The Experts below are selected from a list of 51 Experts worldwide ranked by ideXlab platform

Anthony A. Dicarlo - One of the best experts on this subject based on the ideXlab platform.

  • Phonon spectra prediction in carbon nanotubes using a manifold-based continuum finite element approach
    Computer Methods in Applied Mechanics and Engineering, 2009
    Co-Authors: Michael J. Leamy, Anthony A. Dicarlo
    Abstract:

    Abstract This Work develops a tensor-based, reduced-order shell (two-manifold) finite element formulation for predicting phonon spectra in finite-length cylindrical and toroidal carbon nanotubes (CNTs). The formulation does not require an assumed tube thickness. Displacements referencing two covariant basis vectors lying in the tangent space, and one basis vector orthogonal to the tangent space, capture the systems’ kinematics. These basis vectors compose a curvilinear coordinate system useful for capturing cylindrical, toroidal, and generically-curved nanotube configurations. The finite element procedure originates from a variational statement (Hamilton’s Principle) governing Virtual Work from Internal, external (not considered), and inertial forces. Internal Virtual Work is related to changes in atomistic potential energy accounted for by an interatomic potential computed at reference area elements. Small Virtual changes in the displacements allow a global mass and stiffness matrix to be computed, and these matrices then allow phonon spectra and energies to be predicted via a general eigenvalue problem. Results are generated for example cylindrical and toroidal CNTs documenting accurate prediction of phonon spectra, to include the expected longitudinal, torsional, bending, and breathing-like phonons.

  • Phonon Prediction in Toroidal Carbon Nanotubes Using a Continuum Finite Element Approach
    Volume 1: 21st Biennial Conference on Mechanical Vibration and Noise Parts A B and C, 2007
    Co-Authors: Michael J. Leamy, Anthony A. Dicarlo
    Abstract:

    This Work develops a tensor-based, reduced-order shell finite element formulation used to predict the phonon behavior of toroidal carbon nanotubes (CNTs). Displacements referencing two covariant basis vectors lying in the toroid’s tangent space, and one basis vector orthogonal to the tangent space, capture the kinematics of the toroidal CNT. These basis vectors compose a curvilinear coordinate system. Although specific attention is on toroidal CNTs, the formulation can be quickly adapted to cylindrical or other curvilinear CNTs by appropriate replacement of the metric tensor components and Christoffel symbols. The finite element procedure originates from a variational statement (Hamilton’s Principle) governing Virtual Work from Internal, external (not considered), and inertial forces. Internal Virtual Work is related to changes in atomistic potential energy accounted for by an interatomic potential computed at reference area elements. Small Virtual changes in the displacements allow a global mass and stiffness matrix to be computed, and these matrices then allow phonons to be predicted via the general eigenvalue problem. Results are generated for example toroidal CNTs documenting zero-energy behavior (rigid body motion) and the lowest phonons, which include the expected breathing-like and bending-like phonons.Copyright © 2007 by ASME

Salomón M.a. Jiménez - One of the best experts on this subject based on the ideXlab platform.

  • A principle of Virtual Work for combined electrostatic and mechanical loading of materials
    International Journal of Non-Linear Mechanics, 2007
    Co-Authors: Robert M. Mcmeeking, Chad M. Landis, Salomón M.a. Jiménez
    Abstract:

    Abstract The equations governing mechanics and electrostatics are formulated for a system in which the material deformations and electrostatic polarizations are arbitrary. A mechanical/electrostatic energy balance is formulated for this situation in terms of the electric enthalpy, in which the electric potential and the electric field are the independent variables, and charge and electric displacement, respectively, are the conjugate thermodynamic forces. This energy statement is presented in the form of a principle of Virtual Work (PVW), in which external Virtual Work is equated to Internal Virtual Work. The resulting expression involves an Internal material Virtual Work in which (1) material polarization is Work-conjugate to increments of electric field, and (2) a combination of Cauchy stress, Maxwell stress and a product of polarization and electric field is Work-conjugate to increments of strain. This PVW is valid for all material types, including those that are conservative and those that are dissipative. Such a Virtual Work expression is the basis for a rigorous formulation of a finite element method for problems involving the deformation and electrostatic charging of materials, including electroactive polymers and switchable ferroelectrics. The Internal Virtual Work expression is used to develop the structure of conservative constitutive laws governing, for example, electroactive elastomers and piezoelectric materials, thereby determining the form of the Maxwell or electrostatic stress. It is shown that the Maxwell or electrostatic stress has a form fully constrained by the constitutive law and cannot be chosen independently of it. The structure of constitutive laws for dissipative materials, such as viscoelastic electroactive polymers and switchable ferroelectrics, is similarly determined, and it is shown that the Maxwell or electrostatic stress for these materials is identical to that for a material having the same conservative response when the dissipative processes in the material are shut off. The form of the Internal Virtual Work is used further to develop the structure of dissipative constitutive laws controlled by rearrangement of material Internal variables.

