• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 봄 학술발표회 논문집(I)
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• pp.365-370
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• 1998

The creep strain of the compression zone of concrete beams subjected to cyclic loading should be a significant factor in increasing strain and deflections. An analytical model which is similar to a previous one is presented to predict the increase in cyclic creep strain and the damage using the properties of the constituent materials: concrete and steel. The analytical expressions are compared with our experimental data. The effect of concrete-creep is accounted by the term En, Icr,n, and Mcr,n. In this study, it is proved that cyclic creep exponents 'n' in Cyclic Creep Model, according to the parameters -strength, range of stress- have the various values. It is hoped that with the availability of more experimental data and better understanding of some of the complex behavior, the model could be further improved.

• 한국해양공학회지
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• 제11권4호
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• pp.40-48
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• 1997

There are many research results as individual uni-axial tension creep test of heat-resisting materials. However, there are very few about the study on the high temperature creep test for the Initial Strain Method, and especially any study on it about the friction welded joints of SUH3 to SUH35. One of the important concerns is a reliable method of evaluating static creep properties. No reliable method seems available at present to evaluate or predict static creep properties. So, the reliable method to evaluate and predict them by the ISM and AE techniques was made.

• 지구물리
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• 제7권4호
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• pp.277-282
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• 2004

Creep deformation of concrete is often responsible for excessive deflection at loads which can compromise the performance of elements within structures. Hence, the prediction of the magnitude and rate of creep strain is an important requirement of the design process and management of structures. Although laboratory tests may be undertaken to determine the deformation properties of concrete, these are time-consuming, often expensive and generally not a practical option. Therefore, relatively simple empirically based national design code models are relied upon to predict the magnitude of creep strain.This paper reviews the accuracy of creep predictions yielded by eight commonly used international "code type" models, all of which do not consider the same material parameters and yield a range of predicted strains, when compared with actual strains measured on a range of concretes in seventeen different investigations. The models assessed are the: SABS 0100 (1992), BS 8110 (1985), ACI 209 (1992), AS 3600 (1998), CEB-FIP (1970, 1978 and 1990) and the RILEM Model B3 (1995). The RILEM Model B3 (1995) and CEB-FIP (1978) were found to be the most and least accurate, respectively.

• 한국자동차공학회논문집
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• 제9권6호
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• pp.135-142
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• 2001

The effect of tensile hold time on the creep-fatigue interaction in AISI 316 stainless steel was investigated. To study the fatigue characteristics of the material, strain controlled low cycle fatigue(LCF) tests were carried out under the continuous triangular waveshape with three different total strain ranges of 1.0%, 1.5% and 2.0%. To study the creep-fatigue interaction, 5min., 10min., and 30min. of tensile hold times were applied to the continuous triangular waveshape with the same three total strain ranges. The creep-fatigue life was found to be the longest when the 5min. tensile hold time was applied and was the shortest when the 30min. tensile hold time was applied. The cause fur the shortest creep-fatigue life under the 30min. tensile hold time is believed to be the effect of the increased creep damage per cycle as the hold time increases. The creep-fatigue life prediction using artificial neural network(ANN) showed closer prediction values to the experimental values than by the modified Coffin-Manson method.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.1580-1587
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• 2005

To calculate the long-term allowable strength of geosynthetic reinforcement, replacement method was recommended. The isochronous creep curve by S. Turner was used to define the relation between creep strain and allowable strength. In isochronous curve at given time, one can read the allowable strength at allowable creep strain. The allowable strain gets from specification by directors or manufacturers according to the allowable displacement of reinforced structures. The allowable strength can be determined in relation to the allowable horizontal displacement each structures case by case. The effect of install damage on isochronous behaviors of geosynthetic reinforcement was little. In previous study, install damage increase the creep strain slightly. And the degradation was not identified. But it is supposed that degradation increase the creep strain. In conclusion, The recommended model to determine long-term allowable strength of geosynthetic reinforcements considering tensile deformation of reinforcement and soil is fit for proper, correct and economic design for reinforced earth walls.

• 대한기계학회논문집A
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• 제33권10호
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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.

