• Steel and Composite Structures
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• v.15 no.2
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• pp.221-245
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• 2013

This paper presents an analytical solution to the thermomechanical bending analysis of functionally graded sandwich plates by using a new hyperbolic shear deformation theory in which the stretching effect is included. The modulus of elasticity of plates is assumed to vary according to a power law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic ceramic material. The effects of functionally graded material (FGM) layer thickness, volume fraction index, layer thickness ratio, thickness ratio and aspect ratio on the deflections and stresses of functionally graded sandwich plates are investigated.

• 전자공학회논문지 IE
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• v.49 no.2
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• pp.1-8
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• 2012

The effects of the addition of either monoclinic $ZrO_2(pure)$ or tetragonal $ZrO_2$ containing 5.35wt% $Y_2O_3(Y-TZP)$ on the mechanical properties and thermal shock resistance of $Al_2O_3$ ceramics were investigated. The addition of $ZrO_2$(m) and Y-TZP increased sintered density of $Al_2O_3$. The Vickers hardness also increased as the volume fraction of Y-TZP increased going through a maximum at 20wt%. The hardness of the specimens was found to be dependent on the sintered density. The higher volume fraction of either $ZrO_2(m)$ or Y-TZP resulted in the higher fracture toughness of the composite was. This result may be taken as evidence that toughening of $Al_2O_3$ can be achieved by not only the transformation toughening but microcrack toughening of $ZrO_2$. The thermal shock property for $Al_2O_3-ZrO_2$ composites was improved by increasing the volume fraction of monoclinic $ZrO_2(pure)$. The grain size increased as the volume fraction of $ZrO_2$ did.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.3
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• pp.133-140
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• 2018

This paper is concerned with the 2-D micostructure generation for $Ni-A{\ell}_2O_3$ dual-phase composite materials and the numerical analysis of mechanical characteristic of hierarchical models of microstructure which are defined in terms of the scale of microstructure. The microstructures of dual-phase composite materials were generated by applying the mathematical RMDF(random morphology description functions) technique to a 2-D RVE of composite materials. And, the hierarchical models of microstructure were defined by the number of Gaussian points. Meanwhile, the volume fractions of metal and ceramic particles were set by adjusting the level of RMD functions. The microstructures which were generated by RMDF technique are definitely random even though the total number of Gaussian points is the same. The randomly generated microstructures were applied to a 2-D beam model, and the variation of normal and shear stresses to the scale of microstructure was numerically investigated. In addition, through the crack analyses, the influence of RMDF randomness and Gauss point number on the crack-tip stress is investigated.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.4
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• pp.433-438
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• 2024

Piezoelectric ceramics play an important role in various electronic applications. However, traditional ceramics are difficult to be used in some complicated structures, due to their low flexibility and high brittleness. To solve this problem, this study prepared and investigated ceramic/polymer composites that can utilize a good flexibility of polymers. Polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) and 0.77(Bi_1/2Na_1/2)TiO₃-0.23SrTiO₃ (BNST23) ceramics were selected to fabricate the composites. Ceramic/polymer composites were prepared using various volume fractions of BNST23 ceramics. The distribution of piezoceramic particles in BNST23/PVDF-TrFE composites was investigated using optical microscopy (OM) and scanning electron microscopy (SEM). The dielectric and piezoelectric properties of the composites were significantly influenced by the volume fraction of the piezoelectric ceramics. As a result, the highest piezoelectric constant (d₃₃) of 56 pC/N was obtained in a composites with 70% volume fraction of BNST23 ceramics. Accordingly, it is expected that BNST23/PVDF-TrFE composites can be applied to various sensor applications.

• Journal of the Korean Ceramic Society
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• v.49 no.3
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• pp.272-278
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• 2012

Effects of ceramics on the microwave dielectric properties of polytetrafluoroethylene (PTFE) composites filled with $MgTiO_3$ (MTi) and/or $MgTa_2O_6$ (MTa) were investigated. The dielectric constant ($K$), quality factor ($Qf$), and temperature coefficient of resonant frequency ($TCF$) of the composites were dependent on the type and volume fraction ($V_f$) of the ceramics. For the composites mixed with MTa and MTi, the $K$ and $TCF$ values decreased with increasing MTi content. The $Qf$ values of the composites were affected by relative density. The measured $K$ values of the composites were compared with those predicted by several theoretical models. Good microwave dielectric properties with values of $K$=3.6, $Qf$ = 7,788 GHz, and $TCF$ = -0.19 ppm/$^{\circ}C$ were obtained for the composites with 0.1 $V_f$ ceramics (mixed 0.025MTa and 0.075MTi).

