• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.777-781
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• 1997

In this study, the effect of strain-rate and inital solid fraction on the deformation behaviour of semi-solid material is investigated, when semi-solid forging is performed by the process of closed-die compression using A356 alloy of which the above results can be practically applied for industrical purpose. In order to simulate densification in the deformation of semi-solid material, the semi-solid material is assumed to be composed of solid region following rigid visco-plastic material, the liquid region following Darcy's law for the liquid flow saturated in the interstitial space. Simulation results of closed-die compression and simple upsetting under different strain-rate and initial solid fraction are compared.

• Journal of Advanced Marine Engineering and Technology
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• v.19 no.4
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• pp.42-50
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• 1995

To study the effect of welding methods on the Stress Corrosion Cracking (SCC) behavior of welded AISI type 316L and 304 austenitic stainless steel, the Slow Strain Rate Technique(SSRT) has been adopted in the boiling 45 wt% $MgCl_2$ solution. The results are as follows. 1) Welded sections are more susceptible than base metal in SCC, and the rank of SCC, and the rasistance in welding method is TIG, MIG, $CO_2$ and ARC. 2) The Ultimate tensile strength(UTS) and the strain of both base metal and welded joint are reduced as decreasing extension rate. 3) The SCC resistance of 316L base metal and welded sections are superior than that of 304. 4) The tendency of pitting and the SCC suseptibility are agreed well, and the SCC site is welded deposit section in 316L whereas HAZ in 304.

• Journal of the Korean Society for Heat Treatment
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• v.31 no.6
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• pp.307-314
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• 2018

Simple tensile tests and microstructural investigations have been performed on extrudates of high strength aluminum alloys such as 7075, 7021 and 7xxx(Sc) to understand correlation between extruding conditions and extruded properties. Tensile specimens which were taken from different locations at the same cross section of an extrudate were tested at room temperature and with a strain rate of $8.9{\times}10^{-5}/s$. The microstructures according to the locations at the cross section have been observed using optical microscopy and electron back-scattered diffraction (EBSD) mapping to characterize the effect on stress-strain curve. The results could be classified in three types independent of alloying contents and extusion methods. The fine differences in the stress-strain curves were resulted from inhomogenity in the microstructures according to locations of an extrudate which were performed through instantaneous extruding conditions such as temperature, strain rate and strain.

• Transactions of Materials Processing
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• v.32 no.4
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• pp.215-220
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• 2023

In this study, the correction process of stress-strain curves obtained from hot compression test is introduced since the barreling induced by friction and adiabatic heat generation induced by plastic work occur under high strain rate. A shear friction factor was quantitatively estimated by measuring the dimension of barreling and temperature rise due to adiabatic heat generation was directly measured during compression test. Thereafter, the stress-strain curves were re-evaluated by introducing several equations to correct the effects of the friction and temperature rise. It was found that adiabatic factor at strain rate of 10/s is in the range of about 0.5 to 0.75 for Nimonic 80A and decreases as the assigned temperature increases.

• Transactions of Materials Processing
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• v.11 no.3
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• pp.255-261
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• 2002

The grain size of 7010 Al alloy was refined to submicrometer level by using equal channel angular pressing (ECAP) and additional warm rolling. The mechanisms of grain refinement in ECAP process were fragmentation of coarse grain to ultra fine subgrains after a few passes and continuous recrystallization of the subgrains with the increase o( passes. Because of ultrafine grain size, essentially low temperature and high strain rate superplasticity was observed after ECAP process and warm rolling to form a sheet metal. The maximum elongation of 700% was obtained for an ECA pressed specimen after IS passes without warm rolling at $450^{\circ}C$ with strain rate of 5x$10^{-3}$/sec.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.485-490
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• 2000

The effect of curvature, rotation, variable cross-section can make very complex flow pattern in turbo-machinery such as Pumps, compressors, turbines, In this study of turbulent flow characteristics rotating $90^{\circ}$ curved duct under a Plane rate of strain condition is computationally analyzed. The objective of this study is to understand the complex turbulent flow phenomena in turbo-machinery passage by analyzing the modeled rotating $90^{\circ}$ curved duct flow. RSM(Reynolds Stress Model) was employed for the turbulence modeling of Reynolds stress in momentum equations proposed by Shin(1995). The three dimensional computational code which adopts RSM for trubulence modeling was newly developed for the generalized curvilinear coordinate.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.374-377
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• 2008

High temperature deformation behavior and texture evolution during ECAP(equal channel angular pressing) of Zn-0.3Al alloy were investigated in this study. ECAP was conducted at temperatures from $40^{\circ}C$ to $160^{\circ}C$ on the plate type specimen of 5mm thickness and 20mm width. The specimens obtained by ECAP showed typical texture with basal poles tilted away from the ND toward ED. A series of compression tests was carried out at temperatures from RT to $200^{\circ}C$ under the strain rate from 0.03 to 10/s. With the strain rate increased, serration behavior was observed to be prominent.

• Transactions of Materials Processing
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• v.4 no.2
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• pp.159-168
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• 1995

The torsion tests in the range of $550~800^{\circ}C$, $5.0{\times}10^{-3}~5.0{\times}10^0/sec$ were performed to study the effects of strain rate$(\.{\varepsilon})$ and temperature(T) on the hot strength of Cu-Zn alloy. High temperature flow stresses of this alloy increased with increasing $\.{\varepsilon}$ and/or decreasing T, and than the more grain refinement could be obtained. The flow curves exhibited a peak followed by a steady steady state regime as a result of dynamic recrystallization. The hot strength dependence of $\.{\varepsilon}$ and T was described by a hyperbolic sine law, $\.{\varepsilon}=A(sinh0.017{\sigma})^4.81$exp(-216KJ/mol). Hot strength could be reduced at the arbitary condition, $\.{\varepsilon}$ and T, by constitutive parameter Z(Zenner-Hollomon parameter), $Z=A(sinh{\alpha}{\sigma})^n=\.{\varepsilon}$exp(Q/RT).

• Journal of the Korean Society of Combustion
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• v.12 no.2
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• pp.34-41
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• 2007

The dynamic behaviors of counterflow non-premixed flame have been investigated experimentally to study effects of heat losses and Lewis number on edge flame oscillation, which result from the advancing and retreating edge flame motion of outer flame edge at low strain rate flame. For low strain rate flame, lateral conduction heat loss in addition to radiation heat loss could be more remarkable than the others. Oscillatory instabilities appear at fuel Lewis number greater than unity. But excessive lateral conduction heat loss causes edge flame instability even at fuel Lewis number less than unity. The excessive heat loss caused by the smaller burner diameter in which the flame length is an indicator of lateral conduction heat loss extends the region of flame oscillation and accelerates oscillatory instability in comparison to the previous study with the burner diameter of 26mm. Extinction behaviors quite different from the previous study are also addressed.

• Journal of the Korean Society of Combustion
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• v.17 no.4
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• pp.38-43
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• 2012

Experimental study was conducted to elucidate flame extinction phenomena in counterflow flame. Using a curtain helium flow significantly reduced buoyancy such that the flame can be positioned at the center between the upper and lower nozzles even at the velocity ratio of 1.0. The curves of critical diluent mole fraction versus global strain rate have C-shapes. The flame oscillation was observed prior to low strain rate flame extinction at both flame conditions with and without minimizing buoyancy force. The results show that, at low strain rate flame, the self-excitation frequency with the order of 1.0 Hz in the case of utilizing pure helium gradually decreases in increase of $N_2$ mole fraction in the curtain flow, meaning that buoyancy suppresses the self-excitation of the outer edge flame.