• Tribology and Lubricants
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• v.30 no.1
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• pp.15-20
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• 2014

A more accurate expression for effective viscosity is obtained using a linear regression of the data from Fukui-Kaneko's model, which are obtained through numerical calculations based on the linearized Boltzmann equation. Veijola and Turowski's expression is adopted as a base function for effective viscosity. The four coefficients in that equation are optimized, and sensitivity analysis is conducted for these coefficients. The results show that the coefficient for the first-order Knudsen number is the most accurate, whereas the coefficient in the exponential of the Knudsen number is the least accurate compared with Fukui-Kaneko's results. The expression for effective viscosity is accurate within 0.02% rms of Fukui-Kaneko's results for the inverse Knudsen numbers from 0.01 to 100 and surface accommodation coefficients ranging from 0.7 to 1.

• Journal of the Korean Society for Heat Treatment
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• v.13 no.6
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• pp.405-411
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• 2000

The effects of added elements, such as Co or Nb, on wear properties of high speed steel by powder metaliurgy(PM-HSS) had been eluminated in auther's previous paper. In addition, it is generally known that the wear properties of materials have been influenced by heat-treating conditions as well. Therefore, a study has been done to clarify the effects of heat-treating conditions on wear properties of PM-HSS. The wear tests have been performed under the same conditions as the previous paper using heat-treated PM-HSS(5%Co-1%Nb) with different quenching and tempering temperatures. The result of this paper shows that wear resistance of PM-HSS is improved with relatively high quenching temperature. However, tempering temperature is not sensitive to the wear resistance in the range of high quenching temperature. It may be deduced by the fact that the shear strength of matrix by strengthening mechanisms due to not only the quenching aging but also dispersion-hardening is improved.

• Tribology and Lubricants
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• v.20 no.6
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• pp.337-342
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• 2004

One of the serious challenges in developing rotary compressor with HFC refrigerant is the prediction of scuffing times and wear amounts between vane and roller surfaces. In this study, the tribological characteristics of sliding surfaces using vane-roller geometry of rotary compressor were investigated. The sliding tests were carried out under various sliding speeds, normal loads and surface roughness. During the test, friction force, wear depth, time to failure and surface temperature were monitored. Because severe wear occurred on vane surface, TiN coating was applied on sliding surfaces to prolong the wear life of vane-roller interfaces. From the sliding test it was found that there was the optimum initial surface roughness to break in and to prolong the wear life of sliding surfaces. Depending on the load and speed, the protective layers, which were composed of metallic oxide and organic compound, were formed on sliding surfaces. Those would play an important role in the amounts of friction and wear between roller and vane surfaces.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.06a
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• pp.81-88
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• 2001

To study the influence of the shape of contacting bodies (especially the end profile) on slip regime, wear test is conducted in the case of the contact between tube and support. Two different end profiles of the support are used such as truncated wedge and rounded punch. During the test, 10, 30 and 50 N are applied as normal force and slip displacement varies between 10-200 $\mu\textrm{m}$. The tube and the support specimens are made of Zircaloy-4 and a specially designed wear tester is used. Tests are carried out in air at room temperature. Wear on the tube is examined by measuring microscope. Partial and gross slip regimes are classified from the observed wear shape. Surface roughness tester is also used to measure the wear depth and contour, from which wear volume is evaluated. The transition from partial to gross slip is also investigated by investigating the considerable increase of wear volume. From the result, the boundary between the partial and the gross slip is newly determined in the conventional fretting map for the present specific contact configuration. Since the transition is related with the amount of energy dissipation from the contact surface so is wear, it is regarded that wear can be restrained by designing a proper shape of support.

• Journal of Korean Society of Transportation
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• v.18 no.4
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• pp.107-115
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• 2000

We suggest a method which solves the planar, two vehicle collision reconstruction problem. The method based on the Principle of impulse and momentum determines the pre-impact velocity components from Post-impact velocity components, vehicle Physical data and collision geometry. A novel feature is that although the impact coefficients such as the restitution coefficient and the impulse ratio are unknown, the method can estimate automatically the coefficients and calculate the pre-impact velocity components. This reverse calculation is important for vehicle accident reconstruction, since the pre-impact velocities are unknown and Post-impact Phase is the starting Point in a usual collision analysis. However. an inverse solution is not always Possible with the analytical rigid-body impact model. Mathematically, one does not exist under the common velocity condition. On the other hand, our method has a capability of reverse calculation under the condition if the absorbed energy during the collision process can be estimated using the crush profile. To validate the developed collision reconstruction a1gorithm, we use car-to-car collision test results. The analysis and experimental results agree well in the impact coefficients and the Pre-impact velocity components.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.5
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• pp.113-120
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• 2013

