• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2009.10a
• /
• pp.285-288
• /
• 2009

The purpose of this study is to predict the forming limit diagram (FLD) of strain-rate sensitive materials on the basis of the Marciniak and Kuczynski (M-K) theory. The strain-rate effect is taken into consideration in such a way that the stress-strain curves for various strain-rates are inputted into the formulation as point data, not as curve-fitted models such as power function. Tensile tests and R-value tests were carried out at several levels of temperature and strain-rate from $25^{\circ}C$ to $300^{\circ}C$ and 0.16 to 0.00016/s, respectively to obtain the mechanical properties of AZ31B magnesium alloy sheet. The FLD of this material was experimentally obtained by limit dome height tests with the punch velocity of 0.1 and 1.0 mm/s at $250^{\circ}C$. The M-K theory-based FLD predicted using Yld2000-2d yield criterion was compared with the experimental results.

• Journal of The Korean Astronomical Society
• /
• v.13 no.1
• /
• pp.15-26
• /
• 1980

The BV-photographic photometry was made for 1714 stars (V<19.5) in NGC 6752. The C-M diagram of this cluster shows an unusually extended blue horizontal branch $(V=13.5{\sim}17.8)$ with a wide gap $(V=16{\sim}16.7)$ and the well defined giant branch with gaps at V=13.85 and 16.2. The turnoff point is defined at $V=17.25{\pm}0.15$ and (B-V) = $0.46{\pm}0.02$. If we take $V_{HB}=13.85$ for NGC 6752, then ${\Delta}V=2.80,\;(B-V)_{0,g}=0.76\;and\;{\Delta}V_{TO}=3.40$ and the chemical abundance is estimated to be [Fe/H]=-1.67 or $Z=4.3{\times}10^{-4}\;and\;Y=0.26$. Some other physical parameters of this cluster are derived and compared with those for the well observed clusters M 3, M 13, M 15 and M 92.

• Journal of Korea Soil Environment Society
• /
• v.5 no.3
• /
• pp.65-75
• /
• 2001

This study purpose to elucidate the characteristics of water quality by elevation and groundwater samples has been studied with the samples from 150 selected groundwater represented the watershed of groundwater wells in Cheju Island. The evaluation of the characteristics of water quality utilized the physical and chemical property and the statistical analysis. According to the piper diagram, groundwater in the under 50 m region is shown N $a^{+}$＋ $K^{+}$-C $l^{[-10]}$ type, and that groundwater in the 50~100 m region is shown N $a^{+}$＋ $K^{+}$-HC $O_3$$^{[-10]}$ ＋C $O_3$$^{2-}$ type. and partly N $a^{+}$＋ $K^{+}$-C $l^{[-10]}$ type. In the above 100 m region belongs to N $a^{+}$＋ $K^{+}$-HC $O_3$$^{[-10]}$ ＋C $O_3$$^{2-}$ type. The result of factor analysis, commonly two factors as TDS(Total Dissolved Solid) and the contaminants extracted in the under 50m region and above 100 m region. Three factors were obtained from the result of the factor analysis in the 50~100 m region. Factor 1, consisting of TRS content. Factor 2, consisting of the contaminant and the dissolution of minerals. and Factor 3, consisting of HC $O_3$$^{[-10]}$ content. content.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2009.05a
• /
• pp.172-175
• /
• 2009

The purpose of this study is to predict the forming limit diagram (FLD) of strain-rate sensitive materials on the basis of the Marciniak and Kuczynski (M-K) theory. The strain-rate effect is taken into consideration in such a way that the stress-strain curves for various strain-rates are inputted into the formulation as point data, not as curve-fitted models such as power function. To solve the nonlinear system of equations derived from the equilibrium and constraints in the groove region and the safe zone, the Newton-Raphson method is used. The theoretical FLDs using four different yield criteria, that are von Mises, Hill (1948), Hill (1979), Logan and Hosford, are compared with the experimental, numerical (FEA) and other theoretical results. A new trial is made where a modified M-K model having n-step grooves is introduced to describe a real localized neck.

• Journal of The Korean Astronomical Society
• /
• v.34 no.3
• /
• pp.143-147
• /
• 2001

UBVI CCD photometry of open cluster NGC 2324 is presented. C-M diagrams of this cluster show well-defined main sequence with a red giant clump centered at B - V =1.05, V =13.45. We derived the major cluster characteristics; E(B - V)=0.17$\pm$0.12 from color-color diagram and mean color of red giant clump stars, (m - M)o=13.1$\pm$0.1 from zero age main sequence fitting, and [Fe/H]$\~$-0.32 from comparison the theoretical model developed by Bertelli et al. (1994) to the observed C-M diagrams. We estimate the age of NGC 2324 to be log t$\~$8.8 by applying isochrone fitting and morphological age index method.

