• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.10a
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• pp.25-28
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• 2000

The flow stress of 304 stainless steel during high during hot forming process were determined by conducting hot compression tests at the range of 1273 K-1423 K and 0.05 /s-2.0 /s as these are typical temperature and strain rate in hot forging operation. Based on the observed phenomena, a constitutive model of flow stress was assumed as a function of strain, strain rate, temperature. Dynamic recrystallization was found to be the major softening mechanism with this conditions as previous studies. A finite element analysis was performed to predict the recrystallized volume fraction and the mean grain size in hot compression of 304 stainless steel.

• Transactions of Materials Processing
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• v.10 no.7
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• pp.573-578
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• 2001

The flow stress of 304 stainless steel during hot forming process were determined by conducting hot compression tests at the range of 1273 K∼1423 K and 0.05 /s∼2.0 /s as these are typical temperature and strain rate in hot forging operation. In this material, Dynamic recrystallization was found to be the major softening mechanism with this conditions as Previous studies. Based on the observed phenomena, a constitutive model of flow stress was assumed as a function of strain, strain rate, temperature. In the constitutive model, the effects of strain hardening and dynamic recrystallization were taken into consideration. A finite element method connected to constitutive model was performed to predict the dynamic recrystallization behaviors and also stress-strain curves in hot compression of 304 stainless steel.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.05a
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• pp.68-71
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• 1996

In the study, the thermal and optical properties of SiO$_2$-PbO-K$_2$O-Al$_2$O$_3$ g1asses were investigated. According to Ga$_2$O$_3$ addictions, the properties of bulk glass, transition temperature and softening temperature were increased, whereas thermal expansion coefficient was decreased; In the optical properties, refractive index was increased, and IR cut-off wavelength was enlarged from 4.64$\mu\textrm{m}$ to 5.22$\mu\textrm{m}$. But, the optical loss of fiber was decreased.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.37 no.6
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• pp.406-413
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• 1988

This paper is to investigate relationships between tree inception voltage, tree extension or treeing breakdown voltage and physical characteristics changing as parameter of the post-cured conditions of thermo-setting epoxy resin. According to the results in this paper, the optimal tree inception voltage and treeing breakdown voltage of the samples are obtained for the sample post cured for 15 hours at 100 'C. It can be noticed that these results are closely related with the state of interior molecule coupling and three-dimen sional cross-linked of thermo-setting epoxy resin. And tree inception, tree extension and treeing breakdown of the samples are affected significantly on the post-cured conditions and the cooling method after post-cured of thermo-setting epoxy resin. Moreover, the tree extension by ambient temperature are closely related with softening temperature of thermo-setting epoxy resin.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1155-1156
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• 2006

Hopkinson bar dynamic test under strain rates ranging from 2000 $s^{-1}$ to 8000 $s^{-1}$ at room temperature revealed that the flow stress of tungsten heavy alloys depended strongly on the strain, strain rate, and the content of molybdenum. The variation of flow stress was caused by the competition between work hardening and heat softening in the materials at different strain rates. The high temperature strength of the matrix phase was increased by the addition of molybdenum, which enhanced the strength of the tungsten heavy alloys in high strain rate test.

• Journal of the Korean Ceramic Society
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• v.25 no.6
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• pp.623-630
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• 1988

As a function of the composition and content of frit, the electrical property of Ag and Ag/Pd thick film conductors were investigated with microstructure. With increasing sintering temperature in Ag-frit thick film conductors, electrical sheet resistivity decreased, but again increased above 80$0^{\circ}C$. And when frit contents is 5wt%, compact and homogenious microstructure can be obtained, then electrical sheet resistivity has minimum value. In Ag/Pd-frit film conductor, the electrical sheet resistivity decreased with increasing sintering temperature. The system which having frit with low softing point has lower sheet resistivity then to add high softening point frit.

• 전기의세계
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• v.25 no.2
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• pp.100-106
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• 1976

A comparative study on thermal, static mechanical and dielectric characteristics were made over a temperature range of ca.20.deg.C to 320.deg.C and a frequency range of KHZ to MHZ band on low density polyethylene specimens crosslinked, respectively, by radiation and chemical method. The thermal property of both specimens shows that softening point appears to unchange by crosslinking, however, melting and liquidizing temperatures attain rapid increase at the imitiation of crosslinking. Mechanical properties show little difference to both specimens crosslinked by different method, further the behaviors were discussed in connection with the relaxation of molecular segments in amorphous phase. Dose dependent dielectric characteristics observed at ambient temperature under several fixed frequencies exhibit extremities at ca. 20 Mrad and the behaviors also were interpreted qualitatively by taking into consideration of dipole concentration change in amorphous phase together with the role of specimen geometry to the depth of oxidative layer. Observing frequency dependent dielectric characteristics, it was also proved that ionic conduction loss is appreciably greater in the specimen prepared by chemical method than that by radiation.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.12
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• pp.1105-1111
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• 2007

Because forest fire can give a serious damage to overhead conductors, the thorough understanding about aging behavior of burned conductor is very important in maintaining the transmission line safely. Therefore, a systematic investigation was carried out by heating method. As the heating temperature increases, drastic change of tensile strength of Al wire due to the softening of Al wire occurred. When Al wire is exposed to the flame(about $800\;^{\circ}C$) during only 13 seconds, the remained tensile strength of Al wire showed under 90 %. The detailed results will be given in the text.

• Journal of the Korean Ceramic Society
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• v.45 no.1
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• pp.54-59
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• 2008

Hydrated sodium silicate with 25 wt% water contents was synthesized by hydrothermal reaction using anhydrous sodium silicate. The hydrated sodium silicate was expanded at $370^{\circ}C$ for 30 min. and then pulverized, classified (- 200 mesh) and press-formed. The samples were heat treated at $400{\sim}900^{\circ}C$ for 30 min. in order to study the expansion characteristics depending on heat treatment temperature. A porous body with closed pore was formed above $600^{\circ}C$. The volume expansion ratio and the pore size were increased and the specific gravity was decreased with increasing heat treatment temperature. However, the volume expansion ratio was decreased and the specific gravity was increased above $850^{\circ}C$ due to the softening of the sodium silicate.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.516-517
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• 2007

Because forest fire can give a serious damage to overhead conductors, the thorough understanding about sag behavior of burned conductor is very important in maintaining the transmission line safely. Therefore, a systematic investigation was carried out by heating method. As the heating temperature increases, drastic change of tensile strength of Al wire due to the softening of Al wire occurred. When Al wire is exposed to the flame(about $800^{\circ}C$) during only 13 seconds, the remained tensile strength of Al wire showed under 90%. and then sag of overhead conductor become deteriorated. The detailed results will be given in the text.