• Journal of the Korea Concrete Institute
• /
• v.24 no.1
• /
• pp.79-86
• /
• 2012

Though steel reinforcing bars are the most widely used tensile reinforcement, corrosion problems are encountered due to the exposure to aggressive environments. As an alternative material to steel, the fiber reinforced polymers have been used as reinforcement in concrete structures. However, bond strength of FRP rebar is relatively low compared to steel rebar. It has been reported that fibers in matrix can resist crack growth, propagation and finally result in an increase of toughness. In this study, high-strength concrete reinforced with structural fibers was produced to enhance interfacial bond behavior between FRP rebar and concrete matrix. The interfacial bond-behaviors were investigated from a direct pullout test. The test variables were surface conditions of GFRP bars and fiber types. Total of 54 pullout specimens with three different types of bars were cast for bond strength tests. The bond strength-slip responses and resistance of the bond failure were evaluated. The test results showed that the bond strength and toughness increased according to the increased fiber volume.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.11
• /
• pp.217-223
• /
• 2019

The application of 3D printing technology is expanding due to the production of the complex-shape parts and the one-step manufacturing process. Moreover, various technical solutions in 3D printing are emerging through continuous research and development. Representative technologies include SLS technology, in which a desired area is sintered and laminated by irradiating a powder-type material with a laser. In addition, high-performance engineering plastic parts are being manufactured in increasing numbers. In this study, tensile specimens were fabricated from polyamide 12, a widely available polymer, and the glass bead-reinforced polyamide 12. The specimen-build orientation was divided into 0°, 45°, and 90° on the fabrication platform, and the tensile test temperature was -25℃, 25℃, and 60℃. The test results showed that the tensile modulus of both materials decreases as the build orientation becomes closer to 90°. In addition, the tensile strength of glass bead-reinforced PA12 showed more dependence on the build orientation than PA12. In addition, the tensile modulus and tensile strength decreased with increasing test temperature.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.1 no.2
• /
• pp.74-81
• /
• 1987

The reduction in dielectric strength of insulating polymer material when applying electric field is known to be substantial due to the trapped carrier effect. In this study, the carrier property of Biaxially-Drawn polypropylene, which has superior heat-resistance compared to ordinary one, is examined to improve electrical characteristics by measuring TSC spectra as a function of electric field applied to a sample of ($50{\mu}m$) thickness film. The TSC spectra in the temperature range of 303-413(K) and electric field of 2-80(MV/m) have shown no observable effect below 12(MV 1m) but TSC currents of Hetero-and Homo-peaks formed from trapped space charger and space charger injected from electrode have been observed above that point, which seems eventually lead to dielectric breakdown. Finally, this study has shown the superior dielectric proporty of Biaxially-Drawn polypropylene film compared to the non-oriented one for electrical insulation.

• Proceedings of the KAIS Fall Conference
• /
• 2009.12a
• /
• pp.1026-1029
• /
• 2009

현재 남해안 굴양식산업은 어업인들의 중요한 소득원이 되고 있으나, 굴양식장에서 발생되는 굴패각은 처리곤란 및 악취발생으로 인해 또 다른 해양오염원으로 그 문제성이 심각하게 대두되고 있는 실정이다. 굴양식장에서 연간 약 28~30만여톤의 굴패각이 발생되고 있으며, 그 중 10~20%는 종패부착용이나 비료로 재활용되고 있고, 80~90%는 매립되거나 야적 방치된다고 보고되고 있다. 본 연구에서는 굴패각을 재활용하고자 굴껍질의 성분분석을 실시하여 나노고분자세라믹 코팅제의 세라믹 소재로써의 적용 가능성여부를 확인하였고, 경기도 P정수장 내 여과지 콘크리트 벽면에 코팅처리하여 그 성능을 확인하였다. 그 결과 패각의 굴껍질은 90%이상이 탄산칼슘($CaCO_3$)로 이루어져 있었으며, 굴껍질을 재활용한 나노고분자세라믹 코팅제는 pH 7.5~8.5로서 일반수도를 측정한 pH 7.3~7.8과 유사한 결과를 보였다. 또한, 나노고분자세라믹 코팅제의 콘크리트 벽면에 대한 부착강도는 한국산업규격에 제시된 폴리머의 방수재료 부착강도인 8~10(kg.f/$cm^2$)이상의 값이 나타남에 따라 패각의 굴껍질을 재활용한 나노고분자세라믹 코팅제의 경기도 P정수장 내 여과지 콘크리트 벽면 코팅제로써 적용이 가능한 것으로 확인 되었다.

• Korea-Australia Rheology Journal
• /
• v.11 no.3
• /
• pp.255-263
• /
• 1999

Blends of two thermotropic liquid crystalline polymers, HX2000 and Vectra A950, were prepared by melt blending. Effects of transesterification on these blends are investigated by comparing properties of the blends with and without the addition of an inhibitor, in terms of blend miscibility and rheology. Both the uninhibited and inhibited blends are found to be largely immiscible with very limited miscibility in HX2000-rich phase. No strong evidence indicates the occurrence of transesterification in the blends in the solid state. Dynamic rheological behaviour, such as shear storage modulus (G') and shear loss modulus (G") as a function of frequency, of the blends are interpreted by a three-zone model. HX2000 shows terminal-zone and plateau-zone behaviour, whilst Vectra A950 shows plateau-zone and transition-zone behaviour. The un- inhibited blends show plateau-zone behaviour up to 50% Vectra A950 content and the inhibited blends show plateau-zone behaviour up to 60% Vectra A950 content. Compositional dependence of the complex viscosities of the uninhibited and inhibited blends displayed positive deviations from additivity, which is a characteristic feature for the immiscible thermoplastic blends. When under steady shear, both the uninhibited and inhibited blends show shear thinning behaviour and their viscosities decrease monotonically with the addition of Vectra A950. Compositional dependence of the steady shear viscosities of the two sets of blends displayed negative deviations from additivity and the uninhibited blends were more viscous than the inhibited blends for the full composition range. Although limited agreement with the Cox-Merz rule is found for the inhibited blends, these two sets of blends, in general, do not follow the rule due to their liquid crystalline order and two-phase morphology. Despite being immiscible blends, transesterification, such as polymerization, in the blends might occur during the rheological characterization, supported by the facts that uninhibited blends show HX2000-dominant behaviour at lower Vectra A950 content and are more viscous than the inhibited blends. The addition of transesterification inhibitor in such blends is advised if only physical mixing is desired.ired.

