• Title/Summary/Keyword: Steady state creep rate

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Creep Crack Propagation Properties of Rotor Steel under Constant Load and Constant Ct Condition (일정하중 및 일정Ct에서 로터강의 크리프 귤열전파 특성)

  • Jeong, Soon-Uk
    • Journal of the Korean Society for Precision Engineering
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    • v.18 no.5
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    • pp.105-111
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    • 2001
  • The creep crack growth properties in 3.3NiCrMoV steel were investigated at 55$0^{\circ}C$ by using CT specimen under constant load and constant Ct condition that was held during crack growth of Imm distance. Ct lelied on load line displacement rate, C*usually increased with crack length though load is reduced in order to maintain constant Ct value as crack growth and appeared scatter band. At constant load and Ct region, crack growth slope was 0.900 and 0.844 each, on the other hand C* slope was 0.480. Fully coalesced area(FCA) ahead of crack tip increased as Ct increase to the critical value, and after that value FCA decreased. For the tertiary creep stage of crack growth test, the most of displacement was due to the steady state creep, except only small part due to the primary creep and other effects. Therefore, tests were mainly interrupted in the tertiary stage to obtain high value of Ct.

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New Considerations on Variability of Creep Rupture Data and Life Prediction (크리프 파단 데이터의 변동성에 대한 새로운 고찰과 수명예측)

  • Jung, Won-Taek;Kong, Yu-Sik;Kim, Seon-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.33 no.10
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    • pp.1119-1124
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    • 2009
  • This paper deals with the variability analysis of short term creep rupture test data based on the previous creep rupture tests and the possibility of the creep life prediction. From creep tests performed by constant uniaxial stresses at 600, 650 and $700^{\circ}C$ elevated temperature, in order to investigate the variability of short-term creep rupture data, the creep curves were analyzed for normalized creep strain divided by initial strain. There are some variability in the creep rupture data. And, the difference between general creep curves and normalized creep curves were obtained. The effects of the creep rupture time (RT) and steady state creep rate (SSCR) on the Weibull distribution parameters were investigated. There were good relation between normal Weibull parameters and normalized Weibull parameters. Finally, the predicted creep life were compared with the Monkman-Grant model.

Creep Crack Growth Properties of Rotor Steel under Constant Load and $C_t$ Condition (일정하중 및 일정$C_t$에서 로터강의 크리프 균열전파특성)

  • Jeong, Soon-Uk;Lee, Hun-Sik;Kim, Young-Dae
    • Proceedings of the KSME Conference
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    • 2001.06a
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    • pp.501-506
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    • 2001
  • The creep crack growth properties in 3.5NiCrMoV steel were investigated at $550^{\circ}C$ by using CT specimen under constant $C_t$ condition that was held during crack growth of 1mm distance. $C_t$ lely on load line displacement rate and $C^*$ usually increase with crack length though load is reduced in order to maintain constant $C_t$ value as crack growth. Fully coalesced area(FCA) ahead of crack tip tend to increase as $C_t$ increase to the critical value, and after that value FCA decrease. For the tertiary creep stage of crack growth test, the most of displacement is due to the steady state creep, except only small part due to the primary creep and other effects. Therefore, tests were mainly interrupted in the tertiary stage to obtain high value of $C_t$. At constant load and $C_t$ region, crack growth slope was 0.900 and 0.844 each, on the other hand $C^*$ slope was 0.480.

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The Effect of Cyclic Loading History on the Creep of $SiC_f/Si_3N_4$ Fiber-reinforced Composite (사이클 하중이력이 $SiC_f/Si_3N_4섬유강화 복합재료의 크리프에 미치는 영향)

  • 박용환
    • Journal of the Korean Society of Safety
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    • v.15 no.4
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    • pp.35-40
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    • 2000
  • The influence of cyclic loading history on the creep behavior of the 30 vol% hot-pressed $SiC_f/Si_3N_4copmposite was experimentally investigated at $1200^{\circ}C$. The duration of loading/unloading had great effects on the creep behaviors. The short term duration cyclic loading history test results showed significant reduction in the primary and steady-state creep rates. For example, 300sec loading/300sec unloading history resulted in 70% lower steady-state creep rate than that of the continuous loading. However the long term duration cyclic loading history test results showed little change in creep rates compared to those of the continuous one. The reason for the significant change in the short term duration cycles was estimated due to the change in the stress redistribution between the fiber and matrix during the creep recovery in the primary stage.

