• Nuclear Engineering and Technology
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• v.53 no.5
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• pp.1642-1651
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• 2021

In this study, isophtalic neopentyl glycol polyester (NPG-PES) based composites with different loading ratios of pure tungsten metal (W), tungsten (VI) oxide (WO₃), tungsten boron (WB) and tungsten carbide (WC) composites were prepared as alternative shielding materials for ionizing electromagnetic radiation (IEMR) shielding. Structural characterizations of the composites were done. Gamma spectrometric analysis of composites for 80-2000 keV energy range was performed and their usability as IEMR shielding was discussed. As a result, the produced composites showed a shielding performance of 60-100% of the lead (the most widely used IEMR shielding material) depending on the reinforcement material, reinforcement loading rate and experimental conditions. Thus, it was reported that produced composites could be an alternative to lead shieldings that have several disadvantages as toxic properties, difficulty of processing and inelasticity.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.127-130
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• 2002

The 2.5 vol% TiNi/6061Al composites were fabricated by permanent mold casting, and its microstructures and tensile test for the cold rolled composites with maximum 50% reduction ratio were investigated. In the case of TiNi fiber with 2mm interval in preform, the interface bonding of fabricated composites were good. EPMA analysis results were found the small amount of Mg, Si segregated interface of diffusion layer. Transverse section of TiNi fiber was decreased with increasing reduction ratio and 40% reduction ratio was observed microcrack from TiNi fiber. And the tensile strength of composites at 38% reduction ratio was 194MPa. In the case of over 38% reduction ratio, the decrease of the tensile strength was due to TiNi fiber rupture by excess working. The fracture mode was appeared brittle fracture with increasing reduction ratio

• Fibers and Polymers
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• v.7 no.3
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• pp.286-294
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• 2006

This study has examined the flexural properties of natural and chemically modified coir fiber reinforced cementitious composites (CFRCC). Coir fibers of two different average lengths were used, and the longer coir fibers were also treated with a 1% NaOH solution for comparison. The fibers were combined with cementitious materials and chemical agents (dispersant, defoamer or wetting agent) to form CFRCC. The flexural properties of the composites, including elastic stress, flexural strength, toughness and toughness index, were measured. The effects of fiber treatments, addition of chemical agents and accelerated ageing of composites on the composites' flexural properties were examined. The results showed that the CFRCC samples were 5-12 % lighter than the conventional mortar, and that the addition of coir fibers improved the flexural strength of the CFRCC materials. Toughness and toughness index, which were associated with the work of fracture, were increased more than ten times. For the alkalized long coir fiber composites, a higher immediate and long-term toughness index was achieved. SEM microstructure images revealed improved physicochemical bonding in the treated CFRCC.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.7
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• pp.496-501
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• 2018

In this study, we prepared 40, 45, 50, 55, 60, 65, and 70 wt% content composites filled in epoxy matrix for two micro silica and three micro alumina types for use as a GIS heavy electric machine. As a filler type of epoxy composite, micro silica composites showed excellent AC breakdown strength properties compared to micro alumina composites in the case of electrical properties of micro silica and alumina. The electrical breakdown properties of micro silica composites increased with increasing filler content, whereas those of micro alumina decreased with increasing filler content. In the case of mechanical properties, the micro silica composite showed improved tensile strength and flexural strength compared with the micro alumina composite. In addition, mechanical properties such as tensile strength and flexural strength of micro silica and alumina composites decreased with increasing filler content. This is probably because O-H groups are present on the surface of silica in the case of micro silica but are not present on the surface of alumina in the case of micro alumina.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.4
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• pp.348-351
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• 2007

Recently, Nanotechnology becomes a major issue in most part of industries. Nanotechnology is expected to develop various application products due to nano material mired composites is improved physical and electrical properties compared to conventional composites materials. Dielectric and insulation materials need to develop and improve like other field about nanotechnology. In this paper, we reported dielectric dispersion by size(no filler, $1.2{\mu}m$, 500 nm, 10 nm), frequencies(60, 120, 1 kHz), and temperatures($30{\sim}170^{\circ}C$). Dielectric constant of composites materials with filler shows higher than composites materials without filler and increased depending on rising temperatures in low frequency region. It was the effect that nano-filler and impurities in composites contributed to electrical conductivity. And dielectric properties depending on temperatures shows to change in low frequency region dramatically We analyzed interfacial polarization in low frequency region($10^{-2}$ Hz) and oriented polarization in high frequency region($10^{-5{\sim}6}$ Hz) on composites materials.

