• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.235-235
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• 2018

홍수 시의 산지하천 만곡부는 2차류 발생과 편수위 상승에 따른 하상세굴 및 홍수범람 위험이 크다. 만곡부 외측에 주로 설치되어 있는 콘크리트 옹벽호안은 표면이 매끄러워 홍수피해를 가중 시킨다. 이러한 피해를 저감시키기 위해 콘크리트 옹벽에 돌출줄눈을 설치하여 유속조감 및 설치효과를 분석한 바 있다. 본 연구에서는 기존에 제안된 직사각형 단면의 돌출줄눈보다 내구성을 추구한 사다리꼴 단면의 돌출줄눈을 제시하여 수리모형 실험을 수행하였다. 수리모형 실험은 개수로 직선수로에서 수로경사 0.0035 조건에서 수로 출구 게이트를 조절하면서 이루어졌다. 모형 돌출줄눈의 조도높이는 3cm로 하였으며, 사다리꼴 밑각은 $45^{\circ}$로 완만한 경우이다. 설치간격은 무차원 돌출줄눈 간격을 기준으로 ?형 조도인 6으로 하였다. 돌출줄눈의 설치 유무에 따라 유량에 따른 수위를 측정하고 유속을 산정하여, 마찰저항의 변화를 파악하였다. 공급유량에 따른 Froude 수는 0.168~0.359 범위였으며, 유량이 증가에 따라 Manning의 조도계수는 감소하였다. Froude 수가 0.25보다 큰 경우 돌출줄눈설치의 조도계수가 미설치보다 큰 것으로 파악되었다. 그러나 사다리꼴 돌출줄눈의 흐름저항효과는 직사각형 돌출줄눈에 비해 상대적으로 작았다. 수로 횡단면의 수위분포에 따르면, 돌출줄눈 설치 측벽 주변에서 흐름저항에 따른 유속감소와 수위상승 효과가 나타나는 것으로 파악되었다. 이번 사다리꼴 돌출줄눈은 흐름저항 효과가 크지 않았기 때문에 사다리꼴 밑각을 조정하여 새로운 단면에 대한 추가적인 실험이 필요할 것으로 보인다.

• Journal of the Korean Geosynthetics Society
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• v.12 no.4
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• pp.77-86
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• 2013

Laboratory pullout tests were conducted to evaluate pullout performance of steel strip reinforcements with deformed steel bars as transverse members. The steel strip reinforcement has an installation hole to assemble a deformed steel bar. Jumunjin standard sand is used to form a relative density of ground model to 80%. Frictional resistance of steel strip reinforcement without transverse member increases sharply at the initial displacement and quickly decreases with displacement. Maximum frictional resistance increases linearly as normal pressure increasing, and soil-reinforcement interaction friction angle(${\rho}_{peak}$) of a steel strip reinforcement is estimated to $14.64^{\circ}$. Passive resistance increases with displacement and converge into maximum passive resistance in most cases. Maximum passive resistance increases linearly as normal pressure increasing irrespective of shape of the steel reinforcement. Pullout force of steel strip reinforcements with installation holes or transverse members largely increases about 4 to 7 times compared to frictional resistance force of steel strip reinforcements when embedment length($L_e$) of steel strip reinforcements is 500 mm. In the case of using 2 transverse members, interference effect is observed due to the spacing of 2 transverse members and location of assembly holes and transverse members.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5D
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• pp.813-819
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• 2006

Skid Resistance is a index to represent the friction between tire and road surface, which influences driving safety. Skid resistance varies with the conditions of tire, abrasion of road surface, vehicle speed, drying, wet and freezing condition of road surfaces. Especially, freezing occurs when temperature drops below $0^{\circ}C$ followed by snow or rain causes decrease of skid resistance. To recover the decreased skid resistance deicing work is applied. As a results of deicing works, freezing condition is changed into wet condition. However the wet road surfaces containing the remaining deicings agents may not show the skid resistance of normal wet condition. In this study, skid resistances in the condition of freezing, deicing process and deicing agents remained after snow-removal are evaluated. The test results, skid resistance recover quickly when Pre-wetted salt spreading and NaCl was used as deicing method. Skid resistance of Deicing agents remained on the road surface showed that concrete is higher than asphalt. superior effect. Recovery rate of skid resistance by comparison wet condition is 54~80%.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.444-444
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• 2012

