• Title/Summary/Keyword: Friction Coefficients

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Study on the Effects of System Parameters on the High Cycle Fatigue Life Based on Structural Dynamic Analysis of a Turbine Blade System (터빈 블레이드의 구조동역학해석에 근거한 시스템 인자들의 고사이클 피로수명에 대한 영향도분석)

  • Kwon, Sung-Hun;Song, Pil-Gon;Park, Jong-Hyun;Yoo, Hong-Hee
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2007.11a
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    • pp.875-879
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    • 2007
  • The effects of the statistical properties of the Coulomb friction coefficients on the dynamic responses of a galloping quadruped robot are investigated in this paper. In general, the Coulomb friction coefficients are assumed to be deterministic for a controller design to achieve required motion characteristics. However, the friction coefficients between the ground and the robot legs are not constant in reality. Therefore, statistical characteristics of the friction coefficients need to be considered for a multi-body modeling of the robot galloping on the ground. The effects of the statistical properties on the dynamic responses of the quadruped robots are investigated.

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Estimation of Friction Coefficients Based on Field Data (실측값에 근거한 마찰계수의 추정)

  • Jeon, Se Jin;Park, Jong Chil;Park, In Kyo;Shim, Byul
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.29 no.5A
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    • pp.487-494
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    • 2009
  • Friction coefficients of the prestressing tendon are the basic information required to control the prestressing force introduced to PSC structure during jacking. However, the friction coefficients show considerable differences depending on the specifications, causing much confusion to designers. In this study, the ranges of the friction coefficients presented in domestic and foreign specifications are compared together to clarify the differences. Then, a procedure is proposed that can be used to estimate the wobble and curvature friction coefficients from field data such as elongation and prestressing force and from theory related to the friction. The procedure is applied to various tendon profiles of several PSC bridges constructed by ILM, FCM and MSS. The resulting values are compared with those presented in some specifications and assumed in jacking and a reasonable range of the friction coefficient is discussed. Lift-off tests are also performed in some bridges to further verify the results. The resulting wobble friction coefficients are not as small as those presented in AASHTO specifications but range from the lower limit to mid point of domestic specifications, while the curvature friction coefficients approach or slightly exceed the upper limit.

An Experimental Study on Friction Characteristics in Pre-Coated Sheet Metal Forming (피복된 판재의 성형에서 마찰특성에 관한 연구)

  • 김호윤;최철현;배원병
    • Journal of the Korean Society for Precision Engineering
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    • v.17 no.6
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    • pp.57-62
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    • 2000
  • An experimental study has been performed to investigate friction characteristics of pre-coated metals widely used in domestic appliances. Seven-coated sheet metals are tested by using three friction mechanism such as straight pulling, frictionless roller, and non-rotational roller with three kinds of cylindrical rollers. In this experiment, effects of friction mechanism, blank thickness, and roller diameter on friction coefficient, surface roughness, and scoring factor have been investigated From the experimental results, it has been found that tested pre-coated sheet metals have low friction coefficients ($\mu$ = 0.15~0.20) because films coated on sheets take a role of lubricants. Friction coefficients of pre-coated metals decrease with increasing roller-diameters. Surface of pre-coated metals can be improved by decreasing the blank thickness

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A Feasibility Study of Constitution Discrimination Using a Measurement Device for Dynamic Friction Coefficients of the Back of a Hand (손등피부 운동 마찰계수 측정기를 이용한 체질 판별 가능성 연구)

