• Composites Research
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• 제27권6호
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• pp.236-241
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• 2014

본 연구에서는 공항 포장용 유지보수 재료로 사용되는 폴리머 콘크리트의 자외선 노출에 대한 기계적 물성 변화를 확인하기 위해 자외선 노출 전/후 시편의 압축강도 및 연성인자의 변화를 평가하였다. 현재 공항 포장용으로 사용되는 폴리머 콘크리트의 비율과 선행연구를 통해 얻은 최적 배합비율을 참고하여 시편을 제작하였다. 자외선 발생 램프의 출력을 고려하여 자연상태에서 노출되는 등가시간을 계산한 후 최대 3년에 해당하는 시간만큼의 등가시간 동안 시편을 노출시켰다. 실험결과, 자외선 노출 자체는 재료물성에 거의 영향을 주지 않았으며, 자외선 노출에 따른 온도상승에 의한 재료물성 변화가 주로 관찰되었다. 자외선에 의해 발생된 열에 노출된 후 모든 시편에서 인성은 감소하고, 압축강도는 증가하는 경향을 나타내었다.

• 대한기계학회논문집A
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• 제30권3호
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• pp.249-259
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• 2006

Stress and displacement fields of a propagating Mode III crack in an orthotropic functionally gradient material (OFGM), which has (1) linear variation of shear modulus with a constant density, and (2) an exponential variation of shear modulus and density, are derived. The equations of motion in OFGM are developed and solution to the displacement and stress fields fer a propagating crack at constant speed though an asymptotic analysis. The stress terms associated with $\gamma^{-1/2}\;and\;\gamma^{0}$ are not affected by the FGM constant $\zeta$ which is nonhomogeneous parameter, only on the higher order terms, the influences of nonhomogeneity on the stress are explicitly brought out. When the FGM constant $\zeta\;is\;zero\;or\;\gamma{\rightarrow}0$, the fields for OFGM are almost same as the those for homogeneous orthotropic material. Using the stress components, the effects of nonhomogeneity on stress components are discussed.

• 한국산학기술학회논문지
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• 제8권3호
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• pp.472-476
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• 2007

본 연구에서는 p-형 ZnO 박막 증착법 및 특성의 안정화 방안에 대하여 조사하였다. p-형 ZnO는 AlAs와 ZnO target을 사용하여 RF magnetron sputtering 기법으로 co-deposition하여 제작하였으며 특성 변화를 조사하기 위해 $250^{\circ}C$에서 144시간까지 스트레스 인가 시간을 변화하며 Photoluminescence 및 Hall 측정을 수행하였다. 연구 결과 co-deposition 은 p-형 박막을 제작하기 위해 유효한 방법인 것으로 밝혀졌으며, 특히 고온에서 이루어지는 과정을 수행하기 전 30% H2O2용액에 1분간 처리하는 것이 이후의 열처리 과정 중 발생하는 특성 변화를 크게 억제하는 것으로 관찰되었다.

• Journal of the korean society of oceanography
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• 제38권4호
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• pp.166-172
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• 2003

Multi­Sensor Core Logger (MSCL) is a useful system for logging the physical properties (compressional wave velocity, wet bulk density, fractional porosity, magnetic susceptibility and/or natural gamma radiation) of marine sediments through scanning of whole cores in a nondestructive fashion. But MSCL has a number of problems that can lead to spurious results depending on the various factors such as core slumping, gas expansion, mechanical stretching, and the thickness variation of core liner and sediment. For the verification of MSCL data, compressional wave velocity, wet bulk density, and porosity were measured on discrete samples by Hamilton Frame and Gravimetric method, respectively. Acoustic impedance was also calculated. Physical property data (velocity, wet bulk density, and impedance) logged by MSCL were slightly larger than those of discrete sample, and porosity is reverse. Average difference between MSCL and discrete sample at both sites is relatively small such as 22­24 m/s in velocity, $0.02­-0.08\;g/\textrm{cm}^3$ in wet bulk density, and 2.5­2.7% in porosity. The values also show systematic variation with sediment depth. A variety of factors are probably responsible for the differences including instrument error, various measurement method, sediment disturbance, and accuracy of calibration. Therefore, MSCL can be effectively used to collect physical property data with high resolution and quality, if the calibration is accurately completed.

• 한국주조공학회지
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• 제31권4호
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• pp.191-197
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• 2011

Transparent organic materials have been frequently used as an analog of the solidifying metallic materials, because their transparency permits an in-situ observation of the microstructural development during solidification through optical microscopy. Pivalic acid (PVA)-ethanol system showing an anisotropic property in solid-liquid interfacial energy and interface kinetics was adopted in the present experiment, and the detailed experiments performed are as follows: (1) variation of dendrite tip temperature with growth velocity, (2) correlation between primary dendrite arm spacing (${\lambda}_1$) and the growth orientation away from the heat flow direction (tilt angle: ${\theta}$), (3) variation of dendrite tip radius (R) with growth velocity (V), (4) dendrite tip stability parameter (${\sigma}^*$) and its dependence on the concentration. Concerning the correlation between the dendrite tip temperature and growth velocity the present result is well suited to Hunt-Lu equation. As the tilt angle increases, the average primary dendrite spacing tends to increase.

