• Title/Summary/Keyword: negative friction

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Analysis of the Shaft Resistance of a Pile Embedded in Sand Responding to Ground Deformation by Model Tests of Simulated Ground Heaving (실내모형실험을 통한 지반 융기시 사질토 지반에 매설된 지반 변형 대응형 말뚝의 주면 마찰 저항 분석)

  • Shin, Sehee;Lee, Kicheol
    • Journal of the Korean Geotechnical Society
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    • v.39 no.1
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    • pp.5-14
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    • 2023
  • The pile driving process may lead to ground heaving, causing additional positive skin friction to act on the piles, compromising their stability. This study proposes a new pile foundation type that can reduce positive skin friction. This was investigated by designing and constructing a pile with a hydraulic cylinder which actively responds to ground deformation. The newly proposed pile design was compared against traditional piles in multiple model tests where ground heaving was simulated. In the tests, base load and total shaft resistance were measured during ground heaving and with expansion of the hydraulic cylinder. As a result of the tests, a very small amount of expansion of the hydraulic cylinder member completely reduced the positive skin friction and increased the base load. Excessive expansion of the hydraulic cylinder, however, generates negative skin friction beyond the zero skin friction state. Therefore, it is necessary to estimate the appropriate level of hydraulic cylinder expansion, taking into account the amount of ground heaving and the allowable displacement of the pile.

Design of Pile Foundations in Soft Deposits (연약지반에서의 말뚝기초의 설계)

  • Kim, Ju-Hyong;Kwon, Oh-Sung;Kim, Myoung-Mo
    • Proceedings of the Korean Geotechical Society Conference
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    • 2005.03a
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    • pp.49-56
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    • 2005
  • The negative skin friction on piles, which are installed in currently consolidating soft deposits, creates significant problems on the stability of pile foundations. This study investigated whether or not the pile foundation designs were appropriate in soft deposits with large amount of consolidation settlement. The final settlements of the grounds along the pile depth were estimated by the soil parameters obtained from the laboratory tests and by the field-measured settlement curves, if they were available. The displacement of the piles along the pile depth was estimated by both the load transfer method and the numerical method. Both methods gave similar locations of neutral points and magnitudes of the maximum axial forces. The movements of the ground and the piles were compared to calculate the down drag acting on piles. For the piles whose bearing capacities were less than the design loads including the down drag, slip layer coatings and/or incrementing of the penetration depth into the bearing stratum were proposed to improve the piles capacities.

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Analysis of Pile Behaviors with Friction Resistance of Skin of Steel Pipe Pile in Ground where Settlement is Predicted (침하가 예측되는 지반에서 강관말뚝 주면 마찰 저항에 따른 말뚝의 거동 분석)

  • Lee, Kicheol;Shin, Sehee;Lee, Haklin;Kim, Dongwook
    • Journal of the Korean Geotechnical Society
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    • v.36 no.11
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    • pp.107-117
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    • 2020
  • Open-ended steel pipe piles have outside frictional force and inside frictional resistance in which blocked soil acts on the inside of the steel pipe during installation. It is expected that the ultimate load will change depending on the inside and outside resistance. And, if the ground on which the piles were constructed is clay soil, it is predicted that it will have effect on the negative skin friction caused by the ground settlement. Therefore, in this study, the behavior according to the inside and outside resistance characteristics of steel pipe piles was analyzed numerically, and the frictional force distribution, axial load and settlements before and after the occurrence of ground settlement were calculated. As a result of the analysis, the inside frictional resistance had less influence than the outside frictional resistance. However, inside frictional resistance is considered to be one of the important factors considering the effect on the overall pile behavior, and both resistance factors need to be considered in the design process.