Graphite is commonly used as a solid lubricant leading to low friction coefficient and abrasion. In this study, wear behavior of sealing graphite(HK-6) at elevated temperature was evaluated. Reciprocating wear test was carried out as wear occurred graphite as a seal(HK-6) is positioned between the liner and driving shaft. Variables which are temperature, sliding speed and contact load are set. This study suggest optimized environment conditions through the wear properties of graphite.

• International Journal of Highway Engineering
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• v.13 no.3
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• pp.51-63
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• 2011

Surface of fine-size exposed aggregate portland cement concrete pavements(FS-EAPCC) is consist by exposed coarse aggregate to remove upper 2~3mm mortar of concrete slabs. Advantages of FS-EAPCC are maintaining low-noise and adequate skid-resistance level during the performance period. However, FS-EAPCC is required rational management criteria for field application, since it is early stage for application. Design construction and quality control criteria of FS-EAPCC was temporary laboratory tests which including optimum mix and exposing method, selection of adequate aggregate, resistance against, environmental loading and etc. However, these criteria need to be validated base on field application. In this study, experimental constructions were performed and construction procedure and quality control criteria were suggested based on the performance of the FS-EAPCC.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.12
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• pp.831-840
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• 2019

Flush Air Data Sensing system (FADS) estimates air data states using pressure data measured at the surface of flight vehicles. The FADS system does not require intrusive probes, so it is suitable for high performance aircrafts, stealth vehicles, and hypersonic flight vehicles. In this study, calibration procedures and solution algorithms of the FADS for a sphere-cone shape vehicle are presented for the prediction of air data from subsonic to supersonic flights. Five flush pressure ports are arranged on the surface of nose section in order to measure surface pressure data. The algorithm selects the concept of separation for the prediction of flow angles and the prediction of pressure related variables, and it uses the pressure model which combines the potential flow solution for a subsonic flow with the modified Newtonian flow theory for a hypersonic flow. The CFD code which solves Euler equations is developed and used for the construction of calibration pressure data in the Mach number range of 0.5~3.0. Tests are conducted with various flight conditions for flight Mach numbers in the range of 0.6~3.0 and flow angles in the range of -10°~+10°. Air data such as angle of attack, angle of sideslip, Mach number, and freestream static pressure are predicted and their accuracies are analyzed by comparing predicted data with reference data.

• Journal of the Microelectronics and Packaging Society
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• v.22 no.1
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• pp.21-25
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• 2015

Bending fatigue characteristics of Cu films and $8{\mu}m$ width Cu interconnects on flexible substrates were investigated, and fatigue reliability improvement was achieved through Mo-Ti alloy adhesion layer. Tensile bending fatigue reliability of Cu interconnects is 3 times lower than that of Cu films, and even compressive bending fatigue reliability of Cu interconnects is 6 times lower than that of Cu films. From these results, mechanical crack formation could be fatal in Cu interconnects. With Mo-Ti adhesion layer, fatigue reliability of Cu films and interconnects were enhanced due to the increase of adhesion strength and the suppression of slip induced crack initiation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.5
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• pp.625-630
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• 2013

The friction behavior of a 60-${\mu}m$-thick anodic aluminum oxide (AAO) film having cylindrical nanopores of 45-nm diameter was investigated as a function of impregnated oil viscosity ranging from 3.4 to 392.6 cSt. Reciprocating ball-on-flat sliding friction tests using a 1-mm-diameter steel ball as the counterpart were carried out with normal load ranging from 0.1 to 1 N in an ambient environment. The friction coefficient significantly decreased with an increase in the oil viscosity. The boundary lubrication film remained effectively under all test conditions when high-viscosity oil was impregnated, whereas it was easily destroyed when low-viscosity oil was impregnated. Thin plastic deformed layer patches were formed on the worn surface with high-viscosity oil without evidence of tribochemical reaction and transfer of counterpart material.