• Journal of Magnetics
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• v.13 no.4
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• pp.128-131
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• 2008

We have investigated the electronic structures and magnetic properties of both undoped and doped bcc Ni using the full-potential linearized augmented plane wave (FLAPW) band method. A ferromagnetic ground state is obtained at the equilibrium volume of bcc Ni. When the system is under strain, the nonmagnetic ground state is stabilized. When the Ni is doped with V, the $Ni_{16-x}V_x$ material loses its magnetic properties when x > 2. We have also discussed the possible superconducting properties of $Ni_{16-x}V_x$.

• Structural Engineering and Mechanics
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• v.53 no.6
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• pp.1167-1182
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• 2015

In this study, the stresses and electric potential redistributions of a cylinder made from functionally graded piezoelectric material (FGPM) are investigated. All the mechanical, thermal and piezoelectric properties are modeled as power-law distribution of volume fraction. Using the coupled electro-thermo-mechanical relations, strain-displacement relations, Maxwell and equilibrium equations are obtained including the time dependent creep strains. Creep strains are time, temperature and stress dependent, the closed form solution cannot be found for this constitutive differential equation. A semi-analytical method in conjunction with the Mendelson method of successive approximation is therefore proposed for this analysis. Similar to the radial stress histories, electric potentials increase with time, because the latter is induced by the former during creep deformation of the cylinder, justifying industrial application of such a material as efficient actuators and sensors.

• Coupled systems mechanics
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• v.4 no.1
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• pp.99-114
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• 2015

In this paper, a refined exponential shear deformation beam theory is developed for bending analysis of functionally graded beams. The theory account for parabolic variation of transverse shear strain through the depth of the beam and satisfies the zero traction boundary conditions on the surfaces of the beam without using shear correction factors. Contrary to the others refined theories elaborated, where the stretching effect is neglected, in the current investigation this so-called "stretching effect" is taken into consideration. The material properties of the functionally graded beam are assumed to vary according to power law distribution of the volume fraction of the constituents. Based on the present shear deformation beam theory, the equations of motion are derived from Hamilton's principle. Analytical solutions for static are obtained. Numerical examples are presented to verify the accuracy of the present theory.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.415-420
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• 2007

In analyzing the nano-scale behavior of nano devices or materials, QC method is efficient because it does not treat all the atoms. But for more accurate analysis in QC method, it is important to consider temperature and surface effects. In finite temperature, free energy is considered instead of potential energy. Because the surface area to volume ratio increases as the length scale of a body decreases, the surface effects are more dominant. In this paper, temperature related Cauchy-Born rule and surface Cauchy-Born rule are proposed to configurate the strain energy density. This method is applied to small and homogeneous deformation in two dimensional problem using finite element simulation.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.31-34
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• 2007

In this study, optimum processing condition of AZ31 Mg alloy was investigated utilizing processing map and constitutive equation considering microstructure evolution (dynamic recrystallization) during hot-working. A series of mechanical tests were conducted at various temperatures and strain rates to construct a processing map and to formulate the recrystallization kinetics and grain size relation. Dynamic recrystallization (DRX) was observed to occur revealing maximum intensity at a domain of $250^{\circ}C$ and 1/s. The effect of DRX kinetics on microstructure evolution was implemented in a commercial FEM code followed by remapping of the state variables. The volume fraction and grain size of deformed part were predicted using a modified FEM code and compared with those of actual hot forged one. A good agreement was observed between the experimental results and predicted ones.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.12
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• pp.3227-3235
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• 1994

This paper deals with an evaluation of the residual stress due to shot peening induced in a carburized gear tooth and its application to the fatigue crack propagation problem. A practical method is proposed on the basis of the assumption that the residual stress is caused by the difference of volume expansion in the case and the core, and the influence of both the reduction of retained austenite and the strain due to shot peening are considered. The evaluated residual stress is close to the measured stress, though the surface stress is rather overestimated. The stress intensity factor is computed by the influence function method, and it is shown that the factor is decreased by the residual stress in shot peened gear tooth. The shot peening is fairly effective to the reduction of fatigue crack growth rate. The crack propagation is simulated and the resistance due to shot peening is quantitatively demonstrated and discussed.

• Proceedings of the KSR Conference
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• 2004.10a
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• pp.848-853
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• 2004

This is a basic experimental study elaborated on reinforced concrete beam under load, especially crack behavior, bending stiffness, deflection and strain of concrete and reinforced bar for reinforced concrete and steel fiber reinforced concrete beam in relation to fatigue loading in service ability limit states. Test parameters are concrete strength, volume. and type of steel fiber and fatigue loading in service ability limit states to be changed. In order to obtain the actual conditions of various working loads for the aforesaid reinforced concrete beam, minimum load is applied 10$\%$ of maximum design load and maximum load was applied 60$\%$, 80$\%$ and 100$\%$ respectively. Under the same condition, the test was implemented up to 1 million cycle and the result was thoroughly analyzed and reviewed.

• Wind and Structures
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• v.23 no.1
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• pp.59-73
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• 2016

In this paper, a hyperbolic shear deformation beam theory is developed for free vibration analysis of functionally graded (FG) sandwich beams. The theory account for higher-order variation of transverse shear strain through the depth of the beam and satisfies the zero traction boundary conditions on the surfaces of the beam without using shear correction factors. The material properties of the functionally graded sandwich beam are assumed to vary according to power law distribution of the volume fraction of the constituents. The core layer is still homogeneous and made of an isotropic material. Based on the present refined beam theory, the equations of motion are derived from Hamilton's principle. Navier type solution method was used to obtain frequencies. Illustrative examples are given to show the effects of varying gradients and thickness to length ratios on free vibration of functionally graded sandwich beams.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.410-414
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• 2004

Under longitudinal loading continuous fiber reinforced metal matrix composite(MMC) have interpreted an outstanding performance. However, the applicability of continuous fiber reinforced MMCs is somewhat limited due to their relatively poor transverse properties. Therefore, the transverse properties of MMCs are significantly influenced by the properties of the fiber/matrix interface. In this study, elastic-plastic behavior of transversely loaded unidirectional fiber reinforced metal matrix composites investigated by using elastic-plastic finite element analysis. Different fiber placement(square and hexagon) and fiber volume fractions were studied numerically. The interface was treated as three thin layer (with different properties) with a finite thickness between the fiber and the matrix. The analyses were based on a two-dimensional generalized plane strain model of a cross-section of an unidirectional composite by the ANSYS finite element analysis code.

• The Korean Journal of Ceramics
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• v.5 no.2
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• pp.104-109
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• 1999

Rheological properties of dense slurries over 45 volume % with different monosaccharides and disaccharides were checked in order to increase the solid content of dense slurries without sacrificing plasticity using creep testing method. Strain in creep test showed good correlations with Burger model which is expressed as an exponential function of time. Among several monosaccharides and disaccharides studied here, fructose and sucrose were most effective in making dense alumina slurry plastic than other monosaccharides and disaccharides like glucose, galactose, xyloss and maltose. In the case of dense alumina slurry with sucrose, sucrose content or additional water content enhanced to the plasticity of the slurries.