• Journal of the Korean Society of Manufacturing Process Engineers
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• v.9 no.1
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• pp.25-34
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• 2010

Fretting damage reduces fatigue life of the material due to low amplitude cyclic sliding and changes in the contact surfaces of strongly connected machine and structures such as bolt, key, fixed rivet and connected shaft, which have relative slip of repeatedly very low frequency amplitude. In this study, the fretting fatigue behavior of 7050-T7451 aluminum alloys used mainly in aircraft and automobile industry were evaluated. The plain fatigue test and fretting fatigue test under cyclic bending load carried out commercial bending fatigue tester and specially devised equipments to cause fretting damage. From these experimental work, the following results obtained: (1) The plain fatigue limit for stress ratio R=-l was about 151MPa. (2) In case of fretting fatigue, fatigue limit for stress ratio R=-l about 72MPa, the fatigue limit for R=0 about 81MPa, and the fatigue limit for R=0.3 about 93MPa. (3) The fatigue limit reduction rates by the fretting damage were about 52%(R=-1), 46%(R=0) and 38%(R=0.3) respectively. (4) The fatigue limit reduction rate decreased with stress ratio increase. In fretting bending test, as stress ratio increased, occurrence of initial oblique crack by fretting decreased or phased out, so that fracture surfaces were formed by plain fatigue crack occurrence, and such tendency was notable as stress amplitude increased. (5) Tire tracks and rubbed scars were observed in the fracture surface and contacted surface.

• Journal of IKEEE
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• v.23 no.3
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• pp.904-909
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• 2019

Using the ion-beam irradiated indium zinc oxide (IZO) films which was cured at $100^{\circ}C$, uniform LC and homogeneous alignment of liquid crystal (LC) molecules was achieved. The IZO film was deposited on the glass substrate at the curing temperature of $100^{\circ}C$ and irradiated by the ion-beam which is an LC alignment method. To verify the LC alignment characteristics, polarizing optical microscope and the crystal rotation method were used. Additionally, it was confirmed that the LC cell with the IZO films had an enough thermal budget for high-quality LC applications. Field emission scanning electron microscope was conducted as a surface analysis to evaluate the effect of the ion-beam irradiation on the IZO films. Through this, it was revealed that the ion-beam irradiation induced rough surface with anisotropic characteristics. Finally, electro-optical (EO) performances of the twisted-nematic cells with the IZO films were collected and it was confirmed that this cell had better EO performances than the conventional rubbed polyimide. Furthermore, the polar anchoring energy was measured and a suitable value for stable LC device operation was achieved.

• Journal of Korean Dental Hygiene Science
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• v.5 no.1
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• pp.21-27
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• 2022

Background: This study was conducted to analyze the time for re-detection of bacteria after surface disinfection using wet wipes, isopropyl alcohol, and benzalkonium chloride antibacterial tissue and provide standards for re-execution of surface disinfection with wet and antibacterial tissues. Methods: Seven laptops were wiped with wet tissue and isopropyl alcohol and benzalkonium chloride antibacterial tissues. Test areas were rubbed with a sterile cotton swab at baseline and after 30, 60, and 120 min. After plating on a tryptic soy agar medium, the number of colonies was counted by culturing at 36.5℃ for 24 h. Results: The average number of bacterial colonies was 5.85 ± 4.33 before isopropyl alcohol wiping and nil after wiping. The average number of bacterial colonies was 12.28 ± 14.67 benzalkonium chloride wiping and nil after wiping. Before wiping with wet wipes, the average number of bacterial colonies on laptop surfaces was 3.42 ± 5.22. Bacteria decreased after wiping with wet wipes but increased again over time. Conclusions: Wet wipes can temporarily reduce bacteria but are unsuitable for removing bacteria.

• The korean journal of orthodontics
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• v.44 no.4
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• pp.195-202
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• 2014

