• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1104-1110
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• 2003

There are many applications of nanostructures, have been suggested by lots of researchers. It is highly required to measure the properties of nano-sized materials for design and fabrication of the nanostructures. In this paper, several techniques for measuring the mechanical properties of nano-structures are presented laying emphasis on the activity of Nano Property Measurement Team in KIMM. Some advanced applications of nano-indenter are described for measuring elastic, visco-elastic, frictional and adhesive properties as well as the standard methods of it. Micro-tensile test technique with accurate in-plane strain measurement method is also presented and its role in the property measurement of nanostructures is discussed.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.7 no.4
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• pp.3-9
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• 2008

The ion implantation technology is generally used in order to improve surface mechanical properties, especially tribological properties, of engineering metals. In this study, experimental works were carried out to investigate the surface properties, such as hardness, wear quantity, wear rate and friction force, of a nitrogen ion implanted tool steel STD11 under dry condition. Specimens for the wear test were made to investigate the influences of the initial ion implantation temperature and the total ion radiation. Wear properties, such as the wear quantity and the wear rate, of the nitrogen ion implanted tool steel were considerably improved, especially under the low sliding speed and the low applied load.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.51-52
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• 2002

We report results on microtribological studies of chemically grafted nanoscale polymer layers of different architecture with thickness below 30 nm. We have fabricated the molecular lubrication coatings from elastomeric tri-block copolymers and tested two different designs of corresponding nanocomposite coatings. We observed a significant reduction of friction forces and an increase of the wear stability when a minute amount of oil was trapped within the grafted polymer layer. These polymer gel layers exhibited a very steady friction response and a small value of the coefficient of friction as compared to the initial polymer coating. A polymer 'triplex' coating has been formed by a multiple grafting technique. The unique design of this layer Includes a hard-soft-hard architecture with a compliant rubber interlayer mediating localized stresses transferred through the topmost hard layer. This architecture provides a non-linear mechanical response under a normal compression stress and allows additional dissipation of mechanical energy via the elastic rubber interlayer.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.9 s.174
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• pp.41-48
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• 2005

In this study, to improve the formability of the rear floor in series stamping process, the method for predicting the temperature of tools and steel sheet is proposed using FE analysis. To do this, tensile tests and straight pulling friction tests of three steel sheets are carried out at temperatures up to $300^{\circ}C$, and the effect of temperature on the tensile properties and the characteristics of friction are examined. The steel sheets have a higher n-value in the temperature range of about $50^{\circ}C$, and it is related to the maximum uniform elongation. Also, the blue shortness occurs in the temperature range of about $150^{\circ}C$. When the temperature is higher than $200^{\circ}C$, the friction coefficient increase with increasing temperature. From the FE-simulation, the effects of the punch temperature considering heat expansion in the number of stamping are examined and discussed. The technique developed in this study fur estimating tool temperature can be used to develop more feasible ways to improve continuous productivity in series stamping process.

• Journal of Welding and Joining
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• v.30 no.2
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• pp.47-53
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• 2012

This paper aimed to study and understand the mechanical phenomena of thermal elasto-plastic behavior on the dissimilar butt joint (Al 6061-T6 and STS304) by TIG assisted Friction Stir Welding. Heat conduction and residual stress analysis is carried out using in-house solver. Two-dimensional results of the heat distribution and residual stresses in dissimilar joint for particular tool geometry and material properties are presented. The predicted stress along longitudinal direction in Al 6061-T6 and STS304 are approximately between 12-15% of their respective yield strengths. A comparison is made between experimentally measured and numerically predicted equivalent residual stress values.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.3
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• pp.39-46
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• 2011

The automotive air conditioning hose is used for connecting the components of air conditioner in a vehicle. The hose is usually manufactured by the swaging process to connect the rubber hose with the metal fitting at the end of the hose. In case that the clamping force is small, the refrigerant gas in the hose can leak locally under the severe operating circumstances. The practical test of clamping force is performed by means of the measurement of separation force. In this study, the swaging process of a hose is simulated with the finite element method, to investigate the effect of friction coefficient on the clamping force. The contact condition is used in consideration of real manufacturing process, and the material properties for the Mooney-Rivlin model is obtained by the experimental results. The result interpretations are focused on the contact forces, which is displayed graphically with respect to friction coefficient, on the surfaces between the hose and the metal fittings.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.516-521
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• 2002

