large differences (contrast ratio) in their intrinsic (bulk) thermal conductivity. When random composites are made from particles with very different thermal conductivity (large contrast ratio), a continuous phase of high thermal conductivity constituent is formed when its volumetric concentration reaches beyond the percolation threshold. Such a continuous phase of material can provide a potentially low resistance pathway for thermal transport in random composites. The percolation theory predicts the thermal conductivity of the random composites to increase according to a scaling… More >

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    767

  • Open AccessOpen Access

    ARTICLE

    Buckling in Wurtzite-Like AlN Nanostructures and Crystals: Why Nano can be Different

    C. J. F. Solano, A. Costales, E. Francisco, A. Martín Pendás, Miguel A. Blanco1, K.-C. Lau, H. He, Ravindra Pandey2
    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 143-156, 2008, DOI:10.3970/cmes.2008.024.143
    Abstract The buckling of hexagonal layers in bulk and nanostructures of AlN is analyzed in the framework of atomistic and first principles techniques. At ambient conditions, the wurtzite structure (B4) of AlN consists of buckled hexagons. On the other hand, a non-buckled Bk structure is found to be metastable at zero pressure, being favored at higher pressures. It is suggested that the energy ordering of B4 and Bk may change in finite systems; an assertion tested in this study by considering finite slabs, nanobelts, and nanorings, and comparing the results with the previous studies on small clusters, and periodic nanostructures. We… More >

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    832

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    678

  • Open AccessOpen Access

    ARTICLE

    Strain Energy on the Surface of an Anisotropic Half-Space Substrate: Effect of Quantum-Dot Shape and Depth

    E. Pan1,2, Y. Zhang2, P. W. Chung3, M. Denda4
    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 157-168, 2008, DOI:10.3970/cmes.2008.024.157
    Abstract Quantum-dot (QD) semiconductor synthesis is one of the most actively investigated fields in strain energy band engineering. The induced strain fields influence ordering and alignment, and the subsequent surface formations determine the energy bandgap of the device. The effect of the strains on the surface formations is computationally expensive to simulate, thus analytical solutions to the QD-induced strain fields are very appealing and useful. In this paper we present an analytical method for calculating the QD-induced elastic field in anisotropic half-space semiconductor substrates. The QD is assumed to be of any polyhedral shape, and its surface is approximated efficiently by… More >

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    756

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    689

  • Open AccessOpen Access

    ARTICLE

    Materials Modeling from Quantum Mechanics to The Mesoscale

    G. Fitzgerald1, G. Goldbeck-Wood2, P. Kung1, M. Petersen1, L. Subramanian1, J. Wescott2
    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 169-184, 2008, DOI:10.3970/cmes.2008.024.169
    Abstract Molecular modeling has established itself as an important component of applied research in areas such as drug discovery, catalysis, and polymers. Algorithmic improvements to these methods coupled with the increasing speed of computational hardware are making it possible to perform predictive modeling on ever larger systems. Methods are now available that are capable of modeling hundreds of thousands of atoms, and the results can have a significant impact on real-world engineering problems. The article reviews some of the modeling methods currently in use; provides illustrative examples of applications to challenges in sensors, fuel cells, and nanocomposites; and finally discusses prospects… More >

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    884

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    741

  • Open AccessOpen Access

    ARTICLE

    Coupled Atomistic/Continuum Simulation based on Extended Space-Time Finite Element Method

    Shardool U. Chirputkar1, Dong Qian2
    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 185-202, 2008, DOI:10.3970/cmes.2008.024.185
    Abstract A multiscale method based on the extended space-time finite element method is developed for the coupled atomistic/continuum simulation of nanoscale material systems. Existing single scale approach such as the finite element method has limited capability of representing the fine scale physics in both the spatial and temporal domains. This is a major disadvantage for directly incorporating FEM in coupled atomistic/continuum simulations as it results in errors such as spurious wave reflections at the atomistic/continuum interface. While numerous efforts have been devoted to eliminating the interfacial mismatch effects, less attention has been paid to developing fine scale, atomistic level representations within… More >

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    788

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    642

  • Open AccessOpen Access

    ARTICLE

    Effects of Dopants on the Mechanical Properties of Nanocrystalline Silicon Carbide Thin Film

    Liming Xiong1, Youping Chen1
    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 203-214, 2008, DOI:10.3970/cmes.2008.024.203
    Abstract This paper presents the application of an atomistic field theory (AFT) in modeling and simulation of boron- , boron/nitrogen and silicon/nitrogen-doped nanocrystalline silicon carbide (B-, BN-, SiN-SiC). Intergranular glassy films (IGFs) and nano-sized pores have been obtained in triple junctions of the grains in nanocrystalline SiC (nc-SiC). Residual tensile stress in the SiC grains and compressive stress in the grain boundaries (GBs) are observed. Under uniaxial tension, the constitutive responses of nanocrystalline SiC were reproduced from the simulations. It is found that the mechanical properties of nanocrystalline SiC are strongly dependent on the compositions of GBs. Although there are more… More >

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    868

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    751

  • Open AccessOpen Access

    ARTICLE

    DFT Studies on Ferroelectric Ceramics and Their Alloys: BaTiO3, PbTiO3, SrTiO3, AgNbO3, AgTaO3, PbxBa1-xTiO3 and SrxBa1-xTiO3

    Mustafa Uludoğan1, D. Paula Guarin1, Zully E. Gomez1, Tahir Cagin1, William A. Goddard III2
    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 215-238, 2008, DOI:10.3970/cmes.2008.024.215
    Abstract Aiming at a presentation of the utility of the state of art of first-principles methods (PBE flavor of Density Functional Theory, DFT) in the area of materials science and engineering, we present our studies of the equation of state and ferroelectric-paraelectricphase transition in several ferroelectric systems, including BaTiO3, PbTiO3, SrTiO3, AgNbO3, PbxBa1-xTiO3 and SrxBa1-xTiO3. We also report the Born effective charges, optical dielectric constant, and phonon dispersion relation properties from Density Functional Perturbation Theory. Computed results are compared with other theoretical results (which were mostly on BaTiO3, PbTiO3, cubic SrTiO3 using various approaches, as well as experiments. The studies on… More >

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    1191

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    1615

  • Open AccessOpen Access

    ARTICLE

    Molecular Dynamics Study of Size Effects and Deformation of Thin Films due to Nanoindentation

    Arun K. Nair1, Diana Farkas2, Ronald D. Kriz1
    CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 239-248, 2008, DOI:10.3970/cmes.2008.024.239
    Abstract The indentation response of Ni thin films of thicknesses in the nano scale was studied using molecular dynamics simulations with embedded atom method (EAM) interatomic potentials. Simulations were performed in single crystal films in the [111] orientation with thicknesses of 7nm and 33nm. In the elastic regime, the loading curves observed start deviating from the Hertzian predictions for indentation depths greater than 2.5% of the film thickness. The observed loading curves are therefore dependent on the film thickness. The simulation results also show that the contact stress necessary to emit the first dislocation under the indenter is nearly independent of… More >

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    809

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    597

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