• 한국자동차공학회논문집
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• 제10권1호
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• pp.162-167
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• 2002

An automotive wheel bearing is one of the most important components to guarantee the service life of a passenger car. The endurance life of a bearing is affected by many parameters such as material properties, heat treatment, lubrication conditions, temperature, loading conditions, bearing geometry, internal clearance and so on. In this paper, we analyze the relation between loads and deformations of wheel bearing units. On the basis of it, we calculate the endurance life of wheel bearing units and suggest a method to determine the initial contact angle to achieve a maximum endurance life with considering stress concentration.

• Food Science and Biotechnology
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• 제16권2호
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• pp.234-237
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• 2007

Water resistance of three biopolyester films, such as poly-L-lactate (PLA), poly-hydroxybutyrate-co-valerate (PHBV), and Ecoflex, and low density polyethylene (LDPE) film was investigated by measuring contact angle of various probe liquids on the films. The properties measured were initial contact angle of water, dynamic change of the water contact angle with time, and the critical surface energy of the films. Water contact angle of the biopolyester films ($57.62-68.76^{\circ}$) was lower than that of LDPE film ($85.19^{\circ}$) indicating biopolyester films are less hydrophobic. The result of dynamic change of water contact angle also showed that the biopolyester films are less water resistant than LDPE film, but much more water resistant than cellulose-based packaging materials. Apparent critical surface energy for the biopolyester films (35.15-38.55 mN/m) was higher than that of LDPE film (28.59 mN/m) indicating LDPE film is more hydrophobic.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.205-209
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• 2009

Wetting properties between silver-copper-titanium braze alloys with different titanium contents up to 2.8 mass% and hexagonal boron nitride ceramics were investigated using sessile drop method at 1123K in Argon. The final contact angle is less than $30^{\circ}$ when the Ti content was over 0.41 mass%. Meanwhile, the contact angle curves show different behavior. In case of using braze alloy containing 2.8 mass% of titanium, the initial contact angle is acute angle just after the melting of braze. In case of brazes containing titanium less than 2.26 mass%, the contact angle is larger than $90^{\circ}$ at the beginning and slowly decreases to acute angle. The reaction layer of titanium nitride is observed at the interface. In addition, the reaction of Ti in the braze and N in the bulk h-BN seemed to show diffusion limited spreading.

• 치위생과학회지
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• 제10권3호
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• pp.177-183
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• 2010

탄성 고무인상재의 종류인 폴리설파이드(polysulfide), 폴리이써(polyether), 부가중합형 실리콘(addition silicone)에서 점주도(consistency)가 Type III인 인상재를 각각 1종류 선택하여 증류수 $3.3{\mu}l$를 떠뜨려 접촉각을 측정하고, 세 종류의 인상체에 치과용 경석고를 부어 작업모형을 만들고 표면을 관찰하였다. 접촉각 측정은 전자동접촉 각 측정시스템(DM-700, KYOWA, Japan)을 이용하였고 작업모형의 표면관찰은 전계 방사형 주사 전자현미경(JSM-6700F, JEOL Ltd., JAPAN)을 이용하여 다음과 같은 결론을 얻었다. 1) 초기 접촉각의 평균과 표준편차는 부가중합형실리콘, 폴리이써, 폴리설파이드 제품이 각각 $91.3^{\circ}{\pm}20.5$, $90.0^{\circ}{\pm}2.2$, $101.5^{\circ}{\pm}2.3$로 평균값은 유사하게 나타났으나 부가중합형실리콘의 표준편차값에서 큰 차이를 보여줬다. 이는 술자의 술식에 따라 항상 일정한 특성을 보여주지 않는 다는 것이다. 2) 시간이 흐를수록 부가중합형실리콘 제품은 다른 두 종류에 비해 접촉각이 급속히 감소함을 관찰 할 수 있었고, 초기접촉각이 $91.3^{\circ}$이며 25초 후 $29.4^{\circ}$로 급격히 감소했다. 3) 폴리이써 제품은 초기접촉각이 $101.5^{\circ}$에서 25초 후의 접촉각 $90.7^{\circ}$이였고, 폴리설파이드 제품은 초기접촉각이 90.0에서 25초 후의 접촉각 84.2로 변화가 거의 일어나지 않았고 그 각도도 부가중합형실리콘에 비해 컸다. 4) 세 종류의 탄성고무인상재에서 시간이 흐름으로써 관찰된 접촉각은 유의성이 있었다(p<0.001). 5) 작업모형의 표면관찰에서 부가중합형실리콘이 가장 치밀했고, 그 다음 폴리설파이드, 폴리이써 순서였다. 따라서 탄성고무 인상재에 있어서 접착각이 작은 부가중합형 실리콘은 폴리이써나 폴리설파이드 제품에 비해 더 치밀한 작업모형을 얻을 수 있었고 세 종류의 인상재접착각에서 큰 유의성을 보였다. 그러나 부가중형 실리콘은 접촉각의 편차가 커 술자의 주의가 필요한 것으로 나타났고 폴리설파이드 제품과 폴리이써 제품은 20~25초 후 접촉각이 최초 접촉각과 큰 차이를 보이지 않아 소수성 제품으로 인상채득 시 주의가 요망되는 것으로 보여진다. 향후 Vitro 상태에서 인상재에 영향을 미치는 여러가지 요인들에 대한 계속적인 연구의 필요성을 느낀다.

