• Title/Summary/Keyword: power-law creep

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Estimation of C*-Integral for Defective Components with General Creep-Deformation Behaviors (일반 크리프 거동을 고려한 균열 구조물 C*-적분 예측)

  • Kim, Yeong-Jin;Kim, Jin-Su;Kim, Yun-Jae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.5
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    • pp.795-802
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    • 2002
  • For assessing significance of a defect in a component operating at high (creeping) temperatures, accurate estimation of fracture mechanics parameter, $C^{*}$-integral, is essential. Although the J estimation equation in the GE/EPRl handbook can be used to estimate the $C^{*}$-integral when the creep -deformation behavior can be characterized by the power law creep, such power law creep behavior is a very poor approximation for typical creep behaviors of most materials. Accordingly there can be a significant error in the $C^{*}$-integral. To overcome problems associated with GE/EPRl approach, the reference stress approach has been proposed, but the results can be sometimes unduly conservative. In this paper, a new method to estimate the $C^{*}$-integral for deflective components is proposed. This method improves the accuracy of the reference stress approach significantly. The proposed calculations are then validated against elastic -creep finite element (FE) analyses for four different cracked geometries following various creep -deformation constitutive laws. Comparison of the FE $C^{*}$-integral values with those calculated from the proposed method shows good agreements.greements.

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.

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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    • 2001.06a
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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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Numerical Modeling of Long-Term Behavior of Geosynthetic Reinforced Soil Wall used in Bridge Abutment (보강토 교대 옹벽의 장기 거동에 대한 수치 모델링)

  • Yoo, Chung-Sik
    • Journal of the Korean Geosynthetics Society
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    • v.10 no.4
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    • pp.105-112
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    • 2011
  • This paper presents the numerical modelling technique for modeling the time-dependent behavior of geosynthetic reinforced soil wall under a sustained load. The applicability of power law-based creep models for modeling the creep deformations of geogrid and reinforced soil was first examined. The modeling approach was then used to simulate the long-term performance of a geosynthetic reinforced soil wall used in a bridge abutment. The results indicated that the power law-based models can be effectively used for modelling the long term behavior of geosynthetic reinforced walls under sustained loading. In addition, it was shown that, when using creep deformation susceptible backfill soils, the abutment wall and the sill beam may experience deformations exceeding allowable limits. Practical implications of the findings from this study are discussed in great detail.

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

  • 유효선;백승세;권일현;이송인
    • Journal of Welding and Joining
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    • v.20 no.6
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    • pp.30-30
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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(l0×10×0.5mm). 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℃. 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.

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.

Understanding the role of hydrogen on creep behaviour of Zircaloy-4 cladding tubes using nanoindentation

  • Suman, Siddharth
    • Nuclear Engineering and Technology
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    • v.52 no.9
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    • pp.2041-2046
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    • 2020
  • The present article investigates the influence of hydrogen concentration on the creep performance of cold-worked stress-relieved unirradiated Zircaloy-4 cladding tube using nanoindentation technique. The as-received Zircaloy-4 tube is hydrided to the concentrations of 600 ppm and 900 ppm using gaseous hydrogen charging method. Constant load indentation creep tests are performed for a dwell period of 600 s in the temperature range of 300℃-500 ℃ at 1000 μN, 2000 μN, and 3000 μN. The impact of hydrogen is evaluated in terms of steady state power law creep exponent and activation energy. The power law creep exponent decreases with increase in hydrogen concentration, however, it remains fairly constant with increase in temperature up to 500 ℃. Moreover, activation energy too decreases significantly with increase in hydrogen concentration. The mean stress exponent and activation energy are found to be 3.58 and 28.67 kJ/mol, respectively, for as-received sample.

Thermal stress of concrete structure at high temperature considering inelastic thermal strain change (고온에서의 비선형 변형도를 고려한 콘크리트 구조물에서의 열응력 분포)

  • 강석원;홍성걸;신영수
    • Proceedings of the Korea Concrete Institute Conference
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    • 2000.10b
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    • pp.1145-1150
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    • 2000
  • Concrete behaves as ductile material at high temperature. The existing stress-strain relationship is not valid at high temperature condition. Thus, stress-strain curve of concrete at high temperature is re-established by modifying Saenz's suggestion in this study. A constitutive model of concrete subjected to elevated temperature is also suggested. The model consists of three components; free thermal stain, mechanical strain and thermal creep strain. As the temperature increase, the thermal creep becomes more critical to the failure of concrete. The thermal creep strain of concrete is derived from the modified power-law relation for the steady state creep. The proposed equation for thermal creep employs a Dorn's temperature compensated time theorem

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High-Temperature Mechanical Behaviors of Type 316L Stainless Steel (Type 316L 스테인리스강의 고온 기계적 거동)

  • Kim, Woo-Gon;Lee, Hyeong-Yeon
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.16 no.1
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    • pp.92-99
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    • 2020
  • High-temperature mechanical behaviors of Type 316L stainless steel (SS), which is considered as one of the major structural materials of Generation-IV nuclear reactors, were investigated through the tension and creep tests at elevated temperatures. The tension tests were performed under the strain rate of 6.67×10-4 (1/s) from room temperature to 650℃, and the creep tests were conducted under different applied stresses at 550℃, 600℃, 650℃, and 700℃. The tensile behavior was investigated, and the modeling equations for tensile strengths and elongation were proposed as a function of temperature. The creep behavior was analyzed in terms of various creep equations: Norton's power law, modified Monkman-Grant relation, damage tolerance factor(λ), and Z-parameter, and the creep constants were proposed. In addition, the tested tensile and creep strengths were compared with those of RCC-MRx. Results showed that creep exponent value decreased from n=13.55 to n=7.58 with increasing temperature, λ = 6.3, and Z-parameter obeyed well a power-law form of Z=5.79E52(σ/E)9.12. RCC-MRx showed lower creep strength and marginally different in creep strain rate, compared to the tested results. Same creep deformation was operative for dislocation movement regardless of the temperatures.

Development of new fracture parameter for rigid inclusion with crack shape in creep material (크립재료의 균열형상 강체함유물에 대한 새로운 파괴역학 매개변수 개발)

  • Lee, Kang-Yong;Kim, Jong-Sung
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.12
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    • pp.2165-2171
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    • 1997
  • The analysis model is the infinite power law creep material containing the rigid inclusion with crack shape. The present analysis is performed using the complex pseudo-stress function method. The strain rate intensity factor is developed as new fracture mechanics parameter which represents the stress and strain rate distribution near a crack tip in power law creep material. The strain rate intensity factor is developed in terms of Kolosoff stress functions.