Tribological measurements

Earlier tribological measurements (12) make an evaluation possible of the structural influence on the lubrication. At first the stability of the structure versus temperature is important for the lubricant function and the pertinent problem in this case is thermal stability with added glycerol (12). Table I shows the interesting fact that the temperature for the transition to liquid form is increased by the addition of glycerol. 

In this study, fluorescent labeling of albumin was used to investigate the adsorption of this protein onto the surfaces of artificial implant materials before and during tribological measurements. The la-... 

Tribological measurements, consisting of subambient pressure frictional hysteresis loop measurements, were carried out inside a sealed disk tester with a controlled leak (CETR Olympus, Center for Tribology, Campbell, CA). The disk rotation rate was 7200 rpm, and the slider suspension was mounted on a strain-gauge block to measure the friction force. Scratch measurements on the surface of the tested track were done with an optical surface analyzer. 

For the tribological measurements, the radial position of the slider during the tests was halfway between the inner and outer diameters of the disk, and the pivot-to-center distance was adjusted so that the slider skew angle was close to 0°. The disk rotation was started with the slider suspension on the load/unload ramp just off the edge of the disk. The slider was accessed to the test radius. The pressure control and measurement of the frictional displacement were performed with The National Instruments LabView software on a PC with interface cards. Average displacement and peak amplitude were recorded after each pressure decrement/incre-ment (4000 samples at 20 kHz for 200 ms). The pressure inside the tester was varied linearly from ambient (100 kPa) to 15 kPa and back up to ambient over about 3 min in approximately 1-kPa increments. At the end of the test, the slider was translated back to the load/unload ramp before stopping the disk rotation. 

Tribological Experiments. For tribological measurements, the lateral force lying in the plan of contact between the tip and the surface produces the additional vertical deflection (Figure 2b) or cantilever torsion. Lateral forces arise not only from friction but also from the local surface slope (31, 51). If the sample surface is not flat, the surface normal force will have a component directed laterally and will result in contrast in lateral image. These complications can be avoided by using flat samples whenever possible. 

Molecular dynamics (MD) metliods can be used to simulate tribological phenomena at a molecular level. These have been used primarily to simulate behaviour observed in AFM and SFA measurements. Such simulations are limited to short-timescale events, but provide a weaitli of infonnation and insight into tribological phenomena at a level of detail tliat cannot be realized by any experimental metliod. One of tire most interesting contributions of molecular dynamics... 

FIG. 20-75 Fluid-bed erosion or wear rate as a function of granule material properties. Kq is fracture toughness and H is hardness as measured hy three-point bend tests. [Ennis [Pg.1888]

New experimental techniqnes for the direct measurement of interparticle forces are now available and can be nsed to nnderstand the physicochemical factors that control adhesion, coating phenomena, tribology, and others. 

In Section 2.4, we describe the principle of the Frustrated Total Reflection (FTR) Technique, which was hrst applied by Professor Wen s group at State Key Laboratory of Tribology, Tsinghua University, for measuring him thickness in mixed lubrication [6,7]. 

No general conclusions on the relations among these parameters can be drawn for the scarcity of better information. Experiments should be designed to measure the tribological properties of TFL for engineering applications. 

In the previous section, numerical simulations predicted the change of contact ratio as a function of film thickness. Professor J. B. Luo in the State Key Laboratory of Tribology (SKLT) [68] has conducted an experimental study for measuring the relationships between the contact ratio and influential factors, which are presented in the following. 

The research work on carbon nitride materials was first motivated due to its hypothetical super-hardness. The tribological properties of the CNx films are, of course, the emphasis of the succeeding research works. Although the expected structure and hardness have not been achieved up to the present, the potential interesting properties still stimulate many approaches on the tribological behavior of CNx films. Figure 8 gives the results of hardness measurement reported by the... 

The data of Zink et al. (1998) illustrate the measurement by NRA of near-surface composition profiles in isotopically labelled polymer blends. If a mixture of polymers is adjacent to a phase interface (e.g. a solid or an air surface), often one of the components is preferentially attracted to the surface and will segregate to it, and this phenomenon will influence the tribological behaviour the interface (lubrication, wear and adhesion). 

Tribological behavior has its origin at the molecular level. Current theories suggest that adhesive forces have an important effect on die magnitude of frictional forces measured between two surfaces. At the molecular level, the two... 

Diamond Hints, although not approaching bulk diamond, are harder than most refractory nitride and carbide thin films, which makes them attractive for tribological coatings. Transparency in the visible and infrared regions of the optical spectrum can be maintained and index-of-refraction values approaching that of bulk diamond have been measured. Electrical resistivities of diamond films have been produced within the full range of bulk diamond, and thermal conductivities equivalent to those of bulk diamond also have been achieved. As substrates for semiconductor electronic devices, diamond films can be produced by both the PACVD and IBRD techniques. 

Another interesting and important use of radiotracers in industry is in wear and corrosion studies. In studies of wear (tribology) one labels the part under study with a radionuclide. The radioactivity is concentrated on the surface undergoing wear by plating, diffusion, or ion implantation with a low-energy accelerator. The labeled part is put in service and, typically, one measures the radioactivity released in the lubricant as a measure of wear. Calibrations of the technique can be done to get absolute measures of wear. 

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