• Journal of the Microelectronics and Packaging Society
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• v.17 no.4
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• pp.83-88
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• 2010

The composite electroplating is accomplished by adding inert materials during the electroplating. Permalloy is the term for Ni-Fe alloy and it is used for industrial applications due to its high magnetic permeability. Microhardness for microdevices is enhanced after composite coating and it increases the life cycle. However, the hydroxyl group on the silica makes their surface susceptible to moisture and it causes the silica nanoparticles to be agglomerated in the aqueous solution. The agglomeration problem causes poor dispersion which eventually interrupts uniform deposition of silica nanoparticles. In this study, the dispersion of silica nanoparticles in the permalloy electroplated layer is reported with variation of additives and sonication time. Longer sonication period guaranteed better silica nanopowder dispersion and sonication period also influenced on composition of deposits. The amount of silica nanopowder codeposition and surface morphologies were influenced with variation of additives. In alkaline bath, smooth surface morphology and relatively high contents of silica nanopowder codeposition were obtained with addition of sodium lauryl sulfate.

• Journal of the Korean Ceramic Society
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• v.40 no.5
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• pp.441-446
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• 2003

Fine powders of ZnO were synthesized by the sol-gel method. The shape of gel powders with calcination temperatures changed into the sheet structure, the needle shape, and the spherical grain. The growth rate of grain size was slow to 700$^{\circ}C$ but high above 700$^{\circ}C$. The bigger the grain size is, the higher the degree of crystallization is. The organic element in gel powders evaporated below 300$^{\circ}C$. Temperature dependence of conductances showed the sigmoidal shape, but the temperature range of the constant conductances narrowed with the decrement of the calcination temperature of gel powders. The optimum sensing property for CO gas were observed with the specimen calcined at 500$^{\circ}C$ and degraded with the increment of calcination temperature.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.6
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• pp.707-712
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• 2012

Very high cycle fatigue (VHCF) behavior of aerospace components has emerged much attention due to their long service life. In this study, a piezoelectric ultrasonic fatigue testing (UFT) system has been developed by Mbrosiatec Co., Ltd. to study the high cycle fatigue (HCF) strength of Ti-6Al-4V alloy. Hourglass-shaped specimens have been investigated in the range from $10^6$ to $10^9$ cycles at room temperature under completely reversed R = -1 loading conditions,. Scanning electron microscopy (SEM) analysis revealed that failures occurred in the entire range up to the gigacycle regime, and the fractures have beenfound to be initiated from the surface, unlike in steels. However, it was found from the SEM microgprahs that microcracks transformed into intergranular fractures. Thus, it can be concluded from according to the results that this test method can be applicable to commercialized automotive and railroad parts that require high cycle fatigue strength.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.1
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• pp.41-48
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• 2017

Fine polymeric fibers have been gaining interest from the energy harvesting/storage, tissue, and bioengineering industries because of advantages such as the small diameter, high porosity, permeability, and similarities to a natural extracellular matrix. Electrospinning is one of the most popular methods used to fabricate polymeric fibers because it is not as limited in regards to the materials selection, and it does not require expensive or complex equipment. However, electrospun fibers have a severe aerodynamic instability because the small diameter fibers are able to pass through the atmospheric layer when there is a high electric field. As a result, electrospun fibrous mats have serious difficulties with controlling its shape and geometric properties. In this study, a hybrid nano/microfibrous mat is presented that is fabricated using electrospinning with two different solvent-based PCL solutions. This provides control of the fiber diameter, mat porosity, and mechanical properties. Various hybrid fibrous mats were fabricated after an experimental investigation of the effects of solvent on fiber diameter. It was then demonstrated that the mechanical properties and porosity of the fabricated various hybrid mats could be successfully controlled.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.6
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• pp.423-427
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• 2017

In this paper, an anchor design that improves bonding strength uniformity in the silicon-on-glass (SOG) process is presented. The SOG process is widely used in conjunction with electrode-patterned glass substrates as a standard fabrication process for forming high-aspect-ratio movable silicon microstructures in various types of sensors, including inertial and resonant sensors. In the proposed anchor design, a trench separates the silicon-bonded area and the electrode contact area to prevent irregular bonding caused by the protrusion of the electrode layer beyond the glass surface. This technique can be conveniently adopted to almost all devices fabricated by the SOG process without the necessity of additional processes.

