NetNews Usenet Archive 1993 #1/NN_1993_1.iso/spool/alt/material/simulati/10

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From: [e-mail] (Reza Najafabadi)
Subject: Abstracts (Vol. 1, No. 2)
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Date: Mon, 04 Jan 93 11:47:06 EST
Organization: University of Michigan Engineering, Ann Arbor
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    MODELLING AND SIMULATION
   IN MATERIALS SCIENCE AND ENGINEERING
            Vol. 1 No. 2

             ABSTRACTS
             =========

 Simulation of earing in aluminum single crystals and polycrystals

R Becker, R E Smelser and S Panchanadeeswaran
Fabricating Technology Division, Alcoa Technical Center, Alcoa Center,
PA 15069, USA

Simulations of earing during the deep drawing of single crystals and of
polycrystalline sheets have been performed. The anisotropic
constitutive properties responsible for the earing phenomenon are
derived from crystal plasticity models. These models account for the
evolution of anisotropy at finite strains. The behaviour of the
polycrystalline materials was specified by ascribing part of the
behaviour to the dominant crystal orientations. The remaining volume
fraction was characterized by isotropic plasticity. A detailed finite-
element model and a simplified model of the deforming flange
adequately capture the behaviour of the single-crystal cups. Calculations
depicting the drawing of polycrystalline sheets give earing predictions
which are in reasonable agreement with the experiments. Less
satisfactory agreement is obtained from solutions using a
phenomenological yield surface description. Simplified geometric
models, which approximate the stress and the strain state in the cup, do
not generally result in good agreement with the experiments.


First-principles calculation of the magnetic anisotropy energies of iron-
based metallic multilayers

Kentaro Kyuno, Ryoichi Yamamoto
Institute of Industrial Science, University of Tokyo, Minato-ku, Tokyo
106, Japan
Setsuro Asano, Institute of Physics, College of Arts and Sciences,
University of Tokyo, Meguro-ku, Tokyo 153, Japan

The magnetocrystalline anisotropy energies of X/Fe (X=Pd, Pt, Au, Ag)
multilayers have been calculated from first principles within the local-
spin-density aproximation using the linear muffin-tin orbital (LMTO)
method, including spin-orbit coupling. Although the calculated
magnetostatic energies favour in-plane magnetization directions, the
easy axes of Pd(2ML)/Fe(1ML), Au(2ML)/Fe(1ML) and
Ag(2ML)/Fe(1ML) (ML: monolayer) multilayers are perpendicular to the
film plane, because of the large electronic contribution to the
perpendicular anisotropy. The calculated anisotropy energies of Pd/Fe
multilayers decrease with increasing Fe layer thickness, which is in good
agreement with experiment.


An electronic approach to the prediction of the mechanical properties of
aluminium alloys

M Morinaga, Department of Production Systems Engineering, Toyohashi
University of Technology, Tempaku-cho, Toyohashi, Aichi 441, Japan
S Kamado, Department of Mechanical Engineering, Nagaoka University of
Technology, Kamitomioka, Nagaoka, 940-21, Japan


A quantative method for predicting the mechanical properties of
aluminium alloys was proposed on the basis of the molecular orbital
calculation of electronic structures. A new parameter which is the s
orbital energy level, MK, of alloying elements in aluminium was
introduced into this method. This parameter correlated with the
electronegativity and the atomic radius of elements, and probably
represented the magnitude of dislocation interactions with solute atoms
in the alloys. The compositional average of this parameter varied
linearly with the yield strength and the tensile strength of commercially
wrought aluminium alloys with multiple components. Both the strain
hardening and precipitation hardening of the alloys were also treated
well in terms of this parameter alone. It was shown that this electronic
method was very convenient for designing high-performance
aluminium alloys efficiently.


An ab-initio Hartree-Fock perturbed-cluster study of neutral defects in
LiF

R Nada, C R A Catlow, The Royal Institution of Great Britain, 21
Albemarle Street, London W1X 4BS, UK
C Pisani, R Orlando, Universita di Torino, Laboratorio di Chimica Teorica,
Via P Giuria 5, I-10125 Torino, Italy

An ab initio Hartree-Fock perturbed-cluster enbedding scheme is
applied to the problem of neutral defects in bulk LiF (specifically to Na
substitutionals and the bound Schottky pair), using an extended basis
set. In the present work we highlight the capabilities and drawbacks of
the method, in particular regarding the convergence of the procedure
and the description of polarization and relaxation effects. We also
compare our results with simulations based on the Mott-Littleton
theory. Our results indicate that even in the case of neutral defects,
there are important short-range polarization effects.


Non-empirical calculation of thermal vibration effects on the phase
stability of InP-InSb alloy

Kohji Nakamura, Tetsuo Mohri, Department of Metallurgical Engineering,
Hokkaido University, Sapporo 060, Japan

Based on the Debye-Gruneisen model, thermal vibration effects are
introduced into the non-empirical calculation of the phase stability of
the InP-InSb system. The resultant phase diagram indicates that the
thermal vibration effects stabilize a solid solution. Details of the effects
on the phase stability are discussed.


Thermodynamic propoerties of small zinc clusters based on atomistic
simulations

R Ramprasad, R G Hoagland, Department of Mechanical and Materials
Engineering, Washington State University, Pullman, WA 99164, USA

Molecular-dynamics calculations were performed on zinc atom clusters
to determine their equilibrium configurations using an embedded-atom
method (EAM) potential developed for zinc. Calculation of the
thermodynamic properties at different temperatures involved a Monte
Carlo scheme in conjunction with statistical mechanical techniques. The
harmonic approximation was used in the calculation of the vibrational
contribution to the cluster partition function and the rigid-body
approximation was used in the calculation of the rotational contribution.
The above calculations were used to examine the Helmholtz free energy
of formation of the clusters as a function of cluster size, temperature
and pressure with the aim of determining the nucleation rates and
critical supersaturation pressures. Three cluster-growth patterns were
considered in all the above calculations and stability diagrams were
plotted indicating the relative stability of clusters as a function of
cluster size and temperature for these three growth patterns.


Void nucleation by inclusion debonding in a crystal matrix

X-P Xu, A Needleman, Division of Engineering, Brown University,
Providence, RI 02912, USA

In a numerical micromechanical study of void nucleation, a framework
is used where constitutive relations are specified independently for the
matrix, the void-nucleating particles and the interface. Plane strain
analyses are carried out for a doubly periodic array of circular
cylindrical particles. The particles are taken to be rigid and the elastic-
plastic deformations of the matrix are described in terms of continuum
crystalline plasticity, using a planar crystal model that allows for three
slip systems. Comparison is made with void-nucleation predictions
based on a corresponding flow theory of plasticity with isotropic
hardening. The crystal model can give rise to shear localization at the
particle-matrix interface and shear localization, which leads to large
localized strains in the matrix, is found to inhibit decohesion. The role of
the triaxiality of the stress state in determining whether decohesion or
localization occurs first is investigated. A parametric study is also
carried out for a crystal matrix using two descriptions of the interface
shear behaviour; one is periodic in the shear displacement across the
interface, while the other allows for shear decohesion.