• 한국재료학회지
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• 제26권11호
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• pp.611-622
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• 2016

Particle morphology change and different experimental condition analysis during composite fabrication process by traditional ball milling with discrete element method (DEM) simulation were investigated. A simulation of the three dimensional motion of balls in a traditional ball mill for research on the grinding mechanism was carried out by DEM simulation. We studied the motion of the balls, the ball behavior energy and velocity; the forces acting on the balls were calculated using traditional ball milling as simulated by DEM. The effect of the operational variables such as the rotational speed, ball material and size on the flow velocity, collision force and total impact energy were analyzed. The results showed that increased rotation speed with interaction impact energy between balls and balls, balls and pots and walls and balls. The rotation speed increases with an increase of the impact energy. Experiments were conducted to quantify the grinding performance under the same conditions. Furthermore, the results showed that ball motion affects the particle morphology, which changed from irregular type to plate type with increasing rotation speed. The evolution was also found to depend on the impact energy increase of the grinding media. These findings are useful to understand and optimize the particle motion and grinding behavior of traditional ball mills.

• 한국자기학회지
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• 제4권4호
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• pp.326-334
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• 1994

친수성-고점도 자성유체를 Nd-영구자석과 병용하여 기름밀봉 장치로의 개발을 목표로 실험 검토하였다. etylene glycol 액상중에 $Fe_{3}O_{4}$를 분산시킨 자성유체는 매질의 비등점이 다른 액상보다 높고 점성이 높아서 기름밀봉 성능을 향상시킬 수 있을 뿐만 아니라 본 장치의 부품중 대부분 을 이루고 있는 철강재를 부식시키지 않았다. 본 자성유체중 $Fe_{3}O_{4}$ 농도가 증가할수록 점도 와 자성율이 증가하여 기름밀봉 성능을 향상시킬 수 있었다. 본 장치는 대기압하에서 기름밀봉 성능이 매우 우수하였다.

• 한국주조공학회지
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• 제31권5호
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• pp.274-283
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• 2011

The vacuum die casting is a promising candidate of the stamping process for fabrication of fuel cell bipolar plate due to its advantages, such as precision casting, mass production and short production time. This study proposes vacuum die casting process to fabricate bipolar plates in fuel cell. Bipolar plates were fabricated under various injection conditions such as molten metal temperature and injection velocity. Also, according to injection velocity conditions, simulation results of MAGMA soft were compared to the experimental results. In case of melt temperature $650^{\circ}C$, misrun occurred. When the melt temperature was $730^{\circ}C$, mechanical properties were low due to dendrite microstructure. Injection velocity has to set at more than 2.0 m/s to fabricate the sound sample. When melt temperature, injection velocity (Fast shot), and vacuum pressure are $700^{\circ}C$, 2.5 m/s and 30 kPa respectively, sample had good formability and few casting defects. Simulation results are mostly in agreement with experimental results.

• 대한조선학회논문집
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• 제46권6호
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• pp.595-602
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• 2009

Great number of ships has been built by Korean Shipyards since early of 2,000 due to the expanding worldwide trade. Most of shipyards have enlarged the weight of erection block and many blocks have been assembled in block fabrication factories outside the shipyards to reduce the shipbuilding period. Especially, Giga blocks that exceed 2,000 tons are often assembled by the block fabrication factories outside the shipyard. Generally, the blocks are transported to building dock in shipyard by towing barges. Accident can be occurred during the sea transportation and it may bring about not only the delay of delivery but also a disaster on the ocean environments. Transportation condition of GPE (Grand Pre-Erection) block differs from the ocean going conditions of marine vessels. Special consideration should be included before transportation work in order to guarantee the safety of GPE blocks and barge carriers. In this paper, several examples, which have been investigated to set up the safety standard of transportation of the GPE blocks on coastal routes, are introduced. For the barge transportation on coastal sea route, the design criteria are discussed, considering the design wave, the acceleration induced by wave, structural strength, and the fixture condition of blocks.

• Nano
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• 제13권11호
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• pp.1850126.1-1850126.10
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• 2018

Flexible strain sensors, as the core member of the family of smart electronic devices, along with reasonable sensing range and sensitivity plus low cost, have rose a huge consumer market and also immense interests in fundamental studies and technological applications, especially in the field of biomimetic robots movement detection and human health condition monitoring. In this paper, we propose a new flexible strain sensor based on thick CVD graphene film and its low-cost fabrication strategy by using the commercial adhesive tape as flexible substrate. The tensile tests in a strain range of ~30% were implemented, and a gage factor of 30 was achieved under high strain condition. The optical microscopic observation with different strains showed the evolution of cracks in graphene film. Together with commonly used platelet overlap theory and percolation network theory for sensor resistance modeling, we established an overlap destructive resistance model to analyze the sensing mechanism of our devices, which fitted the experimental data very well. The finding of difference of fitting parameters in small and large strain ranges revealed the multiple stage feature of graphene crack evolution. The resistance fallback phenomenon due to the viscoelasticity of flexible substrate was analyzed. Our flexible strain sensor with low cost and simple fabrication process exhibits great potential for commercial applications.

