• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.7
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• pp.905-912
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• 2013

Rubber is one of the most commonly used materials in various fields because of its unique viscoelastic properties. Friction occurs when a tire constantly makes contact with the ground. As a result, friction causes wear. The frictional energy caused by friction is a primary factor in the wear mechanism. The frictional energy is affected by various conditions (temperature, roughness of ground, shape of rubber, load, and materials). In this study, the analysis was preceded by considering the vertical load and the horizontal velocity to the rubber using ABAQUS/explicit. The contact pressure, and friction energy are derived using the shear force and slip distance. The actual behavior of the rubber test data were compared with the analysis results.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.8
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• pp.54-63
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• 2001

Rapid Prototyping(RP) techniques have their unique characteristics according to the working principles: stair-stepped surface of a part due to layer-by-layer stacking, low build speed caused by point-by-point or line-by-line solidification to build one layer, and additional posts processing to improve surface roughness, so high cost is required to introduce and to maintain the RP apparatus. The objective of this study is to develop a new RP process, Variable Lamination Manufacturing by using expandable polystyrene foam sheet as part material(VLM-S), and to design an apparatus for implementation of the process. So, the process parameters and design criterions of the apparatus were defined and the techniques were proposed to satisfy the design criterion. Based on the results, a knob-shape, pyramid shape. and a solid block were fabricated on the apparatus in which unit shape part(USP) was generated for building each layer.

• Membrane and Water Treatment
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• v.9 no.1
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• pp.43-51
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• 2018

Hollow fiber (HF) membranes are gaining wide interest over flat membranes due to their compaction and high area to surface volume ratio. This work addresses the fabrication of HF from polysulfone (PS) and polyethersulfone (PES) using N-methylpyrrolidone (NMP) as solvent in addition to other additives to achieve desired characteristics. The semi-pilot spinning system includes jacketed vessel, four spinneret block, coagulation and washing baths in addition to dryer and winder. Different parameters affecting dry-wet spinning phase inversion process were investigated. Dope compositions of PES, NMP and polyvinyl pyrrolidone (PVP) of varying molecular weights as additive were addressed. Some critical parameters of importance were also investigated. Those include dope flow rate, air gap, coagulation & washing baths and drying temperatures. The measured dope viscosity was in the range from 1.7 to 36.5 Pa.s. Air gap distance was adjusted from 20 to 45 cm and coagulation bath temperature from 20 to $46^{\circ}C$. The HF membranes were characterized by scanning electron microscope (SEM), atomic force microscope (AFM) and mechanical properties. Results indicated prevalence of finger like structure and average surface roughness from about 29 to 78.3 nm. Profile of stress strain characteristics revealed suitability of the fibers for downstream interventions for fabrication of thin film composite membrane. Different empirical correlations were formulated which enable deeper understanding of the interaction of the above mentioned variables. Data of pure water permeability (PWP) confirmed that the fabricated samples fall within the microfiltration (MF)-ultrafiltration (UF) range of membrane separation.

• Polymer(Korea)
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• v.37 no.4
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• pp.431-436
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• 2013

Polycarbonate (PC) films have been irradiated with various kinds of ions according to energy and dose. Change of the optical transmittance and chemical characteristics were confirmed by UV-VIS and FTIR (ATR) spectroscopy respectively. These UV-A block in 400 nm was variable from 10 to 100% according to energy and doses. Surface electrical resistance of PC film irradiated by ion beam was $10^6-10^{13}{\Omega}/cm^2$, which reveal variation of conduction. Contact angle of film irradiated by ion beam was decreased than the pristine film. Polymer surface morphology was examined by means of atomic force microscopy (AFM). As expected, degradation of polymer film was higher after irradiation with heavier Xe ions but the roughness in the polymer surface morphology were more pronounced for Ar ions. This observed effect can be explained by stronger compaction of polymer surface layer in the case of Xe irradiation, connected with a reduction of free volume available.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.21 no.6
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• pp.225-229
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• 2011

Most of the silicon cutting methods using the multi-wire with the slurry injection have been used for wafers of the crystalline solar cell. But the productivity of slurry injection cutting type falls due to low cutting speeds. Also, the direct contact with the metal wire and silicon block increases the concentration of metallic impurities in the wafer's surface. In addition, the abrasive silicon carbide (SiC) generates pollutants. And production costs are rising because it does not re-use the worn wire. On the other hand, the productivity of the cutting method using the diamond coated wire is about 2 times faster than the slurry injection cutting type. Also, the continuous cutting using the used wire of low wear is possible. And this is a big advantage for reduced production costs. Therefore, the cutting method of the diamond coated wire is more efficient than the slurry injection cutting technique. In this study, each cutting type is analyzed using the surface characteristics of the solar wafer and will describe the effects of the manufacturing process of the solar cell. Finally, we will suggest improvement methods of the solar cell process for using the diamond cutting type wafer.

• Bulletin of the Society of Naval Architects of Korea
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• v.22 no.2
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• pp.35-48
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• 1985

