• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2008년도 춘계학술대회 논문집
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• pp.197-198
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• 2008

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.328-331
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• 2009

Microstructural evolution of alpha and beta phases during dynamic globularization of near-beta Ti-13Nb-13Zr alloy was investigated to determine the optimum processing conditions. The submicrocrystalline alloy sheet with ${\sim}80%$ of high-angle grain boundaries was produced utilizing dynamic globularization at temperature of $600^{\circ}C$, equivalent strain rate of $10^{-1}\;s^{-1}$ and strain of 1.4. The refined structure with the gain size of ${\sim}0.4{\mu}m$ showed 25-60% enhanced mechanical compatibility as compared to those of the conventional mill-annealed or solution treated and aged microstructures.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2002년도 춘계 학술발표회 논문집
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• pp.367-372
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• 2002

In these days, The base isolation system is often used to improve the seismic capacity of the structures instead of conventional techniques of strengthening the structural members. The purpose of this study is to evaluate dynamic properties and mechanical characteristics of the 10tonf-LRB(Lead-Rubber Bearing). Experimental studies were performed to obtain the hysteretic behavior, effective shear stiffness( $K_{eff}$), equivalent damping( $H_{eq}$ ), capacity of energy dissipation( $W_{D}$) of six 10tonf-LRB. Especially, in this study, the response of the LRB for high loading frequency(0.5Hz~3.0Hz) was estimated. The effective shear stiffness of the LRB decreases and the capacity of energy dissipation increases as the shear strain amplitude increases. But the shear behavior of the LRB is not affected sensitively by loading frequency.y.y.

• 대한기계학회논문집A
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• 제37권10호
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• pp.1229-1237
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• 2013

본 연구에서는 증분소성이론에 기초한 구형압입이론을 크리프 물성을 평가하기 위한 압입이론으로 확장했다. 먼저 크리프변형률 기울기가 일정한 지점을 유효 응력-변형률속도 최적 관측지점으로 선정했다. 구형압입시험 전산모사를 이용해 크리프 지수와 계수를 변화시켜 가면서 이에 따른 재료의 거동을 무차원 변수들 (${\xi}$, ${\psi}$)의 회귀식으로 표현해 크리프 물성평가를 위한 새로운 수치 접근법을 구축했다. 이를 토대로 구형압입시험으로부터 재료의 크리프지수 및 계수를 예측하는 물성평가 프로그램을 개발했다. 압입 하중-변위 곡선으로부터 크리프지수는 평균 1.5%, 크리프계수는 평균 1.0% 이내의 오차범위에서 물성치들을 얻을 수 있다.

• 대한기계학회논문집A
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• 제40권12호
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• pp.1013-1019
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• 2016

CFRP는 탄소섬유를 기반으로 수지를 합침하여 제조된 복합소재로, 높은 비 강도와 경량성을 지녀 다양한 분야들에서 널리 사용되어지고 있다. 특히 일방향 탄소섬유는 적층 각도를 적용할 수 있으며 이때 적용된 적층 각도로 구성된 CFRP는 적층 각도가 없는 것보다 더 높은 강성을 가지고 있다. 본 논문에서는 적층 각도 변화에 따른 CFRP 소형 인장시험편의 크랙 전파와 파괴거동에 관한 것으로, 각 적층 각도에 따른 크랙 성장의 특성을 고찰한다. 적층 각도가 증가함에 따라 최대 응력 값이 작게 나타나고 크랙 전파가 더디게 나타나지만, 적층 각도 $60^{\circ}$를 기점으로 그 응력이 다시 증가되므로 서, 적층 각도에 따른 한계를 보이고 있다. 본 연구결과는 기계구조물의 CFRP사용에 있어 구조물내의 결함이 발생하였을 때의 피로파괴 가능성을 검증하는 자료로 사용될 수 있다고 사료된다.

