• 한국기계연구소 소보
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• 제4권1호
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• pp.19-26
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• 1981

Fatigue, the birth and growth of cracks in metal parts subjected to repeated loading, has been a problem plaguing engineers since the Industrial Revolution and the advent of rotating or reciprocating machinery. Designing against metal fatigue was studied briefly in several aspects. Examples of fatigue failures were shown. Fatigue was classified by loading: uniaxial Fatigue, multiaxial fatigue, cumulative fatigue da¬mage. Fatigue design criteria were discussed: Infinite-Life Design, Safe-Life Design, Fail-Safe Design, and Damage Tolerant Design. Mitigation of notch effects by design, improvement of fatigue strength of metal parts by residual stress and surface finishing were discussed. Relative fatigue beha¬vior was studied under various environmantal conditions. Especially the effects of corrosion, temperature, fretting, and irradiation were covered.

• 한국염색가공학회지
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• 제20권4호
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• pp.31-42
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• 2008

Tricrecyl phosphate(TCP)-containing polyurea microcapsules were prepared by interfacial polymerization using aromatic 2,4-toluene diisocyanate(TDI) and ethylenediamine(EDA) as wall forming materials. The effects of the protective colloids of polyvinylalcohol(PVA) and gelatin were investigated through experimentation. The mean size of prepared polyurea microcapsules was smaller and the surface morphology of the microcapsule prepared by the PVA as protective colloid was much smoother than the gelatin. As the concentration of protective colloid increased, the wall membrane of the polyurea microcapsules became more stable, the thermal stability of the wall membrane increased, the mean particle size became smaller, and the particle distribution was more uniform. PET containg microTCPs have a higher activation energy of decomposition, higher char content and lower heat of combustion.

• Journal of Welding and Joining
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• 제23권2호
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• pp.47-51
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• 2005

Rapid Prototyping (RP) technology has helped successfully to reduce time and costs since first emerged in 1986. Recently, RP using functional materials like as metal have been researched. However RP using molten metal and brazing material have been struggling to resolve several drawbacks, such as dimensional inaccuracy, poor surface finish and post finishing because occurring shrinkage and warpage at cooling. So, the purpose of this study is to develop a new RP technique using sheet metal and projection welding for reducing several drawbacks in occurring RP using molten metal. And optimum process variables were determined using desist of experiment(DOE).

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.227-230
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• 2002

New polishing technique for small parts has been tried out using the principle of particle electromechanics. Common fine abrasives such as alumina, diamond, silicon carbide are dielectric materials which are polarized under an electric field, and a non-uniform electric field makes abrasive particles translate along the field line. Using this principle, We make abrasive particles aggregate in the vicinity of the micro tool which is fir the surface finishing of a small part without contact with it. The behavior of particles is optically measured, and the machined depth of glass is examined.

• 한국염색가공학회지
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• 제21권4호
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• pp.57-62
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• 2009

N-Halamines are compounds which have covalent bonding between nitrogen and halogen. N-Halamine materials possess strong antimicrobial properties against wide spectrum of bacteria. The aim of this study is to prepare N-halamine membranes using m-aramid and poly(vinyl alcohol) (PVA). Surface characteristics using scanning electron microscope (SEM), pore size distribution, liquid permeability and mean pore size were measured to confirm feasibility as membrane. The results indicated that increased PYA portion up to 15% in the m-aramid/PVA blend resulted in improved pore size distribution, liquid permeability as well as mean pore size. Furthermore, antibacterial efficacy of the membranes after chlorination was confirmed and the results showed that bacteria in water were inactivated.

• 한국염색가공학회지
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• 제19권5호
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• pp.30-36
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• 2007

Cypermethrin-containing polyurea microcapsules were prepared by interfacial polymerization using aromatic 2,4-toluene diisocyanate(TDI) and Ethylene diamine(EDA) as wall forming materials. The effects of the protective colloids of polyvinylalcohol(PVA) and gelatin were investigated through experimentation. The mean size of the polyurea microcapsules was smaller and the surface morphology of the PVA was much smoother than gelatin. In addition the release behavior was much more controlled and better sustained. As the concentration of protective colloid increased, the wall membrane of the polyurea microcapsules became more stable, the thermal stability of the wall membrane increased, the mean particle size became smaller, and the particle distribution was more uniform. The release behavior of the core material changed according to the concentration. As the gelatin concentration was increased, a more controlled and sustained release behavior was observed. However, in the case of PVA, the increase of PVA concentration lead to a more rapid release rate.

• 한국의류학회지
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• 제25권8호
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• pp.1444-1452
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• 2001

Textile materials are frequently in contact with surfactant solutions during their manufacturing or finishing processes as well as cleaning processes in use. Liquid wetting, wicking and absorbency of textile materials, and the liquid properties, surface characteristics and pore geometry of textile materials, and the liquie-solid interactions, In this paper, 10 different nonionic surfactants, including Span 20, Twen 20, 40, 60, 80, 21, 61, 81, 65, 85, were used. The surfactants were characterized by their hydrophile-lipophile-balance (HLB) values, structures, and surface tensions. The 0.1g/dL and 1.0g/dL surfactant solutions, which were both above critical micelle concentration (CMC), were used to see the concentration effects on the wetting and absorbency of cotton fabrics. The wetting behavior and liquid retention properties of hydrophobic cotton fabrics with different nonionic surfactant solutions are reported. The contact angles are greatly decreased and the water retention values are greatly increased by adding most of the surfactants studied into the system. The extents of this effects are influenced by the characteristics of surfactants and its solutions. Hydrophilic surfactants which have low number of carbon atoms or unsaturated hydrophobe structures are more effective in improving the wetting and absorbancy of hydrophobic cotton fabrics. The water retention of hydrophobic cotton fabrics has positive relations with $cos{\theta}$, adhesion tension and work of adhesion. The 1.0g/dL surfactant solutions show similar, but slightly improved wetting and absorbency characteristics of hydrophobic cotton fabrics compared to the 0.1g/dL surfactant solutions.

