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남승훈(Seung Hoon Nahm),이윤희(Yun-Hee Lee),백운봉(Un Bong Baek),채균식(Kyun Shik Chae),방건웅(Gun Woong Bahng) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.3
Reference standards are usable data to be used repeatedly, widely and continuously in all fields. They are authorized by analyzing scientifically and estimating the accuracy and reliability of measurement data and information. They are physical-chemical constants, authorized properties, authorized scientific- technological statistics, etc. Reference standards are national infra in connection with almost industry field as well as basic scientific technique fields. To develope reference standards evaluation system for tensile properties of metallic materials, evaluation procedure and criterion of tensile properties of metallic materials were described briefly in this study.
UNSM 처리한 베어링 강재의 VHCF 피로 및 파단특성
남승훈(Seung-Hoon Nahm),서민수(Min-Soo Suh),서창민(Chang-Min Suh),편영식(Young-Sik Pyun) 대한기계학회 2018 大韓機械學會論文集A Vol.42 No.6
사용된 베어링강의 UNSM처리효과와 기가사이클 설계기준에 필요한 VHCF 회전굽힘피로특성을 구하기 위한 피로시험을 거쳐 미시적인 파면해석과 EDS 분석을 통하여 표면과 내부에서 파괴되는 기구를 파괴역학적으로 연구하였다. 베어링강은 UNSM처리재와 미처리재중 경면상태의 경우는 duplex S-N 곡선이 얻어졌고, 가공상태의 경우는 표면조도가 크므로 이중 S-N곡선이 형성되지 않았다. 또 미처리재에 비해서 UNSM처리재는 표면의 나노(nano)조직화, 표면경도 상승, 표면조도 감소 및 압축잔류응력형성에 의하여 10⁶ 사이클 피로한도에서 약 28 % 정도 상승하는 경향을 나타내었다. 또 HCF(장수명피로) 범위에서는 표면을 기점으로 하는 표면결함에서 발생한 표면균열에 의해 파괴되는 형태를 취하였고, VHCF(초장수명피로, Nf >10⁶ 사이클) 범위에서는 내부에서 피로균열이 형성되는 어안균열이 주요 파괴기구로 되었다. 이 어안균열은 개재물의 흔적이 명확한 TiN개재물에서 주로 발생하였다. 개재물의 △K는 5 ㎫√m에 접근하며, 또 어안균열의 △K는 10 ㎫√m에 접근하였다. This study was to investigate the influence of ultrasonic nanocrystal surface modification (UNSM) effects on very high cycle fatigue(VHCF) strength and fracture mechanism of a bearing steel. In case of mirror finished specimens with and without UNSM treatment after machined surface, the duplex S-N curves were obtained, but in case of unpolished machined surface condition, the duplex S-N curves were not formed. The UNSM treated specimen showed a tendency to increase about 28% in the fatigue limit of 10⁶ cycles due to the refined structure to nanocrystal, the increased surface hardness, the decreased surface roughness and the increased compression residual stress. In the range of HCF, the fracture was caused by the surface crack generated by the surface defects originating from the surface. In the VHCF range, the dominant fracture mechanism was the fish-eye crack in which the internal originating fracture type was formed. The central part of the fish-eye where cracks initiated was inclusion consist of TiN. The stress intensity factor range (ΔK) of inclusions and fish-eye cracks approached 5 ㎫√m and 10 ㎫√m respectively.
남승훈(Seung Hoon Nahm),김동균(Dong Kyun Kim),박종서(Jong Seo Park),김엄기(Amkee Kim) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
This paper presents an overview of the mechanical properties of carbon nanotubes. The<br/> characteristics of carbon nanotubes were briefly introduced. We then present briefly the experimental<br/> techniques used to measure mechanical properties and the results obtained by other researchers. A<br/> carbon nanotube is too small to be pulled apart with standard tension devices. Manipulators should be<br/> used for mechanical testing. We introduced manipulation methods using nanomanipulators under<br/> field-emission scanning-electron microscope.
남승훈(Seung Hoon Nahm),이윤희(Yun-Hee Lee),백운봉(Un Bong Baek),정인현(In Hyun Chung),이해무(Hae Moo Lee) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.5
In order to guarantee the safety of the facility systems, one of the essential components is information on mechanical properties of materials used for the construction. Corresponding to the urgent needs and poor economical features, the MOCIE designated the Data Center of Mechanical Properties for Metallic Materials (DCMP). The DCMP plays roles of collection, edition and evaluation of the mechanical data and development of reference standards. In this study, several functions of the DCMP and standardization procedures of mechanical properties data will be introduced.
남승훈(SEUNG-HOON NAHM),김용일(YONG-IL KIM),서창민(CHANG-MIN SUH),김동석(DONG-SUK KIM) 한국해양공학회 2002 韓國海洋工學會誌 Vol.16 No.2
The remote measurement system(RMS) as a new experimental method is limited in its application to crack measurements at elevated temperatures because of the oxide layer on the specimen surface. Since TiAlN and Cr coating layers have a high resistance to oxidation and wear, this paper proposed a TiAlN and Cr coating technique for specimens to facilitate the measurement of crack growth behavior using RMS. To investigate the effects of the coating layer, tension and fatigue tests were carried out at room temperature and at 538 ℃. The test material was 1Cr-1Mo-0.25V steel which is widely used as a turbine rotor material. From the experimental results, it was found that the mechanical properties of the TiAlN and Cr coated specimens were similar to those of the substrate. Accordingly, the TiAlN and Cr coated layer had hardly any influence on the fatigue crack propagation.
대형 설비/구조물 안전성에 있어서 국가참조표준의 역할과 전망
남승훈(Seung Hoon Nahm),이윤희(Yun-Hee Lee),백운봉(Un Bong Baek),정인현(In Hyun Chung),이해무(Hae Moo Lee) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
In order to guarantee the safety of the facility systems, one of the essential components is information on mechanical properties of materials used for the construction. However, acquisition or accumulation of the mechanical property data in industrial fields is limited because this operation does not yield profit, excepting few materials production companies. Corresponding to the urgent needs and poor economical features, the MOCIE has founded the National Center for Standard Reference Data in the KRISS and also designated the Data Center of Mechanical Properties for Metallic Materials (DCMP) as a principal operating section. The DCMP plays roles of collection, edition and evaluation of the mechanical data and development of reference standards. In this study, several functions of the DCMP and standardization procedures of mechanical properties data will be introduced the prospective of standard reference researches will be discussed based on active feedbacks from industrial fields.