• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.6
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• pp.695-700
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• 2010

Material properties of the lock plate, which covers the gas-turbine blade, are studied using ultrasonic guided waves. The lock plate is a crucial part of a gas-turbine power plant. The wave velocity and attenuation coefficient are measured to investigate the changes in the material properties under three heat-treatment conditions. Compared to the destructive mechanical tests, the material characterization of Inconel X-750 can be performed more efficiently and nondestructively by using ultrasonic guided waves; this characterization helps identify the changes occurring in its elastic moduli and Poisson's ratio under different heat-treatment conditions. The wave velocity and hardness of Inconel X-750 are proportional to each other. This nondestructive technique for the measurement of material properties can be widely used in various industries to avoid catastrophic failure. It is also expected that the guided-wave technique can be applied as a new cost- and time-saving inspection tool for longer and wider inspection ranges.

• Earthquakes and Structures
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• v.13 no.3
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• pp.255-265
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• 2017

In this paper, an efficient shear deformation theory is developed for wave propagation analysis in a functionally graded beam. More particularly, porosities that may occur in Functionally Graded Materials (FGMs) during their manufacture are considered. The proposed shear deformation theory is efficient method because it permits us to show the effect of both bending and shear components and this is carried out by dividing the transverse displacement into the bending and shear parts. Material properties are assumed graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents; but the rule of mixture is modified to describe and approximate material properties of the functionally graded beams with porosity phases. The governing equations of the wave propagation in the functionally graded beam are derived by employing the Hamilton's principle. The analytical dispersion relation of the functionally graded beam is obtained by solving an eigenvalue problem. The effects of the volume fraction distributions, the depth of beam, the number of wave and the porosity on wave propagation in functionally graded beam are discussed in details. It can be concluded that the present theory is not only accurate but also simple in predicting the wave propagation characteristics in the functionally graded beam.

• Bulletin of the Korean Chemical Society
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• v.34 no.11
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• pp.3227-3232
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• 2013

A novel Cu-Co-O composite nanocatalyst was designed and prepared for the ozonation of phenol. A synergistic effect of copper and cobalt was observed over the Cu-Co-O composite nanocatalyst, which showed higher activity than either copper or cobalt oxide alone. In addition, the Cu-Co-O composite revealed good activity in a wide initial pH range (4.11-8.05) of water. The fine dispersion of cobalt on the surface of copper oxide boosted the interaction between catalyst and ozone, and the surface Lewis acid sites on the Cu-Co-O composite were determined as the active sites. The Raman spectroscopy also proved that the Cu-Co-O composite was quite sensitive to the ozone. The trivalent cobalt in the Cu-Co-O composite was proposed as the valid state.

• Journal of Hydrogen and New Energy
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• v.24 no.5
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• pp.359-366
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• 2013

This work is investigated for the catalytic decomposition of hydrogen iodide (HI). Platinum was used as active material by loading on $ZrO_2-SiO_2$ mixed oxide in HI decomposition reaction. To obtain high and stable conversion of hydrogen iodide in severe condition, it was required to improve catalytic activity. For this reason, a method increasing dispersion of platinum was proposed in this study. In order to get high dispersion of platinum, zirconia was incorporated in silica by sol-gel synthesis. Incorporating zirconia influence increasing platinum dispersion and BET surface area as well as decreasing deactivation of catalysts. It should be able to stably product hydrogen for a long time because of inhibitive deactivation. HI decomposition reaction was carried out under the condition of $450^{\circ}C$ and 1 atm in a fixed bed reactor. Catalysts analysis methods such as $N_2$ adsorption/desorption analysis, X-ray diffraction, X-ray fluorescence, ICP-AES and CO gas chemisorption were used to measurement of their physico-chemical properties.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.1-5
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• 2018

The present study investigated the characteristics of vertical sagging down of high temperature in chamber and characteristics of vertical sagging down in the outdoor asphalt sheet and asphalt seal under korea ltimate condition using asphalt seal products of solvent based type, solventless type, water dispersion type, and heat melting type, which are currently applied in Korea. Prior to the investigation of outdoor vertical sagging down characteristics, the assessment of sagging down performance of single use of sealing products at $20^{\circ}C$, $40^{\circ}C$, $60^{\circ}C$ was conducted and the result showed that sagging down did not occur at $20^{\circ}C$ but some solventless type, water dispersion type specimens at $40^{\circ}C$ had sagging down up to 10 mm. In addition, some solventless type, water dispersion type specimens had sagging down up to 55 mm at $60^{\circ}C$. For specimens to which asphalt seal and renovated asphalt sheet were layered over the outdoor concrete vertical surface, sheet sagging and sagging down occurred up to 50 mm in water dispersion specimens after three month later since the construction in summer.

