Rheology and flows of solid third bodies: background and application to an MoS1.6 coating

After a short background history on solid third bodies, this paper proposes a tribological approach for understanding how a contact takes place when first bodies are in relative movement and are separated by a solid third body. This approach, based on rheology and third body flows, enables friction and wear in contacts “lubricated” by a solid third body to be identified and progressively modelled. Flows and rheology are the two notions used for analysing and structuring dynamic phenomena created by contacts and their interaction with the environment, in the physico-chemical and mechanical sense, i.e. with the ambient atmosphere and the mechanism concerned with the contact, respectively. Due to in-situ instrumentation difficulties, flows are evaluated in relation to those visualised in real time through one transparent first body. Rheology is also evaluated relatively, but by distinguishing the cohesion and ductility of the elements making up the third body that moves in the contact, over a given observation scale. As an illustration, this presentation relies on the behaviour of a contact containing a third body formed in-situ from a coating of MoS1.6.