• Carbon letters
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• 제9권2호
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• pp.121-126
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• 2008

High modulus pitch based carbon fibers (HM) were exposed to isothermal oxidation using tube furnace in carbon dioxide gas to study the oxidation kinetics under the temperature of $800-1100^{\circ}C$. The kinetic equation $f=1-{\exp}(-at^b)$ was introduced and the constant b was obtained in the range of 1.02~1.42. The oxidation kinetics were evaluated by the reaction-controlling regime (RCR) depending upon the apparent activation energies with the conversion increasing from 0.2 to 0.8. The activation energies decrease from 24.7 to 21.0 kcal/mole with the conversion increasing from 0.2 to 0.8, respectively. According to the RCR, the reaction was limited by more diffusion controlling regime for the HM fibers with the conversion increasing. Therefore, it seems that the oxidation which is under the diffusion controlling regime takes place continuously from the skin to the core of the fiber.

• 한국세라믹학회지
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• 제21권1호
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• pp.51-59
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• 1984

In this paper mechanical properties of reaction-bonded silicon nitride are studied with the variation of initial nitrogen partial pressure. At 1, 25$0^{\circ}C$ the amount of nitridation and the nucleation of nitride increase linearly with the nitrogen partial pressure increase. After the nitridation is completed the density of nitride and modulus of rupture at room temperature are increased with the amount of nitridation. When the partial pressure of nitrogen is 0.5 atm the specimen show the optimum properties that is the highest density of nitride and modulus of rupture. Also the microstructure of $\alpha$-matte is deveoped very well at that pressure of nitrogen which contributes to the strength development of specimen. It is shown that with proper control of initial partial pressure of nitrogen high strength silicon nitride body can be manufactured for dynamic applications.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.1707-1711
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• 2008

Landing pier is connect from onshore to offshore with bridge type that a coast structure. The sub-structure is consisted of vertical or batter pile and combined reinforced concrete slab. These days useful design method of quay wall of landing pier type for pile foundation analysis abide by approximate depth of pile supported method, "Harbor and port design criterion, 2005 The ministry of land transport and maritime affairs". The approximate depth of pile supported is calculated two kind of method that one is assume to below depth of 1/$\beta$ from assumed submarine surface and other is 1st fixpoint depth by Chang(1937)'s theory. By this paper, FEM dynamic analysis of 3-dimensions was achieved that it has compared pile fixed end modeling with elastic spring modeling base on winkler theory.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1998년도 가을 학술발표회 논문집
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• pp.183-190
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• 1998

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 가을 학술발표회 논문집
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• pp.411-418
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• 2002

In domestic road construction sites, the compaction control based on strength are widely performed through the direct method with high accuracy, such as Plate Loading Test or Field CBR test. It is impossible to manage all construction sites using the direct method because the direct method requires heavy reaction loads and long measurement time. Therefore, it is necessary to apply the indirect method that could control the relative density of construction sites on the whole. Indirect methods, such as Cone Penetration Test and Fall Cone Test, require extra time for data analyzing and fixed area for test device. In this paper, the field applicability of Soil Impact Hammer (SIH) was investigated comparing with the results of field measurement tests and laboratory compaction tests. SIH developed by Japan Construction Administration and Asanuma Ltd., is a kind of indirect methods for compaction checking. According to the results of SIH performed in domestic road construction site, the subgrade reaction modulus obtained from SIH are similar to that from Plate loading tests in the range of 10 to 40. In comparison with laboratory compaction test, similar compaction line are shown in the dry side of optimum moisture contents.

• 유변학
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• 제11권1호
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• pp.9-17
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• 1999

본 연구에서는 페놀 수지/탄소섬유 복합재료가 상온에서부터 $400^{\circ}C$까지의 온도범위에서 유리 전이와 분해반응을 경험하면서 나타내는 점탄성 특징을 연구하였다. 가교 결합된 페놀메트릭스의 전형적인 유리전이에 따라 저장 탄성율(storage modulus)은 유리전이에 의하여 감소하였고 고무상태(rubbery state)에 도달함과 동시에 후경화 반응과 분해 반응 등을 포함하는 복합적인 고온반응에 의하여 증가하다가, 최대점을 보인 후 다시 감소하는 모습을 보였다. 유리전이 과정은 시간-온도 중첩원리에 따라 해석하였으나, 분해반응이 수반된 고온에서의 점탄성 특징은 저장 탄성율을 수직 및 수평 방향으로 이동시키어 마스터 커브를 완성 할 수 있었다. 이러한 실험적 결과를 토대로 아레니우스식과 Havriliak-Negami식에서 유추된 점탄성 모델을 이용하여 유리전이와 분해반응이 연속적으로 진행되는 과정을 정량적을 해석할 수 있었다. 이때의 완화시간은 유전이 과정을 통하여 감소하다가 고무상태에 이르러 최소값을 보여주고 이후로는 고온반응에 의하여 증가하는 모습을 보여주었다. 본 연구에서 제안된 점탄성 해석 방법은 반응이 수반된 열경화성 복합재료가 보여주는 점탄성 계수의 복잡한 거동을 온도와 주파수(frequency)에 따라 정확하게 묘사함으로서 이 모델링의 유용성을 증명 할 수 있었다.

