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고온고압수에서 저주기 피로시험편의 표점거리 변위측정을 위한 장치개발
정일석(Ill-Seok Jeong),하각현(Gak-Hyun Ha),김태룡(Tae-Ryong Kim),조선영(Sun-Young Cho),전현익(Hyun-Ik Jeon),김영신(Young-Sin Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
Low cycle fatigue experiment in high temperature and high pressure water have been conducted to evaluate environmental fatigue characteristics of nuclear materials which are used in the primary water. The experimental methods of evaluating low cycle fatigue properties are to control by either load or displacement. The study is about the development of extensometer system for measuring displacement in gauge length of low cycle fatigue specimen in autoclave which simulated high temperature and high pressure water. The developed extensometer system showed precise change of displacement data by controlling actuator in room temperature as well as high temperature and high pressure water. This device can be applied to various material testings in high temperature and high pressure environments and is expected to greatly contribute on acquiring more detailed test data.
변형률속도가 CF8M CASS 환경피로 수명에 미치는 영향 평가
정일석(Ill-Seok Jeong),하각현(Gak-Hyun Ha),전현익(Hyun-Ik Jeon) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
The Environmental fatigue life of CF8M cast stainless steel is influenced by mechanical, environmental and metallurgical parameters, such as strain rate, strain amplitude, temperature, dissolved oxygen concentration, water flow rate and so on. In an actual plant, the mechanical and environmental parameters are changing during the plant operation. Therefore, the effect of such mechanical and environmental parameter changes on fatigue life evaluation have to be studied. Low cycle fatigue life of structural materials diminishes remarkably as functions of various parameters in high temperature and high pressure environments. Such reduction can be estimated by the fatigue life reduction factor(Fen). In this study, fatigue tests were performed under changing conditions of strain amplitude, strain rate. Fatigue life was measured in terms of the number of cycles with the variation of strain amplitudes at 0.004 %/s strain rate, and the fatigue life correction factor was evaluated according to the equation modified by U. S. Nuclear Regulatory Commission(U.S.NRC) and Japanese Environmental Fatigue Tests committee(JEFT).
CF8M 스테인리스 강 저주기 환경피로 실험의 주기적 변형률 경화 특성
정일석(Ill-Seok Jeong),하각현(Gak-hyun Ha),김태룡(Tae-Ryong Kim),전현익(Hyun-Ik Jeon),김영신 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
Low-cycle environmental fatigue tests of cast austenitic stainless steel CF8M at the condition of fatigue strain rate 0.04%/sec were conducted at the pressure and temperature, 15MPa, 315℃ of a operating pressurized water reactor. The used test rig was limited to install an extensometer at the gauge length of the cylindrical fatigue specimen inside the small autoclave. So the magnet type LVDT’s were used to measure the fatigue displacement at the specimen shoulders inside the high temperature and high pressure water autoclave. However, the displacement and strain measured at the specimen shoulders is different from the one at the gauge length for the geometry and the cyclic strain hardening effect. FEM calculated the displacement and the strain of the gauge length from the data measured at the shoulders. Tensile test properties in elastic and plastic behavior of CF8M material were used in the FEM analysis. A series of low cycle fatigue tests simulating the cyclic strain hardening effect verified that the FEM calculation was well agreed with the simulated tests. The process and method developed in this study would be so useful to produce reliable environmental fatigue curves of CF8M stainless steel in pressurized water reactors.
정일석(Ill-Seok Jeong),이용성(Yong-Sung Lee),김상재(Sang-Jai Kim),송택호(Taek-Ho Song),조선영(Sun-Young Cho) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
Environmental fatigue crack propagation of CF8M and CF8A steels used in the domestic PWR were investigated on the simulated PWR condition(Temperature: 316 , Pressure: 15MPa). The test equipment for environmental fatigue(high temperature-high pressure loop, autoclave, load frame, measurement system) were designed. As-received and 60-year aged specimens were used in the test. To compare with environmental fatigue test, another test was performed in the air condition. The fracture surface of specimens were difficult to verify the fracture modes such as striation, intergranular crack and cleavage and so on. As the ferrite content of CF8M is increased, more particles covered fracture surface were peeled.
