• Journal of the Korean Applied Science and Technology
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• v.35 no.3
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• pp.595-605
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• 2018

In recent years, researches on organic-inorganic coating films have conducted a nanocomposite system composed of organic resin matrices having excellent flexibility and chemical stability and inorganic materials having excellent mechanical properties. The o-phenylphenoxyethyl acrylate (OPPEA) used as the acrylate monomer has a high refractive index of 1.58, and the bisphenol A ethoxylate diacrylate (BAEDA) has a low refractive index but improves the chemical stability of the organic resin. In addition, zirconia used as an inorganic material exhibits excellent durability and optical properties. In this study, the BAEDA contents in acrylate monomer were controlled to produce a film with suitable optical transparency. And optimum conditions were established by comparing the changes in surface properties of PET films detected with pencil hardness tester, Abbe's refractometer, and UV-vis spectrophotometer. The hydrophobicity and the dispersibility of zirconia in acrylate monomer were much improved after modification with ${\gamma}$-methacryloxypropyltrimethoxysilane (MPS), which is a silane coupling agent. And the existence of ester C=O bond peak at $1716cm^{-1}$ introduced by MPS through FT-IR ATR spectrophotometer confirmed the completion of surface modification of zirconia with MPS. In addition, the presence of silicon atom on the surface modified zirconia was also proved using X-ray fluorescence spectrometer. When the photocurable hybrid coating was prepared by introducing chemically modified zirconia into acrylate monomer, the refractive index of this coated PET film was improved by 1.2%, compared to the only acrylate coated PET film. The homogeneous distribution of zirconia in acrylate coating layer on PET film was also identified through SEM/EDS mapping analysis technique.

• Journal of the Korean Wood Science and Technology
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• v.44 no.1
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• pp.48-56
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• 2016

In this study, to develop the lattice materials with a low environmental load for restoring the destroyed forest, 7 types of wood-concrete hybrid laminated materials were manufactured with domestic four softwoods, three hardwoods and concrete, and the effects of density of wood species on static bending strength performances were investigated. Bending MOEs of wood-concrete hybrid laminated materials increased with increasing density of wood species on the whole, and the values were higher than that of concrete by hybrid-laminating woods on the concrete. It was found that the measure values of bending MOEs were slightly lower than the calculated values calculated using equivalent cross-section method from MOE of each laminae of hybrid laminated materials and the difference between them was less than 10%. Bending proportional limit stresses of hybrid laminated materials showed 1.2-1.6 times higher than that of concrete by hybrid-laminating. Bending strength (MOR) of hybrid laminated materials increased with the density of wood species. By hybrid-laminating, the MOR of concrete was considerably increased. Therefore, it is considered that wood-concrete hybrid laminated materials can be applied as a materials with a low environmental load and durability for ecological restoration.

• Polymer(Korea)
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• v.34 no.6
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• pp.540-546
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• 2010

In this manuscript, in order to reduce methanol permeability and, at the same time, to increase proton conductivity THS-PSA containing silica compound, responsible for methanol permeability reduction, and sulfonic acid, responsible for proton conductivity enhancement, was applied onto PVA/PSSA-MA membranes. And in order to improve durability, the resulting membranes, PVA/PSSAMA/THS-PSA, were exposed to 500ppm F2 gas at varying reaction times. The surface-fluorinated membranes were characterized through the measurement of contact angles, thermo-gravimetric analysis, and X-ray photoelectron spectroscopy to observe the physico-chemical changes. For the evaluation of the electro-chemical changes in the resulting membranes, its water contents, ion exchange capacity, proton conductivity, and methanol permeability were measured and then compared with the commercial membrane, Nafion 115. Finally, the membran electrode assembly(MEA) was prepared and the cell voltage against the current density was measured. As fluorination time increased, the contents of F2 increased up to maximum 4.3% and to depth of 50 nm. At 60 min of fluorination, the proton conductivity was 0.036 S/cm, larger than Nafion 115 at 0.024 S/cm, and the methanol permeability was $9.26E-08cm^2/s$, less than Nafion 115 at $1.17E-06cm^2/s$.

• Journal of the Korea Concrete Institute
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• v.16 no.2 s.80
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• pp.241-248
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• 2004

The rheological properties of cement paste system mixed with mineral admixtures (MAs) used to increase the strength and improve durability and fluidity of concrete were investigated. And cement paste systems were designed as one-, two- and three-ingredients blended paste systems. The rheological properties of paste systems were assessed by Rotovisco RT 20 rheometer (Hakke inc.) having a cylindrical serrated spindle. The rheological properties of one-ingredient paste systems were improved with increasing the dosage of superplasticizer. For two-ingredients paste systems, as increasing the replacement ratio of blast furnace slag (BFS) and fly ash (FA), the yield stress and plastic viscosity were decreased compared with non-replacement. In the ordinary portland cement (OPC)-silica fume (SF) paste systems, in accordance with an increase in the replacement ratio of SF, the yield stress and plastic viscosity were increased steeply. For three-ingredients paste systems, both OPC-BFS-SF and OPC-FA-SF paste systems, the rheological properties were improved compared with the only replacement of SF. In the case of both two-and three-ingredients paste systems, the rheological properties using BFS were improved more than FA.