• 대한조선학회논문집
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• 제47권4호
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• pp.598-605
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• 2010

The structural design of oil tankers and bulk carriers should be performed based on the Common Structural Rules(CSR) which were recently established by the International Association Classification Societies(IACS). At first, in the structural design viewpoint, the scantling and hullweight based on the CSR should be compared with those of existing rules, and then a minimum weight/cost design should be performed by considering the variation of the number of web and the material property. In this study, the optimum web space and material property will be proposed by performing a minimum weight/cost design of a large oil tanker, and the results will be compared with those of existing ship. The longitudinal members are determined by SeaTrust-Holdan developed by the Korean Register of Shipping(KR), and the transverse members are determined by NASTRAN and PULS.

• 한국염색가공학회지
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• 제9권6호
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• pp.10-17
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• 1997

In order to improve the anti-static property of several hydrophobic fibers by sputter etching, polyester, polypropylene and poly(p-phenylene sulfide) have been etched by sputtering in the presence of argon gas and the resulting anti-static property investigated by half time decay, the time of water permeation, weight loss rate and scanning electron microscope(SEM). The temporary change and durability of anti-static property of samples treated with sputter etching were evaluated. The results were as follows; 1) Half time decay of samples treated with sputter etching were decreased about 18~38%. According to increasing sputter etching time, half time decay is decreased. 2) The wettability and weight loss rate of treated samples were increased remarkably. According to the SEM photographs, many microcraters on the substrate surface by the sputter etching were observed. 3) Although the washing treatment and the time elapsed after treatment are allowed longer, the variation of half time decay hardly can find.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.442-448
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• 2008

This paper presents an approach to define an optimal piezoactuator length to actively control structural vibration. The optimal ratio of the piezoactuator length against beam length when a pair of piezoceramic actuator and accelerometer is used to suppress unwanted vibration with direct velocity feedback (DVFB) control strategy is not clearly defined so far. It is well known that direct velocity feedback (DVFB) control can be very useful when a pair of sensor and actuator is collocated on structures with a high gain and excellent stability. It is considered that three different collocated pairs of piezoelectric actuators (20, 50 and 100 mm) and accelerometers installed on three identical clamped-clamped beams (300 * 20 * 1 mm). The response of each sensor-actuator pair requires strictly positive real (SPR) property to apply a high feedback gain. However the length of the piezoactuator affects SPR property of the sensor-actuator response. Intensive simulation and experiment shows the effect of the actuator length variation is strongly related with the frequency range of SPR property. A shorter actuator gave a wider SPR frequency range as a longer one had a narrower range. The shorter actuator showed limited control performance in spite of a higher gain was applied because the actuation force was relatively small. Thus an optimal length ratio (actuator length/beam length) was suggested to obtain relevant performance with good stability with DVFB strategy. The result of this investigation could give important information in the design of active control system to suppress unwanted vibration of smart structures with piezoelectric actuators and accelerometers.

• 터널과지하공간
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• 제26권3호
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• pp.154-165
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• 2016

본 연구에서는 산성수 및 하중의 화학 역학적 영향이 암석 물성에 미치는 영향을 파악하기 위한 실내 실험을 실시하였다. 실험에서는 암석시료에 pH 및 하중조건을 부여한 후, 유효 공극률을 포함한 다양한 암석 물성 변화를 측정하였다. 실험결과, 일정한 하중조건에서 암석을 침수시킨 산성수의 pH가 낮을수록 물성 변화가 증가하는 것으로 나타났다. 이는 산성수의 pH가 낮을수록 암석과 산성수 사이의 화학반응 속도가 증가했기 때문으로 예측된다. 또한 일정한 pH의 산성수에 침수된 암석에서 가해진 하중이 증가함에 따라 암석물성 변화가 감소하는 것으로 나타났다. 이는 균열개시응력 이하의 하중에서 발생된 압축으로 암석과 산성수 사이의 화학반응 영역이 감소했기 때문으로 여겨진다.

• 한국안광학회지
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• 제4권2호
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• pp.33-38
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• 1999

다색 광원에 대한 가우시안 진폭을 갖는 광학계의 결상 특성을 조사하기 위하여 다색 광원에 대한 결상 광학계의 색도(chromaticity) 변화와 조도(illuminance) 분포를 계산하였다. 본 논문에서 고려된 다색 광원은 색온도 2,856K인 텅스텐 백열 램프(incandescent-tungsten lamp)를 나타내는 A광원, 대낮의 평균 햇빛(daylight)을 나타내는 C광원, 대낮의 평균 햇빛의 파장영역을 자외선 영역까지 확대하여 보강한 $D_{65}$광원이다. 다색 광원들의 종류에 따라 기하학적 상점에서의 색도 값이 다르게 나타났으며, 기존의 균일한 진폭을 갖는 광학계에 비해 색도 변화가 매우 작게 나타났다. 조도 분포는 다색 광원의 종류에 따라 거의 변화가 없었으며, 초점 심도는 기존의 균일한 진폭을 갖는 광학계에 비해 크게 나타났다. 이러한 결과로부터 결상 광학계에 입사하는 광의 진폭 형태를 균일한 진폭에서 가우시안 형태로 변조시켜줌으로써 초점 심도는 크게, 색도 변화는 작게 할 수 있다.