Objective: A low-viscosity resin (infiltrant) was used to inhibit the progression of white spot lesions (WSLs) and resolve associated esthetic issues. An alternative pretreatment was explored to increase the pore volume of the surface layer of the WSLs. Also, the penetration effects of the infiltrant were evaluated for various pretreatments. Methods: Sixty two artificial lesions were fabricated on bovine teeth. As a positive control, 15% HCl gel was applied for 120 seconds. Further, 37% $H_3PO_4$ gel was applied for 30 seconds using three methods. The samples were divided as follows: $H_3PO_4$ only group, $H_3PO_4$ sponge group, and $H_3PO_4$ brush group. The acid was gently rubbed with the applicators (i.e., a sponge or brush) throughout the application time. To compare the effects of resin infiltration, twenty paired halves of specimens were treated with an infiltrant (ICON$^{(R)}$). Results: Thicknesses of the removed surface layers and infiltrated areas were evaluated by confocal laser scanning microscope. The positive control and the 37% $H_3PO_4$ brush group failed to show significant differences in the removed thickness (p > 0.05); however, the mean percentage of the infiltrated area was higher in the 37% $H_3PO_4$ brush group ($84.13{\pm}7.58%$%) than the positive control ($63.51{\pm}7.62%$, p < 0.001). Scanning electron microscope observations indicate higher pore volumes for the 37% $H_3PO_4$ brush group than for the positive control. Conclusions: Application of 37% $H_3PO_4$ with a brush for 30 seconds increased the pore volume of WSL surface layers and the percentage of infiltrated areas in comparison to the use of 15% HCl for 120 seconds.

• Journal of Korean Ophthalmic Optics Society
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• v.16 no.3
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• pp.237-245
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• 2011

Purpose: The present study was conducted to investigate whether certain repeated physical and/or chemical stimuli added on ophthalmic lenses might induce any changes of the functions of lens coatings. Methods: The changes in lens surface, light transmittance, foggy duration, durability of ophthalmic lenses were determined after the application of tearing-off with tape, rubbing with acetone, soaking in acetone or distilled water of ophthalmic lens (CR-39 material) as physical and/or chemical stimuli. Results: The change of ophthalmic lens surface was detected after soaking in acetone for longer than 30 minutes by observing the lens surface to figure out the functional change of hard coating. The ophthalmic lens soaked in distilled water for 180 minutes showed little functional change of anti-reflection coating as 1% by measuring light transmittance of lens. However, the function of anti-reflection coating was almost disappeared after the ophthalmic lens was soaked in acetone for 60 minutes. The foggy duration of ophthalmic lens soaked in acetone was increased by estimating foggy duration of lens. The lens coating was shown to be defected when the pre-damaged ophthalmic lenses were torn off with tape, rubbed with acetone and soaked in distilled water or acetone by observing pre-damaged lens surface to evaluate its durability. Conclusions: The careful management during ophthalmic lens dispensing or usual eyeglass wearing is needed since the change in ophthalmic lens coatings was shown by repeated physical and/or chemical stimuli.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.389-396
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• 2002

In XXI century it is necessary to expect the recommencement and development of activities on mastering the Moon. In the long term it is construction of manned lunar bases with industrial, astrophysical, procuring, repair equipment and services. Interplanetary flights from the Moon demand smaller power expenditures, than from the Earth, therefore it is favourable to use its surface for the construction of space-vehicle launching sites. Flights of devices in libration points in the system 'Earth - Moon' are considered. Experience of engineering system creation for the Moon displays the great complexity in provision of serviceability and reliability of friction units. Open friction units should operate under following conditions on the Moon: pressure of environment (vacuum) $p\;>10\;^{-10}$ Pa; wide range of temperature change $+150^{\circ}C\;...170^{\circ}C$; high evaporability of lubricants; influence of temperature gradients and warping of constructions; sublimation of elements of constructional materials; irradiation of different physical nature; effect of micrometeorites; reduced gravitation; influence of abrasive particles of lunar ground; requirements on minimization of size and weight characteristics of a construction (high tension); undesirability (impossibility) of application of liquid and plastic lubricants; vibration, shock, acoustic loadings during start and landings to the Earth; difficulties in repair-regenerative operations in conditions of the Moon etc. Adhesive interaction of conjugated surfaces is the principal reason of possible failures of rubbed units on the Moon. In the research of the Moon automatic interplanetary stations of 'Luna' (USSR), 'Surveyer', 'Apollo' (USA) series were used. Stations executed functions of flying, landing, artificial satellites of the Moon, moon-rovers and manned spacecrafts such as 'Apollo'. The experimental- theoretical researches carried out in the sixtieth years on tribology for conditions of the Moon appeared to be rather useful to engineering of an outer space exploration and the decision of complex problems for the friction units operating in extreme conditions on the Earth. For the creation of highly loaded friction units for the long service life on the Moon it is required not only to use accumulated experience and designed technologies, but also to carry out wide scientific research.