An Analysis of Cutting Force in Micromachining (미소절삭에서의 절삭력 해석)

  • Kim, Dong Sik;Kahng, C.H.;Kwak, Yoon Keun
    • Journal of the Korean Society for Precision Engineering
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    • v.12 no.12
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    • pp.72-80
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    • 1995
  • Ultraprecision machining technology has been playing a rapidly increasing and important role in manufacturing. However, the physics of the micromachining process at very small depth of cut, which is typically 1 .mu. m or less is not well understool. Shear along the shear plane and friction at the rake face dominate in conventional machining range. But sliding along the flank face of the tool due to the elastic recovery of the workpiece material and the effects of plowing due to the large effective negative rake angle resultant from the tool edge radius may become important in micromachining range. This paper suggests an orthogonal cutting model considering the cutting edge radius and then quantifies the effect of plowing due to the large effective negative rake angle.

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Friction Characteristics of Warm a Forging Lubricant Containing Nano Graphite Powder (나노분말이 함유된 온간단조용 윤활제 마찰특성)

  • Kim, D.W.;Kim, Y.R.;Lee, G.A.;Choi, H.J.;Yun, D.J.;Shin, Y.C.;Lee, J.K.;Lim, S.J.
    • Transactions of Materials Processing
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    • v.21 no.1
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    • pp.13-18
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    • 2012
  • During warm forging, materials are formed in the temperature range of 300C900C. In this temperature range, the friction between the forging die and the material is very high and has a negative effect on the forming process causing severe die wear and possible defects in the component because of stick-slip. Thus, lubrication characteristics are a very important factor for productivity during warm forging. In this paper, ring compression experiments were conducted to estimate the friction factor between the die and the materials as the main factor in characterizing the lubricant. Also, ring tests using normal graphite power as a lubricant coating system were compared with tests using nano graphite powder. The results confirm that the nano graphite is superior to the normal graphite in view of its lubricating effect. In addition, the friction factor (m) was estimated with respect to the amount of the nano graphite content in the lubricant. With 10 % nano graphite the friction factor had the lowest value as compared to other amounts. It can be concluded that the amount of the nano graphite in the coating system can be optimized to obtain the best lubrication condition between the die and the material using ring test experiments.

Seasonal Variation of Volume Transport through the Straits of the East/Japan Sea Viewed from the Island Rule

  • Seung, Young Ho;Han, Soo-Yeon;Lim, Eun-Pyo
    • Ocean and Polar Research
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    • v.34 no.4
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    • pp.403-411
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    • 2012
  • Among others, a question that has long been unanswered is why the seasonal variation of volume transport is larger in the Soya and Korea/Tsushima Straits than in the Tsugaru Strait. An attempt is made to answer this question in terms of the island rule with friction being taken into account. The problem is idealized as a simple model. The model results indicate that volume transport through a channel is determined not only by the circulation created around the adjacent island but also by those created around the neighboring islands farther away. The latter is due to the presence of bottom friction in the channels. The volume transports through the Korea/Tsushima, Tsugaru and Soya Straits estimated from the model using observed wind data show the general pattern of observed seasonality, although they contain large errors associated with the uncertain frictional parameter employed in the model. The model indicates that the observed seasonality arises essentially from the fact that wind stress curl changes its sign, from negative in the summer to positive in winter, following a large fluctuation of zero-stress curl latitude east of Hokkaido.

The Low Temperature Deposition of CrN Films by the AIP Method (아크 이온플레이팅법에 의한 저온 CrN 합성)

  • Cho, Yong K.;Kim, Sang K.;Lee, Won B.;Kim, Sung W.
    • Journal of the Korean Society for Heat Treatment
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    • v.20 no.2
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    • pp.78-83
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    • 2007
  • CrN coatings were deposited by cathodic arc ion plating method on the SKD11 steel substrates. Atmosphere temperature of 350C, arc current of 90 A, nitrogen partial pressure of 1.0-5.3 Pa, and negative bias voltage of 30-135 V were selected. The characteristics of microstructure were investigated with XRD. Hardness, adhesion and friction coefficient measured by microhardness tester, scratch tester, and ball on disk tribometer. Microstructures depended on nitrogen partial pressure and bias voltage. The preferred orientation of the films was changed from (200) to (111) with decreasing pressure and increasing bias voltage. Adhesion properties related with microstructure, but microstructure changes slightly influenced on hardness and friction properties. The critical load.(Lc1) and hardness of CrN films deposited at 5.3 Pa, -30 V condition were 55 N(HF1), 2157±47Hk0.025. The friction coefficient were about 0.5 under dry condition.

