SELF-EXCITED OSCILLATIONS IN SLIDING WITH A CONSTANT FRICTION COEFFICIENT - A SIMPLE-MODEL

The sliding of two surfaces with respect to each other involves many i nteracting phenomena. In this paper a simple model is presented for th e dynamic interaction of two sliding surfaces. This model consists of a beam on elastic foundation acted upon by a series of moving linear s prings, where the springs represent the asperities on one of the surfa ces. The coefficient of friction is constant. Although a nominally ste ady-state solution exists, an analysis of rite dynamic problem indicat es that the steady solution is dynamically unstable for any finite spe ed. Eigenvalues with positive real parts give rise to self-excited mot ion which continues to increase with time. These self-excited oscillat ions can lend either to partial loss-of-contact or to stick-slip. The mechanism responsible for the instability is a result of the intel-act ion of certain complex modes of vibration (which result from the movin g springs) with the friction force of the moving springs. It is expect ed that these vibrations play a role in the behavior of sliding member s with dry friction.