• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.2
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• pp.106-111
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• 2007

In this research work attempts were made to study the bonding of thermo-plastics with adhesives using solar radiation. In order to study the curing behaviour necessary experiments were conducted under varying conditions of temperature, exposure time and power of solar energy. The cured samples were then studied under the optical microscope before subjecting to tensile testing in order to study their mechanical properties of thermo-plastics. The fracture surfaces were further studied under the Scanning Electron Microscopy(SEM) in order to research the microstructural changes that are taken place during curing. In order to measure the performance of solar energy cured joints the parameters such as; bond strength, surface morphology, the microstructual changes, variation in properties of adhesives bonded joints are compared to that of specimen cured at ambient conditions and specimen cured using microwave techniques.

• Tribology and Lubricants
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• v.8 no.1
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• pp.48-55
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• 1992

The friction characteristic of plastics (PTFE, Nylon, Acetal and phenolic) was studied on the lubricated condition with a pin on disk machine. Mineral oil without additive (base oil) and water were used as liquid lubricants at the controlled temperature. From the experimental work, it was found out that the coefficient of friction of plastics was controlled by the mechanical properities of plastic more than that of liquid for various load and temperature. Viscosity of liquid has affected on the friction only at low temperature under lighb load. Among the tested plastics, the coefficient of friction of PTFE was the lowest under light load and at low temperature while Nylon at medium load and temperature, and Acetal at heavy load and high temperature. The coefficient of friction of soft plastics like PTFE and Nylon were increased as the load and temperature were increased, while that of hard plastic (Acetal) was decreased and that of thermo setting plastic (phenolic) was mixed. Also for soft plastics, the coefficient of friction under heavy load was always higher than that under light load, while hard plastic was vice versa.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.235-238
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• 2003

Thermo-plastic has generally bad electrical characteristics at high temperature comparing to thermoset-plastics when the plastic apply to electrical power apparatus as an electrical insulator. To solve the problem, we study engineering plastics such as Polyamide and Polyphthalamide as a base resin. And filler of the engineering plastics is glass fiber. Electrical characteristics studied are permittivity, loss factor and breakdown strength according to temperature and frequency of measuring signal. Electrical characteristics of Polyphthalamide has good temperature and frequency dependency comparing to those of Polyamide.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.7
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• pp.99-104
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• 2009

Creep characteristic is an important failure mechanism when evaluating engineering materials that are soft as polymers or used as mechanical elements at high temperatures. One of the popular thermo-elastic plastics, Polyethylene(PE) which is used broadly for engineering purposes, as it has good properties and merits compared to other plastics, was studied for creep characteristic at various level of stresses and temperatures. From the experimental results, the creep limit of PE at room temperature is 75% of tensile strength. Also the creep limits decreased exponentially as the temperatures increased, up to 50% of the melting point. Also the secondary stage among the three creep stages was nonexistent nor was there any rupture failure which occurred for many metals.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.6
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• pp.42-49
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• 2009

The optical elements made of plastics are normally produced by mass production such as injection molding with use of precision dies and molds. It costs to prepare the dies and molds, and it is only justified to prepare such expensive dies and molds when the parts are massively produced. On the other hand, it is too expensive and inefficient when precision plastic parts are needed only in small quantities, such as a case of trial manufacturing of new products. An ultra-precision diamond cutting is one of promising processes to produce the precision plastic parts in such cases. But it is commonly believed that an ultra-precision cutting of plastics for optical components is very difficult, because they are thermo-plastic material. In the present research, an ultra-precision diamond cutting of polycarbonate (PC), that is one of typical optical materials, was tried by using elliptical vibration cutting method. It is experimentally proved that good optical surfaces were obtained by using elliptical vibration cutting in cases of grooving and flat surfaces. The maximum surface roughness of less than 60 nm in peak to valley value is acquired.

