Percorrer por autor "Seabra, J."
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- Film thickness and friction behaviour of thermally aged lubricating greasesPublication . Gonçalves, David; Graça, Beatriz; Campos, Armando José Vilaça; Seabra, J.Non-additized batches of lubricating greases were subjected to an artificial thermal aging procedure. The fresh and aged samples were then tribologically characterized through film thickness measurements and Stribeck curves, over a large range of entrainment speeds on a ball-on-disc test rig at different operating temperatures, ensuring fully flooded conditions. The results were analysed at the light of the physical and chemical changes regarding the fresh greases. The film thickness increased for all greases after the thermal aging. The film thickness plateau at low speeds also changed and for certain greases it disappeared under the same range of entrainment speeds. The friction behaviour also changed considerably given the changes to the lubrication regimes for the same speeds.
- On the friction behaviour of polymer greasesPublication . Gonçalves, David; Graça, Beatriz; Campos, Armando José Vilaça; Seabra, J.Non-additized batches of lubricating greases were tribologically characterized through traction coeffi-cient and Stribeck curves at different operating conditions on a ball-on-disc test rig, ensuring that the contact was fully flooded. The tests were performed at constant load, but different operating tempera-tures while varying the slide-to roll ratio (SRR) or the rolling entrainment speed. The results were correlated to the greases' formulation in terms of base oil viscosity, thickener and/or elastomer content. A relationship between the coefficient of friction (COF) of greases formulated with different thickener content was found and the thickener influence on the COF was addressed.