• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.2
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• pp.167-175
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• 1988

The principle objective of this study is to evaluate the fatigue behavior of structural steel components of highway bridges subjected to service stresses. The main aspects of this investigation are; 1) a measurement and statistical analysis of service stress cycles observed in highway bridge. 2) fatigue tests under equivalent constant-amplitude(CA) loading and simulated variable-amplitude(VA) loading 3) a evaluation of the fatigue behavior under VA-loading by eqivalent root mean cube (RMC) stress range. Theoretically, the RMC model is adequate in evaluation of fatigue behavior under VA-loading, because the regression coefficient (m) of crack growth rate is 3 approximately. The result of fatigue test shows that the RMC model is fitter than the current RMS model in fatigue evaluation under VA-loading. The interaction effects and sequence effects under VA-loading affect little fatigue life of structural components. As the transition rate of stress ranges is higher, the crack growth rate is higher.

• Journal of Welding and Joining
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• v.14 no.3
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• pp.48-57
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• 1996

A study was made to examine the characteristics of base metal and stress relief cracking(SRC) of heat affected zone(HAZ) for HY-100 and Cu-bearing HSLA-100 steels. The Gleeble thermal/mechanical simulator was used to simulate the SRC/HAZ. The details of mechanical properties of base plate and SRC tested specimens were studied by impact test, optical microscopy and scanning electron microscopy. The specimens were aged at $650^{\circ}C$ for HSLA-100 steel and at $660^{\circ}C$ for HY-100 steel and thermal cycled from $1350^{\circ}C$ to $25^{\circ}C$ with a cooling time of $\Delta$t_${800^{circ}C/500^{circ}C}$=21sec. corresponds to the heat input of 30kJ/cm. The thermal cycled specimens were stressed to a predetermined level of 248~600MPa and then reheated to the stress relief temperatures of $570~620^{\circ}C$. The time to failure$(t_f)$ at a given stress level was used as a measure of SRC susceptibility. The strength, elongation and impact toughness of base plate were greater in HSLA-100 steel than in HY-100 steel. The time to failure was decreased with increasing temperature and/or stress. HSLA-100 steel was more susceptible to stress relief cracking than HY-100 steel under same conditions. It is thought to be resulted from the precipitation of $\varepsilon$-Cu phase by dynamic self diffusion of solute atoms. By the precipitation of $\varepsilon$-Cu phase, the differential strengthening of grain interior relative to grain boundary may be greater in the Cu-bearing HSLA-100 steel than in HY-100 steel. Therefore, greater strain concentration at grain boundary of HSLA-100 steel results in the increased SRC susceptibility. The activation energies for SRC of HSLA-100 steel are 103.9kcal/mal for 387MPa and 87.6kcal/mol for 437MPa and that of HY-100 steel is 129.2kcal/mol for 437MPa.

• Proceedings of the KWS Conference
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• 1996.05a
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• pp.186-189
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• 1996

A study was made to examine the characteristics of base metal and stress relief cracking(SRC) of heat affected zone(HAZ) for HY-100 and Cu-bearing HSLA-100 steels. The Gleeble thermal/mechanical simulator was used to simulate the SRC/HAZ. The details of mechanical properties of base plate and SRC tested specimens were studied. The specimens were aged at $650^{\circ}C$ for HSLA-100 steel and at 66$0^{\circ}C$ for HY-100 steel and thermal cycled from 135$0^{\circ}C$ In $25^{\circ}C$ with a cooling time of $\Delta$ $t_{800^{\circ}50}$ $0^{\circ}C$/=21sec. corresponds to the heat input of 30kJ/cm. The thermal cycled specimens were stressed to a predetermined level of 248~600MPa and then reheated to the stress relief temperatures of 570~62$0^{\circ}C$. The time to failure( $t_{f}$) at a given stress level was used as a measure of SRC susceptibility. The strength, elongation and impact toughness of base plate were greater in HSLA-100 steel than in HY-100 steel. The time to failure was decreased with increasing temperature and/or stress. HSLA-100 steel was more susceptible to stress relief cracking than HY-100 steel under same conditions. It is thought to be resulted from the precipitation of $\varepsilon$-Cu phase by dynamic self diffusion of solute atoms. Therefore, greater strain concentration at grain boundary of HSLA-100 steel results in the increased SRC susceptibility.y.

