가압연속주조법에 의한 SiCp / Al 합금기 복합재료의 조직 및 특성

이학주,홍준표 ( Hak Joo Lee,Chun Pyo Hong ) 한국주조공학회 1991 한국주조공학회지 Vol.11 No.1

N/A Microstructure and characteristics of the SiCp/Al-4.5wt%Cu-1wt%Mg composites fabricated by the combination of the compocasting and the pressurized continuous casting process, which is one of the processes to decrease the limitations of the size, and shops of the products, are investigated. The main results are as follows: 1) the SiCp /Al alloy matrix composites can be made continuously 2) as the amount of SiCp addition increases; (1) the degree of directional solidification of matrix structure decreases, and that of SiCp dispersion improves, (2) wear resistance improves, and especially these composites show the excellent wear resistance under the high sliding speed and high final load condition, (3) wear mechanism of these composites is changed from adhesive wear into abrasive wear, and the tendency of that becomes outstanding with increasing sliding speed.

Rheo-compocasting 및 열간압출에 의하여 제조한 Al-Si-Mg / SiC 입자강화 복합재료의 조직 및 기계적 특성

이학주,홍준표 ( Hag Ju Lee,Chun Pyo Hong ) 한국주조공학회 1992 한국주조공학회지 Vol.12 No.4

N/A Aluminum alloy matrix composites reinforced with various amounts of SiC particles have been produced by rheo-compocasting followed by hot extrusion. A relatively uniform distribution of SiC particles in the composites was obtained. The amounts of pore and SiC particles cluster were relatively small in the composites. Particle free zones were observed in the hot extruded composites when the amount of SiC particles was less than 20vol%. However, the width of particle free zone decreases with the increase of SiC particle content. Eutectic Si phase play an important role for improving bonding between SiC particle and matrix. Tensile and yield strength increased with the increase of SiC particle content. the strengthening effect of SiC particle addition was effective even at relatively high temperature of 573K.

동력차용 대차프레임의 피로강도평가

이학주,한승우,이상록,Lee, Hak-Ju,Han, Seung-U,Augagneur Sylvain,Lee, Sang-Rok 한국기계연구원 1997 硏究論文集 Vol.27 No.-

The bogie between the track and the railway vehicle body, is one of the most important component in railroad vehicle. Its effects on the safety of both passengers and vehicle itself, and on the overall performance of the vehicle such as riding quality, noise and vibration are critical. The bogie is mainly consisted of the bogie frame, suspensions, wheels and axles, braking system, and transmission system. The complex shapes of the bogie frame and the complicate loading condition (both static and dynamic) induced in real operation make it difficult to design the bogie frame fulfilling all the requirements. The complicated loads applied to the bogie frame are i) static load due to the weight of the vehicle and passengers, ii) quasi-static load due to the rolling in curves iii) dynamic load due to the relative motion between the track, bogie, and vehicle body. In designing the real bogie frame, fatigue analysis based on the above complicated loading conditions is a must. In this study, stress analysis of the bogie frame has been performed for the various loading conditions according to the UIC Code 6 15-4. Magnitudes of the stress amplitude and mean stress were estimated based on the stress analysis results to simulate the operating loads encountered in service. Fatigue strength of the bogie frame was evaluated by using the constant life diagram of the material. 3-D surface modelling, finite element meshing, and finite element analysis were performed by Pro-Engineer, MSC/PATRAN, and MSC/NASTRAN, respectively.

