• 한국철도학회논문집
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• 제8권2호
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• pp.188-194
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• 2005

Aging characteristics of glass fabric/phenolic composites for tilting train subjected to combined environmental aging factors were investigated. A 2.5KW accelerated aging tester with a xenon-arc lamp was used to provide environmental aging factors such as temperature, moisture, and ultraviolet. A series of aging tests were conducted up to 3000 hours and several types of specimens were prepared along the warp direction and the fill direction. Mechanical degradations for tensile, flexural, and shear properties were evaluated as a function of exposure times through a material testing system. Thermal analysis properties such as storage shear modulus, loss shear modulus, and tan 3 were measured through a dynamic mechanical analyzer. Finally exposed surfaces of the composites were examined using a scanning electron microscope. According to the experimental results, mechanical properties and thermal analysis properties of glass fabric/phenolic composites were found to be slightly degraded as a function of exposure times due to combined environmental effects.

• 한국세라믹학회지
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• 제44권4호
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• pp.198-201
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• 2007

Multi-walled carbon nanotube (M-CNT)/Nafion nanocomposites were prepared by solution casting to elucidate the effect of M-CNT addition, from 0 to 7 wt%, on the viscoelastic behavior of the composites. The M-CNT bundles induced by the Nafion polymer were determined to be uniformly distributed for the 1 wt% M-CNT/Nafion nanocomposites. The 1 wt% M-CNT/Nafion composite exhibited the highest blocking stress of 2.3 kPa due to its high elastic modulus of 0.485 GPa. From a dynamic mechanical analysis, the 1 wt% M-CNT had the highest storage and loss moduli compared with the other samples in all frequency and temperature ranges. From the storage modulus data, the M-CNT loaded composites had similar $T_g$ values near $120^{\circ}C$. The glass transition temperatures of the M-CNT loaded composites were $120^{\circ}C$ (1 wt%), $117^{\circ}C$ (3 wt%), $117^{\circ}C$ (5 wt%), and $135^{\circ}C$ (7 wt%), suggesting that the effect of the M-CNTs on the Nafion film begins at 1 wt%. Thus, it has been concluded that the 1 wt% M-CNT disported composite is attractive for actuator applications.

• Preventive Nutrition and Food Science
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• 제21권4호
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• pp.367-372
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• 2016

To understand the effects of adding different gums (guar, xanthan, and locust bean gums) on naked barley flour (NBF), the rheological and pasting properties of NBF-gum mixtures were measured at different gum concentrations (0, 0.3, and 0.6% w/w). Steady shear rheological properties were determined by rheological parameters for power law and Casson models. All samples showed a clear trend of shear-thinning behavior (n=0.16~0.48) and had a non-Newtonian nature with yield stress. Consistency index, apparent viscosity, and yield stress values increased with an increase in gum concentration. Storage modulus values were more predominant than loss modulus values with all concentrations of gums. There is a more pronounced synergistic effect of elastic properties of NBF in the presence of xanthan gum. Rapid visco analyser pasting properties showed that the addition of gums resulted in a significant increase in the peak, breakdown, setback, and final viscosities, whereas the pasting temperature decreased.

• Fisheries and Aquatic Sciences
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• 제17권3호
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• pp.299-304
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• 2014

The objective of this study was to elucidate the physicochemical characteristics of gelatin extracted from jellyfish Rhopilema hispidum. We investigated the proximate composition, amino acids, gel strength, gelling/melting points, dynamic viscoelastic properties, and viscosity of jellyfish gelatin. Jellyfish gelatin contained 12.2% moisture, 1.5% lipid, 2.1% ash, and 84.8% protein. Glycine, hydroxyproline, proline, and alanine were the predominant amino acids. The gelatin showed a gel strength of 31.2 kPa, a gelling point of $18.0^{\circ}C$, and melting point of $22.3^{\circ}C$. The gelatin was composed of ${\alpha}_1$-chain, ${\alpha}_2$-chain, ${\beta}$-chain, and ${\gamma}$-chain. During cooling and heating process, jellyfish gelatin showed lower elastic modulus (G') and loss modulus (G") values than mammalian gelatin. Jellyfish gelatin did not show superior rheological properties to mammalian gelatin, like other fish gelatin; however, it can be used in various food and cosmetic products not requiring high gel strength.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 춘계학술대회 논문집
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• pp.760-765
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• 2013

Eco-friendly material applied to building would be one of the materials which is must developed for global environmental conservation and reduction of carbon dioxide. For development of eco-friendly material, a cellulose sound-absorbing material has been developed with waste paper through adjustment of various mix proportions. The developed cellulose sound-absorbing material has been tested for its acoustic properties such as acoustic absorptivity and dynamic elastic modulus. The absorptivity was evaluated by developing six samples and using impedance tube and reverberation chamber. As a result of the evaluation, 0.64(NRC) was secured in absorptivity and $4.7MN/m^3$ was indicated in dynamic elastic modulus. Also, for practical use of developed sound-absorbing material as inner heartwood in drywall, comparison test of sound reduction index was performed with existing glass wool sound-absorbing material and constructed drywall of gybsum board. The results have shown 55dB(Rw) of sound reduction index in glass-wool wall and 46dB(Rw) in cellulose.

