표면거칠기를 가진 유리의 입자충격 손상기구에 관한 실험적 연구

서창민,정성묵,이문환,Suh, Chang-Min,Chung, Seong-Muk,Lee, Mun-Hwan 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.7

The damage mechanism by the impact of steel ball on the soda-lime glass having a different surface roughness was investigated. An initiation and a propagation behavior of cracks formed by each impact velocity were quantitatively studied. A 4-point bending test was carried out to evaluate the remaining bending strength of a scratched soda-lime glass which impacted by the steel ball. As the surface roughness was increased, the shape of cracks became more irregular rather than those of the smooth specimens. The phenomenon of turning up in the wing of cone cracks occurred even at the lower velocity than the critical velocity caused the crushing. The threshold velocity of cracks initiation generally became lower than those of smooth specimen. An initiation and a propagation behavior of radial cracks had no relation with the direction of scratch on the surface. The remaning benidng strength of the scratched specimen according to impact velocity had no big difference compared with those of the smooth specimen.

${Al_2}}O_3}-TiO_2$ 플라즈마 코팅된 유리의 입자충격에 의한 손상기구

서창민,이문환,홍대영,Suh, Chang-Min,Lee, Moon-Hwan,Hong, Dea-Yeong 대한기계학회 1998 大韓機械學會論文集A Vol.22 No.3

A quantitative study of impact damage of ${Al_2}}O_3}-TiO_2$ plasma coated soda-lime glasses was carried out and compared with that of the uncoated smooth glass specimen. The shape of cracks by the impact of steel ball was observed by stereo-microscope and the decrease of the bending strength due to the impact of steel ball was measured through the 4-point bending test. At the low velocity, cone cracks were occurred. As the impact velocity increases, initial lateral cracks were propagated on the slanting surface of a cone crack, and radial cracks were generated at the crushed site. When the impact velocity of steel ball exceeds the critical velocity, the contact site of specimen was crushed due to plastic deformation and then radial and lateral cracks were largely grown. Crack length of coated specimens was smaller than that of uncoated smooth specimen due to the effect of coating layer on the substrate surface. According to impact velocity, the bending strength of coated specimens had no significant difference, compared with that of the uncoated smooth specimen. But this represents that the bending strength of coated specimens was increased, considering the effect of sand blasting damage which was performed to increase the adhesion force of coating layer.

시효열화시킨 1Cr-1Mo-0.25V 강의 고온화의 회전굽힘 피로강도에 관한 연구

서창민,허정훈,남승훈,Suh, Chang-Min,Huh, Jeong-Hoon,Namh, Seung-Hoon 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.9

The estimation of the remaining life for the aged components in power plant as well as chemical and petroleum plants has been recently concerned. The raw materials used in this study are the 1Cr-1Mo-0.25V steel which intensified P and S compositions along with the nominal compositions of ASTM A 470 standard. Five kinds of specimens with the different degradation levels were prepared by isothermal aging heat treatment at 630.deg.C. The mechanical properties and rotated bending fatigue strength of virgin and aged 1Cr-1Mo-0.25V steel have been investigated through the hardness, tensile, fatigue test, SEM fractograph and EDS analysis at 538.deg.C and room temperature, respectively. Thus the data of aged specimens were compared with those of virgin specimen to evaluate the aging effects. The main results obtained in this study are as follows ; The decrease of the yield and tensile strength due to degradation was distinguished until 50, 000hrs simulated service time. And it was confirmed that the considerable amount of P, Mn, Cr and S was precipitated at the grain boundary of aged material through the SEM and EDS analysis. The rotated bendingd fatigue strength at 538.deg.C of virgin, 25, 000, 50, 000, 75, 000 and 100, 000 hrs aged material was decreased 44.6 %, 49.6 %, 51.5 %, 52.4% and 53.8% than that of virgin material at 10$_{7}$cycles of room temperature, respectively. The major cracks of virgin and aged materials mainly initiated at the inclusions including Si, P and Mn compositions which were located at the outer periphery of the specimen.n.

