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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% $Y_2O_3-ZrO_2$.
심하게 흡수된 하악골에서 fixed detachable prosthesis를 이용한 임플란트 지지 보철 수복증례
이학주,임영준,권호범,김명주,Lee, Hak-Joo,Lim, Young-Jun,Kwon, Ho-Beom,Kim, Myung-Joo 대한치과보철학회 2017 대한치과보철학회지 Vol.55 No.2
완전 무치악 환자에서 임플란트를 이용한 치료 방법은 환자의 삶의 질 개선에 크게 기여하였으나, 잔존골 상태나 경제력 등에 의해 임플란트의 식립 개수에 제한을 받는 상황이 종종 나타난다. 이러한 경우 일반적으로 임플란트 피개의치나 임플란트 융합 국소의치 형태로 치료계획을 세울 수 있지만, 정확한 설계를 바탕으로 양측성 캔틸레버 형태의 고정성 보철물 역시 고려해 볼 수 있다. 본 증례에서는 심한 치조골 흡수를 보이는 완전 무치악 환자에서 상악 총의치 및 하악 임플란트 지지 고정성 캔틸레버 보철물 제작을 통해 기능적, 심미적으로 양호한 결과를 얻었기에 보고하고자 한다. Implant supported prostheses have improved the quality of lives of totally edentulous patients. However, there are some limitations on the number of implants related to the residual bone level or the economic concern and so on. In this situation, applying fixed detachable prosthesis with bilateral cantilevers can be considered. This clinical report describes implant supported prosthetic rehabilitation of a patient with severe bone resorption. The patient was satisfied and felt comfortable with upper complete denture and lower fixed detachable prosthesis.
우레아 첨가량 변화에 따라 수열합성법으로 제조 된 3mol%Y<sub>2</sub>O<sub>3</sub>-ZrO<sub>2</sub> 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.
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.
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.
평면변형률 상태 하에서 유한요소해석을 이용한 균열닫힘 거동 예측 및 평가
이학주(Hak-Joo Lee),송지호(Ji-Ho Song),강재윤(Jae-Youn Kang) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
An elastic-plastic finite element analysis of fatigue crack closure is performed for plane strain conditions. The stabilization behavior of crack opening level and the effect of mesh size on the crack opening stress are investigated. In order to obtain a stabilized crack opening level for plane strain conditions, the crack must be advanced through approximately four times the initial monotonic plastic zone. The crack opening load tends to increase with the decrease of mesh size. The mesh size nearly equal to the theoretical plane strain cyclic plastic zone size may provide reasonable numerical results comparable with experimental crack opening data. The crack opening behavior is influenced by the crack growth increment and discontinuous opening behavior is observed. A procedure to predict the most appropriate mesh size for different stress ratio is suggested. Crack opening loads predicted by the FE analysis based on the procedure suggested resulted in good agreement with experimental ones within the error of 5%. Effect of the distance behind the crack tip on the crack opening load determined by the ASTM compliance offset method based on the load-displacement relation and by the rotational offset method based on the load-differential displacement relation is investigated. Optimal gage location and method to determine the crack opening load is suggested.
대칭형 탐침을 이용한 자연모사 나노구조물의 점착력 측정
이학주(Hak-Joo Lee),김재현(Jae-Hyun Kim),조기호(Kiho Cho),한승우(Seung Woo Han),이주영(Joo Young Lee),유영은(Young-Eun Yoo),김완두(Wan-Doo Kim),김경식(Kyung-Shik Kim) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
This paper reports a development of a novel AFM cantilever as a highly sensitive sensor and an application of the cantilever into various mechanical tests for characterizing micro/nano-structures. Using single crystal silicon micromachining techniques, we have designed and fabricated rhombus-shaped symmetric AFM probes. After force-calibration of the cantilever, adhesion test was performed. Adhesive force between silicon tip and Cyclic Olefin Copolymer (COC) nano-fiber arrays was measured using the cantilever with a flat tip. Fiber’s diameter was approximately 200 ㎚. The obtained result exhibited the usual characteristics of force curves of COC nano-fiber arrays, in which a pull-off force was detected at the point of unloading.
응력 및 표면 고장물리를 고려한 MEMS 신뢰성 설계 기술
이학주(Hak-Joo Lee),김정엽(Jung Yup Kim),이상주(Sang Joo Lee),최현주(Hyun Ju Choi),김경식(Kyung Shik Kim),김장현(J.-H Kim) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
As semiconductor and MEMS devices become smaller, testing process during their production should follow such a high density trend. A circuit inspection tool probe card makes contact with electrode pads of the device under test (DUT). Nowadays, electrode pads are irregularly arranged and have height difference. In order to absorb variations in the heights of electrode pads and to generate contact loads, contact probes must have some levels of mechanical spring properties. Contact probes must also yield a force to break the surface native oxide layer or contamination layer on the electrodes to make electric contact. In this research, new vertical micro contact probe with bellows shape is developed to overcome shortage of prior work. Especially, novel bellows shape is used to reduce stress concentration in this design and stopper is used to change the stiffness of micro contact probe. Variable stiffness can be one solution to overcome the height difference of electrode pads.
평면응력 및 평면변형률 상태 하에서 유한요소해석을 이용한 균열닫힘 거동 예측
이학주(Hak-Joo Lee),송지호(Ji-Ho Song),박정민(Jungmin Park),강재윤(Jae-Youn Kang) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
An elastic-plastic finite element analyses of fatigue crack closure are performed for plane strain and plane stress conditions. The stabilization behavior of crack opening level and the effect of mesh size on the crack opening stress are investigated. It has been well reported that the crack opening level under plane stress conditions becomes stable after the crack advances beyond the initial monotonic plastic zone. In order to obtain a stabilized crack opening level for plane strain conditions, the crack must be advanced through approximately four times the initial monotonic plastic zone. The crack opening load tends to increase with the decrease of mesh size. The mesh size nearly equal to the theoretical plane strain cyclic plastic zone size may provide reasonable numerical results comparable with experimental crack opening data. The crack opening behavior is influenced by the crack growth increment and discontinuous opening behavior is observed.