The present work develops a method of evaluating thrust deduction and wake for different loads of the propeller using the concerted application of the theoretical tools and experimental techniques. It also shows the applicability of the new method to the design of optimum hull form. Firstly, the problem of hull-propeller interaction was analyzed in terms of inviscid as well as viscous components of the thrust deduction and wake. The wavemaking resistance of a hull and propeller were mathematically represented by sources on the hull surface and sink on the propeller plane, respectively. The strength of sink was determined by utilizing the radial distributions of propeller load and nominal wake. The resistance increment due to a propeller and the axial perturbation flow induced by the hull in the propeller plane were calculated. Especially, the inviscid component of the thrust deduction was calculated by subtraction the wavemaking resistance of a bare hull, the wavemaking resistance of a free-running propeller and the augmentation of propeller resistance due to hull action from the wavemaking resistance of the hull with a propeller. The viscous components of the thrust deduction and wake were estimated as functions of propeller load which were established by the propeller load varying test after deduction the calculated inviscid components. Secondly, an analysis method of powering performance was developed based on the potential theory and the propeller load varying test. The hybrid method estimates the thrust deduction, wake and propeller open-water efficiency for different propeller load. This method can be utilized in the analysis of powering performance for the propeller load variation such as the added resistance due to hull surface roughness, the added resistance due to wind, etc. Finally, the hybrid method was applied to the optimum design of hull form. A series of afterbody shapes was obtained by systematically varying the waterplane and section shapes of a parent afterbody without changing the principal dimensions, block coefficient and prismatic coefficient. From the comparison of the predicted results such as wavemaking resistance, thrust deduction, wake and delivered power, an optimum hull form was obtained. The delivered power of the optimized hull form was reduced by 5.7% which was confirmed by model tests. Also the predicted delivered power by the hybrid method shows fairly good agreement with the test result. It is therefore considered that the new analysis method of powering performance can be utilized as a practical tool for the design of optimum hull form as for the analysis of powering performance for the propeller load variation in the preliminary design stage.

• Journal of Dental Rehabilitation and Applied Science
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• v.22 no.3
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• pp.221-230
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• 2006

Recently, the need for esthetic results has increased the interest for all-ceramic crown prosthesis. Furthermore, the development of zirconium core via CAD/CAM system has allowed the all ceramic restorations to be applied to almost all fixed prosthesis situations. But, the increased strength has been reported to increase in proportion with the bond strength of cement, and recently, the tribochemical system which increases the bond strength through, silica coating and silanization has been introduced. The purpose of this study was to compare the $Rocatec^{TM}$ system and $CoJet^{TM}$ system with the traditional acid etching and silanization method of the irconium based ceramic. The surface character was observed via SEM(X2000), and the bond strength with the resin cement were measured. 50 In-Ceram Zirconia (Adens, Korea) discs were fabricated and embedded in resin, group 1 was treated with glass-bead blasting and cleaning, group 2 was treated with 20% HF for 10 minutes and silanized, group 3 was treated with the $Rocatec^{TM}$ system, and group 4 was treated with the $CoJet^{TM}$ system. Each group was comprised of 10 specimens. The specimens were cemented to a $3mm{\times}5mm$ resin block with Super-Bond C&B. The shear bond strength was measured with the $Instron^{(R)}$ 8871 at a crosshead speed of 0.5mm/min. The results were as follows. 1. According to SEM results, there were little difference between group 1 & group 2, but in group 3 and 4, silica coating was detected and there was increase in surface roughness. 2. The shear bond strength decreased in the order of group 3(46.28MPa), group 4(42.04MPa), group 2(31.56MPa), and group 1(27.46MPa). 3. There was significant differnce between group 1&2 and group 3&4(p<0.05). From the results above, it can be considered that the conventional method of acid etching and silane treatment cannot increase the bond strength with resin cements, and that by applying the tribochemical system of $Rocatec^{TM}$ system and $CoJet^{TM}$ system, we can achieve a stronger all ceramic restoration. Further studies on surface treatments to increase the bond strength are thought to be needed.

• The Journal of Engineering Geology
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• v.12 no.2
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• pp.215-234
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• 2002

Groundwater Dam is one of the reliable techniques to get huge amount of groundwater abstraction for municipal, agricultural, drinking, industrial water supply system. It can be a major technique to solve water shortage problems when it based on the sufficient watershed, proper topology, and adequate aquifer distribution and pollution control, Groundwater Dam had initiated its construction by RDC(former KARICO) in early eighties in Korea and 4 of it in total were added more until late eighty. However, this technique has shrunken its application due to gradually decreased yield rate after sever years of construction. After we studied several existing sites precisely, we concluded that the main reason of decreasing yield rate was come form engineering roughness on construction in early nineties. Theoretically, the technique itself seemed to be little detectives however, there were a little application in the fields in Korea. With the recent advance in engineering fields, those defects in construction would be no longer obstacle to construct underground wall and the technique could be a one of major ground water production technique in the future. It is essential to study following items thoroughly before select the appropriate site. The topography and the site of the underground wall, aquifer distribution, the specific technique for wall construction to block groundwater flow effectively and strict quality control during construction are critical. The surface and ground water monitoring data should be collected. Sustainability of the Groundwater Dam with huge groundwater abstraction in long term should be based on the long-term water balance analysis for each site. The water quality, environmental effect analysis and maintenance achedule should be also analyzed and planned in prior. It is suggested that the two consecutive underground wall in the coastal area to prevent seawater intrusion beneath a single wall.

• Journal of Dental Rehabilitation and Applied Science
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• v.37 no.4
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• pp.177-185
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• 2021

Clinical applications of translucent zirconia as well as traditional zirconia (3 mol% yttria stabilized tetragonal zirconia polycrystal, 3Y-TZP) are increasing. For this reason, studies on factors affecting the optical properties of dental zirconia have been continuously reported. The optical effect of dental zirconia may vary depending on the yttria content, the thickness of the prosthesis, the sintering process, polishing, glazing and cementation in laboratory and clinical procedures. Increasing the yttria concentration can reduce the masking effect. Translucency decreases as the thickness of the restoration increases, but the required thickness may vary depending on the properties of the zirconia block. The high-speed sintering method can shorten the manufacturing time, but in some cases, the translucency of the prosthesis may decrease. In addition, the optical properties can be affected by the surface roughness of zirconia and the polishing process. The use of an appropriate colored cement can help with the masking effect of zirconia and can be useful for color matching for more esthetic results.