• Journal of Korea Foundry Society
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• v.24 no.6
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• pp.331-339
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• 2004

Melt-extrusion process, a metallic melt poured and solidified up to semisolid state in the container can be directly extruded through the die exit to form a product of bar shape without other intermediate processes. In this study, the fabrication characteristics of the process were evaluated with various process parameters, such as preheating temperature of extrusion dies, extrusion temperature and extrusion ratio. AI-Cu alloys were successfully extruded after squeezing out of liquid during melt-extrusion with smaller force compared to the solid extrusion. Soundly AI-Cu alloy bar was fabricated at the preheating temperature of $500{\sim}520^{\circ}C$. The range of extrusion temperature for soundly melt-extruded AI-Cu alloy bar was increased with increasing extrusion ratio. Mechanical properties of melt-extruded AI-Cu alloy bars were found change with Cu content of the melt-extruded bars due to the occurrence of segregation. The various extrusion temperature yielded equiaxed structure with a grains size about 200 ${\mu}m$.

• Analytical Science and Technology
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• v.7 no.4
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• pp.441-453
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• 1994

Two extraction methods, liquid-liquid extraction(LLE) and solid-phase extraction(SPE), coupled with GC/MS were compared as preconcentration procedures for priority pollutants in water. Among the semi-volatile priority pollutants, 11 acid and 44 base/neutral compounds were spiked in reagent water. With LLE, which is a modification of EPA Method 625, the overall mean recovery of the 54 compounds was 91% with a mean relative standard deviation(RSD) of 4.6%. With SPE, the overall mean recovery of the 52 compounds was 53% with a mean RSD of 8.9%. The detection limits of both methods were in the range of $1{\sim}5{\mu}g/l$.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1995.11a
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• pp.11-30
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• 1995

The ignition characteristics of a reactive solid with rough surface by constant heat flux were studied. The geometry of surface was represented by a set of identical protrusions having a shape of wedge based on the block of reactive solid. Several regimes of ignition were found, depending on the ratio of the protrusion length and the depth of the heated layer, formed in course of ignition process: 1) when the substance is ignited as the massive block, and the effect of roughness is not pronounced; 2) when ignited are the individual protrusions; and 3) in the intermediate region between the first two. Critical ignition conditions: ignition time and ignition criterion, are determined for the three regimes. The results are compared with the results for the one-dimensional ignition of the semi-infinite body. It is shown, that the effect of geometry on ignition results in the considerable reduction of ignition delay, and the amount of energy required for the successful ignition is less compared to the one- dimensional case.

• Journal of environmental and Sanitary engineering
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• v.22 no.2
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• pp.9-20
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• 2007

The incineration process has commonly used for wastes amount reduction and thermal treatments of pollutants as the technologies accumulated. However, the process is getting negative public images owing to matter of hazardous pollutants emission. Specially dioxins became a main issue and were mostly emitted from municipal solid wastes incineration. In this reason, pyrolysis/gasification/melting process is presented as an alternative of incineration process. The pyrolysis/gasification/melting process, a novel technology, is middle of verification of commercial plant and development of technologies in Korea. But the survey about the pollutant emission from the process, and background data in these facilities is necessary. So in this survey, t is investigated that the behavior of chlorobenzenes and chlorophenols in plasma type pyrolysis/gasification/melting plant of pilot scale. We investigated discharging behavior of each phase of chlorobenzene through each process in the plsasma type pyrolysis/gasification/melting process. From this result, it was found that about 99 percent of particle-phase chlorobenzene was removed, but on the other hand gas-phase chlorobenzene was increased by about 600 percent through heat exchanger, flue gas cooling, system and semi dry absorption bag filter(SDA/BF). Also, this investigation presented that di-chlorobenzene(DCB) tri-chlorobenzene(TCB), tetra-chlorobenzene(TeCB), penta-chlorobenzene (PCB), except mono-chlorobenzene(MCB) and hexa-chlorobenzene(HCB) were increased through the flue gas cooling system and the semi dry absorption bag filter(SDA/BF). It was investigated that concentration of particle-phase chlorophenol was decreased by about 66 percent, but on the other hand, concentration of gas-phase chlorophenol was increased by about 170 percent through heat exchanger, flue gas cooling system, and semi dry absorption bag filter(SDA/BF). Also, it was found that di-chlorophenol(DCP), tri-chlorophenol(TCP), and penta-chlorophenol(PCP) were increased through the flue gas cooling system, and the semi dry absorption bag filter(SDA/BF). It can be considered that small-scale pilot facility and short investigation period might cause the concentration increase through the flue gas cooling system and the semi dry absorption bag filter(SDA/BF). A further study on real-scale pilot facility and accurate investigation may be required.

