• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.294-294
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• 2007

Spinel cathode material $LiMn_2O_4$ is currently studied as a promising cathode material for lithium ion secondary batteries for future applications because of it is low cost, easy to be prepared and capable to be operated in high voltage range. However as a cathode material, $LiMn_2O_4$ performs a poor capacity retention which leads to short cycle life. In this study, stoichiometric $LiMn_2O_4$ was synthesized with granulation method with ion substitution to stabilize its structure and niobium doping to improve its conductivity. These well-mixed powders were calcined at $850^{\circ}C$ for 6 hours and its properties were investigated. Correlations of dopant and electrochemical properties were examined as well.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.333-334
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• 2006

The objective of this study is to fabricate a piezoelectric composite consisting of a piezoelectric ceramic and a high toughness material and to evaluate their electromechanical properties for high force actuator applications. The mixture of the piezoelectric material, PMNZT, and high toughness material, $ZrO_2$, exhibited high piezoelectric properties as well as good mechanical fracture resistance. Up to 2 vol% of $ZrO_2$ in PMNZT matrix, piezoelectric $d_{33}$ coefficient was above 400 pC/N, being 80% of that for the original PMNZT, and the toughness showed twice of the PMNZT. When the volume fraction of the $ZrO_2$ was above 5%, however, the piezoelectric coefficient became abruptly decreased and it approached 20% of value for the PMNZT.

• Korean Journal of Metals and Materials
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• v.50 no.6
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• pp.427-432
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• 2012

This paper presents the material properties of carbon steels for ships, and offshore structures (ASTM A131) are tested under a series of arctic and cryogenic temperature conditions. For material tension tests, among the ASTM 131 steels, Grades A and B of mild steel and Grade AH of high tensile steel have been used. The obtained mechanical properties of the materials from the material tension tests were applied in a 13,000TEU class container ship to define the effect of low temperature on the ultimate longitudinal strength of the target structure by using the ALPS/HULL intelligent supersize finite element method. The tensile coupon test results showed increased strength and nonuniform fracture strain behaviors within different grades and temperatures. Increasing the material strength resulted in increasing the ultimate longitudinal strength of the ship.

• Journal of the Korean Society of Industry Convergence
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• v.24 no.3
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• pp.283-288
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• 2021

A tungsten material using a pressure sintering process and a titanium sintering additive was prepared to evaluate the microstructure, and mechanical properties of flexural strength and hardness. In addition, the reliability on each hardness data was evaluated by analyzing the distribution of the hardness of the tungsten material using the Weibull probability distribution. In particular, the optimal manufacturing conditions were analyzed by analyzing the correlation between the sintering temperature and the mechanical properties of the tungsten sintered body. Although the sintering density of the tungsten material was hardly changed up to 1700 ℃, but it was increased at 1800 ℃. The hardness of the tungsten sintered material increased as the sintering temperature increased, and in particular, the tungsten material sintered at 1800 ℃ showed a high hardness value of about 1790 Hv. It showed relatively excellent flexural strength at a sintering temperature of 1800 ℃.

• Steel and Composite Structures
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• v.43 no.5
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• pp.603-623
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• 2022

This article is dedicated to predict the natural frequencies of joined conical shell structures made of Functionally Graded Material (FGM). The structure includes two conical segments. The equivalent material properties are found by using the rule of mixture based on Voigt model. In addition, three well-known patterns are employed for distribution of material properties throughout the thickness of the structure. The main objective of the present research is to propose a novel exponential pattern and obtain the related equivalent material properties. Furthermore, the Donnell type shell theory is used to obtain the governing equations of motion. Note that these equations are obtained by employing First-order Shear Deformation Theory (FSDT). In order to discretize the governing system of differential equations, well-known and efficient semi-analytical scheme, namely Generalized Differential Quadrature Method (GDQM), is utilized. Different boundary conditions are considered for various types of single and joined conical shell structures. Moreover, an applicable modification is considered for the continuity conditions at intersection position. In the first step, the proposed formulation is verified by solving some well-known benchmark problems. Besides, some new numerical examples are analyzed to show the accuracy and high capability of the suggested technique. Additionally, several geometric and material parameters are studied numerically.

• Structural Engineering and Mechanics
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• v.85 no.6
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• pp.717-728
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• 2023

The effect of temperature dependent material properties on the free vibration of FG porous beams is investigated in the present paper. A quasi-3D shear deformation solution is used involves only three unknown function. The mechanical properties which are considered to be temperature-dependent as well as the porosity distributions are assumed to gradually change along the thickness direction according to defined law. The beam is supposed to be simply supported and lying on variable elastic foundation. The differential equation system governing the free vibration behavior of porous beams is derived based on the Hamilton principle. Navier's method for simply supported systems is then used to determine and compute the frequencies of FG porous beam. The results of the present formulation are validated by comparing with those available literatures. Finally, the effects of several parameters such as porosity distribution and the parameters of variable elastic foundation on the free vibration behavior of temperature-dependent FG beams are presented and discussed in detail.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.135-138
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• 2001

We report the structural ,optical and electrical properties of ZnO thin films depending on the variation of the film thickness. The properties of the films deposited on sapphire (001) substrates using a pulsed laser deposition technique (PLD) were characterized with XRD, hall measurement and photoluminescence (PL). In our study, the increase of the thickness of ZnO thin films shows the improvement of the structural and optical properties. The electric properties of the films were also well matched with the structural and optical properties

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05c
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• pp.53-57
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• 2002

Reduction of insulation thickness would be beneficial not only for increasing the cable length but would also improve its thermal performance. An interfacial diffusion method was devised to reduce insulation thickness by improving the interfacial properties of XLPE cable insulation. In this paper, to evaluate superficially the interface properties between XLPE insulation and semiconducting layer, the dielectric and insulation properties of tan${\delta}$ and volume resistance were measured with temperature dependence. Above the results, dielectirc and insulation properties with semiconductor/XLPE were more anormal than its bulk caused by the interfacial properties.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.12
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• pp.1060-1069
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• 1998

Electrical properties such as space charge accumulation and water tree length and physical properties such as tensile strength, elongation and degree of crosslinked polyethylene (XLPE)/ethylene n-butyl acrylate copolymer (EnBA) blends were investigated. It was found that electrical properties such as water tree length grown at a specific condition and AC breakdown strength are improved by blending the XLPE with EnBA. The EnBA having higher nBA content showed the better electrical properties in XLPE/EnBA blends. A further improvement of these properties was achieved when a small amount of crosslinking coagent was used in the preparation of XLPE/EnBA blends.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.91-92
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• 2006

Metallic foams have a combination of attractive properties such as high specific mechanical properties and good energy absorption characteristics. This paper presents the properties of steel foam sandwiches produced using powder metallurgy approach. Metallic powder, solid polymeric binder and a foaming agent are dry-mixed and molded into the desired shape. The molded powder mix is then heat-treated to foam, debind and sinter the material. The resulting material has an open cell structure with high porosity. The structure and properties of sandwiches specimens produced with the process are presented and discussed.