• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.30-30
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• 2008

Lead-free piezoelectric ceramics 0.97$(Na_{0.5}K_{0.5})NbO_3$-0.03Ba$(Ti_{1-x}Sn_x)O_3$ [NKN-BTS-x] ceramics doped with 1 mol% $MnO_2$ have been fabricated by a sintering technique with muffling. The $MnO_2$-doped NKN-BTS-x ceramics with x$\leq$0.2 have pure orthorhombic perovskite structure at room temperature. The dense microstructure was developed with grain growth as an increase of amount of Sn. Moreover, the addition of Sn was found to have a significant influence on piezoelectric properties. In particular, the $MnO_2$-doped NKN-BTS-0.1 ceramics showed improved piezoelectric properties of piezoelectric constant ($d_{33}$=145pC/N), relatively large electromechanical coupling factor ($k_p$=43%), dielectic constant (${\varepsilon}^T_{33}/{\varepsilon}_0$=676) dielectric loss (tan$\delta$=1.3%).

• 대한기계학회논문집A
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• 제26권7호
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• pp.1416-1425
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• 2002

In this study, the effects of combined environmental factors on mechanical and thermal analysis properties of graphite/epoxy composites were evaluated by the use of an accelerated aging test. Environmental factors such as temperature, moisture. and ultraviolet were considered. A xenon-arc lamp was utilized for ultraviolet light. and exposure times of up to 3000 hours were applied. Several types of specimens - tensile. bending, and shear specimens those are transverse to the fiber direction, and bending specimens those are parallel to the tiber direction - were used to investigate the effects of environmental factors on mechanical properties of the composites. Also, glass transition temperature, storage shear modulus, loss shear modulus, and tan ${\delta}$ were measured as a function of exposure times through a dynamic mechanical analyzer. In addition. a suitable testing method for determining the effect of environmental factors on mechanical properties is suggested by comparing the results from using two different types of strain measuring sensors. Finally, composite surfaces exposed to environmental factors were examined using a scanning electron microscope.

• Composites Research
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• 제29권5호
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• pp.269-275
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• 2016

Multiscale hybrid composites, which consist of polymeric resins, microscale fibers and nanoscale reinforcements, have drawn significant attention in the field of advanced, high-performance materials. Despite their advantages, multiscale hybrid composites show challenges associated with nanomaterial dispersion, viscosity, interfacial bonding and load transfer, and orientation control. In this paper, carbon nanotube(CNT)/carbon fiber(CF)/polycarbonate(PC) multiscale hybrid composite were fabricated by a solution process to overcome the difficulties associated with controlling the melt viscosity of thermoplastic resins. The dependence of CNT loading was studied by varying the method to add CNTs, i.e., impregnation of CF with CNT/PC/solvent solution and impregnation of CNT-coated CF with PC/solvent solution. In addition, hybrid composites were fabricated through surfactant-aided CNT dispersion followed by vacuum filtration. The morphologies of the surfaces of hybrid composites, as analyzed by scanning electron microscopy, revealed the quality of PC impregnation depends on the processing method. Dynamic mechanical analysis was performed to evaluate their mechanical performance. It was analyzed that if the position of the value of tan ${\delta}$ is closer to the ideal line, the adhesion between polymer and carbon fiber is stronger. The effect of mechanical interlocking has a great influence on the dynamic mechanical properties of the composites with CNT-coated CF, which indicates that coating CF with CNTs is a suitable method to fabricate CNT/CF/PC hybrid composites.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.852-858
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• 2007

The durability of carbon/epoxy composites under salt water environment was investigated through salt water spray tester. Salt water environment was obtained through salt spray and salt immersion. 5% NaCl solution was used for salt water as natural salt water. Mechanical test was performed to obtain tensile properties, flexural properties, and shear properties of carbon/epoxy composite over 12 months under salt water environment. Dynamic mechanical analyzer was used to investigate thermal analysis properties such storage modulus, loss modulus, and tan ${\delta}$. Also FT/IR test was conducted to investigate a change in chemical structure. According to the results, mechanical properties were found to be slowly degraded as a function of exposure times. Regarding to thermal analysis properties, storage modulus was insensitive to exposure times, but loss modulus was shown to be slightly decreased. Although the shape and location of peak in FT/IR were not much changed, the intensity of peak in FT/IR was affected on exposure times. We also found that salt water immersion was more severe to the durability of carbon/epoxy composite rather than salt water spray.

• 한국염색가공학회지
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• 제15권2호
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• pp.59-67
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• 2003

PTT[poly(trimethylene terephthalate)] fiber was annealed by passing on the plate heater to illuminate the effects of annealing on the mechanical properties and dyeability with varying the treatment temperature for 0.5 second. The apparent crystal sizes and crystallinity were increased with increases in temperature. With the increases of the temperature, the dynamic viscoelastic behaviors were analyzed to be reduction in $T_{max} (tan{\delta})$. The initial modulus were observed to be a small enhanced. The shrinkage in hot water were reduced. The dyeability for disperse dye enhanced dramatically, for example, a satisfactory degree of exhaustion was obtained by dyeing at $95^\circ{C}$ for 30 min with the PTT fibers heat treated at $180^\circ{C}$.