온도변화에 대한 고분자 코팅 층에 발생하는 응력 해석

박명규(MYUNG-KYU PARK),이상순(SANG-SOON LEE),서창민(CHANG-MIN SUH) 한국해양공학회 2003 韓國海洋工學會誌 Vol.17 No.6

This paper deals with the stress singularity developed in a polymer layer that is coated to a concrete surface, due to temperature change. The boundary element method is employed to investigate the behavior of interface stresses. The polymeric layer is assumed to be a linear viscoelastic material, and is thermorheologically simple. The order of the singularity is obtained, numerically, for a given viscoelastic model. Numerical results exhibit the relaxation of interface stresses, and large gradients are observed in the vicinity of the free surface. Results show that the stress singularity factor is relaxed with time, while the order of the singularity increases with time for the viscoelastic model.

Very high cycle fatigue characteristics of SCM435 under load variation by ultrasonic nanocrystal surface modification treatment

Chang-Min Suh(서창민),Sung-Min Yoon(윤성민),Ju-Ho Jang,Min-Soo Suh,Young-Sik Pyoun,Tatsuo Sakai 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11

In this study, UNSM technology is applied to the SCM435 steel for VHCF evaluation test. This study reports VHCF test results of SCM435 steel and the effect of UNSM on SCM435 steel comparing before and after UNSM treatment. SCM435 specimens were evaluated to verify the fatigue characteristics of the UNSM treatment by changing the static load levels, 40N, 70N and 100N, respectively.

열전발전용 Bi-Te module에서 미끄럼에 따른 열응력 완화 특성

서창민(CHANG-MIN SUH),우병철(BYUNG-CHUL WOO) 한국해양공학회 2000 韓國海洋工學會誌 Vol.14 No.4

Recently the research for utilization of waste heat produced from electric power plants, casting factories, heat treating factories or commercial building are being afforded by the need for energy saving. The objective of this study is to develop a thermoelectric generation system which converts unused energy from close-at-hand sources such as garbage incineration heat and industrial exhaust etc. into electricity. This paper presents a thermoelectric technology on a optimum system design method and efficiency and cost effective thermoelectric element on order to extract the maximum power output from energy conversion of waste energy. It is shown that the longitudinal stresses of module contacted with two point constrained Al tubes could be released more than those with a one-point constrained.

인코넬 718강의 UNSM처리재의 고온하의 피로특성에 관한 연구

서창민(Chang Min Suh),남승훈(Seung Hoon Nahm),우영한(Young Han Woo),허광호(Kwang Ho Hor),홍상휘(Sang Hwui Hong),김준형(Jun Hyong Kim),편영식(Young Sik Pyun) 대한기계학회 2016 大韓機械學會論文集A Vol.40 No.11

고온기기의 부재로 널리 사용되는 인코넬 718을 사용하여 UNSM 표면처리법에 의한 처리효과를 기기의 사용조건을 고려한 실온, 300℃, 500℃ 및 600℃의 세 가지 온도레벨하의 대기 중에서 고온피로시험을 실시하여 각 시험편의 온도에 따른 피로특성을 연구하였다. 이때 고온회전굽힘피로시험(R= 1)은 할로겐(Halogen) 램프를 사용한 집광식인 가열방식을 선택한 새로운 피로시험기를 사용하였다. 인코넬 718의 고온피로강도는 상온에 비하여 감소하였다. 그러나 설계응력레벨에서는 상온의 내구한도와 유사한 경향을 나타내었다. UNSM 처리된 고온피로특성은 미처리재에 비하여 설계응력레벨에서 크게 향상되었다. 미처리재의 300℃와 500℃ 사이의 온도 영향은 거의 없었지만, 600℃에서는 높은 응력레벨에서 피로수명이 짧아졌지만, 낮은 설계응력레벨에서는 상온의 S-N선도보다 피로수명이 증가되는 경향을 나타내었다. This study investigated the influence of high temperature and UNSM on the fatigue behavior of Inconel 718 alloy at RT, 300, 500, and 600℃. Fatigue properties of Inconel 718 were reduced at high temperatures compared to those at room temperature. However, the endurance limit was similar to that of the room temperature sample at the design stress level. High-temperature fatigue characteristics of the UNSM-treated specimen were significantly improved at the design stress level as compared to the untreated specimens. Specifically, the influence of temperature on the S-N curves at the design stress level of the UNSM-treated specimen showed the tendency of longer fatigue lives than those of untreated ones. Researchers can obtain rotary fatigue test results simply by heating specimens with a halogen lamp to precise temperatures during specific operations.

