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1

A Fatigue Fracture Study on TDCB Aluminum Foam Specimen of Type Mode III Bonded with Adhesive

Lee J. H., Cho J. U.

Archives of Metallurgy and Materials

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2017

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Vol. 62, iss. 2B

1359--1362

EN

This paper studies the characteristics of junction structure of closed-cell type aluminum foam, which is generally used as a shock absorber. TDCB specimens were designed for mode III type with thickness as a variable and performed a fatigue experiment on them by thickness. As the result, the load value of all specimens peaks under 0 to 25 cycles and decreases as the cycles increase. As the specimen thickens by 10 mm, the maximum load value is 1.2 times. When the thickness increases by 20 mm, the maximum value increases by 1.5 times. This study result can be utilized by investigating the mechanical characteristics of TDCB specimens for mode III type under fatigue loading conditions systematically and efficiently.

2

Morphology Change Of Si Deposit In Molten Salt Electrorefining

Ryu H. Y., Kwon S. C., Han M. H., An Y. S., Lee J. S., Lee J. H.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2B

1491--1497

EN

The effects of processing parameters on the morphology change in a Si deposit recovered by means of molten salt electrorefining are evaluated using electrochemical techniques such as cyclic voltammetry and chronopotentiometry at 800°C. It was found that concentration of K2SiF6 and current density were important parameters in determining deposit size. Higher concentrations of K2SiF6 were effective in coarsening the silicon deposit and decreasing the cell potential. Silicon nanofiber was recovered at 5 wt% of K2SiF6 whereas dense particles were prepared at 30 and 50 wt% of K2SiF6. The morphology of the Si deposit was determined by the concentration of Si in the electrolyte which is related to the formation of crystal and growth of Si. The formation mechanism of the Si deposit was interpreted by using high resolution TEM as well as electrochemical properties.

3

Graphite Nanosheet Exfoliation From Graphite Flakes Through Functionalization Using Phthalic Acid

Kim J. H., Lee J. H.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2B

1251--1255

EN

In order to fabricate graphite nanosheets from graphite flakes, edge-functionalized graphite nanosheets were prepared by a functionalization method using phthalic acid as the molecule to be grafted. A polyphosphoric acid/P2O5 solution containing graphite and phthalic acid were heated at different temperatures for 72 h in a nitrogen atmosphere. It was confirmed by transmission electron microscopy and atomic force microscopy that the resultant phthalic acid-functionalized graphite nanosheets had a large surface area of 20.69 μm2 in average and an average thickness of 1.39 nm. It was also found by X-ray diffractometry and Fourier transform infrared spectroscopy (FT-IR) analysis that the functionalization caused the formation of C=O bonds at the edges of the graphite nanosheets. The yield from this functionalization method was found to be dependent on the reaction temperature, only when it is between 70 and 130°C, because of the dehydration of phthalic acid at higher temperatures. This was confirmed by FT-IR analysis and the observation of low thermal energies at low temperatures.

4

Effects Of Process Parameters On Cu Powder Synthesis Yield And Particle Size In A Wet-Chemical Process

Shin Y. M., Lee J. H.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2B

1247--1250

EN

This study presents a simple wet-chemical process to prepare several micron-size Cu powders. Moreover, changes in powder synthesis yield and particle size are examined with different solvents, synthesis temperatures, and amounts of reducing agent during the synthesis. As a reducing agent and capping agent, L-ascorbic acid and polyvinyl pyrrolidone were used, respectively. The yields in distilled water or an ethylene glycol (EG)/distilled water mixture were higher than that in EG alone, and the yield increased with increasing temperature owing to a lower Δ Gred value. Increasing the L-ascorbic acid concentration also increased the yield. The Cu powder synthesized in 3 h at 90°C in distilled water with 272.8 mM of L-ascorbic acid showed the lowest average particle size of 2.52 μm, indicating mechanisms of short burst nucleation and reduced growth via the increased reduction rate of Cu ions. It is estimated that the nucleation step was nearly completed within 10 min in this system. The Cu powders synthesized in an ethylene glycol/distilled water mixture presented an average particle size of 3.76 μm and the highest yield of 87.9%.