• 한국식품영양학회지
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• 제27권5호
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• pp.805-816
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• 2014

We investigated the quality characteristics and resulting sensory evaluation of semi-dried silver pomfret treated with high hydrostatic pressure (HHP) processing and brining for 14 days at 4 and $10^{\circ}C$ to evaluate the effects of treatment with HHP processing. HHP treatment and brining could cause compaction of fibers and the space between muscle. The G' values of all samples were higher than the G" values and the tan ${\delta}$ values of the tissue ranged from 0.222 to 0.251 with no further changes observed during storage. HHP treatment and brining significantly increased the total color difference, and the HHP and brine-treated group scored significantly higher than the others in terms of sensory evaluation. HHP treatment combined with brining could have a significant effect on the quality characteristics of the semi-dried products and their storage stability, and it is suggested from the results that they may have the potential to satisfy the requirements to produce commercially marketable food grade products.

• 한국세라믹학회지
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• 제27권2호
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• pp.187-194
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• 1990

Effects of MnO2 addition ranged from 0.0wt% to 5.0wt% on the microstructure and dielectric and piezoelectric properties of the Pb(Zr0.52 Ti0.48)O3 Ceramics have been investigated. The solubility limit of MnO2 in Pb(Zr0.52 Ti0.48)O3 is about 0.5wt%, and MnO2 as a valence state of Mn3+ is substituted for (Zr, Ti) lattice site in PZT solid-solution. The addition of MnO2 up to 0.5wt% in Pb(Zr0.52 Ti0.48)O3 brings increase of density, but decreased of grain size and tetragonality. Dielectric constant slightly decreases, but both coupling factor(Kp) and mechanical quality factor(Qm) increase with the addition of MnO2. However, excess amount of MnO2 addition more than 0.75wt% results in rapid decrease of resistance. Dielectric constant and tan $\delta$ increase due to the second phase and inhomogeneous Mn distribution.

• 한국세라믹학회지
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• 제46권4호
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• pp.413-418
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• 2009

Glass systems based on Ca, Sr, Ba, and Zn modified alumino-boro silicates were investigated in order to improve the dielectric and mechanical properties of a typical LTCC (low temperature co-fired ceramic) which was developed for high frequency highly-integrated modules. The glass was prepared by a typical melting procedure and then mixed with cordierite fillers to fabricate glass/ceramic composite-type LTCC materials. The amount of cordierite filler was fixed at 50 volumetric%. For an optimal glass composition of 7.5% CaO, 7.5% BaO, 5% ZnO, 10% $Al_2O_3$, 30% $B_2O_3$, and 40% $SiO_2$ in mole ratio, the resultant LTCC composite showed a dielectric constant of 5.8 and a dielectric loss ($tan{\delta}$) of 0.0009 after firing at $900^{\circ}C$. An average bending strength of 160MPa was obtained for the optimal composition.

• 한국전기전자재료학회논문지
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• 제25권4호
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• pp.309-314
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• 2012

To assess the condition of stator insulation, nondestructive and overpotential tests were performed on four high voltage motors. The stator windings under these tests have nominal ratings of 6.6 kV. After completing nondestructive tests, the AC overvoltage applied to the stator windings was gradually increasing until insulation failure in order to obtain the breakdown voltage. No. 1, No. 2, No. 3 and No. 4 of 6.6 kV motors failed near rated voltage of 18.4 kV, 19.8 kV, 19.7 kV and 21.7 kV, respectively. The breakdown voltage of four motors was higher that expected for good quality coils(14.2 kV) in 6.6 kV motors. Almost all of failures were located in a line-end coil at the exit from the core slot. The breakdown voltages and the types of defects showed strong relation to the stator insulation tests such as in the case of AC current, dissipation factor($tan{\delta}$) and partial discharge magnitude.

• Macromolecular Research
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• 제14권4호
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• pp.416-423
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• 2006

The dynamic mechanical thermal properties of poly(hexamethylene terephthalate) (PHT), poly(1,4-cyclohexylenedimethylene terephthalate) (PCT) and their P(HT-co-CT) random copolymers in the amorphous state were examined as a function of temperature and frequency. All the samples exhibited two main relaxation processes in the plot of tan ${\delta}$ versus temperature: the primary ${\alpha}$-relaxation associated with the glass transition and the secondary ${\beta}$-relaxation attributed to the local segmental motions of mostly cyclohexylene rings for PCT and to cooperative motions of methylene, carboxyl, and phenylene groups for PHT. Both ${\alpha}$- and ${\beta}$-relaxation temperatures increased with increasing CT content. The activation energy of the ${\alpha}$-relaxation increased with increasing CT content, whereas that of the ${\beta}$-relaxation decreased. The sub-glassy secondary ${\beta}$-relaxation processes of PCT and PHT were investigated in terms of the cooperativity of main-chain segmental motions.