• 대한금속재료학회지
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• 제48권11호
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• pp.965-973
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• 2010

The small punch creep (SPC) test has recently received much attention as a new alternative to the conventional uniaxial creep test because it needs only a miniature-sized specimen directly detached from an operating system or component without any serious sampling damages. However, it is difficult to obtain the equivalent uniaxial creep data directly from the SPC data. As a specimen is deformed by a punch in the SPC test, the test result is sensitive to the friction between them. Finite element analyses with various friction coefficients was performed and showed a tendency of increased SPC life with an increased friction coefficient. The necking position predicted by the SPC simulation with a proper friction coefficient showed good agreement with that observed from the real SPC test. Finally, a noble method to convert the SPC load and displacement rate into the equivalent uniaxial creep stress and strain rate, respectively, was established in this study.

• 대한금속재료학회지
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• 제49권9호
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• pp.686-691
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• 2011

To develop creep resistant die-cast Mg alloys, various alloying elements, including Ca, Ce, and Sr, were added to a Mg-Al alloy. The AXE710 alloy was produced on a 320 ton high-pressure die casting machine. The microstructure and creep properties of the alloy were examined. The creep behavior was investigated at $150^{\circ}C$ for stresses ranging from 50 to 100 MPa. The stress exponent was derived from the relationship between normalized secondary creep rates and compensated effective stresses. It was found to be 4.9, indicating that the dislocation climb is a dominant creep mechanism.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 추계학술대회 논문집
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• pp.606-612
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• 2008

Creep force is one of the only appeared at conventional train which used to be driven by metallic wheel and rail contact. Due to the elastic deformation of wheel/rail contact patch by the weights of wheel and all the components related to it, creep force generates and becomes to the decision factor of critical speed of bogie(or railway vehicle) which is the criteria of avoiding vehicle to be unstable. There are many kind of factors which affect generation of creep force at a wheel/rail contact surface such as viscosity of contact patch, velocity, wheel and rail geometric profile, mechanical properties of wheel and rail. This paper concentrates on a wheelset simple 2 DOF Equation of Motion being exerted. From the simple numerical analysis using linear solution about getting creep force some factors could find roughly. Among the factors geometric parameter could be the one of most important for this study. In the future we'll prolong the range of study to find out method of measuring creep force easily.

• Nuclear Engineering and Technology
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• 제53권10호
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• pp.3379-3397
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• 2021

In this study, a multi-physics modeling method was developed to analyze a nuclear fuel rod's thermo-mechanical behavior especially for high temperature anisotropic creep deformation during ballooning and burst occurring in Loss of Coolant Accident (LOCA). Based on transient heat transfer and nonlinear mechanical analysis, the present work newly incorporated the nuclear fuel rod's special characteristics which include gap heat transfer, temperature and burnup dependent material properties, and especially for high temperature creep with material anisotropy. The proposed method was tested through various benchmark analyses and showed good agreements with analytical solutions. From the validation study with a cladding burst experiment which postulates the LOCA scenario, it was shown that the present development could predict the ballooning and burst behaviors accurately and showed the capability to predict anisotropic creep behavior during the LOCA. Moreover, in order to verify the anisotropic creep methodology proposed in this study, the comparison between modeling and experiment was made with isotropic material assumption. It was found that the present methodology with anisotropic creep could predict ballooning and burst more accurately and showed more realistic behavior of the cladding.

• Structural Engineering and Mechanics
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• 제72권2호
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• pp.245-256
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• 2019

The experimentally determined mechanical behavior of the material under the prescribed service conditions is the basis of advanced engineering optimum design. To allow experimental data on the behavior of the material considered, uniaxial stress tests were made. The aforementioned tests have enabled the determination of mechanical properties of material at different temperatures, then, the material's resistance to creep at various temperatures and stress levels, and finally, insight into the uniaxial high cyclic fatigue of the material under different applied stresses for prescribed stress ratio. Based on fatigue tests, using modified staircase method, fatigue limit was determined. All these data contributes the reliability of the use of material in mechanical structures. Data representing mechanical properties are shown in the form of engineering stress-strain diagrams; creep behavior is displayed in the form of creep curves while fatigue of the material is presented in the form of S-N (maximum applied stress versus number of the cycles to failure) curve. Material under consideration was 18CrNi8 (1.5920) steel. Ultimate tensile strength and yield strength at room temperature and at temperature of $600^{\circ}C$: [${\sigma}_{m,20/600}=(613/156)MPa$; ${\sigma}_{0.2,20/600}=(458/141)MPa$], as well as endurance (fatigue) limit at room temperature and stress ratio of R = -1 : (${\sigma}_{f,20,R=-1}=285.1MPa$).