• Nuclear Engineering and Technology
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• 제54권3호
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• pp.917-925
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• 2022

Steam generator (SG) tubes in a nuclear power plant can undergo rapid changes in pressure and temperature during an accident; thus, an accurate model to predict short-term creep damage is essential. The theta (𝜃) projection method has been widely used for modeling creep-strain behavior under constant stress. However, many creep test data are obtained under constant load, so creep rupture behavior under a constant load cannot be accurately simulated due to the different stress conditions. This paper proposes a novel methodology to obtain the creep curve under constant stress using a modified 𝜃 projection method that considers the increase in true stress during creep deformation in a constant-load creep test. The methodology is validated using finite element analysis, and the limitations of the methodology are also discussed. The paper also proposes a creep-strain model for alloy 690 as an SG material and a novel creep hardening rule we call the damage-fraction hardening rule. The creep hardening rule is applied to evaluate the creep rupture behavior of SG tubes. The results of this study show its great potential to evaluate the rupture behavior of an SG tube governed by creep deformation.

• 콘크리트학회논문집
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• 제23권5호
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• pp.627-636
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• 2011

최근 고강도 콘크리트의 폭렬 방지용 보강 섬유로서 폴리프로필렌 섬유를 대신하여 나일론 섬유의 사용이 증가됨에 따라 고온에 노출된 나일론 섬유를 혼입한 고강도 콘크리트의 폭렬 및 역학적 특성에 관한 실험적 연구가 수행되고 있다. 그러나, 고온을 받은 나일론 섬유 보강 고강도 콘크리트에 관한 연구는 주로 폭렬 특성, 압축강도 및 탄성계수에 대한 평가만이 수행되고 있으며, 열팽창 변형, 전체 변형, 크리프 변형 및 과도 변형과 같은 거동은 평가된 바가 없다. 따라서 이 연구에서는 W/B 0.30~0.15에 따른 나일론 섬유를 혼입한 고강도 콘크리트에 대하여 열팽창 변형, 전체 변형, 크리프 및 과도 변형 등을 평가하였다. 실험 결과, 나일론 섬유는 고온을 받은 나일론 섬유를 혼입한 고강도 콘크리트의 성능에 특별한 영향을 미치지 않는 것으로 보였으며, 나일론 섬유 보강 고강도 콘크리트는 섬유를 혼입하지 않은 고강도 콘크리트 또는 보통 강도 콘크리트보다 큰 과도 변형을 나타냈다.

• 한국지반공학회지:지반
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• 제9권4호
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• pp.55-64
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• 1993

이방압밀이 비배수크리프파괴거동에 미치는 영향을 연구하기 위하여 4가지의 압밀응력비(a:In'/clc': 1.0, 0.7, 0.5, 0.4)로서 정규압밀시킨 점토시료에 대해서 비배수크리프시험을 수행하였다. 어떤 최소변형률속도에 이르는 경과시간은 압밀응력비의 감소에 따라 줄어들고 이 최소변형률속도에 대한 파괴시간도 감소된다. Finn and Shead(1.1의 제안식에 의해서 구한 상한항복강도는 압밀응력비의 크기에 관계없이 크리프강도와 잘 일치하며 평균구속응력으로서 정규화한 상한항복 강도는 압밀응력비가 증가할수록 감소한다.

• 대한기계학회논문집A
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• 제26권6호
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• pp.1069-1076
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• 2002

The high temperature creep behavior of heat machine systems such as aircraft engines, boilers and turbines in power plants and nuclear reactor components have been considered as an important and needful fact. There are considerable research results available for the design of high temperature tube materials in power plants. However, few studies on the Initial Strain Method (ISM) capable of securing repair, maintenance, cost loss and life loss have been made. In this method, 3 long time prediction Of high temperature creep characteristics can be dramatically induced through a short time experiment. The purpose of present study is to investigate the high temperature creep lift of Udimet 720, SCM 440-STD61 and 1Cr-0.5Mo steel using the ISM. The creep test was performed at 40$0^{\circ}C$ to $700^{\circ}C$ under a pure loading. In the prediction of creep life for each materials, the equation of ISM was superior of Larson-Miller Parameter(LMP). Especially, the long time prediction of creep life was identified to improve the reliability.