International Journal of Computational Materials Science and Engineering

In this paper, structural and electronic properties of L1₂ and D0₁₉-AlSc₃ are presented. Calculations are performed applying crystalline orbital program within the framework of density functional theory. The exchange and correlation are treated following the Perdew–Becke–Ernzerhof ansatz. Other Al–Sc intermetallic compounds and polymorphs of Al₃Sc, Al₂Sc and AlSc are also investigated. The total energy calculations are coupled with the Murnaghan equation of state to determine lattice constants and bulk moduli. The data for D0₁₉-AlSc₃ are provided while deduced structural parameters for other materials are compared with the available results. Current results are reasonably in agreement with the experimental data and other reported calculations. Electronic band structures of a few Al–Sc compounds are studied with a view to examine effect of Al concentration on the formation of bands and bonds in the Al–Sc system.

The superconductivity and magnetic phenomena of the rare earth iron pnictides RFePO (R = La, Sm) are analyzed using ab initio density functional theory in the local density approximation (LDA) with the on-site Hubbard U_eff parameter (LDA + U). The results of the magnetic properties, band structures and Fermi surfaces of the recently synthesized tetragonal layered iron pnictides superconductor SmFePO are presented in comparison with the superconductor LaFePO. The anti-ferromagnetic state [Sm: AFM, Fe AFM_stripe] is found to be the most stable than the other possible phases, which is in agreement with experiment. The effect of the Hubbard correction is investigated and is found to be a necessary requirement for the accurate description of both the electronic structure and the Fermi surfaces.

Vertically aligned multi-walled carbon nanotube arrays (VA-MWCNTs) are novel carbon nanomaterials that have broader applications than individual carbon nanotubes (CNTs). This paper presents the uniform shell modeling of VA-MWCNTs which allow effectively design and characterize these complex materials. Multi-walled nanotubes in the arrays are approximated as equivalent single-walled CNTs and modeled with shell elements. The stiffness and Young's modulus obtained from the equivalent thickness method are comparable to those obtained from the modeling of actual multi-wall structures, but at much efficient computational efforts. VA-MWCNTs have also been designed at various architectures (square, FCC) and areal densities, and the resultant mechanical properties are analyzed.

Detailed investigations on the stress intensity factors (SIFs) for corner cracks emanated from interference fitted dimpled rivet holes are conducted using three-dimensional finite element method. The influences of the crack length a, elliptical shape factor t, far-end stress S and interference magnitude δ on the stress intensity factors are systematically studied. The SIFs for corner cracks emanated from open holes are also investigated for comparisons. An empirical formula of the normalized SIF is proposed by use of the least square method for convenience of the engineering application, which is a function of the crack length a, elliptical shape factor t, far-end stress S, interference magnitude δ and the normalized elliptical centrifugal angle φ_n. Based on the empirical formula, a crack growth simulation for a rivet filled hole is conducted, which shows a good agreement with the test data.

In order to assure structural integrity for operating welded structures, it is necessary to evaluate crack growth rate and crack propagation direction for each observed crack non-destructively. Here, three dimensional (3D) welding residual stresses must be evaluated to predict crack propagation. Today, X-ray diffraction is used and the ultrasonic method has been proposed as non-destructive method to measure residual stresses. However, it is impossible to determine residual stress distributions in the thickness direction. Although residual stresses through a depth of several tens of millimeters can be evaluated non-destructively by neutron diffraction, it cannot be used as an on-site measurement technique. This is because neutron diffraction is only available in special irradiation facilities. Author pays attention to the bead flush method based on the eigenstrain methodology. In this method, 3D welding residual stresses are calculated by an elastic Finite Element Method (FEM) analysis from eigenstrains which are evaluated by an inverse analysis from released strains by strain gauges in the removal of the reinforcement of the weld. Here, the removal of the excess metal can be regarded as non-destructive treatment because toe of weld which may become crack starters can be eliminated. The effectiveness of the method has been proven for welded plates and pipes even with relatively lower bead height. In actual measurements, stress evaluation accuracy becomes poorer because measured values of strain gauges are affected by processing strains on the machined surface. In the previous studies, the author has developed the bead flush method that is free from the influence of the affecting strains by using residual strains on surface by X-ray diffraction. However, stress evaluation accuracy is not good enough because of relatively poor measurement accuracy of X-ray diffraction. In this study, a method to improve the estimation accuracy of residual stresses in this method is formulated, and it is shown numerically that inner welding residual stresses can be estimated accurately from the residual strains measured by X-ray diffraction.

Gold nanorods (GNRs) have great potential widespread applications in biomedical imaging, drug delivery and photothermal therapy due to unique surface plasmon resonance (SPR) ranging from visible to near infrared (NIR) region, facile synthesis and easy functionalization. The frequency of SPR is not only determined by the nature of the metal, but also by a number of other parameters, such as particle size and shape, the presence of a capping shell on the particle surface, or the dielectric properties of the surrounding medium. In this study, use is made of finite element method (FEM) for the calculation of the complex effective permittivity of the gold-core nanorod coated with polymer shells. Such a permittivity allows the determination of the absorption spectrum of these clothed nanoparticles. A simple scheme based on FEM is developed, which enables us to compute the optical properties, such as the effective dielectric function and absorption cross-section of coated-GNRs which are embedded in a dielectric matrix. The influences of the aspect ratio, shell thickness and dielectric constant of the shell on the longitudinal and transversal resonances modes are investigated.