• Title, Summary, Keyword: 크리프

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A Stud on the Creep Characteristics of Concrete for Reactor Containment Structure (원자로 격납구조 콘크리트의 크리프 특성에 관한 연구)

  • 송하원;정원섭;변근주;송영철
    • Magazine of the Korea Concrete Institute
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    • v.9 no.4
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    • pp.155-165
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    • 1997
  • Since the biggest time-dependent prestress loss of reactor containment structure is due to creep of concrete. the creep is one of important structural factors to be considered for the safety maintenance in the containment structure during design. construction and main enance. This paper is about the creep charactoristies of concrete for the reactor containment structure. In this paper, creep test was performed to show the creep characteristics of reactor containment concrete structure made of the type-V cement. Then, in order to evaluate the applicability of creep prediction equations of recently revised Korean Concrete Standard Specification(KSCE-96) and Japanes Concrete Standard Specification. ACI-209. CEB/FIP-90. and HANSEN, creep test results were compared with prediction results obtained from he equations. From the comparisons, it was shown that the equation of th KSCE-96 predicts creep for younger concrete than 1 year, better than the other equations and that all of the equations predicts creep, for older concrete than 1 year, smaller than test. From regression analysis. a creep prediction equation which effectively predicts creep of concrete due to loading after 1year was proposed.

Estimation of Transient Creep C(t)-integrals for SE(B) Specimen Under Elastic-Plastic-Creep Conditions (탄성-소성-크리프 상태에서 SE(B) 시편의 천이크리프 C(t)-적분 평가)

  • Lee, Han-Sang;Je, Jin-Ho;Kim, Dong-Jun;Kim, Yun-Jae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.39 no.9
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    • pp.851-857
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    • 2015
  • In this paper, we estimate the time-dependent C(t) integrals under elastic-plastic-creep conditions. Finite-element (FE) transient creep analyses have been performed for single-edge-notched-bend (SEB) specimens. We investigate the effect of the initial plasticity on the transient creep by systematically varying the magnitude of the initial step load. We consider both the same stress exponent and different stress exponents in the power-law creep and plasticity to elastic-plastic-creep behavior. To estimate the C(t) integrals, we compare the FE analysis results with those obtained using formulas. In this paper, we propose a modified equation to predict the C(t) integrals for the case of creep exponents that are different from the plastic exponent.

Suggestion for Interpretation of Limit Creep Strain of Geogrids (지오그리드의 한계 크리프 변형률 해석을 위한 제안)

  • Jeon, Han-Yong;Mok, Mun-Sung
    • Journal of the Korean Geosynthetics Society
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    • v.6 no.4
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    • pp.1-6
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    • 2007
  • New procedure for evaluation of creep reduction factor by the limit creep strain concept was introduced through the analysis of creep test results. To determine the limit creep strain of the geogrids, the Sherby-Dorm Plots were applied and the results of this procedure were compared and interpreted, respectively. From this, it is seen that the creep reduction factors were 1.45 for the geogrid samples used in this study. Through the comparison of creep reduction factors in 10% creep strain criteria, it was confirmed that the range of creep reduction factor is about 0.06~0.14 for the geogrid samples in this study.

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Time-dependent Analysis of Reinforced and Prestressed Concrete Structures Incorporating Creep Recovery Function (크리프 회복 거동을 고려한 철근콘크리트 및 프리스트레스트 콘크리트 부재의 장기거동해석에 관한 연구)

  • Kim, Se-Hoon;Oh, Byung-Hwan
    • Magazine of the Korea Concrete Institute
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    • v.11 no.1
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    • pp.279-288
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    • 1999
  • The creep of concrete structures caused by variable stresses is generally calculated by step-by-step method based on the superposition of creep function. Although most practical application is carried out by this linear assumption. significant deviations between predictions and experiments have been observed when unloading takes place, that is. stress is reduced. This shows that the superposition of creep function does not describe accurately the effect of sustained compressive preload. The main purpose of this study is to propose a creep analysis model which is expressed with both creep function and creep recovery function where increase or decrease of stress is repeated. In these two function method, the creep behavior is modelled by using linear creep law for loading and creep recovery law for unloading. To apply two function method to time analysis of concrete structures, the calculation method of creep strain increment under varying stress is proposed. The calculation results based on the present method correlates very well with test data, but the conventional superposition method exhibits large deviation from test results. This paper provides a more accurate method for the time dependent analysis of concrete structures subjected to varying stress, i.e. increasing or decreasing stress. The present method may be efficiently employed in the revision of future concrete codes.

SP Creep Degradation of Anisotropic Materials by the Hydride (수소화물에 의한 이방성재료의 소형펀치(SP) 크리프 열화거동)

  • Oh, Dong-Joon
    • 대한공업교육학회지
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    • v.35 no.2
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    • pp.204-223
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    • 2010
  • The purpose of this study was to investigate the high temperature creep behavior of anisotropic Zr-2.4%Nb alloy which includes the hydride. To minimize the effect of the anisotropy and to achieve the bi-axial stress condition, SP creep test was performed using the Zr alloys which have the 50 ppm, 100 ppm and 200 ppm hydride. Each SP creep curve was obtained and compared. While the creep degradation of 50 ppm and 100 ppm hydride specimens was clearly found, the degradation of 200 ppm was not cleared. By the comparison of SP creep constant and stree exponent, this fact was confirmed. As the degradation of 50 ppm and 100 ppm hydride was processed, the SP creep constant was decreased and the stress exponet was increased. However, while the SP creep constant of 200 ppm hydride was decreased, the stree exponent was decreased. Finally, it was confirmed that the creep degradation of 200 ppm was not found. In conclusion, the hydride was the major parameter to control the hight temperature creep degradation of Zr alloy.

