Modelling and Simulation in Materials Science and Engineering

Xu, X -P; Needleman, A

doi: 10.1088/0965-0393/1/2/001pmid: N/A

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 parameteric 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.

Kyuno, K; Yamamoto, R; Asano, S

doi: 10.1088/0965-0393/1/2/002pmid: N/A

The magnetocrystalline anisotropy energies of X/Fe (X=Pd,Pt,Au,Ag) multilayers have been calculated from first principles within the local-spin-density approximation 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.

Nakamura, K; Mohri, T

doi: 10.1088/0965-0393/1/2/003pmid: N/A

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.

Morinaga, M; Kamado, S

doi: 10.1088/0965-0393/1/2/004pmid: N/A

A quantitative 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 available wrought aluminium alloys with multiple components. Both the strain hardening and the 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.

Nada, R; Catlow, C R A; Pisani, C; Orlando, R

doi: 10.1088/0965-0393/1/2/005pmid: N/A

An ab initio Hartree-Fock perturbed-cluster embedding 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. The authors highlight the capabilities and drawbacks of the method, in particular regarding the convergence of the procedure and the description of polarization and relaxation effects. They also compare the results with simulations based on the Mott-Littleton theory. The results indicate that even in the case of neutral defects, there are important short-range polarization effects.

Ramprasad, R; Hoagland, R G

doi: 10.1088/0965-0393/1/2/006pmid: N/A

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. These 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 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.

Becker, R; Smelser, R E; Panchanadeeswaran, S

doi: 10.1088/0965-0393/1/2/007pmid: N/A

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 behavior of the polycrystalline materials was specified by ascribing part of the behavior 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 behavior 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.