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Sliding Velocity (sliding + velocity)
Selected AbstractsNew tribometer designed for the characterisation of the friction properties at the tool/chip/workpiece interfaces in machiningLUBRICATION SCIENCE, Issue 1 2008F. Zemzemi Abstract This work deals with the development of a new tribometer designed for the characterisation of the frictional properties at the tool/chip/workpiece interfaces in cutting processes. Based on a plane,sphere contact configuration, the experimental set-up enables a continuous regeneration of the pin,workmaterial contact. The average contact pressure can be selected up to 3,GPa under sliding velocities reaching 16,m/s. Under such severe conditions, which are not reachable with conventional tribometers, the apparent friction coefficient is quantified in parallel to the heat flux transmitted to the pin. This new system has been applied to the characterisation of the frictional properties during the dry machining of a 27MnCr5 annealed steel with a carbide cutting tool. The influence of the sliding velocity and of an additional TiN layer deposited by PVD on the carbide pins has been investigated in dry conditions. It has been shown that the sliding velocity is the more influential parameter, followed by the coating. Copyright © 2007 John Wiley & Sons, Ltd. [source] Mechanical properties of tribologically modified nanolayersLUBRICATION SCIENCE, Issue 4 2005D. Shakhvorostov Abstract Wear in modern mechanical systems is characterised by ultra-low wear rates in the range of a few nanometres per hour. The surfaces of the materials involved, as well as their volumes, experience modifications as regards morphology, crystalline arrangement, and chemical bonds. The depth of the tribological interactions under given conditions extends to a micrometre or less. To probe these thin modified zones, synchrotron-based X-ray diffraction and nano-indentation were applied. The specimens were taken from tribometer experiments employing the radionuclide technique to measure ultra-low wear rates. To obtain different degrees of tribological interaction, various loads and sliding velocities were applied. The specimens were subdivided according to the total power dissipated during the tribometer experiment. [source] Tribological behavior of pure and graphite-filled polyimides under atmospheric conditionsPOLYMER ENGINEERING & SCIENCE, Issue 8 2003P. Samyn As the use of common engineering plastics in tribological systems is limited to low sliding velocities and low loads because of creep and insufficient temperature resistance, there is increasing interest in application of high-performance polymers such as polyimides, characterized by their ability to maintain favorable mechanical properties up to their melting point. However, for practical design, tribotesting remains necessary for determination of the material's performance under a given contact situation. In this article, two commercially available polyimides are tested at relatively high sliding velocities and contact pressures under atmospheric conditions of temperature and humidity. A consistent overview of tendencies in friction and wear for pure polyimides as a function of applied normal loads and sliding velocities is given. Addition of 15% by weight graphite powder as internal solid lubricant strongly influences friction and wear. Its behavior is compared with pure polyimide grades and differences are discussed in relation with experimental measured bulk-temperatures. A linear temperature law is derived as a function of pv-levels and a steady-state condition is found at different temperature levels, in accordance with thermal conductivity of the polymer bulks. In case of graphite additives, a steady state in temperature coincides with the regime condition of wear rate. [source] Microtubule sliding movement in tilapia sperm flagella axoneme is regulated by Ca2+/calmodulin-dependent protein phosphorylationCYTOSKELETON, Issue 8 2006Masaya Morita Abstract Demembranated euryhaline tilapia Oreochromis mossambicus sperm were reactivated in the presence of concentrations in excess of 10,6 M Ca2+. Motility features changed when Ca2+ concentrations were increased from 10,6 to 10,5 M. Although the beat frequency did not increase, the shear angle and wave amplitude of flagellar beating increased, suggesting that the sliding velocity of microtubules in the axoneme, which represents dynein activity, rises with an increase in Ca2+. Thus, it is possible that Ca2+ binds