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  • 1
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Solid state phenomena Vol. 139 (Apr. 2008), p. 23-28 
    ISSN: 1662-9779
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Physics
    Notes: We studied the atomic-level structure of a model Mg-MgH2 interface by means of theCar-Parrinello molecular dynamics method (CPMD). The interface was characterized in terms oftotal energy calculations, and an estimate of the work of adhesion was given, in good agreementwith experimental results on similar systems. Furthermore, the interface was studied in a range oftemperatures of interest for the desorption of hydrogen. We determined the diffusivity of atomichydrogen as a function of the temperature, and give an estimate of the desorption temperature
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 555 (Sept. 2007), p. 349-354 
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Extensive electronic structure calculations, based on the density-functional theory, areused to characterize the equilibrium properties and the behaviour under pressure of MgH2.Moreover, substitutional solid solutions for several 3d metals (Fe, Ni, Ti, Al, Pd, Co, etc.) in MgH2are characterized by computing both relaxed structures and solution energies. Theoretical results arecombined with experimental results on samples synthesized by ball milling. MgH2 was milled with10 wt.% of 3d metals followed by microstructural characterization and hydrogen desorptionbehaviour. Good correlation between theoretical solution energies and experimental desorptiontemperatures reveals a general trend in these systems. A few notable exceptions can be detected,which can be explained in terms of peculiarities in the experimental composite microstructure
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 539-543 (Mar. 2007), p. 2551-2556 
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A continuum model for composite materials made of short, stiff and tough fibresembedded in a more deformable matrix with distributed microflaws is proposed. Based on thekinematics of a lattice system made of fibres, perceived as rigid inclusions, and of microflaws,represented by slit microcracks, the stress-strain relations of an equivalent multifield continuum isobtained. These relations account for the shape and the orientation of the internal phases andinclude internal scale parameters, which allow taking into account size effects. Some numericalanalyses effected on a sample fibre-reinforced composite pointed out the influence of the size andorientation of the fibres on the gross behaviour of the material
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 3308-3314 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study the nucleation of carbon nanotubes based on the hypothesis that a cylindrical seed can be formed by the spontaneous rolling of a small graphite fragment under thermal fluctuations. We calculate the vibrational spectra of fragments of different sizes by means of a tight-binding model, and compare the spectra to that of an infinite graphite sheet, as a function of temperature. The spectra of finite-size fragments contain an increasing density of low-frequency, large amplitude modes with increasing temperature; it is shown that such modes tend to fold over the fragment into a cylindrical shape. Finally, direct tight-binding molecular-dynamics simulations of the high-temperature fluctuation of parallel graphite fragments demonstrate that nanotube seeds closed at one end can spontaneously form. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 1449-1458 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The unstable structural responses of a model intermetallic lattice to hydrostatic and uniaxial loadings have been determined by elastic stability analysis and molecular-dynamics simulations. Two crystalline phases of Ni3Al, the naturally occurring L12 and a hypothetical D022, are analyzed to correlate the effects of structural symmetry with stress-induced lattice deformations. Under isotropic expansion, the former fcc lattice develops extensive cavitation and amorphization at critical isotropic tensile loading, whereas the latter, a tetragonal lattice, shows cleavage behavior. These qualitative differences do not appear in the elastic stability analysis. Both phases show similar responses to uniaxial tension. In all cases critical strains for lattice instability predicted on the basis of elastic stiffness coefficients are found to be in good agreement with direct simulations. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 1701-1703 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Zr-terminal portion of the Ni–Zr phase diagram was studied by means of molecular dynamics simulations. The internal energy and the enthalpy of mixing at 300 K of the α- and β-Zr(Ni) solid solutions and of the Zr–Ni amorphous phase were calculated for Ni concentrations ≤10 at. %. The values of the enthalpy of mixing obtained are positive for the terminal solid solutions, and negative for the amorphous phase. This behavior is attributed to the differences in strain energy generated in the Zr lattice or in the amorphous phase by Ni atoms. Implications of these results relevant to the problem of amorphization in metallic systems by solid-state reactions are discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The macroscopic fracture response of real materials originates from the competition and interplay of several atomic-scale mechanisms of decohesion and shear, such as inter-planar cleavage and dislocation nucleation and motion. These phenomena involve processes over a wide range of length scales, from the atomic to the macroscopic. We briefly review the attempts to span these length scales in dislocation and fracture modeling by (1) fully atomistic large-scale simulations of millions of atoms or more, approaching the continuum limit from the “bottom-up”; (2) directly coupling atomic-scale simulations and continuum mechanics, in a “top-down” approach; and (3) by defining a set of variables common to atomistic simulations and continuum mechanics and feeding the results of atomistic simulations into continuum-mechanics models in the form of constitutive relations. For this latter approach we discuss in detail the issues crucial to ensuring the consistency of the atomistic results and continuum mechanics. A case study of the constitutive-relation approach is presented for the problem of dislocation nucleation from a crack tip in a crystal under stress; a comparison of the results of atom-istic simulations to the Peierls–Nabarro continuum model is made.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 221-222 (Dec. 2001), p. 307-314 
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Interface science 7 (1999), S. 45-55 
    ISSN: 1573-2746
    Keywords: grain-boundary fracture ; dislocation nucleation ; Peierls-Nabarro model ; molecular dynamics simulations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Fracture experiments on symmetric-tilt grain boundaries in Cu are interpreted using the Peierls-Nabarro continuum model of dislocation nucleation as a starting point. Good agreement is found only when the continuum model is modified according to the results of atomistic simulations. The same experiments are also reproduced by direct Molecular Dynamics simulations of fracture propagation and dislocation emission from a microcrack placed in the interface plane of the symmetric-tilt (221)(221) grain boundary in fcc Cu. Direction-dependent fracture response is observed, namely the microcrack advancing by brittle fracture along the [11 $$\bar 4$$ ] direction and being blunted by dislocation emission along the opposite [ $$\bar 1\bar 1$$ 4] direction. Moreover, the simulations allow us to establish important differences with respect to the continuum-model predictions due to the shielding of the stress field at the crack-tip and to the presence of the residual stress at the interface.
    Type of Medium: Electronic Resource
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