• 대한금속재료학회지
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• 제46권10호
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• pp.691-699
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• 2008

Electrochemical characteristics of Ti-30Ta-xZr alloys coated with HA/TiN by using magnetron sputtering method were studied. The Ti-30Ta containing Zr(3, 7, 10 and 15wt%) were 10 times melted to improve chemical homogeneity by using a vacuum furnace and then homogenized for 24hrs at $1000^{\circ}C$. The specimens were cut and polished for corrosion test and coating, and then coated with HA/TiN, respectively, by using DC and RF-magnetron sputtering method. The analyses of coated surface and coated layer were carried out by using optical microscope(OM), field emission scanning electron microscope(FE-SEM) and X-ray diffractometer(XRD). The electrochemical characteristics were examined using potentiodynamic (-1,500 mV~ + 2,000 mV) and A.C. impedance spectroscopy(100 kHz ~ 10 mHz) in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. The microstructure of homogenized Ti-30Ta-xZr alloys showed needle-like structure. In case of homogenized Ti-30Ta-xZr alloys, a-peak was increased with increasing Zr content. The thickness of TiN and HA coated layer showed 400 nm and 100 nm, respectively. The corrosion resistance of HA/TiN-coated Ti-30Ta-xZr alloys were higher than that of the non-coated Ti-30TaxZr alloys, whic hindicate better protective effect. The polarization resistance($R_p$) value of HA/TiN coated Ti-30Ta-xZr alloys showed $8.40{\times}10^5{\Omega}cm^2$ which was higher than that of non-coated Ti-30Ta-xZr alloys.

• Nuclear Engineering and Technology
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• 제55권9호
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• pp.3450-3463
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• 2023

In the two-step analysis of Pebble-Bed type High-Temperature Gas-Cooled Reactor (PB-HTGR), the lattice physics calculation for the generation of homogenized cross-sections is based on the fuel pebble. However, the randomly-dispersed fuel particles in the fuel pebble introduce double heterogeneity and randomness. Compared to the deterministic method, the Monte Carlo method which is flexible in geometry modeling provides a high-fidelity treatment. Therefore, the Monte Carlo code NECP-MCX is extended in this study to perform the lattice physics calculation of the PB-HTGR. Firstly, the capability for the simulation of randomly-dispersed media, using the explicit modeling approach, is developed in NECP-MCX. Secondly, the capability for the generation of the homogenized cross-section is also developed in NECP-MCX. Finally, simplified PB-HTGR problems are calculated by a two-step neutronics analysis tool based on Monte Carlo homogenization. For the pebble beds mixed by fuel pebble and graphite pebble, the bias is less than 100 pcm when compared to the high-fidelity model, and the bias is increased to 269 pcm for pebble bed mixed by depleted fuel pebble. Numerical results show that the Monte Carlo lattice physics calculation for the two-step analysis of PB-HTGR is feasible.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.399-404
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• 2000

Functionally graded materials(FGMs) involve dual-phase graded layers in which two different constituents are mixed continuously and functionally according to a given volume fraction. For the analysis of their thermo-mechanical response, conventional homogenized methods have been widely employed in order to estimate equivalent material properties of the graded layer. However, such overall estimations are insufficient to accurately predict the local behavior. In this paper, we compare the thermo-elastic behaviors predicted by several overall material-property estimation techniques with those obtained by discrete analysis models utilizing the finite element method, for various volume fractions and loading conditions.

• 한국정밀공학회지
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• 제22권7호
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• pp.170-176
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• 2005

Analysis of structures which are composed of numerous repeated unit structures can be simplified by using homogenized properties. If the unit structure is repeated in one direction, the whole structure may be regarded as a beam. Once the effective stiffness is obtained from the analysis of the unit structure in a proper way, the effort for the detail modeling of the global structure is not required, and the real structure can be replaced simply with a beam. This study proposes a kinematical periodicity constraint to be imposed on the FE model of the unit structure, which improves the accuracy of the effective stiffness. The method is employed to a one dimensionally arrayed 3D structure containing periodically repeated un-symmetric holes. It is demonstrated that the deformation behavior of the homogenized beam agrees well with that of the real structure.