본 연구에서는 흑연(graphite)과 티타늄(titanum; Ti) 타겟이 양쪽에 부착되어 있는 비대칭 마그네트론 스퍼터링 장치를 이용하여 Ti가 도핑되어진 탄소(a-C:Ti) 박막을 증착하였다. 흑연 타겟의 파워는 고정하고 Ti 타겟 파워를 증가시켜 탄소 박막내에 Ti의 함량을 증가시켰으며, Ti 금속 함량에 따른 탄소박막의 경도와 마찰계수, 표면의 거칠기, 접촉각 등의 물리적 특성과 비저항 등 전기적 특성을 고찰하였으며, XPS와 라만등을 이용하여 a-C:Ti 박막의 구조적 특성을 고찰하여 Ti 금속 함량에 따른 구조적 특성과 물리적 특성, 전기적 특성과의 관계를 규명하였다.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.8
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• pp.99-109
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• 2022

In this study, an electric resistance-heated surface friction spot-welding process was proposed and tested for the spot-welding ability of copper and aluminum dissimilar metal sheets using electric resistance heating and surface friction heating. This process has welding variables, such as the current value, energizing cycles, rotational speed, and friction time. The current value and energizing cycle can affect the resistance heat, and the rotational speed of the rotating pin and friction time influence frictional heat generation. Resistance heating before friction heating has a preheating effect on the Cu-Al contact interface and a positive effect on preventing friction heat loss during the friction stage. However, because resistance preheating can soften the copper sheet and affect the contact stress and friction coefficient, it has difficulties that may adversely affect frictional heat generation. Therefore, the optimal combination of welding variables should be determined through simulations and experiments of the spot-welding process to determine the effects of electric resistance preheating on the suggested process. Through this procedure, it is known that the proposed spot-welding process can improve the welding quality during the spot welding of Cu-Al sheets.

• Journal of the Korean Geotechnical Society
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• v.33 no.11
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• pp.35-43
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• 2017

In this study, the pull-out resistance behavior of the anchor with the bump type resistors at the anchor body was experimentally investigated. In the model tests, the pull-out resistance was measured by pulling out the anchor at a constant speed. Anchor body was installed in the center of the circular sand tank. Pull-out tests were conducted for 10 conditions. The anchor type (existence of the resistor), the friction conditions of the anchor body surface ($1/3{\phi}$, $2/3{\phi}$, ${\phi}$), the bump type resistor set number (1set, 2set, 4set), and the height of resistors (0.05d, 0.10d, 0.20d) were varied. The load-displacement relationship for each conditions was measured during the pull-out tests at a constant speed (1 mm/min). Maximum pull-out length was 80 mm. As a result, the pull-out behavior of the friction type anchor and the expansion type anchor was different. As the number of resistor increased, the maximum pull-out resistance increased and the residual pull-out resistance ratio increased significantly, which were at 171~591 percent larger than that of the friction type anchor.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.04a
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• pp.41-46
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• 1997

TiN 코팅은 마모에 대한 저항성 및 고체 윤활 효과가 매우 우수하여 내마모성 및 저마찰이 요구되는 절삭공구나 피스톤 베어링 및 각종 축계의 코팅막으로 사용이 증가되고 있다. 일반적으로 재료의 경도와 인성은 서로 상반 관계를 갖고 있어 공학적으로 경도와 인성을 모두 요구하는 표면을 얻기 위해 연질 모재 위의 세라믹 코팅은 그 요구를 만족시킬 수 있는 가장 각광받는 표면처리 방법중의 하나이다. 그러나, TiN과 같은 경질 박막의 공학적 적용시 가장 요구되는 마모수명은 모재의 조도나 경도, 증착 방법, 접촉 상태, 코팅막의 두께 및 마모의 발생 기구 등에 따라 마찰 및 마모 메커니즘의 현저한 차이를 나타내기 때문에 예측이 거의 불가능한 실정이고, 아직까지 이러한 마모수명 비교 평가방법에 대한 기준 설정 및 정량적 정립이 이루어지지 않고 있다. 본 연구에서는 모재의 경도, 조도, 코팅 두께가 다른 TiN 경질 박막에 압입시험과 스크래치시험시 발생되는 균열 발생 메커니즘과 미끄럼 시험시 발생되는 마모 메커니즘의 연계성을 밝히고 압입 및 스크래치 시험시 코팅막이 손상되는 임계하중과 미끄럼 시험시 접촉하중 변화에 따른 마모수명의 정량적 연관성을 찾아보고자 한다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.11a
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• pp.283-283
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• 2015

