Evaluation of frictional characteristics for a pin-on-disk apparatus with different dynamic parameters

Frictional characteristics in response to changes of the dynamic parameters of a pin-on-disk apparatus were experimentally and theoretically investigated for dry sliding. The apparatus has been designed and built to allow control of sliding speed, load, stiffness and loading mechanism. Dynamic friction and normal force were measured for various conditions of the system parameters, e.g. different stiffness in the normal direction, loading mechanisms and test materials. For a normal load, mechanisms using a dead weight, a compression-type spring and a pneumatic cylinder were selectively applied. Stiffness in the loading direction was also varied using a spring with different stiffness. Steel, rosin and polytetrafluoroethylene were tested because they have different types of frictional behavior. Test results showed that frictional characteristics at various loading mechanisms were different even though the operating parameters were the same. They are also strongly dependent on both the sliding velocity and the run-out of the disk surface. Effects of the surface run-out on the friction behavior were further evaluated using a tapered steel disk. When the surface run-out was high, the coefficient of friction was computed differently with the data processing. A theoretical analysis for a simple model of a pin-on-disk apparatus showed that surface irregularities, such as surface roughness, waviness and run-out, result in dynamic normal forces which depend on both the dynamic parameters of the system and the sliding velocity. (C) 1997 Elsevier Science S.A.