• Composites Research
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• v.18 no.5
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• pp.21-26
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• 2005

The validity of Eshelby-type model with Mori-Tanaka's mean field theory to predict the effective material properties of composites have been investigated in terms of filler size and its arrangement. The 2-dimensional plate composites including constant volume fraction of fillers are used as the model composite for the analytical studies, where the filler size and its arrangement are considered as parameters. The exact effective material properties of the composites are computed by finite element analysis(FEA), which are compared with effective material properties from the Eshelby-type model. Although the fillers are periodically or randomly arranged, the average Young's moduli by Eshelby-type model and FEA are in good agreement, specially for the ratio of specimen size to filler size being smaller than 0.03. However, Poisson's ratio of the composite by the Eshelby-type model is overestimated by $20\%$.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.15 no.1
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• pp.39-48
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• 2006

In this paper, polymer composites based sandwich structures like beams and plates are optimised by using parametric study. The structures are composed of fibre reinforced composites for facial material and resin concrete and PVC foam for core materials. The stacking sequences and thickness of the composites are controlled as major parameters to find out the optimal condition for machine tool components. For the plate structure of machine tool bed composites-skined sandwich structure which has several ribs are proposed to enhance bending stiffnesses in two major directions at the same time. Dynamic robustness of a machine tool structure is investigated using modal analysis. From the results optimal configuration and materials for high precesion machine tools are proposed. And the plate was made of fiber reforced composite material and PVC foam.

• Journal of the Korean Ceramic Society
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• v.37 no.8
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• pp.805-810
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• 2000

The formation, microstructure and properties of MoSi2/SiC ceramic composites by polymer pyrolysis were investigated for the application of heating element material. Polymethylsiloxanes were mixed with Si, SiC, MoSi2 as filler and ceramic composites prepared by pyrolysis in N2 atmosphere at 1320~145$0^{\circ}C$ were studied. Dimensional change, density variation and phases were analyzed and correlated to the resulting material properties. Microstructures of ceramic composite prepared by polymer pyrolysis were composed of MoSi2, SiC and silicon oxycarbide glass matrix. Depending on the pyrolysis conditions, ceramic composites with a density of 86~90 TD%, a fracture strength of 213~284 MPa, a thermal expansion coefficient of 4~7$\times$10-6 were obtained. The electrical resistivity of the specimen decreased with increasing of temperature up to 50$0^{\circ}C$.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.345-348
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• 2004

In this paper it is to establish a comprehensive model for predicting damping in sandwich Laminated composites on the basis of strain energy method. In this model, the effect of transverse shear on the material damping has been considered with in-plane stresses. Results showed that the viscoelastic core thickness in the sandwich beam and the Length of a beam have a high impact on the material damping. The transverse shear appears to be highly influenced by the damping behavior in $0^0$ laminated sandwiched composites. However, it is Little influenced by that in $90^0$ laminated sandwiched composites.

• Structural Engineering and Mechanics
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• v.57 no.5
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• pp.897-920
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• 2016

The objective is to determine the mechanical properties of the composites formed in two types, theoretically. The first composite includes micro-particles in a matrix while the second involves long, thin fibers. A fictitious, homogeneous, linear-elastic and isotropic single material named as effective material is considered during calculation which is based on the equality of the strain energies of the composite and effective material under the same loading conditions. The procedure is carried out with volume integrals considering a unique strain energy in a body. Particularly, the effective elastic shear modulus has been calculated exactly for small-particle composites by the same procedure in order to determine of bulk modulus thereof. Additionally, the transverse shear modulus of fiber reinforced composites has been obtained through a simple approach leading to the practical equation. The results have been compared not only with the outcomes in the literature obtained by different method but also with those of finite element analysis performed in this study.