• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.7
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• pp.2939-2944
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• 2011

The performance and efficiency of a Molten Carbonate Fuel Cell system will improve with the aids of numerical simulations such as finite element analysis. For best simulation results, the virtual model must accurately reflect the actual model including the material properties. It is very difficult, however, to make a detailed numerical model of the stack that consists of hundreds of layers of unit cells composed of various materials like metal, ceramics, polymer, etc. Instead, a practical approach is to find a homogenized material property of the stack as a whole as an approximate replacement. In this paper, the compression ratio of a unit cell is introduced, and a new method is proposed to estimate the homogeneous material properties for both the active and the manifold regions of the stack under the assumption that the compressive deformation occurs only at the separators and matrices in the unit cells. The estimated properties are applied successfully to simulating an actual stack.

• Composites Research
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• v.35 no.3
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• pp.188-195
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• 2022

This paper proposes a multiscale process-structural analysis methodology and applies to a battery housing part made of the short fiber-reinforced and fabric-reinforced composite layers. In particular, uncertainties of the material properties within the microscale representative volume element (RVE) were considered. The random spatial distribution of matrix properties in the microscale RVE was realized by the Karhunen-Loeve Expansion (KLE) method. Then, effective properties of the RVE reflecting on spatially varying matrix properties were obtained by the computational homogenization and mapped to a macroscale FE (finite element) model. Morever, through the hybrid process simulation, a FE (finite element) model mapping residual stress and fiber orientation from compression molding simulation is combined with one mapping fiber orientation from the draping process simulation. The proposed method is expected to rigorously evaluate the design requirements of the battery housing part and composite materials having various material configurations.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.467-474
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• 2020

Carbon nanotube has excellent mechanical strength and functionality, so it has been utilized in various applications. In recent years, utilization of carbon nanotube in construction material has started to get interests from researchers in the area of construction materials. However, there is limited amount of work with respect to the rheological properties of cement paste using carbon nanotube. In this work, solution made of multi-walled carbon nanotube with dispersing agent of polyvinyl pyrrolidone was used to prepare cement paste specimens, and rheological properties and 28 day compressive strengths of cement paste using multi-walled carbon nanotube were measured. According to the experimental results, as the amounnt of multi-walled carbon nanotube increased, plastic viscosity and yield stress of cement paste specimens also increased. It was also found that such effect was higher with lower w/c cement paste specimens. With respect to the compressive strength, it was maximized at carbon nanotube content of 0.1wt.% for w/c 0.30 cement paste, whereas the maximum strength of w/c 0.40 cement paste was observed with carbon nanotube content of 0.2wt%.

• Composites Research
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• v.35 no.3
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• pp.134-138
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• 2022

In this study, Ti powder/Polymer concrete composites were processed by adding the PZT powder, one of the piezoelectric materials, to improve the vibration damping effect of Polymer concrete. Ti powder was added at a constant ratio in order to maximize the vibration damping effect using the piezoelectric effect. Three types of composite material specimens were prepared: a specimen without PZT powder, specimens with 2.5 wt% and 5 wt% of PZT powder. The vibration characteristics and compression properties were analyzed for all specimens. As a result, it was confirmed that as the addition ratio of PZT powder increased, the Inertance value at the resonant frequency decreased due to the piezoelectric effect when the vibration generated from Ti powder/polymer concrete was transmitted. Especially, the Inertance value was decreased by about 19.3% compared to the specimen without PZT at the resonant frequency. The change in acceleration with time also significantly decreased as PZT powder was added, confirming the effect of PZT addition. In addition, through the compression strength test, it was found that the degree of deterioration in compression properties due to the addition of PZT up to 5 wt% was insignificant, and it was confirmed that the powder was evenly dispersed in the composites through the cross-sectional analysis of the specimen.

