• Title/Summary/Keyword: Low cycle fatigue test

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Thermal-mechanical Fatigue Life Prediction of 12Cr Forged Steel Using Strain Range Partitioning method (변형률분할법에 의한 12Cr 단조강의 열피로 수명예측)

  • 하정수;옹장우;고승기
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.5
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    • pp.1192-1202
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    • 1994
  • Fatigue behavior and life prediction were presented for thermal-mechanical and isothermal low cycle fatigue of 12Cr forged steel used for high temperature applications. In-phase and out-of-phase thermal-mechanical fatigue test at 350 to 600.deg. C and isothermal low cycle fatigue test at 600.deg. C were conducted using smooth cylindrical hollow specimen under strain-control with total strain ranges from 0.006 to 0.015. Cyclic softening behavior was observed regardless of thermal-mechanical and isothermal fatigue tests. The phase difference between temperature and strain in thermal-mechanical fatigue resulted in significantly shorter fatigue life for out-of-phase than for in-phase. The difference in fatigue lives was dependent upon the magnitudes of inelastic strain ranges and mean stresses. Increase in inelastic strain range showed a tendency of intergranular cracking and decrease in fatigue life, especially for out-of-phase thermal-mechanical fatigue. Thermal-mechanical fatigue life prediction was made by partitioning the strain ranges of the hysteresis loops and the results of isothermal low cycle fatigue tests which were performed under the combination of slow and fast strain rates. Predicted fatigue lives for out-of-phase using the strain range partitioning method showed an excellent agreement with the actual out-of-phase thermal-mechanical fatigue lives within a factor of 1.5. Conventional strain range partitioning method exhibited a poor accuracy in the prediction of in-phase thermal-mechanical fatigue lives, which was quite improved conservatively by a proposed strain range partitioning method.

Thermal-Mechanical and Low Cycle Fatigue Characteristics of 12Cr Heat Resisting Steel with Hold Time Effects (유지시간 효과를 고려한 12Cr 내열강의 열피로 및 저주기 피로 특성)

  • Ha, J.S.;Koh, S.K.;Ong, J.W.
    • Transactions of the Korean Society of Automotive Engineers
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    • v.3 no.1
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    • pp.1-12
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    • 1995
  • Isothermal and thermal-mechanical fatigue characteristics of 12Cr heat resisting steel used for high temperature applications were investigated including hold time effects. Isothermal low cycle fatigue test at $600^{\circ}C$ and in-phase, out-of-phase thermal-mechanical fatigue test at 350 to $600^{\circ}C$ were conducted using smooth cylindrical hollow specimen under strain-control with total strain ranges from 0.006 to 0.015. Regardless of thermal-mechanical and isothermal fatigue tests, cyclic softening behavior was observed and much more pronounced in the thermal-mechanical fatigue tests with hold times due to the stress relaxation during the hold time. The phase difference between temperature and strain in thermal-mechanical fatigue tests resulted in significantly shorter fatigue life for out-of-phase compared to in-phase. The differences in fatigue lives were dependent upon the magnitudes of plastic strain ranges and mean stresses. During the hold time in the strain-controlled fatigue tests, the increase in the plastic strain range and the stress relaxation were observed. It appeared that the increase in plastic strain range per cycle and the introduction of creep damage made important contributions to the reduction of thermal-mechanical fatigue life with hold time, and the life reduction tendency was more remarkable in the in-phase than in the out-of-phase thermal-mechanical fatigue. Isothermal fatigue tests performed under the combination of fast and slow strain rates at $600^{\circ}C$ showed that the fatigue life decreased as the strain rate and frequency decreased,especially for the low strain ranges.

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STRAIN RATE CHANGE FROM 0.04 TO 0.004%/S IN AN ENVIRONMENTAL FATIGUE TEST OF CF8M CAST STAINLESS STEEL

  • Jeong, Ill-Seok;Kim, Wan-Jae;Kim, Tae-Ryong;Jeon, Hyun-Ik
    • Nuclear Engineering and Technology
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    • v.43 no.1
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    • pp.83-88
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    • 2011
  • To define the effect of strain rate variation from 0.04% to 0.004%/s on environmental fatigue of CF8M cast stainless steel, which is used as a primary piping material in nuclear power plants, low-cycle fatigue tests were conducted at operating pressure and temperature condition of a pressurized water reactor, 15 MPa and $315^{\circ}C$, respectively. A high-pressure and high-temperature autoclave and cylindrical solid fatigue specimens were used for the strain-controlled low-cycle environmental fatigue tests. It was observed that the fatigue life of CF8M stainless steel is shortened as the strain rate decreases. Due to the effect of test temperature, the fatigue data of NUREG-6909 appears a slightly shorter than that obtained by KEPRI at the same stress amplitude of $1{\times}10^3$ MPa. The environmental fatigue correction factor $F_{en}$'s calculated with inputs of the test data increases with high strain amplitude, while the $F_{en}$'s of NUREG-6909 remain constant regardless of strain amplitude.

