• Title/Summary/Keyword: 크리프

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Creep Behaviour of Al-Zn-Mg Ternary Aluminum Alloy (Al-Zn-Mg 3원계 알루미늄 합금의 크리프 거동)

  • 윤종호;황경충
    • Transactions of the Korean Society of Automotive Engineers
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    • v.12 no.1
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    • pp.203-208
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    • 2004
  • To make practical applications of Al-Zn-Mg ternary aluminum alloy effectively in various field, a series of static creep tests under the 16 temperature-stress combination conditions had been performed. The creep tester with constant stress loading was designed and made by the authors and used in this study. The higher the creep temperature rose, the less the stress exponents became. The bigger the applied stresses became, the less values the creep strain activation energy showed. The life prediction constant of Larson-Miller parameter was calculated as about 2.3. In the fractography, the ductile fracture with dimples by intergranular breakage was primarily observed. We can make practical use of these test data in the design, the life prediction and the prevention of the accidents of the thermal facilities, etc.

Creep Characteristic of the Polymethyl Methacrylate(PMMA) at Stresses and Temperatures (응력과 온도에 따른 아크릴(PMMA)의 크리프특성)

  • Kang, Suk-Choon
    • 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.

Damage in Constitutive Modeling for Soils (지반재료 구성모델에 있어서의 데미지)

  • Kim Dae-Kyu
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.5 no.5
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    • pp.471-479
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    • 2004
  • In this study, a time-dependent constitutive model was developed for cohesive soils. A damage law was included in the model, using which the undrained creep behavior was predicted. The mathematical and physical derivation of the model was performed in the sense of adopting only few model parameters. The model prediction was well agreed with the experimental result of creep testing including creep rupture.

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The Creep-Rupture Life of Al Alloy (Al합금의 크리프 파단수명에 관한 연구)

  • Bae, Choon-Ik;Chin, Do-Hun
    • Journal of the Korean Society of Mechanical Technology
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    • v.13 no.4
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    • pp.125-130
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    • 2011
  • Technological mode progress demands the use of materials at high temperature and pressure. Constant load creep tests have been carried out over the range of stresses at high temperatures. One of the most critical factors in considering such applications as the most critical one is the creep behavior. In order to investigate the creep behavior in this study, the stress exponents during creep were determined over the temperature range of $275^{\circ}C$ to $325^{\circ}C$ and the stress range of 36MPa to 72MPa. The applicability of modified Monkman-Grant relationship was also discussed.

원전 고온구조재의 크리프 수명예측 신뢰성 평가 기술

  • Kim, U-Gon
    • 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.

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Development of Assessment Methodology on Creep-Fatigue Crack Behavior for a Grade 91 Steel Structure (Mod.9Cr-1Mo 강 구조의 크리프-피로 균열 거동 평가법 개발)

  • Lee, Hyeong-Yeon;Lee, Jae-Han
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.34 no.1
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    • pp.103-110
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    • 2010
  • In this study, an assessment method on creep-fatigue crack initiation and crack growth for a Mod.9Cr-1Mo steel (ASME Grade 91) structure has been developed with an extension of the French RCC-MR A16 procedure. The current A16 guide provides defect assessment procedure for a creep-fatigue crack initiation and crack growth for an austenitic stainless steel, but no guideline is available yet for a Mod.9Cr-1Mo steel which is now widely being adopted for structural materials of future nuclear reactor system as well as ultra super critical (USC) thermal plant. In the present study an assessment method on creep-fatigue crack initiation and crack growth is provided for the FMS (Ferritic-Martensitic Steel) and assessment on the creep-fatigue crack behavior for a structure has been carried out. The assessment results were compared with the observed images from a structural test.

