• Korean Chemical Engineering Research
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• v.44 no.6
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• pp.602-608
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• 2006

Carbon fiber (CF) reinforced papers using polyacrylonitrile (PAN) based CF and wood pulp were prepared by varying the lengths and the concentrations of CF, and the basis weight of paper to investigate adhesive state between CF and pulp, and physical properties and electrical conductivity of the paper. The reinforcement was caused by physical entanglement and adhesion at the interface of the different fibers rather than by chemical bonds. The tear strength and the thickness of the paper increased as increasing the concentration of CF, while the tensile and the burst strength of the paper decreased. The improved dispersion of CF in the paper was obtained from mixing shorter CF, but the maximum electrical conductivity of the paper was gained from mixing 10 mm chopped CF. The electrical conductivity of the paper increased sharply from 2 wt％ to 8 wt％ of CF showing S-curve, and increased linearly as increasing the basis weight of the paper. Therefore, in order to improve the electrical conductivity and the physical property of the paper, the increase of basis weight of the paper is also important as the increase of CF content in the paper.

• Elastomers and Composites
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• v.38 no.3
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• pp.243-250
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• 2003

Polyurethane waterproof (PW) coatings are increasingly demanded in Korea for repairing cracks on old building roofs and construction of many sporting facilities. Calcium carbonate, a common filler, is incorporated in PW compositions. In this study, PW coatings were prepared by substituting a part of calcium carbonate with fly ash. The maximum amounts of calcium carbonate which can be substituted by fly ash obtained in the cyclone and bag filter dust collectors were 20 and 10%, respectively. It was found that the curing rate of PWs ran be controlled by varying the amount of Pb-octoate catalyst. The elongations at break as well as tensile strength and tear strength of PW coatings containing fly ash could also be adjusted such that their values were comparable to those of a standard PW coating by varying relative amounts of some components. However, the amount of cadmium, mercury, and lead leached from PW coatings containing fly ash obtained from the bag filter collector exceeded the respective allowed upper limits, mainly due to the initial high contents of them in the fly ash. On the other hand, PW coatings containing fly ash obtained from the cyclone collector exhibited better mechanical properties and did not release any significant amounts of the heavy metals. Thus, it was concluded that PW coatings containing fly ash can be utilized for practical applications as long as an appropriate fly ash is used.

• Journal of the Korea Institute of Building Construction
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• v.22 no.1
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• pp.11-21
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• 2022

Currently, in the domestic construction industry, the free web method has been emerging as a potential solution to the shortage of skilled workers due to the prolonged COVID-19 crisis, as it helps in securing economic feasibility through shortening the construction period and reducing labor costs. To consider one part of the construction method, in this study, the bending behavior according to the load was evaluated for the SY slope-type beam formwork, which was manufactured at a factory, assembled with rebar, brought into the site, and then poured into the site. For the SY Beam standard cross-sectional shape, a cross-sectional dimensional width of 400mm and depth 600mm determined through structural modeling using the MIDAS GEN program were applied. A total of 6 specimens were made with a member length of 5,000mm, 5 specimens and one RC specimen in the comparison group were manufactured in real-size format using the thickness of the steel plate(0.8, 1.0, 1.2mm) as a variable, and bending experiments were performed. In the bending test, the steel plate deck showed high initial stiffness and maximum strength as it yielded, which showed that it sufficiently contributed to the flexural strength. It is judged that additional analysis and experimental studies for 1.05, 1.1, and 1.15mm are needed to derive the appropriate steel plate thickness and the method for calculating the tensile force contribution of the steel plate to secure the manufacturing, construction and economic feasibility of SY Beam in the future.

• Journal of the Korean Geosynthetics Society
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• v.22 no.1
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• pp.53-66
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• 2023

In this study, the results of the elasto-plastic beam analysis, finite element analysis and optimization design of the steel pipe sheet pile applied as an earth retaining wall under the deep excavation were presented. Through this study, it was found that the high-strength and sea resistant steel pipe has high allowable stress, excellent structural properties, favorable corrosion, and high utilization as an earth retaining wall, and the C-Y type joint has significantly improved the tensile strength and stiffness compared to the traditional P-P type. In addition, it was investigated that even if the leak or defect of the wall occurs during construction, it has the advantage of being able to be repaired reliably through welding and overlapping. In the case of steel pipe wall, they were evaluated as the best in views of the deep excavation due to the large allowable bending stress and deformation flexibility for the same horizontal displacement than CIP or slurry wall. Elasto-plastic and finite element analysis were conducted in consideration of ground excavation under large-scale earth pressure (uneven pressure), and the results were compared with each other. Quantitative maximum value were found to be similar between the two methods for each item, such as excavation behavior, wall displacement, or member force, and both analysis method were found to be applicable in design for steel pipe sheet pile wall. Finally, it was found that economical design was possible when determining the thinnest filling method with concrete rather than the thickest hollow shape in the same diameter, and the depth (the embedded length through normality evaluation) without rapidly change in displacement and member force.

