• Journal of Ocean Engineering and Technology
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• v.10 no.1
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• pp.47-52
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• 1996

This paper deals with a study on improvement of long-time creep life prediction of steam turbine rotor steels by using initial strain method as a new approach at high temperatures of 500 to 70$0^{\circ}C$ . The main result shows that the inital strain method could be reliably utilized to predict and evaluate the long-time creep life as creep rupture strength and that the predicting equation for long-time creep life under a certain creep stress at a certain high temperature could be empirically derived out from each initial instantaneous strain measured.

• Journal of the KSME
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• v.55 no.10
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• pp.26-30
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• 2015

이 글에서는 제4세대 원전 고온구조재료인 Gr. 91강을 대상으로 하여 장시간 크리프 수명을 예측하고 파단수명을 확률적 신뢰도를 가지고 평가할 수 있는 방법에 대해 실 예제를 통하여 서술한다.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.441-444
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• 2001

PVC로 코팅된 폴리에스테르 섬유로 만들어진 지오그리드 보강재에 대해 변형률을 달리하여 단일 또는 다단 크리프 하중단계를 포함한 하중을 연속적으로 작용시킴으로써 그 인장파괴강도를 검토하였다. 연구결과, 동일한 변형률에서 지오그리드의 인장파괴강도는 극한인장파괴가 되기 전에 작용된 웅력이력에 의해서 거의 영향을 받지 않는다. 또한 지오그리드의 설계파단강도는 적정한 변형률하에서 정의되어야 하며, 변형률 속도가 빠른 인장시험을 통해 지오그리드의 설계파단강도를 얻을 경우 이에 대한 보정이 필요할 것으로 사료된다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.57.2-57.2
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• 2011

MX 석출물 형성 원소인 V과 Nb을 첨가한 11Cr-1Mo-VNb 페라이트계 내열강의 각각의 시험 온도에서 파단 시간에 따른 미세조직의 변화를 연구하였다. 초기 조직은 템퍼드 마르텐사이트 조직을 갖고 있었으며, 고온 강도를 저하시키는 ${\delta}$-페라이트는 존재하지 않았다. 주 석출상은 $M_{23}C_6$와 MX로 확인되었다. 또한, 모든 크리프 파단재에서 응력을 받은 게이지 부분이 응력을 받지 않은 그립 부분보다 석출물 및 마르텐사이트 래스 폭의 성장이 가속되는 결과를 나타내었다. 이는 크리프 변형 중 응력 집중에 의해 래스 경계를 따라 전위가 집적되고, 이에 따른 용질원자의 확산 속도가 증가하여 석출물의 성장에 따른 래스 경계의 이동이 일어나 게이지 부분이 그립 부분보다 마르텐사이트 회복이 가속된 것으로 판단된다.

• Journal of Power System Engineering
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• v.14 no.4
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• pp.56-62
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• 2010

This paper is concerned with the stochastic nature of elevated temperature tensile strength and creep rupture time in 18Cr-8Ni stainless steels. The Weibull statistical analysis using the NRIM data sheet has been performed to investigate the effects of variability of the elevated temperature tensile strength and creep rupture time on the testing temperature. From those investigations, the distributions of temperature tensile strength and creep rupture time were well followed in 2-parameter Weibull. The shape parameter and scale parameter for the Weibull distribution of tensile strength were decreased with increasing the testing temperature. For the creep rupture time, generally, the shape parameter were decreased with increasing the testing temperature.

