Dynamic characteristics of compliant journal bearings considering thermal effects

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Polymers in tribology: challenges and opportunities

Seminal characteristics such as good corrosion resistance, self-lubrication ability and acceptable wear resistance have made polymer based materials to become popular in a wide and diverse range of tribological applications. Despite numerous applications and decades of research in polymer tribology, a considerable number of questions remain unsolved both regarding fundamental understanding and engineering design issues. One of the reasons is the vast number of different polymers and polymer based composites that are in use, but also the diversity in applications and the difficulties to observe the governing tribomechanisms. Material and component producers are often the only owners of composition and basic material characteristics. Thus, designers and application engineers are obviously forced to rely on catalogue information and scattered literature data. For that reason prior to application of a chosen material/component functional and tribological tests with scale models or laboratory set-ups are performed to obtain better confidence in the proposed design solutions. Each time again the definition of an adequate test program is of major concern. The present paper discusses some challenges related to the use and testing of polymer based tribocomponents such as bearings, sliders, gears, rollers, etc. Attention is not only given to basic influencing parameters such as contact load, sliding/rolling velocity, environmental conditions, mating surface conditions, etc. Also experimental strategies and advanced measuring techniques that allow to follow the dynamic nature of transfer film formation and wear are considered. Finally, actual trends in reinforcements (e.g. natural fibres) and lubricant additives (nanoparticles) are discussed together with opportunities for improved tribobehaviour

Wear in wind turbine pitch bearings—A comparative design study

We tested two types of ball bearings with an outer diameter of 750 mm to learn more about the challenges of oscillating motions for pitch bearings. The experimental conditions are derived from aero-elastic simulations, long-term wind speed measurements and a scaling method that considers loads and pitch angles. As a result, the parameters relevant for pitch bearings are represented appropriately, and the findings are transferable to other bearing sizes. For the tested parameter sets, severe wear occurred for over 90% of the exposed contact areas after 12 500 oscillating cycles. Decreasing the number of cycles to 1250 leads to a mix of exposed areas with 13% severe wear, 32% mild wear and 55% no wear, with no apparent pattern. The results demonstrate that a comparatively small amount of consecutive cycles can lead to severe wear. A new type of bearing tested showed less wear for the selected operating conditions. © 2021 The Authors. Wind Energy published by John Wiley & Sons Ltd

Acceleration of diffusion in ethylammonium nitrate ionic liquid confined between parallel glass plates

The bulk self diffusion of the ethylammonium cation and the nitrate anion can both be described by respective single diffusion coefficients. Diffusion of the anion is 1.7 times higher than that of the cation. This indicates no tight association of the ions in the ionic liquid. For the ethylammonium cation confined between glass plates the effective diffusion coefficient along, as well as normal to the confining glass plates is higher by a factor of 1.86 as compared to that in the bulk. The same time, NMR T2 relaxation of protons of NH3 group of the EA cation is faster by a factor of 22 than that in bulk. 2H NMR spectra of selectively labeled CH2 and CH3 groups of EA do not demonstrate any ordering of the EA between the glass plates. We suggested that these data favor a model where a bulk isotropic sponge like structure of EAN is saved in the confinement, but sizes of connecting channels increases. Those leads to faster translational diffusion and faster exchange processes of protons of NH3 group, in comparison with the bulk.Comment: 11 pages, 5 figures, 1 tabl