• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.10a
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• pp.26-32
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• 2000

It was confirmed that the life predictive equation by LMP-ISM are effective only up to 10$^2$hours and can not be used for long times of 10$^3$~10$^{5}$ hours, but that by ISM can be used for long times creep life prediction with more reliability. The predictive creep life equation of ISM has better reliability than those by LMP and LMP-ISM, and its realizably is getting better for long time creep prediction(10$^3$~10$^{5}$ H).

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.7 s.178
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• pp.1833-1840
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• 2000

Commercially pure copper is tested to obtain creep curves at 2500C. Constitutive relations adopting continuum damage mechanics concept is found to be appropriate to model the creep defor mation up to the tertiary stage. Microscopic observation by SEM reveals that creep condition induces cavities and microcracks subsequently. The constitutive equations along with evaluated creep parameters are implemented into finite element analysis code. The analysis reproduces creep curves under step loading as well as constant loading with reasonable accuracy. Distribution and evolution of damage under creep loading are numerically simulated for two different types of notched specimen. Predicted creep life agrees quite well with rupture test results. The influence of mesh size at notch tip on rupture time prediction is studied, and a degree of refinement is suggested for the specific notched specimens.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.2
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• pp.129-144
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• 1999

플랜트와 같은 장치산업은 내구성 구조물이므로 사용중에 열화가 발생하는 것은 필연적이다. 특히 고온, 고압의 부식환경하에서 사용되는 설비는 손상이 심하므로 가동중에 돌발적인 고장이 발생하여 플랜트의 가동을 중지하거나 파손사고가 일어나 생산손실은 물론 경우에 따라서는 안전사고의 발생, 환경오염 등 사회적인 문제를 일으키므로 이들 설비의 경년열화 실체를 충분히 이해하고 대책을 수립하는 것은 대단히 중요하다. 따라서 본고에서는 장치산업에서 발생하는 열화현상(재료의 연화, 경화 및 취화, 크리프, 피로, 부식, 마모 등)중 손상의 주류를 이루는 연화, 경화 및 취화, 크리프 피로에 대하여 기본적인 손상기구(damage mechanism)와 비파괴적 진단 및 평가 방법에 주안점을 두어, 현재 국내의 각종 플랜트 진단에 실용화된 기술을 해설하여 이 분야에 종사하는 관계자 여러분의 이해에 조금이라도 기여코자 한다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.12
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• pp.1995-2001
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• 2001

In this study, a small punch creep(SP-Creep) test using miniaturized specimen(10${\times}$10${\times}$0.5mm) is described to develop the new creep test method for high temperature structural materials. The SP-Creep test is applied to 2.25Cr-lMo(STBA24) steel which is widely used as boiler tube material. The test temperatures applied for the creep deformation of miniaturized specimens are between 550∼600$^{\circ}C$. The SP-Creep curves depend definitely on applied load and creep temperature, and show the three stages of creep behavior like in conventional uniaxial tensile creep curves. The load exponent of miniaturized specimen decreases with increasing test temperature, and its behavior is similar to stress exponent behavior of uniaxial creep test. The creep activation energy obtained from the relationship between SP-Creep rate and test temperature decreases as the applied load increases. A predicting equation or SP-Creep rate for 2.25Cr-lMo steel is suggested. and a good agreement between experimental and calculated data has been found.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.9 s.252
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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.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.04a
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• pp.35-35
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• 2000

터빈의 핵심구동부품은 손상이 누적되어 파괴에 이를 경우 치명적인 결과를 야기할 수 있기 때문에, 부품사용조건에서의 소성변형과 이에 따른 손상 누적을 정확히 예측하고 평가함으로써 균열생성 시점을 정확히 파악하여야 할 필요가 있다. 현재 터빈디스크와 같이 고온 고응력에서 사용되고 있는 소재부품의 수명은 궁극적으로 크리프변형과 피로시험의 공동작용으로 결정되며, 재료특성모델링 시험에 있어서도 dwell time 피로시험을 통해 dwell time 효과를 점검하고 점소성 재료변형에 근거하여 피로에 의한 변형 현상을 설명할 수 있다.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.3
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• pp.7-10
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• 2009

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.643-647
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• 2003

Power plant Piping operating at elevated temperature often fails prematurely by the growth of microcracks under creep conditions. Therefore, the life assessment of high temperature components that contain cracks is an important technological problem. The mechanisms of crack growth in simple metals and alloys have been investigated using both mechanical and microstructural approaches. In this study, life prediction accounting for creep, crack growth and thermal stress is analyzed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.10a
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• pp.39-40
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• 2006

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.10
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• pp.1185-1191
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• 2014

Gas turbine blades that have complex geometry of the cooling holes and cooling passages are usually subjected to cyclic and sustained thermal loads due to changes in the operating characteristic in combined power plants; these results in non-uniform temperature and stress distributions according to time to gas turbine blades. Those operation conditions cause creep or thermo-mechanical fatigue damage and reduce the lifetime of gas turbine blades. Thus, an accurate analysis of the stresses caused by various loading conditions is required to ensure the integrity and to ensure an accurate life assessment of the components of a gas turbine. It is well known that computational analysis such as cross-linking process including CFD, heat transfer and stress analysis is used as an alternative to demonstration test. In this paper, temperatures and stresses of gas turbine blade were calculated with fluid-structural analysis integrating fluid-thermal-solid analysis methodologies by considering actual operation conditions. Based on analysis results, additionally, the total lifetime was obtained using creep and thermo-mechanical damage model.