• Proceedings of the KSME Conference
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• 2002.08a
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• pp.159-160
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• 2002

New S-shaped aeroelastic mesoflaps are utilized to control normal shock/boundary-layer interactions. New generation of the mesoflaps is designed f3r a better rigidness and a good flow uniformity across the ulteractions. ,Major advantages of the mesoflap system can be a better total pressure recovery downstream of the interactions due to the lambda shock structure over the flap system, and a rehabilitation of the thickened boundary layer due to bleeding through a cavity underneath the flap system. Skin friction has been measured downstream of the interactions, using the laser interferometer skin friction (LISF) meter, which optically detects the rate of thinning of an oil film applied to the test surface. Various flap-thicknesses of the S-shaped mesoflap arrays are tested, and the results are compared to the solid-wall reference case. Overall, not much difference in the level of skin friction is noticed for the S-shaped flap arrays of various thicknesses, and its level is lower than the skin friction downstream of the solid-wall interaction

• Journal of the Korean Society for Precision Engineering
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• v.30 no.8
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• pp.864-869
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• 2013

As the size of mechanical components decreases, capillary forces and surface tension become increasingly significant. A major problem in maintaining high reliability of these small components is that of large frictional forces due to capillary action and surface tension. Unlike the situation with macro-scale systems, liquid lubrication cannot be used to reduce friction of micro-scale components because of the excessive capillary and drag forces. In this work, the feasibility of using evaporation to coat a thin film of organic lubricant on a solid surface was investigated with the aim of reducing friction. Petroleum and silicone oils were used as lubricants to coat a silicon substrate. It was found that friction could be significantly reduced and, furthermore, that the effectiveness of this method was strongly dependent on the coating conditions.

• Journal of the korean Society of Automotive Engineers
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• v.12 no.4
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• pp.35-46
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• 1990

The instantaneous friction in main bearings of a single cylinder diesel engine was determined by measuring the instantaneous angular velocity, calculating the resulting forces acting on the bearings, and solving the unsteady Reynolds equation in combination with the mobility method. The considered system consists of only the crankshaft with flywheel and oil pump. The thermal effects were not considered because of the short testing time. The tests were conducted using an electric start motor. The results indicated that when the bearing is not near equilibrium for very small speeds, simple film lubrication theories are not accurate. The details of grooves and unsteady terms in the Reynolds equation cannot be ignored for increasing efficiency of instantaneous friction calculation of the engine bearings. The effects of speed on instantaneous friction and energy lost in friction were determined.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.3
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• pp.361-366
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• 2018

Ice crushing occurs in many situations that involve a sliding frictional component such as sports involving ice-contact, ice interaction with ship hulls, and ice-on-ice sliding/crushing within glaciers and between interacting sea ice floes. Ice crushing-friction tests were conducted in the lab at $-10^{\circ}C$ using a set of acrylic ice-crushing platens that included a flat smooth surface and a variety of high-roughness surfaces with regular arrays of small prominences. The experiments were part of Phase II tests of the Blade Runners technology for reducing ice-induced vibration. Ice was crushed against the platens where the ice movement had both a vertical and a horizontal component. High-speed imaging through the platens was used to observe the ice contact zone as it evolved during the tests. Vertical crushing rates were in the range 10-30 mm/s and the horizontal sliding rates were in the range 4.14-30 mm/s. Three types of freshwater ice were used. Friction coefficients were extraordinarily low and were proportional to the ratio of the tangential sliding rate and the normal crushing rate. For the rough surfaces all of the friction coefficient variation was determined by the fluid dynamics of a slurry that flowed through channels that developed between leeward-facing facets of the prominences and the moving ice. The slurry originated from a highly-lubricating self-generating squeeze film of ice particles and melt located between the encroaching intact ice and the surfaces.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.7
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• pp.939-947
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• 1997

An experimental study of the skin friction measurement in a turbulent boundary-layer has been carried out. The skin friction measurements are made using the laser interferometer skin friction (LISF) meter, which optically detects the rate of thinning of an oil applied to the test surface. This technique produces reliable skin friction data over a wide range of flow situations up to 3-dimensional complicated flows with separation, where traditional skin friction measurement techniques are not applicable. The present measured data in a turbulent boundary-layer on a flat plate using the LISF technique shows a good comparison with the result from the previous velocity profile techniques, which proves the validity of the present technique. An extensive error analysis is carried out for the present technique yielding an uncertainty of about .+-.8%, which makes them suitable for CFD code validation purposes. Finally the measurements of the skin friction in a separated region after a surface-mounted obstacle are also presented.

