Friction coefficient, torque

The friction coefficient (p) was evaluated from the friction torque measurement using... 

The friction torque Tf of the lip at the sealing zone is measured by the load cell connected to the housing. The friction coefficient f of the seal lip at the sealing zone can be expressed as equation (1) employing the radial load Pj- and the shaft diameter d. 

The coefficient of friction data in Table 3-7 were obtained with the thrust washer test apparatus. The test specimen is run in against the standard wear ring until 360-deg contact between the raised portion of the thrust washer and wear ring is made. Temperature of the test specimen is then allowed to stabilize at the test conditions (generally 40 psi, 50 ft/min, room temperature, and dry). After thermal equilibrium, the dynamic frictional torque generated is determined with... 

A further reason for the reduction in frictional torque may be a decreasing coefficient of friction in the conical surface due to altered tribological conditions. This impairing effect is referred to as decrease in the coefficient of fnction. 

Friction torque was measured with a piezo transducer installed Just under the cupholder. The axial load was measured by a lo transducer mounted under the gimbal support Hie friction coefficient was... 

Fig. 7 shows the torque necessary to obtain the specified body force under construction conditions and in tbe state when removed from the bridge. It can well be seen that the change of the friction coefficient causes a very big scattering, and the necessary torque is much bigger than specified. The distribution of the results of a measurement performed on 1,127 bolts is presented in Figure 8. An average of 80% of nominal body force was found by the new method. The traditional method found the nuts could be swivelled much further than specified on 42 bolts, these bolts were found to have 40 - 60 % body force by the new method. 

The traditional method for investigating the forces originating in the body of the bolt, which is based on measuring the torque of the nut, can detect only the bolts with a very great lack of body force since tbe friction coefficient worsens with time. 

In regard to screw threads, certain observations should be considered. First, the torque values are based on the coefficients of friction of the mating parts and can thus vary significantly. The use of any compatible lubricant that reduces friction will increase the shear and hoop stresses if the torque remains the same. Therefore, with lubricants, reduce the amount of allowable torque. 

Here m(r) is a random torque equal to zero on average while rotational friction is proportional to rotation rate J// with a coefficient When averaged, Eq. (1.26) turns into Eq. (1.20). Hence... 

FIGURE 26.28 Side force coefficient and self-aligning torque of a radial ply tire 175 R 14 on two wet road surfaces of different friction coefficient, at three slip angles and loads as function of the quantity c (Equation 26.17c) aU on log scales. The sohd hnes correspond to the brush model. (From Schallamach, A. and Grosch, K.A., Mechanics of Pneumatic Tires, S.K. Clark (ed.). The US Department of Transportation, National Highway Safety Administration, Washington DV.)... 

Here, M is the torque of the rolling object, hr is the coefficient of rolling friction, FL is the normal force (load), Ff is the friction force and R is the radius of the rolling object (see Fig. 11.4). In this case the friction coefficient is not dimensionless but has the unit of length. Other definitions use... 

Next we proceed with the force and torque balances. Since pressure builds up in the down-channel direction, the force and torque balances are made on a differential increment in the down-channel direction this is illustrated in Fig. 9.29, where the various forces acting on the element are also depicted. These forces can be expressed in terms of the coefficients of friction, local geometry, and the differential pressure increment, which compensate for the other forces and torques. For an isotropic stress distribution, these are... 

In many situations the actual value of the coefficient of friction is not a critical design factor. Torque-limited designs can occur in spacecraft and to a lesser extent in aircraft, but more often the requirement is that friction should be reasonably predictable and consistent, without seizure or stick-slip. The friction of a solid lubricant is generally smooth, but its value varies with load, speed, temperature and environment. 

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