• Journal of the Korean Society for Heat Treatment
• /
• v.24 no.5
• /
• pp.262-270
• /
• 2011

Carbide precipitation and dissolution behavior at various temperatures during heat treatment has been studied in STD11 cold working die steel through confocal scanning laser microscopy; dilatometry; and X-ray diffraction analysis. The equilibrium phase diagram and phase fractions with temperature were calculated using a FactSage program. Confocal laser microscopic observation revealed that ${\alpha}$ to ${\gamma}$ transformation temperature is near $800^{\circ}C$; M7C3 carbides melt at $1245^{\circ}C$; and the melting temperature of STD11 is near $1370^{\circ}C$. XRD results indicated that the M23C6 carbides dissolve in the matrix if austenitized at over $1030^{\circ}C$; while the M7C3 carbides remain up to $1200^{\circ}C$ although their amount decreases. The calculated equilibrium phase diagram showed good agreement with experimental results on carbide dissolution and phase transformation temperatures.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.44 no.12
• /
• pp.43-53
• /
• 2007

We have analyzed low current operation characteristics of a VCSEL transmitter operating at fixed Current over wide temperature range. Used 850 nm oxide VCSEL has low temperature dependence of the threshold current and $d^2I_{th}/dT^2$ is approximately $1.346\times10^{-4}mA/^{\circ}C^2$. We fixed on-current so that output power from the chip is 1 mW at $20^{\circ}C$ and investigated the turn-on, turn-off characteristics and eye-diagram of the 850 nm oxide VCSEL transmitter with varying ambient temperature and off-current. We measured rise time, fall time, extinction ratio and timing jitter by changing tile ambient temperature and off-current. With the fixed off-current of around $0.1\sim0.2mA$ lower than the lowest threshold current the transmitter successfully operated at 1.25 Gbps over a wide temperature range from $-20^{\circ}C$ to $80^{\circ}C$.

• Journal of The Korean Astronomical Society
• /
• v.31 no.1
• /
• pp.39-50
• /
• 1998

We present UBV CCD photometry of Be 2, previously unstudied open cluster. Our photometry covers a field of $3'.2\times3'.8$ of the sky centered on the cluster, which is slightly smaller than the cluster diameter estimated to be about 260'. We have determined the reddening, distance, age and metallicity of the cluster by fitting the Pad ova isochrones to the observed stellar distributions in color-magnitude diagram as well as main sequence fitting: $E(B-V)=0.8\pm0.05,\;(m-M)_o=13.6\pm0.1,\;log(t) =8.9\pm0.1$, and Z=0.008. The present photometry shows that Be 2 is a distant open cluster of intermediate age. that it is a distant intermediate-age open duster.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2009.05a
• /
• pp.152-157
• /
• 2009

Titanium alloy sheets have excellent specific strength and corrosion resistance as well as good performance at high temperature. Recently, titanium alloys are widely employed not only aerospace parts but also bio prothesis and motorcycle. But the database is insufficient of the titanium alloy for press forming process. In this study, the effect of temperature on the forming limit diagram was investigated for Ti-6Al-4V titanium alloy sheet through the Hocker's punch stretching test at elevated temperature. Experimental results obtained in this study can provide a database for development of press forming process at elevated temperature of Ti-6Al-4V titanium alloy sheet. From the experimental studies it can be concluded that the formability of Ti-6Al-4V titanium alloy sheet is governed by the ductile failure for the testing temperature below and vice versa neck-induced failure above the recrystalization temperature $0.5T_m$. The formability of Ti-6Al-4V titanium alloy sheet at $750^{\circ}C$ increases about 7 times compared with that at room temperature.

• Journal of The Korean Astronomical Society
• /
• v.28 no.2
• /
• pp.153-167
• /
• 1995

More than 22,300 stars in NGC 6752 were measured over the region of 5' < r < 23' in B and V AAT plates. The most of these are main sequence(MS) stars and about 130 blue horizontal branch(BHB) stars were detected. The C-M diagram of all measured stars shows gaps appearing at $V{\approx}15.^{m}2$ and $16.^{m}2$ along the red giant branch(RGB) and their appearance shown by Lee & Cannon(1980) is found to be independent of measured region. The bimodal distribution of BHB stars is confirmed again and a wide gap shown by Lee & Cannon(1980) at $V{\approx}16^m$ is clearly seen for stars in the outer part (8' < r < 13') in the cluster. It is noted, however, that this gap is occupied by about a dozen of BHB staIs located in the inner region (5' < r < 8'). The number ratio of bright BHB star (V < $15^m$) to faint BHB stars (V > $15^m$) decreases with increasing radial distance from the cluster center. Three faintest BHB stars were found, and two stars ($V{\approx}18.^{m}5$) of there are located in the inner region of $r{\approx}6'$ and the other faintest one ($V{\approx}19.^{m}3$) located in the outer part of $r{\approx}13'$. Also a bluest star of (B - V) $\approx$ -0.5 at $V{\approx}17.^{m}2$ is found but it is located at the outer part of $r{\approx}13'$ in NE region. Therefore, the membership of the faintest BHB star and bluest star is suspected. The luminosity function(LF) and mass function(MF) for NGC 6752 were derived for MS stars. The LF for stars of $M_v\;<\;6^m$ in the outer part of r > 8' shows a consistency with that derived by Penny & Dickens(1986).