• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2004.05a
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• pp.546-549
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• 2004

This paper describes the electrical characteristics of the polymer lightning arresters(L.As) used to protect distribution lines and power facilities from surge. For the relative comparison, the characteristics assessment was done for 2 states of L.As before and after water immersion treatment. The L.As for the comparative test were immersed with water of $95[^{\circ}C]$ considered a severe condition. After the immersion treatment, the assessment was carried out for material analyses in chemical structure(FTIR : fourier transform infrared spectrophotometer). Electrical performance measured insulation resistance measurement, leakage current measurement, critical operation voltage measurement etc.. In addition to, the results were compared with those for the L.As deteriorated in the field. Thus, the accelerative deterioration degree of polymer materials by immersion treatment was evaluated, by which the structural defects of the polymer L.As could be inferred.

• Journal of the Korea Institute of Military Science and Technology
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• v.7 no.1
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• pp.5-12
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• 2004

This paper includes the comparative study between Cr plating and nitriding process with an aim at improving corrosion, wear and maintainability for KNR(Korean Next Generation Rifle) 5.5mm barrel. The endurance test was conducted to compare the performance of standard barrel, Cr plating barrel and nitriding barrel. Main activities are described as follows; optimal Cr plating and nitriding process set-up for KNR 5.56mm barrel; durability test of each barrel(20,000 rounds); salt water immersion test; dispersion, initial velocity, inner diameter data acquisition. According to the results of this firing test, Cr plating barrel is superior to standard barrel and nitriding barrel in view of corrosion, wear and maintainability.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.5
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• pp.199-205
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• 2018

A geopolymer was produced from coal ash generated from an integrated gasification combined cycle (IGCC) plant and its water resistance was evaluated. For this purpose, the geopolymer specimens were immersed in water for 30 days to measure changes in microstructure and alkalinity of the immersion liquid. Particularly, the experiment was carried out with foaming status of the geopolymers and parameters of room temperature aging condition, and immersion time. The foamed geopolymer containing 0.1 wt% Si-sludge had pores with a diameter of 1 to 3 mm and exhibited excellent foamability. Also, the calcium-silicate-hydrate crystal phase appeared in the foamed geopolymer. In the geopolymer immersion experiment, the pH of the immersion liquid increased with time, because the un-reacted alkali activator remained was dissolved in the immersion liquid. From the pH change of the immersion liquid, it was found that geopolymer reaction in the foamed specimen was completed faster than the non-foamed specimen. Through this study, it was possible to successfully produce foamed and non-foamed geopolymers recycled from IGCC coal ash. Also the necessary data for the safe application of IGCC coal ash-based geopolymers to areas where water resistance is needed were established; for example, the process conditions for room temperature aging time, effect of foaming status, immersion time and so on.

• Journal of Ocean Engineering and Technology
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• v.12 no.3 s.29
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• pp.31-41
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• 1998

Single fiber fragmentation technique was used to evaluate the change of interfacial properties by degradation of fiber tensile strength in the fiber reinforced composites. The influences of fiber tensile strength on the interfacial properties have been evaluated by the fragmentation specimens(weak fiber samples) of glass fiber/epoxy resin that was made using the pre-degraded glass fiber in distilled water at $80^{circ}C$ for specified periods. The effects of the immersion time on the interfacial properties in the distilled water at $80^{circ}C$ also have been evaluated by the fragmentation specimens(original fiber samples) of glass fiber/epoxy resin that was made using the received glass fiber. As the result, the tensile strength of glass fiber was decreased with the increasing of the treatment time in the distilled water at $80^{circ}C$ and the interfacial shear strength was independent of the change of the glass fiber strength in the single fiber fragmentation test. But in the durability test using the single fiber fragmentation specimen, interfacial shear strength decreased with the increasing of the immersion time in distilled water ar $80^{circ}C$. And it turned out that the evaluating of interfacial shear strength using original fiber tensile strength was valuable in the durability test for the water environment by the single fiber fragmentation technique.

• Composites Research
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• v.21 no.6
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• pp.1-7
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• 2008

The main objective of this study is to investigate the effect of salt water on the mechanical properties of a high modulus carbon-epoxy composite. Specimens were made of a carbon-epoxy composite UPN139B of SK Chemical and tested under inplane tension and shear after 0, 1, 3, 6, 9, and 12 months immersion in 3.5% salt water. Acceleration technique such as temperature elevation was not used. The tensile strengths and modulli in fiber and matrix direction did not show any remarkable degradation until 12 months immersion. In contrast to the tensile properties, shear strength and modulus started to gradually decrease up to about 10% of values of dry specimens after 12 months immersion. It was confirmed through the test that the material UPN139B can be an effective material for the shell structures in salt water to resist against the external pressure buckling because of the high fiber directional modulus and corrosion resistance.

