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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),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),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.
수소취화된 스테인리스강 304의 VHCF(Very High Cycle Fatigue) 피로특성과 UNSM처리 효과에 관한 연구
남승훈(Seung-Hoon Nahm),백운봉(Un-Bong Baek),서창민(Chang-Min Suh),편영식(Young-Sik Pyun) 대한기계학회 2018 大韓機械學會論文集A Vol.42 No.6
실온에서 미처리재와 UNSM 처리재, 수소취화재(10 MPa, 300 ℃, 120 h) 및 이 수소취화재의 UNSM 처리재의 스테인리스강 304 시험편의 재료특성파악을 위한 실험에서 수소취화재는 기존의 미처리재의 S-N곡선보다 피로강도가 거의 비숫한 경향을 나타내었으며, 수소취화효과는 미미하였다. 미처리재와 수소취화재의 피로한도는 400 ㎫로 같았고, 약 8.1배의 많은 수소를 함유함에도 수소취화영향은 거의 없었다. 미처리재에 비해서 UNSM처리재의 피로한도는 약 50 % 상승하였고, 수소취화재의 UNSM처리재는 수소취화재보다 약 50 % 상승하는 경향을 나타내었다. EBSD에 의한 IQ, IPF, KAM 및 phase diagram map에서 UNSM처리 후, 이 처리의 영향을 받는 나노 입자 표면층의 두께는 약 112 ㎛이다. This study is to investigate the influence of hydrogen attack and UNSM on fatigue behaviors of STS 304. Fatigue endurance limit of untreated material and hydrogen treated one was the same at 400 ㎫, and hydrogen embrittlement had little influence even though it contained about 8.1 times more hydrogen. Thus the sensitivity of hydrogen gas of this STS 304 material is very low. The fatigue endurance limit of the UNSM treated material rose by about 50 % compared with the untreated material and showed a tendency to increase by about 50 % as compared with the hydrogen treated material. After the UNSM treatment with IQ, IPF, KAM and phase diagram map by EBSD, the thickness of the nanoparticle surface layer affected by this treatment is about 112 ㎛.
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.
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),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.5
STB2-A재와 STB2-R재의 HCF(장수명피로) 범위에서는 표면을 기점으로 하는 표면결함에서 발생한 표면균열에 의해 파괴되는 형태를 취하였고, VHCF(초장수명피로, Nf >10<SUP>6</SUP> 사이클)범위에서는 내부에서 피로균열이 형성되는 어안균열 파괴기구로 되면서 이중 S-N 곡선이 얻어졌다. 이 어안균열의 중심부의 개재물은 TiN, Al₂O₃를 주성분으로 하며, 흔적이 명확하게 발생하였다. 그러나 STB2-B재에서 생긴 어안균열의 중심부는 Cr매트릭스(matrix)이며, 인근부분의 SEM 사진과 EDS분석 결과는 서로 매우 유사하나, SEM사진상에서는 특정 개재물을 판별할 수 없었다. 그리고 이 어안균열 파괴모드가 장수명피로 영역에서도 발생되면서 이중 S-N곡선이 형성되지 않았다. 개재물의 △K는 STB2-A재와 STB2-R재는 5MPa√m에 접근하며, 강재의 △Kth(하한계응력확대계수범위)의 값과 유사하다. 또 어안균열의 △K는 10 MPa√m에 접근하며 타 연구와 일치하는 경향을 나타내었다. 그러나 STB2-B의 어안균열과 개재물의 △K는 STB2-A재와 STB2-R재보다 약간 높은 값을 취하는 경향을 나타내었다. In the HCF range of STB2-A and STB2-R materials, the fracture was caused by the surface crack generated by the surface defects originating from the surface. In the VHCF range (Nf >10<SUP>6</SUP>), the fracture mechanism of the fish-eye crack in which the internal originating fracture type was formed and the duplex S-N curves were obtained for the both bearing steels. At the center of this fish-eye crack, the inclusions consisted mainly of TiN and Al₂O₃. However, the center part of the fish-eye crack generated in STB2-B material was Cr matrix. And the SEM photographs and the EDS analysis results of the neighboring parts of the Cr matrix were very similar to each other, and the inclusions could not be discriminated from the SEM photographs. In addition, this fish-eye crack failure mode also occurred in the long life fatigue region, so that no the duplex S-N curve was formed. ΔK of the inclusions was close to 5 MPa√m for STB2-A and STB2-R materials and was similar to the value of △Kth (threshold stress intensity factor range) of steels. In addition, ΔK of fish-eye crack approached 10 MPa√m and showed a tendency to agree. However, the fish-eye cracks and inclusions of STB2-B material tended to take slightly higher values than the STB2-A and STB2-R materials.
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.