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김대진(D. J. Kim),석창성(C. S. Seok),구재민(J. M. Koo),박재실(J. S. Park),서정원(J. W. Seo),구병춘(B. C. Goo) 한국철도학회 2004 한국철도학회 학술발표대회논문집 Vol.- No.-
Under cyclic loading, the fatigue failures of welded joints occur at weld toes which induce stress concentration by weld shape. So we need to obtain the peak stress and the S-N curve to assess the fatigue strength of welded joints. However the measurement of peak stress is of high uncertainty and low reproducibility, so we use nominal stress instead in fatigue tests of welded joints. In this study, fatigue tests to obtain S-N curves am FE analyses to obtain stress concentration factors were conducted for the two types of cruciform fillet welded joints, that is, load-carrying and non load-carrying types. Then we changed the obtained S-N curves to that based on peak stress using the bot-spot stress concept. From the analyses of the S-N curves obtained, we have concluded that there is a need to develop a new method to evaluate the fatigue life.
박재실(J. S. Park),석창성(C. S. Seok),구재민(J. M. Koo),김대진(D. J. Kim),신재호(J. H. Shin),구병춘(B. C. Goo) 한국철도학회 2004 한국철도학회 학술발표대회논문집 Vol.- No.-
In this study, we compared the fatigue characteristics of weld metal with those of base metal. Also we examined the influence of heat treatment and weld bead profiles for the fatigue life of weld metals. From the experimental results, it was seen that the fatigue characteristics of welded specimens with a grinded toe of bead are slightly better than those are not grinded. Also the fatigue life is affected more by the stress concentration on the profile change in the weld toe rather than by residual stress influence, because the fatigue characteristic of weld metals was not influenced whether the heat treatment is conducted or not.
Ventilated Disk Brake의 피로 수명 해석
박재실(J. S. Park),이영훈(Y. H. Lee),석창성(C. S. Seok),김성호(S. H. Kim),이동근(D. G. Lee) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3
Brakes in cars and trucks are safety parts. Requirements not only in performance but also in comfort, serviceability and working lifetime are high and rising. In this study, we used the ventilated disk brake in 11 ton-bus. Mechanical stress analysis and thermal stress analysis were performed using ABAQUS software. Especially, characteristics of the rotor were analyzed in considering deceleration, initial temperature and intial velocity of brake. And tensile test and fatigue test were performed on those of brake. Form the comparing the results of experiment and FEM analysis, the standard for durability of brake was presented.
이영민(Y. M. Lee),박재실(J. S. Park),석창성(C. S. Seok),이찬우(C. W. Lee),김재훈(J. H. Kim) 한국정밀공학회 2005 한국정밀공학회 학술발표대회 논문집 Vol.2005 No.10월
A brake disk and a pad are important parts that affect the braking stability of a railway vehicle. Especially, because a brake disk stops the vehicle using conversion of the kinetic energy to frictional energy, thermal fatigue cracks are generated by the cyclic thermal load, as frictional heat, on a frictional surface and these cracks cause the fracture of a brake disk. Therefore, many researches for the thermal stress must be performed to improve the efficiency of brake disk and ensure the braking stability. In this study, we performed the thermal stress analysis for a ventilated brake disk with 3-D analysis model. For that, we simplified the shape of a ventilated hole to minimize problems that could be occurred in analysis process . Thermal stress analysis was performed in case that pressure distributions on a frictional surface is constant and is not. To determine pressure distributions of irregular case, pressure distribution analysis for a frictional surface was carried out. Finally using the results that were obtained through pressure distribution analysis, we carried out thermal stress analysis of each case and investigated the results of thermal stress analysis.
이영민(Y. M. Lee),최정훈(J. H. Choi),허용(Y Huh),박재실(J. S. Park),석창성(C. S. Seok),최경진(K. J. Choi) 한국철도학회 2004 한국철도학회 학술발표대회논문집 Vol.- No.-
In this study, we compared the strength of a material used in the A-type disk brake with that in the B-type. From tensile test results, it has been found that the strength of the B-type disk brake is higherthan that of the A-type. The microstructure observation and chemical analysis were conducted to determine the cause of the difference between the strength of A and B types of disk brake materials. From the experimental results, it has been confirmed that the difference in the strength between the two types of disk brake is due to the difference in the shape of graphite.
CF8M 주조 오스테나이트 스테인리스강의 열취화에 따른 재료물성치 평가
김철(C. Kim),방흥배(H. B. Park),진태은(T. E. Jin),정일석(I. S. Jeong),석창성(C. S. Seok),박재실(J. S. Park) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
CF8M cast austenitic stainless steel is used for several components such as primary coolant piping,<br/> elbow, pump casing, and valve bodies in light water reactors. These components are subject to thermal<br/> aging at the reactor operating temperature. Thermal aging results in spinodal decomposition of the<br/> delta-ferrite leading to increased strength and decreased toughness. In this study, three kinds of the<br/> aged CF8M specimen were prepared using an artificially simulated aging method. The objective of this<br/> study is to summarize the method of estimating ferrite contents, Charpy impact energy and J-R curve,<br/> and to evaluate the thermal embrittlement of the CF8M cast austenitic stainless steel piping used in the<br/> domestic nuclear power plants.
가속시험을 통한 불규칙하중을 받는 실구조물의 피로수명평가
김형익(H. I. Kim),배봉국(B. K. Bae),박재실(J. S. Park),석창성(C. S. Seok),모진용(J. Y. Mo) 한국정밀공학회 2004 한국정밀공학회 학술발표대회 논문집 Vol.2004 No.10월
A fatigue test was used to evaluate the fatigue life of an actual structure. The loaded state and the constraint condition of an actual structure must be same as the specimen in order to apply the test results to an actual structure by the specimen. The loaded state and constraint conditions can"t be same as the specimen in the actual structure which is complicated. In order to reduce these differences, an actual structure test with a lot of frequencies is need to get a fatigue life curve. Therefore, ten sets of accelerated test units which attached unbalanced mass were composed in this study. Acceleration history about the vibration of an actual structure was acquired. Rainflow counting was used on acceleration history, and the life curve return formula was assumed. The return formula that damage satisfied `1" was acquired in a feedback process by the Miner"s rule, which was the linear cumulative damage theory. A conservative fatigue life curve was determined with a return formula to have been presumed by each set. The fatigue life of regular rpm condition was calculated by these conservative fatigue life curves.
울진 원자력 발전소 3 , 4 호기 1 차계통 배관소재의 파괴저항특성 평가
석창성,김수용,강병구,박재실,윤병곤 한국산업안전학회 1999 한국안전학회지 Vol.14 No.1
The objective of this paper is to evaluate the fracture resistance characteristics of SA508 CL.la carbon steel, TP347 stainless steel and their associated welds manufactured for primary coolant system of Ulchin 3,4 nuclear power plants. The effect of various parameters such as pipe size, welding method, chemical composition, crack plane orientation, metallography and fractography on the material properties were discussed. Test results showed that the effect of pipe size on fracture toughness is negligible while the effect of welding method on fracture toughness is significant. In addition, the drop of fracture toughness in the field fabrication weld of TP347 stainless steel is probably due to the large amount of σ-phase precipitated on the δ-ferrite boundary and the large size dimples.