• 한국해양공학회지
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• 제12권1호
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• pp.76-84
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• 1998

In this 1st report, the relationship between pure creep properties and initial strain was studied and also its acoustic emission test was performed during creep test at 500, 600 and $700^{\circ}C$. And the applicability of the acoustic emission technique was investigated to analyze the quantitive relationship between all the pure properties (creep strength, creep repture time or creep life, steady state creep rate, total creep rate, creep strain, total creep strain, etc.) and the initial strains as well as to analyze AE properties during the pure creep loading condition.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.105-110
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• 2001

It has recently been raised main issue how solve the problem of insufficient energy. One of the solution is to increase the thermal efficiency of power generation system. For the purpose of high efficiency, it is necessary to increase the steam temperature and pressure. So, the use of modified $9{\sim}12%Cr$ steel having superior creep rupture strength and oxidation resistance is required to endure such severe environment. The evaluation of creep properties of those heat resistance material is very important to secure the reliability of high temperature and pressure structural components. Since creep properties are determined by microstructural change such as carbide precipitation and coarsening, It is certain that there are some relationship between creep properties and hardness affected by microstructure. In this study, SP-Creep ruptured test for newly developed 9Cr steel being used as boiler valve material was performed, and creep properties of the material were evaluated. Also, hardness test were performed and hardness results were related to the creep properties such as LMP and creep strength to verify the availability of SP-Creep test as creep test method.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.279-284
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• 2004

In this study, we suggested the ring creep test using the ring specimen of Arsene for estimating the burst creep properties of the cladding in stead of burst creep test. For this objective, we used the load-displacement conversion relationship of ring specimen called LCRR which had been determined on our previous study at high temperature by performing the ring tensile test and the numerical analysis. Then we carried out both the ring creep test and the burst creep test between 350 $^{\circ}C$ and 600$^{\circ}C$ which were higher then the in-service temperature of the cladding in a reactor. The creep properties from the ring creep test with applying LCRR were compared with those from the burst creep test of closed-end specimens. From the results, it could be seen an very strong relationship between them, especially in Larson- Miller parameter. So, it is expected that we can easily anticipate the creep properties of not only claddings but also various small pressure pipes using the ring creep test.

• 대한기계학회논문집A
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• 제29권7호
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• pp.964-969
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• 2005

In this study, we suggested the ring creep test using the ring specimen of Arsene for estimating the burst creep properties of the cladding in stead of burst creep test. For this objective, we used the load-displacement conversion relationship of ring specimen called LCRR which had been determined on our previous study at high temperature by performing the ring tensile test and the numerical analysis. Then we carried out both the ring creep test and the burst creep test between $350^{\circ}C$ and $600^{\circ}C$ which were higher than the in-service temperature of the cladding in a reactor. The creep properties from the ring creep test with applying LCRR were compared with those from the burst creep test of closed-end specimens. From the results, it could be seen an very strong relationship between them, especially in Larson-Miller parameter. So, it is expected that we can easily predict the creep properties of not only claddings but also various small pressure pipes using the ring creep test.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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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.

• 한국터널지하공간학회 논문집
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• 제3권2호
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• pp.33-56
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• 2001

모든 암석들이 취성이나 시간변형거동인 Creep 특성을 나타낸다는 것은 잘 알려진 사실이다. 암석들에 대한 시간변형거동의 이해는 토목이나 터널기술분야에 필수적인 요건이 된다. 그러므로 다양한 하중조건과 물리적 환경상태에서 암석과 콘크리트에 대한 Creep특성을 조사하였다. 두가지 다른 Creep변형예측공식을 사용하여 그 결과를 비교함으로서 이들 재료들의 유사점을 찾아보았다. Creep 변형 예측공식을 사용하여 3축압축 상태에서 얻어진 실험결과들과 비교 평가하였다.

• 대한기계학회논문집A
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• 제25권9호
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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.

• 한국주조공학회지
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• 제33권1호
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• pp.1-7
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• 2013

The effect of the Mo addition on the high temperature creep properties of the 9Cr-3W steel was also evaluated. Two experimental steels, (9Cr-3W and 9Cr-3W-0.5Mo), were prepared using a vacuum induction melting process, followed by hot rolling and heat treatment processes. Three types of precipitates, ($M_{23}C_6$, Nb-rich MX and V-rich MX) were observed in a typical tempered martensitic matrix. Significant effects of the Mo addition on the tensile properties were not observed. However, the creep properties at $650^{\circ}C$ under applied stresses of 140 and 150 MPa were considerably enhanced by the Mo addition. The microstructural observation after the creep test indicated that the addition of Mo could function to retain the recovery of the martensitic matrix, thus resulting in the enhanced creep properties of the 9Cr-3W-0.5Mo steel. Furthermore coarsening of the $M_{23}C_6$ carbides and formation of Laves phases were observed in both samples after the creep tests.

• 동력기계공학회지
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• 제6권1호
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• pp.55-60
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• 2002

There has been no report on the life prediction for gas turbine materials at high temperatures based on the creep properties and their relationship with the AE(acoustic emission) properties as a means of real-time non-destructive testing. One of the important issues is thus to develop a reliable method of evaluating creep properties by the AE technique. In this paper, the real-time evaluation of high temperature creep time and AE cumulative counts for nickel-based superalloy Udimet 720 was performed on round-bar type specimens under pure load at the temperatures of 811, 922 and 977K. The total AE cumulative counts until the starting point of secondary creep($N_1$) and that of tertiary creep($N_2$) have quantitative relationship with the tertiary creep time and the rupture time. It is thus possible to construct the life prediction system based on creep and the prevention system of tertiary creep by using AE technique.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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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.