Stribeck diagram

In practical applications we often encounter a combination of boundary and hydrodynamic lubrication which is called mixed lubrication. For example, bearings that are usually lubricated hydrodynamically, experience mixed lubrication when starting and stopping. This is shown in the Stribeck diagram (Fig. 11.12) At low speeds, boundary lubrication with high friction... 

Figure 11.12 Stribeck diagram Plot of friction coefficient /u versus ijkv/P,where rjk is the kinematic viscosity, v the velocity, and P the contact pressure. From left to right there are three different friction regimes Boundary lubrication with high friction and wear, mixed lubrication with medium friction and wear, and hydrodynamic lubrication with low friction and wear.

The Stribeck diagram (Figure 10.9) presents the friction coefficient of a lubricated contact as a function of a parameter S, which has units of length. 

Since the main difference between A and SP is the inclusion of the roughness in the first one, similar curves to those of the Stribeck diagrams can be obtained with lambda on the horizontal axis, Fig.2. The values of A shown in this figure are only suggested values for the change of lubrication regimes, but they can be rather different, as discussed later in the paper. 

Although not present in the usual Stribeck diagrams, a reduction of f, probably related to thermal effects, can also occur by increasing the speed after reaching the fiiU fluid regime for nonconformal contacts. However, shape, dimensions and temperatime can alter the trends of the friction curves, as shown in Fig. 18, and in particular the hmiting A values for which the transitions between the different regimes of lubrication occur. 

Figure 9.13 Stribeck diagram for a lubricated friction contact. Coefficient of friction [X versus r V(il pP is plotted, where p is the density of the lubricant, vo the velocity, and P the contact pressure. From left to right, there are three...

The process of transition from hydrodynamic to boundary lubrication can be described qualitatively by plotting the measured friction coefficients against film thickness, which depends on the operational conditions, such as load, sliding velocity and lubricant viscosity. A typical diagram known as the "Stribeck Curve is schematically shown in Fig. 27, in which the friction coefficients are given as a function of, ... 

The evolutions of the friction coefficient, in particular for nonconformal contacts, can be very different from those of the typical Stribeck or A diagrams. Many variables such as shape and dimension of a lubricated contact, roughness, materials, lubricant characteristics and thermal effects influence the friction trends. 

Figures 6.12 and 6.13 show the effect of the Stribeck friction fi and the linear negative friction (/Tj) parameters on the amplitude bifurcation diagram, respectively. In these figures, bifurcation plots are drawn with respect to the applied axial force, R, as the control parameter. As shown, 2 controls the domain of attraction of the stable trivial solution without significant change to the limiting value of R. The...

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