• 한국태양에너지학회 논문집
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• 제27권4호
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• pp.113-120
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• 2007

The 5kWt dish solar collector is designed and the preliminary performance test for this is carried out. The diameter of the parabolic dish is 3.2 m, and its focal length is 2 m. It consists of 10 small reflectors which have their own curvatures, and the effective reflecting area is $5.9\;m^2$, and the rim angle of the dish is $43.85^{\circ}$. The reflectivity of reflectors is 0.95, and the thermal capacity of the system is about 5 kW thermal. The aperture diameter of the cylindrical-shape receiver which is made of stainless steel is 100 mm, and the height is 210 mm. A quartz window is installed at the receiver aperture to minimize the convective heat loss and prevent air leakage. In order to increase the heat transfer area, porous materials (nickel-alloy) are inserted into the receiver. Air flows into the upper part of the receiver which is the opposite side of the aperture. After the air flows through the inside of the receiver, that goes out of the receiver through 3 exits which are located near the aperture. The volumetric flow rates of air are varied from 600 to 1200 L/min. The results show that the system efficiency and receiver efficiency increase as the volume flow rate increases.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.266-269
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• 2009

Iron-based soft magnetic materials are widely used as cores, such as transformer transformers, motors, and generators. Reducing losses generated from soft magnetic materials of these applications results in improving energy conversion efficiency. Recently, the new P/M soft magnetic material realized an energy loss of 68 W/kg with a drive magnetic flux of 1 T, at a frequency of 1 kHz, rivaling general-purpose electromagnetic steel sheet in the low frequency range of 200 Hz to 1 kHz. In this research, the effect of rolling parameters on soft magnetic properties of Fe-based powder cores was investigated. The Fe-based soft magnetic plates were produced by the hot powder rolling process after both pure Fe and Fe-4%Si powders were canned, evacuated, and sealed in Cu can. The soft magnetic properties such as energy loss and coercive power were measured by B-H curve analyzer. The soft magnetic properties of rolled sheets were measured under conditions of a magnetic flux density of 1 T at a frequency of 200 kHz. It was found that rolling reduction ratio is the most effective parameter on reducing both energy loss and coercivity because of increasing aspect ratio with reduction ratio. By increasing aspect ratio from 1 to 9 through hot rolling of pure Fe powder, a significant loss reduction of one-third that of SPS sample was achieved.

• 한국주조공학회지
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• 제20권4호
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• pp.254-259
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• 2000

Metal matrix composites(MMCs) reinforced with hard particles have many potential application in aerospace structures, auto parts, semiconductor package, heat resistant panels, wear resistant materials and so on. In this work, the effect of SiC partioel sizes(50 and 100 ${\mu}m$) and additional elements such as Si, Cu and Ti on the microstructure and the wear property of $Al-5Mg-X(Si,Cu,Ti)/SiC_p$ composites produced by pressureless infiltration method have been investigated using optical microscopy, scanning eletron microcopy(SEM) with EDS(energy dispersive spectrometry), hardness test, X-ray diffractometer(XRD) and wear test. In present study, the sound $Al-5Mg-X(Si,Cu,Ti)/SiC_p$(50 and 100 ${\mu}m$) composites were fabricated by pressureless infiltration method. The $Al-5Mg-0.3Si-O.1Cu-O.1Ti/SiC_p$ composite with $50 {\mu}m$ size of SiC particle has higher hardness and better wear property than any other composite with $100{\mu}m$ size of SiC particle produced by pressureless infiltration method. The hardness and wear property of $Al-5Mg/SiC_p$(50 and 100 ${\mu}m$) composites were enhanced by the addition of Si, Cu and Ti in Al-5%Mg matrix alloy.

