http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
위성 열제어 부품 이차면경상의 수상돌기 성장 매카니즘 분석
이춘우(Choon-Woo Lee),이균호(Kyun-Ho Lee),김희경(Hui-Kyung Kim) 한국항공우주연구원 2012 항공우주기술 Vol.11 No.2
본 연구는 위성 열제어 주요 구성품중 하나인 SSM(이차면경) 표면에서 나타난 수상돌기(Dendrite) 현상에 대한 고장탐구 수행 내역과 그 결과를 정리한 것이다. 본 고장탐구 시편 시험을 통하여 SSM 표면의 은도금 층은 황 또는 염소 화합물이 함유된 환경에 장기간 직접 노출시키는 경우, 은도금 층이 황화 변색되는 현상이 나타날 수 있음을 확인하였으며 SSM 수상돌기(Dendrite) 현상을 방지하기 위해서는 가황 처리된 고무 패드와 직접 접촉하지 않도록 격리 보관할 필요가 있음을 알 수 있었다. The purpose of this paper is to present the summary of trouble shooting result on the dendrite defect of SSM(Second Surface Mirror) which is one of major thermal control elements for satellite. Through this failure analysis on SSM dendrite, it is found that the dendrite defect may happen to silver coated layer of SSM if SSM is directly exposed to the environment containing sulfur or chlorine compound. As a preventive action, it is required that SSM shall not contact directly with rubber pad containing sulfur compound.
원심주조방법으로 제조된 고속도강 압연롤의 미세조직과 파괴특성
이성학,이희춘,황근철 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.12
A study was made of the effects of alloying elements on microstructural factors of nine high speed steel (HSS) rolls manufactured by centrifugal casting method. Particular emphasis was placed on the role of hard carbides located along solidification cell boundary and the type of the martensite matrix. Microstructural observation, X-ray diffraction analysis, and hardness measurement were conducted on the rolls to identify carbides. Various types of carbides mostly segregated in the intercellular regions were dependent upon alloying elements and their amount, and played an important role in overall roll hardness. The effects of alloying elements were analyzed on the basis of the liquidus surface diagram, suggesting that the proper contents of carbon, tungsten, molybdenum, chromium, and vanadium were 1.9-2.0%, 3-4%, 3-4%, 5-7%, and 5-6%, respectively.
고속도강 압연롤의 고온마모특성에 미치는 템퍼링 온도의 영향
이정호,박준욱,이성학,이희춘,오준철 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.2
This study is concerned with the effects of tempering temperature on wear properties and surface roughness of a high speed steel (HSS) roll manufactured by centrifugal casting method. Hot-rolling simulation test was carried out using a high-temperature wear tester capable of controlling speed, load, and temperature. The test results revealed that the peak-tampered roll specimen showed the best wear resistance because it contained a hard matrix. However, its surface roughness deteriorated as the scratching wear proceeded, thereby leading to increase in friction coefficient. In the over-tempered specimens containing a number of fine spherical carbides in the matrix, the abrasive wear occurred predominantly as fine carbides were fallen off from the worn surface, and thus the surface roughness was enhanced by more homogeneous wear of matrix and carbides. These findings suggested that over-tempering would be more desirable in order to improve wear resistance with consideration of the surface roughness of the HSS roll.
이성학,김낙준,이희춘,이창길,손기선 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.3
The main objective of the present study is to clarify the microstructural factors such as tempered martensite matrix, coarse primary carbides, eutectic structures, and fine secondary carbides, which influence fracture properties of high speed steel (HSS) rolls. Three HSS rolls with different Cr content were manufactured by a centrifugal casting method, and the microstructures of their shell regions were investigated quantitatively. MC type primary carbides, together with eutectic ledeburite structures, were observed in the intercellular regions. The observation of fracture processes indicated that these primary carbides cleaved first to form microcracks at very low stress levels. These microcracks were easily propagated along the intercellular networks, leading to predominantly cleavage mode of fracture on fracture surfaces. To improve microstructures for use in the HSS rolls, therefore, it is suggested that the cell size must be minimized to achieve the homogeneous distribution of primary carbides
고속도강 압연롤의 고온마모특성에 미치는 탄소 및 크롬 첨가의 영향
이성학,이희춘,오준철,강용중 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.5
A study was made of the effects of carbon and chromium addition on microstructural factors and wear properties of five high speed steel(HSS) rolls manufactured by centrifugal casting method. Based on the basic chemical composition of Fe-2.0C-5.0V-3.0Mo-1.5W-6.2Cr-0.75Si-0.35Mn(wt.%), the rolls were made with varying additions of carbon and chromium in order to examine their respective effects. They were then austenitized at 1050℃, air cooled, and double-tempered at the temperature range from 470℃ to 600℃. A simulation test was carried out using a high-temperature wear tester capable of controlling speed, load, and temperature. The test results revealed that the HSS roll containing a smaller amount of chromium showed the best wear resistance because it contained a number of hard MC carbides. However, it showed a very rough roll surface because of the preferential removal of the matrix and the sticking of the rolled material to the roll surface during the wear process, thereby leading to increase in friction coefficient and rolling force. In order to improve wear resistance with consideration of the roll surface roughness, the increase in the chromium content, i.e., the increase the amount of M_7C₃ carbides which can give good surface roughness, was suggested.
Induction of Oral Tolerance by Gamma-Irradiated Ovalbumin Administration
Hui Yang,Jung Lim Lee,Ji Hyun Seo,Kwang Hoon Oh,Young Ho Cho,Yung Choon Yoo 한국축산식품학회 2016 한국축산식품학회지 Vol.36 No.1
Oral administration of soluble antigen can induce peripheral tolerance to the antigen. This study was conducted to evaluate whether gamma-irradiated ovalbumin (OVA) can induce oral tolerance. To investigate this, we administrated intact or irradiated OVA to mice, induced allergic response using intact OVA and alum, then compared humoral and cellular immune responses. Mice treated with gammairradiated OVA had less OVA-specific IgE compared with those who were administered intact OVA. There was no difference in levels of OVA-specific IgG+A+M, IgG1, and IgG2a. Splenocytes of mice administered irradiated OVA showed similar OVA-specific T cell proliferation and secretion of IFN-γ and IL-4. However, there was an increase in IL-2 and a decrease of IL-6 secretion in mice treated with irradiated OVA. These results indicate that gamma-irradiated OVA have similar effects to intact OVA on antigen tolerance.