Current Issue : January - March Volume : 2013 Issue Number : 1 Articles : 4 Articles
When an elastic body of revolution rolls tractively over another, the period from commencement of rolling until gross rolling\r\nensues is termed the prerolling regime. The resultant tractions in this regime are characterized by rate-independent hysteresis behavior\r\nwith nonlocal memory in function of the traversed displacement. This paper is dedicated to the theoretical characterization\r\nof traction during prerolling. Firstly, a theory is developed to calculate the traction field during prerolling in function of the instantaneous\r\nrolling displacement, the imposed longitudinal, lateral and spin creepages, and the elastic contact parameters. Secondly,\r\nthe theory is implemented in a numerical scheme to calculate the resulting traction forces and moments on the tractive rolling of a\r\nball. Thirdly, the basic hysteresis characteristics are systematically established by means of influence-parameters simulations using\r\ndimensionless forms of the problem parameters. The results obtained are consistent with the limiting cases available in literature\r\nand they confirm experimental prerolling hysteresis observations. Furthermore, in a second paper, this theory is validated experimentally\r\nfor the case of V-grooved track....
When solids are subjected to tribological loads, structural changes can occur both at the surface and in depth, immediately below the loaded area; in the case of some materials, especially metals, these changes are known as solid-solid phase transformations or Tribological Surface Transformations (TSTs). A thermomechanical model is presented in the present study in order to describe these TSTs. The ability of the model to take account TSTs is assessed with a 2D finite element analysis....
Gold/1-butyl-3-methylimidazolium hexafluorophosphate (Au/[Bmim][PF6]) nanofluids containing different stabilizing\r\nagents were fabricated by a facile one-step chemical reduction method, of which the nanofluids stabilized by\r\ncetyltrimethylammonium bromide (CTABr) exhibited ultrahighly thermodynamic stability. The transmission electron\r\nmicroscopy, UV-visible absorption, Fourier transform infrared, and X-ray photoelectron characterizations were\r\nconducted to reveal the stable mechanism. Then, the tribological properties of these ionic liquid (IL)-based gold\r\nnanofluids were first investigated in more detail. In comparison with pure [Bmim][PF6] and the nanofluids\r\npossessing poor stability, the nanofluids with high stability exhibited much better friction-reduction and anti-wear\r\nproperties. For instance, the friction coefficient and wear volume lubricated by the nanofluid with rather low\r\nvolumetric concentration (1.02 Ã?â?? 10-3%) stabilized by CTABr under 800 N are 13.8 and 45.4% lower than that of\r\npure [Bmim][PF6], confirming that soft Au nanoparticles (Au NPs) also can be excellent additives for high\r\nperformance lubricants especially under high loads. Moreover, the thermal conductivity (TC) of the stable\r\nnanofluids with three volumetric fraction (2.55 Ã?â?? 10-4, 5.1 Ã?â?? 10-4, and 1.02 Ã?â?? 10-3%) was also measured by a\r\ntransient hot wire method as a function of temperature (33 to 81Ã?°C). The results indicate that the TC of the\r\nnanofluid (1.02 Ã?â?? 10-3%) is 13.1% higher than that of [Bmim][PF6] at 81Ã?°C but no obvious variation at 33Ã?°C. The\r\nconspicuously temperature-dependent and greatly enhanced TC of Au/[Bmim][PF6] nanofluids stabilized by CTABr\r\ncould be attributed to micro-convection caused by the Brownian motion of Au NPs. Our results should open new\r\navenues to utilize Au NPs and ILs in tribology and the high-temperature heat transfer field....
A low cost, compact, real-time, and quick measurement optical device based on the absorbance of white light, which comprised\r\nof photodiodes in a 3-element color-sensor, feedback diodes, water and temperature sensing element, and so on, was developed\r\nand tested in low absorption mineral oil. The device, a deviation from conventional electrical, mechanical, and electrochemical\r\ntechniques, uses color ratio (CR) and total contamination index (TCI) parameters based on transmitted light intensity in RGB\r\nwavelengths for oil condition monitoring. Test results showed that CR corroborated CIE chromaticity (X-Y Coordinates) and\r\nincreased with oil degradation unlike Saturation S and Hue H. CR was found to be independent of the particulate contaminants\r\nof oil, but dependent on chemical degradation. TCI depended on both chemical degradation and particulate contaminants in oil,\r\nbeing most sensitive in the blue wavelength range and least in the green. Furthermore, results agreed with those of viscometry, total\r\nacid number (TAN), and UV-VIS photospectrometry. CR and TCI gave clearer indication of oil degradation than key monitoring\r\nparameters like TAN and were found to be effective criteria for characterizing the degradation of hydraulic mineral oils....
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