• 대한기계학회논문집B
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• 제38권4호
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• pp.347-355
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• 2014

전자장치들의 소형화 및 박형화가 됨에 따라 전자장치의 수명과 직결되는 열적문제가 중요해지고 있다. 열적문제를 해결하기위해 열확산과 단열을 통한 열적 안정성 연구가 필요하다. 허니컴 샌드위치 평판은 이방성의 열전도계수를 갖는다. 허니컴 샌드위치 평판이 적용된 시스템에 대해 온도분포와 열변형을 해석하기 위하여 열 및 탄성 물성치가 필요하다. 본 연구에서는 허니컴 코어의 크기, 두께 그리고 구성된 재료에 따라 허니컴 샌드위치 평판의 물성치가 변하기 때문에 허니컴 샌드위치 평판의 열전도계수, 열팽창계수, 탄성계수, 전단탄성계수, 푸아송비와 같은 열 및 탄성 물성치를 예측하였다.

• Nuclear Engineering and Technology
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• 제34권1호
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• pp.90-103
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• 2002

The thermal and mechanical properties of compacted bentonite and bentonite-sand mixture were collected from the literatures and compiled. The thermal conductivity of bentonite is found to increase almost linearly with increasing dry density and water content of the bentonite. The specific heat can also be expressed as a function of water ontent, and the coefficient of thermal expansion is almost independent on the dry density. The logarithm of unconfined compressive strength and Young’s modulus of elasticity increase linearly with increasing dry density, and in the case of constant dry density, it can be fitted to a second order polynomial of water content. Also the unconfined compressive strength and Young’s modulus of elasticity of the bentonite-sand mixture decreases with increasing sand content. The Poisson’s ratio remains constant at the dry density higher than 1.6 Mg/m$_3$, and the shear strength increases with increasing dry density.

• 터널과지하공간
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• 제1권
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• pp.32-38
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• 1991

9 nuclear power plants are presently in operation in Korea. They produce radioactive waste of which the most long-lived radioactive elements need to be safely stored for hundreds of thousands of years, isolated from humanity and the environment. The safe disposal of high level radioactive waste in mined cavities requires knowledge of the mechanical. thermal and fluid flow characteristics of rock as perturbed by a thermal pulse The literature review was performed to assemble data on the following properties: modulus tensile strength compressive strength thermal expansion specific heat, thermal conductivity thermal diffusivity and permeability.

• 한국전기전자재료학회논문지
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• 제17권4호
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• pp.443-447
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• 2004

In this study, we investigated the necessity of encapsulation layer to maximize flexibility of brittle indium-tin-oxide (ITO) on polymer substrates. And, Young's modulus (E) of encapsulation layer han a significant effect on external bending stress and the coefficient of thermal expansion (CTE) of that han a significant effect on internal thermal stress. To compare the magnitude of total mechanical stress including both bending stress and thermal stress, the mechanical stress of triple-layer structure (substrate / ITO / encapsulation layer or substrate / buffer layer / ITO) can be quantified and numerically analyzed through the farthest cracked island position. As a result, it should be noted that multi-layer structures with more elastic encapsulation material have small mechanical stress compared to that of buffer and encapsulation structure of large Young's modulus material when they were externally bent.

• 대한기계학회논문집A
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• 제20권3호
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• pp.753-764
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• 1996

The metal matrix composites(MMC) are currently receiving a great deal of attention. These composites possess exellent mechanical and physical properties such as modulus, strength, wear resistance and thermal stability, which make them very attractive for use in automotive piston. In this study, $Al/{Al_2}{O_3}$(15%) composites are fabricated by the squeeze casting method. Mechanical properties such as tensile strength and ductility are performed at room and elevated temperature($250^{\circ}C$ and $350^{\circ}C$), respectively. Through thermomechanical analyser, thermal expansion coefficient of $Al/{Al_2}{O_3}$ composites are conducted for ranging from room temperature to ($400^{\circ}C$.And bending fatigue tests are also performed by the rotary bending machine at room temperature.The tensile strength and elastic modulus have been improved up to 38% and 35% by the addition of the reinforcements, respectively. Thermal expansion coefficients of MMCs which is located normal and parralel to the applied pressure are showed slightly different less than 10%. Fatigue strengh of the composite was improved by about 20% compared with that of unreinforced Al alloy. The results of this study will be used to understand the basic fracture behavior of MMCs and eventually to expand the applocation of MMCs as a machine parts undertaken various loadings.

