• Journal of the Korean Society for Precision Engineering
• /
• v.16 no.8
• /
• pp.100-105
• /
• 1999

This work analyses the effects of electrical conductivities of dielectric and cobalt amount on output parameters such as metal removal rate and the surface roughness value of cemented carbides cut by wire electrical discharge machining(W-EDM). Especially, the cracking behaviour of W-EDM machined surface and optimal machining condition of three kinds of cemented carbides, which have different chemical composition of tungsten carbide and cobalt are also tested. Experimental result shows that increases in cobalt content and electrical conductivity of the dielectric affect the metal removal rate and substantially worsen the final surface quality as a greater quantity of solidified metal deposits on the eroded surface.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2001.11a
• /
• pp.172-178
• /
• 2001

Using dislocation pileup theory, the near surface crack initiation life was calculated. The crack initiation life calculted in the previous study is not a real life strictly and just for the cracking in substrate. In this study, two life equations which can be applied for each near-surface and substrate were used for a comparative study. The downward tendency of life at near surface and substrate was similar and the crack initiation life at near-surface was much shorter than the life in substrate. The improvement of the crack initiation life equations which were proposed by W. Cheng was discussed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.05c
• /
• pp.62-65
• /
• 2001

The effects of accelerated UV radiation on EPDM used for a polymeric insulator were investigated by contact angle, surface voltage decay after corona charging, SEM-EDX, ATR-FTIR and XPS. EPDM occurs as loss of hydrophobicity by UV treatment, which followed by surface cracking and chalking. The surface voltage decay on UV-treated EPDM show that the shorter decay time corresponded to the treated samples with a longer UV exposure time. The surface oxygen and aluminum content were found to increase and carbon decrease, as is observed in EDX analysis. The ATR-FTIR and XPS indicated that C-C and C-H groups decreased and the highly oxidized carbon bonds such as C-O, C=O and O-C=O increase with time. Also, the effects of surface charges on hydrophobicity based on our results is discussed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2003.05c
• /
• pp.53-56
• /
• 2003

The properties of YBCO thick film coated on Ag wire with YBCO powder is deeply affected by cracking on its surface which was deposited in organic solution by electrophoretic method. YBCO superconducting thick films were prepared on Ag wire$({\Psi}0.8mm)$ by electrophoresis in acetone with added PEG (Poly-Ethylene Glycol, 3% in Acetone), 1ml for being crack-free. The surface properties of YBCO superconducting wire was evidently improved with adding PEG. Added PEG which molecular weight is 600, 1000, 3400 was affected with variation of deposition voltages to the surface properties of samples. As a result, with adding PEG (its molecular weight is 3400), YBCO superconducting wire was better on its surface properties.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2003.11a
• /
• pp.243-247
• /
• 2003

The effect of accelerated weathering(UV) on three type of ethylene propylene diene monomer(EPDM) composite used for higher voltage insulator were investigated by weather-emoter. For weatherability of EPDM composite, surface resistance, dielectric breakdown strength, change of contact angle, surface composition were measured according to UV accelerated weathering time. From the resort of the measurement of surface resistivity, contact angle of EPDM composite decreased and showed chalking and cracking phenomenon when UV weathweing time was for 1500 h and 2000 h. The analysis of surface atomic composition indicated that surface aluminiu(Al) content was detected due to chalking phenomenon after 1500 h of UV weathering, Oxygen content of all composite increased due to the oxidation.