Axisymmetric Thick Turbulent Boundary Layer Around a Rotating Body of Revolution (회전하는 회전체 주위의 축대칭 두꺼운 난류경계층 연구)

  • Shin-Hyoung,Kang;Jung-Ho,Hwang
    • Bulletin of the Society of Naval Architects of Korea
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    • v.23 no.1
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    • pp.13-22
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    • 1986
  • Axisymmetric turbulent thick boundary layers on a rotating body of revolution are calculated numerically in the paper. Richardson number is introduced to the mixing length to take account of swirl effects on Reynolds stresses. Interactions of the boundary layer and the external potential flow are included by adding the displacement thickness of boundary layers on the original body. Pressure distributions on the body surface are estimated by integrating normal momentum equation across the boundary layer. A model is designed and tested in the wind tunnel. Mean velocities are measured. Through the present study, swirl effects on the thick axisymmetric boundary layer development are considerable in comparison with those of non-totating cases. Rotational motion generally increase boundary layer thickness, axial skin friction coefficients, and form drags. Circumferential flow can be reversed to induce negative skin friction when the section area is reduced.

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Effect of Particulate Contamination on the Friction and Wear of Head-Disk Interface with Picoslider (오염입자가 Picoslider의 헤드-디스크 인테페이스 마찰 마모에 미치는 영향)

  • ;Bharat Bhushan
    • Tribology and Lubricants
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    • v.16 no.5
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    • pp.395-402
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    • 2000
  • The effect of particulate contamination on friction and wear between a negative-pressure picoslider and a laser-textured disk was studied. Particles of different concentrations, materials and sizes were injected to the head-disk interface (HDI), consisting of disks with various textures, at the same speed. In a contaminated environment, durability of head-disk interface gradually decreased as the particle concentration increased. Large particles caused HDI failure early and resulted in an extensive damage to the slider and disk surfaces. Hard particles also caused HDI failure earlier and damages more extensive than soft ones. Based on the test results, mechanisms of HDI failure with picoslider were presented.

Submicron-scale Polymeric Patterns for Tribological Application in MEMS/NEMS

  • Singh R. Arvind;Yoon Eui-Sung;Kim Hong Joon;Kong Hosung;Jeong Hoon Eui;Suh Kahp Y.
    • KSTLE International Journal
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    • v.6 no.2
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    • pp.33-38
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    • 2005
  • Submicron-scale patterns made of polymethyl methacrylate (PMMA) were fabricated on silicon-wafer using a capillarity-directed soft lithographic technique. Polyurethane acrylate (PUA) stamps (Master molds) were used to fabricate the patterns. Patterns with three different aspect ratios were fabricated by varying the holding time. The patterns fabricated were the negative replica of the master mold. The patterns so obtained were investigated for their adhesion and friction properties at nano-scale using AFM. Friction tests were conducted in the range of 0-80 nN. Glass (Borosilicate) balls of diameter 1.25 mm mounted on cantilever (Contact Mode type NPS) were used as tips. Further, micro-friction tests were performed using a ball-on-flat type micro-tribe tester, under reciprocating motion, using a soda lime ball (1 mm diameter) under a normal load of 3,000 mN. All experiments were conducted at ambient temperature (24±1C) and relative humidity (45±5%). Results showed that the patterned samples exhibited superior tribological properties when compared to the silicon wafer and non-patterned sample (PMMA thin film) both at the nano and micro-scales, owing to their increased hydrophobicity and reduced real area of contact. In the case of patterns it was observed that their morphology (shape factor and size factor) was decisive in defining the real area of contact.