• Journal of the Korean Society for Heat Treatment
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• v.7 no.4
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• pp.244-252
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• 1994

The morphological changes of primary solid particles as a fuction of process time on Al-Si alloys during semi-solid state processing with a shear rate of 200s were studied. In hypereutectic Al-15.5wt%Si alloy, it was observed that primary Si crystals are fragmented in the early stage of stirring and morphologies of primary Si crystals change from faceted to spherical during isothermal shearing for 60 minutes. In quaternary Al-12.5wt%Si-2.9wt%Cu-0.7wt%Mg alloy system, it was observed both primary silicon and ${\alpha}$-alumunum particles. Microstructural evolution of primary Si crystals was similar to that of the hypereutectic Al-Si alloy but equiaxed ${\alpha}$-Al dendrites are broken into nearly spherical at the early stage of shearing and later stage of the isothermal shearing ${\alpha}$- Al particles are slightly coarsoned by Ostwald ripening. Mechanical properties of Al-Si-Cu-Mg alloy were compared to those from other processes (squeeze casting and gravity casting). After T6 heat treatment, comparable values of hardness were obtained while slightly lower compressive strength values were observed in rheocast alloy. The elongation, on the other hand, exhibited significant increasement of 15% over gravity cast alloy.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.6
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• pp.631-638
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• 2015

In this study, semiquantitative failure mode, effects, and criticality analysis (FMECA) for the reliability analysis of a solid rocket propulsion system is performed. The semiquantitative FMECA is composed of failure mode and effects analysis (FMEA) and criticality analysis (CA). To perform FMECA, the structure of the solid rocket propulsion system is divided into 43 parts down to the component level, and FMEA is conducted at the design stage considering 137 potential failure modes. CA is then conducted for each failure mode, during which the criticality number is estimated using the failure rate databases. The results demonstrate the relationship between potential failure modes, causes, and effects, and their risk priorities are evaluated qualitatively. Additionally, several failure modes with higher criticality and severity values are selected for high-priority improvement.

• Journal of Korean Society on Water Environment
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• v.22 no.5
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• pp.879-886
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• 2006

The analytical methods of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans (PCDD/Fs) for water sample with extremely low concentration was developed to extract large volume and to improve fast chromatography for clean up. Semi-automated solid phase extraction (SPE) system and column coupling chromatography using elution pump was optimized and applied to each processes of treatment plant. Results of disk type SPE indicated that this system was applicable below 40 L of aqueous sample with a flow rate of 0.08 ~ 0.2 L/min. Average recoveries of SPE using labeled sampling spike of $^{37}Cl$-2,3,7,8-TCDD was 97%. Column coupling method resulted in reduced clean up time, solvent volume, increased average recoveries with constant elution rate. The combined methods were applied to the monitoring of drinking water treatment plant. Limits of detection (LOD) of each process were calculated. For example, LOD of raw and treated water ranged 0.094~0.968 pg/L and 0.028~0.364 pg/L, respectively. Combined methods of extraction and cleanup techniques provided fast analysis of PCDD/Fs with high accuracy and low LODs for water samples.

• Tribology and Lubricants
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• v.22 no.6
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• pp.320-328
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• 2006

In this study, the simulation of rolling contact fatigue based on stress analysis is conducted under Elastohydrodynamic Lubrication state. To predict a crack initiation life accurately, it is necessary to calculate contact stress and subsurface stresses accurately. Contact stresses are obtained by contact analysis of a semi-infinile solid based on the use of influence functions and the subsurface stress field is obtained using rectangular patch solutions. And a numerical algorithm using Newton-Rapson method was constructed to calculate the Elastohydrodynamic lubrication pressure. Based on these stress values, several multiaxial high-cycle fatigue criteria are used and the critical loads corresponding to fatigue limits are calculated.

• Tribology and Lubricants
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• v.20 no.5
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• pp.252-258
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• 2004

In this study, using high cycle fatigue (HCF) criteria, the simulation of rolling contact fatigue is conducted under elliptical contact. The HCF criteria fall into three categories: the critical plane approach, the stress invariant approach and the approach based on the mesoscopic scale. The accurate calculation of contact stresses and subsurface stresses is essential to the prediction of crack initiation life. Contact stresses are obtained by contact analysis of a semi-infinite solid based on the use of influence functions and the subsurface stress field is obtained using rectangular patch solutions. The simulation results show that the critical load is decreasing rapidly and the site of crack initiation also moves rapidly to the surface from the subsurface when the friction coefficient exceeds a specific value for all of three fatigue criteria.

• Structural Engineering and Mechanics
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• v.14 no.3
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• pp.365-380
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• 2002

Following a series of experiments on isolated low-rise RC shear walls with openings, a theoretical study on the backbone curve of a perforated shear wall shows that there are some important observations from experimental results that make clear a semi-empirical formula of the backbone curve of a perforated wall. Critical shear zones can be depicted from the configuration of shear walls with openings. Different factors, including the size and location of shear wall openings, the wall's height/width ratio, horizontal and vertical steel bar ratios, and location and amount of diagonal steel bars are involved in the derivation of the backbone curve. Bending and shear effects are also considered in the paper. In addition, a comparison of load and displacement for solid and perforated shear walls is discussed. Generally, the comparison between experimental curves and computed backbone curves is favorable.