• Fashion & Textile Research Journal
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• v.22 no.1
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• pp.66-75
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• 2020

This study helps develop cool-touch functional dance sportswear. We suggest a draft design for dance sportswear that chooses appropriate cool-touch functional materials based on an investigation of the changes of body surface temperature before and after exercise, the physical properties of cool-touch materials on the market, and the preference for cooling tools. The results are as follows. First, cool-touch functional sportswear products on the market utilize materials such as PCM, Delta fabric, high gauge fabric, and ice chips as well as incorporate functions such as UV block and eyelets for enhanced breathability. Polyester and polyurethane fibers are mainly used for cool-touch functional sportswear. Second, the neck area showed the highest surface temperatures (32.7℃ and 32.1℃) before and after exercise. Body surface temperatures measured after exercise were also lower than temperatures measured before exercise when wearing dance sportswear. Third, as for the physical properties of cool-touch materials, material 1 showed amaximum drying speed (130 min), material 3 the best moisture absorption speed (122 × 132 min), and material 4 the best thermal conductivity (0.013 7 w/m·K). Fourth, a draft design for a cool-touch functional dance sportswear was suggested, including a neckband made of removable soft PVC material on the neck area and applying material 4 in F1, B4, S2 and lower arm areas and material 1 in the armpit area. Deodorant tape was also attached to the armpit area for added comfort and antibacterial deodorant effect.

• Korean Journal of Materials Research
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• v.1 no.1
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• pp.54-61
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• 1991

YBCO films deposited on MgO(100) and Si(100) by rf-magnetron sputtering using stoichiometric single target were annealed under oxygen atmosphere at $880^{\circ}C$ for 1 hr. The microstructure and superconducting properties of YBCO thin films depended on the composition of pre-annealed thin films. Basal planesuperconducting particles grown on MgO(100) substrate had small and rod-like shade due to preferred orientation, while superconducting film grown on the basal plane-superconducting particles showed round-shape particles. If pre-annealed thin film had nonstoichiometric composition, liquid phase was formed during the heat treatment, which made it easy for particles to grow in the preferred orientation and thus to form textured structure. But the thin films with the textured structure did not show good superconducting properties, especially $T_c$, since the liquid phase transformed into second phase in the grain boundary during the cooling. The effect of the second phase on $T_{c, \;zero}$ was greater than that on $T_{c, \;on}$.

• Journal of Sensor Science and Technology
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• v.14 no.3
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• pp.160-168
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• 2005

ZnO epilayer were synthesized by the pulesd laser deposition(PLD) process on $Al_{2}O_{3}$ substrate after irradiating the surface of the ZnO sintered pellet by the ArF(193 nm) excimer laser. The epilayers of ZnO were achieved on sapphire ($Al_{2}O_{3}$) substrate at a temperature of $400^{\circ}C$. The crystalline structure of epilayer was investigated by the photoluminescence. The carrier density and mobility of ZnO epilayer measured with Hall effect by van der Pauw method are $8.27{\times}1016cm^{-3}$ and $299cm^{2}/V{\cdot}s$ at 293 K, respectively. The temperature dependence of the energy band gap of the ZnO obtained from the absorption spectra was well described by the Varshni's relation, $E_{g}(T)$=3.3973 eV-($2.69{\times}10^{-4}$ eV/K)$T^{2}$/(T+463K). The crystal field and the spin-orbit splitting energies for the valence band of the ZnO have been estimated to be 0.0041 eV and 0.0399 eV at 10 K, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the ${\Delta}so$ definitely exists in the ${\Gamma}_{6}$ states of the valence band of the ZnO. The three photocurrent peaks observed at 10 K are ascribed to the $A_{1}-$, $B_{1}-$, and $C_{1}-$exciton peaks for n = 1.

