BOUNDARY AND MIXED FRICTION IN THE PRESENCE OF DYNAMIC NORMAL LOADS .1. SYSTEM MODEL

The instantaneous normal motion between bodies in a sliding contact is an important variable in determining dynamic friction under unsteady sliding conditions. In order to model friction under dynamic condition s, it is therefore necessary to combine a dynamic model of the sliding system with an accurate model of the friction process. In the present work, the nonlinear normal dynamics of a friction test apparatus are described by a linearized model at a particular steady loading and sli ding condition in a mixed or boundary-lubricated regime. The geometry is a line contact. The Hertzian bulk contact compliance and film and a sperity damping and stiffness characteristics are included as discrete elements. In Part I of the paper, a fifth-order model is developed fo r the normal dynamics of the system, using both the Eigen-system Reali zation Algorithm (ERA) and classical experimental modal analysis techn iques. In Part II, this system model is combined with a friction model , developed independently, to describe dynamic friction forces under b oth harmonic and impulsive applied normal loads.