• Title, Summary, Keyword: 멱수법칙 크리프

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Constitutive Models for Final Stage Densification of Powder Compacts with Power-Law Creep Deformation (Power-law 크리프 변형을 따르는 분말 성형체의 말기 치밀화 모델)

  • Yang, Hoon-Chul;Kim, Ki-Tae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.7
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    • pp.930-939
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    • 2004
  • Constitutive models for final stage densification of metal powder compacts with power-law creep deformation were investigated. The constitutive models were implemented into a finite element program (ABAQUS) by using user subroutine CREEP and, from FEM results, useful densification curves were obtained when hydrostatic and uniaxial stress were applied to the powder compacts at various pressures and temperatures. Because the densification behavior varied as the constitutive models, the equivalent stress surface on each constitutive equation was investigated to analyze the difference of densification behavior.

Near-net-shape forming of ceramic powder under hot pressing and hot isostatic pressing (가압소결과 열간 등가압소결에 의한 세라믹 분말의 정형 성형)

  • Kwon, Yeong-Sam;Kim, Ki-Tae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.1
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    • pp.73-82
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    • 1997
  • High temperature densification behaviors of alumina powder compacts were investigated under hot pressing and hot isostatic pressing. An alumina part of valve-head shape was fabricated under hot pressing and its forming process was simulated by finite element calculation. an alumina powder compact encapsulated by a stainless steel container was also densified under hot isostatic pressing. Inhomogeneous deformations during hot isostatic pressing due to the canning effect were observed experimentally and predicted by finite element analysis.

Densification behavior and grain growth of zirconia powder compacts at high temperature (지르코니아 분말 성형체의 고온 치밀화 거동과 결정립 성장)

  • Kim, H.G;Kim, K.T
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.8
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    • pp.1175-1187
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    • 1997
  • Densification behavior and grain growth of zirconia powder compacts are investigated under high temperature. Experimental data are obtained for zirconia powder under pressureless sintering, sinter forging and hot isostatic pressing. The constitutive equations by Kwon et al. are used for diffusional creep and grain growth. The constitutive equations by McMeeking and co-workers are also included to study the effect of power-law creep. These constitutive equations are implemented into a finite element program (ABAQUS) to investigate the friction effect during sinter forging and the canning effect during hot isostatic pressing. The agreements between experimental data and finite element results are very good in pressureless sintering and hot isostatic pressing, but not as good in sinter forging.

A Study on Evaluation of High Temperature Creep Properties of 9Cr1MoVNb Steel by Small Punch-Creep test (소형펀치-크리프 시험에 의한 9Cr1MoVNb강의 고온 크리프 특성 평가 연구)

  • Yu, Hyo-Sun;Na, Sung-Hoon;Baek, Seung-Se;Kwon, Il-Hyun;Ahn, Byung-Guk;Na, Eui-Gyun
    • Proceedings of the KSME Conference
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    • pp.99-104
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    • 2000
  • This paper describes the high temperature creep characteristics for virgin material of 9Cr1MoVNb steel using small punch creep(SP-Creep) test technique which is developing recently. In addition, the several results of SP-Creep test are compared with that of 2.25Cr- 1Mo steel which is widely used as boiler materials and that of conventional uniaxial creep test. The obtained SP-Creep curves show the creep behaviors of three regimes like that obtained from conventional uniaxial creep test, and SP-Creep properties are definitely depended on applied load and test temperature. The correlation of SP-Creep rate and creep rupture life with applied load has been determined like the correlation between creep rate/rupture life and stress in uniaxial creep test, and also is satisfied with Power law. The creep rupture times of newly 9Cr1MoVNb steel are higher than those of 2.25Cr1Mo steel at the same creep temperature and applied loading condition, and the decrease extent of creep rupture life with loads is very lower compared with 2.25Cr1Mo steel.

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Development of Creep Properties Evaluation Technique for Steel Weldment of Power Plant (발전설비 강 용접부의 크리프 특성 평가 기술 개발)