• Applied Chemistry for Engineering
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• v.26 no.1
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• pp.35-39
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• 2015

Polyvinylchloride (PVC) thin films having a microporous structure could be prepared by using the solubility difference in solvents. PVC thin film with a water contact angle of $150^{\circ}$ or more was obtained from the PVC solution consisting of the mixture of tetrahydrofuran as a solvent and propanol as a non-solvent. In the drying process of dip-coated PVC film, the increase of drying temperature reduced the tendency of roughened surface, which led the decrease of surface hydrophobicity. As the addition of propanol in the solution with 1 wt% PVC increased, the uniformity of surface roughness was improved. In the case of oxygen plasma treatments, even though the surface structure of PVC thin film was not notably changed, the surface property of the film was changed from the super-hydrophobicity to hydrophilicity as a function of the plasma exposing time.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.2
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• pp.151-157
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• 2004

Ultrasonic testing is a kind of nondestructive test to detect a crack or discontinuity in materials or on material surfaces by sending ultrasound to it. This conventional ultrasonic technique has some limitations in reliably detecting crack or accurately assessing materials in the case of complex-shaped power plant components such as a turbine blade root. An alternative method for such a difficult inspection is highly needed. In this study, application of a phased array ultrasonic testing (UT) system to a turbine blade, one of the critical power plant components, has been considered, and the particular incident angle has been determined so that the greatest track detectability and the most accurate crack length evaluation nay be achieved. The response of ultrasonic phased array was also analyzed to establish a special method to determine the track )ength without moving the transducer. The result showed that the developed method for crack length assessment is a more accurate and effective method, compared with the conventional method.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.1
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• pp.149-158
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• 2004

In most RP processes, the inherent stair-stepped surfaces and shrinkage-induced warping of the parts require post processing such as surface finishing. To minimize such defects, VLH-ST, a newly developed RP process, employs a 3.9-mm thick expandable polystyrene (EPS) foam sheet and a hot wire to contour it to have slant linear-interpolated sides. The use of relatively thick sheets for layers, however, limits the process capability of constructing fine details, especially smaller than the layer thickness. This study is focused on the development of a post processing method fo fine details of VLM-ST parts. The post-processing tool was designed to meet all the requirements for the desirable post processing. It adopted a hot wire as a means of melting the EPS foam sheet. Various basic experiments on the post processing were carried out to obtain the optimal process conditions. The dominant process parameters such as the radiated heat input, the tool speed, and the gap between the tool tip and the foam sheet (tool height) were considered in the experiments. The effectiveness of the developed post-processing method fo forming or engraving fine details on the VLM-ST parts has been thus demonstrated. The experiments on engraving several sets of letters, such as CANESM, 인간, and 한국과학기술원, on the EPS foam sheet were carried out. In addition, a flowery shape was engraved on a three-dimensionally curved surface of a pottery-shape VLM-ST part.

• Tribology and Lubricants
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• v.36 no.4
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• pp.193-198
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• 2020

Fluid film bearings are among the best devices used for overcoming friction and reducing wear. Surface texturing is a new surface treatment technique used for processing grooves and dimples on the lubricated surface, and it helps to minimize friction further and improve the wear resistance. In several studies, parallel surfaces, such as thrust bearings and mechanical face seals, have been investigated, but most sliding bearings have a convergent film shape. This paper presents the third part of a recent study and focuses on the effect of the groove shape on the lubrication performance of inclined slider bearings, following the two previous papers on the effects of the groove position and depth. We adopted the continuity and Navier - Stokes equations to conduct numerical analyses using FLUENT, which is a commercial computational fluid dynamics code. The groove shape adopted in the numerical analysis is rectangular and triangular, and its depth is varied. The results show that the streamlines, pressure distributions, and groove shape significantly influence the lubrication performance of the inclined slider bearing. For both shapes, the load-carrying capacity (LCC) is maximum near the groove depth, where vortices occur. In the shallow grooves, the LCC of the rectangular shape is higher, but in deeper grooves, that of the triangular shape is higher. The deeper the rectangular groove, the higher the decrease in the frictional force. The results of this study can be used as design data for various sliding bearings.

• Korean Journal of Materials Research
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• v.11 no.7
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• pp.569-574
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• 2001

The crystal structure, surface morphology and preferred orientation of the copper electrodeposit were investigated by the using sulfate bath with $SiO_2$suspensions and the cathode substrate Au sputtered. As by the addition of colloidal silica in copper electrolytic bath and Au pre-coating on substrate, the crystal particles of deposits was fined-down, made uniform and the account of particles were increased. Hardness of copper electrodeposits with colloidal silica increased about 15% in comparison with that of pure copper deposit film and (111), (200) and (311) plane of X-ray diffraction patterns were almost swept away, so preferred orientation of the copper deposits changed from (111) to (110) plane by codeposit $SiO_2$ and precoating the substrate.