to flagellar proteins to activate flagellar motility as a result of the enhanced dynein activity. One Ca2+ -binding protein (18 kDa, pI 4.0), calmodulin (CaM), was detected by 45Ca overlay assay and immunologically. A CaM antagonist, W-7, suppressed the reactivation ratio and swimming speed, suggesting that the 18 kDa Ca2+ -binding protein is CaM and that CaM regulates flagellar motility. CaMKIV was detected immunologically as a single 48 kDa band in both the fraction of low ion extract of the axoneme and the remnant of the axoneme, suggesting that CaMKIV binds to distinct positions in the axoneme. It is possible that CaMKIV phosphorylates the axonemal proteins in a Ca2+/CaM-dependent manner for regulating the dynein activity. A 32P-uptake in the axoneme showed that 48, 75, 120, 200, 250, 380, and 400 kDa proteins were phosphorylated in a Ca2+/CaM kinase-dependent manner. Proteins (380 kDa) were phosphorylated in the presence of 10,5 M Ca2+. It is possible that an increase in Ca2+ induces Ca2+/CaM kinase-dependent regulation, including protein phosphorylation for activation/regulation of dynein activity in flagellar axoneme. Cell Motil. Cytoskeleton 2006. © 2006 Wiley-Liss, Inc. [source] New tribometer designed for the characterisation of the friction properties at the tool/chip/workpiece interfaces in machiningLUBRICATION SCIENCE, Issue 1 2008F. Zemzemi Abstract This work deals with the development of a new tribometer designed for the characterisation of the frictional properties at the tool/chip/workpiece interfaces in cutting processes. Based on a plane,sphere contact configuration, the experimental set-up enables a continuous regeneration of the pin,workmaterial contact. The average contact pressure can be selected up to 3,GPa under sliding velocities reaching 16,m/s. Under such severe conditions, which are not reachable with conventional tribometers, the apparent friction coefficient is quantified in parallel to the heat flux transmitted to the pin. This new system has been applied to the characterisation of the frictional properties during the dry machining of a 27MnCr5 annealed steel with a carbide cutting tool. The influence of the sliding velocity and of an additional TiN layer deposited by PVD on the carbide pins has been investigated in dry conditions. It has been shown that the sliding velocity is the more influential parameter, followed by the coating. Copyright © 2007 John Wiley & Sons, Ltd. [source] Geometric effects in high-temperature vapour-phase lubrication using hydrocarbon feed gasesLUBRICATION SCIENCE, Issue 2 2002J. E. Gardner Abstract The effectiveness of ,far-field' vapour-phase lubrication, in which areas of a bearing surface that are cycled through the contact are exposed to vapour while outside the contact, has been demonstrated in both sliding and combined roll slide tests using acetylene vapours to deposit pyrolytic graphite. Friction coefficients as low as , = 0.008 have been measured for steel at 540°C with far-field acetylene concentrations as low as 5%. Effective vapour-phase lubrication depends on solid lubricant deposition that exceeds the contact's capacity to remove solid lubricant through wear. While the rate of removal is increased by increasing the sliding velocity, in far-field vapour-phase lubrication the rate of lubricant deposition, and therefore the lubrication effectiveness, is augmented by increased areas available for far-field deposition, such as those provided by performing wear tests with increased wear-track diameters. These geometric concepts may be considered in rolling-element bearing and gear set applications where vapour-phase lubrication is to be employed. [source] Influence of operating conditions on friction and temperature characteristics of a wet clutch engagementLUBRICATION SCIENCE, Issue 2 2000Mikael HolgersonArticle first published online: 9 MAR 200 Abstract To optimise the gear change in automatic transmissions, more knowledge is needed of the engagement behaviour of wet clutches. A factorial design investigation of the engagement of a wet clutch has been carried out. The friction and temperature characteristics have been studied. The experiments were carried out in an apparatus that can vary sliding velocity, drive torque, inertia, force rate, and lubricant flow. The results show how these parameters affect the response data: engagement time, developed energy, temperature rise, maximum torque, maximum power, static friction, dynamic friction, and initial friction. There are interaction effects