A study was carried out to grow an understanding of the microstructural development of friction stir welds on an AZ91D magnesium alloy, and to evaluate the mechanical properties of the welds. AZ91D plates with the thickness of 4mm were used, and the microstructural development of the weld zone was investigated using optical and scanning electron microscopes. Square butt welding joint with good quality was obtained at the conditions of under 187mm/min of travel speed with 1100 to 1250 rpm of tool rotation speed. The microstructure within the weld region consisted of fine equiaxed grains with no evidence of the original dendritic structure. The hardness tests showed slightly increased harness in the weld region, and the minimum hardness measured is in that of the parent material. Tensile strength of the weld zone was remarkably improved due to very fine recrystallized structure. XRD pattern of weld zone revealed the removal of $\beta$ intermetallic compounds, $Mg_{17}$Al$_{12}$, which had been distributed in the base metal.l.

• KSTLE International Journal
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• v.4 no.2
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• pp.60-65
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• 2003

Tribological properties of novolac resin composites containing particulate barite (BaSO$_4$) or potassium titanate (K$_2$Oㆍ6(TiO$_2$))whiskers (two typical space fillers for commercial automotive brake linings) were investigated. The emphasis of the current investigation was given to the effect of the two fillers on the propensity of the stick-slip phenomena and formation of stable rubbing surface. A block-on-disk type tribometer was used for friction assessment. Results showed that the BaSO$_4$-filled composite produced large friction force oscillations at slow sliding speeds and created severe damage on the gray iron counter surface. On the other hand, the composite with $K_2$Oㆍ6(TiO$_2$) whiskers formed a stable rubbing surface and showed smooth sliding behavior without large friction force fluctuation. The microscopic observation of the rubbing surface revealed that the $K_2$Oㆍ6(TiO$_2$)whiskers played a key role in the formation of stable rubbing surface and smooth sliding behavior by effectively reinforcing the resin.

• Journal of Ocean Engineering and Technology
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• v.27 no.1
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• pp.37-42
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• 2013

The presence of a crack can increase the local stress or strain, which can cause inelastic deformation and significantly reduce the life of a component or structure. Therefore, in this study, the fatigue crack growth (FCG) behaviors of friction stir welded Al 2024-T3 and Al 7075-T6 specimens were examined, with fatigue cracks growing parallel to the dynamically recrystallized zone at variable ${\Delta}K$ values and an R ratio of 0.3. In addition, the FCG values of the base metal Al 2024-T3 and Al 7075-T6 were tested under the same conditions and parameters as comparative groups. The results showed that compared with the base metal Al 2024 specimen, which had the best fatigue property, the welded specimen had only 88% of the fatigue cycles.

• Carbon letters
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• v.12 no.4
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• pp.249-251
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• 2011

Carbon/epoxy woven composites are prominent wear-resistant materials due to the strength, stiffness, and thermal conductivity of carbon fabric. In this study, the effect of oilabsorption on the wear behaviors of carbon/epoxy woven composites was investigated. Wear tests were performed on dry and fully oil-absorbed carbon/epoxy woven composites. The worn surfaces of the test specimens were examined via scanning electron microscopy to investigate the wear mechanisms of oil-absorbed carbon/epoxy woven composites. It was found that the oil absorption rate was 0.14% when the carbon/epoxy woven composites were fully saturated. In addition, the wear properties of the carbon/epoxy woven composites were found to be affected by oilabsorption. Specifically, the friction coefficients of dry and oil-absorbed carbon/epoxy woven composites were 0.25-0.30 and 0.55-0.6, respectively. The wear loss of the oilabsorbed carbon/epoxy woven composites was $3.52{\times}10^{-2}\;cm^3$, while that of the dry carbon/epoxy woven composites was $3.52{\times}10^{-2}\;cm^3$. SEM results revealed that the higher friction coefficient and wear loss of the oil-absorbed carbon/epoxy woven composites can be attributed to the existence of broken and randomly dispersed fibers due to the weak adhesion forces between the carbon fibers and the epoxy matrix.