• Title, Summary, Keyword: Creep

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Development of High Temperature Creep Properties Evaluation Method using Miniature Specimen (미소시험편을 이용한 고온 크리프 특성 평가법 개발)

  • Yu, Hyo-Sun;Baek, Seung-Se;Lee, Song-In;Ha, Jeong-Soo
    • Proceedings of the KSME Conference
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    • pp.43-48
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    • 2000
  • In this study, a small punch creep(SP-Creep) test using miniaturized specimen$(10{\times}10{\times}0.5mm)$ has been described for the development of the newly semi-destructive creep test method for high temperature structural components such as headers and tubes of boiler turbine casino and rotor and reactor vessel. The SP-Creep testing technique has been applied to 2.25Cr-1Mo(STBA24) steel used widely as boiler tube material and the creep test temperature are varied at $550^{\circ}C{\sim}600^{\circ}C$. The overall deformations of SP-Creep curves are definitely depended with applied load and creep test temperature and show the creep behaviors of three steps like conventional uniaxial creep curves. The steady state creep rate${\delta}_{ss}$ of SP-Creep curve for miniaturized specimen increases with increasing creep temperature, but the exponential value with creep loading is decreased. The activation energy$(Q_{spc})$ during SP-Creep deformation with various test temperatures shows 605.7kJ/mol that is g.eater than 467.4kJ/mol reported in uniaxial creep test. This may be caused by the difference of stress states during creep deformation In two creep test. But from the experimental results, e.g. SP-Creep curve behaviors, the steady state creep rate${\delta}_{ss}$ with creep temperature, and the exponential value(n) with creep loading, it can be summarized that the SP-Creep test may be a useful test method to evaluate the creep properties of the heat resisting material.

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Creep Characteristics of Rocks and Concrete - A Comparison (암(岩)과 콘크리트의 Creep 특성에 대한 비교평가)

  • Kim, Hak-Moon
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.3 no.2
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    • pp.33-56
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    • 2001
  • It is well known fact that all rocks exhibit brittle properties and time depends strain properties (creep). An understanding of the time dependent deformation behaviour of rocks is believed to be essential in the field of civil and tunnelling. The rock and concrete creep in various forms of loading conditions and physical environment are reviewed. A comparison of creep behaviour between rocks and concrete is provided, in order to bring two existing relatively independent methods of predicting creep strain closer together. It was felt that the physical process in the creep of rocks would be similar to the process in creep of concrete. Since experiments and observations have shown that non-elastic (creep) mechanical behaviour of all crystalline solids (i.e., concrete, rocks, ceramics and refractories) and single materials have a common base. Also a comparison of the results for the accepted methods of estimating creep in rocks and concrete under - multiaxial loading was attempted to extend the knowledge of deformational characteristics of these two materials.

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A Study on the Creep Characteristics of Marine Clay (해성점토의 Creep 특성에 관한 연구)

  • Jeong, Hyeong-Sik;An, Sang-Ro;Lee, Seung-Ho
    • Geotechnical Engineering
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    • v.7 no.4
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    • pp.65-74
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    • 1991
  • Earth structures which located on the weak foundation settle for the long time due to the their own weight (embankment) simultaneously. Because of the consolidation and creep which are timedependent behaviour. This paper is presented creep test Processes using triaxial spparatus, and investigated creep charateristics of marine clay by creep test according to stress level And required and appropriate creep parameters of soil used in the creep equation are investigated by the creep test.

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Characteristics of Short-Term Creep Rupture in STS304 Steels (STS304강의 단시간 크리프 파단특성 평가)

  • Kim, Seon-Jin;Kong, Yu-Sik
    • Journal of Ocean Engineering and Technology
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    • v.21 no.4
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    • pp.28-33
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    • 2007
  • The objective of this paper is to investigate the relationship between the short-term creep rupture time and the creep rupture properties at three different elevated temperatures in STS304 stainless steel. Uniaxial constant stress creep rupture tests were performed on the steel to observe the creep rupture behaviors at the elevated temperatures of 600, 650 and 700, according to the testing matrix. It is very important to predict creep life in practical creep design problems. As one of the series of studies on the statistical modelling of probabilistic creep rupture time and the development of creep life prediction techniques, the relationship between applied stress and creep rupture behaviors, such as creep strain rate and rupture time, were investigated. In addition, the Monkman-Grant relationship was observed between the steady-state creep rate and the creep rupture time. The creep rupture surfaces observed by SEM showed up dimple phenomenon at all conditions.