Fatigue Life Analysis of SA508 Gr. 1A Low-Alloy Steel under the Operating Conditions of Nuclear Power Plant (원자력발전소 운전환경에서 SA508 Gr. 1A 저합금강의 피로 수명 분석)

  • Lee, Yong Sung;Kim, Tae Soon;Lee, Jae Gon
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.6 no.1
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    • pp.50-56
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    • 2010
  • Fatigue has been known as a major degradation mechanism of ASME class 1 components in nuclear power plants. Fatigue damage could be accelerated by combined interaction of several loads and environmental factors. However, the environmental effect is not explicitly addressed in the ASME S-N curve which is based on air at room temperature. Therefore many studies have been performed to understand the environmental effects on fatigue behavior of materials used in nuclear power plants. As a part of efforts, we performed low cycle fatigue tests under various environmental conditions and analyzed the environmental effects on the fatigue life of SA508 Gr. 1a low alloy steel by comparing with higuchi's model. Test results show that the fatigue life depends on water temperature, dissolved oxygen and strain rate. But strain rate over 0.4%/s has little effect on the fatigue life. To find the cause of different fatigue life with ANL's and higuchi's model, another test performed with different heat numbered and heat treated materials of SA508 Gr. 1a. On a metallurgical point of view, the material with bainite microstructure shows much longer fatigue life than that with ferrite/pearlite microstructure. And the characteristics of crack propagation as different microstructure seem to be the main cause of different fatigue life.

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Comparison and Evaluation of Low-Cycle Fatigue Life Prediction Methods Using Cu-Cr Alloy Developed for Rocket Engines (로켓엔진용 구리크롬 합금의 저주기 피로수명 예측방법 비교 및 평가)

  • Jongchan Park;Jae-Hoon Kim;Keum-Oh Lee
    • Journal of the Korean Society of Propulsion Engineers
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    • v.26 no.5
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    • pp.1-10
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    • 2022
  • For Cu-Cr alloy developed for rocket engines, estimated fatigue lives were calculated using various fatigue life prediction methods and compared with fatigue life acquired from low-cycle fatigue tests. The utilized methods for fatigue life prediction are as follows: Coffin-Manson relation, plastic/total strain energy density relations, Smith-Watson-Topper relation, Tomkins relation, and Jahed-Varvani relation. As results of estimation of fatigue lives, it satisfied within scatter band two compared to the test fatigue lives in all methods. The quantitative calculation of the deviation of predicted fatigue lives gives that the total strain energy density relation presents the best result.

A study on the thermal-mechanical fatigue life prediction of 12 Cr steel (12 Cr 강의 열피로 수명단축에 관한 연구)

  • Ha, Jeong-Soo;Kim, Kun-Young;Ahn, Hye-Thon
    • Journal of the Korean Society for Precision Engineering
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    • v.11 no.4
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    • pp.114-125
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    • 1994
  • Fatigue behavior and life prediction method were presented for themal-mechanical and isothermal low cycle fatigue of 12 Cr forged steel used for high temperature applications. In-phase and out-of-phase thermal-mechanical fatigue test from 350 .deg. C to 600 .deg. C and isothermal low cycle fatigue test at 600 .deg. C, 475 .deg. C, 350 .deg. C were conducted using smooth cylindrical hollow specimen under strain-control with total strain ranges from 0.006 to 0.015. The phase difference between temperature and strain in thermal-mechanical fatigue resulted in significantly shorter fatigue life for out-of-phase than for in-phase. Thermal-mechanical fatigue life predication was made by partitioning the strain ranges of the hysteresis loops and the results of isothermal low cycle fatigue tests which were performed under the combination of slow and fast strain rates. Predicted fatigue lives for out-of-phase using the strain range partitioning method showed an excellent agreement with the actual out-of-phase thermal-mechanical fatigue lives within a factor of 1.5. Conventional strain range partitioning method exhibited a poor accuracy in the prediction of in-phase range partitioning method in a conservative way. By the way life prediction of thermal-mechanical fatigue by Taira's equivalent temperature method and spanning fartor method showed good agreement within out-of-phase thermal-mechanical fatigue.

