• Proceedings of the Korean Radioactive Waste Society Conference
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• 2015.10a
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• pp.145-146
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• 2015

• Korean Journal of Materials Research
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• v.2 no.5
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• pp.343-352
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• 1992

The high temperature deformation behavior of microalloyed hot forging steels has been examined as a function of the temperature, the strain rate, and the alloying element by using high temperature compression test. The high temperature deformation mechanism, which was obtained by analyzing the flow stress-strain curve and microstructure, could be considered to dynamic recrystallization. The peak stress of Nb-V-Mo steel was more increased and the dynamic recrystallization of Nb-V-Mo steel was faster than those of Nb-V steel. The peak stress of 1.2Mn-0.09Nb steel was more increased and the dynamic recrystallization of 1.2Mn-0.09Nb was delayed a little bit than those of 1.0Mn-0.05Nb. The peak stress of C-Nb-V steel was more increased and the dynamic recrystallization of C-Nb-V steel was delayed than those of C-steel. The constitutive equation of high temperature deformation had a power law type. The grain size of dynamic recrystallization was refined as the Zener-Hollomon parameter was increased. The relation of the dynamic recrystallization grain size and Zener-Hollomon parameter could be quantified to power law.

• 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.

• 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.

• 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.

• 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.

• 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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.3 s.174
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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.

• Journal of the Korean Geotechnical Society
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• v.27 no.10
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• pp.81-92
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• 2011

The rheological properties of Wyoming bentonites are strongly influenced by the size of particles, cation exchangeable capacity, arrangement and morphology of clay mineral. This paper presents the results of rheological investigations on the Wyoming bentonites aqueous dispersions: two types of particle flocculation were considered. For the Wyoming bentonite, 0g/L and 30g/L NaCl equivalent salinity were added in fresh and salt water to examine the rheological behavior. This paper examined the general rheological characteristics, compatibility of rheological models and correlation between soil structure and change in rheological properties of Wyoming bentonite caused by increasing salinity. From flow curves of bentonites hydrated with fresh water and salt water, the observed general flow behavior is very close to shear thinning with yield stress (or ideal Bingham fluid with yield stress and plastic viscosity). However, the change of shear stress at the same shear rate is clear, particularly for lower shear rate. Well-known rheological models are used to fit the data. There is a good agreement between rheological model and data: Carreau, Herschel-Bulkley and power-law for S=0g/L and bilinear, Herschel-Bulkley and power-law for S=30g/L. It may be due to the fact that the internal structural bonding (strong modification of particle-particle interactions from edge-to-edge and/or edge-to-face to face-to-face) in soil matrix is affected from the evolution of rheological properties with different salinities.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.11
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• pp.951-956
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• 2008

The high temperature creep properties of the generating plant's high temperature tube, pipe and header and such are very significant in accordance with long-time exposure to the high temperature and pressure environment. Not only this, but as the welding procedure is compulsory for the cohesion of components, the creep properties regarding the local microstructures of steel weldment are very important. In order to understand the creep properties regarding the local microstructures of steel weldment, the SP-Creep test which is easy to get sample from the field component was conducted. The local microstructure of steel weldment, that is, W.M. and B.M.'s microstructures were observed using the SEM. The rupture time of W.M. was longer as 110 % averagely in a same condition, which is the consequence of the difference of the microstructure. Each lethargy coefficient of B.M. and W.M. is evaluated by the relation among the temperature, load and the rupture time from SP-Creep Test. The life estimation equation can be induced by the transformation of Power-law. B.M. and W.M. for each $550\;^{\circ}C$ and $575\;^{\circ}C$, the very similar to normal temperature of the domestic thermal power generation in working, are estimated.