Assessment of Creep Properties of 9Cr Steel Using Small Punch Creep Testing (소형펀치 크리프 시험을 이용한 9Cr강의 크리프 상수 평가)

  • Yun, Gi-Bong;Park, Tae-Gyu;Sim, Sang-Hun;Jeong, Il-Seok
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.9
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    • pp.1493-1500
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    • 2001
  • Recently small punch creep testing (or miniature disc bend creep test) has received much attention through European collaborative research projects. This method was considered as a substitute for the conventional creep rupture testing by which the residual creep life is measured from the specimen taken out from serviced components of high temperature plants. It would be beneficial if the material creep properties such as power law creep constants as well as the creep rupture life can be measured from the small punch creep test. In this paper a method of assessing creep constants from the small punch creep testing is proposed. Finite element analyses were performed to investigate evolution of stress and strain rate at the weakest locations of the small punch creep specimen. Elastic-plastic-secondary creep analyses were carried out. The estimation equations for creep constants by the small punch creep testing are proposed based on the finite analysis results. Small punch creep tests were also performed with 9Cr steel and the accuracy of the proposed equation was verified by the experimental results.

Accelerated Tensile Creep Test Method of Geosynthetics for Soil Reinforcement (보강용 지오신세틱스의 가속 인장 크리프 시험방법)

  • Koo, Hyun-Jin;Cho, Hang-Won
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.196-203
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    • 2008
  • Durability of geosynthetics for soil reinforcement is accounted for creep and creep rupture, installation damage and weathering, chemical and biological degradation. Among these, the long-term creep properties have been considered as the most important factors which are directly related to the failure of geosynthetic-reinforced soil(GRS). However, the creep test methods and strain limits are too various to compare the test results with each other. The most widely used test methods are conventional creep test, time-temperature superposition and stepped isothermal method as accelerated creep tests. Recently developed design guidelines recommend that creep-rupture curve be used to determine the creep reduction factor($RF_{CR}$) which is a conservative approach. In this study, the different creep test methods were compared and the creep reduction factors were estimated at different creep strain limits of 10% of total creep strain and creep rupture. In order to minimize the impact of creep strain to the GRS structures, the various creep reduction factors using different creep test methods should be investigated and then the most appropriated one should be selected for incorporating into the design.

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A Study on New Technique Development for Creep Evaluation of Heat Resistant Steel Weldment (I) (내열강 용접부의 크리프 평가 신기술 개발에 관한 연구(I))

  • 유효선;백승세;권일현;이송인
    • Journal of Welding and Joining
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    • v.20 no.6
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    • pp.754-761
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    • 2002
  • It has been reported that the creep characteristics on weldment which is composed of weld metal(W.M), fusion line(F.L), heat-affected zone(HAZ), and base meta(B.M) could be unpredictably changed in severe service conditions such as high temperature and high pressure. However, the studies done on creep damage in power plant components have been mostly conducted on B.M and not the creep properties of the localized microstructures in weldment have been thoroughly investigated yet. In this paper, it is investigated the creep characteristics for three microstructures like coarse-grain HAZ(CGHAZ), W.M, and B.M in X20CrMoV121 steel weldment by the small punch-creep-(SP-Creep) test using miniaturized specimen($10{\times}10{\times}0.5mm$). The W.M microstructure possesses the higher creep resistance and shows lower creep strain rate than the B.M and CGHAZ. In the lower creep load the highest creep strain rate is exhibited in CGHAZ, whereas in the higher creep load the B.M represents the high creep strain rate. The power law correlation for all microstructures exists between creep rate and creep load at $600^{\circ}C$. The values of creep load index (n) based on creep strain rate for B.M, CGHAZ, and W.M are 7.54, 4.23, and 5.06, respectively and CGHAZ which shows coarse grains owing to high welding heat has the lowest creep loade index. In all creep loads, the creep life for W.M shows the highest value.

