• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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• pp.151-155
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• 2003

An apparatus was developed to repetitively apply a -196 $^{\circ}C$ thermal load to coupon-sized mechanical test specimens. Using this device, IM7/5250-4 (carbon / bismaleimide) cross-ply and quasi-isotropic laminates were submerged in liquid nitrogen (L$N_2$) 400 times. Ply-by-Ply micro-crack density, laminate modulus, and laminate strength were measured as a function of thermal cycles. Quasi-isotropic samples of IM7/977-3 (carbon / epoxy) composite were also manually cycled between liquid nitrogen and an oven set at 120 $^{\circ}C$ for 130 cycles to determine whether including elevated temperature in the thermal cycle significantly altered the degree or location of micro-cracking. In response to thermal cycling, both materials micro-cracked extensively in the surface plies followed by sparse cracking of the inner plies. The tensile modulus of the IM7/5250-4 specimens was unaffected by thermal cycling, but the tensile strength of two of the lay-ups decreased by as much as 8.5 %.

• 대한치과보존학회:학술대회논문집
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• 대한치과보존학회 2001년도 추계학술대회(제116회) 및 13회 Workshop 제3회 한ㆍ일 치과보존학회 공동학술대회 초록집
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• pp.560.1-560
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• 2001

To evaluate the micro-shear bond strength of current adhesive systems to cervical and mid-coronal enamel. Materials and Two commercially available resin adhesives were investigated; a self-etching primer system(Clearfil SE Bond, Kyraray) and a one-bottle adhesive system(Single Bond, 3M) intended for use with the total-etch wet-bonding technique were employed. Two regions of enamel, cervical and mid-coronal regions, were chosen from the buccal surface of extracted molars and were then bonded with each adhesive system and submitted to the micro-shear bond test.(중략)

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 추계학술대회논문집
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• pp.276-279
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• 2004

The factors affecting Ni-Co alloy electroforming were investigated to determine the optimum bath composition and electroplating parameters, like pH, temperature, and current density, suitable for high speed fabrication of a micro mold with longer lifetime. To obtain alloy deposits having uniform thickness and composition, electroplating parameters were finely tuned with home-made electroforming apparatus. Ni-Co alloy deposits had linearly increased Co with $Co^{2+}$ ion concentration in electroplating bath, and showing $412H_v$ of Victors hardness at $23wt\%$ of Co content. For Ni-Co alloy, sulfonate and diol related organic additives were very effective to alleviate its residual stress and surface roughness. The maximum deposition rate was $106{\mu}m/hr$ at 10ASD and the tensile strength of alloy deposit was 2 times larger than that of Ni only case.

• 한국정밀공학회지
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• 제25권7호
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• pp.124-130
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• 2008

The effect of nitrogen gas pressure in arc ion plating on surface properties of the TiN-coated high speed steel(SKH51) is presented in this paper. The surface roughness, micro-particle, micro-hardness, coated thickness, atomic distribution of TiN, and adhesion strength are measured fur various nitrogen gas pressures. It has been shown that the nitrogen gas pressure has a considerable effect on the surface roughness, adhesion strength, atomic distribution of TiN, and surface deposition of TiN of the high speed steels but that it has little influence on the micro-hardness and coated thickness.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2018년도 추계 학술논문 발표대회
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• pp.75-76
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• 2018

MiDF, Micro Defect Free concrete, is the concrete made for high strength development by minimizing the defects such as micro pore and ITZ. Since MiDF exhibits strength through hydro-thermal synthesis reaction, it is essential to select the optimum C/S mole ratio. In this study, the basic characteristics of MiDF were evaluated by controlling the C/S mole ratio by SF and QP.

• 한국공작기계학회논문집
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• 제16권6호
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• pp.193-200
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• 2007

Micro forming is a suited technology to manufacture very small metallic parts(several $mm{\sim}{\mu}m$). Al5083 superplastic alloy with very small grains has a great advantage in achieving micro deformation under low stress due to its relatively low strength at a specific high temperature range. Micro forming of $Zr_{62}Cu_{17}Ni_{13}Al_8$ bulk Metallic glass(BMG) as a candidate material for this developing process are feasible at a relatively low stress in the supercooled liquid state without any crystallization during hot deformation. In this study, the micro formability of Al5083 superplastic alloy and bulk metallic glass, $Zr_{62}Cu_{17}Ni_{13}Al_8$, was investigated with the specially designed micro vibration forming system using pyramid-shape, V-shape and U-shape micro die pattern. With these dies, micro vibration forming was conducted by varying the applied load, time. Micro formability was estimated by comparing the hight of formed shape using non-contact surface profiler system. The vibration load effect to metal flow in the micro die and improve the micro formability of Al5083 superplastic alloy and $Zr_{62}Cu_{17}Ni_{13}Al_8$ bulk Metallic glass(BMG).