• Explosives and Blasting
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• v.21 no.4
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• pp.23-35
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• 2003

This study is to clarify the comparative relationship and a mechanical anisotropy of rock on the subject of granite distributed in the Namwon area Uniaxial compressive and Brazilian strengths with respect to the horizontal and vertical axes of granite are shown the linear relation. In the case of the result of the p-wave velocity measurement. it is represented that the velocity of vortical direction is faster about 10 to 15% than other two horizontal directions. The difference between velocities is caused by a developmental pattern of microcracks distributed in rock. Moreover, this result is very consistent with the result investigated through thin sections. The proportion of uniaxial compression strength to Index of point load strength ($Is_{(50)}$) is 18~20 times in case of granite. Uniaxial compressive strength is relatively good relationship with point load strength, Schmidt hammer rebound value, and tensile strength point load strength of them is the best comparative relationship. It is indicated that point load test is the most useful tool to estimate uniaxial compressive strength, comparing with other experimental methods.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.177-177
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• 2011

현재 대부분 사용되는 지하매설물용 뒤채움재는 다짐공법을 많이 사용하고 있으며, 실제로 이러한 방법은 부적절한 다짐으로 인해 침하 및 내구성 저하로 인해 파손을 초래하는 경우가 많다. 이러한 문제를 해결 할 수 있는 하나의 대안으로 유동성 뒤채움재를 이용할 수 있다. 유동성 뒤채움재는 초기 유동성, 시간에 따른 자기 강도 발현 무다짐공법 적용 등 많은 장점을 가지고 있다. 본 연구에서는 현장발생토사, 정수장슬러지 및 폐타이어분말 등 재활용 재료를 이용한 유동성 뒤채움재의 기본물성을 평가하였다. 각각의 재활용재료에 대한 입도 및 비중을 평가하였고, 최적배합설계를 결정하였으며, 모형 시험과 유한요소 해석을 위한 기본 물성값을 위해 일축압축시험, 삼축압축시험, 공진주시험 등을 수행하였다. 최적배합설계를 산정하는 과정에서 수행한 실험중 대표적인 시험으로 자가수평능력 및 자기다짐등에 필요한 유동성을 판단하는 Flow시험(ASTM D 6133) 결과 기준으로 정한 20cm이상의 값을 얻을 수 있었으며 일축압축강도의 경우 시공 후 유지 보수가 용이한 강도인 $3.0kg/cm^2{\sim}5.6kg/cm^2$이하로 설계하였으며 28일재령 일축압축강도 결과 $3.15{\sim}3.74kg/cm^2$라는 유지보수에 적당한 결과값을 나타내었다. 이 배합이 현장에서 사용이 가능하다는 것으로 판단하고 현장모형시험과 유한요소해석를 통하여 현장에서 사용하였을 때 관의 변형과 관에 작용하는 하중변화를 확인하고 현장모형시험과 유한요소해석 간의 상관관계를 규명하였다. 현장 모형 시험은 현장과 비슷하게 제작된 모형을 이용하였으며 최대한 현장과 비슷한 조건에서 뒤채움재를 타설과정 중과 타설이 완료된 상태에서 7일 양생 후 하중재하와 같이 두가지 경우에서 수직 수평토압, 관의 수직 수평변위, 관의 종단변형을 측정하였다. 유한요소해석 프로그램은 Midas GTS를 이용하여 실시하였으며 관의 변형률, 유효응력을 측정하여 규명하였다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.5C
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• pp.211-220
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• 2012

Coarse granular materials such as gravel, rubble is used as major fill materials in earth structures of railway, road and dam. Therefore, it is essential to accurately evaluate properties of these materials for reasonable design and construction. In the precedent study, we built large triaxial testing system and verified system compliance with a focus on the dynamic properties. And we could secured the reliability of the system. In this study, the cyclic triaxial tests were performed in various experimental conditions on coarse granular material. Two series of parallel graded samples are prepared by mixing crushed rock. The influence of grain size, loading pattern, loading frequency, and fine contents were analyzed and discussed.