• 대한기계학회:학술대회논문집
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.117.2-117.2
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• 2005

• 소성∙가공
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• 제17권3호
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• pp.189-196
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• 2008

Alloy718 is the nickel-base super alloy well used as gas turbine components under severe operating conditions because of its high strength at high temperature and excellent creep resistance. In this study, a coupling bolt for the gas turbine component is manufactured by hot heading process instead of whole machining in order to improve the mechanical properties. Die shape for the hot heading has been designed by general design rule of hot forging and also optimal process condition has been investigated by finite element method. The initial billet temperature and the punch speed have been determined by $1150^{\circ}C$ and 600mm/s on the basis of finite element analysis, respectively. The coupling bolt has been manufactured by 200ton screw press and evaluated by experiment in order to investigate the mechanical properties. As a result of experiment, the mechanical properties such as hardness, tensile strength and creep behavior have been superior to those manufactured by machining.

• 한국지반신소재학회논문집
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• 제4권1호
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• pp.37-46
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• 2005

폐기물 매립지 관련 특성을 조사하기 위하여 PVA 지오텍스타일/HDPE 지오멤브레인 복합재료를 제조하였다. PVA 지오텍스타일의 인장특성, 인열 및 파열강도, 유효구멍크기와 투수성 등을 각각 측정하였다. 또한 침출수에 대한 화학저항성과 자외선 안정성도 측정하였으며, 하중조건에 따른 크리프 변형거동과 마찰특성도 측정하였다. 이들 결과로부터 PVA 지오텍스타일/HDPE 지오멤브레인 복합재료는 일반적으로 폐기물 매립지에 적용되는 폴리프로필렌이나 폴리에스테르 지오텍스타일에 비해 우수한 특성을 나타내었다. 끝으로, 감소인자 분석으로부터 PVA 지오텍스타일/HDPE 지오멤브레인 복합재료의 크리프 변형거동도 폴리프로필렌이나 폴리에스테르 지오텍스타일에 비해 안정함을 알 수 있었다.

• Journal of the Korean Wood Science and Technology
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• 제48권5호
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• pp.608-617
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• 2020

For efficient use and expansion of domestic small- and medium-diameter woods, cross-laminated wood panels composed of tropical hardwoods and domestic temperate woods were fabricated, and the bending creep behavior under long-term loading was investigated. The bending creep curve of the cross-laminated wood panels showed an exponential function graph with a sharp increase at the top right side. The wood panel composed of a teak top layer and larch core and bottom layers recorded the highest initial deformation, and that composed of a merbau top layer and tulip core and bottom layers showed the lowest initial deformation. Creep deformation of the cross-laminated wood panels showed the highest value in that composed of a teak top layer and larch core and bottom layers and showed the lowest value in that composed of a merbau top layer and tulip core and bottom layers. The obtained creep deformation is 3.1-4.3 times that of merbau, however, it is remarkably lower than that of tulip and larch. The highest relative creep was recorded by the wood panel composed of merbau top layer and larch core and bottom layers, whereas that composed of the teak top layer and tulip core and bottom layers showed the lowest relative creep.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.612-615
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• 2004

The objective of this experimental study was to understand inelastic strain of concrete incorporating hwangtoh or combination of hwangtoh and slag. Main variables were replacement level of admixtures, hwangtoh and slag. We studied the properties of concrete such as heat of hydration, drying shrinkage and creep according to the replacement level of hwangtoh and slag. Test results showed that the heat of hydration of concrete decrease with increasing hwangtoh and slag replacement. Also drying shrinkage and creep of concrete increase with increasing hwangtoh replacement.