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.

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.

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.

자동차용 엔진 마운트의 피로거동에 관한 연구

서창민(Chang-Min Suh),오상엽(Sang-Yeob Oh),박대규(Dae-Kyu Park),장주호(Ju-Ho Jang) 한국해양공학회 2009 韓國海洋工學會誌 Vol.23 No.5

In this study, Finite Element Analysis (FEA) was used to decide three kinds of material property of vibration proof rubber with the unique characteristic of non-linear and large deformation. As well, three types of hardness (Hs 50, 55, 60) were compared with the result of fatigue tests, fatigue life was able to be predicted. The request for fatigue life becomes strict more and more as increasing stress under conditions like a compaction, high load and high temperature for parts because it is main characteristics of rubber mount for automotive. Regarding to the fatigue life under dynamic deformation condition, it can be predicted as checking forced deformation extends and its frequency and its strain-life curve. As for material property tests of uniaxial tension test, uniaxial compression test, pure shear test, Ogden model was used far FEA by observing relations between stress and strain's rate as curve fitting. As a result of FEA, fatigue life for rubber mount was predicted and accorded well with the experimental data of fatigue test with hourglass specimens. In addition, its property of the predictable fatigue life method suggested in this study was accorded well with the experimental data by comparing the predicted fatigue life of FEA with the result of fatigue test for rubber component of engine rubber mount.

FEM을 이용한 상용차용 S-cam 브레이크슈의 구조해석

서창민(Chang-Min Suh),지현철(Hyun-Chul Jee) 한국해양공학회 2009 韓國海洋工學會誌 Vol.23 No.4

Structural analysis of a brake shoe for commercial vehicle was performed using finite element method. Since the strength of a brake shoe is affected by the magnitude and distribution shape of the contact pressure with the drum, the contact pressure between the shoe friction material and drum was calculated using a 2-Dimensional non-linear contact analysis in a state. And the brake was actuated by input air pressure and the drum of it was calculated both stationary and dynamic based on forced torque applied to the drum during the static state analysis. The results of the above analysis were then used as the load boundary conditions for a 3-Dimensional shoe model analysis to determine the maximum strain on the shoes. In the analysis model, the values of tensile test were used for the material properties of the brake shoes and drum, while the values of compression test were used for the friction material. We assumed it as linear variation, even though the properties of friction material were actually non-linear. The experiments were carried out under the same analysis conditions used for fatigue test and under the same brake system which equipped with a brake drum based on the actual axle state in a vehicle. The strains were measured at the same locations where the analysis was performed on the shoes. The obtained results of the experiment matched well with those from the analysis. Consequently, the model used in this study was able to determine the stress at the maximum air pressure at the braking system, thereby a modified shoe model in facilitating was satisfied with the required endurance strength in the vehicle.

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.

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.

2 1/4 Cr-1 Mo鋼의 작은 表面균열의 成長에 관한 基礎的 硏究

徐昌敏(Chang Min Suh),姜用求(Yong Goo Kang) 한국해양공학회 1987 韓國海洋工學會誌 Vol.1 No.1

Fatigue tests by axial loading (R=0.05) were carried out to investigate fatigue crack growth characteristics of small surface cracks in 2 1/4 Cr-1 Mo steel at room temperature by using flat specimens with a small artificial pit.<br/> All the data of the fatigue crack growth rate obtained in the present test are determined as a function of the stress intensity factor range about a semi-elliptical crack, so that the application of linear fracture mechanics to the surface fatigue crack growth and to the fatigue crack growth into depth, and all the data obtained from tests were discussed in comparison with the data of Type 304 stainless steel and two type of mild steel under the same test conditions.<br/> The obtained results are as follows :<br/> 1) When the cycle ratios are same, surface fatigue crack length and its depth are almost same and fall within a narrow scatter band in spite of different stress levels.<br/> 2) Relations of the surface fatigue crack growth rate (da/dN) and fatigue crack growth rate into depth (db/dN) to its stress intensity factor range (ΔKIa, ΔKIb) can be plotted as a straight line at log-log diagram without dependence of stress level and coincide with the data of part-through crack in various steels.