IP R&D 연계를 위한 마이크로그리드기술 특허 분석

이학주,Lee, Hak-Ju 대한전기협회 2012 전기저널 Vol.- No.424

Inductively Coupled Plasma Etching of Chemical-vapor-deposited Amorphous Carbon in N₂/H₂/Ar Chemistries

이학주,권봉수,박영록,안정호,김진성,N.-E. Lee,J. W. Shon 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.5

In this study, we investigated the etching characteristics and the mechanism of an amorphous carbon (a-C) layer for a multi-level resist (MLR) structure. CVD (chemical-vapor-deposited) a-C layers with a SiO₂ hard-mask were etched in an ICP (inductively coupled plasma) etcher while varying the process parameters, such as the top electrode power, the bottom electrode power, and the gas flow ratio in the N₂/H₂/Ar plasma. The results indicated that the etch rate and the profile angle of the CVD a-C increased with increasing H₂ gas flow ratio in the N₂/H₂/Ar plasma. As the H₂ flow ratio increased, the etch rate and the profile angle increase, due to the increased formation of H radicals in the plasma, leading to enhanced chemical reactions with carbon atoms. Also, the etch rate of the CVD a-C increased with increasing top and bottom electrode powers.

Y₂O₃안정화제 첨가량에 따라 수열합성법으로 제조된 ZrO₂-Xmol% Y₂O₃분말의 합성 및 기계적 특성

이학주,김택남,배성철,고명원,류재경,Lee, Hak-Joo,Kim, Taik-Nam,Bea, Sung-Chul,Go, Myung-Won,Ryu, Jae-Kyung 한국재료학회 2010 한국재료학회지 Vol.20 No.10

In this study, partially stabilized zirconia was synthesized using a chemical $Y_2O_3$ stabilizer and hydrothermal method. First, $YCl_3-6H_2O$ and $ZrCl_2O-8H_2O$ was dissolved in distilled water. Y-TZP (a $Y_2O_3$-doped toughened zirconia polycrystalline precursor) was also prepared by conventional co-precipitates in the presence of an excess amount of $NH_4OH$ solution under a fixed pH of 12. The Y-TZP precursors were filtered and repeatedly washed with distilled water to remove $Cl^-$ ions. $ZrO_2$-Xmol%$Y_2O_3$ powder was synthesized by a hydrothermal method using Teflon Vessels at $180^{\circ}C$ for 6 h of optimized condition. The powder added with the Xmol%- $Y_2O_3$ (X = 0,1,3,5 mol%) stabilizer of the $ZrO_2$ was synthesized. The crystal phase, particle size, and morphologies were analyzed. Rectangular specimens of $33mm{\times}8mm{\times}3$ mm for three-point bend tests were used in the mechanical properties evaluation. A teragonal phase was observed in the samples, which contains more than 3 mol% $Y_2O_3$. The $3Y-ZrO_2$ agglomerated particle size was measured at $7.01{\mu}m$. The agglomerated particle was clearly observed in the sample of 5 mol % $Y_2O_3-ZrO_2$, and and the agglomerated particle size was measured at 16.4 um. However, a 20 nm particle was specifically observed by FE-SEM in the sample of 3 mol% $Y_2O_3-ZrO_2$. The highest bending fracture strength was measured as 321.3 MPa in sample of 3 mol% $Y_2O_3-ZrO_2$.

Rheo-compocasting 및 열간압출에 의한 제조한 Al-Si-Mg / Al2O3 단섬유강화복합재료의 특성

이학주,홍준표 ( Ha Ju Lee,Chun Pyo Hong ) 한국주조공학회 1991 한국주조공학회지 Vol.11 No.4

N/A Aluminum alloy matrix composites reinforced with various amounts of Al₂O₃ short fibers have been produced by a combined technique of rheo-compocasting and hot extrusion. Distribution of fibers in the composites fabricated by rheo-compocasting was relatively uniform. A good degree of uniaxial fiber alignment has been achieved by hot extrusion, but a lot of fibers fractured during extrusion. The tendency of fiber fracturing increases as the aspect ratio and the amount of fibers increase. Relatively good bonding between fiber and matrix was obtained by the formation of MgAl₂O₄, and Mg(Al, Fe)₂O₄at the interface between fiber and matrix. In extruded composites, fiber strengthening effect was relatively small since a lot of fibers fractured during hot extrusion. On the other hand, dispersion strengthening effect may increase. In order to improve the fiber strengthening effect, it is important to optimize the extrusion condition with consideration of metal flow in extrusion die.

