• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.1
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• pp.16-20
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• 2021

In this study, we tried finding new materials to improve the stain resistance properties of polymer insulating materials. Using the filtered vacuum arc source (FVAS) with a graphite target source, DLC thin films were deposited on silicon and polymer insulator substrates depending on their thickness to confirm the surface properties, physical properties, and structural properties of the thin films. Subsequently, the possibility of using a DLC thin film as a protective coating material for polymer insulators was confirmed. DLC thin films manufactured in accordance with the thickness of various thin films exhibited a very smooth and uniform surface. As the thin film thickness increased, the surface roughness value decreased and the contact angle value increased. In addition, the elastic modulus and hardness of the DLC thin film slightly increased, and the maximum values of elastic modulus and hardness were 214.5 GPa and 19.8 GPa, respectively. In addition, the DLC thin film showed a very low leakage current value, thereby exhibiting electrical insulation properties.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.460-463
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• 2003

In this paper, we present the properties of water absorption of elastic epoxy for high voltage. The ratio of water absorption shows linearly increase according to ${\sqrt}t$ till 66 hours. And rigid epoxy is 0.053 [%], elastic epoxy at addictives 35 [phr] is 0.309 and it at addictives 70 [phr] is 0.44 [%]. The reason where absorption of elastic epoxy is high is because of micro void. It can be confirmed by SEM analysis. Dieletric constant increased linearly by addictives' concentration and tans is also increased by addictives' concentration.

• Coupled systems mechanics
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• v.9 no.3
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• pp.201-217
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• 2020

This paper employs differential quadrature method (DQM) and nonlocal strain gradient theory (NSGT) for studying free vibrational characteristics of porous functionally graded (FG) nanoplates coupled by visco-elastic foundation. A secant function based refined plate theory is used for mathematical modeling of the nano-size plate. Two scale factors are included in the formulation for describing size influences based on NSGT. The material properties for FG plate are porosity-dependent and defined employing a modified power-law form. Visco-elastic foundation is presented based on three factors including a viscous layer and two elastic layers.The governing equations achieved by Hamilton's principle are solved implementing DQM. The nanoplate vibration is shown to be affected by porosity, temperature rise,scale factors and viscous damping.

• Steel and Composite Structures
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• v.33 no.3
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• pp.403-432
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• 2019

Axially functionally graded (AFG) beams are a new class of composite structures that have continuous variations in material and/or geometrical parameters along the axial direction. In this study, the exact analytical solutions for the free vibration of AFG and uniform beams with general elastic supports are obtained by using Euler-Bernoulli beam theory. The elastic supports are modeled with linear rotational and lateral translational springs. Moreover, the material and/or geometrical properties of the AFG beams are assumed to vary continuously and together along the length of the beam according to the power-law forms. Accordingly, the accuracy, efficiency and capability of the proposed formulations are demonstrated by comparing the responses of the numerical examples with the available solutions. In the following, the effects of the elastic end restraints and AFG parameters, namely, gradient index and gradient coefficient, on the values of the first three natural frequencies of the AFG and uniform beams are investigated comprehensively. The analytical solutions are presented in tabular and graphical forms and can be used as the benchmark solutions. Furthermore, the results presented herein can be utilized for design of inhomogeneous beams with various supporting conditions.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.8
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• pp.1876-1888
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• 1995

In this paper, glass surface-mat reinforced epoxy(G.S.R.E.) is developed, It is assured that the material(G.S.R.E.) can be used as photoelastic model material and it satisfy with the required properties of photoelastic model material. Therefore, the material can be used as model material of transparent photoelastic experiment when we analyze the stress distributions of transversely isotropic material by photoelastic experiment. When we use G.S.R.E. as photoelastic experiment model material, we had better use the G.S.R.E. which fiber volume ratio is less than 0.7% in the high temperature(stress freezing method) and than 1.74% in the room temperature. Relationships between stress fringe value and elastic modulus in transversely isotropic material are developed in this paper, it is assured by experiment that they are established in the room temperature or in the high temperature. Therefore we can obtain stress fringe value or elastic modulus from the relationships between stress fringe value and elastic modulus.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.10a
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• pp.217-220
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• 2003

The effective thermoelastic properties of porous metals are discussed herein after each material forming process such as hot pressing or extrusion. The voids in metal matrix are assumed to be initially spherical in shape and to be distributed randomly. Once the porous material deforms plastically due to each material forming process, the voids change their shape from a sphere to an ellipsoid and align in one direction. Since the voids are compressible in nature, the void volume fraction is assumed to be decreasing during each material forming process.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.1
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• pp.31-38
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• 2004

PMN-PT, a piezoelectric single crystal, has many useful applications such as sensors and actuators. In this paper, all the elastic, piezoelectric, and dielectric constants of the PMN-32％PT single crystals were measured by the resonance method. For the rhombohedral symmetry, a total of twelve independent material constants were measured such as six elastic compliance constants at constant electric field, two dielectric constants at constant stress, and four piezoelectric constants d. Seven sets of crystal samples of each different geometry were prepared for the measurement of length-thickness extensional, thickness extensional, radial, length extensional and thickness shear modes of vibration, respectively. In order to check the validity of the measurement, experimental impedance spectrum of the PMN-PT crystal was compared with numerical data spectrum calculated with the measured material constants. The good agreement between the two spectra confirmed validity of the results in this paper.

• Korea-Australia Rheology Journal
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• v.16 no.4
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• pp.169-173
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• 2004

The control of the rheological properties of a fluid during processing is important and can determine the efficiency of the production in addition to the performance of the final product. The vast majority of process fluids are viscoelastic, hence an instrument that measures both the viscous and elastic properties of the material during processing would be of great practical use. However, most in-line instruments commercially available to date are only capable of measuring viscosity at a single shear rate. An in-line rheometer that measures both the viscous and elastic properties of fluids over a wide range of shear rates simultaneously has been described in a previous publication (Glasscock et at., 2003) in which the results of measurements on flowing sunflower oil were presented. Before this instrument can be used in an industrial situation, it must be demonstrated that the generated results are the same as, or bear some fixed relationship to, the results obtained by conventional off-line rheometers. To this end, the present investigation describes the measurements of a standard reference fluid, polyisobutylene dissolved in 2,6,10,14-tetramethylpentadecane, labelled SRM2490 by the National Institute of Standards and Technology (NIST) in the USA. The results obtained using the in-line rheometer show remarkably good correlation for viscosity, using a modified Cox­Merz rule, with the results supplied with the reference material from NIST.

• Proceedings of the KSR Conference
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• 2000.11a
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• pp.311-318
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• 2000

In this paper, the process of development of resilient sleepers, which improves the train safety, passenger comport and reduces the noise and vibration, is discussed. To determine the required material properties of elastic pad, static and dynamic simulations are performed and is applied in manufacturing. From the experiment results, it is investigated that the displacement is less for sleeper with elastic pad than that in ordinary PC form. The rate of displacement is also shown In be less for the sleeper with elastic pad. These results indicate that the elastic pad can reduce possibility of rail-corrugations and thus resulting in the reduction of maintenance costs.

• The Journal of the Acoustical Society of Korea
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• v.19 no.1E
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• pp.43-47
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• 2000

The paper describes a theoretical study on the speed of torsional elastic waves propagating in a circular rod whose material properties vary periodically as harmonic functions of the axial coordinate. An approximate solution for the phase speed has been obtained by using the perturbation technique for sinusoidal modulation of small amplitude. This solution shows that the wave speed in the nonuniform rod is dependent on the wave frequency as well as the periodic variation of the material properties. It implies that the torsional waves considered in this paper are dispersive even in the fundamental mode.