• 대한의용생체공학회:의공학회지
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• 제17권3호
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• pp.327-336
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• 1996

This study was performed to investigate the effec% of immersion in water and thermal cycling on the mechanical peoperties of light cured restorative composite resins. Five commerically available light-cured composite resins(Photo Clearfil A : CA, Lite-Fil A . LF, Clearril Photo Posterior CP, Prisms AP.H.. PA, 2100 : ZH) were unto The specimens of 12 m in diameter and 0.7 m in thickness were made, and an immersion in $37^{\circ}C$ water for 7 days and a thermal cycling of 1000 cycles at 15 second dwell time each in $5^{\circ}C$ and $55^{\circ}C$ baths were performed. Biaxial flexure test was conducted using the ball-on-three-ball method at the crosshead speed of 0.5mm/min. In order to investigate the deterioration of composite resins during the thermal cycling test, Weibull analysis for the biaxial flexure strengths was done. Fracture surfaces and the surfaces before and after the thermal cycling test were examined by SEM. The highest Weibull modulus value of 10.09 after thermal cycling tests which means the lowest strength variation, was observed in the CP group, and the lowest value of 4.47 was obsered in the LF Group. Biaxial flexure strengths and Knoop hardness numbers significantly decreased due to the thermal cycling ($\textit{p}$< 0.01), however, they recovered when specimens were drie4 The highest biaxial flexure strength of 125.65MPa was observed in the ZH group after the thermal cycling test, and the lowest value of 64.86MPa was observed in the CA group. Biaxial flexure strengths of ZH and CP groups were higher than those of PA, CF, and CA groups after thermal cycling test($\textit{p}$< 0.05). Knoop hardness numbers of CP group after the thermal cycling test was the highest(95.47 $\pm$ 7.35kg/$mm^2$) among the samples, while that of CA group was the lowest(30.73 $\pm$ 2.58kg/$mm^2$). Knoop hardness numbers showed the significant differences between the CP group and others after the thermal cycling test(($\textit{p}$< 0.05). Fracture surfaces showed that the composite resin failure developed along the matrix resin and the filler/resin interface region, and the cracks propagated in the conical shape from the maximum tensile stress zone.

• 항공우주기술
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• 제9권1호
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• pp.143-150
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• 2010

본 연구는 다양한 찬물 온도에 손가락을 침수시켰을 경우 추위유발성혈관확장(Cold-induced vasodilation)이 어떻게 나타나며, 이 반응이 재발현되는지 평가하는데 목적을 두었다. 이를 위해 10명의 건강한 대학생($21.4{\pm}2.5$ yrs, $175.8{\pm}4.1$ cm, $69.6{\pm}7.6$ kg, $11.2{\pm}3.7$ %fat)이 두 번의 실험에 참가하였다. 첫 번째 실험은 상온환경에서 다섯 번의 실험과정 반복으로 이루어졌다. 실험과정은 $43^{\circ}C$의 물에 오른손 가운데 손가락을 5분 동안 담갔다가, 그 후 25분 동안 상온에서 휴식을 가지고, 그 다음 무작위로 물 온도 5, 8, 11, 14, 또는 $17^{\circ}C$ 중 하나에 손가락을 담갔다. 한 과정이 끝나면 다른 수온에서 같은 방식으로 실험이 진행되었다. 재발현 반응을 평가하기 위해 첫 실험 후 최소 5일 후에 같은 방법으로 두 번째 실험이 진행되었다. 실험 중 심박수, 직장온도, 손톱주위온도가 매 6초마다 측정되었다. 결론적으로 재현성에는 최대손가락온도(Tfmax)와 Tfmax-물온도(Tw)에서 재생산 반응을 보였다. 추위자극에 따른 CIVD의 반응은 추위자극이 높을수록 최소손가락온도(Tfmin)와 Tfmax의 반응은 높게 나타났으며, 추위자극이 낮을수록 Tfdiff의 반응은 증가되었다. 그러나 모든 반응시간에는 유의한 차이는 보이지 않았다.

• 한국전기전자재료학회논문지
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• 제16권12호
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• pp.1136-1141
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• 2003

The primary insulation materials used in an oil filled transformer are kraft paper, wood, porcelain and oil. Modern transformers use chemically treated paper to improve its tensile strength and resistance to aging caused by immersion in oil. But these insulation papers are mainly aged by thermal stress. Over the life time of the insulation paper and oil, it is exposed to high temperatures, oxygen and water. Its interaction with the steel of the tank and core plus the copper and aluminium of the windings will eventually cause the chemical properties of the oil to decay. High temperature have an effect on mechanical strength of cellulous paper used in the layer insulation. We made two aging cells in which insulation papers and mineral oil are conducted to test thermal properties. It is measured dielectric strength, number of acid, moisture, etc. of insulation paper and oil aged in the aging cells.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집
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• pp.406-409
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• 2002

The primary insulation system used in an oil-filled transformer is Kraft paper, wood, porcelain and, of course, oil. Modern transformers use paper that is chemically treated to improve its tensile strength properties and resistance to aging caused by immersion in oil. These insulation papers are mainly aged to thermal stress. Over the course of the insulation paper and oil's life it is exposed to high temperatures, oxygen and water. Its interaction with the steel of the tank and core plus the copper and aluminium of the windings will eventually cause the chemical properties of the oil to decay. High temperature have an effect on mechanical strength of cellulous paper using the layer insulation. We made two aging cell in which thermal aging tests of insulation papers and mineral oil are conducted. It is measured dielectric strength, number of acid, moisture, etc. of insulation paper and oil aged in the aging cells.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 제2회 학술대회 논문집 일렉트렛트 및 응용기술전문연구회
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• pp.25-28
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• 2000