• Nuclear Engineering and Technology
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• v.26 no.3
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• pp.401-410
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• 1994

Validation study of two radionuclide migration models for single fracture developed in geologic medium the hydrodynamic dispersion diffusion model(HDDM) and the channeling dispersion diffusion model(CDDM), was studied by migration experiment of tracers through an artificial granite fracture on the labolatory scale. The tracers used were Uranine and Sodium lignosulfonate know as nonsorbing material. The flow rate ranged 0.4 to 1.5 cc/min. Related parameters for the models were estimated by optimization technique. Theoretical breakthrough curves with experimental data were compared. In the experiment, it was deduced that the surface sorption for both tracers did not play an important role while the diffusion of Uranine into the rock matrix turned out to be an important mass transfer mechanism. The parameter characterizing the rock matrix diffusion of each model agreed well The simulated result showed that the amount of flow rate could not tell the CDDM from the HDDM quantitatively. On the other hand, the variation of fracture length gave influence on the two models in a different degree. The dispersivity of breakthrough curve of the CDDM was more amplified than that of the CDDM when the fracture length was increased. A good agreement between the models and experimental data gave a confirmation that both models were very useful in predicting the migration system through a single fracture.

• Journal of the Society of Disaster Information
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• v.20 no.1
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• pp.47-59
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• 2024

Purpose: This study aims to propose measures for the prevention of fire and explosion accidents within manufacturing facilities by improving the existing classification criteria for hazardous locations based on the leakage patterns of flammable liquids. The objective is to suggest ways to safely manage ignition sources and combustible materials. Method: The hazardous locations were calculated using "KS C IEC 60079-10-1," and the calculated explosion hazard distances were visualized in 3D. Additionally, the formula for the atmospheric dispersion of flammable vapors, as outlined in "P-91-2023," was utilized to calculate the dispersion rates within the hazardous locations represented in 3D. Result: Visualization of hazardous locations in 3D enabled the identification of blind spots in the floor plan, facilitating immediate recognition of ignition sources within these areas. Furthermore, when calculating the time taken for the Lower Explosive Limit (LEL) to reach within the volumetric space of the hazardous locations represented in 3D, it was found that the risk level did not correspond identically with the explosion hazard distances. Conclusion: Considering the atmospheric dispersion of flammable liquids, it was concluded that safety management should be conducted. Therefore, a method for calculating the concentration values requiring detection and alert based on realistically achievable ventilation rates within the facility is proposed.

• Journal of Powder Materials
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• v.19 no.2
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• pp.117-121
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• 2012

Tool steels serve a large range of applications including hot and cold workings of metals and injection mouldings of plastics or light alloys. The high speed steels (HSS) are specifically used as cutting tools and wear parts because it has high strength, wear resistance and hardness along with appreciable toughness and fatigue resistance. From the view of HSS microstructure, it can be described as metallic matrix composites formed by a ferrous with a dispersion of hard and wear resistant carbides. The experimental specimens were manufactured using the PIM with T42 powders (50~80 vol.%) and polymer (20~50 vol.%). The green parts were debinded in n-hexane solution at $60^{\circ}C$ for 8 hours and thermal debinded at an $N_2-H_2$ mixed gas atmosphere for 8 hours. Specimens were sintered in high vacuum ($10^{-5}$ Torr) and various temperatures.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.2
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• pp.137-141
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• 2015

The purpose of this study is examining thermal dissipation materials for the lighting and radiate efficiency improvement of 8W LED and confirming the properness of the thermal dissipation materials for LED heat sink. Solid Works flow simulation on 8W class COB was done based on the material characteristics of thermal conductive polymer materials. According to the result of simulation, Al had better thermal dissipation performance than PET. Highest temperature was $7.6^{\circ}C$ higher while lowest temperature was $7.8^{\circ}C$ lower. The test on the heat sinks made by the materials, highest temperature was $4.1^{\circ}C$ higher and lowest temperature was $3.9^{\circ}C$ lower. It is possible to confirm that Al heat sink has better thermal dissipation efficiency because it has better dispersion of heat generated at junction temperature and less heat cohesion. The weight of PET heat sink was reduced than Al heat sink by 46.9% by the density difference between Al and PET. In conclusion, thermal dissipation performance of thermal conductive polymer is lower than Al material however, it is possible to lighting heat sink because thermal conductive polymer has better formability, has lower specific weight and enables various design options.

• Geomechanics and Engineering
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• v.18 no.1
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• pp.85-96
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• 2019

A free vibration analysis and wave propagation of triclinic and orthotropic plate has been presented in this work using an efficient quasi 3D shear deformation theory. The novelty of this paper is to introducing this theory to minimize the number of unknowns which is three; instead four in other researches, to studying bulk waves in anisotropic plates, other than it can model plates with great thickness ratio, also. Another advantage of this theory is to permits us to show the effect of both bending and shear components and this is carried out by dividing the transverse displacement into the bending and shear parts. Hamilton's equations are a very potent formulation of the equations of analytic mechanics; it is used for the development of wave propagation equations in the anisotropic plates. The analytical dispersion relationship of this type of plate is obtained by solving an eigenvalue problem. The accuracy of the present model is verified by confronting our results with those available in open literature for anisotropic plates. Moreover Numerical examples are given to show the effects of wave number and thickness on free vibration and wave propagation in anisotropic plates.