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  • 1
    Electronic Resource
    Electronic Resource
    Activation analysis of dislocation nucleation from crack tip in α-Fe (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 2088-2096 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Guided by a recent molecular dynamics simulation study of mode I crack-tip environment in α-Fe using an embedded atom method potential, an activation analysis of the nucleation of a half-square dislocation loop from the tip of a tensile crack has been carried out based on the Rice and Thomson approach [Philos. Mag. 29, 78 (1974)]. The effects of elastic softening due to stress and temperature as well as the nonlinear stress distribution around the crack are introduced by incorporating the simulation results self-consistently into the analysis, reducing the previously overestimated activation barrier by a factor of over 15.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348735
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  • 2
    Electronic Resource
    Electronic Resource
    Stress induced martensitic transition in a molecular dynamics model of α-iron (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 4009-4014 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A structural transition bcc→hcp induced by uniaxial tensile stress is observed by molecular dynamics simulation using an interatomic potential function for α-iron derived by the embedded atom method. The transformation is reversible with hysteresis. The deformation mechanism for the forward transition is found to be different from that for the backward transition. The critical stress required for the transition decreases with increasing temperature, as is expected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350846
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  • 3
    Electronic Resource
    Electronic Resource
    Atomic-level stress in an inhomogeneous system (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5688-5690 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The distribution of local stress in an atomic system can be calculated from its mechanical definition. While this leads, for a homogeneous system, to an expression equivalent to that derived from the virial theorem (thermodynamic definition), when local inhomogeneities are present the equivalence can be demonstrated only in the sense of a volume average which effectively eliminates the inhomogeneities. Atomistic simulation results are presented to show that for a relaxed crystal with a planar free surface, the normal stress on each atomic plane parallel to the surface, when calculated according to the mechanical definition, vanishes uniformly as expected, whereas if the virial expression were applied the resulting stress distribution shows unphysical oscillations in the surface region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350186
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  • 4
    Electronic Resource
    Electronic Resource
    Atomistic Simulations of Materials Fracture and the Link between Atomic and Continuum Length Scales (1998)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    Details
    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
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02368.x
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  • 5
    Electronic Resource
    Electronic Resource
    Lattice instability in β-SiC and simulation of brittle fracture (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2719-2725 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Brittle fracture of β-SiC (polytype 3C) under hydrostatic tension has been modeled by molecular dynamics simulation using an interatomic potential function that treats the solid as fully covalent. The critical stress at which the lattice becomes structurally unstable is shown to agree quantitatively with that predicted by stability analysis based on elastic stiffness coefficients. The instability mode is the spinodal (vanishing of bulk modulus), and decohesion occurs as spontaneous nucleation of cracking on {111} shuffle planes. Atomic relaxation on the newly generated cracked surfaces appears to take place immediately following crack opening.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357575
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  • 6
    Electronic Resource
    Electronic Resource
    Lattice instability analysis of a prototype intermetallic system under stress (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 1449-1458 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.359577
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  • 7
    Electronic Resource
    Electronic Resource
    Empirical bond-order potential description of thermodynamic properties of crystalline silicon (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 96-106 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thermodynamic properties of silicon (diamond cubic phase) are calculated using an empirical many-body potential developed by Tersoff [Phys. Rev. Lett. 56, 632 (1986)] based on the concept of bond order. It is shown that this model gives predictions in good agreement with experiment for those properties governed by energetics (free energy, entropy, and heat capacity). The thermal expansion coefficient is less well described, which is traced to the fact that the model potential, in its present version, is overly stiff and therefore unable to account properly for the volume dependence of the transverse acoustic modes. Furthermore, sensitivity of the potential to whether each atom remains bonded to only four neighbors indicates that the short-range nature of the potential may necessitate model improvement before it is suitable for studies of thermomechanical properties at elevated temperatures or large deformations. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364102
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  • 8
    Electronic Resource
    Electronic Resource
    The importance of Grüneisen parameters in developing interatomic potentials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 5378-5381 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We show that three representative interatomic potential functions for Si fail to describe properly the Grüneisen parameters γn, although one model is able to give a satisfactory account of the thermal expansion coefficient, α, by virtue of a fortuitous cancellation of errors in γn for the acoustic and optic modes. This suggests that in developing robust interatomic potentials intended to predict the thermomechanical behavior of crystals, the database used in parameter adjustment should include the fundamental quantities, γn, rather than the composite quantity α. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366305
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  • 9
    Electronic Resource
    Electronic Resource
    Molecular dynamics study of pressure in molecular systems (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 3747-3756 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In molecular dynamics simulation of molecular systems, an atomistic model is needed to describe the intramolecular effects on system properties such as pressure. An expression for computing the pressure is derived based on the virial theorem, with explicit kinetic, intra-, and intermolecular contributions. It is shown that the virial terms arising from three- or four-body forces that depend only on internal angles are zero by using the Wilson S vector technique, and that only the two-body forces appear in the pressure expression. Molecular dynamics simulations are carried out for an atomistic model of benzene with intramolecular interactions based on ab initio harmonic potentials and intermolecular interactions given by semiempirical atom–atom potentials. Calculated total pressure depends on parameters of intermolecular potentials. An intramolecular contribution to the pressure is studied for both solid and liquid phases. In solids where the molecules are compressed, the intramolecular pressure contributions are appreciable and positive, while in liquids where molecular deformations are relatively small, the contributions are small and negative. A possible further improvement of the atomistic model of benzene is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466362
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  • 10
    Electronic Resource
    Electronic Resource
    Thermally induced fragmentation in an ice lattice (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 3216-3221 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics simulation of isobaric heating of an H2O lattice with diamond cubic structure reveals a distinct two-step sequence of hydrogen-bond breaking in a temperature range clearly below the melting point. Partial breakage, signaled by an abrupt increase in local atomic coordination and the coupling of intermolecular torsions with intramolecular angle bending, first occurs and leaves the lattice in a fragmented but still ordered state. This is then followed by full breakage at a temperature about 20–30 K higher, bringing the lattice to an orientationally disordered state characterized by a vibrational spectrum similar to that of water.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467567
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