• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.19-20
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• 2003

Brownian-dynamics simulation on highly charged colloidal suspensions is performed by employing Tokuyama effective force recently proposed. The radial distribution function suggests that there exist three novel phases, a gas phase, a liquid droplet phase, and a face-centered cubic (FCC) crystal droplet phase, depending on the minimum values of that potential. The dynamics of droplet growth is also investigated both in liquid droplet phase and in crystal droplet phase. Thus, different types of characteristic growth stages are found.

• Journal of Magnetics
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• v.10 no.1
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• pp.28-32
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• 2005

The magnetic properties and ordering behavior of Nb-doped FePt alloy films prepared by dc-magnetron sputtering were investigated. It was found that Nb addition retarded the ordering reaction from the disordered face-centered-cubic (fcc) Al phase to the ordered face-centered-tetragonal (fct) L1₀ phase. The tetragonality (c/a ratio) of the ordered fct L1₀ phase increased with the Nb concentration. Nb addition hampered c-axis contraction during ordering, probably because the larger Nb atoms occupy Pt sites. Consequently, the coercivity and magnetocrystalline anisotropic energy of Nb-doped FePt alloy films are lower than those of un-doped FePt film under equivalent annealing conditions.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.6
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• pp.199-209
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• 2000

Particles reinforced MMCs have higher specific modulus, higher specific strength, better properties at elevated temperatures and better wear resistance than monolithic metals. But the coefficient of thermal expansion(CTE) of Al6061 is 5 times larger than that of SiCp. The discrepancy of CTE makes some residual stresses inside of MMCs. This work investigates Si$C_p$/Al6061 composites at high temperatures in the microscopic view by three-dimensional elasto-plastic finite element analyses and compares the analytical results with the experimental ones. The theoretical model is not able to consider the nonuniform shape of particle. So the shape of particle is assumed to be perfect global shape. And also particle distribution is not homogeneous in experimental specimen. It is assumed to be homogeneous in simulation model. The type of particle distribution is face-centered cubic array(FCC array). Furthermore, non-homogeneous distribution is modeled by combination of several volume fractions.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.6
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• pp.124-138
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• 1998

Particles reinforced MMCs have many advantages over monolithic metals including a higher specific modulus, higher specific strength, better properties at elevated temperatures and better wear resistance. SiC$_p$/A16061 composites have good results in its mechanical properties. This work investigates SiC$_p$/A16061 composites in the microscopic view and compares the analytical results with the experimental ones. The discrepancy of the material properties between the reinforced particle, SiC$_p$, and the matrix material, A16061 appears to be so significant. Especially the coefficient of thermal expansion(CTE) of A16061 is 5 times larger than that of SiC$_p$. Thermal residual stress in MMCs is induced at high temperatures. The shape of particle is various but the theoretical model is not able to consider the nonuniform shape. Particle distribution is not homogeneous in experimental specimen. However, it is assumed to be homogeneous in simulation model. The shapes of particles are assumed to be not only perfect global but hexahedral shapes. The types of particle distribution are two - simple cubic array(SC array) and face-centered cubic array(FCC array).

• Journal of the Korean Society for Heat Treatment
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• v.37 no.2
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• pp.58-65
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• 2024

In the present study, the effect of annealing condition on the microstructures and mechanical properties of the cold-rolled CoCrFeMnNi high entropy alloys were studied. Annealing treatment was performed under six different temperatures. Microstructural analyses confirmed that annealing below 800℃ resulted in the formation of intermetallic sigma (σ) phase within face-centered cubic (FCC) matrix, and this σ phase has beneficial effects on the formation of fine-grained structures through retardation of grain growth and recrystallization due to Zener pinning effect. This led to the enhanced yield strength and tensile strength of ~646 and ~855 MPa, respectively. The microstructures annealed above 800℃ demonstrated single FCC phase, and fully-recrystallized single FCC microstructure resulted in a slight increase in ductility with a considerable decrease in strength. The evolution of mechanical properties, such as strength, ductility, and strain hardening exponent, will be discussed.

