• Korean Journal of Materials Research
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• v.29 no.3
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• pp.155-159
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• 2019

Surface plasmon resonance is the resonant oscillation of conduction electrons at the interface between negative and positive permittivity material stimulated by incident light. In particular, when light transmits through the metallic microhole structures, it shows an increased intensity of light. Thus, it is used to increase the efficiency of devices such as LEDs, solar cells, and sensors. There are various methods to make micro-hole structures. In this experiment, micro holes are formed using a wet chemical etching method, which is inexpensive and can be mass processed. The shape of the holes depends on crystal facets, temperature, the concentration of the etchant solution, and etching time. We select a GaAs(100) single crystal wafer in this experiment and satisfactory results are obtained under the ratio of etchant solution with $H_2SO_4:H_2O_2:H_2O=1:5:5$. The morphology of micro holes according to the temperature and time is observed using field emission - scanning electron microscopy (FE-SEM). The etching mechanism at the corners and sidewalls is explained through the configuration of atoms.

• Steel and Composite Structures
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• v.42 no.1
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• pp.91-106
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• 2022

Concrete-filled square stainless steel tubes (CFSSST), which possess relatively large flexural stiffness, high corrosion resistance and require simple joint configurations and low maintenance cost, have a great potential in constructional applications. Despite that the use of stainless steel may result in high initial cost compared to their conventional carbon steel counterparts, the whole-life cost of CFSSST is however considered to be lower, which offers a competitive choice in engineering practice. In this paper, a comprehensive experimental and numerical program on 24 CFSSST stub column specimens, including 3 austenitic and 3 duplex stainless steel square hollow section (SHS) stub columns and 9 austenitic and 9 duplex CFSSST stub columns, has been carried out. Finite element (FE) models were developed to be used in parametric analysis to investigate the influence of the tube thickness and concrete strength on the ultimate capacities more accurately. Comparisons of the experimental and numerical results with the predictions made by design guides ACI 318, ANSI/AISC 360, Eurocode 4 and GB 50936 have been performed. It was found that these design methods generally give conservative predictions to the ultimate capacities of CFSSST stub columns. Improved calculation methods, developed based on the Continuous Strength Method, have been proposed to provide more accurate estimations of the ultimate resistances of CFSSST stub columns. The suitability of these proposals has been validated by comparison with the test results, where a good agreement between the predictions and the test results have been achieved.

• Korean Journal of Soil Science and Fertilizer
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• v.44 no.5
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• pp.727-733
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• 2011

A new Korean standard for the determination of Cr(VI) in soils has been officially published as ES 07408.1 in 2009. This analytical method is based on the hot alkaline digestion and colorimetric detection prescribed by U.S. EPA method 3060A and 7196A. The hot alkaline digestion accomplished using 0.28 M $Na_2CO_3$ and 0.5 M NaOH solution (pH 13.4) at $90{\sim}95^{\circ}C$ determines total Cr(VI) in soils extracting all forms of Cr(VI), including water-soluble, adsorbed, precipitated, and mineral-bound chromates. This aggressive alkaline digestion, however, proved to be problematic for certain soils which contain large amounts of soluble humic substances or active manganese oxides. Cr(III) could be oxidized to Cr(VI) by manganese oxides during the strong alkaline extraction, resulting in overestimation (positive error) of Cr(VI). In contrast, Cr(VI) reduction by dissolved humic matter or Fe(II) could occur during the neutralization and acidic colorimetric detection procedure, resulting in underestimation (negative error) of Cr(VI). Futhermore, dissolved humic matter hampered the colorimetric detection of Cr(VI) using UV/Vis spectrophotometer due to the strong coloration of the filtrate, resulting in overestimation (positive error) of Cr(VI). Without understanding the mechanisms of Cr(VI) and Cr(III) transformation during the analysis it could be difficult to operate the experiment in laboratory and to evaluate the Cr(VI) results. For this reason, in this paper we described the theoretical principles and limitations of Cr(VI) analysis and provided useful guidelines for laboratory work and Cr(VI) data analysis.