고온고압 환경피로실험 오토클래이브 내부용 미소변위 측정장치 개발
정일석(Ill-Seok Jeong),하각현(Gak-hyun Ha),김태룡(Tae-Ryong Kim),전현익(Hyun-Ik Jeon),김영신(Young-Sin Kim) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11
An extensometer system to measure strain and displacement of cylindrical fatigue specimen in a autoclave of high temperature and high pressure environment has been developed by KEPRI. The extensometer reads the displacement caused by fatigue loads at the target length of the specimen installed inside the autoclave. The performance of the extensometer were tested at 15㎫, 315℃of a operating pressurized water reactor. Two LVDT’s of magnet type were connected to the extensometer and used for converting the fatigue displacement to electronic signal. The device is being used for developing environmental fatigue curve of CF8M cast austenitic stainless steel (CASS) in the test condition of low cycle and low strain. This paper introduces the background and results of the development.
정일석(Ill-Seok Jeong),김상재(Sang-Jai),홍승열(Sung-Yull Hong) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.8
Among published environmental fatigue test data of stainless steels, Type 304 SS, Type 316 SS, Type 316N SS, Type 316 Weld SS, and cast stainless steel CF8M in Japan and U.S., useful data were quoted for analyzing the effect of sensitizing stainless steels in LWR environments. Temperature of the test data are 288~325℃ which is operating temperature range of LWR plants. Data were classified in terms of dissolved oxygen levels, strain rates in tension stroke, and sensitization. Then data were compared with logarithmic graph of vertical strain rate and horizontal fatigue life. Trend of sensitization was investigated for each type of stainless steels.
정일석(Ill-Seok Jeong),김상재(Sang-Jai Kim),홍승열(Sung-Yull Hong) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
Among published environmental fatigue test data of stainless steels, Type 304 SS, Type 316 SS, Type 316N SS, Type 316 Weld SS, and cast stainless steel CF8M in Japan and U.S., useful data were quoted for analyzing the effect of sensitizing stainless steels in LWR environments. Temperature of the test data are 288~325℃ which is operating temperature range of LWR plants. Data were classified in terms of dissolved oxygen levels, strain rates in tension stroke, and sensitization. Then data were compared with logarithmic graph of vertical strain rate and horizontal fatigue life. Trend of sensitization was investigated for each type of stainless steels.
영향계수를 이용한 원통용기 축방향 표면결함의 응력확대계수의 계산
장창희,문호림,정일석,김태룡,Jang, Chang-Heui,Moon, Ho-Rim,Jeong, Ill-Seok,Kim, Tae-Ryong 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.11
For integrity analysis of nuclear reactor pressure vessel, including the Pressurized thermal shock analysis, the fast and accurate calculation of the stress intensity factor at the crack tip is needed. For this, a simple approximation scheme is developed and the resulting stress intensity factors for axial semi-elliptical cracks in cylindrical vessel under various loading conditions are compared with those of the finite element method and other approximation methods, such as Raju-Newman's equation and ASME Sec. Xl approach. For these, three-dimensional finite-element analyses are performed to obtain the stress intensity factors for various surface cracks with t/R = 0.1. The approximation methods, incorporated in VINTIN (Vessel INTegrity analysis-INner flaws), utilizes the influence coefficients to calculate the stress intensity factor at the crack tip. This method has been compared with other solution methods including 3-D finite clement analysis for internal pressure, cooldown, and pressurized thermal shock loading conditions. The approximation solutions are within $\pm$2.5% of the those of FEA using symmetric model of one-forth of a vessel under pressure loading, and 1-3% higher under pressurized thermal shock condition. The analysis results confirm that the VINTIN method provides sufficiently accurate stress intensity factor values for axial semi-elliptical flaws on the surface of the reactor pressure vessel.