• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.10a
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• pp.549-550
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• 2012

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.1347-1348
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• 2013

• 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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.2
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• pp.279-285
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• 2013

The feasibility of substituting a composite mold for an aluminum mold in the fabrication of a small ship propeller was investigated. A small three-blade aluminum propeller was used as a plug for manufacturing the composite mold. A GRPG composite mold and propeller were made from an unsaturated polyester resin, Epovia gelcoat, and woven and mat glass fibers using the compression and vacuum method at room temperature. The hardness and surface roughness and the strength and deformation of the compression and suction molds were experimentally determined. The results were compared with the ISO 484/2 standard and some aluminum alloy materials. The results showed that the deformation of the mold satisfied the tolerance of the thickness of the blade. Some characteristics of the GRPG composite mold were better than those of the aluminum alloy mold (surface smoothness, weight, performance, and cost), and some characteristics were similar (detachment ability and life-cycle). Therefore, the composite mold is considered suitable for the fabrication of a small composite ship propeller.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.18 no.4
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• pp.310-317
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• 2008

The objective of the survey is to define and judge exposure profiles semi-qualitative data in high risk processes using styrene. The survey was conducted on 98 factories out of 229 factories based on data from periodic working environment monitoring for styrene. Styrene is widely utilized as a raw material for PS and co-polymers such as ABS, SAN, SBR, SBL, unsaturated polyester resins(UPR) and others. An approximate breakdown of styrene's markets in Korea is PS 30%, expandable PS 17%, ABS 33%, SAN 5%, SBL 4%, SBR 3%, UPR 1% and other 7%. Although UPR accounts for 1% of total amount of styrene, workers dealing with it are exposed to very high concentrations up to 64 ppm. Especially styrene is widely used in the laminating process of fiberglass reinforced plastics(FRP) manufacturing industry. The Applications using styrene are largely classified into two sections which are applied to styrene monomer(SM) and UPR. SM is utilized for a raw material of resins, surfactant and adhesive. UPR is employed for FRP and non-FRP. For SM control targets are mixing colors and packing in the gelcoat resins manufacturing industry(MI), for UPR control targets out of works using UPR are 1) laminating in the MI of plastics, automobile parts and boats, 2) mixing and packing in the SMC/BMC MI, 3) molding and cutting in the other specific plastics MI, 4) mixing and coating in artificial marble product MI, 5) dipping in the electric motors & transformers MI, 6) molding in the button MI, 7) painting in the musical instrument MI. Findings from the study have given the information for the high risk processes and working practices so that occupational health professionals could focus on targeted workplaces to prevent occupational diseases. It is also useful to develop a control strategies and specific controls for high risk processes and facilities using styrene.