Lubrication modes mixed

From an engineering standpoint, SF can be regarded as an aqueous electrolyte solution containing proteins, lipids and hyalnronic acid [12]. SF is also important for implants since a few weeks into the healing process, it surrounds the artificial joint. The predominant lubrication mode is in the mixed and boundary regimes [13]. In this study, we focus on the role of the most abundant protein in SF—human serum albumin (HSA). A screening study involving proteins and lipids was used... 

It has been demonstrated elsewhere [10,13] that the mode of lubrication (boundary mixed fluid-film) plays a major role in determining the steady-state wear rate in metal-on-metal total replacement hip joints. 

This dimensionless term is known as the hydrodynamic factor , where Fig. 8.2 represents the Stribeck curve in the log scale and shows that a compromise must be made with respect to lubricant viscosity, between the friction losses in the region of hydrodynamic (HD) lubrication, and bearing wear when passing through the regime of mixed friction. Both hydrodynamic and hydrostatic bearings operate with infinite service life below some critical value of load and above a critical value of speed assuming other modes of wear such as corrosion and erosion are not experienced. 

A cam-flat follower geometry allows the transducer to be positioned at any wanted location (see section 3), thus permitting many measurements. The mode of lubrication is medium till full elastohydrodynamic, or mixed film. 

Thouless, M.D., Mixed-mode fracture of a lubricated interface. Acta Metall. Mater, 40, 1281-1286(1992). 

The direct measuremoit of the sq>aration between two bearing surfeces of metal-on-metal hip implants tested in a hip simulator under normal walking conditions was carried out by Dowson et al (2000) using the above electrical resistance technique. The mode of lubrication in flieir experimental study was mixed, with some periods of very effective surface separatioi and others of metal-on-metal contact in each simulated walking cycle. Using the same technique, Smith et al (2001a) have demonstrated surface separation of the femoral head and acetabular cup by a lubricating film in ceramic-on-ceramic hip implants. However, it was not clear whether protein films enhanced the sur ce separation in both of these studies. 

The modes of lubrication in metal-on-metal hip implants range frtnn boundary, mixed to fluid-film... 

Much has been done [3,4,5,6] to reveal the mode of lubrication in such Joints through the measurement of friction in Joint simulators of increasing sophistication. Each simulator was capable of measuring the friction to high accuracy. The recorded values of friction were generally similar to those associated with mixed or boundary lubrication. When plotted in the form of a Stribeck curve, the friction factors revealed variations consistent with the expected characteristics for mixed lubrication, with suggestions of either boundary or fluid-film lubrication when relatively low or high viscosity lubricants were used respectively. 

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