• Composites Research
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• v.33 no.1
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• pp.25-29
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• 2020

A liquid crystalline thermosetting-epoxy-based composite was fabricated using diglycidyl ether of 4,4'-biphenol, tin(IV) oxide as a filler, and sulfanilamide as a curing agent. To investigate the thermal behavior, Thermogravimetric Analysis and Laser Flash Apparatus were performed using 3.0-7.0 wt% Tin(IV) oxide. The result showed that the activation energy and thermal conductivity were proportional to the amount of added filler.

• Journal of Biomedical Engineering Research
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• v.17 no.2
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• pp.247-254
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• 1996

The relationship between the isothermal age-hardening behavior and the phase transformation in the commercial dental Au-Ag-Cu-Pd alloy was investigated Age-hardening was mostly attributed to the lattice distortions of the supersaturated w phase resulting from the transformation to the metastable phasel which were more distinct at lower aging temperature. The lattice distortions resulting from the transformation of the metastable phases to the equilibrium phases also made a contribution to the age-hardening.

• Transactions of Materials Processing
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• v.17 no.1
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• pp.19-26
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• 2008

In the present work, the ratcheting behavior under uniaxial cyclic loading is analyzed. A comparison between the published and the results from the present model is also included. In order to simulate the ratcheting behavior, Two-Back Stress model is proposed by combining the non-linear Armstrong-Frederick rule and the non-linear Phillips hardening rule based on kinematic hardening equation. It is shown that some ratcheting behaviors can be obtained by adjusting the control material parameters and various evolutions of the kinematic hardening parameter can be obtained by means of simple combination of hardening rules using simple rule of mixtures. The ultimate back stress is also derived for the present combined kinematic hardening models.

• Transactions of Materials Processing
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• v.17 no.8
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• pp.579-585
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• 2008

Numerous experimental investigations on metallic materials and solid polymers have shown that relaxation behavior is nonlinearly dependent on prior strain rate. The stress drops in a constant time interval nonlinearly increase with an increase of prior strain rate. And the relaxed stress associated with the fastest prior strain rate has the smallest stress magnitude at the end of relaxation periods. This paper deals with the performance of three classes of unified constitutive models in predicting the characteristic behaviors of relaxation. The three classes of models are categorized by a rate sensitivity of kinematic hardening rule. The first class uses rate-independent kinematic hardening rule that includes the competing effect of strain hardening and dynamic recovery. In the second class, a stress rate term is incorporated into the rate-independent kinematic hardening rule. The final one uses a rate-dependent format of kinematic hardening rule.

• Journal of the Korean Society for Heat Treatment
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• v.24 no.4
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• pp.193-198
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• 2011

Effect of CaO addition on age hardening response has been studied by using optical microscopy, scanning electron microscopy and differential thermal analysis in AZ91 and CaO-containing ECO-AZ91 alloys. After solution treatment, the ${\beta}$($Mg_{17}Al_{12}$) phase formed during solidification mostly disappeared in the microstructure in the AZ91 alloy, whereas numerous ${\beta}$ precipitates containing Ca were still observed in the ECO-AZ91 alloy due to its enhanced thermal stability. The ECO-AZ91 alloy showed the delayed peak aging time and higher peak hardness compared with those of the AZ91 alloy. The activation energies for ${\beta}$ precipitation calculated by means of Kissinger method increased from 71.4 to 85.6 kJ/mole by the addition of CaO, which implies that CaO plays a role in reducing ${\beta}$ precipitation rate in the AZ91 alloy.

• Journal of the Korean Geotechnical Society
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• v.16 no.6
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• pp.117-125
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• 2000

자가굴착식 프레셔미터 시험(Self-Boring Pressuremeter Test, SBPT)은 지반의 교란을 최소화할 수 있기 때문에 점성토의 비배수 전당강도($S_{u}$ )를 비교적 정확하게 평가할 수 있는 방법 중의 하나로 알려져 있으며, 많은 연구자들에 의하여 SBPT 결과로부터 $S_{u}$ 를 산정하는 여러 가지 방법들이 제안되었다. 본 연구에서는 국내 5개지역에서 총 33회의 SBPT를 수행한후, 기존에 제안된 여러 가지 방법들을 이용하여 $S_{u}$ 를 산정하고, 그 중 변형률 경화 거동을 보이는 지반에서의 $S_{u}$ 를 동일 현장에서 수행한 현장베인시험 결과와 비교. 분석하여 각 방법들의 적용성과 신뢰성을 분석하였다. 그리고, $S_{u}$ 산정 결과에 대한 프레셔미터 멤브레인의 유일한 길이의 영향을 수치해석으로 분석하였으며, 그 결과를 이용하여 기존의 접선영 방법(Subtangent method)을 보정하는 식을 제안하였다. 새로이 보정된 방법으로 산정한 $S_{u}$ 를 현장베인시험 결과와 비교하여 개선 효과를 확인하였다.

• Magazine of the Korean Society of Agricultural Engineers
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• v.44 no.4
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• pp.114-122
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• 2002

Up to now, many constitutive models for clay have been proposed and studied based on the elasto-plastic or elasto-viscoplastic theory and it has been recognized that the effect of time on the loading process is a salient feature. In the present study, cyclic behavior characteristics of clay was studied with a viscoelastic-viscoplastic constitutive model for clay based on the non-linear kinematic hardening rule. In order to examine the behavior of clay several cyclic untrained triaxial tests and also their numerical simulations were performed. As results of that, it was found that the proposed model can well describe cyclic behaviors of clay such as frequency dependent characteristics, and have the high feasibility of numerical simulation for dynamic analysis.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2002.05a
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• pp.152-157
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• 2002

The cure and rheological behavior of Diglycidyl ether of bisphenol F, catalyzed by four kinds of imidazoles and a Nadic methyl anhydride curing agent were studied using a differential scanning calorimeter (DSC) and rheometer. The isothermal traces were employed to analyze cure reaction. The DGEBF/anhydride conversion profiles showed autocatalyzed reaction characterized by maximum conversion rate at 20~40 % of the reaction. The rate constants obtained from isothermal test showed temperature dependance, but reaction order did not. The order of reaction (m+n) was calculated to be close to 3. The measurements of viscosity and relation time in the presence of inorganic fillers were carried out at different isothermal curing temperatures. The viscosity and gelation time increased with filler content at the same isothermal temperature.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.953-956
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• 2006

Sulfate resistance of mortar specimens with or without alkali-free accelerator exposed to sulfate solutions for 360 days was investigated. Test results confirms a negative effect of alkali-free accelerator on the sulfate deterioration, irrespective of attacking sources. Based on the ASTM C1012 expansion test, the experimental findings demonstrated that higher $C_3A$ content in cement led to the higher expansion, especially in the mortar specimens with alkali-free accelerator.

• Tunnel and Underground Space
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• v.20 no.2
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• pp.73-81
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• 2010

The paper presents the application of FE simulations of NATM tunnel using different constitutive models. The results from a series of two dimensional plane strain finite element analyses of medium-liner interaction for NATM are presented. Four types of constitutive models are considered, namely, linear elastic, elasto-plastic Mohr-Coulomb, Hardening-Soil, Soft-Soil model. The design for tunnels requires a proper estimate of surface settlement and lining forces. It is shown that the advanced constitutive model gives better predictions for both ground movement and structural forces.