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윤송남(Song-Nan Yin),김우곤(Woo-Gon Kim),정익희(Ik-Hee Jung),김용완(Yong-Wan Kim) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
The nickel-based Hastelloy X alloy is one of the candidate materials for structural components of the high temperature gas-cooled reactor (HTGR). Its creep data was obtained from the creep tests under several stress levels at 950℃, and using this data, the creep behavior was investigated by the θ-projection model. The proper fitting range was determined from the creep curves at any stress level because the θ<SUB>i</SUB>-parameters are dependent on a fitting strain range. A stress dependency for the B-parameters was established to accurately predict the creep curve of a low stress level. The time to 1%-low strains was predicted for various stress levels, and the ratios between the time to 1%-low strain and time to rupture were lower than 15%. Also, a predicted minimum creep rate revealed a good agreement with the experimental data.
Taylor 급수를 이용한 Alloy 617 의 장시간 크리프 수명 예측 모델의 적용성
윤송남(Song-Nan Yin),김우곤(Woo-Gon Kim),박재영(Jea-Yeong Park),김용완(Yong-Wan Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
Creep life prediction has been commonly used by a time-temperature parameter (TTP) which is correlated to a rupture time and temperature, such as Larson-Miller (LM), Orr-Sherby-Dorn (OSD), Manson-Haferd (MH) and Manson-Succop (MS) parameters. A Taylor series model(T-SM) based on Arrhenius, McVetty and Monkman-Grant equations was newly proposed through a mathematical procedure and in order to reduce the fitting errors the McVetty’s equation was transformed by taking the first three-terms of Taylor series equation. The model parameters were properly determined by means of a technique of maximum likelihood estimation of statistical method, and this model was applied to the creep data of Alloy 617. The T-SM results revealed better agreement than the Eno’s model and the LM parameter one. Especially, it was identified that the T-SM showed a good estimation in predicting the long-term creep life of Alloy 617.
Alloy 617 의 장시간 크리프 수명 예측을 위한 다중회귀 선형 모델의 제안 및 평가
윤송남(Song-Nan Yin),김우곤(Woo-Gon Kim),정익희(Ik-Hee Jung),김용완(Yong-Wan Kim) 대한기계학회 2009 大韓機械學會論文集A Vol.33 No.4
Creep life prediction has been commonly used by a time-temperature parameter (TTP) which is correlated to an applied stress and temperature, such as Larson-Miller (LM), Orr-Sherby-Dorn (OSD), Manson-Haferd (MH) and Manson-Succop (MS) parameters. A stress-temperature linear model (STLM) based on Arrhenius, Dorn and Monkman-Grant equations was newly proposed through a mathematical procedure. For this model, the logarithm time to rupture was linearly dependent on both an applied stress and temperature. The model parameters were properly determined by using a technique of maximum likelihood estimation of a statistical method, and this model was applied to the creep data of Alloy 617. From the results, it is found that the STLM results showed better agreement than the Eno’s model and the LM parameter ones. Especially, the STLM revealed a good estimation in predicting the long-term creep life of Alloy 617.
Taylor 급수를 이용한 617 합금의 장시간 크리프 수명 예측
윤송남(Song-Nan Yin),김우곤(Woo-Gon Kim),박재영(Jae-Young Park),김선진(Soen-Jin Kim),김용완(Yong-Wan Kim) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.4
본 연구에서는 McVetty 와 Monkman-Grant 의 모델에 기초하여 만들어진 새로운 크리프 수명예측 모델인 Taylor 급수(T-S) 모델을 제안하였다. 본 모델은 회귀분석에서 발생하는 오차를 줄이기 위하여 McVetty 모델에서 sinh 함수를 Taylor 급수에 의해 변환한 후 첫 3 개항을 취한 것으로서 모델중의 상수 값은 통계학적 방법인 최대가능성 기법을 이용하여 결정되었다. T-S 모델을 이용하여 Alloy 617 의 크리프 수명을 예측한 결과 Eno, 지수함수 및 Larson-Miller(L-M) 방법에 비해 더 정확한 예측을 하는 것으로 나타났다. 또한 T-S 모델은 특정 온도에서 크리프 수명 예측을 할 수 있는 등온 T-S(IT-S) 모델로 표현될 수 있었으며, IT-S 모델은 Alloy 617 의 장시간 크리프 수명예측에서 가장 좋은 예측을 하는 것으로 나타났다. In this study, a Taylor series (T-S) model based on the Arrhenius, McVetty, and Monkman-Grant equations was developed using a mathematical analysis. In order to reduce fitting errors, the McVetty equation was transformed by considering the first three terms of the Taylor series equation. The model parameters were accurately determined by a statistical technique of maximum likelihood estimation, and this model was applied to the creep data of alloy 617. The T-S model results showed better agreement with the experimental data than other models such as the Eno, exponential, and L-M models. In particular, the T-S model was converted into an isothermal Taylor series (IT-S) model that can predict the creep strength at a given temperature. It was identified that the estimations obtained using the converted ITS model was better than that obtained using the T-S model for predicting the long-term creep life of alloy 617.
