• Polymer(Korea)
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• v.37 no.5
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• pp.557-562
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• 2013

The thermal expansion and mechanical properties of diglycidyl ether of bisphenol A (DGEBA) with mercaptan hardeners were studied by a comparative method with an amine-adduct type hardener. Thermal expansion and dynamic mechanical properties were measured by thermo mechanical analysis (TMA) and dynamic mechanical ananlysis (DMA), respectively. The $T_g$ and the coefficient of thermal expansion (CTE) of epoxy/amine-adduct type hardener system were $82.6^{\circ}C$ and 71.2 $ppm/^{\circ}C$, respectively. As the number of -SH functional group of mercaptan hardener increased, the $T_g$ rapidly decreased and gradually increased up to ca. $80^{\circ}C$ and the CTE under the $T_g$ rapidly increased to ca. 200 $ppm/^{\circ}C$ from 80 $ppm/^{\circ}C$ and decreased to ca. 100 $ppm/^{\circ}C$. The crosslinking density of epoxy with amine-adduct type hardener was ca.1.5 $mol/cm^3$, while that of epoxy with mercaptan hardeners increased from 1.0 to 1.7 $mol/cm^3$, as the number of -SH functional group increased. The storage modulus can increase up to 2700MPa at $30^{\circ}C$.

• Polymer(Korea)
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• v.24 no.5
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• pp.599-609
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• 2000

In order to improve the mechanical properties of unsaturated polyester (UPE) resins, the UPE resins with different glycol molar ratios were prepared. The effects of molar ratios of the UPE resins on the curing behaviors and mechanical properties were investigated. The microgel reaction mechanism was employed to characterize the system. It was found that the final conversion increased with increasing NPG molar ratios, and the conversion at the peak of differential scanning calorimetry (DSC) thermogram appeared to decrease with increasing NPG molar ratios. The flexural strength, tensile modulus, water resistance, and infiltration increased with increasing NPG content, but the tensile strength, tensile elongation, and flexural modulus decreased. Among the UPE resins prepared from the glycols with the molar ratios (PG/NPG) of 0.5/0.5, 0.25/0.75, those of laminated composites plates showed better mechanical properties.

• Applied Chemistry for Engineering
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• v.5 no.6
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• pp.1030-1035
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• 1994

Curing behavior and glass transition temperatures of epoxy resins into which reactive diluents were added to control processability were investigated. Heat of cure generated of the epoxy resin was reduced with butyl glycidyl ether(BGE) and phenyl glycidyl ether(PGE) contents. $T_g$ of the resin was decreased with the amount of reactive diluents and it was attributed to increased molecular weight between crosslink points. Cure kinetics of the resins was studied employing autocatalytic reaction model and found that reaction constants decreased as the contents of reactive diluent was increased.

• Geotechnical Engineering
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• v.10 no.3
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• pp.17-32
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• 1994

To model the anisotropic behavior of soils in the case of reverse loading, an anisotropic hardening description is proposed on the basis of generalized isotropic hardening(GIH) rule. There is a core of the GIH rule in the allowance of the concept that the center of homology of isotropic hardening can be any proper stress states inside a yield surface. The plastic deformations could be represented for the condition of reverse loading, and an explicit constitutive relationship was formulated by utilizing a simple hardening function. The proposed hardening description has been compared with other anisotropic hardening models. For verification three sets of triaxial test results have been predicted for the drained and undrained behavior of overconsolidated clays and Ko consolidated clays.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.917-920
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• 2008

ECC is a special kind of high performance cementititous composite which exhibits typically more than 2% tensile strain capacity by bridging microcracks at a crack section. Therefore, micromechanics should be adopted to obtain multiple cracking and strain hardening behavior. This paper propose a linear elastic analysis method to simulate the multiple cracking and strain hardening behavior of ECC. In an analysis, the stress-crack opening relation modified considering the orientation of fibers and the number of effective fibers is adopted. Furthermore, to account for uncertainty of materials and interface between materials, the randomness is assigned to the tensile strength(${\sigma}_{fci}$), elastic modulus($E_{ci}$), peak bridging stress(${\sigma}_{Bi}$) and crack opening at peak bridging stress(${\delta}_{Bi}$), initial stress at a crack section due to chemical bonding, (${\sigma}_{0i}$), and crack spacing(${\alpha}_cX_d$). Test results shows the number of cracking and stiffness of cracked section are important parameters and strain hardening behavior and maximum strain capacity can be simulated using the proposed method.

