The interfacial properties of perfluoropolyether (PFPE) films having the [(CF2)nO] main chain with n = 1.5, 3 and 4, were systematically compared on carbon surfaces. The monolayer thickness decreases with increasing n, indicating that stiffer chains (larger n) lie flatter on the surface. The surface energy-derived disjoining pressure also increased with increasing n. Spin-stand tribological experiments indicated that clearance (slider-disk spacing) increased and PFPE lubricant pick-up decreased with increasing disjoining pressure and main chain stiffness. Slider wear rate increased with decreasing PFPE coverage and increasing main chain stiffness. Structure-property correlations are developed and discussed.
In this study, using a self-made impact test rig controlled by the electromagnet and the time relay, a steel ball in an upper clamp is impacted on to 40Cr testing specimens fixed in a lower clamping fixture reciprocatingly. Three contact conditions are employed: dry contact and two lubricated contacts. One lubricant with lower viscosity and the other with higher viscosity were employed in the experiments to study the influence of the viscosity. After experiments, the impact dent is measured by SEM and a surface profiler. The results show that in the dry contact, the repeated impact firstly forms a hardened layer on the metal surface which is damaged in the following impacts. Using the low viscosity oil, the plastic deformation can be restrained effectively. Moreover, using high viscosity oil, the dent can be effectively protected from plastic deformation and impact wear if the lubricant is supplied fully. However, if the lubricant is not supplied fully, a long and sharp local dent is produced in the impact dent, resulting in further damage to the metal.
Magnetorheological (MR) fluids, to be used as brake friction materials, must have high heat transfer rate to dissipate the heat generated during the braking action. The aim of this manuscript is to synthesize MR fluids with nano-silver and nano-copper particles to increase the heat transfer rate and characterize the demagnetizing effect of those particles on the shear stress of MR fluids. Five different MR fluids, containing a different percentage of silver and copper nano particles, were synthesized. Shear stresses of all five MR fluids were measured using magnetorheometer and the results have been plotted. A flywheel based MR brake experimental setup was developed to analyze the performance of synthesized MR fluids. “T” type thermocouples were used to measure the temperature distribution of the fabricated MR brake. The results of the temperature distribution of brakes containing five synthesized MR fluids have been presented and compared.
The aim of the present paper is to investigate and predict the static performance of finite journal bearing in turbulent flow condition considering non-Newtonian lubrication. The Navier-Stokes equation has been modified considering turbulent as well as non-Newtonian lubrication and is solved for steady state parameters. Ng and Pan’s linear turbulence model is utilised in the analysis. The momentum and continuity equations in cylindrical coordinates representing the flow field in the clearance space of a finite circular journal bearing using a Newtonian lubricant were solved by the finite element method. The non-Newtonian lubrication effect is introduced by modifying the viscosity term using the cubic shear stress law in each iteration. In this paper, the effect of turbulence and non-Newtonian lubrication has been determined by solving the modified Navier-Stokes equations obtained by the application of linear theory proposed by Ng and Pan and using the cubic shear stress law model simultaneously. The modified Navier-Stokes equations, in cylindrical coordinates, have been solved by finite element method using Galerkin's technique and a suitable iteration procedure. Steady-state performance characteristics of a finite circular journal bearing have been analysed in terms of Sommerfeld number, load carrying capacity, friction coefficient variable, temperature rise parameter and total flow at various eccentricities for different Reynolds numbers up to 13300 and various values of non-linear factor of cubic shear stress law of non-Newtonian model. Computed results have been compared with the published results obtained by linearized theory of Ng and Pan and cubic shear stress law of non-Newtonian lubrication. The results obtained revealed better performance in turbulent regime as compared to laminar condition for cubic shear stress non-Newtonian model.
The Japanese Society of Tribologists is pleased to announce that the 2014 Paper Award of Tribology Online was awarded to: “Experimental Analysis of the Distribution of Traction Coefficient in the Shoe-Ground Contact Area during Running,”by Kenta Moriyasu, Tsuyoshi Nishiwaki, Takeshi Yamaguchi and Kazuo Hokkirigawa, Vol. 7, No. 4 (2012) 267-273. and “Oil-Free Bearings and Seals for Centrifugal Hydrogen Compressor,”by Hooshang Heshmat, Andrew Hunsberger, Zhaohui Ren, Said Jahanmir and James F. Walton, II, Vol. 8, No. 1 (2013) 44-63. The Award Medals were presented to the authors by Prof. Takahisa Kato, the President of the Japanese Society of Tribologists, at the JAST Annual Meeting on 28th May, 2015. The Paper Award of Tribology Online is given annually to the author(s), either the JAST members or non-members, of the paper(s) judged as the best paper(s) published in Tribology Online (TROL) for the previous three years. All papers that appeared in TROL for the three years are reviewed by the JAST Awards Committee.