• The Journal of Advanced Prosthodontics
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• 제11권3호
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• pp.162-168
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• 2019

PURPOSE. The aim of this study was to evaluate the effect of occlusal adjustments on the surface roughness of yttria-tetragonal zirconia polycrystal (Y-TZP) and wear of opposing artificial enamel. MATERIALS AND METHODS. Twenty-five Y-TZP slabs from each brand (Lava, 3M and Bruxzir, Glidewell Laboratories) with different surface conditions (Control polished - CPZ; Polished/ground - GRZ; Polished/ground/repolished - RPZ; Glazed - GZ; Porcelain-veneered - PVZ; n=5) were abraded (500,000 cycles, 80 N) against artificial enamel (6 mm diameter steatite). Y-TZP roughness (in ${\mu}m$) before and after chewing simulation (CS) and antagonist steatite volume loss (in $mm^3$) were evaluated using a contact surface profilometer. Y-TZP roughness was analyzed by three-way analysis of variance (ANOVA) and steatite wear by two-way ANOVA and Tukey Honest Difference (HSD) (P=.05). RESULTS. There was no effect of Y-TZP brand on surface roughness (P=.216) and steatite loss (P=.064). A significant interaction effect (P<.001) between surface condition and CS on Y-TZP roughness was observed. GZ specimens showed higher roughness after CS (before CS - $3.7{\pm}1.8{\mu}m$; after CS - $13.54{\pm}3.11{\mu}m$), with partial removal of the glaze layer. Indenters abraded against CPZ ($0.09{\pm}0.03mm^3$) were worn more than those abraded against PVZ ($0.02{\pm}0.01mm^3$) and GZ ($0.02{\pm}0.01mm^3$). Higher wear caused by direct abrasion against zirconia was confirmed by SEM. CONCLUSION. Polishing with an intraoral polishing system did not reduce the roughness of zirconia. Wear of the opposing artificial enamel was affected by the material on the surface rather than the finishing technique applied, indicating that polished zirconia is more deleterious to artificial enamel than are glazed and porcelain-veneered restorations.

• 공업화학
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• 제2권2호
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• pp.175-184
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• 1991

PVC 와 Polystyren 과 같은 고분자가 자외선에 노출될 때 이들 표면을 보호하고, 물성을 유지하기 위해서 자외선 경화 도료를 도장하지만, PVC 는 epoxy acrylate 에 대해서, 그리고 Polystyren 은 대부분의 UV도료에 부착력이 약하므로, 반응희석제의 조성을 변화시키거나, 다관능기 acrylate를 표면에 photografting 시키거나, 표면을 광화학적으로 활성화시켜 부착력을 향상시킴을 목적으로 하였다. 미리 침투시킨 광개시제에 의한 grafting이나 표면 활성화로 부착력은 현저히 증가하였고, 각 희석제에 있어 Tripropylene glycol diacrylate는 유연성 향상과 부착력 증가를 가져오나, 황변 현상과 표면 산화에 의한 경화 밀도의 증가로 grafting을 제외한 다른 도장 방법은 시간이 지남에 따라 도막의 부착력이 감소하였다. 여기에 비해 Trimethylol propane triacrylate 는 원래 다관능기에 의해 높은 경화 밀도를 가지고 이에 따른 단단한 도막 때문에 부착력에 문제가 있으나, 두가지 도장법에서는 오히려 다관능기에 의한 화학 결합으로 부착력이 향상되었다. 그리고, 고분자 표면의 표면 에너지를 활성화를 통해 증가시킴으로 해서 UV 도료의 상용성 문제를 grafting 과 표면 활성화를 통해 해결해 도료 배합의 다양화와 기능화를 가져올 것이 기대된다.

• 한국염색가공학회지
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• 제22권1호
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• pp.43-50
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• 2010

The thermal treatment for carbon nanotube was applied to remove the water, metal catalyst and other impurities in carbon nanotube. The surface of carbon nanotube was changed into open structure with acid treatment by mixed solution of $HNO_3$ and $H_2SO_4$. The dispersion property of the functionalized and modified carbon nanotube was assessed with naked eyes by dispersing it in DMF. Carbon nanotube mixd polyurethane film was made to estimate the dispersion property by reflectance of the film with UV-Vis spectrometer. Also the internal structure of carbon nanotube was observed with SEM and TEM and thermal pyrolysis property of the carbon nanotube was measured by TGA and DSC. The surface modification of carbon nanotube by thermal and acid treatments improved the dispersion property of carbon nanotube/polyurethane mixed materials.