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HIGH TEMPERATURE RANDOM STACK CREEP PROPERTY OF Ni-Cr-Al BASED POWDER POROUS METAL MANUFACTURED WITH POWDER SINTERING PROCESS

  • TAE-HOON KANG;KYU-SIK KIM;MAN-HO PARK;KEE-AHN LEE
    • Archives of Metallurgy and Materials
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    • v.64 no.2
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    • pp.513-518
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    • 2019
  • Recently, attempts have been made to use porous metal as catalysts in a reactor for the hydrogen manufacturing process using steam methane reforming (SMR). This study manufactured Ni-Cr-Al based powder porous metal, stacked cubic form porous blocks, and investigated high temperature random stack creep property. To establish an environment similar to the actual situation, a random stack jig with a 1-inch diameter and height of 75 mm was used. The porous metal used for this study had an average pore size of ~1161 ㎛ by rolling direction. The relative density of the powder porous metal was measured as 6.72%. A compression test performed at 1073K identified that the powder porous metal had high temperature (800℃) compressive strength of 0.76 MPa. A 800℃ random stack creep test at 0.38 MPa measured a steady-state creep rate of 8.58×10-10 s-1, confirming outstanding high temperature creep properties. Compared to a single cubic powder porous metal with an identical stress ratio, this is a 1,000-times lower (better) steady-state creep rate. Based on the findings above, the reason of difference in creep properties between a single creep test and random stack creep test was discussed.

Circumferential steady-state creep test and analysis of Zircaloy-4 fuel cladding

  • Choi, Gyeong-Ha;Shin, Chang-Hwan;Kim, Jae Yong;Kim, Byoung Jae
    • Nuclear Engineering and Technology
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    • v.53 no.7
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    • pp.2312-2322
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    • 2021
  • In recent studies, the creep rate of Zircaloy-4, one of the basic property parameters of the nuclear fuel code, has been commonly used with the axial creep model proposed by Rosinger et al. However, in order to calculate the circumferential deformation of the fuel cladding, there is a limitation that a difference occurs depending on the anisotropic coefficients used in deriving the circumferential creep equation by using the axial creep equation. Therefore, in this study, the existing axial creep law and the derived circumferential creep results were analyzed through a circumferential creep test by the internal pressurization method in the isothermal conditions. The circumferential creep deformation was measured through the optical image analysis method, and the results of the experiment were investigated through constructed IDECA (In-situ DEformation Calculation Algorithm based on creep) code. First, preliminary tests were performed in the isotropic β-phase. Subsequently in the anisotropic α-phase, the correlations obtained from a series of circumferential creep tests were compared with the axial creep equation, and optimized anisotropic coefficients were proposed based on the performed circumferential creep results. Finally, the IDECA prediction results using optimized anisotropic coefficients based on creep tests were validated through tube burst tests in transient conditions.

A Study on High Temperature Creep and Stress Relaxation Properties of Zr-4 (Zr-4의 고온 크리프 및 응력이완 특성에 관한 연구)

  • Oh, Sea-Kyoo;Park, Chung-Bae;Han, Sang-Deok
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.28 no.1
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    • pp.71-78
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    • 1992
  • Zr-4 used for a cladding and an end plug of reactor component has creep deformation under operation at high temperature. Creep is regarded as the time dependent deformation of a material under constant applied stress. Although the major source of the deformation of zirconium component in water-cooled reactors is irradiation creep, the thermal creep may give a rise to significant deformation in reactor component especially at relatively high temperatures and at various constant stresses, and therefore it must be predicted accurately. Stress relaxation is the time dependent change of stress at constant strain and it is a process related intimately to creep. In this paper, the creep behavior and stress relaxation of Zr-4 is examined at the temperature of 50$0^{\circ}C$ that is 40% of the absolute melting temperature of Zr-4 under the stress below yield stress and under the various constant strains. The results obtained are summarized as follows: 1) With an increase of stress, the steady state creep rate increases and the creep rupture time decreases. 2) The steady state creep rate $\varepsilon$(%/s) for the stress $\sigma$sub(c) (kgf/mm super(2)) of Zr-4 increases outstandingly. All the empirical equations computed for Zr-4 increases outstandingly. All the empirical equations computed for Zr-4 are in accord with Norton's model equation($\varepsilon$=K$\sigma$ sub(c) super (n)). The constants of materials computed are as follows: K=3.9881$\times$10 super(-5), n=1.9608 3) The rupture time T sub(r) (hr) decreases linearly with the increase of stress on the log-log scaled graph. The empirical equations computed for Zr-4 are in accord with Bailey's model equation (T sub(r)=K sub(1)$\sigma$sub(c) super(m)). The constants of materials computed are as follows: K sub(1)=1.2875$\times$10 super(16), m=-3.467 4) It seems clear that the strain could be quantitatively dependent on the high temperature creep properties such as creep stress, rupture time, steady state creep rate and total creep rate. It is found that these relationships are linear on the log-log graph. 5) In stress relaxation test, as the critical constant strain that can be allowed to the specimen is larger, stress relaxation becomes more rapid, and as the constant strain is smaller, the stress relaxation becomes slower.

