• Polymer(Korea)
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• v.27 no.2
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• pp.113-119
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• 2003

The thermal properties and crystallization behaviors of poly(ethylene terephthalate) (PET) were investigated by controlling the annealing conditions of PET sample, such as relative humidity, temperature, and time. The variations of moisture content, glass transition temperature ($T_g$) and cold crystallization temperature ($T_{\propto}$) were examined after annealing the PET sample. Subsequently crystallization process was performed with the annealed PET specimen, and then the degree of crystallinity and heat distortion temperature (HDT) of variously crystallized PET specimen were examined. Residual stress relaxation in the injection molded PET sample after annealing was also observed through polarized films. Moisture content in the PET specimen increased up to 6000 ppm with increasing the relative humidity, temperature, and time of annealing. $T_g$ and $T_{\propto}$ of the annealed PET specimen decreased with increasing moisture content. The degree of crystallinity increased as increasing moisture content in the PET specimen. However for same moisture content, the degree of crystallinity varied with annealing conditions. The relaxations of residual stress in the PET sample differed from annealing conditions, and the maximum degree of crystallinity increased with decreasing residual stress in the PET sample.

• Applied Chemistry for Engineering
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• v.16 no.4
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• pp.502-506
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• 2005

In the presence of various clays, nylon/clay nanocomposites were synthesized by anionic polymerization of ${\varepsilon}$-caprolactam (CL) via monomer casting method. The effect of each clay on polymerization reaction was investigated and the change in gallery structure of clays during polymerization was analyzed by X-ray diffraction. When the three kinds of organo-clays were used in the amount of 2 wt% of CL, polymerizations were not successful due to an increase in viscosity during polymerization. Significant changes were not observed in the mechanical and thermal properties of the composites containing organo-clays with 1 wt%. On the other hand, composites containing natural clay up to 5 wt% were successfully prepared, and the composite with 5 wt% showed a decrease in tensile strength and elongation, and remarkable improvement in thermal properties.

• Composites Research
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• v.23 no.6
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• pp.32-38
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• 2010

The effect of the atmospheric pressure plasma(APP) treatments is experimentally investigated to ascertain the optimum condition to yield the best adhesive properties between a polyamide woven fabric and acrylonitrile butadiene rubber(NBR). For the atmospheric pressure flame plasma(APFP) treatment, the optimum number of treatment at given conditions is 2 times. The thermal deformation of the fabric is more serious with increasing the number of APFP treatment. The adhesive strength of the case with APFP treated fabric is increased about 35% when compare to the case with non-APFP treated one for the interface(bonding agent one or two coatings). When the surface is coated twice with the bonding agent, the adhesive energy with APFP treated fabric is increased about 4 times. It was found that the surface modification of polyamide woven fabric by APFP treatment is a fast, economic and applicable method to improve the adhesive properties between woven fabric and rubber when compared to other APP treatments.

• Journal of the Korea Concrete Institute
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• v.17 no.2 s.86
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• pp.247-254
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• 2005

Recently, since the advanced nano technology develops unique physical and chemical properties different from those of the conventional materials. Normal concretes mixed with nano - $SiO_2$ have been studied to improve the fire-resistance with high strength and lower heat conductivity. In this pilot study, the nano-particle contents in the specimens (${\Phi}100{\times}200 mm$) were 0, 2, 4, and $6\%$ by weight of cement, and fire-temperatures $200^{\circ}C$, $500^{\circ}C$, and $800^{\circ}C$ were considered. The results show that as the nano-particle contents increases, the weight loss of concrete gradually decreases, and the compressive strength after fire-attack increases effectively.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2015.11a
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• pp.162-163
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• 2015

Thermal deformation behavior of high-strength concrete (HSC) exposed to fire is different from that of normal strength concrete (NSC). In case of ultra-high-strength concrete (UHSC), it is well known that thermal deformation behavior is greater than HSC. With increasing research of UHSC in buildings, it is necessary to understand the performance of UHSC at elevated temperatures considering loading condition. Therefore, evaluation on properties of thermal strain behavior properties of ultra high strength concrete by loading and high temperature was conducted.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.145-148
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• 2003

Thermal characteristics according to the bearing preload arc studied for the four type spindles with high frequency motor. For the analysis. three dimensional models are built considering heat transfer characteristics such as natural and forced convection coefficients, Bearing and motor are main heat generation, and heat generation by ball bearings as a function of load. viscosity and gyroscopic moment effect are considered. Unsteady-state temperature distributions and thermal displacements according to the bearing preload are analyzed by using the finite clement method.

• Proceedings of the Korean Geotechical Society Conference
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• 1994.03b
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• pp.47-62
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• 1994

Polyol을 주성분으로 하는 A액과 MDI계 isocyanate로 구성된 B약을 배합비와 배합속도를 각각 1:2에서 1:4까지, 300rpm에서 900rpm까지 변화시키면서 혼합하였다. 생성된 foamed polyurethane은 600rpm의 배합속도에서 배합비가 1:2에서 1:4로 감소함에 따라 발포율이 증가하는 현상을 보였다. 300rpm의 배합속도에서는 거의 발포가 되지 않았음, 900rpm의 배합속도에서는 발포는 되었으나 brittle한 물성을 보였다. 열변형온도 및 하중에 대한 변형율은 600rpm에서 1:2에서 1:3의 배율시 가장 우수한 것으로 관찰되었다.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.193-197
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• 2008

Array of micro-dimple on polyoxymethylene (POM) surface was fabricated using Q-switched Nd:YAG laser and its characteristics were studied in terms of heat affected zone (HAZ), dimple geometry, and the effect of specimen surface roughness. Process parameters such as lamp current, process time, and the stream of air in order to minimize HAZ and flow of molten polymer into cavity were extensively studied in this work. Dimple geometry was further investigated by 3-D optical microscopy to provide deep insight into morphological analysis near the dimples. This paper also presents the applicapability of micro-dimples in polymeric tribological system, such as a thrust bearing. Micro-dimples were expected to provide low coefficient of friction and enhanced lubricity at the sliding interface.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2015.05a
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• pp.80-81
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• 2015

Thermal deformation behavior of high-strength concrete (HSC) exposed to fire is different from that of normal strength concrete (NSC). In case of ultra-high-strength concrete (UHSC), it is well known that thermal deformation behavior is greater than HSC. With increasing research of UHSC in buildings, it is necessary to understand the performance of UHSC at elevated temperatures considering loading condition. Therefore, evaluation on properties of thermal strain behavior properties of ultra high strength concrete by loading and high temperature was conducted.

• Journal of Energy Engineering
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• v.23 no.3
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• pp.116-124
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• 2014

In the plants operated under high temperature condition, piping system load analysis is often performed to prevent accidents caused by thermal deformation and also to locate inspection prioritity points of the piping system. In this study, piping system stress analysis was performed for a pipe system between the reactors in a process plant. The piping system includes typically installed hangers and expansion joints. In order to evaluate the effects of structural components such as hangers and expansion joints, the case for the expansion joint or the hanger under abnormal operation is considered. By comparison anlaysis results of piping system during normal operation and abnormal operation, the role of each pipe components are studied.