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Evaluation of Creep Properties of W-substituted 2205 Duplex Stainless Steel (W치환 2205 이상 스테인리스강의 크리프 특성 평가에 관한 연구)

  • Kim, Gi-Yeob;Choi, Byong-Ho;Nam, Ki-Woo;Ahn, Yong-Sik
    • Journal of the Korean Society for Nondestructive Testing
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    • v.24 no.1
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    • pp.29-37
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    • 2004
  • The effect of the substitution of Tungsten(W) for Molybdenum(Mo) on the creep behaviour of 22Cr-5Ni duplex stainless steel(DSS) has been investigated. Creep tests were carried out at $600^{\circ}C\;and\;650^{\circ}C$. Intermetallic ${\sigma}$ phase is precipitated during creep at $650^{\circ}C$, at which creep rupture time was much lower compared with at $600^{\circ}C$. The substitution of W for Mo in the duplex stainless steel was known to retard the formation of ${\sigma}$ phase. Minimum creep rate and creep rupture time, however, were hardly influenced by the substitution of 2wt.% W. An ultrasonic measurement for the creep specimens has been carried out for the evaluation of creep damage. The sound velocity increases propotionally with the increase of creep rupture time at $600^{\circ}C$ of creep temperature. On the contrary, the sound velocity decreases with the increase of rupture time at $650^{\circ}C$, which can be correlated with the microstructural evolution during creep.

Estimation of Transient Creep Crack-tip Stress Fields for SE(B) specimen under Elastic-Plastic-Creep Conditions (탄성-소성-크리프 상태에서 SE(B) 시편의 천이크리프 균열 선단 응력장 평가)

  • Lee, Han-Sang;Je, Jin-Ho;Kim, Dong-Jun;Kim, Yun-Jae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.39 no.10
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    • pp.1001-1010
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    • 2015
  • This paper estimates the time-dependent crack-tip stress fields under elastic-plastic-creep conditions. We perform Finite-Element (FE) transient creep analyses for a Single-Edge-notched-Bend (SEB) specimen. We investigate the effect of the initial plasticity on the transient creep by systematically varying the magnitude of the initial step-load. We consider both the same stress exponent and different stress exponent in the power-law creep and plasticity to determine the elastic-plastic-creep behaviour. To estimation of the crack-tip stress fields, we compare FE analysis results with those obtained numerically formulas. In addition, we propose a new equation to predict the crack-tip stress fields when the creep exponent is different from the plastic exponent.

Investigation on Factors Influencing Creep Prediction and Proposal of Creep Prediction Model Considering Concrete Mixture in the Domestic Construction Field (크리프 예측 영향요인 검토 및 국내 건설현장 콘크리트 배합을 고려한 크리프 예측 모델식 제안)

  • Moon, Hyung-Jae;Seok, Won-Kyun;Koo, Kyung-Mo;Lee, Sang-Kyu;Hwang, Eui-Chul;Kim, Gyu-Yong
    • Journal of the Korea Institute of Building Construction
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    • v.19 no.6
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    • pp.503-510
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    • 2019
  • Recently, construction technology of RC structures must be examined for creep in concrete. The factors affecting the creep prediction of concrete and the results of creep in domestic construction field were reviewed. The longer the creep test period and the higher the compressive strength, the higher the creep prediction accuracy. The higher the curing temperature, the higher the initial strength development of the concrete, but the difference in the creep coefficients increased over time. Based on the results of creep evaluation in the domestic construction field and lab. tests, a modified predictive model that complements the ACI-209 model was proposed. In the creep prediction of real members using general to high strength concrete, the test period and temperature should be considered precisely.

The Creep Properties of Pb-free Sn-3.5Ag-$\chi$Cu Solder Alloys (Sn-3.5Ag-xCu무연 솔더의 크리프 성질 연구)

  • Joo, Dae-Kwon;Yu, Jin
    • Proceedings of the International Microelectronics And Packaging Society Conference
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    • pp.141-145
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    • 2001
  • Sn-3.5Ag 무연 솔더에 Cu를 첨가한 3원계 합금을 만든 후 압연과 열처리한 후 크리프 특성을 연구하였다. 모든 솔더 합금에서 1차 크리프는 거의 관찰되지 않았으며, 2차와 3차 크리프가 대부분을 차지하였고, 최소 크리프 변형율은 Cu 함량이 0.75 wt %에서 최소이었고, 응력 지수는 약 4이었으며, 파단 시간 또한 0.75 wt% Cu에서 가장 길었다. 크리프 기구는 격자 확산에 의한 전위의 상승과 전위 활주에 의한 고온 크리프임을 앞 수 있었으며, Cu의 첨가는 1 wt% 가지 연성에 큰 영향을 주지 않았으나, 1.5 wt% 첨가했을 경우 연성은 크게 감소하였다.

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Evaluation of Physical Properties and Long-term Stability of Expansion Materials for Emergency Repair by Temperature (긴급복구용 팽창재료의 온도에 따른 물리적 특성 및 장기 안전성 평가)

  • Park, Jeongjun;Kim, Kisung;Kang, Hyounhoi;Kim, Ju-Ho;Hong, Gigwon
    • Journal of the Society of Disaster Information
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    • v.14 no.1
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    • pp.79-88
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    • 2018
  • In this study, the changes of the expansion and strength according to the temperature of the emergency repairing expansion material were examined by cup foaming test and uniaxial compressive strength test, and the accelerated compression creep test was carried out to confirm the long term stability. Ramp & Hold test and accelerated compressive creep test were performed to evaluate the creep performance. The short - term creep test was used to determine the initial creep strain of the expanding material. The isothermal method using time - To evaluate the long - term compressive creep performance.