• 농업과학연구
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• 제43권3호
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• pp.441-449
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• 2016

Agricultural tractors are designed using the empirical method due to the difficulty of measuring precise load cycles under various working conditions and soil types. Especially, directly drives various tractor implements, the power take off (PTO) gear. Therefore, alternative design methods using gear design software are needed for the optimal design of tractors. The objective of this study is to simulate fatigue life of the PTO gear according to the operating point of the tractor engine. The PTO gear was made with SCr415 alloy steel with carburizing and quenching treatments. The fatigue life of the PTO gear was simulated by using bending and contact stress according to the torque of the load levels. The PTO gear simulation was conducted by the KISSsoft commercial software for gear analysis. Bending and contact stress were calculated by the ISO 6336:2006 Method A and B. The simulation of fatigue life was calculated by the Miner's cumulative damage law. The total fatigue life of tractors can be estimated to 3,420 hours; thus, 3,420 hours of fatigue life were used in the simulation of the PTO gear of tractors. The main simulation results showed that the maximum fatigue life of the PTO gear was infinite fatigue life at maximum engine power. Minimum fatigue life of the PTO gear was 19.61 hours at 70% of the maximum engine power. Fatigue life of the PTO gear changed according to load of tractor. Therefore, tractor work data is needed for optimal design of the PTO gear.

• 대한기계학회논문집A
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• 제21권6호
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• pp.961-970
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• 1997

A numerical method is presented to predict and analyze the shape of a growing billet produced from the "spray forming process" which is a fairly new near-net shape manufacturing process. It is important to understand the mechanism of billet growing because one can obtain a billet with the desired final shape without secondary operations by accurate control of the billet shape, and it can also serve as a base for heat transfer and deformation analysis. The shape of a growing billet is determined by the flow rate of the alloy melt, the mode of nozzle scanning which is due to cam profile, the initial positio of the spray nozzle, scanning angle, and the withdrawal speed of the substrate. In the present study, a theoretical model is first established to predict the shape of the billet and next the effects of the most dominent processing conditions, such as withdrawal speed of the substrate and the cam profile, on the shape of the growing billet are studied. Process conditions are obtained to produce a billet with uniform diameter and flat top surface, and an ASP30 high speed steel billet is manufactured using the same process conditions established from the simulation.imulation.

• 한국재료학회지
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• 제25권8호
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• pp.386-390
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• 2015

Fe-base superalloy powders with $Y_2O_3$ dispersion were prepared by high energy ball milling, followed by spark plasma sintering for consolidation. High-purity elemental powders with different Fe powder sizes of 24 and 50 mm were used for the preparation of $Fe-20Cr-4.5Al-0.5Ti-O.5Y_2O_3$ powder mixtures (wt%). The milling process of the powders was carried out in a horizontal rotary ball mill using a stainless steel vial and balls. The milling times of 1 to 5 h by constant operation (350 rpm, ball-to-powder ratio of 30:1 in weight) or cycle operation (1300 rpm for 4 min and 900 rpm for 1 min, 15:1) were applied. Microstructural observation revealed that the crystalline size of Fe decreased with an increase in milling time by cyclic operation and was about 15 nm after 3 h, forming a FeCr alloy phase. The cyclic operation had an advantage over constant milling in that a smaller-agglomerated structure was obtained. The milled powders were sintered at $1100^{\circ}C$ for 30 min in vacuum. With an increase in milling time, the sintered specimen showed a more homogeneous microstructure. In addition, a homogenous distribution of Y-compound particles in the grain boundary was confirmed by EDX analysis.

• 한국전기전자재료학회논문지
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• 제17권11호
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• pp.1241-1245
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• 2004

Continuous physical vapor deposition (PVD) method is one of many processes to fabricate long length coated conductor which is required for successful large-scale application of superconducting power devices. Three film deposition systems (pulsed laser deposition, sputtering, and evaporation) equipped with reel-to-reel(R2R) metal tape moving apparatus were installed and used to deposit multi-layer oxide thin films. Both RABiTS and IBAD texture templates are used. IBAD template consists of CeO$_2$(PLD)/YSZ(IBAD) on stainless steel(SS) metal tape, and RABiTS template has the structure of CeO$_2$/YSZ/Y$_2$O$_3$ which was continuously deposited on Ni-alloy tape using R$_2$R evaporation and DC reactive sputtering in a deposition system designed to do both processes. 0.4 m-long coated conductor with Ic(77 K) of 34 A/cm was fabricated using RABiTS template. 0.5 m and 1.1 m-long coated conductor with Ic(77 K) of 41 A/cm and 26 A/cm were fabricated using IBAD template.