• Journal of The Korean Astronomical Society
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• v.39 no.2
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• pp.41-50
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• 2006

We present the results of new multi-color CCD photometry for the contact binary XZ Leo, together with reasonable explanations for the period and light variations. Six new times of minimum light have been determined. A period study with all available timings confirms Qian's (2001) finding that the O-C residuals have varied secularly according to $dP/dt\;=\;+8.20{\times}10^{-8}\;d\;yr^{-l}$. This trend could be interpreted as a conservative mass transfer from the less massive cool secondary to the more massive hot primary in the system with a mass flow rate of about $5.37{\times}10^{-8}\;M_{\odot}\;yr^{-l}$. By simultaneous analysis of our light curves and the previously published radial-velocity data, a consistent set of light and velocity parameters for XZ Leo is obtained. The small differences between the observed and theoretical light curves are modelled by a blue third light and by a hot spot near the neck of the primary component. Our period study does not support the tertiary light but the hot region which may be formed by gas streams from the cool secondary. The solution indicates that XZ Leo is a deep contact binary with the values of q=0.343, $i=78^{\circ}.8$, ${\Delta}(T_1-T_2)=126\;K$, and f=33.6 %, differing much from those of Niarchos et al. (1994). Absolute parameters of XZ Leo are determined as follows: $M_1=1.84\;M_{\odot},\;M_2=0.63\;M_{\odot},\;R_1=1.75\;R_{\odot},\;R_2=1.10\;R_{\odot},\;L_1=7.19\;L_{\odot},\;and\;L_2=2.66\;L_{\odot}$.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.8
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• pp.348-353
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• 2003

This paper was the research of high voltage suspension insulator (400 [kN]) including pottery stone, feldspar, clay and alumina of 17 [wt%]. The slurry was fabricated after ball milling mixed raw materials. Green compacts were made by the extrusion of jiggering method and were sintered at 1300[$^{\circ}C$] for 50 [min.] in the tunnel kiln. The sintered density was reached to 97% of theoretical density, and the bending strength was 1658 [k $g_{f}$/$\textrm{cm}^2$] and hardness and fracture toughness which was measured by ICL( indentation crack length ) method were 1658 (kgf/$\textrm{cm}^2$) and 27.5 [Gpa], respectively. In measurement of tana and insulation break voltage of 400 (kN) porcelain, tan$\delta$ took some numerical value between 17${\times}$10$_{-3}$ and 61${\times}$10$_{-3}$ and insulation break voltage value was 19.9$\pm$1.4 [㎸/mm]. The test was performed to research whether the shape of pin affect a overvoltage break load or not As a consequence, when a pin was designed a pin diameter 51 [mm] with the bottom form of two-step constructed with straight in the suspension insulator, Insulator showed overvoltage break load 52 [ton] of the highest value and reflected a fine characteristic in aged deterioration test which is one of the accelerated aging test. Also it could be confirmed a fine characteristic through performing the test that electrical property of insulator was established correctly in accordance with IEC 60383-1 standards.s.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.6
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• pp.11-17
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• 2016

BTTN and TMETN are representative energetic plasticizers used for various propellants. However these compounds are sensitive relatively. So, in order to develop insensitive energetic plasticizer, this study attempted to synthesize derivative of triazole, 4,5-bis(azidomethyl)-(2-methoxyethyl)-1,2,3- triazole (DAMETR). Also, the prepared compound was characterized by NMR, IR spectroscopy, and physicochemical properties such as glass transition temperature, melting point, decomposition temperature, density, viscosity and impact sensitivity. In addition, the heats of formation (${\Delta}H_f$) and detonation properties (pressure and velocity) of DAMETR were calculated using Gaussian 09 and EXPLO5 programs. Especially, 1-DAMETR(>50 J) was more insensitive than BTTN(1 J) and TMETN(9.2 J).

• Journal of the Korean Chemical Society
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• v.30 no.1
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• pp.33-39
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• 1986

The x-values of nonstoichiometry chemical formulas, Sm$O_{1.5+x}$ and Zr$O_{2+x}$, have been measured in temperature range from 500$^{\circ}$C to 1000$^{\circ}$C under oxygen pressure of 2 ${\times}10^{-1}$ to 1 ${\times}10^{-5}$ atm by gravimetric method. The enthalpies of formation of defect in samarium sesquioxide and zirconium dioxide decrease with decreasing oxygen pressure and are all positive. The 1/n values calculated from the slopes of the plots of log x vs. log $PO_2$ increase with temperature and are positive values which mean the higher oxygen pressure dependence at higher temperature. From x-values and thermodynamic data, it is found out that the nonstoichiometric defect is fully ionized metal vacancy. The conduction mechanisms of the systems are also discussed with respect to the nonstoichiometric compositions.