• Resources Recycling
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• v.17 no.4
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• pp.30-36
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• 2008

The preparation of porous lightweight materials as well as the measurement of physical properties has been performed by using SSA(sewage sludge ash) as the raw material. For this aim, two types of lightweight filler, that is, perlite and silica sphere were employed respectively and bentonite was also used as an inorganic binder. The properties of lightweight specimen calcined at 1,000 were measured in terms of density, compressive strength, thermal conductivity and sound absorption to examine the effect of material composition as well as the preparation condition on the properties of lightweight material. As a result, the density of specimen prepared with perlite was ranged from 1.23 to $1.37g/cm^3$ and the compressive strength was ranged from 242.3 to $370.5kg/cm^2$. In case of specimen prepared with silica sphere, it was found that the compressive strength was less than $100kg/cm^2$ even though density was lower than that of specimen with perlite. As far as the thermal conductivity of specimen was concerned, it was ranged from 0.3 to $0.5W/m^{\circ}K$ depending on material composition so that the insulation effect was superior to conventional concrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.1
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• pp.69-75
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• 2012

The study was conducted to determine the effects of adding pig blood as an admixture to both mortar and concrete. The mortar tests included the determination of its unit weight, flow and its compressive strength. Moreover, the concrete test includes the determination of air content, slump, bleeding, setting time compressive strength and freeze-thaw resistance of the material. As the test result, the utilization of pig blood, as an additive to both mortar and concrete mixtures causes air entrainment. The mortar flow increased and both the unit weight and the compressive strength of mortar decreased. As the blood replacement rate increases, the air content decreases over time, the setting and amount of bleeding showed a tendency to decline and reduced compressive strength, and the freeze-thaw resistance of the concrete increased.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 2002.05a
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• pp.17-17
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• 2002

국내 제지 산업에서 큰 비중을 차지하고 있는 골판지 원지는 주로 국내에서 발생되는고지를 원료로 생산되고있다. 2001년 제지 통계에 따르면 우리나라의 고지재활용율은 세계 최고 수준으로 지류 재활용 비율이 약 72%에 달하며 그중 국산 폐지사용량은 해마다 꾸준히 증가하여 2001년 62%에 이르렀다. 하지만 고지의 재활용율이 증가함에 따라 많은 기술적, 품질적 문제가야기되어 강도저하, 공정 및 품질 저하가 날로 심각해지고있는 것이 현실이다. 본 연구에서는 국내 골판지 원지의 해섬특성을 알아보고 조성이 상이한 원료 물질의 해섬특성 곡선을 조사한 후 골판지 원지의 원료로 가장 널리 사용되고 있는 KOCC의 물성개선 가능성을모색하기 위해 분급 및 기계적 처리를 적용하고 도입 효과를 살펴보았다. 다양한 조성으로 구성된 OCC 고지의 해리에 따른 해섬 현상을 살펴보기 위해 각각의 원지와 조성이 상이한 원료물질의 해섬 특성 곡선을 조사하였다. 저농도 해리기를 이용하여 농도와 revolution의 변수를 주어 해리를 실시하고 스크린을 이용하며 미해리분을 측정하여 해섬 특성 곡선을 평가하였다. 또한 가장 널리 사용되고 있는 원료인 KOCC의 분급에 의한 물성 개선 가능성을 모색하기 위해 실험실적인 모텔링에 의한 분급과 기계적인 처리를 실시하여 물성을 평가하였다. 모델링은 UKP와 KOCC 100%인 골판지 원지를 이용하였으며 압축강도, 인장강도, 파열강도를 측정하였다. 현장에서의 적용가능성을 살펴보기 위해 현장에서의 Multi fractor를 이용하여 분급된 지료를 채취하여 물리적인 처리를 가한 후 수초하여 물성을 평가하였다. 그 결과 분급 및 기계적인 처리에 의한 펄프의 특성은 단섬유의 재활용에 대한 고려가 있을 경우 물성개선을 위한 해결방법으로 활용될 수 있다고 판단되었다.