• 한국지반공학회논문집
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• 제22권10호
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• pp.77-91
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• 2006

국내 숏크리트 관련 기술들은 지금까지 많은 발전을 이루어 왔으나 재료, 시공 및 관련 품질규격 등에서 여전히 문제들을 가지고 있다. 국외의 경우 $39.2{\sim}58.8 MPa$에 이르는 고강도 숏크리트 시공이 가능하여 터널에서 2차 라이닝의 대체나 장기내구성의 확보가 충분히 가능한 반면, 국내의 경우 설계강도가 20.6MPa 내외로 낮은 편이며 장기내구성도 신뢰하지 못하고 있는 실정이다. 본 연구에서는 국내 숏크리트의 강도 증진을 위해 고품질 혼화재와 고성능 급결제를 적용한 현장실험을 실시하였고, 유럽통합규격(EFNARC)에 의거하여 품질평가를 수행하였다. 또한, 탄산화와 동결융해의 복합인자에 의한 열화시험을 수행하여 고강도 숏크리트의 장기내구성을 평가하였다. 실험결과 알칼리 프리계 급결제를 사용한 경우 초기강도 증진율이 $90{\sim}97%$로 가장 높게 나타났고, 실리카 흄을 혼입한 숏크리트의 압축강도는 $45.2{\sim}55.8MPa$, 휨강도는 $5.01{\sim}6.66MPa$로 혼입하지 않은 경우에 비해 각각 $37{\sim}79%$, $17{\sim}61%$의 강도 증진 효과가 나타났다. 또한, 실리카 흄 치환율이 $7.5{\sim}10%$일 때 강도증진 효과가 가장 우수한 것으로 나타났다. 특히, 실리카 흄의 치환은 강섬유 혼입에 의한 숏크리트의 열화현상을 최소한으로 감소시켜, 숏크리트의 장기내구성을 확보하는데 효과가 있음을 알 수 있었다.

• 대한토목학회논문집
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• 제26권2C호
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• pp.121-131
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• 2006

국내 숏크리트 강도기준은 고강도 숏크리트의 개발과 적용이 활발한 유럽과 비교해 볼 때 상대적으로 낮게 설정되어 있어서 고강도 숏크리트의 품질을 평가하기에는 어려움이 있다. 본 연구에서는 국내 숏크리트의 강도증진과 장기 내구성을 향상시킬 수 있는 방법을 모색하기 위해 현장실험을 실시하였다. 현장실험은 고품질 혼화재와 고성능 급결제를 적용한 고강도 숏크리트를 지향하였고, 숏크리트의 강도증진에 미치는 혼화재와 급결제의 영향을 파악하고자 하였다. 그리고 유럽통합규격(EFNARC)에 의거하여 품질평가를 수행하였는데, 실험결과 알칼리프리계 급결제를 사용한 경우의 초기강도 증진율이 90~97%로 가장 높게 나타나 초기강도 증진효과에 알칼리프리계 급결제가 효과적이었다. 또한, 실리카 흄을 혼입한 숏크리트는 압축강도가 45.2~55.8MPa, 휨강도가 5.01~6.66MPa로 혼입하지 않은 경우에 비해 각각 37~79%, 17~61%의 강도증진 효과가 나타났고, 실리카 흄 치환율은 7.5~10%일 때 강도증진 효과가 가장 우수한 것으로 나타났다. 현장실험 결과 국내 숏크리트의 고강도화를 위해서는 알카리프리계 급결제와 실리카 흄과 같은 고품질 혼화재의 사용이 필요할 것으로 판단된다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.991-996
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• 2004

Plastics are widely used in industry, because they are light, easily manufactured, and have high specific strength. And many researches to increase the strengths and to reduce the price are being conducted at now. One of these researches is concerning to additives. Foaming techniques are used to endow insulation properties, to improve specific strength, or reduce the material cost. Due to their unique properties, foamed plastics are applied to refrigerator, pipe, and insulators. Micro-cellular foaming is the latest foaming technique that was invented at 1980 in MIT. It is known that many tiny small cells are generated in the polymer matrices and micro-cellular foamed plastics show relatively high specific strength. We investigated the role of CaCO3 which is one of the most widely used additives in plastics industry as an additive for nucleation in view of cell morphology. CaCO3 used in this paper was treated to increase the dispersibility and to lower the density, so it has many pores at his body. Two experiments were conducted, in order to check the role of an additive for nucleation. One is compound-ability and the other one is role of nucleation agents.

• 한국전기전자재료학회논문지
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• 제25권10호
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• pp.779-785
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• 2012

The epoxy/micro-and nano-mixed silica composites(EMNC) systems were prepared and the AC insulation breakdown strength was evaluated. Glass transition temperature (Tg) and crosslink density were also measured by dynamic mechanical analyzer(DMA) in order to correlate them with the electrical and mechanical properties, and the effect of silane coupling agent on the electrical properties was also studied. Electrical properties and crosslink density of epoxy/micro-silica composite were noticeably improved by addition of nano-silica and silane coupling agent, and the highest breakdown strength was obtained by addition of 0.5~5 phr of nano-silica and 2.5 phr of silane coupling agent, and the highest tensile and flexural strength were obtained by addition of 2.5 phr of nano-silica.