Michael J. Leamy - One of the best experts on this subject based on the ideXlab platform.

  • Phonon spectra prediction in carbon nanotubes using a manifold-based continuum finite element approach
    Computer Methods in Applied Mechanics and Engineering, 2009
    Co-Authors: Michael J. Leamy, Anthony A. Dicarlo
    Abstract:

    Abstract This Work develops a tensor-based, reduced-order shell (two-manifold) finite element formulation for predicting phonon spectra in finite-length cylindrical and toroidal carbon nanotubes (CNTs). The formulation does not require an assumed tube thickness. Displacements referencing two covariant basis vectors lying in the tangent space, and one basis vector orthogonal to the tangent space, capture the systems’ kinematics. These basis vectors compose a curvilinear coordinate system useful for capturing cylindrical, toroidal, and generically-curved nanotube configurations. The finite element procedure originates from a variational statement (Hamilton’s Principle) governing Virtual Work from Internal, external (not considered), and inertial forces. Internal Virtual Work is related to changes in atomistic potential energy accounted for by an interatomic potential computed at reference area elements. Small Virtual changes in the displacements allow a global mass and stiffness matrix to be computed, and these matrices then allow phonon spectra and energies to be predicted via a general eigenvalue problem. Results are generated for example cylindrical and toroidal CNTs documenting accurate prediction of phonon spectra, to include the expected longitudinal, torsional, bending, and breathing-like phonons.

  • Phonon Prediction in Toroidal Carbon Nanotubes Using a Continuum Finite Element Approach
    Volume 1: 21st Biennial Conference on Mechanical Vibration and Noise Parts A B and C, 2007
    Co-Authors: Michael J. Leamy, Anthony A. Dicarlo
    Abstract:

    This Work develops a tensor-based, reduced-order shell finite element formulation used to predict the phonon behavior of toroidal carbon nanotubes (CNTs). Displacements referencing two covariant basis vectors lying in the toroid’s tangent space, and one basis vector orthogonal to the tangent space, capture the kinematics of the toroidal CNT. These basis vectors compose a curvilinear coordinate system. Although specific attention is on toroidal CNTs, the formulation can be quickly adapted to cylindrical or other curvilinear CNTs by appropriate replacement of the metric tensor components and Christoffel symbols. The finite element procedure originates from a variational statement (Hamilton’s Principle) governing Virtual Work from Internal, external (not considered), and inertial forces. Internal Virtual Work is related to changes in atomistic potential energy accounted for by an interatomic potential computed at reference area elements. Small Virtual changes in the displacements allow a global mass and stiffness matrix to be computed, and these matrices then allow phonons to be predicted via the general eigenvalue problem. Results are generated for example toroidal CNTs documenting zero-energy behavior (rigid body motion) and the lowest phonons, which include the expected breathing-like and bending-like phonons.Copyright © 2007 by ASME

Robert M. Mcmeeking - One of the best experts on this subject based on the ideXlab platform.

  • A principle of Virtual Work for combined electrostatic and mechanical loading of materials
    International Journal of Non-Linear Mechanics, 2007
    Co-Authors: Robert M. Mcmeeking, Chad M. Landis, Salomón M.a. Jiménez
    Abstract:

    Abstract The equations governing mechanics and electrostatics are formulated for a system in which the material deformations and electrostatic polarizations are arbitrary. A mechanical/electrostatic energy balance is formulated for this situation in terms of the electric enthalpy, in which the electric potential and the electric field are the independent variables, and charge and electric displacement, respectively, are the conjugate thermodynamic forces. This energy statement is presented in the form of a principle of Virtual Work (PVW), in which external Virtual Work is equated to Internal Virtual Work. The resulting expression involves an Internal material Virtual Work in which (1) material polarization is Work-conjugate to increments of electric field, and (2) a combination of Cauchy stress, Maxwell stress and a product of polarization and electric field is Work-conjugate to increments of strain. This PVW is valid for all material types, including those that are conservative and those that are dissipative. Such a Virtual Work expression is the basis for a rigorous formulation of a finite element method for problems involving the deformation and electrostatic charging of materials, including electroactive polymers and switchable ferroelectrics. The Internal Virtual Work expression is used to develop the structure of conservative constitutive laws governing, for example, electroactive elastomers and piezoelectric materials, thereby determining the form of the Maxwell or electrostatic stress. It is shown that the Maxwell or electrostatic stress has a form fully constrained by the constitutive law and cannot be chosen independently of it. The structure of constitutive laws for dissipative materials, such as viscoelastic electroactive polymers and switchable ferroelectrics, is similarly determined, and it is shown that the Maxwell or electrostatic stress for these materials is identical to that for a material having the same conservative response when the dissipative processes in the material are shut off. The form of the Internal Virtual Work is used further to develop the structure of dissipative constitutive laws controlled by rearrangement of material Internal variables.