between some of the input parameters, but they are relatively small. The friction coefficient varies over time but is independent of the input parameters, except for dynamic friction, which decreases with increasing sliding velocity, drive torque, and inertia. The temperature rise was found to be proportional to developed energy and both these were most affected by sliding velocity. The drive torque and force rate have the greatest effect on the engagement time. [source] Digital image analysis of the flagellar beat of activated and hyperactivated suncus spermatozoaMOLECULAR REPRODUCTION & DEVELOPMENT, Issue 4 2007Takane Kaneko Abstract The flagellar beat of hyperactivated Suncus spermatozoa was analyzed by digital imaging and was compared to that of the nonhyperactivated (activated) spermatozoa in order to examine the function of the accessory fibers during the flagellar beat and the sliding filament mechanism inducing the motility of the hyperactivated spermatozoa. Unusual large and long characteristics of the accessory fibers were involved in generating the gently curved bends and a low beat frequency. Examination of the motility parameters of the flagellar beat of the activated and hyperactivated spermatozoa attached to a slide glass by their heads revealed that there were two beating modes: a frequency-curvature dependent mode in the activated flagellar beat and a nearly constant frequency mode in the hyperactivated flagellar beat. The hyperactivated flagellar beat was characterized by sharp bends in the proximal midpiece and a low beat frequency. The sharp bends in the proximal midpiece were induced by the increase in the total length of the microtubule sliding at the flagellar base. The rate of microtubule sliding (sliding velocity) in the axoneme remained almost constant in the flagellar beat of both the activated and hyperactivated spermatozoa. Comparison of the sliding velocity in Suncus, golden hamster, monkey, and sea urchin sperm flagella with their stiffness suggests that the sliding velocity is determined by the stiffness at the flagellar base and that the same sliding microtubule system functions in both mammalian and echinoderm spermatozoa. Mol. Reprod. Dev. 74: 478,485, 2007. © 2006 Wiley-Liss, Inc. [source] Measurement of sliding velocity and induction time of a single micro-bubble under an inclined collector surfaceTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2008Aref Seyyed Najafi Abstract In this study, interactions between a gas bubble and a flat solid surface were investigated by determining two dynamic parameters, bubble sliding velocity underneath an inclined solid surface and induction time of the gas bubble attaching to the solid surface in aqueous solutions. A single micro-bubble was allowed to move vertically toward an inclined solid surface. After reaching its terminal velocity, the bubble approaches the inclined solid surface and slides underneath it. Complete trajectory of the bubble movement was monitored and recorded by a high-speed CCD video imaging system. Various types of gas bubbles (CO2, air, H2, and O2) and solid surfaces such as bitumen-coated Teflon, hydrophobized and hydrophilic silica were used in sliding velocity and induction time measurements. The effect of water chemistry (industrial process water and de-ionized water) and surface heterogeneity on bubble sliding velocity and induction time was investigated. The results showed that the sliding velocity of micro-bubbles under an inclined solid surface is a strong function of water chemistry, gas type, temperature and hydrophobicity of the solid surface. This study provides relevant information on bubble,solid interactions that would assist in the understanding of bubble,solid attachment under diverse conditions. Dans cette étude, on a étudié les interactions entre une bulle de gaz et une surface solide plane en déterminant deux paramètres dynamiques, la vitesse de glissement de bulle sous une surface de solides inclinée ainsi que le temps d'induction de l'attachement d'une bulle de gaz à une surface solide en solution aqueuse. On a fait se déplacer une micro-bulle unique verticalement vers une surface solide inclinée. Après avoir atteint sa vitesse terminale, la bulle s'approche de la surface solide inclinée et glisse sous elle. La trajectoire complète de la bulle a été enregistrée par un système d'imagerie vidéo CCD à haute vitesse. Différents types de bulles de gaz (CO2, air, H2, et O2) et de surfaces solides telles que du téflon enduit de bitume, de la