• 한국태양에너지학회 논문집
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• 제39권3호
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• pp.9-17
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• 2019

Laser cutting cell of solar cells can achieve high voltage and efficiency through more array than conventional 6 inch cell compared to same area. In this study, we fabricated c-Si cutting cell with various lasers and laser conditions such as power, speed, and number of times. In the case of picosecond laser, excellent surface characteristics were obtained due to small surface defects and low thermal damage at the output of 20W and the speed of 100 mm/s. However, it is not possible to fabricate a cutting cell having good characteristics due to nonuniform cutting inside the wafer when the processing for forming a cutting cell is not sufficiently performed. For nanosecond lasers, the best wafer characteristics were obtained for fabrication of excellent cutting cells at a frequency of 500 kHz and a laser speed of 100 mm/s. However, the nanosecond laser has not been processed sufficiently in the condition of a number of times. As a result, it was confirmed that the wafer thickness was cut by $63{\mu}m$ of the cell thickness of $170{\mu}m$ in the condition of five times of laser process. It was found that more than 30% of the wafer thickness had to be processed to fabricate the cutting cell. After cutting the 6-inch cell having the voltage of 0.65 V, we obtained the voltage of about 0.63 V.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 추계학술발표대회 논문집
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• pp.9-12
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• 2001

Composite materials can be used economically and efficiently in broad civil engineering applications when standards and processes for analysis, design, fabrication, construction and quality control are established. Many of the bridge systems, including the girders and cross-beams, and concrete decks behave as the special othotropic plates. Such systems with boundary conditions other than Navier or Levy solution types, or with irregular cross sections, analytical solution is very difficult to obtain. Numerical method for eigenvalue problems are also very much involved in seeking such a solution. A method of calculating the natural frequency corresponding to the first mode of vibration of beam and tower structures with irregular cross-sections was developed and reported by the author in 1974 Recently, this method was extended to two dimensional problems including composite laminates, and has been applied to composite plates with various boundary conditions with/without shear deformation effects and reported at several international conferences including the Eighth Structures Congress of American Society of Civil Engineers in 1990. In this paper, the result of application of this method to the special orthotropic plates with various boundary condition is presented.

• Macromolecular Research
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• 제14권6호
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• pp.624-629
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• 2006

The cellulose-based, Electroactive Paper (EAPap) has recently been reported as a smart material with the advantages of lightweight, dry condition, biodegradability, sustainability, large displacement output and low actuation voltage. However, it requires high humidity.. This paper introduces an EAPap made with a cellulose solution and lithium chloride (LiCl), which can be actuated in room humidity condition. The fabrication process, performance test and effect of LiCl content of the EAPap actuator are illustrated. The bending displacement of the EAPap actuators was evaluated with actuation voltage, frequency, humidity and LiCl content changes. At a LiCl/ cellulose content of 3:10, the displacement output was maximized at a room humidity condition. Even though the displacement output was less than that of a high humidity EAPap actuator, the mechanical power output was not reduced due to the increased resonance frequency, which is promising for developing EAPap actuators that are less sensitive to humidity.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 학술대회 논문집
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• pp.129-132
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• 2003

Yttria stabilized zirconia (YSZ) buffer layers were deposited by a metal organic chemical vapor deposition (MOCVD) technique using single liquid source for the application of YBa$_2$Cu$_3$$O_{7-x}$ (YBCO) coated conductor. Y:Zr mole ratio was 0.2:0.8, and tetrahydrofuran (THF) was used as a solvent. The (100) single crystal MgO substrate was used for searching deposition condition. Bi-axially oriented CeO$_2$ and NiO films were fabricated on {100}〈001〉 Ni substrate by the same method and used as templates. At a constant working pressure of 10 Torr, the deposition temperatures (660~80$0^{\circ}C$) and oxygen flow rates (100~500 sccm) were changed to find the optimum deposition condition. The best (100) oriented YSZ film on MgO was obtained at 74$0^{\circ}C$ and $O_2$ flow rate of 300 sccm. For YSZ buffer layer with this deposition condition on CeO$_2$/Ni template, full width half maximum (FWHM) values of the in-plane and out-of-plane alignments were 10.6$^{\circ}$ and 9.8$^{\circ}$, respectively. The SEM image of YSZ film on CeO$_2$/Ni showed surface morphologies without microcrack.k.

• 복식문화연구
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• 제3권1호
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• pp.109-124
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• 1995

This study is purposed to analyze the degree of content and wearing style of fur cloths in order for women to buy them effectively and to wear them contentedly. So scrutinized buying style and wearing condition of fur clothes. To show whether women's buying fur clothes are suitable for their body or not, this study was examined characteristics, sorts, method of fabrication and manufacture, buying pattern and trends of fur clothes. The conclusion from this study examining the degree of possession, decision making of buying and recognition of fur clothes are as followings: 1. When women wears fur clothes, style of fur clothes have nothing to do with their body and height, and women who are 150∼160cm tall content to fur clothes commonly. 2. Condition of buying fur clothes, many 40's women whose only husband earns family's bread belong to fur clothes, and buy them, talking with a husband. Also, according to income a month, and to the ind of a job, in case of a couple's earning family's bread together, women whose whose income is 800,000 to 1,000,000￦ level. 3. Condition of wearing fur clothes, the cause that women feel like wearing fur clothes is as following: economic stability their own pride, and contentment to wear them. Women want to wear those different from fur clothes that they possess, and half coat, because of working conveniently. As the above mention, purchasers recognite the conception of fur clothes for themselves, and buy economically them, and must wear those of which design and style are suitable for body.