5

Compositional Dependence of Hardness of Ge-Sb-Se Glass for Molded Lens Applications

Park J. K., Lee J. H., Shin S. Y., Yi J. H., Lee W. H., Park B. J., Choi J. H., Kim N. Y., Choi Y. G.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2B

1205--1208

EN

Chalcogenide glass in the ternary Ge-Sb-Se system is inherently moldable, thus being considered as a strong candidate material for use in infrared-transmitting lens applications from the viewpoint of thermal and mechanical stability. In an effort to experimentally determine compositional region suitable for the molded lens applications, we evaluate its compositional dependence of hardness. Among the constituent atoms, Ge content turns out to exert a most conspicuous correlation with hardness. This phenomenological behavior is then explained in connection with the structural evolution that Ge brings about.

6

Towards Safe Navigation by Formalizing Navigation Rules

Kreutzmann A., Wolter D., Dylla F., Lee J. H.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2013

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Vol. 7, no. 2

161--168

EN

One crucial aspect of safe navigation is to obey all navigation regulations applicable, in particular the collision regulations issued by the International Maritime Organization (IMO Colregs). Therefore, decision support systems for navigation need to respect Colregs and this feature should be verifiably correct. We tackle compliancy of navigation regulations from a perspective of software verification. One common approach is to use formal logic, but it requires to bridge a wide gap between navigation concepts and simple logic. We introduce a novel domain specification language based on a spatio‐temporal logic that allows us to overcome this gap. We are able to capture complex navigation concepts in an easily comprehensible representation that can directly be utilized by various bridge systems and that allows for software verification.

7

Development of the intelligent algorithm to control on-line bead height for robotic welding process

Son J. S., Kim I. S., Lee J. H., Park M.H., Jeon G.S.

Journal of Achievements in Materials and Manufacturing Engineering

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2013

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Vol. 58, nr 2

87--93

EN

Purpose: The demand to increase productivity and quality, the shortage of skilled labour and strict health and safety requirements finally led to the development of the robotic welding process to deal with many problems of the welded fabrication. Many techniques were developed to control process parameters to get the optimal bead geometry during welding process by minimizes their magnitude in the affected area. Design/methodology/approach: The development of thermo mechanical mechanism in some techniques is not fully understood. To solve this problem, we have carried out the sequential experiment based on a Taguchi method and identified the various problems that result from the robotic GMA welding process. Findings: To characterize the GMA welding process and establish guidelines for the most effective joint design. Also using multiple regression analysis with the help of a standard statistical package program, SPSS, on an IBM-compatible PC, a quadratic model has been developed for on-line control which studies the influence of process parameters on bead height and compares their influences on the bead height to see which one of process parameters is most affecting. Originality/value: This model developed has been employed the prediction of optimal process parameters and assisted in the generation of process control algorithms.

8

A study on simulation model and kinematic model of welding robot

Jeong J. W., Kim I. S., Chand R. R., Lee J. H.

Journal of Achievements in Materials and Manufacturing Engineering

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2012

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Vol. 55, nr 1

66--73

EN

Purpose: This study tries to develop a simulation model of six degree freedom for Faraman AM1 welding robot using CATIA V5 and compares with the computed kinematic model for robotic welding. The error varification of simulated model and kinematics of the robot is also being carried out. Design/methodology/approach: CATIA (Computer Aided Three dimensional Interactive Application) is a multi-platform PLM/CAD/CAM/CAE commercial software suite to use to develop six degree freedom for Faraman AM1 welding robot. The forward kinematic and inverse kinematic equations are also used to verify the developed model. Findings: The results obtained from the six degree freedom for Faraman AM1 simulated model has a good agreement with computed kinematic models equations. The catia V5 a very powerful tool which could used in develope a simulation for robotic welding system. The the angle error between simulated model and computed inverse kinmenatic equation obtained too very small. Research limitations/implications: The developed simulated in Catia is mainly aimed to be used in GMA welding process. D-H (Denavit-Hartenberg) convection is used to determine the orthonormal coordinate frames at different joints of a robotic manipulator and determining four kinematic parameters. Originality/value: The six degree freedom for Faraman AM1 welding robot is model to analysed and compared with forward and inverse knimatic.

