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1

Fabrication of Porous Silica Fibers by Electrospinning for Sound Absorbing Materials

Cho Y.-S., Lee H. J.

Archives of Metallurgy and Materials

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2018

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Vol. 63, iss. 3

1497--1502

EN

Macroporous silica fibers having spherical cavities were fabricated by electrospinning using the spinning solution prepared from the mixed dispersion of tetraethylorthosilicate (TEOS) and polystyrene nanospheres as precursor and sacrificial templates, respectively, by injection through metallic nozzle. By applying electric field, the electro-spun fibers obtained by evaporation-driven self-assembly were collected on flat substrate or rotating drum, followed by the removal of the templates by calcination. The sound absorption coefficient of the porous fibers was measured by impedance tube, and the measured value was larger than 0.9 at high frequency region of incident waves. The surface of the resulting fibers was modified using fluorine-containing silane coupling agent to produce superhydrophobic fibrous materials to prevent the infiltration of humidity.

2

High Temperature Deformation Flow Of A ZK60A Magnesium Alloy After Extrusion

Kawasaki M., Lee H. J., Oh M. C., Ahn B.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2B

1327--1330

EN

Flow behavior of a ZK60A magnesium alloy after continuous casting and subsequent extrusion was examined in tension at a range of strain rates of 3.0×10-6 − 1.0×10-2 s-1 at temperatures of 473-623K. The results demonstrated that the alloy exhibited a maximum elongation of ~250% at 523K when tested at an initial strain rate of 1.0×10-5 s-1 and strain rate sensitivity, m, of ~0.3-0.4 and the activation energy of ~94 kJ/mol were calculated under the testing conditions. The detailed investigation suggested that the high temperature flow of the ZK60A alloy having submicrometer grains demonstrates quasi-superplastic flow behavior controlled by a dislocation viscous glide process.

3

The effect of silicon content on the pitting corrosion of duplex stainless steel weldment

Lee B.H., Lee H.J., Kang D.W., Lee H.W.

Archives of Materials Science and Engineering

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2014

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Vol. 67, nr 2

60--69

EN

In this study, the effect of Si content at a welded DSS on the pitting resistance was investigated. Design/methodology/approach: The δ-ferrite fraction increased due to addition of Si, and the amount of γ2 decreased. In the ferric chloride pitting test, the weight reduction range decreased due to an increase in the Si content. As to the location, pittings occurred intensively at the grain boundary or within the austenite grain due to the difference in PREN caused by the differential solid solubility in each phase. Findings: As a result of the potentiodynamic polarization test, while the Epit(Critical Pitting Potential) of all specimens depending on the temperature were observed to be similar at froom temperature up to 45°C, the reduction range of the Epit was found to be small at the temperature higher than 45°C as Si content increased. This was found to be because of formation of SiO2 in the passive film. Research limitations/implications: Higher the addition of Si, the more the number of pittings generated at the grain boundary decreased as the coherence of the passive film increased by the Si accumulated at the boundary. Originality/value: In this study, we intend to investigate the effect of Si element addition on the pitting resistance of the duplex stainless steel welding zone.

4

Boundary element modelling of wave diffraction by interaction with wave-offshore structure and dredged region

Kim S. D., Lee H. J.

Polish Maritime Research

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2010

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nr 2

67-71

EN

The purpose of this study is to estimate the wave height at the front face of breakwater (Refracted breakwater and Straight breakwater), when dredging like the submarine pit is performed in the distant offshore from outer breakwater. The wave field of the problem is considered to be two dimensional planes and the configuration of the pit region is designated by a single horizontal long-rectangular system. The numerical approach uses the Green function based on the boundary integral approach. The results of the present numerical works are illustrated by applying the normal and inclined incidence. It is shown that in the case of normal incidence, the ratio of wave height reduction at the front face of both types of breakwaters is approximately more than 20% due to the effect of the submarine pit on the sea bed. Furthermore, regardless of the type of breakwater and the difference in incident wave angles, the ratio of wave height was shown to be reduced.

5

Complex convexity of Orlicz-Lorentz spaces and its applications

Choi C., Kamińska A., Lee H. J.

Bulletin of the Polish Academy of Sciences. Mathematics

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2004

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Vol. 52, nr 1

19-38

EN

We give sufficient and necessary conditions for complex extreme points of the unit ball of Orlicz-Lorentz spaces, as well as we find criteria for the complex rotundity and uniform complex rotundity of these spaces. As an application we show that the set of norm-attaining operators is dense in the space of bounded linear operators from d* (w, 1) into d(w, 1), where d*(w, 1) is a predual of a complex Lorentz sequence space d[w, 1), if and only if w [is an element of] c0 \ L2.

6

M-ideal properties in Marcinkiewicz spaces

Kamińska A., Lee H. J.

Annales Societatis Mathematicae Polonae. Seria 1: Commentationes Mathematicae

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2004

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Vol. 44, nr spec.

123-144

EN

We study M-ideal properties of function and sequence Marcinkiewicz spaces. In particular we calculate the duals of the space L - L1 + L°° equipped with two standard norms and investigate when its subspace of order continuous elements is an M-ideal in E.