• Journal of the Korean Institute of Gas
• /
• v.10 no.3 s.32
• /
• pp.34-40
• /
• 2006

This paper presents the optimized design of O-rings with a rectangular groove and dovetails, which are strongly related on the sealing performance of LPG filling unit. The computed results on the optimal design are analyzed by non-linear MARC finite element program with Taguchi method. O-rings with 4 different groove models are analyzed for 3 different elastomeric materials. The design parameters are given to polymer materials, groove depth, groove width, and diameter of O-rings. The FEM computed results showed that the affection ratios of O-ring diameter and material property are the most influential parameter among the groove width, groove depth, and compression ratio. Thus, this paper recommends model III for a rectangular groove and model IV for a dovetail groove with a given gas supply pressure of 1.764 MPa.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.10
• /
• pp.1549-1554
• /
• 2010

Recently, plastic screws have replaced metal screws because of the former's light weight, thermal and electrical insulating properties, and anticorrosion characteristics. Plastic screws are usually produced by injection molding, which involves material shrinkage during the solidification of the polymer. This shrinkage results in the degeneration of the dimensional accuracy. In the present study, the effect of injection-molding conditions on the dimensional accuracy of plastic screws was investigated through a numerical simulation of injection molding; on the basis of this simulation, we could determine the mold-design parameters. The design of experiment was applied in accordance with the numerical analysis in order to optimize the injection-molding conditions with a view to improving the dimensional accuracy of the precision plastic screw.

• Journal of Biomedical Engineering Research
• /
• v.14 no.4
• /
• pp.307-314
• /
• 1993

Plasma protein adsorption is the first event in the blood-material interaction and influenc- es subsequent platelet adhesion towards thlㅈombus formation. Thiㅈomboembolic events are strongly influenced by surface characteristics of materials and fluid dynamics inside the blood pump. In vitro flow visualizaion and an amimal experiment with the moving actuator type TAH were Performed in order to investigate fluid dynamic effects on the protein adsorption. The diffel'encl level, j of shear rate inside the ventricle Lvere determined by consid- ering the direction of the major opening of four healt valves in the implanted TAH and the visualized flow patterns as well. Each ventricle of the explanted TAH was sectionalized into 12 segments according to the shear rate level. The adsorbed protein on each segment was quantified using the ELISA method after soaking in 2% (wye)SDS/PBS for two days. Adsorbed protein layer thicknesses Itvere measured by the Immunogotd method under TEM. The SEM observation show that right ventricle (RV) , immobilized with albumin, displayed different degrees of platelet adhesion on each segment, whereas the left ventricle (LV), grafted by PEO-sulronate, indicated nearly , iame platelet adhesion behavior, regardless of shear rates. The surface concentrations of adsorbed proteins in the low shear rate region are hlghel'than those in the high region, which was confirmed statistically. A modified adsorption model of plasma protein onto polyurethane surface was suggested by considering the effect of the fluid dynamic characteristics.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.20 no.2
• /
• pp.24-28
• /
• 2006

Electrochemical hydrogenation/dehydrogenation properties were studied for a single particle of a Mm-based(Mm : misch metal) hydrogen storage alloy($MmNi_{3.55}Co_{0.75}Mn_{0.4}Al_{0.3}$) for the anode of Ni-MH batteries. A carbon fiber microelectrode was manipulated to make electrical contact with an alloy particle, and the cyclic voltammetry and the galvanostatic charge/discharge experiments were performed. A single particle of the alloy showed the discharge capacity of 280[mAh/g], the value being 90[%] of the theoretical capacity. Data were compared with that of the composite film consisting of the alloy particles and a polymer binder, which is more practical form for Ni-MH batteries. Additionally, pulverization of the alloy particles are directly observed. Compared with the conventional composite film electrodes, the single particle measurements using the microelectrode gave more detailed, true information about the hydrogen storage alloy.

• Applied Chemistry for Engineering
• /
• v.8 no.1
• /
• pp.114-121
• /
• 1997

The positive active material for polymer film-battery was prepared by using polyphenlenediamine(PPD) synthesized in our lab. and 2,5-dimercapto-1,3,4-thiadiazole(DMcT) with various mixture ratio. The transference measurement of surface morphology and thermal stability of the prepared composite film was carried out by using SEM and TGA, respectively. Electrochemical property and electrical conductivity of the composite film were also measured by using cyclic voltammetry and four-probe method in dry box, respectively. The thermal stability of prepared composite film was up to $200^{\circ}C$. The electrical conductivity of the composite film increased and showed the highest value(about 3 S/cm) when doped at 0.4% $LiCIO_4$ solution. And we could confirm that DMcT was effective on reactivation of PPD through cyclic voltammogram.