Current Issue : July - September Volume : 2013 Issue Number : 3 Articles : 6 Articles
Density functional theory- (DFT-) based ab initio calculations were used to investigate the surface-to-surface interaction and\r\nfrictional behavior of two hydrogenated C(100) dimer surfaces. A monolayer of hydrogen atoms was applied to the fully relaxed\r\nC(100)2x1 surface having rows of C=C dimers with a bond length of 1.39 Ã?° A. The obtained C(100)2x1-H surfaces (Cââ?¬â??H bond length\r\n1.15 Ã?° A) were placed in a large vacuum space and translated toward each other. A cohesive state at a surface separation of 4.32 Ã?°A that\r\nis stabilized by approximately 0.42 eV was observed. An increase in the charge separation in the surface dimer was calculated at\r\nthis separation having a 0.04 e transfer from the hydrogen atom to the carbon atom.TheMayer bond orders were calculated for the\r\nCââ?¬â??C and Cââ?¬â??H bonds and were found to be 0.962 and 0.947, respectively. ?? Cââ?¬â??H bonds did not change substantially from the fully\r\nseparated state. A significant decrease in the electron density difference between the hydrogen atoms on opposite surfaces was seen\r\nand assigned to the effects of Pauli repulsion. The surfaces were translated relative to each other in the (100) plane, and the friction\r\nforce was obtained as a function of slab spacing, which yielded a 0.157 coefficient of friction....
We fabricated supersmooth probes for use in pin-on-disk sliding tests by applying gas cluster ion beam irradiation to glass convex\r\nlenses. In the fabrication process, various changes were made to the irradiation conditions; these included one-step irradiation\r\nof Ar clusters or two-step irradiation of Ar and N2 clusters, with or without Ar cluster-assisted tough carbon deposition prior\r\nto N2 irradiation, and the application of various ion doses onto the surface. We successfully obtained probes with a centerline\r\naveraged surface roughness that ranged widely from 1.08 to 4.30 nm. Using these probes, we measured the friction forces exerted\r\non magnetic disks coated with a molecularly thin lubricant film. Perfluoropolyether lubricant films with different numbers of\r\nhydroxyl end groups were compared, and our results indicated that the friction force increases as the surface roughness of the pin\r\ndecreases and that increases as the number of hydroxyl end groups increases....
Little has been published on the behaviour of polymer gears operating under lubricated conditions. An experimental and analytical programme was undertaken to classify the regimes of EHL under which polymer spur gears operate. In doing so theoretical film thicknesses were calculated and then used to classify the regime according to Johnson''s Map. The effects of lubrication on the operating efficiencies of high-performance polymer gears were interpreted and from these results coefficients of friction were derived. In addition to this the effect of tooth geometry was investigated and the beneficial influence of high-pressure angle tooth geometry is demonstrated. At loads typically associated with polymer gears the operating regime is shown to be mixed film lubrication. When high-pressure angle gears were tested at high loads the operating regime became full film lubrication and relatively little tooth flank damage occurred....
A new test method based onmultipass scratch testing has been developed for evaluating the mechanical and tribological properties\r\nof thin, hard coatings. The proposed test method uses a pin-on-disc tribometer and during testing a Rockwell C diamond stylus is\r\nused as the ââ?¬Å?pinââ?¬Â and loaded against the rotating coated sample. The influence of normal load on the number of cycles to coating\r\ndamage is investigated and the resulting coating damage mechanisms are evaluated by posttest scanning electron microscopy. The\r\npresent study presents the test method by evaluating the performance of Ti0.86Si0.14N, Ti0.34Al0.66N, and (Al0.7Cr0.3)2O3 coatings\r\ndeposited by cathodic arc evaporation on cemented carbide inserts. The results show that the test method is quick, simple, and\r\nreproducible and can preferably be used to obtain relevant data concerning the fatigue, wear, chipping, and spalling characteristics\r\nof different coating-substrate composites. The test method can be used as a virtually nondestructive test and, for example, be used\r\nto evaluate the fatigue and wear resistance as well as the cohesive and adhesive interfacial strength of coated cemented carbide\r\ninserts prior to cutting tests....
Molecularly thin lubricant films are used for the lubrication of head disk interfaces in hard disk drives. The film thickness is reduced\r\nto 1-2nm to minimize the magnetic spacing, and optimal, precise design is required to obtain sufficient lubrication.However, until\r\nnow, there was no generally applicable method for investigating such thin films. Therefore, we developed a highly sensitive shear\r\nforce measuring method and have applied it to the viscoelastic measurement of lubricant films coated on magnetic disk surfaces.\r\nIn this paper, we review the method and summarize the useful findings we have demonstrated so far....
Some interactions between the dynamic and tribological behaviour of geared transmissions are examined, and a number of\r\nexperimental and simulation results are compared. A model is introduced which incorporates most of the possible interactions\r\nbetween gears, shafts and hydrodynamic journal bearings. It combines (i) a specific element for wide-faced gears that includes\r\nthe normal contact conditions between actual mating teeth, that is, with tooth shape deviations and mounting errors, (ii) shaft\r\nfinite elements, and (iii) the external forces generated by journal bearings determined by directly solving Reynolds� equation. The\r\nsimulation results are compared with the measurement obtained on a high-precision test rig with single-stage spur and helical\r\ngears supported by hydrodynamic journal bearings. The experimental and simulation results compare well thus validating the\r\nsimulation strategy both at the global and local scales....
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