Modeling friction phenomena in flexible multibody dynamics

The dynamic response of flexible systems of arbitrary topology and complexity are now readily modeled using multibody dynamics analysis concepts. In most formulations, the joints connecting the flexible bodies of the system are not modeled per se: only the effect of joints is modeled through a set of kinematic constraints. This paper focuses on the development of methodologies for the analysis of unilateral contact conditions in joints and of the resulting normal and friction forces. This involves a host of phenomena such as: contact kinematics, contact conditions, and the modeling of the normal and tangential contact forces. Furthermore, the high level of nonlinearity associated with a number of these phenomena implies challenging numerical issues. Although friction forces can be readily evaluated using Coulomb friction law, the resulting accuracy is questionable: sticking and slipping can co-exist in different parts of the contact area, a phenomenon known as micro-slip. Numerous models of friction have been developed and presented in the literature; application of the LuGre model will be discussed in this paper.