• Title, Summary, Keyword: Power-Law Creep

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The Settlement Characteristics of Waste Landfill Site by Consolidation Test (압밀시험에 의한 쓰레기매립지의 침하특성)

  • Shin, Bang-Woog;Lee, Bing-Jik;Bae, Woo-Seok;Lee, Jong-Kyu;Ahn, Byung-Chul
    • Journal of the Korean Geoenvironmental Society
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    • v.1 no.1
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    • pp.35-42
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    • 2000
  • The settlement characteristics of waste landfill site must be considered in the design of sanitary landfill as well as in the course of the rehabilitation of the landfill site. Among prediction methods for settlement of landfill site, especially Gibson and Lo model and Power Creep Law have been successfully applied to the landfill site where the amount of settlement was large and the secondary settlement was obvious. Therefore, the effects of organic content on the model parameter values utilized in both Gibson Lo model and Power Creep Law were studied by using a large consolidation testing apparatus. The organic content is each 20%, 40%, 60% of total volume and consolidation load is $0.1{\sim}1.6kg/cm^2$. The main results can be summarized as follows: (1) The reference compressibility of Power Creep Law is decreased according to the increments of consolidation load: (2) The field measurement is more similar to the Power Creep Law than the Gibson and Lo model.

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Creep Modelling of Reinforced Earth using Power Law-based Creep Models (Power Law 기반의 크리프 모델을 이용한 보강토 구조물의 크리프 모델링)

  • Kim, Jae-Wang;Kim, Sun-Bin;Yoo, Chung-Sik
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.164-178
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    • 2009
  • The importance of long-term performance of reinforced earth structures has been gaining its attention as the use of reinforced earth structures as load supporting structures is increasing. When using reinforced earth structures as loading supporting structures the stability as well as serviceability requirements must be met. In that respect the time-dependent long term deformation characteristics should be well understood. In this study the applicability of power law-based creep models for modeling of creep deformation of the components of reinforced earth structures are examined.

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Constitutive Models for Final Stage Densification of Powder Compacts with Power-Law Creep Deformation (Power-law 크리프 변형을 따르는 분말 성형체의 말기 치밀화 모델)

  • Yang, Hoon-Chul;Kim, Ki-Tae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.7
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    • pp.930-939
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    • 2004
  • Constitutive models for final stage densification of metal powder compacts with power-law creep deformation were investigated. The constitutive models were implemented into a finite element program (ABAQUS) by using user subroutine CREEP and, from FEM results, useful densification curves were obtained when hydrostatic and uniaxial stress were applied to the powder compacts at various pressures and temperatures. Because the densification behavior varied as the constitutive models, the equivalent stress surface on each constitutive equation was investigated to analyze the difference of densification behavior.

Analysis of Hot Isostatic Pressing of Powder Compacts Considering Diffusion and Power-Law Creep (확산과 Power- law 크립을 고려한 압분체 열간정수압압축 공정의 해석)

  • Seo M. H.;Kim H. S.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.66-69
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    • 2000
  • In order to analyze the densification behaviour of stainless steel powder compacts during hot isostatic pressing (HIP) at elevated temperatures, a power-law creep constitutive model based on the plastic deformation theory for porous materials was applied to the densification. Various densification mechanisms including interparticle boundary diffusion, grain boundary diffusion and lattice diffusion mechanisms were incorporated in the constitutive model, as well. The power-law creep model in conjunction with various diffusion models was applied to the HIP process of 316L stainless steel powder compacts under 50 and 100 MPa at 1125 $!`\acute{\dot{E}}$. The results of the calculations were verified using literature data It could be found that the contribution of the diffusional mechanisms is not significant under the current process conditions.

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Creep Behavior Analysis of 25Cr-20Ni Stainless Steels by Omega Method (오스테나이트계 25Cr-20Ni 스테인리스강의 Ω법을 이용한 고온 크리프 거동 해석)

  • Park, In-Deok;Nam, Gi-U
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.2
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    • pp.349-356
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    • 2002
  • For two kinds of 25Cr-20Ni stainless steels, STS310J1TB and STS310S with and without a small amount of Nb and N, creep behavior has been studied in a stress and temperature range from 147 to 392 MPa and from 923 to 773 K with a special reference to tertiary creep. The average creep life of STS310J1TB was about 100 times longer than that of the STS310S. The apparent activation energy for the initial creep rate was 330 kJ/mol in STS310J1TB, while that of the STS310S was 274kJ/mol in a power law creep region and 478 kJ/mol in a region of power law breakdown (PLB). The activation energy for STS310S below PLB is close to the for self-diffusion. When compensating for the temperature dependence of the Young's modulus and the omega value, it was found that the apparent activation energy for STS310J1TB was reduced to the activation energy for diffusion of chromium atom in gamma steel. The stress exponent of STS310S was about 12.3 above PLB and 5.1 in a power law creep region. Notwithstanding that the creep condition for STS310J1TB was in a power law creep region, its stress exponent was 7.9 larger than that of STS310S corresponding to the same creep conditions. This was ascribed to the presence of fine precipitates in STS310J1TB.

