• Journal of the Korean Ceramic Society
• /
• v.45 no.2
• /
• pp.105-111
• /
• 2008

Symmetric three layer composites have been prepared by freeze casting and then pressureless sintered at $l700-1800^{\circ}C$ in $N_2$ gas atmosphere. The relative sintered density of multilayer composites having microstructural characteristics of later intermediate-stage densification increased with sintering temperature and reached about 95% theoretical value at $1800^{\circ}C$. Although the indentation strength of the multilayer composites was generally reduced with increasing Vickers indentation load up to 294N, the damage resistance of multilayer composites was superior compared to monolithic layer 95AL/5SN material. The three-point bend strength of the layered materials remained at the values 266-298 MPa after indentation with a load of 49N, while that of the monolithic 95AL/5SN material was 219 MPa. The fracture toughness of the multilayer material was $5.4-6.6\;MPa\;m^{1/2}$.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2011.05a
• /
• pp.19.1-19.1
• /
• 2011

Effects of particle size, crystal structures and multilayer structures of $ATiO_3$, $ATa_2O_6$, $ANb_2O_6$, $AWO_4$, and $AMoO_4$ (A=Ni, Mg, Zn, Co) ceramic fillers on the dielectric properties of polystyrene (PS), polypropylene (PP) and polytetrafluoroethylene (PTFE) polymer matrices were investigated at microwave frequencies. The microwave dielectric properties of $ATiO_3$ (ilmenite), $ATa_2O_6$ (tri-rutile), $ANb_2O_6$ (columbite), AWO4 (wolframite), and AMoO4 (wolframite) ceramics were largely dependent on the structural characteristics of oxygen octahedra. The dielectric constant (K) of the composites was increased with the ceramic content. However, the dielectric loss (tan ${\delta}$) of the composites was affected by the type of ceramics and the crystallinity of polymers. For the composites with same amount of ceramics, the K was decreased and the tan ${\delta}$ was increased with the particle size of ceramics. Also, the dielectric properties of the composites were dependent on the multilayer structures with different arrangements. Several theoretical models have been employed to predict the effective dielectric properties of the composites. The frequency dependence of dielectric properties and the temperature coefficient of resonant frequency (TCF) of the composites were also discussed.

• Advances in aircraft and spacecraft science
• /
• v.3 no.1
• /
• pp.15-28
• /
• 2016

Although the aircraft industry was the first to use fibre composites, now they are increasingly used in a range of structural applications such as flooring, decking, platforms and roofs. Interlayer delamination is a major failure mode which threatens the reliability of composite structures. Delamination can grow in size under increasing loads with time and hence leads to severe loss of structural integrity and stiffness reduction. Delamination reduces the natural frequency and as a consequence may result in resonance. Hence, the study of the effects of delamination on the free vibration behaviour of multilayer composite structures is imperative. The focus of this paper is to develop a 3D FE model and investigate the free vibration behaviour of fibre composite multilayer sandwich panels with interlayer delaminations. A series of parametric studies are conducted to assess the influence of various parameters of concern, using a commercially available finite element package. Additionally, selected points in the delaminated region are connected appropriately to simulate bolting as a remedial measure to fasten the delamination region in the aim of reducing the effects of delamination. First order shear deformation theory based plate elements have been used to model each sandwich layer. The findings suggest that the delamination size and the end fixity of the plate are the most important factors responsible for stiffness reduction due to delamination damage in composite laminates. It is also revealed that bolting the delaminated region can significantly reduce the natural frequency variation due to delamination thereby improving the dynamic performance.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.06a
• /
• pp.45-45
• /
• 2008