• 콘크리트학회논문집
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• 제13권3호
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• pp.228-236
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• 2001

매스콘크리트 구조물에서 발생하는 온도응력을 예측하기 위해 많은 연구가 해석적인 방법과 실험적인 방법을 통해 수행되어왔다. 그러나 이러한 해석적인 방법과 실험적인 방법으로 온도응력을 예측하는 것은 한계가 있다. 해석적인 방법은 콘크리트의 탄성계수, 열팽창계수와 같은 물성치를 정확히 알아야 한다. 그리고 실험적인 방법은 대부분이 실제 구조물이나 모형구조물을 통하여 직접 온도응력을 측정한다. 그러나 이와 같은 방법은 경제적인 문제뿐만 아니라 현장의 불확실한 조건들을 감수해야 한다. 본 연구에서는 온도응력을 실내에서 직접적으로 측정할 수 있는 시험장치를 개발하였다. 개발된 온도응력 시험장치는 콘크리트와 다른 열팽창계수를 갖는 재료를 이용하여 실제 구조물에서 발생할 수 있는 콘크리트의 내/외부 구속에 의한 온도응력의 변화를 구현할 수 있으며, 이를 정량적으로 예측할 수 있다. 실험은 해석을 통해 얻은 온도이력을 구현할 수 있는 항온항습조에서 수행하였고, 온도응력은 장비에 부착된 변형률게이지를 통해 얻은 변형률을 이용하여 계산하였다. 개발된 장비의 검증을 위해 매립게이지를 이용하여 온도응력을 측정하는 실험을 동시에 수행하였고, 이 결과에 의하면 개발된 시험장치는 불확실한 콘크리트의 초기재령 물성치를 고려하여 보다 정확하게 온도응력을측정할 수 있으며, 검증실험 결과에 의해 그 객관성과 타당성을 입증할 수 있었다.

• 대한기계학회논문집A
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• 제20권11호
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• pp.3538-3548
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• 1996

In this study, as a part of basic study for developing the simulation program for the assemssment of reliability of electronic EMC packaging which covers from EMC mixing step to thermal analysis, comparison between a measured and predicted values of material properties of EMC and finitde element analysis of thermal stress are performed. For the experimental testing specimens of fifty, sixty hive and eighty percent filler($13\mu m$, spherical silica) weight fraction are fabricated using tranfer molding. Coefficient of thermal expansion, elastic modulus and thermla conductivity are measured using these specimens and then these measured values are compared with the predicted values by various equations ( such as dilute suspension method. self consistent method, generalized self consistent method, Hashin-Shtrikman's bounds. Shapery's bounds, Nielsen's method and others). Measured values are distributed within the upper and lower bounds of equations. Measured elastic modulus and coefficient of thermal expansion approaches closely the perdicted values with self consisten mehtod and upper bound of Shaperys equation respectively. However small differences of thermal conductivity between the different filler volume fraction are obserbed. FEM analysis indicates that firstly stress is concentrated at the corner section of EMC and secondly EMC with eighty percent filler weight fraction shows less thermal stress when package is cooling down and relatively high thermal stress when package is heating up.

• 한국전기전자재료학회논문지
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• 제25권10호
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• pp.798-804
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• 2012

This paper focuses on thermal properties of a newly prepared composite material by nano-silica and micro-silica mixture. Nano-silica and micro-silica mixture composites were made by dispersing surface treated nano-silica(average radius: 10 nm) and micro-size silica in epoxy resin. To investigate the effects of nano-silica and micro-size silica mixture(ENMC), the glass transition temperature (Tg), coefficients of thermal expansion(CTE) and elastic modulus of DMA properties by DSC, TMA and DMA devices were measured for the ENMC according to increase nano-silica addition contents and EMC. All properties of the neat epoxy were improved by the addition of micro-silica, which was improved much further by the addition of surface treated nano-silica to the EMC system.

• 대한기계학회논문집A
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• 제31권12호
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• pp.1157-1164
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• 2007

Ceramic honeycomb structures have performed successfully as catalyst supports for meeting hydrocarbon, carbon monoxide and nitrous emissions standards for gasoline-powered vehicles. Three-way catalyst converter has to withstand high temperature and thermal stress due to pressure fluctuations and vibrations. Thermal stress constitutes a major portion of the total stress which the ceramic catalyst support experiences in service. In this study, temperature distribution was measured at ceramic catalyst supports. Thermal durability was evaluated by power series dynamic fatigue damage model. Radial temperature gradient was higher than axial temperature gradient. Thermal stresses depended on direction of elastic modulus. Axial stresses are higher than tangential stresses. Tangential and axial stresses remained below thermal fatigue threshold in all engine operation ranges.

• 대한기계학회논문집A
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• 제37권5호
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• pp.657-664
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• 2013

에폭시 수지에 다중벽 탄소나노튜브를 첨가하여 초음파 처리와 전단혼합 방법으로 분산시켜 다중벽 탄소나노튜브로 강화된 에폭시 복합재료를 제조하였으며, 에폭시 수지 내 다중벽 탄소나노튜브의 분산 적정성을 판단하고 기계적 및 열적 물성을 고찰하였다. 충전재 분산에 대한 평가를 위해 정성적인 방법으로 주사전자현미경(scanning electron microscope, SEM) 이미지를 사용하였고, 정량적인 판단을 위해 인장실험을 실시하였다. 또한, 열적 특성을 평가하기 위해 열팽창계수(coefficient of thermal expansion, CTE)를 측정하였다. 주사전자현미경 사진 및 인장 강도와 영률(Young's modulus)의 작은 편차를 통해서 다중벽 탄소나노튜브가 에폭시 수지 내에 적절히 분산되었음을 확인하였다. 충전재 함량에 따라 인장 강도와 영률이 증가함을 보였고 열팽창계수 측정에서는 열안정성 개선을 고찰하였다.