Physico-Chemical Modeling of Third Body Rheology

The well-known concept of third body was introduced by Godet in the seventies to characterise the discontinuous and heterogeneous interface that separates two bodies in contact. This thin layer (from some nanometers to some micrometers high) appears to possess its own rheology depending of contact conditions, material properties and often, extra unknown parameters. If its main common role concerns essentially mechanical aspects such as velocity accommodation, load carrying capacity and solid lubricant, it plays an important role in other physical aspects. For example, it ensures the thermal continuity between two bodies in contact and explains the jump of temperature observed experimentally. Moreover, it is able to capture the maximal temperature through its thickness. Due to the difficulty to instrument a real contact without disturbing the local rheology, observations of the third body rheology occur only on simplified experimental set-up. To reproduce and try to understand “real contact in presence of third body”, numerical tools have been developed and adapt to face new challenge raised by the third-body concept. The discontinuity and heterogeneity of such interface led researchers to use discrete element methods (DEM) to describe its evolution. Several improvments of the method allow to deal with the mechanical and the thermal behaviour of such media but without interactions. The integration of physicochemical aspects is presented in the paper to link thermal and mechanical behaviour and proposed a model able to represent the multi-physical feature of a contact interface.