• Journal of the Korean Society for Nondestructive Testing
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• v.10 no.2
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• pp.50-55
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• 1990

Flaws in GFRP(Glass Fiber Reinforced Plastics) were thermally detected using cholesteric liquid crystals. Presence of flaws changes the thermal conductivity of GFRP, and disturbs heat flow. When a uniform heat source is applied, the surface temperature of flawed region is different from that of sound region. The surface temperature distributions were measured by thermo-optic properties of liquid crystal. Since the colors of liquid crystal indicate temperature distribution of GFRP surface, the thermal disturbance by flaws could be detected. The locations of flaws in GFRP could be determined from the distribution of liquid crystal colors.

• Proceedings of the Korean Institute of Resources Recycling Conference
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• 2006.09a
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• pp.39-54
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• 2006

An experimental study on the hydro-cracking of recycling oil obtained from refused plastics was performed for up-grading of its fuel characteristics. Major experimental parameters were reaction temperature ($300^{\circ}C{\sim}700^{\circ}C$) and presence of catalysts (Al-Si, activated carbon, zeolite). The effect of the experimental parameters on the liquid product characteristics such as flash point, kinetic viscosity, and solid content was investigated. The hydro-cracking reactions of the recycling oil at $300^{\circ}C{\sim}400^{\circ}C$ improved the oil characteristics of the liquid products. Activated carbon was revealed as a stable and active catalyst in the hydro-cracking reaction at a temperature range investigated.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.34-37
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• 2004

In the present research, a ultra-precision diamond cutting of thermo-plastic materials, polycarbonate (PC) and cyclic olefin polymer (COC), is carried out by applying a method named ultrasonic elliptical vibration cutting developed by the authors. It is experimentally proved that good optical surfaces are obtained by applying the elliptical vibration cutting in cases of machining of flat surfaces and grooves as compared with the conventional diamond cutting. The maximum surface roughness in peak to valley value obtained is less than 60 nm and 20 nm for PC and ZEONEX, respectively.

• Carbon letters
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• v.7 no.2
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• pp.87-96
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• 2006

This paper describes the physical properties of filled Nylon6 composites resin with nano-sized carbon black particle and graphite nanofibers prepared by melt extrusion method. In improving adhesions between resin and fillers, the surface of the carbon filler materials were chemically modified by thermo-oxidative treatments and followed by treatments of silane coupling agent. Crystallization temperature and rate of crystallization increased with increases in filler concentration which would act as nuclei for crystallization. The silane treatments on the filler materials showed effect of reduction in crystallization temperature, possibly from enhancement in wetting property of the surface of the filler materials. Percolation transition phenomenon at which the volume resistivity was sharply decreased was observed above 9 wt% of carbon black and above 6 wt% of graphite nanofiber. The graphite nanofibers contributed to more effectively in an increase in electrical conductivity than carbon black did, on the other hand, the silane coupling agent negatively affected to the electrical conductivity due to the insulating property of the silane. Positive temperature coefficient (PTC) phenomenon, was observed as usual in other composites, that is, temperature increase results conductivity increase. The dispersity of the fillers were excellently approached by melt extrusion of co-rotational twin screw type and it could be illustrated by X-ray diffraction and SEM.

• Advanced Composite Materials
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• v.16 no.4
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• pp.335-347
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• 2007

Green composites composed of long maize fibers and poly $\varepsilon$-caprolactone (PCL) biodegradable polyester matrix were manufactured by the thermo-mechanical processing termed as 'Sequential Molding and Forming Process' that was developed previously by the authors' research group. A variety of processing parameters such as fiber area fraction, molding temperature and forming pressure were systematically controlled and their influence on the tensile properties was investigated. It was revealed that both tensile strength and elastic modulus of the composites increase steadily depending on the increase in fiber area fraction, suggesting a general conformity to the rule of mixtures (ROM), particularly up to 55% fiber area fraction. The improvement in tensile properties was found to be closely related to the good interfacial adhesion between the fiber and polymer matrix, and was observed to be more pronounced under the optimum processing condition of $130^{\circ}C$ molding temperature and 10 MPa forming pressure. However, processing out of the optimum condition results in a deterioration in properties, mostly fiber and/or matrix degradation together with their interfacial defect as a consequence of the thermal or mechanical damages. On the basis of microstructural observation, the cause of strength degradation and its countermeasure to provide a feasible composite design are discussed in relation to the optimized process conditions.