• The korean journal of orthodontics
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• v.35 no.5 s.112
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• pp.361-370
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• 2005

Fiber reinforced composite (FRC) has been widely used in operative and prosthetic fields of dentistry and its use is expanding into the orthodontic field. The purpose of this study was to examine the changes of flexural properties of FRC reinforced with silica glass fiber (FibreKor, Jeneric/Pentron Inc.. Wallingford. U.S.A.) according to the duration of water absorption. Specimens were grouped according to their shape as round and rectangular cross sections, and were immersed in distilled water at room temperature $(23^{\circ}C)$ for 0 hour 1 hour 1 week. 15 days, 1 mouth and 3 mouths. The number of specimens was 5 for each duration and bending test was done using a torque tester The flexural stiffness after 24 hour water immersion was reduced to 59% for round specimens and 25% for rectangular specimens and after 3 mouths of water immersion it was reduced to 29% and 19% stiffness of the 0 hour-specimen respectively Yield flexural moment after 24 hour water immersion was reduced to 45%for round specimens and 76% for rectangular specimens and after 3 months of water immersion it was reduced to 29% and 60% stiffness of the 0 hour-specimen respectively Ultimate flexural moment after 24 hour water immersion was reduced to 35% for round specimens and 76% for rectangular specimens and after 3 mouths of water immersion it was reduced to 25% and 37% stiffness of 0 hour-specimen respectively. Those results suggested that the flexural stiffness of FibreKor decreased greatly after initial water immersion. Consequently, further research for the maintenance of strength against water will be necessary

• Journal of Ocean Engineering and Technology
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• v.20 no.2 s.69
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• pp.52-58
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• 2006

The effect of various environmental conditions on the durability of E-glass fiber/vinylester resin composites have been investigated using the tensile test specimen of strand type. It was found that the durability test method performed by the stand type specimen was more convenient and reliable than other conventional test method. The weight gains increased with the immersion time in both water and alkaline solution, and the Weight gains at $50^{\circ}C$. were much bigger than those at $20^{\circ}C$ in both conditions. The tensile strength decreased with the pass of immersion time in all aqueous solution, and the tensile strength at $80^{\circ}C$ in alkaline solution decreased very steeply at beginning of immersion time. The decrement of tensile strength according to the immersion time in various environmental conditions was mainly caused by the degradation of interface and the damage of glass fiber surface.

• International Journal of Highway Engineering
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• v.19 no.5
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• pp.13-20
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• 2017

PURPOSES : This research was a laboratory study for evaluating the Reclaimed Asphalt Pavement (RAP) mixture added developed rejuvenator for warm mix recycling. Waste asphalt mixtures occupy about 18.2% of construction wastes in Korea. Moreover, most rejuvenators were imported from Europe or the U.S. Therefore, improving usage of RAP with a developed rejuvenator material provides environmental protection at a reduced cost. METHODS : The specimen used for this experiment was performed by only using RAP. A suitable rejuvenator for Target PG was then added. In addition, a conventional rejuvenator was selected to compare performance and specimens introduced with the same procedure as the developed rejuvenator was prepared. In order to evaluate rutting resistance and water susceptibility, we conducted a deformation strength test, a tensile strength ratio test, and a dynamic immersion test with the prepared mixtures. RESULTS :Laboratory test results indicated that both the developed additive and conventional additive improved performance of the recycled asphalt mixtures compared to mixtures without the rejuvenator. In addition, the deformation strength test and TSR test results satisfied standards for domestic recycling asphalt mixtures. The dynamic immersion test showed that the developed rejuvenator has superior scaling resistance than the conventional rejuvenator. CONCLUSIONS : In terms of rutting resistance and moisture susceptibility, the warm mix recycled asphalt mixtures with the developed rejuvenator appeared to effectively recovered performance.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.358-363
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• 2003

Spot welded structure is operated in diverse situation because of temperature, humidity and precipitation. In addition factors of environmental pollution such as acid rain, that courses corrosion, have the tendency to increase, But spot welded structure strength is affected by dampness and environment temperatures. Therefore, it is important to evaluate effect of temperature of spot welded part, In this study, the strength distribution of spot welded plates is evaluated about the environmental temperature of zine coated steel plates and test is conducted with welded part immersed in distilled and synthetic sea water. Specimens are immersed into water for 10, 100, 500 and 1000hours to evaluate the effects of water immersion time on tensile-shear strength under the conditions of -40, 0, 20 and $50^{\circ}C$. Strength is evaluated by tensile-shear test. The conditions of spot welding are 240kgf electrode force, 10KA welding current with 0 and 5mm clearance. From this study, spot welded specimens with clearance have lower tensile-shear strength in the distilled water or synthetic sea water comparing with spot welded specimens without clearance. And they have lower tensile-shear strength under $-40^{\circ}C$ and over $50^{\circ}C$.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.852-858
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• 2007

The durability of carbon/epoxy composites under salt water environment was investigated through salt water spray tester. Salt water environment was obtained through salt spray and salt immersion. 5% NaCl solution was used for salt water as natural salt water. Mechanical test was performed to obtain tensile properties, flexural properties, and shear properties of carbon/epoxy composite over 12 months under salt water environment. Dynamic mechanical analyzer was used to investigate thermal analysis properties such storage modulus, loss modulus, and tan ${\delta}$. Also FT/IR test was conducted to investigate a change in chemical structure. According to the results, mechanical properties were found to be slowly degraded as a function of exposure times. Regarding to thermal analysis properties, storage modulus was insensitive to exposure times, but loss modulus was shown to be slightly decreased. Although the shape and location of peak in FT/IR were not much changed, the intensity of peak in FT/IR was affected on exposure times. We also found that salt water immersion was more severe to the durability of carbon/epoxy composite rather than salt water spray.