• Proceedings of the KWS Conference
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• 2004.05a
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• pp.146-148
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• 2004

최근 전세계적으로 활발히 진행되고있는 화력발전소용 내열강의 연구는 화력발전소의 열효율 향상을 위한 주증기 조건의 고온ㆍ고압화를 실현하기 위해 고온 크리프 파단강도 개선에 모든 연구력이 집중되고있다. (중략)

• Journal of Ocean Engineering and Technology
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• v.21 no.4
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• pp.28-33
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• 2007

The objective of this paper is to investigate the relationship between the short-term creep rupture time and the creep rupture properties at three different elevated temperatures in STS304 stainless steel. Uniaxial constant stress creep rupture tests were performed on the steel to observe the creep rupture behaviors at the elevated temperatures of 600, 650 and 700, according to the testing matrix. It is very important to predict creep life in practical creep design problems. As one of the series of studies on the statistical modelling of probabilistic creep rupture time and the development of creep life prediction techniques, the relationship between applied stress and creep rupture behaviors, such as creep strain rate and rupture time, were investigated. In addition, the Monkman-Grant relationship was observed between the steady-state creep rate and the creep rupture time. The creep rupture surfaces observed by SEM showed up dimple phenomenon at all conditions.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.2
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• pp.236-242
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• 1989

In order to investigate the effects of hot corrosion on the creep rupture properties and creep life of 304 stainless steel being used as tube materials of heavy oil fired boiler, the creep rupture tests were carried out at temperature 630.deg.C, 690.deg.C and 750.deg.C in static air for the specimens with or without coating of double layer corrosives according to the new hot corrosion test method simulating the situation commonly observed on superheater tubes of the actual boiler. The double layer corrosives are 85% V$_{2}$O$_{5}$ + 10% Na$_{2}$So$_{4}$ + 5% Fe$_{2}$O$_{3}$ as the inner layer corrosive being once melted at 900.deg. C and crushed to powder, and 10% V$_{2}$O$_{5}$ + 85% Na$_{2}$SO$_{4}$ +5% Fe$_{2}$O$_{3}$ as the outer layer corrosive. As results, in the specimen coated with the double layer corrosives, the rupture strength was extremely lowered and showed a large difference each other. The rupture ductility also lowered remarkably as a result of the brittle fracture mode due to hot corrosion. These results indicate that hot corrosion could essentially alter the creep fracture mechanism. From the metallographic observation, it was clarified that the rupture life of 304 stainless steel subjected to hot corrosion was chiefly determined by the behavior of the aggressive intergranular penetration of sulfides.des.

• Journal of Korean Ophthalmic Optics Society
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• v.13 no.4
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• pp.89-94
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• 2008

Purpose: To observe the high temperature creep test and the fracture surface of the samples of 9% Ni alloy steel generally used for all kinds of mahine parts and predict the durability of that by determining a constant of C with a Larson-Miller variable. Methods: The equipment of this test was made into lever-beam style designed by Andrade and F. Garofalo et al.. The condition of creep test was set under 16 kinds of conditions after fixing 4 kinds of temperature condition and 4 kinds of stress condition to check how it effects the samples. Results: The temperature of creep test was increased, the stress index (n) of creep deformation was gradually decreased from 3.97 to 3.55. The activation energy of creep deformation was decreased from 90.39 to 83.64 kcal/mol when the stress was increased. A constant of C value by calculation of larson-Miller variable was about 22 and if temperature for use is suggested, the durability could be calculated. Conclusions: By analyzing the fracture phenomenon and suggesting the observation result of the fracture surface of the samples and creep test of 9% Ni alloy steel, the basic design data for the practical use of accessories in the field of equipment could be constructed and used to predict the durability of the equipment.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.12
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• pp.1403-1410
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• 2011

Creep characteristic is an important failure mechanism when evaluating engineering materials that are soft material as polymers or used as mechanical elements at high temperatures. One of the popular thermo-elastic polymers, Polymethyl methacrylate(PMMA) which is used broadly for engineering polymer, as it has excellent mechanical and thermal properties compared to other polymers, was studied for creep characteristic at various level of stresses and temperatures. From the experimental results, the creep limit of PMMA at room temperature is 85 % of tensile strength. which is higher than that of PE (75%)at room temperature. Also the creep limits decreased to nil linearly as the temperatures increased, up to $120^{\circ}C$ of the melting point($267^{\circ}C$). Also the first and third stage among the three creep stages were non-existent nor were there any rupture failure which occurred for many metals at high temperatures.