9

An experimental study on the prediction of back-bead geometry in pipeline using the GMA welding process

Kim J.S., Kim I. S., Lee J.H., Jung S.M.

Archives of Materials Science and Engineering

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2011

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Vol. 49, nr 1

53-61

EN

Purpose: of this research paper is to select optimal welding condition for a root-pass welding for pipeline and to provide a best process for desirable welding quality. Design/methodology/approach: In this study, a variety of welding experiments were carried out to optimize an automated welding process using a GMA (Gas Metal Arc) process, these has been applied for root-pass welding. Welding current, welding speed, wire feed speed and torch angle were chosen as input parameters, while back-bead geometry representing quality of root-pass welding as output parameter. Findings: Based on the results from welding experiments, optimal welding conditions were selected after analyzing correlation between welding parameters and back-bead geometry such as back-bead width and back-bead height. Moreover, not only effectiveness of empirical models developed was compared and analyzed. The optimized empirical models were finally developed for predicting back-bead geometry by analyzing the main effect of each factor and their influence on interaction. Research limitations/implications: This research was concentrated on the developed empirical models that can predict back-bead width and height for root-pass welding in pipeline. Originality/value: This study is intended to define correlations between process parameters and back-bead geometry as welding quality and eventually select optimal welding condition by performing root-pass welding experiment under various conditions.

10

Optical guided dispersions and subwavelength transmissions in dispersive plasmonic circular holes

Kim K. Y., Cho Y. K., Tae H. S., Lee J. H.

Opto-Electronics Review

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2006

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Vol. 14, No. 3

233-241

EN

The light transmission through a dispersive plasmonic circular hole is numerically investigated with an emphasis on its subwavelength guidance. For a better understanding of the effect of the hole diameter on the guided dispersion characteristics, the guided modes, including both the surface plasmon polariton mode and the circular waveguide mode, are studied for several hole diameters, especially when the metal cladding has a plasmonic frequency dependency. A brief comparison is also made with the guided dispersion characteristics of a dispersive plasmonic gap [K.Y. Kim, et al., Opt. Express 14, 320-330 (2006)], which is a planar version of the present structure, and a circular waveguide with perfect electric conductor cladding. Finally, the modal behaviour of the first three TM-like principal modes with varied hole diameters is examined for the same operating mode.

11

Fault diagnosis and fault tolerant control of linear stochastic systems with unknown inputs.

Lee J.H., Lyou J.

Systems Science

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2001

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Vol. 27, nr 3

59-76

EN

This paper presents an integrated robust fault detection and isolation (FDI) and fault tolerant control (FTC) scheme for a fault in actuators or sensors of linear stochastic systems subjected to unknown inputs (disturbances). As usual in this kind of works, it is assumed that single fault occurs at a time and the fault treated is of random bias type. The FDI module is constructed using banks of robust two-stage Kalman filters, which simultaneously estimate the state and the fault bias, and generate residual sets decoupled from unknown disturbances. All elements of residual sets are evaluated by using a hypothesis statistical test, and the fault is declared according to the prepared decision logic. The FTC module is activated based on the fault indicator, and additive compensation signal is computed using the fault bias estimate and combined to the nominal control law for compensating the fault's effect on the system. Simulation results for the simplified longitudinal flight control system with parameter variations, process and measurement noises demonstrate the effectiveness of the approach proposed.

12

Characteristics of infrared photodiode using SiO₂ insulator on InSb wafer with p-i-n structure

Cho J. Y., Kim J. S., Son S. H., Lee J. H., Choi S. Y.