• Journal of Mechanical Science and Technology
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• 제18권7호
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• pp.1187-1195
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• 2004

The objective of this study is to investigate the effects of fuel temperature on the spray characteristics of a dual-orifice type swirl injector used in a gas turbine. The major parameters affecting spray characteristics are fuel temperature and injection pressure entering into the injector. In this study, the spray characteristics of a dual-orifice type swirl injector are investigated by varying fuel temperature from - 30$^{\circ}C$ to 120$^{\circ}C$ and injection pressure from 0.29 to 0.69 ㎫. Two kinds of fuel having different surface tension and viscosity are chosen as atomizing fluids. As a result, injection instability occurs in the low fuel temperature range due to icing phenomenon and fuel property change with a decrease of fuel temperature. As the injection pressure increases, the range of kinematic viscosity for stable atomization becomes wider. The properties controlling the SMD of spray is substantially different according to the fuel temperature range.

• 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.

• 한국기계가공학회지
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• 제21권9호
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• pp.85-91
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• 2022

The demand for electric vehicles has increased because of environmental regulations. The lithium-ion battery, the most widely used type of battery in electric vehicles, is composed of a cathode, an anode, and an electrolyte. It is manufactured according to the pole plate, assembly, and formation processes. To improve battery performance and increase manufacturing efficiency, the manufacturing process must be optimized. To do so, simulation can be used to reduce wasted resources and time, and a finite-element method can be utilized. For high simulation quality, it is essential to reflect the material properties of the electrode by considering the pores. However, the material properties of electrodes are difficult to derive through measurement. In this study, the representative volume element method, which is a homogenization method, was applied to estimate the representative material properties of the electrode considering the pores. The representative volume element method assumes that the strain energy before and after the conversion into a representative volume is conserved. The method can be converted into one representative property, even when nonhomogeneous materials are mixed in a unit volume. In this study, the material properties of the electrode considering the pores were derived. The results should be helpful in optimizing the electrode manufacturing process and related element technologies.

• 한국정밀공학회지
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• 제28권5호
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• pp.623-631
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• 2011

Metallic sandwich panels based on a truss core structure have been developed for a wide range of potential applications with their lightweight and multi-functionality. Structural performance of sandwich panels can be predicted from the studies on mechanical behavior of a unit cell of truss core structures. Analytical investigations on the unit cell provide approximated guidelines for the design of overall core structures for a specific application in short time. In this study, the effects of geometrical parameters on mechanical behavior of a pyramidal shape of unit cell were investigated with analytical models. The unit cell with truss member angle of 45 degree was considered as reference model and other models were designed to have the same weight and projected area but different truss member angle. All truss members were assumed to be connected with pin joint in analytical models. Under the assumptions, the equivalent strength and stiffness of the unit cell under compressive and shear loads were predicted and compared. And finally, the optimum core member angle to have maximum mechanical property could be calculated and verified with FE analysis results.

• 대한기계학회논문집A
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• 제34권12호
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• pp.1909-1915
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• 2010

고온의 연소가스에서 운전되는 국내 가스터빈 부품들은 매일 기동정지를 반복함으로써 열사이클에 의해 재료특성에 변화가 발생한다. 최근 많은 가스터빈 고온부품들이 단결정 초내열 합금으로 제작되어 지지만 재료열화 예측을 통한 부품 교체와 정비에 대한 기준이 없어서 대부분 제작사에 의존하고 있는 실정이다. 본 연구에서는 향후 수명평가와 손상분석의 기초자료로 활용하기 위해 실제 운전된 가스터빈 1 단 블레이드의 열화상태를 조사하였다. 사용한 블레이드는 25,000 및 52,000 의 등가운전시간(EOH : Equivalent Operating Hour)을 가졌으며, 재질은 단결정 초내열합금인 CMSX-4 이다. 사용된 블레이드에서 직접 시험편을 채취하여 기계적특성 시험 및 미세조직을 관찰하였다.