• Composites Research
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• v.29 no.6
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• pp.395-400
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• 2016

Recently, many research groups have studied on the epoxy-based multifunctional electrolyte to develop the structural composite bearing high mechanical properties without sacrificing the ionic conductivity at the same time. The studies on the optimal content and material selection for structural electrolyte have been published, while its curing behavior has not much analyzed yet. In this study, epoxy-based structural electrolyte containing solid electrolyte was prepared by varying the curing temperature and time. In addition, the ionic conductivities and mechanical properties of specimens were measured. We also find out the optimal hardening condition where the epoxy domain enables to be hardened within the range of temperature at which the thermal decomposition of electrolyte does not occur. Finally, we propose the multifunctional structural electrolyte showing achievable electrical and mechanical properties (282 MPa and $9{\times}10^{-6}S/cm@25^{\circ}C$).

• Polymer(Korea)
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• v.24 no.3
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• pp.350-357
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• 2000

Curing behaviors of glass/epoxy prepreg for printed circuit boards (PCB) were studied by using dielectrometer and differential scanning calorimeter. This prepreg was showed the lowest ionic viscosity at about 115$^{\circ}C$, and then the ionic viscosity was gradully increased up to 15$0^{\circ}C$. This indicated that the curing reaction of this prepreg started at 115$^{\circ}C$ and the molecular weight was increased by the accelerated thermal cross-linking reaction. The loss factor and tan $\delta$ values were also measured and discussed. The dielectric behaviors of this prepreg system were also measured according to the cure cycle for PCB. This material was found to be thermally stable up to about 30$0^{\circ}C$ and then was showed an abrupt decomposition beyond this temperature.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.483-484
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• 2009

The purpose of this study is to evaluate the compressive behavior of SHCC mixing Fly ash. The parameter of this study are replacement level of fiber and Fly ash.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.855-862
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• 2004

부산점토에 대하여 Wheeler의 경화모형의 적용성을 평가하였다. 이를 위하여 양산지역의 부산점토에 대한 삼축 및 압밀시험 결과가 이용되있으며, 그 모형에 적합한 매개정수들이 결정되있다. 적용결과 예측된 거동은 실험결과와 정량적으로 잘 일치하는 것으로 나타났으나, 향후 압밀 및 장기거동 해석등을 위하여 더 많은 연구가 요구된다.

• Polymer(Korea)
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• v.24 no.6
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• pp.837-844
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• 2000

The cure behavior of commercial epoxy molding compounds (EMC) commonly used for IC package was studied at constant cure temperatures as well as at constant heating rates using differential scanning calorimetry (DSC), rheometer, and dielectric analyzer (DEA). The cure kinetics were obtained using autocatalytic reaction model according to the Ryan Dutta method after assuming m+n equal to 2. The prediction of reaction rates by the model equation corresponded well to experimental data at all temperatures except for 10$0^{\circ}C$. The phase transitions such as gelation and vitrification occurred during network formation. At each isothermal cure temperature, $T_{g}$ was measured in accordance with cure time, and the vitrification point was attained when $T_{g}$ was equal to $T_{cure}$. The temperature dependence of gel points and vitrification points showed good agreement with Arrhenius relation. DEA using parallel plate electrode was effective for the monitoring of EMC cure. we knew that if the resin systems are materials of comparable quality, $_{gel}$$T_{g}$ is constant regardless of accelerator concentration in TTT (Time-Temperature-Transformation) diagram.