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  • Open Access

    ARTICLE

    Computational Simulations of Micro-Indentation Tests Using Gradient Plasticity

    Jian Chen1, Huang Yuan2, Folker H. Wittmann3

    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.6, pp. 743-754, 2002, DOI:10.3970/cmes.2002.003.743

    Abstract Experimental observation confirms that micro-hardness of metallic materials depends significantly on the indentation depth. In the present paper we discuss simulations of micro-indentation tests based on the gradient plasticity model using the finite element method. The role of intrinsic material length parameters in the gradient plasticity model is investigated. The computational results confirm that the gradient plasticity model is suitable to simulate micro-indentation tests and predicts the depth-dependent hardness in micro- and nano-indentations. Variations of micro-hardness is correlated with the intrinsic material length parameters. More >

  • Open Access

    ARTICLE

    Analysis of Elastodynamic Deformations near a Crack/Notch Tip by the Meshless Local Petrov-Galerkin (MLPG) Method

    R. C. Batra1, H.-K. Ching1

    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.6, pp. 717-730, 2002, DOI:10.3970/cmes.2002.003.717

    Abstract The Meshless Local Petrov-Galerkin (MLPG) method is used to analyze transient deformations near either a crack or a notch tip in a linear elastic plate. The local weak formulation of equations governing elastodynamic deformations is derived. It results in a system of coupled ordinary differential equations which are integrated with respect to time by a Newmark family of methods. Essential boundary conditions are imposed by the penalty method. The accuracy of the MLPG solution is established by comparing computed results for one-dimensional wave propagation in a rod with the analytical solution of the problem. Results… More >

  • Open Access

    ARTICLE

    SGBEM (for Cracked Local Subdomain) -- FEM (for uncracked global Structure) Alternating Method for Analyzing 3D Surface Cracks and Their Fatigue-Growth

    Z. D. Han1, S. N. Atluri1

    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.6, pp. 699-716, 2002, DOI:10.3970/cmes.2002.003.699

    Abstract As shown in an earlier work, the FEM-BEM alternating method is an efficient and accurate method for fracture analysis. In the present paper, a further improvement is formulated and implemented for the analyses of three-dimensional arbitrary surface cracks by modeling the cracks in a local finite-sized subdomain using the symmetric Galerkin boundary element method (SGBEM). The finite element method is used to model the uncracked global (built-up) structure for obtaining the stresses in an otherwise uncracked body. The solution for the cracked structural component is obtained in an iteration procedure, which alternates between FEM solution More >

  • Open Access

    ARTICLE

    Bonding Geometry and Bandgap Changes of Carbon Nanotubes Under Uniaxial and Torsional Strain

    Liu Yang1, Jie Han, M. P. Anantram, Richard L. Jaffe

    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.5, pp. 675-686, 2002, DOI:10.3970/cmes.2002.003.675

    Abstract Bonding geometry and bandgap of carbon nantotubes under uniaxial and torsional deformation are studied computationally for nanotubes of various chiralities and diameters. Bonding geometries are obtained with Tersoff-Brenner potential from molecular mechanics simulations. Bandgaps as function of strain are calculated from the molecular mechanics structures using one (p) and four (2s and 2px, 2py, 2pz) orbital tight-binding models. For small strains, the bandgap results are qualitatively consistent with those predicted by the one orbital analytical model. Response of the electronic properties of nanotubes to large strains is characterized by a change in sign of d(bandgap)/d(strain). These originate More >

  • Open Access

    ARTICLE

    Atomic Modeling of Carbon-Based Nanostructures as a Tool for Developing New Materials and Technologies

    D.W. Brenner, O.A. Shenderova, D.A. Areshkin, J.D. Schall1, S.-J. V. Frankland2

    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.5, pp. 643-674, 2002, DOI:10.3970/cmes.2002.003.643