• Coupled systems mechanics
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• 제4권2호
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• pp.137-155
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• 2015

This paper presents a simple procedure to obtain a substitute, homogenized mechanical response of single layer graphene sheet. The procedure is based on the judicious combination of molecular mechanics simulation results and homogenization method. Moreover, a series of virtual experiments are performed on the representative graphene lattice. Following these results, the constitutive model development is based on the well-established continuum mechanics framework, that is, the non-linear membrane theory which includes the hyperelastic model in terms of principal stretches. A proof-of-concept and performance is shown on a simple model problem where the hyperelastic strain energy density function is chosen in polynomial form.

• 소성∙가공
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• 제23권3호
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• pp.171-177
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• 2014

The current collector for the molten carbonate fuel cell (MCFC) which has sheared protrusions is manufactured by the three-stage forming process that integrates slitting, preforming and final forming. Due to the repetition of sheared protrusions, an effective simulation method is required to predict the mechanical behavior. In the current study, a sheet with sheared protrusions was assumed to be an orthotropic plate, which has the same length, width and height. FEM simulations were conducted to evaluate the homogenized properties of the current collector, which has 4 (longitudinal direction) x 4 (transverse direction) sheared protrusions. The simulation model was constructed using hexahedral mesh coarsening. From the verification examples, it was found that the proposed simulation method was efficient within reasonable accuracy. The calculated homogenized properties can be applied to the design of a stack for molten carbonate fuel cells and the prediction of mechanical behavior for other applications.

• Nuclear Engineering and Technology
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• 제53권5호
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• pp.1403-1415
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• 2021

The transient capability of a SP₃ based pin-wise core analysis code SPHINCS is developed and verified through the analyses of the C5G7-TD benchmark. Spatial discretization is done by the fine mesh finite difference method (FDM) within the framework of the coarse mesh finite difference (CMFD) formulation. Pin size fine meshes are used in the radial fine mesh kernels. The time derivatives of the odd moments in the time-dependent SP₃ equations are neglected. The pin homogenized group constants and Super Homogenization (SPH) factors generated from the 2D single assembly calculations at the unrodded and rodded conditions are used in the transient calculations via proper interpolation involving the approximate flux weighting method for the cases that involve control rod movement. The simplifications and approximations introduced in SPHINCS are assessed and verified by solving all the problems of C5G7-TD and then by comparing with the results of the direct whole core calculation code nTRACER. It is demonstrated that SPHINCS yields accurate solutions in the transient behaviors of core power and reactivity.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제24권2호
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• pp.215-227
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• 2020

A new multiscale finite element method for elliptic problems with highly oscillating coefficients are introduced. A hybridization yields a locally flux-conserving numerical scheme for multiscale problems. Our approach naturally induces a homogenized equation which facilitates error analysis. Complete convergence analysis is given and numerical examples are presented to validate our analysis.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1998년도 가을 학술발표회 논문집
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• pp.3-10
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• 1998

Optimization problems may be devided into geometry optimization problems and topology optimization problems. In this paper, a method using tile equivalent material properties prediction techniques of a particulate-reinforced composites is proposed for the topology optimization. This method makes use of penalty factor in order that regions with intermediate value of design variables can be penalized. The computational results being obtained from PLBA algorithm of some values of penalty factor are presented.

• Composites Research
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• 제29권6호
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• pp.347-352
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• 2016

적층 복합재료 주름판에 대한 진동특성을 이론적 방법을 이용하여 분석하였다. 고려된 주름 형상은 사다리꼴을 기본으로 삼각형, 사각형 및 요각 사다리꼴형이다. 3차원 주름 구조물을 해석적으로 기계적 거동을 표현하는 것이 매우 어렵기 때문에 본 해석에서는 주름판의 진동특성을 분석하기 위해 등가균질모델을 적용하였다. 이를 위해 단위 주름을 직교이방성재료로 등가시켰으며, 해석에서 등가 신장 강성 및 굽힘 강성이 모두 고려되었다. 이론해석 결과의 타당성을 검증하기 위해 셸요소를 적용한 3차원 유한요소해석을 수행하였으며, 두 방법을 이용해 얻은 고유진동수 및 진동형상을 비교하였다. 주름판의 기하형상에 따른 영향을 분석하기 위해 다양한 수치예가 제시되었다.