TiN 코팅 공정 개선에 의한 1Cr-1Mo-0.25V 강재의 피로강도 특성

서창민(Chang-Min Suh),김경렬(Kyung-Ryul Kim) 한국해양공학회 1997 韓國海洋工學會誌 Vol.11 No.4

This paper deals with the effect of coating layer on the fatigue strength of TiN coated 1Cr-lMo-0.25V steel prepared by using the arc ion plating (AIP) process, in which it was characterized by the presence of extractor grid (ion filter). The rotary bending fatigue tests were carried out under room air conditions, and the fatigue crack initiation and growth behavior were observed by using plastic replica method. As experimental results, it was found that the obvious improvement of fatigue life at lower stress region was confirmed in TiN coated specimen processed with ion filter. It was also explained that the increase of fatigue life in the case of an improved AIP process with ion filter was attributed to the retardation of crack initiation of the substrate surface due to hard coating layer, more densly formed with the reduced size and density of droplets.

Arc Ion Plating 方式에 依한 TiCN 蒸着시 反應가스가 코팅층에 미치는 影響

서창민(Chang-Min Suh),김창근(Chang-Geun Kim),유임준(Im-Jun Yoo) 한국해양공학회 1997 韓國海洋工學會誌 Vol.11 No.3

This work was intended to study the effect of a partial pressure ratio and a total pressure of reactive gases on the properties of TiCxN1-x coated layer. In this regard, various TiCxN1-x coatings were synthesized with C₂H₂ and N₂ mixture gas of different compositions by Arc Ion Plating process which has been highlighted for an industrial purpose. It was revealed from colors and X-ray diffraction patterns that the concentration of carbon of a TiCxN1-x coating increases with a partial pressure ratio (PC₂H₂/PN₂) as well as a total pressure of C₂H₂ and N₂ mixture gas. Accordingly, the hardness of TiCxN1-x coated layer increased but the adhesion to the substrate of SKH 51 was degraded. On the other hand, the deposition rate was independent of a partial pressure ratio and a total pressure of mixture gas. It was found that a uniform gas distribution is critical for an industrial application since the composition of a coating depends strongly on the location of a substrate inside of the furnace. As a result of milling tests with different TiCxN1-x coated end mills, the one which has a low carbon concentration was better than others studied in this work.

시효 열화시킨 터빈 로터강의 피로강도에 관한 연구

서창민(Chang-Min Suh),허정훈(Jeong-Hoon Huh),이해무(Hae-Moo Lee),서덕영(Duck-Young Suh) 한국해양공학회 1996 韓國海洋工學會誌 Vol.10 No.2

The estimation of the remaining life for the aged components in power plant as well as chemical and petroleum plants has been recently concerned. The raw materials used in this study are the 1Cr-1Mo-0.25V rotor steel which intensified P and S compositions along with the nominal compositions of ASTM A470 standard. Five kinds of specimens with the different degradation levels were prepared by isothermal aging heat treatment at 630℃. The mechanical properties and fatigue strength of virgin and aged 1Cr-1Mo-0.25V rotor steel have been investigated through the hardness, tensile, fatigue test, SEM fractograph and EDS analysis at room temperature. Thus, the data of aged specimens were compared with those of virgin specimen to evaluate the aging effects.<br/> The main results obtained in this study are as follows; The decrease of the hardness due to degradation was distinguished until 50,000hrs simulated service time. And it was confirmed that the considerable amount of P, Mn, Cr and S was precipitated at the grain boundary of aged material through the SEM and EDS analysis. The fatigue strength of 25,000, 50,000, 75,000 and 100,000hrs aged material was decreased 29.5%, 24.4%, 28.6%, 35.7% than that of virgin material at 10<SUP>7</SUP> cycles of room temperature.<br/> The major cracks of virgin and aged materials initiated at the inclusions including Si, P and Mn compositions which were located at the outer periphery of the specimen.