Biaxial creep property of ethylene tetrafluoroethylene (ETFE) foil

  • Li, Yintang;Wu, Minger
    • Structural Engineering and Mechanics
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    • v.54 no.5
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    • pp.973-986
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    • 2015
  • Ethylene tetrafluoroethylene (ETFE) foil is a novel structural material which has being used in shell and spatial structures. This paper studies biaxial creep property of ETFE foil by creep tests and numerical simulation. Biaxial creep tests of cruciform specimens were performed using three stress ratios, 1:1, 2:1 and 1:2, which showed that creep coefficients in biaxial tension were much smaller than those in uniaxial one. Then, a reduction factor was introduced to take account of this biaxial effect, and relation between the reduction factor and stress ratio was established. Circular bubble creep test and triangle cushion creep test of ETFE foil were performed to verify the relation. Interpolation was adopted to consider creep stress and reduction factor was involved to take account of biaxial effect in numerical simulation. Simulation results of the bubble creep test embraced a good agreement with those measuring ones. In triangle cushion creep test, creep displacements from numerical simulation showed a good agreement with those from creep test at the center and lower foil measuring points.

A Study on Evaluation of High Temperature Creep Properties of 9Cr1MoVNb Steel by Small Punch-Creep test (소형펀치-크리프 시험에 의한 9Cr1MoVNb강의 고온 크리프 특성 평가 연구)

  • Yu, Hyo-Sun;Na, Sung-Hoon;Baek, Seung-Se;Kwon, Il-Hyun;Ahn, Byung-Guk;Na, Eui-Gyun
    • Proceedings of the KSME Conference
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    • pp.99-104
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    • 2000
  • This paper describes the high temperature creep characteristics for virgin material of 9Cr1MoVNb steel using small punch creep(SP-Creep) test technique which is developing recently. In addition, the several results of SP-Creep test are compared with that of 2.25Cr- 1Mo steel which is widely used as boiler materials and that of conventional uniaxial creep test. The obtained SP-Creep curves show the creep behaviors of three regimes like that obtained from conventional uniaxial creep test, and SP-Creep properties are definitely depended on applied load and test temperature. The correlation of SP-Creep rate and creep rupture life with applied load has been determined like the correlation between creep rate/rupture life and stress in uniaxial creep test, and also is satisfied with Power law. The creep rupture times of newly 9Cr1MoVNb steel are higher than those of 2.25Cr1Mo steel at the same creep temperature and applied loading condition, and the decrease extent of creep rupture life with loads is very lower compared with 2.25Cr1Mo steel.

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Assessment of Material Properties Using Finite Element Analysis for Small Punch Creep Testing (SP 크리프 시험의 유한요소해석을 이용한 재료물성 평가)

  • Park, Tae-Kyu;Ma, Young-Wha;Yoon, Kee-Bong;Jeong, Ill-Seok
    • Proceedings of the KSME Conference
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    • pp.511-516
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    • 2001
  • Recently small punch creep testing (or miniature disc bend creep test) has received much attention through European collaborative research projects. This method was considered as a substitute for the conventional creep rupture testing by which the residual creep life is measured from the specimen taken out from serviced components of high temperature plants. It would be beneficial if the material creep properties such as power law creep constants as well as the creep rupture life can be measured from the small punch creep test. In this paper a method of assessing creep constants from the small punch creep testing is proposed. Finite element analyses were performed to investigate evolution of stress and strain rate at the weakest locations of the small punch creep specimen. Elastic-plastic-secondary creep analyses were carried out. The estimation equations for creep constants by the small punch creep testing are proposed based on the finite analysis results. Small punch creep tests were also performed with 9Cr steel and the accuracy of the proposed equation was verified by the experimental results.

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