• Title/Summary/Keyword: coefficients of friction

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Dynamic Friction Behavior of Interfaces Between Dense Dry Granular Soils and Construction Material(Concrete) (조밀한 건조조립토와 건설재료(콘크리트) 사이의 동마찰계수)

  • 김대상
    • Journal of the Korean Geotechnical Society
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    • v.17 no.6
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    • pp.207-213
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    • 2001
  • Shaking table tests to investigate the dynamic friction behavior of interfaces between dense dry granular soils and construction material(concrete) were performed and the results are reported. The results show the variation of dynamic interface friction coefficients between dense dry granular soils and construction material was small in the sliding velocity range employed in this study. It was also observed that dynamic interface friction coefficients decreased as mean grain sizes of granular soils increased. These coefficients were compared with the friction coefficients obtained from the peak internal friction angles of the same granular soils by plane strain compression tests.

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Measurement of Wear and Friction Coefficients for the Prediction of Fretting Wear (프레팅 마멸계수 및 마찰계수 측정에 관한 연구)

  • Cho, Yong Joo;Kim, Tae Wan
    • Tribology and Lubricants
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    • v.28 no.3
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    • pp.124-129
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    • 2012
  • The prediction of fretting wear is a significant issue for the design of contacting mechanical components such as flexible couplings and splines, jointed structures and so on. In our earlier study, we developed a numerical model to predict the fretting wear using boundary element method. The developed algorithm needs experimental fretting wear coefficients and friction coefficients between two moving materials to get more reliable results. In this study, therefore, we demonstrated the measurement method of the fretting wear coefficients and friction coefficients using disk on plate tribometer with piazo actuator and gap sensor. For four different material combinations, the fretting wear coefficients and friction coefficients are acquired through the fretting wear experiment and the analysis of the measured values. Thess results are useful to predict the quantative fretting wear rate in the developed algorithm.

Effect of Contact Pressure on the Variations in Coefficients of Friction Between Porcine Knee Joint Cartilage and Co-Cr Alloy in a Repeat Pass Sliding Motion (반복 회전운동에서 코발트 크롬 합금과 미끄럼 접촉하는 돼지 무릎 관절연골의 접촉압력이 마찰계수 변화에 미치는 영향)

  • Lee, Kwon-Yong;Kim, Hwan;Lee, Young-Ze
    • 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.

Research on the friction characteristics of multi purpose oils as mission (다용도 미션오일의 마찰특성에 관한 연구)

  • Myung, Byoung-Soo;Ryu, Hee-Bong;Lee, Yang-Kun
    • Journal of the Korean Society of Industry Convergence
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    • v.8 no.3
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    • pp.135-141
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    • 2005
  • The static friction coefficients of 4 samples against each different temperatures were similar values. Compared against RT, at $80^{\circ}C$ the static friction coefficients decreased from 0.130 to 0.116 that was equal from 88% to 90% of the static friction coefficients respectively. Otherwise the dynamic friction coefficients compared against RT, decreased from 0.138 to 0.088 which was from 71% to 77.5% respectively at $80^{\circ}C$. The noise characteristics were judged by s/d value. And when the s/d value was limited less than 0.8, noise concerns were released. At 3000 engaging cycles the static friction and the dynamic friction coefficient were 0.137 and 0.073 respectively. When plate pressure rose up to $195kg_f/cm^2$, the static friction coefficient decreased from 0.137 to 0.125 but this decreasing could be considered as stable. When speed rose up to 2200rpm, the static friction coefficient decrease from 0.14 to 0.13 but this decreasing could be considered as stable. At 3000 engaging cycles the amount of worn out was 0.04 : the thickness of disc was decrease from 4.72mm to 4.68mm. But regarding the normal operation condition, further more worn-out could not be expected. Therefore concerning worn-out, the basic oil could be considered as appropriate.

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The Relationship between Welding Conditions and Ultrasonic Reflection Coefficients of Dissimilar Metals Friction Welded Joints (이종재 막찰용접 이음부에서의 초음파 반사계수와 용접조건과의 관계)

  • 오세규;김동조;한상덕
    • Journal of Ocean Engineering and Technology
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    • v.1 no.1
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    • pp.138-143
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    • 1987
  • Friction welding has emerged as a reliable process for high-production commercial applications with significant economic and technical advantages. But nondestructive test in friction weld was not clearly developed. Therefore the experimental verification is necessary in order to understand the characteristcs of the pulse echo effects according to various change in welding conditions. This paper presents an attempt to determine the relationship between the varios welding conditions and the coefficients of reflection using the ultrasonic pulse echo method in dissibilar metals friction weld. The new approach of calculating the coefficients of reflection based on measured amplitudes of the echoes is applied in this paper. These coefficients provides a single quantitative measurement which involves both acoustic energy reflected at the welded interface as well as transmitted across the interface. As a result, it was known that the quantitave relationship between welding conditions and the coefficients of reflection using the ultrasonic pulse echo exists in dissimilar metals friction weld.

