Current Issue : January - March Volume : 2018 Issue Number : 1 Articles : 5 Articles
Laser surface texturing has been successfully applied in the past to various machine\nelements in order to improve their tribological performance. In this study, direct laser interference\npatterning was used to produce periodic cross-like surface patterns on commercial cylinder roller\nbearings. The wear behavior of as-patterned bearings was studied by a modified FE8 test rig under\nboundary lubrication. A mineral oil (ISO VG 100) as a base oil additivated with 0.02 wt % zinc\ndialkyldithiophosphate (ZDDP) was used for the tribological tests which were performed under\na Hertzian pressure of 1.92 GPa and maintained at 80 ââ??¦C and 20 rpm for 2 h. The laser-patterned\nbearings showed a significantly reduced mass loss by two orders of magnitude compared to the\nunpatterned reference bearings. A closer look at the samples proved the formation of the characteristic\nblue-colored ZDDP tribofilm on top of the laser-induced topography maximum positions. Due to the\nhigher contact pressure at the laser-induced peaks, the tribofilm formation was preferable at those\npositions thus protecting against wear. The laser patterns nearly remained unworn compared to the\nreference samples. A subsequent Raman analysis of the laser-patterned bearings clearly revealed the\nformation of zinc and iron sulfides as well as phosphates at the peak points....
Theacquisition and evaluation of acoustic emissions (AE) in tribology have proven to be ameaningful tool for conditionmonitoring\nand offer possibilities to deepen the understanding of tribological processes. The authors used this technology with the aim of\nexpanding existing test methodologies towards increased visualization capability of tribological processes and investigated the\ncorrelation between tribological processes and acoustic emissions on a Ring-on-Disc and a close-to-component journal bearing\ntest setting.The results of this study include the description of friction as well as wear processes and prove the usability of several\nAE evaluation parameters whereby a close correlation between AE and tribological processes can be shown. Consequently, it was\npossible to expand the visualization and evaluation capabilities of the test settings offering additional insights by making use of AE....
Recording of Stribeck-like curves is a common way to study the effect of laser-patterned\nsurfaces on the frictional efficiency. However, solely relying on the coefficient of friction when\nidentifying the lubrication regime and the underlying working principles can be misleading.\nConsequently, a ball-on-disc tribometer was combined with an electrical resistivity circuit to\nsimultaneously measure Stribeck-like curves and solid-solid contact ratios for polished and\nlaser-patterned samples. Line-like surface patterns with different periodicities were produced by\ndirect laser interference patterning on steel substrates (AISI304). The reference shows a Stribeck-like\nbehavior well correlating with the contact ratios. The behavior deviates for high sliding velocities\n(high contact ratios) due to a loss of lubricant induced by centrifugal forces pulling the lubricant out\nof the contact zone. In contrast, the solidââ?¬â??solid contact ratio of the laser-patterned samples is around\n80% for all sliding velocities. Those values can be explained by higher contact pressures and the\nstructural depth induced by the surface topography which make a full separation of the surfaces\nunlikely. Despite those high values for the contact ratio, laser-patterning significantly reduces friction,\nwhich can be traced back to a reduced real contact area and the ability to store oil in the contact zone....
To investigate the influence of surface features, in the form of pits, on the wear resistance of grey cast iron (GCI), a finite\nelement model of the pin-on-disc friction system, with pits distributed in a curved radial direction, was developed using APDL\nprogramming and the tribological behavior of textured surfaces was studied.The influence of relative rotation direction between\nthe disc and the pin on the thermal behavior of the friction system under dry wear conditions was researched. GCI and C30E steel\nsamples with pit textured surfaces were manufactured using laser marking equipment and tested using a tribology wear testing\nrig. The mass losses were measured and the worn surfaces were characterized. The influence of different rotation directions on\nthe tribological behavior of the pit textured surfaces was also investigated. The simulation and test results revealed that rotation\ndirection was a crucial parameter in determining the tribological behavior of surfaces with these features, regardless of thematerial.\nUnder the conditions tested, when the pin rotated anticlockwise, the samples showed better friction and wear behavior than when\nthe pin rotated clockwise. These results can provide important guidance for the optimization of the design of heavy-load brake\nsystems and other similar applications....
Ultralow friction is achieved by ZrO2 as the friction mate material for DLC (Diamond like\ncarbon) films under various environments. Coefficient of friction (CoF) of ZrO2/DLC films is as\nultra low as 0.02 in ambient air at the temperature of 200 ââ??¦C, and 0.03, 0.04 and 0.05 in hydrogen,\nnitrogen and vacuum environments at the temperature of 100 ââ??¦C, respectively. It is concluded that\nthe transferred films are formed on the worn surface of ZrO2 ball and amorphous carbon films.\nUltralow friction of the friction pair is related with hydrogen, which is derived from DLC films,\nhydrogen environment or the liberation hydrogen due to hydrothermal oxidation. The ultralow\nfriction mechanism is attributed to the formation of hydrogenated amorphous carbon films on ZrO2\nball and the shielding action of hydrogen from DLC films and the transferred films simultaneously....
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