• 열처리공학회지
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• 제18권4호
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• pp.247-255
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• 2005

Although heat treatment is a process of great technological importance in order to obtain desired mechanical properties such as hardness, the process was required a tedious and expensive experimentation to specify the process parameters. Consequently, the availability of reliable and efficient numerical simulation program would enable easy specification of process parameters to achieve desired microstructure and mechanical properties without defects like crack and distortion. In present work, the developed numerical simulation program could predict distributions of microstructure and thermal stress in steels under different cooling conditions. The computer program is based on the finite difference method for temperature analysis and microstructural changes and the finite element method for thermal stress analysis. Multi-phase decomposition model was used for description of diffusional austenite decompositions in low alloy steels during cooling after austenitization. The model predicts the progress of ferrite, pearlite, and bainite transformations simultaneously during quenching and estimates the amount of martensite also by using Koistinen and Marburger equation. To verify the developed program, the calculated results are compared with experimental ones of casting product. Based on these results, newly designed heat treatment process is proposed and it was proved to be effective for industry.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.2
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• pp.1274-1277
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• 2004

최근 에너지 소비구조의 선진화에 따라 전력수요는 매년 10%이상 증가하고 있지만 철탑부지확보 및 환경 문제 둥에 의해 신규 송전선의 건설은 점차 어려워지고 있다. 이에 대한 대책으로 철탑의 교체 없이 송전선의 전류용량간 증가시키는 방안이 우선적으로 고려되어 적용되고 있다. 이미 국내에서도 기존 송전선인 ACSR 전선을 중용량 저이도의 특성을 가진 STACIR/AW(Super Thermal-resistant Aluminum alloy Conductors, aluminum-clad Invar-Reinforced)송전선으로 교체하여 전력 수송량을 증가시키고 있다. STACIR/AW전선은 도체의 내열성을 향상시켜 연속허용온도$(210^{\circ}C)$를 높임으로 전류용량을 증가시키고, ACSR에 사용되는 강심재료인 고탄소강선을 선팽창계수가 낮은 인바강선(INVAR)으로 대체함으로 고온환경에 따른 이도증가를 방지하고 있다. 그러나 STACIR/AW 송전선은 ACSR 송전선에 비하여 연속허용온도가 높고 경간의 거리가 멀기 때문에 열화에 의한 피로특성의 변화 가능성이 높다. 따라서 본 연구에서는 증용량저이도전선의 강심소재인 INVAR/AW강선을 소정의 온도에서 경년 열화하고, 열화시간에 따른 강도와 피로특성의 변화를 조사하여, STACIR/AW전선의 안정적 운전을 위한 재료물성적 관리인자를 도출하고자 하였다.

• 대한금속재료학회지
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• 제48권6호
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• pp.477-488
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• 2010

Zr-based amorphous alloy matrix composites reinforced with stainless steel (STS) and tantalum continuous fibers were fabricated without pores or defects by a liquid pressing process, and their quasi-static and dynamic deformation behaviors were investigated by using a universal testing machine and a Split Hopkinson pressure bar, respectively. The quasi-static compressive test results indicated that the fiberreinforced composites showed amaximum strength of about 1050~1300 MPa, and its strength maintained over 700 MPa until reaching astrain of 40%. Under dynamic loading, the maximum stresses of the composites were considerably higher than those under quasi-static loading because of the strain-rate hardening effect, whereas the fracture strains were considerably lower than those under quasi-static loading because of the decreased resistance to fracture. The STS-fiber-reinforced composite showed a greater compressive strength and ductility under dynamic loading than the tantalum-fiber-reinforced composite because of the excellent resistance to fracture of STS fibers.