    Abstract The derivation of a bond-order potential energy function and a self-consistent tight-binding scheme is presented, followed by a survey of the application of these methods to calculating properties of carbon nanostructures. The modeling studies discussed include properties of functionalized and kinked carbon nanotubes, Raman shifts for hydrogen stored in nanotubes, nanotubes in a composite, properties of nanotubes in applied potential (electrical) fields, and structures and properties of nanocones, nanodiamond clusters and rods, and hybrid diamond-nanotube structures. More >

  • Open Access

    ARTICLE

    JavaGenes: Evolving Molecular Force Field Parameters with Genetic Algorithm

    Al Globus1, Madhu Menon2, Deepak Srivastava1

    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.5, pp. 557-574, 2002, DOI:10.3970/cmes.2002.003.557

    Abstract A genetic algorithm procedure has been developed for fitting parameters for many-body interatomic force field functions. Given a physics or chemistry based analytic form for the force field function, parameters are typically chosen to fit a range of structural and physical properties given either by experiments and/or by higher accuracy tight-binding or ab-initio simulations. The method involves using both near equilibrium and far from equilibrium configurations in the fitting procedure, and is unlikely to be trapped in local minima in the complex many-dimensional parameter space. As a proof of concept, we demonstrate the procedure for… More >

  • Open Access

    ARTICLE

    Multiscale Modeling of Laser Ablation: Applications to Nanotechnology

    Leonid V. Zhigilei1, Avinash M. Dongare1

    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.5, pp. 539-556, 2002, DOI:10.3970/cmes.2002.003.539

    Abstract Computational modeling has a potential of making an important contribution to the advancement of laser-driven methods in nanotechnology. In this paper we discuss two computational schemes developed for simulation of laser coupling to organic materials and metals and present a multiscale model for laser ablation and cluster deposition of nanostructured materials. In the multiscale model the initial stage of laser ablation is reproduced by the classical molecular dynamics (MD) method. For organic materials, the breathing sphere model is used to simulate the primary laser excitations and the vibrational relaxation of excited molecules. For metals, the… More >

  • Open Access

    ARTICLE

    Computational Nanotechnology: A Current Perspective

    Deepak Srivastava1, Satya N. Atluri2

    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.5, pp. 531-538, 2002, DOI:10.3970/cmes.2002.003.531

    Abstract The current status of the progress and developments in computational nanotechnology is briefly reviewed, from the perspective of its applications. The enabling tools and techniques of physics- and chemistry-based simulations, within a multi-scale context , are briefly reviewed . More >

  • Open Access

    ARTICLE

    A Numerical Model for Elastoplastic Rough Contact

    P. Sainsot1, C. Jacq2, D. Nélias1

    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.4, pp. 497-506, 2002, DOI:10.3970/cmes.2002.003.497

    Abstract Pressure distributions calculated in the simulation of rough contacts show high values and induce high stresses just beneath the surface. These stresses often exceed the yield strength of the material, therefore, a purely elastic contact model is restrictive. Plastic flow occurs and modifies the surface shape and consequently modifies the surface pressure.
    This paper presents a numerical model for 3D-elastoplastic rough contact. It allows the determination of real pressure and permanent surface displacement (flattening of asperities) as well as residual stresses and plastic strains useful in fatigue analysis. The material is assumed to follow the More >

  • Open Access

    ARTICLE

    Steady-State Temperature Rise in Coated Halfspaces and Halfplanes

    Michael J. Rodgers1, Leon M. Keer, Herbert S. Cheng

    CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.4, pp. 483-496, 2002, DOI:10.3970/cmes.2002.003.483

    Abstract The steady-state temperature rise due to frictional heating on the surface of coated halfspaces and halfplanes is described by closed form expressions in the Fourier transformed frequency domain. These frequency response functions (FRFs) include the effects of the coating and the speed of the moving heat source and apply for all Peclet number regimes. Analytical inversion of these expressions for several special cases shows the Green's functions as infinite series of images, which may be costly and slowly convergent. Also, the influence coefficients integrated from these Green's functions are not available in closed form. Applying… More >

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