• Elastomers and Composites
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• v.37 no.4
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• pp.224-233
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• 2002

This study has investigated the flame retardant properties of EPDM rubber with the addition of various flame retardants. Carbon black, stearic acid, zinc oxide cross-linking agent were mixed with EPDM rubber to produce the base rubber E0 without the addition of flame retardants. Phosphorus flame retardant Tricrecyl phosphate(TCP) was added to E0 in 0.5, 1, 1.5, 2 phr to make E1~E4 samples and red phosphorus was added in 3, 6, 9, 12 phr to make E5~E8 samples. A flame retardant of the bromine family Decabromodiphenyloxide(DBDPO), and a chlorinated paraffin retardant of the chlorine family was added to E0 in 3, 6, 9, 12 phr to make E9~E12 and E13~E16 samples, repectively. Basic physical properties such as tensile strength, tear strength and hardness were measured for all the rubber samples with various flame retardant additions. There was no substantial differences. On the other hand, Oxygen index and UL94 were measured to study flame retardant properties. From oxygen index measurements E0 sample showed a value of 23.5%, indicating the improvement of flame retardant properties. Also from UL94 measurements, it was found that addition of red phosphorus resulted in maximum flame retardant effect. It was found that increasing the amount of addition resulted in decreasing combustion rate and improving flame retardant effect regardless of the kind of flame retardant.

• Journal of the Korean Ceramic Society
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• v.39 no.11
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• pp.1042-1047
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• 2002

The sedimentation characteristics of ceramic fiber were analyzed when viscosity of the slurry for ceramic paper formation was varied and zeta potential change and degree of dispersion with pH were studied as well. The proper viscosity of the slurry for dispersion of fibers was between 28 and 31 cps. Zeta potential of the slurry was sensitively changed with pH adjustment and showed maximum value of -35~-36 mV at ph 7.5~9.5, which indicated better dispersion of ceramic fiber as zeta potential of the slurry was increased. The sedimentation rate of ceramic fiber in a slurry was reported minimum at the maximum zeta potential. Water content of the casted paper should be lower than 83% after vacuum dehydration for retention of binder and lower than 62% after press rolling for wet paper handling. The obtained ceramic paper had tensile strength and basis weight, $102 kgf/cm^2$ and $98 g/m^2$, respectively.

• Journal of the Korea Concrete Institute
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• v.26 no.4
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• pp.491-497
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• 2014

The corrosion of steel reinforcement in reinforced concrete bridge decks significantly affects the degradation of the capacity. Due to the advantageous characteristics such as high tensile strength and non-corrosive property, fiber reinforced polymer (FRP) has been gathering much interest from designers and engineers for possible usage as a alternative reinforcement for a steel reinforcing bar. However, its application has not been widespread, because there data for short- and long-term performance data of FRP reinforced concrete members are insufficient. In this paper, seven full-scale decks with dimensions of $4000{\times}3000{\times}240mm$ were prepared and tested to failure in the laboratory. The test parameter was the bottom reinforcement ratio in transverse direction. The decks were subjected to various levels of concentrated cyclic load with a contact area of $577{\times}231mm$ to simulate the vehicle loading of DB-24 truck wheel loads acting on the center span of the deck. It was observed that the glass FRP (GFRP) reinforced deck on a restraint girder is strongly effected to the level of the applied load rather than the bottom reinforcement ratio. The study results showed that the maximum load less than 58% of the maximum static load can be applied to the deck to resist a fatigue load of 2 million cycles. The fatigue life of the GFRP decks from this study showed the lower and higher fatigue performance than that of ordinary steel and CFRP rebar reinforced concrete deck. respectively.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.4
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• pp.393-399
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• 2017

In a reciprocating compressor, the piston and connecting rod are important parts. Excess mechanical stress on these parts may cause damage, and broken parts are expensive and difficult to replace. Therefore, it is necessary to analyze the mechanical stress affecting durability and longevity. The main purpose of this study was to identify locations of maximum stress on pistons and connecting rods. Based on dynamic calculation of the working process of a specific air compressor, an analysis of piston and connecting rod performance has been completed. A three-dimensional model for the air compressor's pistons and connecting rods was built separately, and FEM analysis of these components was carried out using a numerical method. The pistons were loaded by pressure which was changed according to crankshaft angle without thermal boundary conditions. The simulation results were used to predict and estimate stress concentration as well as the value of this stress on pistons and connecting rods. The maximum equivalent stress calculated are over 190 MPa on pistons and 123 MPa on connecting rods at crank angle $135^{\circ}$ and $225^{\circ}$ but these are under tensile yield strength. Besides, the calculated safety factors of connecting rods and pistons is higher than 1. Moreover, the results obtained can be used to provide manufacturers with references to optimize the design of pistons and connecting rods for reciprocating compressors.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.2
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• pp.129-140
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• 2018