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Kinetic Friction of Grains on Surfaces (곡물의 동마찰계수 측정에 관한 연구)

  • 김만수;이동호
    • Journal of Biosystems Engineering
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    • v.1 no.1
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    • pp.49-54
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    • 1976
  • No reliable basic data were available on the kinetic friction coefficients between grains and frictional surfaces being used in grain handling equipments in Korea. In order to determine appropriate kinetic friction coefficient between three grains (Tongil, Jinheung, barley) and two surfaces at four levels of moisture content of grain, the laboratory tests using the newly designed experimental apparatus and strain gage measuring system were carried out, and the relationship among factors that affect kinetic friction coefficients of grains were analyzed. The results of this study are summarized as follows ; 1. Kinetic friction coefficient of samples being tested was dependent on surfaces and moisture content of grains . The ranges of them were 0.369-0.512 for Tongil variety , 0.347-0.469 for Jinheung variety, and 0.360-0.502 for barley, respectively. 2. There was a little difference of kinetic friction coefficients between two varieties of rice at the same testing conditions. Because the interaction had been large among treatments , each value of kinetic friction coefficient determined in this study should be used only for the corresponding conditions in this study . 3. Kinetic friction coefficients in creased linearly with increase in moisture content of grains and their regression equations were shown in Table.4. 4. Kinetic friction coefficients on a PVC surfaces was shown a little lower values than on the steel surfaces at various moisture levels, but especially in Jinheung and barley, a big difference was shown.

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Calculation of equivalent friction coefficients in V-belt (V벨트에서 상당마찰계수 계산)

  • Hong, J.P.
    • Proceedings of the KSME Conference
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    • 2001.11a
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    • pp.740-745
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    • 2001
  • There are two kinds of method to calculate the equivalent friction coefficients at V groove. One is to consider the firction in radial direction. The other is to neglect the friection in radial direction. The values calculated from the two methods is different of which ratio is in the range from two times to five times. So it is necessary to study which is correct in the view of force equilibrium and machine design.

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Friction of a Brownian Particle in a Lennard-Jones Solvent: A Molecular Dynamics Simulation Study

  • Lee, Song-Hi
    • Bulletin of the Korean Chemical Society
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    • v.31 no.4
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    • pp.959-964
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    • 2010
  • In this work, equilibrium molecular dynamics (MD) simulations in a microcanonical ensemble are performed to evaluate the friction coefficient of a Brownian particle (BP) in a Lennard-Jones (LJ) solvent. The friction coefficients are determined from the time dependent friction coefficients and the momentum autocorrelation functions of the BP with its infinite mass at various ratios of LJ size parameters of the BP and solvent, ${\sigma}_B/{\sigma}_s$. The determination of the friction coefficients from the decay rates of the momentum autocorrelation functions and from the slopes of the time dependent friction coefficients is difficult due to the fast decay rates of the correlation functions in the momentum-conserved MD simulation and due to the scaling of the slope as 1/N (N: the number of the solvent particle), respectively. On the other hand, the friction coefficient can be determined correctly from the time dependent friction coefficient by measuring the extrapolation of its long time decay to t=0 and also from the decay rate of the momentum autocorrelation function, which is obtained by time integration of the time dependent friction coefficient. It is found that while the friction coefficient increases quadratically with the ratio of ${\sigma}_B/{\sigma}_s$ for all ${\sigma}_B$, for a given ${\sigma}_s$ the friction coefficient increases linearly with ${\sigma}_B$.

Evaluation of the Friction Coefficient from the Dynamometer Test of the Aircraft

  • Woo, Gui-Aee;Jeon, Jeong-Woo;Lee, Ki-Chang;Kim, Yong-Joo
    • 제어로봇시스템학회:학술대회논문집
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    • 2003.10a
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    • pp.548-552
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    • 2003
  • In the braking system, the friction force is the most important factor of the design. For long time, many researchers have been strived for getting the exact friction coefficients. But the friction coefficients are affected by the road condition and changed by lots of parameters, such as normal force and characteristics between two contacted materials, temperature, etc. For the development of ABS of the aircraft, HILS(Hardware-In-the-Loop-Simulation) test and dynamometer test was carried out. For the calculation of the friction coefficients, the wheel moments were measured using the load cell mounted on the housing of the wheel. The test conditions were dry and greasy, as the 0.7 and 0.4 in friction coefficient, respectively. In this paper, the test results of the friction coefficients were represented and the improvement method was suggested.

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Experimental investigation of friction in guide zone of tube hydroforming with material and lubricant (튜브 액압성형 공정의 가이드영역에서 소재 및 윤활에 따른 마찰 특성의 실험적 연구)

  • Yi, H.K.;Yim, H.S.;Lee, G.Y.;Lee, S.M.;Chung, C.S.;Moon, Y.H.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2008.10a
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    • pp.83-86
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    • 2008
  • In this study, friction test was proposed to obtain coefficient of friction between tube and die in guide zone of tube hydroforming and friction coefficients were evaluated at different materials, viscosity of lubricants and internal pressures. For this study, STKM11A and SUS tubes were prepared. The tube was expanded by an internal pressure against the tool wall. By pushing the tube through the tool, a friction force at the contact surface between the tube and the tool occurs From the recorded axial feeding forces, the friction coefficients between tube and die at the guide zone in tubular hydroforming can be estimated. The effects of the various internal pressures, viscosity of lubricants, tube materials, tube size and die coating on the friction forces and friction coefficients are discussed.

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