Opto-Electronics Review

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1999

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Vol. 7, No. 4

369-374

EN

A highly sensitivite photovoltaic infrared diode was fabricated for detecting a 3-5 µm wavelength range in an InSb wafer with a p-i-n structure grown by MOCVD. The formation of silicon dioxide (SiO₂) insulator films for the junction interface and surface of the photodiode were prepared using remote plasma enhanced chemical vapour deposition (PECVD) as InSb has a low melting point and evaporation temperature for surface atoms. The structural characteristics of SiO₂ films and electrical characteristics of metal-insulator-semiconductor structures were initially examined. The leakage current density at 1 MV/cm was about 22 nA/cm², the breakdown electric field of the MIS capacitor using SiO₂ film deposited at 105°C was about 3.5 MV/cm, and the interface-state density at the mid-band gap extracted from the 1 MHz capacitance-voltage measurement was about 2x10¹¹ cm⁻² eV⁻¹. Thereafter, the characteristics of the infrared photodiode were examined. The product of zero-bias resistance by area (R₀A) showed 1.56 x 10⁶ Ωcm² and normalized detectivity exhibited about 1x10¹¹ cm⁻² W⁻¹.

13

Mossbauer studies of La-Ca-Mn-Fe-O compounds

Kim C. S., Park S. I., Lee J. H., Rhie K., Lee J. G.

Electron Technology

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1998

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Vol. 31, No. 1

90-95

EN

Magnetic and structural properties of La0.67 Ca0.33 Mn1-x Fex O3 (x=0.0-0.05) powders have been studied with Mossbauer spectroscopy vibrating sample magnetometer (VSM), and X-ray diffraction. A single phase of the polycrystalline perovskite powder has been prepared using the metal-salt routed sol-gel method. The results of X-ray measurements show that there was not appreciable change in the value of the lattice parameter when a small amount of iron was added. However, the results of Mossbauer and VSM measurements demonstrate that the Curie temperature of the perovskite powder (x = 0.05) has descreased from 282 K to 180 K and that the large decrease of the saturation magnetization from 84 emu/g to 40 emu/g at 77 K has been observed as ⁵⁷Fe(x =0.05) was introduced into the compound. Mossbauer spectra of La0.67 Ca0.33 Mn0.95 Fe0.05 O3 powders have been taken at various temperatures ranging from 4.2 K to room temperature. It is observed that the pattern of the spectra were changed from a doublet line to a 6-line as the temperature decreased. Four experimental magnetic hyperfine fields at 4.2 K are found to be 465, 514, 489, and 417 kOe and isomer shifts at 4.2 K are ).37, 0.38, 0.35, and 0.29 mm/s. These isomer shifts indicate that the valence state of Fe ions is ferric (Fe³⁺), which are relative to A-Fe at room temperature. It should be noted that superparamagnetic relaxation begins at 37 K.

14

Angular dependencies of longitudinal magnetoresistivity and planar hall effect of single and multilayered thin films

Ko T. W., Lee J. H., Park B. K., Jang P. W., Hwang D. G., Lee S. S., Kim M. Z., Rhee J. R.

Electron Technology

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1998

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Vol. 31, No. 1

70-79

EN

Magnetoresistivity and planar Hall effect of a Glass/Fe₇₀Å/(Co₂₁Å/Cu₂₅Å)₂₀ multilayer coupled antiferromagnetically a single layer (Co₈₁Nb₁₉) thin film, and NiO based Glass/NiO₃₅Å/Py₅₀Å/Cu₂₀Å/Py₅₀Å spin valve spin valve are studied. Planar Hall resistivity is analyzed concurrently with the resistivity of each sample. With variation of direction and strength of the applied fields, we found thwt the magnetization process affects significantly the planar Hall effect. We devwloped a simple method to find the easy axis of single layer magnetic thin films. We also observed the variation of magnetization of each layer separately for an antiferromagnetically coupled multilayer, and a NiO-based spin valve with the planar Hall effect.