• Journal of the Korea Concrete Institute
• /
• v.14 no.6
• /
• pp.851-863
• /
• 2002

Corrosion products of reinforcement in concrete induce pressure to the adjacent concrete due to the expansion of steel. This expansion causes tensile stresses around the reinforcing bar and eventually induces cracking through the concrete cover The cracking of concrete cover will adversely affect the safety as well as the service life of concrete structures. The purpose of the this study is to examine the critical corrosion amount which causes the cracking of concrete cover. To this end, a comprehensive experimental and theoretical study has been conducted. Major test variables include concrete strength and cover thickness. The strains at the surface of concrete cover have been measured according to the amount of steel corrosion. The corrosion products which penetrate into the pores and cracks around the steel bar have been considered in the calculation of expansive pressure due to steel corrosion. The present study indicates that the critical amount of corrosion, which causes the initiation of cracking, increases with an increase of compressive strength. A realistic relation between the expansive pressure and average strain of corrosion product layer in the corrosion region has been derived and the representative stiffness of corrosion layer was determined. A concept of pressure-free strain of corrosion product layer was introduced to explain the relation between the expansive pressure and corrosion strain. The proposed theory agrees well with experimental data and may be a good base for the realistic durability design of concrete structures.

• Korean Chemical Engineering Research
• /
• v.46 no.2
• /
• pp.291-300
• /
• 2008

Catalytic cracking of n-octane was carried out over H-ZSM-5 zeolite catalysts after calcination with air and steaming with 100% steam in the temperature range of $550-750^{\circ}C$ for 24 h and compared with the results of thermal cracking. The increase of calcination and steaming temperature resulted in the decrease of surface area, pore volume, and strong acid sites, which was mainly caused by the dealumination of H-ZSM-5 framework. It was found by $^{27}Al$ and $^{29}Si$ MAS NMR that the dealumination was proceeded through the transformation process of tetrahedral framework Al${\rightarrow}$penta-cordinated Al ${\rightarrow}$ octahedral framework Al and the phenomena was much more severe in steaming conditions than that of calcination. In the catalytic cracking of n-octane, as the temperatures of calcination and steaming were increased, the conversion of n-octane, the selectivity of light olefins and ethylene to propylene ratio were decreased due to the dealumination of framework aluminum resulting the loss of acidic strengths. The conversion, selectivity of light olefins and ethylene to propylene ratio reached almost to the level of thermal cracking after steaming at $750^{\circ}C$ for 24 h.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.47 no.3
• /
• pp.267-272
• /
• 2011

The behavior of abrasive wear on counterpart roughness of glass fiber reinforcement polyurethane resin (GF/PUR) composites were investigated at ambient temperature by pin-on-disc friction test. The friction coefficient, cumulative wear volume and surface roughness of these materials against SiC abrasive paper were determined experimentally. The major failure mechanisms were lapping layers, ploughing, delamination, deformation of resin and cracking by scanning electric microscopy (SEM) photograph of the tested surface. As increasing the counterpart roughness the GF/PUR composites indicated higher friction coefficient. The surface roughness of the GF/PUR composites was increased as the sliding velocity was higher and the counterpart roughness was rougher in wear test.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.48 no.3
• /
• pp.277-283
• /
• 2012

The characteristics of abrasive wear on sliding speed of glass fiber reinforcement (GF/PUR) composites were investigated at ambient temperature by pin-on-disc friction test. The cumulative wear volume, friction coefficient and surface roughness of these materials on sliding speed were determined experimentally. The major failure mechanisms were lapping layers, deformation of resin, ploughing, delamination, and cracking by scanning electric microscopy (SEM) photograph of the tested surface. As increasing the sliding speed the GF/PUR composites indicated higher friction coefficient. The surface roughness of the GF/PUR composites was increased as the sliding speed was higher in wear test.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2000.11a
• /
• pp.489-493
• /
• 2000

Turbine blade has trouble of cracking at root region. Fracture surface of blade root is surveyed by SEM and AFM to clear relation between fracture mechanical parameter and surface parameter (striation width and surface roughness). Service stress is predicted by maximum height roughness $R_{max}$, on fractured surface and stress analysis on turbine blade. It is to thought that turbine blade is fractured by abnormal condition such as incorrect fittings between pin and pin hole but isn't fractured by normal service conditions such as steam pressure, centrifugal force and torsional force.