Coefficient of friction curve

The bearing health can be best described by plotting a ZNjP versus coefficient of friction curve. Figure 13-10 shows such a curve where Z is the lubricant viscosity in centipoise, N the rpm of the journal, and P is the projected area unit loading. 

The minimum coefficient of friction for pure MoS2 is significantly lower than that for MoS2 xOx, and the peak in the coefficient of friction curve occurs for relatively low concentrations of oxygen in the film. The friction rises rapidly for... 

FIGURE 4.17 Coefficient of friction curves during conditioning at different temperatures (from Ref. 11). 

For load values from Pmin up to Pmax with stepwise velocity increase, a limiting value for sliding velocity (Vmeix) is found at which the material suffers frictional failure. In the course of testing the coefficient of friction (curve l) and temperature in the subsurface layer of the polymeric specimen (curve 2) are recorded. 

FIGURE 5.201 Typical ZN/P versus coefficient of friction curve. 

See Fig. P-21 for a definition of lead angle.) With this rubbing speed noted at the bottom of the diagram, read vertically upward until you intersect the coefficient-of-friction curve. Read the value of the coefficient of friction from the left-hand side of the diagram. 

FIGURE 26.21 Coefficient of friction (A) and the temperature rise (B) in the contact area between a natural rubber (NR) gum compound and a thermocouple slider as function of speed at different loads. Also shown are the data when plotted against log a v (C), indicating a rising portion of a single master curve which absorbs also the apparent load effect. 

FIGURE 5-1. Strelbeck Curve Comparing the Relationship Between the Coefficient of Friction and an Operating System s Viscosity, Speed, and Load... 

ZN/P curve—general graphic representation of the equation p = (f) ZN/P, where p (die coefficient of friction in a journal bearing) is a function (f) of the dimensionless parameter ZN/P, (viscosity x speed)/pressure. This is the fundamental lubrication equation, in which the coefficient of friction is... 

Temperature plays a significant role for the coefficient of friction p as demonstrated in Fig. 2.66 for polyamide 66 and polyethylene. In the case of polyethylene, the friction first decreases with temperature. At 100°C, the friction increases because the polymer surface becomes tacky. The friction coefficient starts to drop as the melt temperature is approached. A similar behavior can be seen in the polyamide curve. 

Fig. 5.1. Stribeck-Hersey curve coefficient of friction (f or p) as function of viscosity (Z) velocity (V) / load parameter (L) h = thickness of lubricant film (Fusaro, 1995)...

Fig. 5. 2. Schematic dependence of friction coefficient for MoS2 films as a function of oxygen concentration in the film. Coefficients of friction (pi) for pure MoS2 are significantly lower than for MoS2.xOx. The peak in the pi curve occurs at some relatively low concentration of oxygen in the films. Additional substitution of oxygen in the MoS2 has the combined effect of atomically smoothing the surface and reducing the coefficient of friction pi (Fleischauer and Lince, 1999)...

Lubrication mechanism How do you expect each of the following regimes to change in going from thickness of lubricating film h to a coefficient of friction, p in the Stribeck-Hersey curve Fig.5.1 There are three defined regimes of liquid lubrication (a) hydrodynamic, h 25 pm, (b) elastohydrodynamic, h = 0.025 to... 

Fig. 9 Changes in the crack initiation times and crack depths in an epoxy resin as a function of the amplitude of the imposed cyclic displacement, a Number of cycles to the initiation of the primary cracks at the edge of the contact zone, b Measured depths of the primary cracks at various number of cycles and displacement amplitudes. Circles 103 cycles, solid diamonds 5 x 103 cycles, squares 5 x 104 cycles, c Calculated values of the maximum tensile stress at the edge of the contact using Hamilton (gross slip condition) or Mindlin—Cattaneo (partial slip condition) theories. The two curves correspond to calculations using the initial (/x = 1.0) and the steady-state (/x = 1.5) values of the coefficient of friction. PSR Partial slip regime, MR mixed regime, GSR gross slip regime...

In principle, the endpoint methodology considers that as a particular layer clears, the material on the next layer exhibits a different coefficient of friction (change in the current due to a difference of frictional loading). However another factor affecting the curve traces was found to be the carrier arm movement motion across the primary platen and the conditioning head (both... 

The detergent in a transmission or farm tractor hydraulic fluid formulation is a key component for setting the frictional properties of the fluid, including the dynamic coefficient of friction, the static coefficient of friction and the slope of a friction versus sliding speed curve with a particular set of friction elements. Even more importantly, a detergent retains these properhes for extended periods of time [27-29]. 

Thus, in Fig. 9-6, which is based on the data by Sakurai et a . [18], the convergence of the curves for the lubricants consisting of solutions of dibenzyl disulfide and diphenyl disulfide in cetane, as well as the downward trend in the curve for dissolved sulfur, might be attributed to fluid film effects. The coefficients of friction observed at the lower speeds (5-10 cm/s), however, indicate a specific additive effect rather than a fluid film contribution. 

In physical terms, the behavior of a strong junction is governed by the dominant influence of the tensile phase of junction rupture. A weak junction is one in which translational motion of one asperity relative to the other can occur by sliding while the junction is still under compressive stress. In analytical terms, remains at a lower level and the peak of the curve for p. is broader than is found for a strongly adhesive junction. For either a strong or a weak junction, substitution of the results of the stress/strain analysis into Eqns 12-56a and 12-56b gives a steady-state, non-fluctuating value for the coefficient of friction. 

Figure 2. Dependence of friction zone temperature (T) (curve 2) and the coefficient of friction (f) (curve l) upon PV.

The thusly determined type-1 and -2 coefficient-of-firiction curves are undescriptive, because they were derived from a function (equation 1) with a premise - namely that the coefficient of friction is not a function of pressure - that the given system does not satisly. Consequently, the more reliable material parameter in this case is not the coefficient of friction but the shear stress. 

Abrasive wear consists of the rupture of small particles of elastomer under the action of frictional forces, when sliding takes place between the elastomer surface and a substrate. A suitable measure of the rate of wear is provided by the ratio A/p, where A is the volume of rubber abraded away per unit normal load and per unit sliding distance, and ju is the coefficient of friction. This ratio, termed abradability, represents the abraded volume per unit of energy dissipated in sliding. Master curves for the dependence of abradability on the speed of sliding, reduced to a convenient reference temperature by means of the... 

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