시간-온도 파라미터법과 최소구속법에 의한 크리프 수명예측과 오차 분석
윤송남(Song-Nan Yin),김우곤(Woo-Gon Kim),류우석(Woo-Seog Ryu),이원(Won Yi) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.3
To predict long-term creep lifetime from short-term creep data, various parametric methods such as Larson-Miller (L-M), Orr-Sherby-Dorn (O-S-D), Manson-Haferd (M-H) parameters, and Minimum Commitment Method (MCM) were suggested. A number of the creep data were collected through literature surveys and experimental data produced in KAERI for predicting the creep life of type 316LN SS. The polynomial equations for predicting the creep life were obtained by the time-temperature parameters (TTP) and the MCM. Standard error (SE) and standard error of mean (SEM) values were compared for the each method with temperatures. The TTP methods were good in the creep-life prediction, but the MCM was much superior to the TTP ones at 700℃ and 750℃. It was found that the MCM were lower in the SE values when compared to the TTP methods.
316LN 스테인리스강의 크리프 균열성장속도의 확률적 평가
김우곤(Woo-Gon Kim),윤송남(Song-Nan Yin),류우석(Woo-Seog Ryu),김선진(Seon-Jin Kim),이원(Won Yi) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.3
This paper is to describe a probabilistic evaluation of the creep crack growth rate (CCGR) for type 316LN stainless steel. To logically obtain the Band q values in the CCGR equation of a = B(C<SUP>*</SUP>)<SUP>q</SUP>, three methods of the least square fitting method (LSFM), a mean value method (MVM) and a probabilistic distribution method (PDM) were adopted. The three methods did not show a large difference in the CCGR lines, but the PDM was most useful because the CCGR line can be evaluated with a probabilistic reliability. Both the Band q coefficients followed a lognormal distribution, even though the B ones were a little scattered for the points of the data. In the case of a standard deviation of I 0' for the probability variables, P (B, q), the results of the Monte Carlo simulation (MCS) and the PDM were compared for the distribution ranges of the CCGR lines.
초고온가스로 중간 열교환기용 Alloy 617의 장시간 크리프 변형률-시간 곡선 모델링
김우곤 ( Woo Gon Kim ),윤송남 ( Song Nan Yin ),김용완 ( Yong Wan Kim ) 대한금속·재료학회 2009 대한금속·재료학회지 Vol.47 No.10
The Kachanov-Rabotnov (K-R) creep model was proposed to accurately model the long-term creep curves above 10(5) hours of Alloy 617. To this end, a series of creep data was obtained from creep tests conducted under different stress levels at 950℃. Using these data, the creep constants used in the K-R model and the modified K-R model were determined by a nonlinear least square fitting (NLSF) method, respectively. The K-R model yielded poor correspondence with the experimental curves, but the modified K-R model provided good agreement with the curves. Log-log plots of ε*-stress and ε*-time to rupture showed good linear relationships. Constants in the modified K-R model were obtained as λ=2.78, and κ=1.24, and they showed behavior close to stress independency. Using these constants, long-term creep curves above 10(5) hours obtained from short-term creep data can be modeled by implementing the modified K-R model.
Modified 9Cr-1Mo 강의 크리프 균열성장 거동에 관한 통계적 해석
정익희 ( Ik Hee Jung ),김우곤 ( Woo Gon Kim ),윤송남 ( Song Nan Yin ),류우석 ( Woo Seog Ryu ),김선진 ( Seon Jin Kim ) 대한금속재료학회 ( 구 대한금속학회 ) 2009 대한금속·재료학회지 Vol.47 No.5
This paper dealt with a statistical analysis for evaluating the creep crack growth rate (CCGR) for Modified 9Cr-1Mo (ASTM Grade 91) steel. The CCGR data was obtained by the creep crack growth (CCG) tests conducted under various applied loads at 600℃. To obtain logically the B and q values used in the CCGR equation, three methods such as the least square fitting method (LSFM), the mean value method (MVM) and the probabilistic distribution method (PDM) were adopted and their CCGR lines were compared, respectively. In addition, a number of random variables were generated by using the Monte Carlo simulation (MCS), and the CCGR lines were predicted probabilistically. It was found that both the B and q coefficients followed a 2-parameter Weibull distribution well. In the case of the ranges of 10~90% for the probability variables, P(B, q), the CCGR lines were predicted. Fractographic study was conducted from the specimen after the CCG tests. (Received January 19, 2009)
개량 9Cr-1Mo 강의 확률론적 크리프 균열 성장 거동
박재영(Jae-Young Park),김우곤(Woo-Gon Kim),윤송남(Song-Nan Yin),류우석(Woo-Seog Ryu),김선진(Seon-Jin Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
This paper deals with a probabilistic analysis for creep crack growth (CCG) behavior of Modified 9Cr-1Mo steel for next generation nuclear reactors. The CCG data were obtained by the CCG tests performed on 1/2 compact tension (CT) specimens under the applied load of 5000N at the identical temperature condition of 600℃. The CCG behavior was analyzed statistically by using the empirical equation between the CCG rate, da/dt and C* parameter. The B and q values were investigated by the least square fitting method for each specimen. The probabilistic distribution functions for the B and q were investigated by using the normal, log-normal and weibull distribution. It appeared that the results of the B and q constants followed Log-normal distribution well. From this result, it was identified that the CCG rate could be evaluated probabilistically for Modified 9Cr-1Mo steel.