• Steel and Composite Structures
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• v.36 no.4
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• pp.447-462
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• 2020

The paper aims to investigate the mechanical mechanism and seismic effect of stiffeners in blind bolt endplate connection to CFST column. A precise 3D finite element model with considering the cyclic properties of concrete and steel materials was established, and the efficiency was validated through monotonic and cyclic test data. The deforming pattern and the seismic performance of the unstiffened and stiffened blind bolt endplate connections were investigated. Then a parametric analysis was conducted to analyze the contribution of stiffeners and the joint working behaviors with endplate under cyclic load. The joint stiffness classifications were compared and a supplement stiffness classification method was proposed, and the energy dissipation ability of different class connections were compared and discussed. Results indicated that the main deformation pattern of unstiffened blind bolt endplate connections was the local bending of end plate. The vertical stiffeners can effectively alleviate the local bending deformation of end plate. And influence of stiffeners in thin endplate and thick endplate was different. Based on the stiffness of external diaphragm welded connection, a more detailed rigidity classification was proposed which included the pin, semi-rigid, quasi-rigid and rigid connection. Beam was the main energy dissipation source for rigid connection. For the semi-rigid and quasi-rigid connection, the extended endplate, stiffeners and steel beam would all participate in the energy dissipation.

• Journal of the Korean Ceramic Society
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• v.46 no.1
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• pp.74-80
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• 2009

Electrospinning process is the useful and unique method to produce nanofibers from metal precursor and polymer solution by controlled viscosity. In this study, the NiZn ferrite nanofibers were prepared by electrospinning with a aqueous metal salts/polymer solution that contained polyvinyl pyrrolidone and Fe (III) chloride, Ni (II) acetate tetrahydrate and zinc acetate dihydrate in N,N-dimethylformamide. The applied electric field and spurting rate for spinning conditions were 10 kV, 2 ml/h, respectively. The obtained fibers were treated at $250^{\circ}C$ for 1 h to remove the polymer. Finally, the NiZn ferrite fibers were calcined at $600^{\circ}C$ for 3 h and annealed at $900{\sim}1200^{\circ}C$ in air. By tuning the viscosity of batch solution before electrospinning, we were able to control the microstructure of NiZn ferrite fiber in the range of $150{\sim}500\;nm$ at 770 cP. The primary particle size in $600^{\circ}C$ calcined ferrite fiber was about 10 nm. The properties of those NiZn ferrite fibers were determined from X-ray diffraction analysis, electron microscopy, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, thermal analysis, and magnetic measurement.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.1
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• pp.115-122
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• 2011

Recently, we have proposed a hypothesis that spinal structures have a stress sensor driving feedback mechanism, In the human spine, spinal structure could react to modify muscular action in such a way so as to equalize stress at the disc, therefore reduce the risk of injury, In this analysis, abdominal muscle and abdominal pressure, which were not included in the previous study, were added to identify those effects in spine stability during upright stance posture for the case where the intervertebral disc plays the role of mechanoreceptor, The musculoskeletal FE model was consisted with detailed whole lumbar spine, pelvis, sacrum, coccyx and simplified trunk model. Muscle architecture with 46 local muscles containing paraspinal muscle and 6 rectus abdominal muscles were assigned according to the acting directions. The magnitude of 4kPa was considered for abdominal pressure. Minimization of the nucleus pressure deviation and annulus fiber average tension stress deviation was chosen for cost function. Developed model provide nice coincidence with in-vivo measurement (nucleus pressure). Analysis was conducted according to existence of co-activation of abdominal muscle and abdominal pressure. Antagonistic activity of abdominal muscle produced stability of spinal column with relatively small amount of total muscle force. In contrast to the abdominal muscle, effect of abdominal pressure was not clear that was partly depending on the assumption of constant abdominal pressure.