현재 LAC 베어링에 적용되는 표면 처리는 일반적으로 하드터닝+슈퍼피니싱 가공이 적용되고 있고, 장수명을 위한 표면 처리 기술이 보다 더 요구되는 추세이다. Burnishing 기술은 매끄럽고 단단한 공구를 베어링 궤도면에 충분한 압력을 가하여 서로 문질러(rubbing) 마찰면을 소성 변형시켜 표면 거칠기 및 압축 잔류 응력 등을 향상 시키는 기술이며, 베어링과 같은 금속의 경우 버니싱 가공 적용 시 광택을 띠는 특성을 가지므로 외관 품질 향상에 기여하므로 슈퍼 피니싱 공정을 대신할 수 있다. 또한 표면 finishing, 표면 경도, 내마모성 및 피로/부식 저항성을 향상시킨다. 이에 본 연구에서는 슈퍼 피니싱 가공을 대신하기 위한 버니싱 가공의 물성을 검토하였고, 다른 공정과의 비교를 통한 버니싱 기술의 효과 확인하였다.

• International Journal of Highway Engineering
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• v.9 no.4
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• pp.117-127
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• 2007

The exposed aggregate PCC(EAP) pavements have been successfully used in Europe and Japan as low-noise pavements. Coarse aggregate are exposed on the pavement surface texture of EAP by removing mortar of surface. The pavement surface texture should maintain not only low-noise characteristic but also adequate skid resistance level during the performance period. Skid resistance decreased with wearing and polishing of tire and pavement surface due to the repetition of tire-pavement contact. Since the tires mainly contact the exposed coarse aggregate, the shape and rock type of coarse aggregate significantly influence wearing and polishing of EAP pavements. The test for resistance to abrasion coarse aggregate by use of the Los Angeles machine(KS F 2508) and the method of test for resistance to abrasion coarse aggregate by use of the Accelerated Polishing Machine(ASTM D 3319-90) are generally used to evaluate polishing characteristics of aggregate. In this study, polishing of coarse aggregate of different five rock types were evaluated by KS F 2508(LA abrasion test) and ASTM D 3319-90(PSV method). The results of LA abrasion test and PSV method were contrary to each other. Since LA abrasion test is estimated the quantity of abrasion by the impact of aggregate, it may not be adequate to evaluate the polishing of aggregate by the repetition of tire. In the case of PSV method, the resistance of polishing is estimated the skid resistance variation of polished aggregate after repetition of tire. The PSV method is adequate for the evaluation on polishing of coarse aggregate. From the test results of PSV method, it was founded that rock type, specific gravity, coarse aggregate angularity, flat or elongated particles in coarse aggregate are significant to the resistance characteristic of coarse aggregate.

• Journal of the Korean Geotechnical Society
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• v.38 no.2
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• pp.29-38
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• 2022

The friction anisotropy of shear resistance can be selectively used in geo-structures. For example, larger axially loaded deep foundation, soil nails, and tiebacks increase load carrying capacity due to induced large shear resistance while pile penetration and soil sampling produce minimal shear resistance. Previous studies confirmed direction-dependent shear resistance induced by interface between soil and surface asperity of plate inspired by geometrical shape of snake scale. The aim of this paper is to quantitatively evaluate interface friction angle with different surface asperities. Using the modified direct shear test, a total of 51 cases, which sand are prepared at the relative density of 40%, are conduced including 9 plates, two shear direction (shearing direction against the height of surface asperity is increased or decreased during shearing test), and three initial vertical stress (100 kPa, 200 kPa, 300 kPa). Experimental results show that shear stress is increased with higher height of surface asperity, shorter length of surface asperity, and the shearing direction that the height of surface asperity increases. Also, interface friction angle is decreased with larger surface asperity ratio, and shearing direction with increasing height of surface asperity produces larger interface friction angle regardless of the surface asperity ratio.