• 유변학
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• 제10권4호
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• pp.227-233
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• 1998

잠재성 경화제인 N-benzylpyrazinium hexafluoroantimonate(BPH)를 Cycloaliphatic계 에폭시 (CAE)/DGEBA계 에폭시의 혼합물에 1 mol% 첨가 시킨 후 혼합 조성비에 따른 유변학적 특성과 경화 동력학에 대해 연구하였다. 잠재특성은 등온 DSC를 이용하여 각각 $150^{\circ}C$와 $50^{\circ}C$의 반응 온도에 대한시간의 함수로서 전화량을 구하여 측정하였다. 블렌드 시스템의 유변학적 특성은 레오미터를 사용한 등온 실험을 통하여 storage modulus (G'), loss modulus (G") 그리고 damping factor (tan$\delta$)를 구한 후 이들 데이터로부터 겔화 시간을 측정하였다. 겔화 시간과 경화 온도를 Arrenius equation에 적용시킨 결과 가교 활성화 에너지 ($E_c$)를 구할 수 있었으며 겔화 시간과 활성화 에너지 모두 DGEBA의 함량이 증가할수록 증가하였다. 경화 활성화 에너지 ($E_a$)를 동적 DSC를 이용하여 Kissinger method에 의해 구하였는데 활성화 에너지는 CAE의 함량이 증가할수록 감소함으로써 높은 반응성을 나타내었는데, 이는 짧은 반복 단위와 단순한 곁사슬기 그리고 반응 매질 내의 점도 등에 기인한다.기인한다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.501-506
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• 2001

An experimental study was carried out to investigate recycling of an oyster shell, which is disposed in open-dumped way at coastal oyster factory area. For this purpose, the chemical component and reaction of oyster shell with cement paste was examined. And, the characteristics of hardened concrete was quantitatively investigated in terms of fineness modulus and blending rate of the crushed oyster shell. Test results show that interaction between oyster shell and cement paste was not occurred and the crushed oyster shell can be used as the fine aggregate of concrete. And it is found that blending of an oyster shell caused not to reduce the 28 day compressive strength of concrete. Elastic modulus of the concrete blended with crushed oyster shells decreases with increases the blending rate which the modulus reduced about 10% when oyster shells is blended up to the 20% of the sand substitution.

• Fibers and Polymers
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• 제5권1호
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• pp.59-67
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• 2004

The development of high tenacity, high modulus monofilaments from Polypropylene/Clay nanocomposite has been investigated. Pure sodium montmorillonite nanoclay was modified using hexadecyl trimethyl ammonium bromide (HTAB) via an ion exchange reaction. Pure and modified clay were characterized through X-ray diffraction, FTIR and TGA. The modified clay was melt blended with polypropylene (PP) in presence of a swelling agent. Composite filaments from PP/Clay nanocomposite were prepared at different weight percentages of nanoclay and the spinning and drawing conditions were optimized. The filaments were characterized for their mechanical, morphological and thermal properties. The composite PP filaments with modified clay showed improved tensile strength, modulus and reduced elongation at break. The composite filaments with unmodified clay did not show any improvement in tensile strength but the modulus improved. The sharp and narrow X-ray diffraction peaks of PP/nanoclay composite filaments indicate increase in crystallinity in presence of modified clay at small loadings (0.5 %). The improved thermal stability was observed in filaments with modified as well as unmodified clays.

• 한국철도학회논문집
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• 제3권1호
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• pp.34-41
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• 2000

The analysis of static and dynamic characteristics of reinforced roadbed materials was performed through model and laboratory tests. The strength characteristic of reinforced roadbed materials such as HMS-25 and soil were investigated through the unconfined axial compression test, the model soil box test and the combined resonant column and torsional shear test. The unconfined axial compression strength of HMS-25 shows a steady increasement in strength due to the chemical hardening reaction between HMS-25 and water. The result of model soil box test reveals that railroad roadbed of HMS-25 is better than that of soil in several aspects, such as, bearing capacity and settlement. The combined resonant column and torsional shear test result indicates that shear modulus of HMS-25 and soil increase with the power of 0.5 to the confining pressure and linear relationship to normalized shear modulus and damping ratio.