  • Kim, Keun-Ho;Woo, Yung-Jae;Lee, Hae-Jung;Lee, Yu-Jung;Kim, Jong-Yeol
    • Journal of Sasang Constitutional Medicine
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    • v.22 no.4
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    • pp.20-29
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    • 2010
  • 1. Objectives Our goal is to observe the feasibility of constitution discrimination from computing quantitative roughness index from dynamic friction coefficients and their gradients with the measurement device of skin friction with 3-Axis load cell sensor. 2. Methods In the traditional Korean medicine, skin diagnosis is one of the examination methods to discriminate Sasang constitution since it was known that Tae-eumin has rough skin, and Soyangin has smooth one. It is based on the skin roughness on the back of one's hand for the discrimination. The measurement device of skin friction with 3-axis load cell sensor has been developed in order to provide quantitative skin roughness through dynamic friction coefficients. The effective interval of the coefficients is obtained from the automatic sampling algorithm to use their curvature and slope. Then, Fisher's discriminant function of them makes the discrimination. 3. Results The success rate of extracting the effective interval was about 90% and the discriminant accuracy between Tae-eumin and Soyangin was 70% and 68% for men and women, respectively. The entire methods showed the possibility to distinguish between Tae-eumin and Soyangin by using stochastic properties of roughness index, which can make the entire system to include the measurement, the computation of the roughness index and the discrimination of constitution automatical. 4. Conclusions The measurement device, the automatic sampling algorithm of dynamic friction coefficients and the constitution discrimination algorithm were developed, respectively, and their combination can become the serial and automatic procedure for quantitative and objective skin diagnosis, which mimics the movement of the Oriental medical doctors' skin diagnosis. It can be applied to healthcare as well as the diagnosis of constitution in a u-Health system soon.

Seismic Performance Evaluation of Seismically Isolated Nuclear Power Plants Considering Various Velocity-Dependent Friction Coefficient of Friction Pendulum System (마찰진자시스템의 마찰계수 변화에 따른 면진된 원전구조물의 거동특성 비교)

  • Seok, Cheol-Geun;Song, Jong-Keol
    • Journal of the Earthquake Engineering Society of Korea
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    • v.20 no.2
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    • pp.125-134
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    • 2016
  • In order to improve seismic safety of nuclear power plant (NPP) structures in high seismicity area, seismic isolation system can be adapted. In this study, friction pendulum system (FPS) is used as the seismic isolation system. According to Coulomb's friction theory, friction coefficient is constant regardless of bearing pressure and sliding velocity. However, friction coefficient under actual situation can be changed according to bearing pressure, sliding velocity and temperature. Seismic responses of friction pendulum system with constant friction and various velocity-dependent friction are compared. The velocity-dependent friction coefficients of FPS are varied between low-and fast-velocity friction coefficients according to sliding velocity. From the results of seismic analysis of FPS with various cases of friction coefficient, it can be observed that the yield force of FPS becomes larger as the fast-velocity friction coefficient becomes larger. Also, the displacement response of FPS becomes smaller as the fast-velocity coefficient becomes larger.

Experimental Study on the Helical Flow Field in a Concentric Annulus with Rotating Inner Cylinders (안쪽축이 회전하는 환형관내 헬리컬 유동장의 실험적 연구)

  • Hwang, Young-Kyu;Kim, Young-Ju
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.6
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    • pp.822-833
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    • 2000
  • This experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure drops and skin-friction coefficients have been measured for the fully developed flow of water and that of glycerine-water solution (44%) at a inner cylinder rotational speed of $0{\sim}600$ rpm, respectively. The transitional flow has been examined by the measurement of pressure drops and the visualization of flow field, to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients and to understand the flow instability mechanism. The present results show that the skin-friction coefficients have the significant relation with the Rossby numbers, only for laminar regime. The occurrence of transition has been checked by the gradient changes of pressure drops and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, it is gradually declined for turbulent flow regime. Consequently, the critical (axial-flow) Reynolds number decreases as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the excitation of taylor vortices.

Tribology of friction materials containing different metal fibers (마찰재에 함유된 금속섬유의 종류에 따른 마찰 특성)

  • Ko, Kil-Ju;Jang, Ho
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 2001.06a
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    • pp.55-63
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    • 2001
  • Friction and wear properties of brake friction materials containing different metal fibers (Al, Cu or Steel fibers) were investigated using a pad-on-disk type friction tester. Two different materials(gray iron and Al-MMC)) were used for disks rubbing against the friction materials. Results from ambient temperature tests revealed that the friction material containing Cu fibers sliding against cast iron disk showed a distinct negative ${\mu}$-ν (friction coefficient vs. sliding velocity) relation implying possible stick-slip generation at low speed. The negative ${\mu}$-ν relation was not observed when the Cu-containing friction materials were rubbed against the. Al-MMC counter surface. As applied loads increased, friction materials showed higher friction coefficients comparatively. Friction materials slid against cast iron disks exhibited higher friction coefficients than Al-MMC 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 the steel fibers were not compatible with Al-MMC disks showing severe material transfer and erratic friction behavior during sliding at elevated temperatures.