• Tribology and Lubricants
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• v.25 no.6
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• pp.409-413
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• 2009

This paper presents the hardness and friction characteristics of pb-free pin-bush bearing metal, which is manufactured by a centrifugal casting technology. A bronze metal with a high hardness and low friction properties is usually used for Diesel engine pin-bush bearing and high pressure cylinder. Pb-free metal for pin-bush bearings shows a little high hardness of 120 Hv compared with that of a conventional Pb bearing metal of 100~110 Hv. In general, the friction coefficient of pin-bush bearings is affected by a rotating speed and a load for various rubbing contact modes. But a contact load is more influential parameter when the contact rubbing mode transits from a mixed lubrication to a dry friction contact. The experimental result shows that the friction coefficient is more unstable at the dry contact mode compared with that of other two rubbing modes such as oil film contact and mixed friction conditions.

• Tribology and Lubricants
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• v.25 no.4
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• pp.231-235
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• 2009

In this study, the influence of contact pressure on the variation in coefficients of friction between porcine knee joint cartilage and Co-Cr alloy in a repeat pass sliding motion was investigated. Flat-ended cartilage pin specimens(9 mm diameter, 8 mm long) were prepared from porcine(6 months old) knee joints by a drill-type punch. Friction tests were conducted by using a pin-on-disk type friction tester for an hour in PBS lubricated condition under the contact pressures of 0.5, 1 and 2 MPa with 50 mm distance per a cycle at ambient condition. As a result, coefficients of friction increased as the test duration increased for all contact pressures. The maximum coefficients of friction were 0.082, 0.06 and 0.098 for 0.5, 1, and 2 MPa, respectively. It showed that coefficients of friction of porcine knee joint cartilage against Co-Cr alloy depended on the level of contact pressure and related to squeeze film lubrication mechanism.

• Tribology and Lubricants
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• v.33 no.6
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• pp.282-287
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• 2017

SU-8 is an epoxy-type photoresist widely used for the fabrication of high-aspect-ratio (HAR) micro-structures in micro-electro-mechanical systems (MEMS). To fabricate highly integrated structures, chemical mechanical polishing (CMP) has emerged as the preferred manufacturing process for planarizing the MEMS structure. In SU-8 CMP, an oxidizer decomposes organic impurities and particles in the CMP slurry remove the chemically reacted surface of SU-8. To fabricate HAR microstructures using the CMP process, the adhesion between SU-8 and substrate material is important to avoid the delamination of the SU-8 film caused by the mechanical-dominant material removal characteristic. In this study, the friction force during the CMP process is measured with a CMP monitoring system to detect the delamination phenomenon and investigate the delamination of the SU-8 film from the silicon substrate under various pressure conditions. The increase in applied pressure causes an increase in the frictional force and wafer-edge stress concentration. The frictional force measurement shows that the friction force changes according to the delamination phenomenon of the SU-8 film, and that it is possible to monitor the delamination phenomenon during the SU-8 CMP process. The delamination at a high applied pressure is explained by the effect of stress distribution and pad deformation. Consequently, it is necessary to control the pressure of polishing, which can avoid the delamination in SU-8 CMP.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.54-54
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• 2011

The demand for low-friction, wear and corrosion resistant components, which operate under severe conditions, has directed attentions to advanced surface engineering technologies. The Filtered Vacuum Arc Cathode Deposition (FVACD) process has demonstrated atomically smooth surface at relatively high deposition rates over large surface areas. Preparation of Ti-Si-C-N nanocomposite coatings on (100) Si and stainless steel substrates with tetramethylsilane (TMS) gas pressures to optimize the film preparation conditions. Ti-S-C-N coatings were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, nanoindentation, Rockwell C indentation and ball-on-disk wear tests. The XRD results have confirmed phase formation information of TiSiCN coatings, which shows mixing of TiN and TiC structure, corresponding to (111), (200) and (220) planes of TiCN. The chemical composition of the film was investigated by XPS core level spectra. The binding energy of the elements present in the films was estimated using XPS measurements and it shows present of elemental information corresponding to Ti2p, N1s, Si 2p and C1. Film hardness and elastic modulus were measured with a nano-indenter, and film hardness reached 40 GPa. Tribological behaviors of the films were evaluated using a ball-on-disk tribometer, and the films demonstrated properties of low-friction and good wear resistance.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.8
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• pp.514-519
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• 2017

TiN (titanium nitride) films were prepared using the RF magnetron sputtering technique. The films were deposited by pure $N_2$ plasma sputtering. Their mechanical properties, such as nano-indentation hardness, friction coefficient, and surface wettability, have been investigated. X-ray diffraction (XRD) studies revealed that the orientation of $TiN_X$ films changed towards the (111) orientation with decreasing working pressure due to a strong compressive stress during deposition. The strongest TiN (111) orientation was found when the film was deposited at a working pressure of 1 Pa. This film showed the largest hardness (16 GPa) and smallest friction coefficient (0.17) among the studied samples. Moreover, this film was found to be accompanied by a water-repellent surface with water contact angle more than $100^{\circ}$.