EQUIVALENT VISCOUS DAMPING MODELS OF COULOMB-FRICTION IN MULTI-DEGREE-OF-FREEDOM VIBRATION SYSTEMS

Friction is difficult to model in multi-degree-of-freedom mechanical s ystems. Experimental studies of damping in vibrating mechanical system s typically use modal damping factors to represent the damping. Energy lost by friction is included in these factors. This paper presents an analysis of the friction energy dissipated by each mode to derive sev eral models of equivalent friction modal damping. These friction dampi ng factors can be subtracted from the overall modal damping factors wh en doing computer simulations where the dynamic friction forces are ca lculated directly. In order to verify whether the equivalent friction damping models are reasonable, a two degree of freedom system is simul ated using three approaches: a piecewise continuous analytical method, numerical integration with a spring-damper friction model, and numeri cal integration with equivalent friction damping. Five cases with peri odic and non-periodic excitation are considered. The equivalent fricti on damping works very well for cases where sliding motions predominate ; for long periods of sticking, the overall motions are predicted well but the detailed motions are approximated. (C) 1995 Academic Press Li mited