Variable slip technique

Variable slip technique is used to measure the friction coefficient between tire and pavement. The test equipment consists of an automotive vehicle. Each test wheel contains a variable brake system. The resulting resistive force caused by friction between the tire and the pavement surface is sampled and recalculated to slip friction numbers. Frictional properties of pavement surface as a function of speed are measured by a d5mamic friction tester. A disk spins with its plane parallel to the test surface. The rubber sliders come into contact with the pavement, and torque is monitored when rotational velocity reduces, due to friction. A graph of friction vs. speed is plotted. 

Operated on Fixed Braking Slip Continuous Friction Measuring Equipment. ASTME1859/E1859M-llel Standard Test Method for Friction Coefficient Measurements Between Tire and Pavement Using a Variable Slip Technique. 

The definition of friction factor using mean fluid properties has been most widely used because it reduces to the correct single-phase value for both pure liquid and pure gas flow. This technique is very similar to the so-called homogeneous model, because it has a clear physical significance only if the gas and liquid have equal velocities, i.e., without slip. Variations of this approach have also been used, particularly the plotting of a ratio of a two-phase friction factor to a single-phase factor against other variables. This approach is then very similar to the Lockhart-Martinelli method, since it can be seen that (G4)... 

Evanescent wave microscopy has already yielded a number of contributions to the fields of micro-and nanoscale fluid and mass transport, including investigation of the no-slip boundary condition, applications to electrokinetic flows, and verification of hindered Brownian motion. With more experimental data and improvements to TIRE techniques, the accuracy and resolution of these techniques are certain to improve. Areas of potential improvements include development of rmiform-sized and bright tracer particles, creation of high-NA imaging optics and high-sensitivity camera systems, and further development of variable index materials for better control of the penetration-depth characteristics. 

The experimental challenge generated a considerable progress in experimental tools for investigating flow boundary conditions using the most recent developments in optics and scanning probe techniques. A large variability still exists in the results of slip experiments, so it is important first to consider the different experimental methods used to measure a slip. Two broad classes of experimental approaches have been used so far, indirect and direct (local) methods. 

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