• Journal of the Korean Vacuum Society
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• v.20 no.1
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• pp.70-76
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• 2011

High-quality double-walled carbon nanotubes (DWCNTs) were synthesized by catalytic decomposition method at $800^{\circ}C$ using Tetrahydrofuran. The as-synthesized DWCNTs typically have catalytic impurities and amorphous carbon, which were removed by two-step purification process, consisting of thermal oxidation and H2O2, HNO3, HCl treatment. The DWCNT suspension was prepared by dispersing the purified DWCNTs in an aqueous sodium dodecylbenzenesulfonate solution with horn-type sonication. This was then sprayed on ITO glass to fabricate CNT field emitters. The quality of purified DWCNTs was estimated with X-ray diffraction and Thermal Gravity Analysis. The field emission properties were improved by increasing the process time of HCl treatment.

• Structural Engineering and Mechanics
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• v.63 no.1
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• pp.1-9
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• 2017

Shot peening is a cold surface treatment employed to induce residual stress field in a metallic component beneficial for increasing its fatigue strength. The experimental investigation of parameters involved in shot peening process is very complex as well as costly. The most attractive alternative is the explicit dynamics finite element (FE) analysis capable of determining the shot peening process parameters subject to the selection of a proper material's constitutive model and numerical technique. In this study, Ansys / LS-Dyna software was used to simulate the impact of steel shots of various sizes on an aluminium alloy plate described with strain rate dependent elasto-plastic material model. The impacts were carried out at various incident velocities. The influence of shot velocity and size on the plastic deformation, compressive residual stress and force-time response were investigated. The results exhibited that increasing the shot velocity and size resulted in an increase in plastic deformation of the aluminium target. However, a little effect of the shot velocity and size was observed on the magnitude of target's subsurface compressive residual stress. The obtained results were close to the published ones, and the numerical models demonstrated the capability of the method to capture the pattern of residual stress and plastic deformation observed experimentally in aluminium alloys. The study can be quite helpful in determining and selecting the optimal shot peening parameters to achieve specific level of plastic deformation and compressive residual stress in the aluminium alloy parts especially compressor blades.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.2
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• pp.73-79
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• 2014

The sandwich shell with Egg-box core has been used for the combustion chamber case of air breathing propulsion system. The alteration on pitch length and thickness of Egg-box core was required to be lighter and save manufacturing time and cost of combustion chamber case. In this paper, the finite element analysis method which simulated bending test was used to predict the equivalent shear modulus which affect structural stability of sandwich shell in short time. The result of FE calculation on sandwich panel with homogeneous material, H130-foam core, showed a good agreement with the values available in the reference. The equivalent shear modulus of Egg-box core according to the variation of pitch length and thickness can be obtained.

• Journal of Welding and Joining
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• v.33 no.3
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• pp.62-67
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• 2015

A very large shell-structure built in shipyards like ship hulls or offshore structures are joined by welding through full process. As the welding contains a high thermal cycle at a local area, the welded structures should be distorted unavoidably. Because a distorted ship block should be revised to the designed value before the next stage, the ability to predict and to control the weld distortion is an accuracy level of the yard itself. Despite the ship block size, several present thermal distortion methodologies can deal those sizes, but it is a different story to deal full ship size model. Even a fully constructed ship hull not remaining any welding can have an accuracy issue like outfitting installation problems. Any present thermal distortion methodology cannot accept this size for its recommended element size and the number. The ordinary welding breadth at erection stage is about 20~40 mm. It can hardly be a good choice to make finite element model of these sizes considering human effort and computational environment. The finite element model for structure analysis of a ship hull is prepared at front-end engineering design stage which is the first process of the project. The element size of the model is as fine as the longitudinal space, and it is not proper to obtain a weld distortion at the erection stage. In this study, a methodology is suggested that a weldment can be shrunk at original place instead of using structural finite element model. We cut the original shell elements at erection weld-line and put truss elements between the edges of cut elements for weld shrinkage. Additional truss elements are used to facsimile transverse weld shrinkage which cannot be from the weld-line truss element shrink. They attach to weld-line truss element like twigs from barks. The capacity of developed elements is verified through an accuracy check of erection process of a container vessel at the apt. hull. It can be a useful tool for verifying a centering accuracy after renew and for block-separating planning considering accuracy.