Philippe Boisse - One of the best experts on this subject based on the ideXlab platform.

  • Modelling composite reinforcement forming processes
    Composite Reinforcements for Optimum Performance, 2011
    Co-Authors: Philippe Boisse, Nahiene Hamila
    Abstract:

    Abstract: In this chapter various finite element approaches for the simulation of woven reinforcement forming are presented. Some are based on continuous modelling, while others, known as discrete or mesoscopic approaches, model each yarn of the fabric. The intermediary semi-discrete approach is also examined. During this approach the shell finite element interpolation formula maintains the continuity of the displacement field, but the Internal Virtual Work is obtained as the sum of tension, in-plane shear and bending cells, of all the woven unit cells within the element. When using continuous approaches, the necessity of taking the strong specificity of the fibrous material into account causes difficulties. The main goal of the hypoelastic and hyperelastic constitutive models presented in this chapter is to describe this specific mechanical behaviour. During discrete and semi-discrete approaches the directions of the yarns are ‘naturally’ followed because the yarns themselves are modelled. The advantages and drawbacks of the different approaches are also discussed.

  • Numerical simulation of multi‐layered textile composite reinforcement forming
    2011
    Co-Authors: Peng Wang, Nahiene Hamila, Philippe Boisse
    Abstract:

    One important perspective in aeronautics is to produce large, thick or/and complex structural composite parts. The forming stage presents an important role during the whole manufacturing process, especially for LCM processes (Liquid Composites Moulding) or CFRTP (Continuous Fibre Reinforcements and Thermoplastic resin). Numerical simulations corresponding to multi‐layered composite forming allow the prediction for a successful process to produce the thick parts, and importantly, the positions of the fibres after forming to be known. This paper details a set of simulation examples carried out by using a semi‐discrete shell finite element made up of unit woven cells. The Internal Virtual Work is applied on all woven cells of the element taking into account tensions, in‐plane shear and bending effects. As one key problem, the contact behaviours of tool/ply and ply/ply are described in the numerical model. The simulation results not only improve our understanding of the multi‐layered composite forming process but also point out the importance of the fibre orientation and inter‐ply friction during formability.

  • Hypoelastic, hyperelastic, discrete and semi-discrete approaches for textile composite reinforcement forming
    International Journal of Material Forming, 2010
    Co-Authors: Philippe Boisse, Yamina Aimène, Sébastien Gatouillat, Muhammad Aurangzeb Khan, Samia Dridi, Fabrice Morestin, Nahiene Hamila, Abdelwaheb Dogui, Tarek Mabrouki, Emmanuelle Vidal-sallé
    Abstract:

    The clear multi-scale structure of composite textile reinforcements leads to develop continuous and discrete approaches for their forming simulations. In this paper two continuous modelling respectively based on a hypoelastic and hyperelastic constitutive model are presented. A discrete approach is also considered in which each yarn is modelled by shell finite elements and where the contact with friction and possible sliding between the yarns are taken into account. Finally the semi-discrete approach is presented in which the shell finite element interpolation involves continuity of the displacement field but where the Internal Virtual Work is obtained as the sum of tension, in-plane shear and bending ones of all the woven unit cells within the element. The advantages and drawbacks of the different approaches are discussed.

  • A mesoscopic approach for the simulation of woven fibre composite forming
    Composites Science and Technology, 2004
    Co-Authors: Philippe Boisse, Bassem Zouari, Alain Gasser
    Abstract:

    A finite element simulation of composite woven reinforcement forming requires the knowledge of the fabric mechanical behaviour. In the presented mesoscopic approach, the tensile and shear mechanical behaviour of the elementary cell (mesoscopic level) are used in a finite element made of woven meshes. The principal stiffness of the fabric is the tensile rigidity. Because of the weaving, the tensile behaviour is non-linear. It is analysed by biaxial tensile tests and 3D finite element computations of the woven unit cells. The in plane shear rigidity of fabrics is very weak up to a limit angle. In this first stage, it is shown by optical measures that the yarns are subjected to rigid rotations. A second stage in which the yarns are laterally crushed leads to larger stiffness. A first simplified form of the dynamic equation is based only on tensile Internal Virtual Work. A second one takes also shear Internal Work into account. A fabric square box forming simulation is performed with both approaches. It shows the importance to account for shear when the limit shear angle is exceeded.