• Polymer(Korea)
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• v.27 no.5
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• pp.484-492
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• 2003

How the characteristics and stability of the rubbing-induced alignment of nematic liquid crystals (LCs) relate to the interfacial characteristics of LC-polyimide has been studied. The characteristics of the LC alignment (such as the LC texture, the pretilt angle, and the anchoring energy) and their thermal stability have been investigated for 5 polyimides synthesized for this work. The work showed that the rubbed polyimide alignment layer induces the strong LC anchoring and that the characteristics and stability of LC alignment are determined by the short-ranged interactions between LC and polyimide molecules at the alignment layer surface. The increased flexibility of the polyimide accelerates thermal imidization, increases the pretilt angle, and improves the alignment stability. It also turned out that fluorination of the polyimide tends to deteriorate the alignment uniformity and stability. No distinct differences in the alignment characteristics were shown for the aromatic- and alicyclic-dianhydride polyimides.

• Tribology and Lubricants
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• v.17 no.4
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• pp.267-275
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• 2001

Friction and wear properties of brake friction materials containing different metal fibers (Al, Cu or Steel fibers) were investigated. Based on a simple experimental formulation, friction materials with the same amount of metal fibers were tested using a pad-on-disk type friction tester. Two different materials (gray cast iron and aluminum metal matrix composite (MMC)) were used for disks rubbing against the friction materials. Results front ambient temperature tests revealed that the friction material containing Cu fibers sliding against gray cast iron disk showed a distinct negative $\mu$-v (friction coefficient vs. sliding velocity) relation implying possible stick-slip generation at low speeds. The negative $\mu$- v relation was not observed when the Cu-containing friction materials were rubbed against the Al-MMC counter surface. Elevated temperature tests showed that the friction level and the intensity of friction force oscillation were strongly affected by the thermal conductivity and melting temperature of metallic ingredients of the friction couple. Friction materials slid against cast iron disks exhibited higher friction coefficients than Al-MMC (metal matrix composite) disks during high temperature tests. On the other hand, high temperature test results suggested that copper fibers in the friction material improved fade resistance and that steel fibers were not compatible with Al-MMC disks showing severe material transfer and erratic friction behavior during sliding at elevated temperatures.

• Journal of Conservation Science
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• v.34 no.6
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• pp.525-538
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• 2018

Myazedi Quadrilingual Stone Inscription of Myanmar, inscribed to the World Heritage List in 2015, is a rare historical artifact which has an exact date of inscription. It is a written record that displays the history, religion, and culture of Myanmar. Since the surface of the Stone Inscription has been rubbed with ink many times during the process of making printed copies for interpretation and academic research, it has developed a serious stain problem. Therefore, scientific analysis of the stain and research on the treatment for its removal have been conducted. In particular, an experiment was conducted on stain removal using laser cleaning and chemical treatment. The stains are mostly ink dirt, which accumulated from previous ink-rubbing processes. In order to conduct the experiment under similar conditions, a sample with similar stain has been reproduced, and a set of different conditions for treatment was applied to the sample to determine an effective solution. Laser cleaning was found to be effective in removing stains from most samples. However, chemical treatment showed different results. The physical friction method using ethanol provided the best result. In conclusion, laser cleaning is an effective universally-applicable technique but chemical treatment with laser cleaning can be considered an alternative method in certain situations.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.430-430
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• 2007

In general, polyimides (PIs) are used in liquid crystal displays (LCDs) as alignment layer of liquid crystals (LCs). Up to date, the rubbing alignment technique has been widely used to align liquid crystals on the PI surface, which is suitable for mass-production of LCDs because of its simple process and high productivity. However, this method has some disadvantages. Rubbed PI surfaces include the debris left by the cloth and the generation of electrostatic charges during rubbing process. Therefore, rubbing-free techniques for LC alignment are strongly required in LCD technology. In this experiment, PI was uniformly coated on indium-tin-oxide electrode substrates to form LC alignment layers using a spin-coating method and the PI layers were subsequently imidized at 433 K for 1 h. The thickness of the PI layer was set at 50 nm. The LC alignment layer surfaces were exposed to an $Ar^+$ ion-beam under various ion-beam energies. The antiparallel cells and twisted-nematic (TN) cells for the measurement of pretile angle and electro-optical characteristics were fabricated with the cell gap of 60 and $5\;{\mu}m$, respectively. The LC cells were filled with nematic LC (NLC, MJ001929, Merck) and were assembled. The NLC alignment capability on ion-beam-treated PI was observed using photomicroscope and the pretilt angle of the NLC was measured by the crystal-rotation method at room temperature. Voltage-transmittance (V-T) and response time characteristics of the ion-beam irradiated TN cell were measured by a LCD evaluation system.