• 한국전기전자재료학회논문지
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• 제33권3호
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• pp.245-248
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• 2020

The wettability of silicon carbide (SiC) crystal, which has 6H-SiC and 4H-SiC regions prepared using the physical vapor transport (PVT) method, is quantitatively analyzed using dispensed deionized (DI) water droplets. Regardless of the polytypes in SiC, the average of five contact angle measurements showed a difference of about 6° between the Si-face and C-face. The contact angle on the Si-face (C-face) is measured after the removal of the native oxide using BOE (6:1), and revealed a significant decrease of the contact angle from 74.9° (68.4°) to 47.7° (49.3°) and from 75.8° (70.2°) to 51.6° (49.5°) for the 4H-SiC and 6H-SiC regions, respectively. The contact angle of the Si-face recovered over time during room temperature oxidation in air; in contrast, that of the C-face did not recover to the initial value. This study shows that the contact angle is very sensitive to SiC surface polarity, specific surface conditions, and process time. Contact angle measurements are expected to be a rapid way of determining the surface polarity and wettability of SiC crystals.

• 대한물리의학회지
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• 제5권1호
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• pp.53-61
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• 2010

Purpose : The purpose of this study is to compare the distribution of foot pressure, knee and ankle joint angle between treadmill walking and ground walking in normal person. Methods : 18 Person of subject has participated this study, let subject to walk in ground and treadmill in order to gain data of foot distribution and knee, ankle joint angle using by parotec system. and Dartfish system. Walking velocity was constrained by 2Km/h and more 10sec. Date analysis was used by paired-t test using SPSS/PC statistical programs for window. Results : Result show that total contact times has shown symmetry between both legs, and more increase of left foot pressure in treadmill walking. Foot pressure of treadmill walking was significantly decreased in right hind foot and fore foot and hallux area. The ankle joint angle of treadmill walking was significantly decreased in initial contact phase. Conclusion : Results of this study show that foot pressure of treadmill walking was more decreased than ground walking in right hind foot and fore foot, hallux area. And the ankle joint angle of treadmill walking was significantly decreased in initial contact phase.

• Tribology and Lubricants
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• 제9권1호
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• pp.32-37
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• 1993

The equations are derived for the evaluation of the axial contact forces. The contact forces of rubber seals are analyzed as a function of the ratio of real contact length, the thickness of seal lip, the inclined angle of seal lip, and the interference between the edge of seal lip and the rotating inner ring. The experimental apparatus is developed for the test of seal lip contact force. The data for designing rubber seals are presented in terms of the ratio of real contact length, initial inclined lip angle, lip thickness. and the interference. The results obtained from the derived equation for the contact force are in good agreement with the experimental results.

• 한국분무공학회지
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• 제20권4호
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• pp.236-240
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• 2015

This study aims to experimentally investigate the evaporation characteristics of nanofluid droplet on heated surface at boiling temperature of DI-water. In particular, textured surface was used to examine the effect of wettability on evaporation. At the initial stage of evaporation process, dynamic contact angle (DCA) of nanofluid droplet with 0.01 vol.% concentration on textured surface rapidly increased over its equilibrium contact angle by generated large bubble inside the droplet due to lower wettability. However, contact angle of nanofluid droplet with higher concentration on textured surface decreased with surface tension. In addition, total evaporation time of droplet on textured surface was considerably delayed due to reduction of contact area between droplet and solid surface. Thus, evaporation characteristics were highly affected by the nanofluid concentration and surface wettability.

• 대한기계학회논문집
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• 제16권12호
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• pp.2261-2267
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• 1992

본 연구에서는 시일 립의 간섭량과 접촉력에 관련된 이론적 연구를 수행한다. 시일의 접촉면에서 축방향 접촉력이 크게 설계되면 시일 립 선단에서는 마찰과 마멸이 심하게 진행되어 시일수명을 크게 단출시킬 우려가 있고, 접촉력이 작으면 밀봉된 유 체의 누설유려가 증가되면서 볼과 레이스사이의 윤활상태를 나쁘게 하여 베어링 수명 을 크게 단축하는 결과를 초래하게 되므로 시일 립의 접촉력에 관련된 연구는 대단히 중요하다.

• 한국안전학회지
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• 제23권1호
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• pp.35-45
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• 2008

This study was performed to compare the kinematics among three different safety shoes(type 1: ergonomically designed and high quality shoes, 2: curved and cushioned safety shoes, and 3: regular safety shoes) and to find the effect of insole during walking. Ten healthy subjects were recruited for this study. The range of motion of knee and ankle joint, angle of rear foot and angle of heel contact were measured using a three dimensional motion analysis system. In the second peak, the angle of heel contact showed statistically significant difference between safety shoes and insole, however, there was no statistical significance among three different safety shoes. The angle of ankle increased significantly at initial contact, first peak, the second peak and the toe off phase compared with type 1 and 2 safety shoes, and the angle of ankle showed statistically significant difference between with and without applying the insole. During the first peak, the second peak and the toe off phase, the angle of knee was statistical significance between safety shoes and insole. In heel contact, the angles of Achilles' tendon showed statistically significant difference between safety shoes and insole. The rear foot angles showed statistically significant difference between safety shoes and insole during heel contact and early heel contact. These results suggest that the type 1 safety shoes were superior to others in the statistics, and applying insole could be a possible method to prevent fatigue of lower extremity and musculoskeletal disorders. Further studies are needed to find the effect of ergonomically designed safety shoes and insole on practical value in prevention of musculoskeletal disorder, fatigue and satisfaction of workers.