• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.4
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• pp.153-160
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• 2001

In order to analyze the degradation process of epoxy/glass fiber for outdoor condition, FRP laminate was exposed to high temperature. Then, the degradation process was evaluated by comparing contact angle, surface potential, surface resistivity, and XPS. The experimental results showed that the amount of weight loss, contact angle, surface potential and surface resistivity increased up to 200 $^{\circ}C$ as a function of temperature. These phenomena show the existence of hydrophobic surface. With the change to the hydrophobic surface and the electrical potential and resistivity on FRP surface increased. In XPS to analyze surface chemical structures, the increased hydrophobicity in thermal increase of unsaturated double bond in carbon chains. Aslo, thermal treatment caused the discoloration on the point of treated surface. These phenomena were attributed to the generations of ether group.

• Elastomers and Composites
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• v.50 no.3
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• pp.175-183
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• 2015

A series of fluorinated aromatic poly(hydroxyamide)s (PHAs) were synthesized by direct polycondensation of diacides containing 2,6-dimethylphenoxy group and quinoxaline ring in the main chain with 2,2-bis-(3-amino-4-hydroxyphenyl) hexafluoropropane. The PHAs had relatively low inherent viscosities in the range of 0.35~0.43 dL/g at $35^{\circ}C$ in DMAc solution. All PHAs exhibited excellent solubility in aprotic solvents such as NMP, DMAc, DMF and DMSO as well as in common organic solvents such as pyridine, THF, and m-cresol at room temperature. However, the poly(benzoxazole)s (PBOs) were quite insoluble in all organic solvents except partially soluble in concentrated sulfuric acid. The PBOs showed glass transition temperatures between 233 and $284^{\circ}C$ by DSC and maximum weight loss temperatures in the range of $536-546^{\circ}C$ by TGA.

• Elastomers and Composites
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• v.43 no.4
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• pp.264-270
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• 2008

$\alpha$-D-mannosyl fullerene[$C_{60}$]-functionalized gold nanoparticle films were selfassembled using the layer-by-layer method on the reactive of glass slides functionlized with 3-aminopropyltrimethoxysilane. The functionalized glass slides were alternately soaked in the solutions containing $\alpha$-D-mannosyl fullerene[$C_{60}$] and 4-aminothiophenoxide/hexanethiolate-protected gold nanoparticles. $\alpha$-D-mannosyl fullerene[$C_{60}$]-functionalized gold nanoparticle films have grown up to 5 layers depending on the immersion time. The self-assembled nanoparticle films were characterized using UV-vis spectroscopy showed that the surface plasmon band of gold at 530 nm gradually became more evident as successive layers were added to the films.

• Journal of the Korean Wood Science and Technology
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• v.27 no.2
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• pp.15-22
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• 1999

Polymeric meterials that are used for noise and vibration damper in wood/polymer/wood sandwich composites, must have a high loss factor(tan ${\delta}$), and at the same time the storage modulus(E) of $5{\times}10^7$ to $10^9$ dyne/$cm^2$ must withstand over a wide temperature and frequency ranges. In this study, the series of epoxy resinlpolyacrylate interpenetrating polymer networks(IPNs) were synthesized by simultaneous polymerization. Their dynamic tensile properties were measured at 110Hz using Rheovibron instrument. Composite damping factor(tan ${\delta}_c$) and dynamic bending modulus($E_c,\;E_^{\prime\prime}c$) of wood/polymer/wood sandwich composites were measured at 110Hz using a Rheovibron in bending mode of vibration. These dynamic tensile studies indicated that cured epoxy resin/polyacrylates IPNs were semicompatible in the sense that both the shifting of T($E^{\prime\prime}_{max}$) or T(tan ${\delta}_{max}$) and the broadening of glass transition temperature range were observed. Especially, the cured Epikote871/P(n-BMA) IPNs of composition 70/30 to 50/50 showed a relatively high tan a and appropriate E' value over a wide temperature range; consequently the tan a e curves of wood/IPNs/wood sandwich composites was broadened over a wide temperature range.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.6
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• pp.3990-3996
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• 2014

Because the physical properties can be decreased when a Nylon 66/glass fiber composite is injected into a mold over $300^{\circ}C$, a systematic study of the thermal history in the case of re-use is needed. Nylon 66/glass fiber extrudates as a function of the extrusion number were prepared using a twin screw extruder at 305/290/273/268/265/$260^{\circ}C$. The chemical structure, thermal properties, melt index, crystal structure, Izod impact strength, and rheological properties were measured by Fourier transform infra-red (FT-IR), melt indexer, DSC, TGA, XRD, Izod impact tester, and dynamic rheometer. The FT-IR spectra indicated that the number of extrusions did not affect the chemical structure. The decrease in molecular weight with increasing extrusion number was confirmed by the melt index and the complex viscosity of extrudates. Based on the DSC and TGA results, the thermal history had no effect on the melting temperature, regardless of the number of extrusions, but the degradation temperature decreased up to $20^{\circ}C$ with increasing extrusion number. The Izod impact strengths of the extrudates were found to decrease with increasing extrusion number. No structural change after extrusion was also confirmed because there was no change in the slope and shape of the G'-G" plot.

• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.169-177
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• 2018

Glass fiber reinforced polyester (GFRP) composites are widely used as structural materials in harsh environment such as underground pipes, tanks and boat hulls, which requires long-term water resistance. Especially, these materials might be damaged due to delamination between gelcoat and composites through an osmotic process when they are immersed in water. In this study, GFRP laminates were prepared by surface treatment of UPE (unsaturated polyester) gelcoat by vacuum infusion process to improve the durability of composite materials used in underground pipes. The composite surface coated with gelcoat was examined for surface defects, cracking, and hardness change characteristics in water-immersion environments (different temperatures of $60^{\circ}C$, $75^{\circ}C$, and $85^{\circ}C$). The penetration depth of cracks was investigated by micro CT imaging according to water immersion temperature. It was confirmed that cracks developed into the composites material at $75^{\circ}C$ and $85^{\circ}C$ causing loss of durability of the materials. The point at which the initial crack initiated was defined as the failure time and the life expectancy at $23^{\circ}C$ was measured using the Arrhenius equation. The results from this study is expected to be applied to reliability evaluation of various industrial fields where gelcoat is applied such as civil engineering, construction, and marine industry.

• International Journal of Automotive Technology
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• v.4 no.4
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• pp.203-211
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• 2003

This paper describes a method for a falling weight impact test to estimate the impact energy absorbing characteristics and impact strength of CFRP (Carbon-fiber reinforced plastics) laminate plates based on considerations of stress wave propagation theory, which were converted to measurements of load and displacement verses time. The delamination area of impacted specimens for the different ply orientations was measured with an ultrasonic C-scanner to determine the correlation between impact energy and delamination area. The energy absorbed by a quasi-isotropic specimen having four interfaces was higher than that of orthotropic laminates with two interfaces. The more interfaces, the greater the energy absorbed. The absorbed energy of a hybrid specimen embedding GFRP (Glass-fiber reinforced plastics) layer was higher than that of normal specimens. Also, a falling weight impact tester was built to evaluate the characteristics and impact strength of CFRPs.

• Journal of Technologic Dentistry
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• v.29 no.1
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• pp.23-34
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• 2007

The quantity of MgO in the Zirconia of 20wt% Frit has been varied and the sintering temperature has been differentiated to monitor the changes in the mechanical features. The rise of sintering temperature from 1100$^{\circ}C$ to 1300$^{\circ}C$ was followed by higher sintering density. And, at a sintering temperature, the increase of the quantity of MgO was followed by lower sintering density. The bending strength has been lowered as the quantity of MgO increases in the Zirconia of 20wt% Frit, which seems to be because the MgO functions as impurities degrading the mechanical features. In terms of micro-structure analysis, the pore has been greatly enlarged, while the density varied very little, when the MgO of 3wt% was added. The size of pore became smaller as the added quantity of MgO increased larger in the sequence of 5wt% and 7wt%. But, the pore-generating rate became higher as the added quantity of MgO increased in the sequence of 3wt%, 5wt% and 7wt%. Thus, it is possible to summarize that the small quantity of MgO, say, of 3wt%, promotes the grain growth, and the large quantity of MgO, say, of 7wt%, hinders the grain growth. Also, if the quantity of MgO exceeds some level, the MgO hinders substances from moving, which, ultimately, keeps blowholes from becoming enlarged or extinct, and makes pores small and dispersed in broad area. In conclusion, the study on the change in the size of pore shows that the larger the quantity of MgO is, the more the micro pores are, thereby degrading the mechanical features.

• Korean Journal of Materials Research
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• v.16 no.4
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• pp.235-240
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• 2006

We investigated the effect of ZnO filler on the microstructure of $BaO-B_2O_3-ZnO-P_2O_5$ glass system to find an etching mechanism of barrier ribs. The sintering behavior of composites heated in the temperature range $560-600^{\circ}C$ was studied by volumetric shrinkage rate and microstructure. The etching test was carried out in $HNO_3$ solution at $50^{\circ}C$ for 10 min. The volumetric shrinkage of sintered sample decreased with the increased firing temperature because of the formation of two crystals. Glass and ZnO filler react forming the $BaZn_2(PO_4)_2$ crystal phases during the sintering process. Etching phenomenon of sintered samples by $HNO_3$ showed that the $BaZn_2(PO_4)_2$ crystal phase was strongly leached compared to glass matrix, crystal phases and fillers. Therefore, the control of interface by condition of sintering is so important to achieve etching effect in barrier ribs.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.6
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• pp.567-573
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• 2015

This paper aims to evaluate the variation in the mechanical properties of carbon/epoxy composites under in situ low- and high-temperature environments. In situ low- and high-temperature environments were simulated with temperature ranging from $-40^{\circ}C$ to $220^{\circ}C$ using an environmental chamber and furnace. The variation in the mechanical properties of the composites was measured for longitudinal and transverse tensile properties, in-plane shear properties and interlaminar shear strength. Under the low temperature of $-40^{\circ}C$, all mechanical properties increased moderately compared to the baseline properties measured at room temperature. The changes in the longitudinal tensile properties decreased moderately with increasing temperature. However, transverse tensile properties, in-plane shear properties and interlaminar shear strength each showed a significant drop due to the glass transition behavior of the matrix after $140^{\circ}C$. Notably, the tensile property value near $100^{\circ}C$ increased compared to baseline property value, which was an unusual occurrence. This behavior was a direct result of post-curing of the epoxy resin due to its exposure to high temperature.