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수소취화된 스테인리스강 316L의 VHCF(Very High Cycle Fatigue) 피로특성과 UNSM 효과에 관한 연구
남승훈(Seung-Hoon Nahm),백운봉(Un-Bong Baek),서창민(Chang-Min Suh),편영식(Young-Sik Pyun) 대한기계학회 2017 大韓機械學會論文集A Vol.41 No.11
본 연구는 실온에서 미처리재와 UNSM처리재, 수소취화재(100 bar, 300℃에서 120 h) 및 이 수소취화재의 UNSM처리재의 스테인리스강 316L 시험편의 재료특성파악을 위한 실험을 실시하였다. 여기서 수소취화재는 기존의 미처리재의 S-N곡선보다 피로강도가 약간 감소하는 경향을 나타내었으며, 수소취화효과는 적게 나타났다. 미처리재에 비해서 UNSM처리재의 피로한도는 약 43.8 % 상승하였고, 수소취화재의 UNSM처리재는 수소취화재보다 약 57.1 % 상승하는 경향을 나타내었다. EBSD에 의한 IQ, IPF 및 KAM 맵에서 UNSM처리 후, 이 처리의 영향을 받는 나노 입자 표면층의 두께는 약 152 μm이다. 그러나 세 가지 맵에서 수소취화의 깊이 영향을 정량적으로 평가할 수 없었다. 시험편상에서 발생하는 표면균열은 수소취화의 영향으로 평균입경(35 μm)보다 작은 균열의 비율이 약 90 %를 차지하였다. This study was conducted to investigate the material properties of stainless steel 316L specimens of untreated and UNSM treated material, hydrogen attacked material(100 bar, 300 °C at 120 h) and UNSM treated hydrogen attacked material at room temperature. Results demonstrated that the hydrogen attacked materials showed a tendency toward a slightly decreased fatigue strength, while the hydrogen embrittlement effect was smaller than the S-N curve of conventional untreated material. As compared to untreated material, the fatigue limit of the UNSM treated material increased by 43.8%, while it was 57.1% higher in the UNSM treated hydrogen attacked material than in untreated hydrogen attacked material. The plastic deformation layer was ~152 μm thick, as confirmed by maps showing the level of local plastic deformation affected by the UNSM treatment in three ways: an image quality map, inverse pole figure map, and kernel average misorientation map captured via electron back scatter diffraction. Owing to hydrogen embrittlement, about 90% of surface cracks were smaller than the average grain size of 35 μm.
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.
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.
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.
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),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.
크리프-피로 하중조건하에서의 가스터빈 엔진 디스크의 균열성장 수명예측에 관한 연구
남승훈(Seung Hoon Nahm),박종화(Jonghwa Park),김종엽(Jong Yup Kim) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.3
For gas turbine engines, safe life methodology has historically been used for fatigue life management of failure critical engine components. The objective of this study is to introduce the damage tolerant design concept instead of safe life methodology which has been used to apply the life management for aircraft engine component. Crack growth data were collected on a nickel base superalloy which have been subjected to combined static and cyclic loading at elevated temperatures. Stress analysis for turbine disk was carried out. The program for computing creep-fatigue crack growth was developed. We tried to estimate remaining life of turbine disk component under various temperature and conditions using creep-fatigue crack growth data. The largest stress was occurred in disk bore part. The magnitude and direction of the maximum stress were 937㎫ and in the hoop direction. Creep crack growth life in disk bore occupied approximately the half of the total crack growth life.