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Correlation Between Transient Regime and Steady-State Regime on Creep Crack Growth Behavior of Grade 91 Steel (Grade 91 강의 크리프 균열성장 거동에 대한 천이영역과 정상상태영역의 상관 관계)

  • Park, Jae-Young;Kim, Woo-Gon;Ekaputra, I.M.W.;Kim, Seon-Jin;Kim, Eung-Seon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.39 no.12
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    • pp.1257-1263
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    • 2015
  • A correlation between the transient regime and steady state regime on the creep crack growth (CCG) for Grade 91 steel, which is used as the structural material for the Gen-IV reactor systems, was investigated. A series of CCG tests were performed using 1/2" CT specimens under a constant applied load and at a constant temperature of $600^{\circ}C$. The CCG rates for the transient and steady state regimes were obtained in terms of $C^*$ parameter. The transient CCG rate had a close correlation with the steady-state CCG rate, as the slope of the transient CCG data was very similar to that of the steady state data. The transient rate was slower by 5.6 times as compared to the steady state rate. It can be inferred that the steady state CCG rate, which is required for long-time tests, can be predicted from the transient CCG rate obtained from short-time tests.

Cyclic Creep Strain of Cu Pure Metal (CU 순금속의 사이클릭 크리프 변형)

  • Jeong, S.U.;Lee, H.S.
    • Proceedings of the KSME Conference
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    • 2000.04a
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    • pp.194-199
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    • 2000
  • The creep rate is affected by the temperature and in fact. if the temperature above $T_M/2(T_M:melting\;point)$. The aim of the present investigation is to study the relationship of static creep and cyclic creep behavior of pure copper and the formulation of these phenomena with the special attention to the instantaneous strain. strain rate from time and number of cycles have the same inclination Steady state creep rate depend upon maximum stress and can be expressed as linear function according to Power law creep equations Creep rupture time has relation with creep rate. and it make a group represented as the same direct line regardless of max stress, stress ratio and the temperature. Initial strain effect on continuous creep deformation. and have guantitative relationship between elastic and Plastic strain. LMP have similar tendency than OSDP and MHP according to temperature

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High Temperature Creep Behavior of Cr3C2 Composites (크롬-카바이드 복합체의 고온 크리프 거동)

  • 김지환;한동빈;김기태
    • Journal of the Korean Ceramic Society
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    • v.32 no.11
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    • pp.1219-1226
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    • 1995
  • Creep behaviors of Cr3C2 composites containing 90 wt% Cr3C2 and 10 wt% Ni were studied at high temperature. Compression tests at 100$0^{\circ}C$ and bending tests at 100$0^{\circ}C$ and 105$0^{\circ}C$ were done in argon environment. In all test conditions primary and steady-state creep behaviors were observed. Stress exponent and activatiion energy were determined from the experimental data. By microstructural analysis of Cr3C2 composites after creep test, the separate agglomerations of Ni phase were observed. Numerical analysis was also studied to analyze bending creep behaviors of Cr3C2 by assumming different tensile and compressive creep behavior in a bending sample. From the analysis, it was found that the stress state at the compressive region as applied stress increased. The observed creep rates were compared with the predicted creep rates by estimating power-law creep parameters from bending test data.

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