| Apart from the effects vibration has on strength, creep and wear, the influence of vibration on the process of friction is quite important. Vibration superimposed upon static forces has been used to reduce and control friction [1]. It is also important to consider, in the design process, how vibration might affect friction.;Many experiments have been conducted on the effects of vibration on friction. It has been observed that external vibration applied normally [3--8] or tangentially to a friction interface [2:9--11] decreases the static (break-away) and mean friction forces, and reduces stick-slip motion. In addition, one investigation found that the mean friction force increased as a result of external vibration [11].;Experiments performed in this study applied vibration simultaneously in the normal and tangential directions. Results show a decrease in the static (breakaway) friction and, depending on the vibration parameters, either a decrease or increase in the average kinetic friction force. A decrease in stick-slip motion was also observed.;It is believed that the main contributory factor in the reduction of friction is a reduction of the real area of contact [6:8:12--18]. However, there has been little experimental confirmation. Resistance experiments were used to estimate the real area of contact and to determine a relationship between a change in friction and the change in real area of contact. It was found that when friction decreased, the real area of contact also decreased and vice versa.;A Hertzian contact model was used to investigate the effects of vibration on an asperity contact. The model shows that a decrease in the kinetic friction is almost solely due to the normal component of vibration which increases the separation between the contacting bodies and thereby decreases the real area of contact. Whereas the tangential components does more to reduce the maximum pulling force and stick-slip motion. The model also showed that an increase in friction is most likely a result of increased damping. |