• Journal of the Korean Ceramic Society
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• v.40 no.5
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• pp.405-409
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• 2003

The effect of substitution of Gd ions for Ca ions in the B $i_{1.84}$P $b_{0.34}$S $r_{1.91}$(C $a_{1-x}$ G $d_{x}$)$_{2.03}$ C $u_{3.06}$ $O_{ 10+{\delta}}$/ (x=0.0~0.06) was investigated by measuring x-ray diffraction patterns, lattice constants, do resistivity and Hall effect. We found the solubility limit of Gd in the 110 K phase to be x < 0.015. Within the solubility limit, the c-axis seemed to decrease with increasing x. In the region of the 110 K single phase, the critical temperature $T_{c}$ gradually decreased with an increasing the Gd concentration x, corresponding to a small change of the carrier concentration.

• Journal of the Korean Ceramic Society
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• v.45 no.10
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• pp.638-643
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• 2008

Biomimetic apatite formation and deposition behaviors of Ti-6Al-7Nb and Ti-6Al-4V plates in simulated body fluids(SBF) under various conditions were examined. In case of regular samples without collagen treatments the weight gain due to apatite precipitation on the surface in Ti-6Al-4V was found to be higher than in Ti-6Al-7Nb. In case of collagen-coated samples, the weight gain in Ti-6Al-4V continued to be higher than in Ti-6Al-7Nb, but the difference between the two became smaller. Both Ti-6Al-7Nb and Ti-6Al-4V samples with collagen coating exhibited an appreciable increase of weight gain, which may be caused by the interaction between collagen and $Ca^{+2}$ ions. The weight gain was found to be not much affected by the addition of collagen to SBF. The ill-defined granular structure in the presence of collagen can be associated with the increasing volume fraction of amorphous calcium phosphate.

• Journal of the Korean Ceramic Society
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• v.33 no.1
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• pp.119-125
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• 1996

Magnetic properties through controlled nucleation and crystallization wer studied for ferrimagnetic 40Fe2O3-20CaO-40SiO2 glass useful as thermoseeds for hyperthermia of tumor therapy. The maximum nucleation and crystal growth temperature are $700^{\circ}C$ and 100$0^{\circ}C$ respectively. The glass showed the maximum saturation magnetization of 168.4 emu/cm3 when nucleated $700^{\circ}C$ for 60 min and crystal grown at 100$0^{\circ}C$ for 4hrs. The maximum coercive force was 390 Oe when uncleated $700^{\circ}C$ for 60 min and crystal grown at 975$^{\circ}C$ for 2 hrs. The variation of the saturation magnetization could be well quantitatively interpreted in terms of the volume fraction of the magnetite whereas that of the coercive forces could be explained only qual.itatively in terms of the particle size of the magnetite. Hysteresis losses showed the maximum value of 0.18W/cm3 when heat treated at 100$0^{\circ}C$ for 4 hrs pre-necleated at $700^{\circ}C$ for 60 min and temperature increase of 7K under AC magnetic field of 10 kOe and 10kHz.

• Journal of the Korean Ceramic Society
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• v.48 no.3
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• pp.257-262
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• 2011

Dependencies of dielectric properties on $MgTa_2O_6$, $MgNb_2O_6$, and $MgWO_4$ (Mg-based ceramics) fillers of the polystyrene (PS) matrix composites were investigated as a function of frequency. With increasing frequency from 1 GHz to 7.3 GHz, the dielectric constant (K) of the composites was not changed significantly, while the dielectric loss (tan${\delta}$) of the composites was slightly decreased. The K, tan${\delta}$, and temperature coefficient of resonant frequency (TCF) of the composites were dependent on the type and amount of ceramics at 11 GHz. Also, several theoretical models have been employed to predict the effective dielectric constant of the composites and the results were compared with experimental data. Typically, a K value of 6.67, tan${\delta}$ of $0.56{\times}10^{-3}$, and TCF of -4.99 $ppm/^{\circ}C$ were obtained for the PS composites with 0.4 volume fraction of $MgNb_2O_6$ at 11 GHz.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.60-60
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• 2008

We manufactured Liquid Crystal Polymer (LCP) and (1-x)$BaTiO_3-xSrTiO_3$(BST) ceramic composites and investigated dielectric properties to use as embedded capacitor in printed circuit boards and replace LTCC substrates. The dielectric properties of these composites are varied with volume fraction of BST and ratios of BT/ST. Dielectric constants are in the range of 3~28. In addition, we could get low TCC and High Q value that could not achieve in other ceramic-polymer composites. Especially, in composite with x=0.4 and 50vol% BST, the dieletric constant and Q-value are 27 and 300, respectively. And more TCC is -116~145ppm/$^{\circ}C$ in the temperature range of -55~$125^{\circ}C$. We think that this composites can be used high-Q substrate material like LTCC and embedded temperature compensation capacitor in printed circuit boards.