Creep Damage Evaluation of High-Temperature Pipeline Material for Fossil Power Plant by Frequency Spectrum Analysis Method (주파수분석법에 의한 발전소 고온배관재료의 크리프손상 평가)

  • Lee, Sang-Guk;Lee, In-Cheol;Chang, Hong-Keun
    • Journal of the Korean Society for Nondestructive Testing
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    • v.20 no.1
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    • pp.10-17
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    • 2000
  • In boiler high-temperature pipelines such as main steam pipe, header and steam drum in fossil power plants, conventional measurement techniques(replica method, electric resistance method, and hardness test method) for measuring creep damage have such disadvantages as complex preparation and measurement procedures, too many control parameters. And also, these techniques have low practicality and applied only to component surfaces with good accessibility. It needs to apply a reliable and quantitative ultrasonic nondestructive evaluation method that can be replaced for these equipment. In this study, both artificial creep degradation test using life prediction formula and frequency analysis by ultrasonic tests for crept specimens were carried out for the purpose of nondestructive evaluation for creep damage. As a result of ultrasonic tests for crept specimens, we conformed that the high frequency side spectra decrease and central frequency components shift to low frequency band, and also their bandwidth decreases as increasing creep damage in backwall echos.

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Microstructural Evolution and Magnetic Property of Creep-Fatigued Ferritic 9Cr Heat-Resisting Steel (크리프-피로 손상된 페라이트기 9Cr 내열강의 미세조직 발달과 자기적 특성)

  • Kim, Chung-Seok;Kwun, S.I.;Park, Ik-Keun
    • Journal of the Korean Society for Nondestructive Testing
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    • v.27 no.5
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    • pp.417-425
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    • 2007
  • The ferritic 9Cr-1Mo-V-Nb heat-resisting steel was experimentally studied in order to characterize its microstructural evolution during creep-fatigue by coercivity measurement. The creep-fatigue test was conducted at $550\;^{\circ}C$ with the tensile holding time of 60s and 600s, respectively. The coercivity decreased until the failure and the hardness monotonously decreased for the whole fatigue life. As the life fraction of creep-fatigue increased, the $M_{23}C_6$ carbide coarsened following the Ostwald ripening mechanism. However, the MX carbonitrides did not grow during creep-fatigue due to so stable at $550\;^{\circ}C$. The width of martensite lath increased because of the dislocation recovery at the lath boundaries. The magnetic coercivity has an influence on the microstructural properties such as dislocation, precipitates and martensite lath boundaries, which interpreted in relation to microstructural changes. Consequently, this study proposes a magnetic coercivity to quantify the level of damage and microstructural change during the creep-fatigue of ferritic 9Cr-1Mo-V-Nb steel.

The Creep Behavior of Shale in Daegu Area (대구지역 셰일의 크리프 특성)

  • 김영수;정성관;차주석;방인호
    • Tunnel and Underground Space
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    • v.13 no.2
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    • pp.100-107
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    • 2003
  • Deformation is found by an external force in the rock which has internal stress. So, deformation is increased in time what is stressed under constant load. Rock materials collapse suddenly in a long period when the creep rate increases slightly. So mechanical deformability of the ground is an essential condition for determination of long term safety in structures. The result of analysis in 40%, 50%, 60%, 70% of constant load in creep test, strain velocity constants $\alpha$ and ${\gamma}$ increase with load increasement. Griggs equation is more exact than Li and Xia, Singh equation, and G$_2$of a flow constant by Burger's model decreases with stress increasement, but η$_1$$_2$and G$_1$ manifest irregularly in this study.

Creep Behavior of Plastics Used in Automobile Instrument Panels (자동차 인스트루먼트 패널에 사용되는 플라스틱의 크리프 거동)

  • Kim, Young-Sam;Jeon, Chi-Hoon;Tumur-Ochir, Erdenebat;Yum, Young-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.35 no.12
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    • pp.1549-1556
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    • 2011
  • Tensile and creep tests were performed at various temperatures to investigate the mechanical properties of plastics used in automotive instrument panels. Mechanical properties such as Young's modulus and Poisson's ratios changed markedly with the test temperature. Three-point bending creep tests were performed for three kinds of plastics under four loading conditions. Coefficients in the time-hardening power law creep equation were obtained from the experiment, and the creep behavior was represented by a simple expression. The results of finite element creep analysis showed good agreement with the experimental results, while the difference between the numerical and experimental results increased with the load.