• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.1A
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• pp.85-93
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• 2009

The primary objective of this study is to construct more simple and reasonable rheological model and propose a methodology for predicting a phenomenon of concrete creep. Deformations of concrete under sustained stress can be expressed by the sum of immediately elastic deformation, time-dependent and time-independent short-term creep, and long-term creep according to the mechanism and time-dependency. To simulate these deformations, a rheological model having six parameters was constructed. In the composing of each parameter, the microprestress-solidification theory and design model code were incorporated together with the numerical approach for the components which can not be theoretically approached. Finally, actual test data were applied in the verification of the proposed model, and suitability of the model was confirmed by comparisons with existing predicting models and design codes.

• Journal of Korea Foundry Society
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• v.41 no.6
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• pp.505-515
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• 2021

Creep properties of directionally solidified Ni-based superalloy CM247LC under various temperature and stress conditions have been investigated. In the heat-treated specimen, some portion of eutectic γ-γ' remained, and uniform cubic γ' was observed in the dendrites. At low temperature (750℃) and high stress condition, a large amount of deformation occurred during the primary creep, while the tertiary creep region accounted for most of the creep deformation under high temperature and low stress condition. γ' particles are sheared by dislocation dissociated into super lattice partial dislocations separated by stacking faults at 750℃. No stacking faults in γ' were found at and above 850℃ due to the temperature dependence of the stacking fault energy. Raft structure of γ' was found after creep test at high temperature of 950℃ and 1000℃. At 850℃, the deformation mechanism was shown to be dependent on the stress condition, and so rafting was observed only under low stress condition.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.61-64
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• 2006

This paper presents experimental analysis of a friction-driven wheel responsible for generating wheel squeal. Squeal noise generating mechanism has been examined under the laboratory condition by the model rig. Creep characteristics and squeal noise were observed by varying relative velocity of the wheel with respect to the rail and friction coefficient. Computational radiating noise analysis was also performed based on the modal analysis and noise transfer function measurement of the object wheel.

• Transactions of Materials Processing
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• v.10 no.5
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• pp.383-388
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• 2001

In describing the plastic deformation behaviour of ultrafine-grained materials, a phase mixture model in which a polycrystalline material is regarded as a mixture of a crystalline phase and a grain boundary phase has been successful. The deformation mechanism for the grain boundary phase, which is necessary for applying the phase mixture model to polycrystalline materials, is modelled as a diffusional flow of matter along the grain boundary. A constitutive equation for the boundary diffusion creep of the boundary phase was proposed, in which the strain rate is proportional to (stress/grain siz $e^{2}$). The upper limit of the stress of the boundary phase was set to equal to the strength to the amorphous phase. The proposed model can explain the strain rate and grain size dependence of the strength of the grain boundary phase. Successful applications of the model compared with published experimental data are described.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.2
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• pp.31-40
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• 1993

Many reseachers have performed extensive studies on the creep and shrinkage of concrete. Mechanism of creep and shrinkage however is not quite well-known, especially for high strength concrete. Therefore, the purpose of this study is to explore the shrinkage and creep characteristics of high strength concrete. The main variables investigated include condition of drying, reinforcement and duraton of load. The effects of drying and reinforcements are clarified and compared with various exsiting models. The present study provides useful data for the design and analysis of high stength concrete structures.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.5
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• pp.73-78
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• 2006

In this paper, creep tests of Mg-Zn-Mn and Mg-Zn-Mn-Ca alloys, which were casted by mold with Mg-3%Zn-1%Mn and Mg-3%Zn-1%Mn-0.2%Ca, were done under the temperature range of 473-573K and the stress range of 23.42-78.00Mpa. The activation energies and the stress exponents were measured to investigate the creep plastic deformation of those alloys, and the rupture lifes of Mg-Zn-Mn alloy were also measured to investigate the fracture behavior. From the results, the activation energy of Mg-Zn-Mn and Mg-Zn-Mn-Ca alloys under the temperature range of 473-493K were measured as 149.87, 145.98KJ/mol, respectively, and the stress exponent were measured as 5.13, 6.06 respectively. Also the activation energies Mg-Zn-Mn and Mg-Zn-Mn-Ca alloys under the temperature range of 553-573K were obtained as 134.41, 129.22KJ/mol, respectively, and tress exponent were obtained as 3.48, 4.63, respectively. Finally stress dependence of rupture life and the activation energy of rupture life of Mg-Zn-Mn under the temperature range of 473-493K was measured as 8.05, 170.0(KJ/mol), respectively, which were a little higher than the results of steady state creep.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 1998.11a
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• pp.41-46
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• 1998

최근 항공기나 자동차 분야에서 엔진의 경량화 및 출력 향상 둥의 목적으로 고온 구조용 세라믹스가 큰 주목을 받고 있는 가운데, monolith 세라믹스의 인성 부족을 보완하기 위하여 세라믹 휘스커나 장섬유를 이용하는 새로운 세라믹 복합재료의 개발에도 많은 연구가 수행되고 있다. (중략)

• Journal of Power System Engineering
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• v.10 no.3
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• pp.45-50
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• 2006

In this paper, creep tests of Mg-Zn-Mn and Mg-Zn-Mn-Ca alloy casted by mold under the temperature range of 473.00-573.00K, and the stress range of 23.42-87.00Mpa were done with the equipment of automatic controlled temperature and computer for data acquisition. The activation energies were obtained by relationship between creep rate and temperature, and the stress exponents were obtained by relationship between creep rate and stress. From the experiment results, the activation energies of Mg-Zn-Mn and Mg-Zn-Mn-Ca alloy were 149.87kJ/mol, 147.97kJ/mol, respectively, and the stress exponents of those alloy were 5.13, 5.59, respectively, under the temperature of 473.00-493.00K and the stress range of 62.43-78.00Mpa. And the activation energies of those alloy were 134.41kJ/mol, 129.22kJ/mol, respectively, and the stress exponent of those alloy were 3.48, 3.77, respectively, under the temperature of 553-573Mpa and the stress range of 23.42-39.00Mpa. Also the lifes of Mg-Zn-Mn-Ca alloy were higher than those of Mg-Zn-Mn alloy, and the results of SEM showed fracture surfaces under low temperature had smaller dimples than those under high temperature.

• Corrosion Science and Technology
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• v.21 no.1
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• pp.62-67
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• 2022

The objective of this study was to perform failure analysis of an inlet pipe located in a governor valve of a steam turbine in a district heating system. During the operation, the temperature of the governor valve was increased to as high as ~500 ℃, which induced thermal expansion of the inlet pipe along both axial and radial directions. While the inlet pipe did not have contact with the valve seat, the side plane of the upside was constrained by the casing part, which led the inlet pipe to experience stress field in the form of fatigue and creep. The primary crack was initiated at about 30 mm below the top where the complex stress field was anticipated. These results suggest that the main failure mechanism is a combination of thermal fatigue and creep during the operation supported by the observation of apparent beach marks on the fracture surface and pores near the cracks, respectively.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.411-412
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• 2006

It is very difficult to analyze the dynamic characteristic because railway vehicle is a very complex system which are connected various mass element with railway vehicle system. To realize and analyze actual phenomenon has restriction that usual commercial software calculates creep force under creep theory about wheel-rail contact mechanism as basic analyzing, and approach about contact point are based on two dimensional non-linear contact theory and simplified Hertzian contact which considers just displacement change on the YZ plain. Therefore, to solve these problems there should be a new approach difference with existing one. In this research, a new algorithm for finding wheel-rail contact position, calculation method of contact force and applied force will be presented.