Rheo-compocasing 법에 의한 SiCp / Al 합금기 복합재료의 제조 및 마모특성

이학주,곽현만,홍준표 ( Hak Joo Lee,Hyun Man Kwak,Chun Pyo Hong ) 한국주조공학회 1991 한국주조공학회지 Vol.11 No.2

N/A Microstructure and wear characteristics of SiCp /Al - 6.5wt%Si - 1.7wt%Mg composite materials fabricated by rheo-compocast and hot press were investigated in this study. The results obtained are as follows : 1) It was possible to fabricate favorable composite materials containing SiCp which is up to 26 vol% by rheo-compocast and hot press. 2) Si and Al₂Si₄O_(10) were formed on the surface of SiC particles, and fairly good bonding condition was obtained on the interface between SiCp and matrix alloy. 3) Wear mechanism was transformed into adhesion, oxidation and fusion on the matrix alloy as wear rate increases, but in the composite material, the abrasive mechanism was shown not depending on the wear rate. 4) Wear resistance was improved as the amount of SiCp increases, however, no remarkable change in wear resistance was found above 8vol% of SiCp.

Ad-hoc 네트워크에서 다중경로를 지원하는 ATP 프로토콜에 대한 연구

이학주,장재신,이종협,Lee, Hak-Ju,Jang, Jae-Shin,Lee, Jong-Hyup 한국시뮬레이션학회 2009 한국시뮬레이션학회 논문지 Vol.18 No.3

Wireless networks have several unique features : node mobility, restricted bandwidth, time-variable bandwidth, large latency, and high bit error rates time due to channel fading. These features at wireless networks intend to decrease the performance TCP protocols are used in wireless networks. Lots of studies have been done for finding appropriate wireless transport protocols for current wireless communications. However, related studies have not provided good performance or some protocols have a good performance only in specific circumstances. Thus, these are not suitable for general wireless circumstance. Therefore, we propose a new wireless transport protocol which provides better performance than the previous ones. And we'd like to solve a problem that previous protocols cannot maintain their connections even though they have multiple paths until another path is successfully set up. To solve these problems, a new protocol ATP-M is proposed which is designed on already known TCP-M and ATP protocols. With NS-2 computer simulation, it is shown that this newly proposed protocol has better system throughput than TCP, TCP-M and ATP protocols.

우레아 첨가량 변화에 따라 수열합성법으로 제조 된 3mol%Y₂O₃-ZrO₂ 분말의 합성 및 기계적 특성 평가

이학주,고명원,김택남,Lee, Hak-Joo,Go, Myung-Won,Kim, Taik-Nam 한국재료학회 2011 한국재료학회지 Vol.21 No.8

The industrial manufacturing of YSZ products can be summarized as a three step process: a) hydrolysis of zirconyl chloride and mixing of other solutions, b) precipitation, and c) calcination. The addition of ammonia or OH- is essential in the precipitation process. However, a strong agglomeration was observed in the results of an ammonia or OH- addition. Thus, it is necessary to disperse the powders smoothly in order to improve the mechanical strength of YSZ. In this study, YSZ was synthesized using the urea stabilizer and hydrothermal method. YSZ powders were synthesized using a hydrothermal method with Teflon Vessels at $180^{\circ}C$ for 24 h. The mole ratio of urea to Zr was 0, 0.5, 1, and 2. The crystal phase, particle size, and morphologies were analyzed. Rectangular specimens ($33\;mm{\times}8\;mm{\times}1{\pm}0.5\;mm$) for three-point bend tests were used in the mechanical properties evaluation. The crystalline of YSZ powders observed a tetragonal phase in the sample with a ratio of Zr:urea = 1:2 addition and a hydrothermal reaction time of 24 h. The average primary particle size of YSZ was measured to be 9 nm to 11 nm. The agglomerated particle size was measured from 15 nm to 30 nm. The three-point bending strength of the YSZ samples was 142.47 MPa, which is the highest value obtained for the Zr:urea = 1:2 ratio addition YSZ sample.