silice hydrophobe et hydrophile, ont été utilisés dans les mesures de vitesse de glissement et de temps d'induction. L'effet de la chimie de l'eau (eau de procédés industriels et eau déminéralisée) et de l'hétérogénéité de la surface sur la vitesse de glissement et le temps d'induction a été étudié. Les résultats montrent que la vitesse de glissement des micro-bulles sous une surface solide inclinée dépend fortement de la chimie de l'eau, du type de gaz, de la température et de l'hydrophobicité de la surface solide. Cette étude fournit des informations pertinentes sur les interactions bulles-solides pouvant permettre de comprendre l'attachement bulles-solides dans des conditions diverses. [source] Tribological properties of hydrophilic polymer brushes under wet conditionsTHE CHEMICAL RECORD, Issue 4 2010Motoyasu Kobayashi Abstract This article demonstrates a water-lubrication system using high-density hydrophilic polymer brushes consisting of 2,3-dehydroxypropyl methacrylate (DHMA), vinyl alcohol, oligo(ethylene glycol)methyl ether methacrylate, 2-(methacryloyloxy)ethyltrimethylammonium chloride (MTAC), 3-sulfopropyl methacrylate potassium salt (SPMK), and 2-methacryloyloxyethyl phosphorylcholine (MPC) prepared by surface-initiated controlled radical polymerization. Macroscopic frictional properties of brush surfaces were characterized by sliding a glass ball probe in water using a ball-on-plate type tribotester under the load of 0.1,0.49,N at the sliding velocity of 10,5,10,1,m,s,1 at 298,K. A poly(DHMA) brush showed a relatively larger friction coefficient in water, whereas the polyelectrolyte brushes, such as poly(SPMK) and poly(MPC), revealed significantly low friction coefficients below 0.02 in water and in humid air conditions. A drastic reduction in the friction coefficient of polyelectrolyte brushes in aqueous solution was observed at around 10,3,10,2,m,s,1 owing to the hydrodynamic lubrication effect, however, an increase in salt concentration in the aqueous solution led to the increase in the friction coefficients of poly(MTAC) and poly(SPMK) brushes. The poly(SPMK) brush showed a stable and low friction coefficient in water even after sliding over 450 friction cycles, indicating a good wear resistance of the brush film. © 2010 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 10: 208,216; 2010: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.201000001 [source] Flagellar oscillation: a commentary on proposed mechanismsBIOLOGICAL REVIEWS, Issue 3 2010David M. Woolley Eukaryotic flagella and cilia have a remarkably uniform internal ,engine' known as the ,9+2' axoneme. With few exceptions, the function of cilia and flagella is to beat rhythmically and set up relative motion between themselves and the liquid that surrounds them. The molecular basis of axonemal movement is understood in considerable detail, with the exception of the mechanism that provides its rhythmical or oscillatory quality. Some kind of repetitive ,switching' event is assumed to occur; there are several proposals regarding the nature of the ,switch' and how it might operate. Herein I first summarise all the factors known to influence the rate of the oscillation (the beating frequency). Many of these factors exert their effect through modulating the mean sliding velocity between the nine doublet microtubules of the axoneme, this velocity being the determinant of bend growth rate and bend propagation rate. Then I explain six proposed mechanisms for flagellar oscillation and review the evidence on which they are based. Finally, I attempt to derive an economical synthesis, drawing for preference on experimental research that has been minimally disruptive of the intricate structure of the axoneme. The ,provisional synthesis' is that flagellar oscillation emerges from an effect of passive sliding direction on the dynein arms. Sliding in one direction facilitates force-generating cycles and dynein-to-dynein synchronisation along a doublet; sliding in the other direction is inhibitory. The direction of the initial passive sliding normally oscillates because it is controlled hydrodynamically through the alternating direction of the propulsive thrust. However, in the absence of such regulation, there can be a perpetual, mechanical self-triggering through a reversal of sliding direction due to the recoil of elastic structures that deform as a response to the prior active sliding. This provisional synthesis may be a useful basis for further examination of the problem. [source] | |||||||||||||