• Interaction and multiscale mechanics
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• v.2 no.1
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• pp.45-68
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• 2009

An aim of the study is to develop an efficient numerical simulation technique that can handle the two-scale analysis of fluid permeation filters fabricated by the partial sintering technique of small spherical ceramics. A solid-fluid mixture homogenization method is introduced to predict the mechanical characters such as rigidity and permeability of the porous ceramic filters from the micro-scale geometry and configuration of partially-sintered particles. An extended finite element (X-FE) discretization technique based on the enriched interpolations of respective characteristic functions at fluid-solid interfaces is proposed for the non-interface-fitted mesh solution of the micro-scale analysis that needs non-slip condition at the interface between solid and fluid phases of the unit cell. The homogenization and localization performances of the proposed method are shown in a typical two-dimensional benchmark problem whose model has a hole in center. Three-dimensional applications to the body-centered cubic (BCC) and face-centered cubic (FCC) unit cell models are also shown in the paper. The 3D application is prepared toward the computer-aided optimal design of ceramic filters. The accuracy and stability of the X-FEM based method are comparable to those of the standard interface-fitted FEM, and are superior to those of the voxel type FEM that is often used in such complex micro geometry cases.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.309-312
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• 2001

FEM simulating system of the cross-rolling texture formation offers a systematic and efficient way of exploring the relationship between the process variables and the state of plastic anisotropy of sheet product. Cross-rolled sheets possess higher average plastic strain ratios and lower planer anisotropy than those of the straight-rolled sheets. The employed model is a finite-element polycrystal model which each element used in FEM is assumed to be a crystal having different orientation by Takahashi. Texture development, deformation textures due to cross-rolling are predicted for face-centered cubic sheet metal. Crystal orientations are assigned on the basis of the pole figures obtained by X-ray diffraction. Development of anisotropy during cross rolling of an fcc sheet material is predicted theoretically with respected to flow stress and R-value in tensile test.

• Corrosion Science and Technology
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• v.15 no.5
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• pp.237-244
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• 2016

2205 duplex stainless steels have been used for the construction of the marine environment, because of their excellent corrosion resistance and high strength. However, the resistance to hydrogen embrittlement (HE) may be less than that of 316L austenitic stainless steel. The reason why 316L stainless steels have better resistance to HE is associated with crystal structure (FCC, face centered cubic) and the higher stacking faults energy than 2205 duplex stainless steels. Furthermore 2205 stainless steels with or without tungsten were also examined in terms of HE. 2205 stainless steels containing tungsten is less resistible to HE. It is because dislocation tangle was formed in 2205 duplex stainless steels. Slow strain-rate tensile test (SSRT) was conducted to measure the resistance to HE under the cathodic applied potential. Hydrogen embrittlement index (HEI) was used to evaluate HE resistance through the quantitative calculation.

• Bulletin of the Korean Chemical Society
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• v.33 no.4
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• pp.1242-1246
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• 2012

The Co oxide microfibers were synthesized using the electrospinning process and formed $Co_3O_4$ microfibers after being calcined at high temperatures. The calcination temperature influenced the diameters, morphology, crystalline phase, and chemical environment of the fibers. The surface morphology of the obtained fibers was examined by using the scanning electron microscope (SEM). As the calcination temperatures increased from room temperature to 873 and 1173 K, the diameters of the cobalt oxide fibers decreased from 1.79 to 0.82 and 0.32 mm, respectively. The structure of the fibers was investigated with X-ray diffraction (XRD) and transmission electron microscopy (TEM). The calcined $Co_3O_4$ fibers had crystalline face-centered cubic (fcc) structure. The X-ray photoelectron spectroscopy (XPS) results revealed that increasing the calcination temperature promoted the formation of $Co^{2+}$ and $Co^{3+}$ species.

• Journal of the Korean institute of surface engineering
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• v.36 no.1
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• pp.1-8
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• 2003

In general, the microstructure in thin films was known to evolve in similar manner according to the energy striking the condensing film at similar homologous temperature, Th for the materials of the same crystal structure. The fundamental factors affecting particle energy are a function of processing parameters such as working pressure, bias voltage, target/sputtering gas mass ratio, cathode shape, and substrate orientation. In this study, Al, Cu, Pt films of the same crystal structure of face centered cubic (FCC) have been prepared under various processing parameters. The influence of processing variables on the microstructures and residual stress states in the films has been studied.