In this paper, the technology for accelerating degradation & life estimation on the traction motor was introduced with the stator form-winding sample coils of the 200 Class insulation system The accelerative degradation was performed in 10 cycles, which were composed of thermal stress, fast rising surge voltage, vibration, water immersion and overvoltage applying. After aging of 10 cycles, condition diagnosis test such as insulation resistance & polarization index, capacitance & dielectric loss and partial discharge properties were investigated in the temperature range of $20{\sim}160^{\circ}C$. Relationship between degradation conditions and diagnosis results were analyzed to find an dominative degradation factor at the end-life point

• 한국전기전자재료학회논문지
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• 제15권1호
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• pp.93-101
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• 2002

In this study, the stator form-winding sample coils based on silicone resin and polyimide were made for fault prediction and reliability estimation on the C-Class(200$\^{C}$ ) insulation system of traction motors. The complex accelerative degradation was periodically performed during 10 cycles, which was composed of thermal stress, fast rising surge voltage, vibration, water immersion and overvoltage applying. After aging of 10 cycles, the condition diagnosis test such as insulation resistance '||'&'||' polarization index, capacitance '||'&'||' dielectric loss and partial discharge properties were investigated in the temperature range of 20 ∼ 160$\^{C}$. Relationship among condition diagnosis tests was analyzed to find a dominative degradation factor and an insulation state at end-life point.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 하계학술대회 논문집
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• pp.763-766
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• 2000

In this paper, stator form-winding sample coils based on silicone resin and polyimide were made for fault prediction and reliability estimation on the 200 Class insulation system of traction motors. The complex accelerative degradation was performed by periods during 10 cycles, which was composed of thermal stress, fast rising surge voltage, vibration, water immersion and overvoltage applying. After aging of 10 cycles, condition diagnosis test such as insulation resistance & polarization index, capacitance & dielectric loss and partial discharge properties were investigated in the temperature range of 20∼160$^{\circ}C$. Relationship among condition diagnosis test was analyzed to find an dominative degradation factor and an insulation state at end-life point.

• 대한치과보존학회:학술대회논문집
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• 대한치과보존학회 2003년도 제120회 추계학술대회 제 5차 한ㆍ일 치과보존학회 공동학술대회
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• pp.605-605
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• 2003

Novel silane coupling agents containing hydrophobic phenyl group 3-(3-methoxy-4-methacryloyloxyphenyl) propyl-trimethoxysilane(p-MPS), -triisocyanatesilane (p-MBI), -trichlorosilane (p-MBC) were synthesized. The bonding durability of these silanes against water immersion and thermal stress was investigated. 3-methacryloyloxypropyltrimethoxysilane (3-MPG) was used as a control. The glass modified with those silanes at a concentration of 2wt％ were kept for 3 minutes at $120^{\circ}C$, and then were bonded to the heaped metal with self-cured resin composite.(omitted)

• 터널과지하공간
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• 제14권1호
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• pp.69-77
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• 2004

암석의 시간 의존 변형거동은 암석의 가장 근본적인 역학적 성질 중의 하나이며, 크립거동의 특성과 메커니즘에 대한 연구는 지하 암반 구조물의 장기적 안정성을 평가하는데 필수적이라 할 수 있다. 이에 본 연구에서는 국내 화강암을 대상으로 단축압축하중 하에서 크립시험을 실시하였고, 수분과 응력 수준을 달리하여 각각의 조건에 따른 크립 특성을 비교, 분석하였다. 크립시험 결과 화강암은 1차, 2차 및 3차로 확연히 구분된 크립거동을 보였다. 1차 크립거동은 대체로 24시간 내에 종결되었으며, 2차 크립 변형률은 단축압축강도에 대한 재하응력의 비율이 증가함에 따라 증가하였다. 일정 응력하에서 화강암의 최대강도는 시간에 따라 감소하는 경향을 보였다. 완전 포화된 시료는 자연 건조된 시료보다 훨씬 큰 크립 변형량 및 변형률을 보였으며, 포화시료의 파괴강도 및 파괴시간은 급격히 감소하였다. 본 연구의 크립시험 결과를 버거모델(Burger's model) 및 이전 연구자들에 의해 제안된 두 개의 경험적 모델에 적용하여 크립의 유동상수를 구하였다. 세 개의 모델 모두 화강암의 크립거동을 잘 나타내었으나, 그 중 버거모델이 실험결과와 가장 잘 일치하였다. 각각의 모델에서 결정된 유동상수들은 함수량과 응력 수준에 영향을 받았다. 또한 본 실험결과에 기초하여 자연건조 및 완전 포화된 화강암 시료에 대하여 응력 수준과 시간의존변형의 경험적 관계식을 유도하였다.

• Corrosion Science and Technology
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• 제13권5호
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• pp.186-194
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• 2014

Establishment of adhesion strength measurement procedure for marine epoxy coatings was conducted in order to ensure reliability of the test results. It was found that (1) the increase in thickness of the substrates would induce increase of pull-off strength. Especially, the increase in adhesion strength with the substrate thickness increment was attributed to the transition of stress mode to the pure tensile mode excluding bending effect. (2) The longer curing time, the higher pull-off strength. It may be due to higher cross-linking density of the coating (3) The pull-off strength increases as coating thickness increases due to the diminishment of bending effect (4) The longer drying time after water immersion, the higher pull-off strength. It may be due to the evaporation of water molecule at the coating-substrate interface.