Current Issue : April - June Volume : 2014 Issue Number : 2 Articles : 6 Articles
Tribological Surface Transformations (TSTs), which are irreversible near-surface solid-solid phase transformations, tend to occur\r\non railroads frequented by heavy freight trains. The present study is proposed to assess the contribution of thermomechanical\r\ncoupling processes to the emergence and development of TSTs near the surface of the rails....
?e development of corrosion- and wear-resistant high-performance coatings is important to improve components of mobile\r\nand stationary turbines, aerospace undercarriages, combustion engines, and hydraulic modules. New micro- and nanostructured\r\ncoating materials and processes to machine these coatings are developed in order to increase the performance of workpieces and\r\ncomponents, to enhance durability, and to reduce maintenance and manufacturing costs. At the Institute of Machining Technology\r\n(ISF), milling and grinding procedures have been developed for the preparation of the workpiece surface for the subsequent coating\r\nprocess. In contrast to conventional applications, the workpieces are not manufactured with the aim of achieving a minimized\r\nresulting surface roughness. Instead of this, a de??ned and adequate structure has to be generated, providing a good adhesion of the\r\nthermal sprayed coating on the workpiece surface. A??er ??rst coating of the prepared substrates by a High-Velocity-Oxygen-Fuel\r\n(HVOF) coating process, the resulting surface topography does not have the required surface quality for a subsequent (Diamond\r\nLike Carbon) DLC coating process. In order to generate a more uniform surface structure, the deteriorated surface resulting from\r\nthe HVOF coating process also has to be processed. ?erefore, the application of an adapted grinding process with diamond wheels\r\nis used....
This paper presents the application of an improved Yasutomi correlation for lubricant viscosity at high pressure in a Newtonian\r\nelastohydrodynamic line contact simulation. According to recent experimental studies using high pressure viscometers, the Yasutomi\r\npressure-viscosity relationship derived fromthe free-volume model closely represents the real lubricant piezoviscous behavior\r\nfor the high pressure typically encountered in elastohydrodynamic applications. However, the original Yasutomi correlation suffers\r\nfrom the appearance of a zero in the function describing the pressure dependence of the relative free volume thermal expansivity.\r\nIn order to overcome this drawback, a new formulation of the Yasutomi relation was recently developed by Bair et al. This new\r\nfunction removes these concerns and provides improved precision without the need for an equation of state.Numerical simulations\r\nhave been performed using the improved Yasutomimodel to predict the lubricant pressure-viscosity, the pressure distribution, and\r\nthe film thickness behavior in a Newtonian EHL simulation of a squalane-lubricated line contact. This work also shows that this\r\nmodel yields a higher viscosity at the low-pressure area, which results in a larger central film thickness compared with the previous\r\npiezoviscous relations....
The tribological behaviour of graphene oxide nanosheets in mineral oil was investigated under a wide spectrum of conditions,\r\nfrom boundary and mixed lubrication to elastohydrodynamic regimes. A ball-on-disc setup tribometer has been used to verify the\r\nfriction reduction due to nanosheets prepared by a modified Hummers method and dispersed in mineral oil. Their good friction\r\nand antiwear properties may possibly be attributed to their small structure and extremely thin laminated structure, which offer\r\nlower shear stress and prevent interaction between metal interfaces. Furthermore, the results clearly prove that graphene platelets\r\nin oil easily form protective film to prevent the direct contact between steel surfaces and, thereby, improve the frictional behaviour\r\nof the base oil. This evidence is also related to the frictional coefficient trend in boundary regime....
?is paper discusses the effects of adhesive wear and thermal degradation on the dry frictional characteristics of paper-based\r\nfriction materials against steel material. Some commercial paper-based friction materials typically used for clutch applications were\r\nsubjected to adhesive wear and thermal degradation and the dry frictional characteristics were then measured at different states on\r\na rotational tribometer. ?e experimental results reveal that both adhesive wear and thermal degradation have opposite effects on\r\nthe frictional characteristics, where the static and kinetic coefficients of friction increase due to adhesive wear but decrease due to\r\nthermal degradation....
Different systems of direct oil supply have been developed in order to facilitate efficient introduction of fresh lubricant to the oil gap\r\nand reduction of churning power loss in tilting pad thrust bearings. Up to now there is no documented application of the supply\r\ngroove in large thrust bearings used in water power plants. ?e results of modeling lubricant ??ow in the lubricating groove of a\r\nthrust bearing pad will be presented in the paper. C??D so?ware was used to carry out ??uid ??lm calculations. Such analysis makes it\r\npossible to modify groove geometry and other parameters and to study their in??uence on bearing performance. According to the\r\nresults a remarkable decrease in total power loss due to avoiding churning losses can be observed in the bearing....
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