$SrTiO_3$/Organic composites 는 Inorganic/organic 복합재료로, 유전 특성이 우수하고, 저온하여 제조단가의 감소가 가능하다. 이를 바탕으로 $SrTiO_3$/Organic composites 복합재를 이용한 가능성을 확인하기 위해 Multilayer 구조의 Coupler를 설계, 제작 후 특성을 분석하였다. Coupler 는 RF signal을 분기하기 위한 목적으로 평행한 한 쌍의 Conductor line 구조를 가진다. 2개의 Line 의 길이를 특정주파수 $f_0$의 wavelength $\lambda$/4 로 설계하여 서로 근접 시켰을 때 $f_0$를 중심으로 RF 신호 분기 현상이 나타난다. 보다 넓은 대역에 걸쳐서 신호분기를 하기 위해서는 두 line 간의 간격을 좁혀 Signal coupling 효과를 증가 시킨다. single layer conductor 구조에서는 물리적인 한계가 있으므로, multilayer 구조를 사용하면 보다 넓은 대역의 Coupled line coupler 로서 기능하게 된다.

• Korean Journal of Materials Research
• /
• v.10 no.10
• /
• pp.677-683
• /
• 2000

Three- and five-layer 3Y-YZP/12Ce- TZP composites prepared by a slip casting method have been char­acterized in terms of mechanical properties. The fracture strength of mutilayer c$\alpha$nposites determined in a diametral compression test was 327~534 MPa. Although the indentation strength of the materials was generally reduced with i increasing Vickers indentation load up to 300 N, the damage resistance of multilayer composites was superior com­pared to monolithic layer TZP material. The four-point bend strength of the layered material remained at the values of 620~674 MPa after indentation with a load of 49 N, while that of the monolithic TZP material was 129~339 MPa. The microindentation toughness of the multilayer material was $7.7~13.1\;MPa{\cdot}m^{1/2}$.

• Proceedings of the Korean Ceranic Society Conference
• /
• 2000.04a
• /
• pp.85.1-85.1
• /
• 2000

• Proceedings of the Korean Ceranic Society Conference
• /
• 2000.04a
• /
• pp.84.2-84.2
• /
• 2000

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2005.05a
• /
• pp.89-89
• /
• 2005

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.11a
• /
• pp.264-265
• /
• 2008

While the reliability of bulk insulation has become important particularly in multilayer boards and embedded boards, electronics are to be used under various environments such as at high temperature and in high humidity. We observed internal space charge behavior for two types of epoxy composites under dc electric fields to investigate the influence of water at high temperature. In the case of glass/epoxy specimen, homocharge is observed at water-treated specimen, and spatial oscillations become clearer in the water-treated specimens. Electric field in the vicinity of the electrodes shows the injection of homocharge. In aramid/epoxy specimens, heterocharge is observed at water-treated specimens, i.e. negative charge accumulates near the anode, while positive charge accumulates near the cathode. Electric field is enhanced just before each electrode. In order to further examine the mechanism of space charge formation, we have developed a new system that allows in situ space charge observation during ion migration tests at high temperature and high humidity. Using this in situ system.

• Korean Journal of Materials Research
• /
• v.10 no.8
• /
• pp.545-550
• /
• 2000

3Y-TZP, 12Ce-TZP 및 3Y-TZP, 12Ce-TZP 현탁액의 제타포텐셜과 겉보기점도의 측정으로부터 슬립주입공정에 의한 다층복합체의 제조조건을 조사하였다. 아울러 다층복합체의 소결밀도, 미세구조, 결정상에 미치는 열처리의 영향을 검토하였다. 3Y-TZP와 12Ce-TZP 현탁액의 등전점을 pH 8부근이었으나 3Y-TZP/12Ce-TZP의 등전점은 pH8.6이었다. 현탁액은 전단속도의 증가와 더불어 점도가 감소하는 의가소성유동을 나타내었다. 15 및 20vol% 고체함량을 갖는 3Y-TZP와 3Y-TZP/12Ce-TZP 현탁액은 소량(0.3wt%)의 유기해교제의 첨가만으로 슬립주입에 적당한 유동성을 보유하였으나, 12Ce-TZP의 경우는 점도를 감소시키기 위하여 부가적인 전해질이 필요하였다. 이론밀도의 98% 이상을 보유하고 0.3~$2.2\mu\textrm{m}$의 입경을 갖는 치밀한 다층복합체가$ 1500^{\circ}C$ 소결로 얻어졌다.