  • Lee, Dong-Hwan;Jeoung, Young-Hun;Baek, Seung-Se;Ha, Jeong-Soo;Song, Gee-Hook;Lee, Song-In;Yu, Hyo-Sun
    • Proceedings of the KSME Conference
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    • pp.180-185
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    • 2001
  • In the life assessment for plant structural component, the research on deterioration of toughness and material properties occurred in weldments has been considered as very important problems. In general, the microstructures composed in weldments are hugely classified with weld metal(W.M), fusion line(F.L), heat affected zone(HAZ), and base metal(B.M). It has been reported that the creep characteristics on weldments having variable microstructures could be unpredictably changed. Furthermore, it is also known that HAZ adjacent to F.L exhibits the decreased creep strength compared to those in base or weld metals, and promotes the occurrence of Type III and Type IV cracking due to the growth of grains and the coarsening carbides precipitated in ferritic matrix by welding and PWHT processes. However, the lots of works reported up to date on creep damage in power plant components have been mostly conducted on B.M and the creep properties on a localized microstructures in weldments have not as yet been throughly investigated. In this paper, for various microstructures such as coarse grain HAZ(CGHAZ), W.M and B.M in X20CrMoV121 steel weldment, the small punch-creep(SP-Creep) test using miniaturized specimen(t=0.5mm, 0.25mm) is performed to investigate a possibility for creep characteristics evaluation.

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Densification Behavior of Mixed Metal Powders under High Temperature (혼합 금속 분말의 고온 치밀화 거동)

  • Jo, Jin-Ho;Kim, Gi-Tae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.3
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    • pp.735-742
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    • 2000
  • Densification behaviors of mixed metal powder under high temperature were investigated. Experimental data of mixed copper and tool steel powder with various volume fractions of Cu powder were obtained under hot isostatic pressing and hot pressing. By mixing the creep potentials of McMeeking and co-workers and of Abouaf and co-workers originally for pure powder, the mixed creep potentials with various volume fractions of Cu powder were employed in the constitutive models. The constitutive equations were implemented into a finite element program (ABAQUS) to compare with experimental data for densification of mixed powder under hot isostatic pressing and hot pressing. Finite element calculations by using the creep potentials of Abouaf and co-workers agreed reasonably well with experimental data, however, those by McMeeking and co-workers underestimate experimental data as observed in the case of pure metal powders.

Creep Densification of Metal Powder Compacts (금속분말 성형체의 크리프 치밀화 거동)

  • Song, Min-Cheol;Kim, Hong-Gi;Kim, Gi-Tae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.3
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    • pp.816-824
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    • 1996
  • The densification behaviors of copper powder under high temperature processing were investigated. Experimental data were obtained for copper powder under hot isostatic pressing, hot pressing and uniaxial compression. Finite element calculations from the constitutive models by McMeeking and co-workers were compared with the experimental data, The agreements between experimental data and theoretical calculations are reasonably good when hydrostatic stress is dominant, but not as good then deviatoric stress increases.

High Temperature Densification Forming Process of Tool Steel Powder Compact (공구강 분말 성형체의 고온 치밀화 성형공정)

  • Choi, Hak-Hyeon;Jeon, Yun-Cheol;Kim, Gi-Tae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.7
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    • pp.2182-2195
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    • 1996
  • Densification characteristics and behavior of tool steel powder compact during high temperature forming processes were investigated under pressure less sintering, sinter forging and hot isostastic pressing. In pressureless sintering, full density was obtained at a closely controlled temperature near the solidus of the material. Finite element calculations from constitutive model for densification by power law creep and diffusional flow were compared with experimental data. Agreements between theoretical calculations and experimental data were good in hot isostatic pressing but not as good in sinter forging.

Creep Damage and Hardness Properties for 9Cr Steel by SP-Creep Test Technique (SP-Creep 시험기법에 의한 9Cr강의 크리프 손상과 경도 특성)

  • Baek, Seung-Se;Lyu, Dae-Young;Kim, Jeong-Ki;Kwon, Il-Hyun;Chung, Se-Hee;Yu, Hyo-Sun
    • Proceedings of the KSME Conference
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    • pp.105-110
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    • 2001
  • It has recently been raised main issue how solve the problem of insufficient energy. One of the solution is to increase the thermal efficiency of power generation system. For the purpose of high efficiency, it is necessary to increase the steam temperature and pressure. So, the use of modified $9{\sim}12%Cr$ steel having superior creep rupture strength and oxidation resistance is required to endure such severe environment. The evaluation of creep properties of those heat resistance material is very important to secure the reliability of high temperature and pressure structural components. Since creep properties are determined by microstructural change such as carbide precipitation and coarsening, It is certain that there are some relationship between creep properties and hardness affected by microstructure. In this study, SP-Creep ruptured test for newly developed 9Cr steel being used as boiler valve material was performed, and creep properties of the material were evaluated. Also, hardness test were performed and hardness results were related to the creep properties such as LMP and creep strength to verify the availability of SP-Creep test as creep test method.

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