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Transitional Flow study on non-newtonian fluid in a Concentric Annulus with Rotating Inner Cylinder (안쪽축이 회전하는 환형관내 비뉴튼 유체의 천이 유동 연구)

  • Kim, Young-Ju;Hwang, Young-Kyu;Kwon, Hyuk-Jung;Suh, Byung-Taek;Hwang, In-Ju
    • Proceedings of the KSME Conference
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    • 2001.11b
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    • pp.324-329
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    • 2001
  • This experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure losses and skin-friction coefficients have been measured for the fully developed flow of $0.1\sim0.4%$ aqueous solution of sodium carbomethyl cellulose (CMC), respectively at inner cylinder rotational speed of $0\sim600rpm$. The transitional flow has been examined by the measurement of pressure losses to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients. The present results show that the skin-friction coefficients have the significant relation with the Rossby numbers, only for laminar regime. The occurrence of transition has been checked by the gradient changes of pressure losses and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficients due to the rotation in uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, is gradually declined for turbulent flow regime. Consequently, the critical(axial-flow) Reynolds number decrease as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the onset of taylor vortices.

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Moisture-dependent Physical Properties of Detarium microcarpum Seeds

  • Aviara, Ndubisi A.;Onaji, Mary E.;Lawal, Abubakar A.
    • Journal of Biosystems Engineering
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    • v.40 no.3
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    • pp.212-223
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    • 2015
  • Purpose: Physical properties of Detarium microcarpum seeds were investigated as a function of moisture content to explore the possibility of developing bulk handling and processing equipment. Methods: Seed size, surface area, and 1,000-seed weight were determined by measuring the three principal axes, measuring area on a graph paper, and counting and weighing seeds. Particle and bulk densities were determined using liquid displacement and weight in a measuring cylinder, respectively. Porosity was computed from particle and bulk densities. Roundness and sphericity were measured using shadowgraphs. Angle of repose and static and kinetic coefficients of friction were determined using the vertical cylindrical pipe method, an inclined plane, and a kinetic coefficient of friction apparatus. Results: In the moisture range of 8.2%-28.5% (db), the major, intermediate, and the minor axes increased from 2.95 to 3.21 cm, 1.85 to 2.61 cm, and 0.40 to 1.21 cm, respectively. Surface area, 1,000-seed weight, particle density, porosity, and angle of repose increased from 354.62 to $433.19cm^2$, 3.184 to 3.737 kg, 1060 to $1316kg/m^3$, and 30.0% to 53.1%, respectively, whereas bulk density decreased from 647.6 to $617.2kg/m^3$. Angle of repose increased from $13.9^{\circ}$ to $28.4^{\circ}$. Static and kinetic coefficients of friction varied between 0.096 and 0.638 on different structural surfaces. Conclusions: Arithmetic mean, geometric mean, and equivalent sphere effective diameters determined at the same moisture level were significantly different from each other, with the arithmetic mean diameter being greatest. Surface area, 1,000-seed weight, particle density, porosity, and angle of repose all increased linearly with moisture content. Bulk density decreased linearly with moisture content. The coefficients of friction had linear relationships with moisture content. The highest values of static and kinetic coefficients of friction were observed on galvanized steel and hessian fabric, respectively, whereas the lowest values were observed on fiberglass.

Experimental studies on the material properties of high-strength bolt connection at elevated temperatures

  • Li, Guo-Qiang;Yin, Ying-Zhi;Li, Ming-Fei
    • Steel and Composite Structures
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    • v.2 no.4
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    • pp.247-258
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    • 2002
  • The high-temperature material properties of steel are very important to the fire resistance analysis of high-strength bolt connections. This paper reports on the results of the experimental studies on the high-temperature properties of 20 MnTiB steel which is widely used in high-strength bolts, and the friction coefficient of 16Mn steel plates at elevated temperature which is a necessary parameter for bolted frictional connection analysis. The test data includes yield strength, limit strength, modulus of elasticity, elongation and expansion coefficient of 20MnTiB steel at elevated temperature, and the friction coefficients between two 16Mn steel plates under elevated temperatures and after cooling. Based on the data from the tests, the mathematical models for predicting the mechanical properties of 20MnTiB steel and friction coefficients of 16Mn steel plates have been established.