• Journal of the Korea Concrete Institute
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• v.26 no.5
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• pp.573-579
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• 2014

Typical composite girder has been composed with conventional concrete deck and steel girder. Recently, ultrahigh-performance-concrete (UHPC) deck is proposed in order to enhance durability and reduce weight of deck as well as to increase stiffness and strength of the composite girder. This study investigates that a headed stud is still compatible as a shear connector for the UHPC deck and steel girder composite beam. Twelve push-out specimens are prepared to evaluate the static strength of stud shear connectors embedded in the UHPC deck. The test program proves that the static strength of the stud shear connectors embedded in UHPC well meets with design codes described in AASHTO LRFD. Chosen experimental variables are aspect ratio of height to diameter of stud, thickness of deck and thickness of concrete cover over the head of stud. From the test program, aspect ratio and cover thickness are investigated to mitigate the regulations of the existing design codes. The minimum aspect ratio and the minimum cover thickness given in AASHTO LRFD are four and 50mm, respectively. This limitation hinders to lower the thickness of the UHPC deck. The results of the experiment program give that the aspect ratio and the cover thickness can be lower down to three and 25mm, respectively. Eurocode-4 regulates characteristic relative slip at least 6mm. However, test results show that stud shear connectors embedded in UHPC provide the characteristic relative slip only about 4mm. Therefore, another measures to increase ductility of stud should be prepared.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.25 no.3
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• pp.117-123
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• 2019

The general Impulse Sealer has a problem of sealing quality because continuously sealing process results in an undesirable temperature rise, which may accumulate the heat during the operation. In order to address such a drawback, the controlled sealing temperature method can be effectively utilized compared with the general controlled time method. As such, a temperature sensor with capability of detecting the sealing temperature was installed, and a separate PCB was manufactured to control the sealing temperature by measuring and calculating the detected temperature. The temperature changes during the temperature rise and maximum temperature after continuously operation were investigated using an Impulse Sealer system. Next, the results obtained from experiment were compared with each other. As such, the maximum temperature was 70.3℃, whereas 8.9℃ was recorded as control temperature. It implies that this controlled temperature system prevented the undesirable temperature rise, thereby causing a consistent sealing quality.

• Composites Research
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• v.23 no.4
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• pp.44-51
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• 2010

Recently, to solve the problems associated with the neutralization and corrosion of reinforced concrete compression members, the structural configurations such as CFFT (Concrete Filled GFRP Tube) and RCFFT (Reinforced Concrete Filled GFRR Tube) have been developed and applied to main members of civil engineering structure. These members can increase structural performance in terms of structural stability, ductility as well as chemical resistance compared with conventional concrete structural members. Many researches in numerous institutions to predict the load carrying capacity of the concrete compression member strengthened with FRP materials have been conducted and they have been suggested an equation for the prediction of the load carrying capacity of the members. Through the review of the research results, it was found that their results are similar each other. Moreover, it was also found that the results are not directly applicable to our specimens since the results are largely depended upon the member configurations. Also, since the accurate design criteria for the RC members strengthened with FRP such as RCFFT have not been established properly, relevant theoretical and experimental investigations must be conducted for the application to the practical structures. In this study, structural behavior of RCFFT was evaluated through compressive and quasi-static flexural tests in order to formulate design criteria for the structural design. In addition, the RCFFT members were also investigated to examine their confinement effect and the equations capable of estimating the compressive ultimate strength and flexural stiffness of the RCFFT members were proposed.

• Journal of Energy Engineering
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• v.24 no.2
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• pp.34-39
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• 2015

This study confirmed the characteristics of hydrogen production according to electrode materials by producing non-diaphragm alkaline water electroanalyzer that can be controlled at medium temperature to produce hydrogen. As a result of the electrochemical characteristics by electrode material ($IrO_2/Ti$, $RuO_2/Ti$, Ti), the highest efficiency was found in $RuO_2/Ti$, as a result of hydrogen production experiment by electrolyte concentration, electrolyte concentration has a tendency to be proportional to hydrogen production and the condition of 30% KOH showed the highest hydrogen production as $118.9m^3/m^3/day$. In the experiment that confirmed hydrogen production according to electrode materials, in case of combination of anode ($IrO^2/Ti$) and cathode ($RuO^2/Ti$), it was $157.55m^3/m^3/day$ that showed a higher hydrogen production by around 6.97% than that of $IrO^2/Ti$ and cathode. It is presumed that the improvement of electrochemical activation of DSA electrode increases hydrogen production and influences the improvement of durability compared to the former electrode so that it enables stable alkaline water electrolysis.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.5
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• pp.511-521
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• 2015

The thermal bridge occurring in a building influences its thermal performance and durability. The domestic typical multi-unit residential buildings suffer thermal losses resulting from thermal bridges of the balcony slab. To minimize the thermal loss between inside and outside of the balcony slab, thermal bridge breaker(TBB) systems have been developed and applied in building construction. Although thermal bridge breaker systems for reinforced concrete(RC) wall-slab joints can improve the thermal performance of a building, it is necessary to verify the structural performance of TBB systems whether they provide proper resistance for cyclic loading. In order to investigate the structural characteristics of TBB systems embedded in RC slabs, cyclic tests of wall-slab joints were performed by applying two reversed cycles at each up to 30 cycles. The test results show that the RC slabs embedding TBBS systems can present excellent structural performance and the maximum moment capacity, energy dissipation capacity and ductility of TBBs systems are enhanced compared to those of the typical RC slabs.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.10
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• pp.117-124
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• 2019

Military Vehicles of the Korean army had been developed before 2004 and used manual transmissions. Manual transmissions contain a clutch system regulating the force from engine to transmission. In this study, a 2.5-ton military vehicle's clutch system was investigated. The existing clutch system had the characteristics that need to adjust the clearance between the clutch cover and release bearing. Improper clearance led to early wear of the clutch disk and failure of the clutch cover. To solve these problems, an improved clutch system was suggested and tested. The improved clutch system contains auto adjustment of the clearance and an enhanced clutch disk. To verify the improved clutch systems, 2 stage tests were conducted: an accelerated life test of the clutch system, and a driving test by trainee of driving more than 3,000km. As a result, the problems caused by the improper clearance adjustment were solved and this design was verified.