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Effect of grain boundary precipitation on low-cycle fatigue behavior aat elevated temperature of SUS 316 stainless steel (SUS 316鋼 의 高溫低사이클 피勞擧動 에 미치는 粒界절出物 의 影響)

  • 오세욱;국미무;산전방박;좌등철
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.4 no.4
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    • pp.152-159
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    • 1980
  • The temperature and the grain boundary precipitation have the great influence on the low-cycle fatigue behavior of austenite stainless steel at elevated temperature. For the purpose of investigating the mechanism concerning the change of fatigue micro crack mode in SUS 316 under various conditions low-cycle fatigue test was carried out at the elevated temperature 600.deg.C, plastic strain range 2% and constant strain rate .5c.p.m. A special attention is given to the observation of intergranular crack initiation. The results obtained are summarized as follows. The low-cycle fatigue behavior of SUS 316 at 600.deg.C is affected by transition of crack initiation mode from intergranular to transgranular. The transition is due to the aging effect, which is caused by grain boundary precipitations of Cr$\_$23/C$\_$6/. Since the intergranular crack initiation is brought about by the grain boundary sliding, the transgranular crack initiates in case that the strengthening of grain boundary due to the precipitation of Cr$\_$23/C$\_$6/ carbides takes place ahead of the intergranular crack initiation.

Low Cycle Fatigue Life Behavior of GFRP Coated Aluminum Plates According to Layup Number (적층수에 따른 GFRP 피막 Al 평활재의 저주기 피로수명 평가)

  • Myung, Nohjun;Seo, Jihye;Lee, Eunkyun;Choi, Nak-Sam
    • Composites Research
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    • v.31 no.6
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    • pp.332-339
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    • 2018
  • Fiber metal hybrid laminate (FML) can be used as an economic material with superior mechanical properties and light weight than conventional metal by bonding of metal and FRP. However, there are disadvantages that it is difficult to predict fracture behavior because of the large difference in properties depending on the type of fiber and lamination conditions. In this paper, we study the failure behavior of hybrid materials with laminated glass fiber reinforced plastics (GFRP, GEP118, woven type) in Al6061-T6 alloy. The Al alloys were coated with GFRP 1, 3, and 5 layers, and fracture behavior was analyzed by using a static test and a low cycle fatigue test. In the low cycle fatigue test, strain - life analysis and the total strain energy density method were used to analyze and predict the fatigue life. The Al alloy did not have tensile properties strengthening effect due to the GFRP coating. The fatigue hysteresis geometry followed the behavior of the Al alloy, the base material, regardless of the GFRP coating and number of coatings. As a result of the low cycle fatigue test, the fatigue strength was increased by the coating of GFRP, but it did not increase proportionally with the number of GFRP layers.

Determination of the Fatigue Limit by Using a Tensile Testing Data (인장 실험 데이터를 이용한 피로한도 결정에 관한 연구)

  • Kim, Tae-Hun;Kim, Hak-Yun;O, Heung-Guk;Jin, Eok-Yong
    • Korean Journal of Materials Research
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    • v.10 no.2
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    • pp.155-159
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    • 2000
  • Microstructural processes during high cycle fatigue are investigated according to plastic-strain hardening, crack formation, crack propagation and fracture. It is shown that the fatigue test resembles the uniaxial tensile test. The logarithm of the number of cycles to failure is proportional to the elongation in the tensile test. Under high cycle fatigue test, the strain is normally elastic. If the strain is absolutly elastic, fatigue could not result. But this is over simplication. Nearly all metals undergo a minor amount of plastic strain even at low stress. Damage accumulation leadling to crack formation can continue in the persistent slip bands at very low average plastic strain amplitude. In the ten­s sile test the overall specimen follows the failure procedure whilst in the high cycle fatigue test the local persistent slip band follows the failure procedure. However accumulations of strain per unit volume in the deforming region before failure in both cases are equal locally.

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Effect of Local Strain on Low Cycle Fatigue using ESPI System (ESPI System을 이용하여 측정한 국부 변형률이 저사이클 피로수명에 미치는 영향에 관한 연구)

  • Kim, Kyung-Su;Kim, Ki-Sung;Kwon, Jung-Min;Park, Seong-Mo;Kim, Beom-Il
    • Journal of the Society of Naval Architects of Korea
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    • v.43 no.2 s.146
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    • pp.213-219
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    • 2006
  • Low cycle fatigue cracks are mainly detected at discontinuous welded locations with high stresses under repeated cyclic static loads due to cargo leading and unloading. Theoretical and analytical methods have been used for evaluation of local stress and strain which have an effect on a prediction of fatigue life, but those have difficulties of considering stress concentration at notched location and complicated material behavior of welded joint or heat affected zone. Electronic speckle pattern interferometry(ESPI) system is nondestructive and non-contact measurement system which can get the relatively accurate full field strain at critical positions such as welded zone and structural discontinuous location. In this study, local strain was measured on welded cruciform joint by ESPI system and then low cycle fatigue test was performed. Effect of local strain on low cycle fatigue life was examined by measured values using ESPI system. Moreover, experimental fatigue life was compared with established S-N curves using theoretical local strain and stress calculated by Neuber's rule.