• 한국식품과학회지
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• 제29권5호
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• pp.932-938
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• 1997

Changes in viscosity and dynamic theological properties of Job's-tears were measured by Bohlin dynamic tester as a function of moisture, and measurement was performed within a linear viscoelastic range. The result of the shear stress vs shear rate of Job's-tears at different moisture contents $(50{\sim}75%)$ was applied to mathematical models and Herschel-Bulkley model showed the highest correlation coefficient. Lower moisture content (55%) produced higher yield stress and consistency index, but lower flow behavior index, whereas higher moisture content showed reverse effects. Job's-tears with $50{\sim}70%$ moisture contents showed a higher storage modulus (G') than loss modulus (G') at all frequencies, showing a higher concentrated polymer characteristics. However, higher moisture content (>75%) showed crossover point between G' and G', and frequency dependency. As the moisture content was increased, the amount of viscoelastic properties such as G', G', complex viscosity decreased during heating, and initial temperature and miximum value of viscoelastic properties shifted to higher temperatures, representing the moisture-dependence of Job's-tears upon theological properties.

• 대한치과의사협회지
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• 제48권4호
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• pp.297-307
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• 2010

Noncarious cervical lesions(NCCLs) are characterized as structural defects found on the tooth surface of the cement-enamel junction. Loss of tooth structure through noncarious mechanisms may vary in etiology and clinical presentation for each individual but presently many clinician now classify this as tooth failure of abfraction due to the stress applied in the cervical area of the tooth under oral physiological and pathological loads. In the current study, we investigated the stress distribution of maxillary premolar with NCCL using simulated 3D finite element analysis. The results were as follows: 1. In the sound maxillary premolar, the stresses were highly concentrated at cervical enamel surface of the mesiobuccal line angle, asymmetrically. 2. Once the lesion has been formed, the highest stress concentration was observed around the apex of the wedge shaped lesion. 3. In four types of NCCL, the patterns of stress distribution were similar and the peak stress was observed at mesial corner and also stresses concentrated at lesion apex. 4. Lesion cavity modification of rounding apex, reduced stress of lesion apex. 5. When restoring the notch-shaped lesion, material with high elastic modulus worked well at the lesion apex and material with low elastic modulus worked well at the cervical cavosurface margin.

• Macromolecular Research
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• 제14권3호
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• pp.373-382
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• 2006

A series of crosslinkable, waterborne polyurethanes (I-WBPUs) were prepared by in-situ polymerization using isophorone diisocyanate (IPDI)/poly(tetramethylene oxide) glycol (PTMG, $M_n$=2,000)/dimethylol propionic acid (DMPA)/ethylene diamine (EDA)/triethylamine (TEA)/aminoplast[hexakis(methoxymethyl)melamine (HMMM)] as a crosslinking agent. Typical crosslinkable, waterborne polyurethanes (B-WBPUs) blended from WBPU dispersion and aqueous HMMM solution was also prepared to compare with the I-WBPUs. The crosslinking reaction between WBPU and HMMM was verified using FTIR and XPS analysis. The effect of the HMMM contents on the dynamic mechanical thermal, thermal, mechanical, and adhesion properties of the I-WBPU and B-WBPU films were investigated. The storage modulus(E'), glass transition temperatures of the soft segment ($T_{gs}$) and the amorphous regions of higher order ($T_{gh}$), melting temperature ($T_m$), integral procedural decomposition temperature (IPDT), residual weight, $T_{10%}$ and $T_{50%}$ (the temperature where 10 and 50% weight loss occurred), tensile strength, initial modulus, hardness, and adhesive strength of both I-WBPU and B-WBPU systems increased with increasing HMMM content. However, these properties of the I-WBPU system were higher than those of the B-WBPU system at the same HMMM content. These results confirmed the in-situ polymerization used in this study to be a more effective method to improve the properties of the WBPU materials compared to the simple blending process.

• International Journal of Railway
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• 제1권3호
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• pp.113-116
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• 2008

The long-tenn exposure of polymeric composite materials to extreme-use environments, such as pressure, temperature, moisture, and load cycles, results in changes in the original properties of the material. In this study, the effect of combined environmental factors such as ultraviolet ray, high temperature and high moisture on mechanical and thermal analysis properties of glass fabric and phenolic composites are evaluated through a 2.5 KW accelerated environmental aging tester. The environmental factors such as temperature, moisture and ultraviolet ray applied of specimens. A xenon-arc lamp is utilized for ultraviolet light and exposure time of up to 3000 hours are applied. Several types of specimens - tensile, bending, and shear specimens that are warp direction and fill direction are used to investigate the effects of environmental factors on mechanical properties of the composites. Mechanical degradations for tensile, bending and shear properties are evaluated through a Universal Testing Machine (UTM). Also, storage shear modulus, loss shear modulus and tan a are measured as a function of exposure time through a Dynamic Mechanical Analyzer (DMA). From the experimental results, changes in material properties of glass fabric and phenolic composites are shown to be slightly degraded due to combined environmental effects.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제53권4호
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• pp.192-199
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• 2004

Elastic-factor of elastic epoxy were investigated by TMA (Thermomechanical Analysis), DMTA (Dynamic Mechanical Thermal Analysis), TGA (Thermogravimetric Analysis) and FESEM (Field Emission Scanning Electron Microscope) for structure-images analysis as toughness-investigation to improve brittleness of existing epoxy resin. A range of measurement temperature of the TMA and DMTA was changed from -20($^{\circ}C$) to $200^{\circ}(C)$, and TGA was changed from $0^{\circ}(C)$ to $600^{\circ}(C)$. Glass transition temperature (Tg) of elastic epoxy was measured through thermal analysis devices with the content of 0(phr), 20(phr) and 35(phr). Also, thermal expansion coefficient (a), high temperature, modulus and loss factor were investigated through TMA, TGA, and DMTA. In addition, the structure of specimens was analyzed through FESEM, and then elastic-factor of elastic epoxy was visually showed by FESEM. As thermal analysis results, 20(phr) was more excellent than 30(phr) thermally and mechanically. Specially, thermal expansion coefficient, high temperature, modulus, and damping properties were excellent. By structure-images analysis through FESEM, we found elastic-factor of elastic epoxy that is not existing epoxy, and proved high impact.