A residual stress generated in the steel structure is broadly categorized into initial residual stress during manufacturing steel material, welding residual stress caused by welding, and heat treatment residual stress by heat treatment. Initial residual stresses induced during the manufacturing process is combined with welding residual stress or heat treatment residual stress, and remained as a final residual stress. Because such final residual stress affects the safety and strength of the structure, it is of utmost importance to measure or predict the magnitude of residual stress, and to apply this point on the design of the structure. In this study, the initial residual stress of steel structures having thicknesses of 25 mm and 70 mm during manufacturing was measured in order to investigate initial residual stress (hereinafter, referred to as initial stress). In addition, thermal elastic plastic FEM analysis was performed with this initial condition, and the effect of initial stress on the welding residual stress was investigated. Further, the reliability of the FE analysis result, considering the initial stress and welding residual stress for the steel structures having two thicknesses, was validated by comparing it with the measured results. In the vicinity of the weld joint, the initial stress is released and finally controlled by the weld residual stress. On the other hand, the farther away from the weld joint, the greater the influence of the initial stress. The range in which the initial stress affects the weld residual stress was not changed by the initial stress. However, in the region where the initial stress occurs in the compressive stress, the magnitude of the weld residual compressive stress varies with the compression or tension of the initial stress. The effect of initial stress on the maximum compression residual stress was far larger when initial stress was considered in case of a thickness of 25 mm with a value of 180 MPa, while in case of thickness at 70 mm, it was 200 MPa. The increase in compressive residual stress is almost the same as the initial stress. However, if initial stress was tensile, there was no significant change in the maximum compression residual stress.

• The korean journal of orthodontics
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• v.31 no.1 s.84
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• pp.149-157
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• 2001

The purpose of this study was to investigate the property of a new Korean stainless steel wire(Jinsung Ind.) comparing with other foreign Products. Five types of stainless steel wires (Standard, Resilient, HI-T of Unitek, Stainless steel of Ormco and Jinsung Ind.) in 0.016x0.022 and 0.019x0.02 were tested to observe for Composition analysis, size difference, tensile properties, flexure bending property, tortion property, surface hardness and surface topography by means of SEM. The findings suggest that: 1. In maximum tensile strength of tensile properties, Unitek Hi-T showed the greatest value, followed by Unitek Resilient, Jinsung Stainless Steel, Ormco Stainless Steel, Unitek Standard in 0.016x0.022, and Unitek Hi-T showed highest value, followed by Jinsung Stainless Steel, Ormco Stainless Steel, Unitek Resilient, Unitek Standard in 0.019x 0.025. 2. In elongation rate, Unitek Standard showed the greatest value, fellowed by Ormco Stainless Steel, Unitek Hi-T, Unitek Resilient, Jinsung Stainless Steel in 0.016x0.022, and Unitek Hi-T showed the highest value, followed by Unitek Standard, Ormco Stainless Steel, Jinsung Stainless Steel, Unitek Resilient in 0.019x0.025. 3. In modulus of elasticity, Jinsung Stainless Steel showed the greatest value, followed by Unitek Hi-T, Unitek Resilient, Ormco Stainless Steel, Unitek Standard in 0.016x0.022, and Unitek Resilient showed the highest value followed by Jinsung Stainless Steel, Ormco Stainless Steel, Unitek Hi-T, Unitek Standard in 0.019x0.025. 4. In bending fatigue test, Jinsung Stainless Steel showed the greatest fracture resistance, followed by Unitek Hi-T, Unitek Standard, Unitek Resilient, Ormco Stainless Steel in 0.016x0.022, and Unitek Hi-T showed the greatest fracture resistance followed by Jinsung Stainless Steel, Unitek Resilient, Unitek Standard, Ormco Stainless Steel in 0.019x0.025. 5. In twist test, Unitek Resilient showed the greatest fracture resistance, followed by Jinsung Stainless Steel, Unitek Hi-7, Ormco Stainless Steel, Unitek Standard in 0.016x0.022, and Jinsung showed the greatest fracture resistance, followed by Unitek Resilient, Unitek Standard, Ormco Stainless Steel, Unitek Hi-T. 6. In surface topography, every products showed indentation and pitting. Jinsung stainless steel wire showed long thin indentation and relatively smooth surface. Unitek wires showed indentation and pitting and Ormco wire showed a lot of irregular pittings.