Creep Behavior Analysis of 25Cr-20Ni Stainless Steels With Omega Methods (오스테나이트계 25Cr-20Ni 스테인리스강의 $\Omega$ 법을 이용한 고온 크리프 거동 해석)

  • Park, In-Duck;Nam, Ki- Woo
    • Proceedings of the KSME Conference
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    • pp.117-122
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    • 2001
  • For two kinds of 25Cr-20Ni stainless steels, SUS310J1TB TB and SUS310S with and without a small amount of Nb and N, creep behavior has been studied in a stress and temperature range from 147 to 392MPa and from 923 to 973K with a special reference to tertiary creep. The average creep life of SUS310J1TB was about 100 times longer than that of the SUS310S. The apparent activation energy for the initial creep rate was 330 kJ/mol in SUS310J1TB, while that of the SUS310S was 274 kJ/mol in a power law creep region and 478 kJ/mol in a region of power law breakdown (PLB). The activation energy for SUS310S below PLB is close to the that for self-diffusion. When compensating for the temperature dependence of the Young's modulus and the omega value, it was found that the apparent activation energy for SUS310J1TB was reduced to the activation energy for diffusion of chromium atom in a gamma steel. The stress exponent of SUS310S was about 12 above PLB and 5.1 in a power law creep region. Notwithstanding that the creep condition for SUS310J1TB was in a power law creep region, its stress exponent was 8.3 larger than that of SUS310S corresponding to the same creep conditions. This was ascribed to the presence of fine precipitates in SUS310J1TB.

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Creep Characterization of 9Cr1Mo Steel Used in Super Critical Power Plant by Conversion of Stress and Strain for SP-Creep Test (SP-Creep 시험의 응력 및 변형률 환산에 의한 초임계압 발전설비용 9Cr1Mo강의 크리프 특성 평가)

  • Baek, Seung-Se;Park, Jung-Hun;Yu, Hyo-Sun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.9
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    • pp.1034-1040
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    • 2006
  • Due to the need of increasing thermal efficiency, supercritical pressure and temperature have been utilized in power plants. It is well known that 9Cr1Mo steel is suitable fer use in power plants operating at supercritical conditions. Therefore, to ensure the safety and the soundness of the power plant, creep characterization of the steel is important. In this study, the creep characterization of the gCr1Mo steel using small punch creep(SP-Creep) test has been described. The applied load and the central displacement of the specimen in SP-Creep test have been converted to bearing stress and strain of uc, respectively. The converted SP-Creep curves clearly showed the typical three-stage behavior of creep. The steady-state creep rate and the rupture time of the steel logarithmically changed with the bearing stress and satisfied the Power law relationship. Furthermore, the Larson-Miller parameter of the SP-Creep test agreed with that of the tensile creep test. From the comparison with low Cr-Mo steels, the creep characteristics of 9Cr1Mo steel proved to be superior. Thus, it can be confirmed that the 9Cr1Mo steel is suitable for supercritical power plant.

Modelling the Densification Behaviour of Powders Considering Diffusion and Power-Law Creep Mechanisms during Hot Isostatic Pressing (열간정수압압축 시 확산기구 및 Power-law크립기구를 고려한 분말 치밀화거동의 모델링)

  • 김형섭
    • Journal of Korean Powder Metallurgy Institute
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    • v.7 no.3
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    • pp.137-142
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    • 2000
  • In order to analyze the densification behaviour of stainless steel powder compacts during hot isostatic pressing (HIP) at elevated temperatures, a power-law creep constitutive model based on the plastic deformation theory for porous materials was applied to the densification. Various densification mechanisms including interparticle boundary diffusion, grain boundary diffusion and lattice diffusion mechanisms were incorporated in the constitutive model, as well. The power-law creep model in conjunction with various diffusion models was applied to the HIP process of 316L stainless steel powder compacts under 50 and 100 MPa at $1125^{\circ}C$. The results of the calculations were verified using literature data. It could be found that the contribution of the diffusional mechanisms is not significant under the current process conditions.

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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.