• Proceedings of the KIEE Conference
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• 1997.07d
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• pp.1405-1407
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• 1997

A microstructure of realistic ZnO varistor is constructed by Voronoi network and studied via computer simulation. In this network, the grain boundary condition is fitted from the experimental data. The effect of the variation of the uniformity of the varistor on the electrical characteristic of the varistor is simulated by using this boundary condition.

• Journal of the Korean Ceramic Society
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• v.33 no.2
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• pp.169-176
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• 1996

The specimens which were prepared from $\alpha$-Si3N4 with additions of YAG(3Y2O3.5Al2O3)-10 wt% and various AlN contents were sintered in N2 atmosphere at 1$700^{\circ}C$ The effect of $\alpha$,$\beta$-solid solution contents and sintering time on mechanical properties were investigated. As the content of $\beta$-solid solution and sintering time increased the hardness is reduced but the hardness of specimen sintered over 10 hours is constant irrespective of sintering time. While the fracture toughness increased with increasing of $\beta$-solid solution and sintering time. The fracture toughness of specimen with 80% $\beta$-solid solution content increased from 3.89 to 6.66 MPam1/2 with sintering sintering up to 20 hours/ But the amount of increased fracture toughness of specimen with below 20% $\beta$-solid solution content is not significant.

• Journal of Welding and Joining
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• v.23 no.4
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• pp.17-26
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• 2005

HAZ (Heat Affected Zone) which occurs during welding thermal cycle has an important effect on the mechanical properties of the weld metal. So there were many efforts to develop the model which is able to predict the microstructure and mechanical properties in weld HAZ and lots of metallurgical models have reported since early 1940. These models are justifiable based on the reasonable assumption and analytical approach, but they also have limitation by interesting alloying system and assumption in each literature. Therefore, this study summaries the previous models for prediction of properties in weld HAZ. Then several issues to solve for developing the more reliable model were proposed.

• Journal of the Korean Ceramic Society
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• v.30 no.12
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• pp.1015-1022
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• 1993

The formation process of polycrystalline YIG(Y3Fe5O12) prepared by conventional method in Fe2O3-Y2O3 system was investigated. Effect of the microstructure of sintered body on electromagnetic properties was also investigated. Orthoferrite (YFeO3) was formed between 900 and 110$0^{\circ}C$. Formation of YIG phase begin at 110$0^{\circ}C$ with sharp increased saturation magnetization simultaneously. YIG phase is identified as single phase above 120$0^{\circ}C$. The microstructures and electromagnetic properties of sintered bodies are varied due to calcination condition of starting materials. The sintered YIG of calcined sample at 110$0^{\circ}C$ has such magnetic properties as Bs=1580G, BHC=1.89Oe, Tc=570K, ΔH(9.3GHz)=78Oe.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2578-2582
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• 2008

In predicting the critical heat flux (CHF) in pool boiling systems, the contact angle between the boiling surface and the liquid and the surface roughness are considered to be the important parameters. From the microscopic viewpoint, those are affected by the micro/nano structure of the surface. Several studies have been reported on the dependence of CHF on the surface microstructure such as height and width of the cavities and distances between them. In this paper, the effects of the boiling surface characteristics on CHF are reviewed and the future research issues are discussed for better prediction of CHF.

• Journal of the Korean Ceramic Society
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• v.51 no.6
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• pp.612-617
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• 2014

The microstructure, nonlinear properties, and impulse clamping characteristics of Pr/Co/Cr/Al co-doped zinc oxide ceramics were investigated with various contents of $Er_2O_3$. Increasing $Er_2O_3$ content increased the density of the sintered pellets from 5.69 to $5.83g/cm^3$, and decreased the average grain size from 10.6 to $6.5{\mu}m$. With increased $Er_2O_3$ content, the breakdown field increased from 2318 to 4205 V/cm, and the nonlinear coefficient increased from 19.4 to 40.2. The clamp characteristics were improved with the increase of the content of $Er_2O_3$. The varistors doped with 2.0 mol% exhibited the best clamp characteristics, in which the clamp voltage ratio was 1.40-1.73 at 1-50 A in an impulse current.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.112-115
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• 2000

In this work the results of the systematic investigations on the effect of organic addition by using polymer compound as starting materials on the superconducting properties of YBCO electrophoretic deposited films on silver substrate are presented. The characteristics of the films were examined by X-ray diffraction and SEM observation. Our results show that the adhesion and microstructure of these films are sensitive to the nature of polymer compounds and sintering conditions (electrophoretic deposition, drying and heat-treatment procedures). To develop optimum microstructures for samples processed in this manner it is necessary to have an understanding of how these processes affect the microstructure and hence the properties of ceramic superconductors.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.303-304
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• 2006

The mechanical properties of ferrous powder metallurgy (P/M) materials are directly related to their microstructure. Ferrous P/M materials with sufficient hardenability will develop microstructures containing significant percentages of martensite in the as-sintered condition. Recently, sinter-hardening has developed into a highly cost effective production method through hardened P/M parts without the need for additional heat-treatments. This paper reviews the advances of sinter-hardening as well as some key processing parameters such as sintering temperature, cooling rate, tempering required to produce high quality sinter-hardened components. Specific topics including effect of alloying elements, alloying methods, and the Characterization and observation of microstructure are discussed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.108-110
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• 2000

The aim of this paper is to investigate the effect of Al and Ti on microstructure of Fe-Cr-Al alloy systems for applying electrical resistance wires of electrical furnace. From the preliminary study, the amount of recovered addition elements increased in the case of both vacuum and Ar-atmosphere melting than that in the case of air-atmosphere melting. Also, optimum Cr content for good performance at high temperature was approximately 24wt% from the observation of microstucture. The precipitates of Fe-Cr, Al-Cr and Al phases were observed, adding Al and Ti. Especially, Sharp rectangular shapes of precipitates were observed with increasing amount of Ti.

• Coupled systems mechanics
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• v.6 no.1
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• pp.1-15
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• 2017

Despite the exceptional mechanical properties of individual carbon nanotubes (CNTs), the effective properties of CNT-reinforced composites remain below expectations. The composite's microstructure has been identified as a key factor in explaining this discrepancy. In this contribution, a method for generating representative volume elements of aligned CNT sheets is presented. The model captures material characteristics such as random waviness and entanglement of individual nanotubes. Thus it allows studying microstructural effects on the composite's effective properties. Simulations investigating the strengthening effect of the application of a pre-stretch on the CNTs are carried out and found to be in very good agreement with experimental values. They highlight the importance of the nanotube's waviness and entanglement for the mechanical behavior of the composite. The presented representative volume elements are the first to accurately capture the waviness and entanglement of CNT sheets for realistically high volume fractions.