The Third Body Flows Approach - Wear of Filled PTFE
International Tribology Conference - Nagasaki 2000 - October 29 / November 2
L. Mahé and Y. Berthier

Abstract

Since the discovery of polytetrafluoroethylene (PTFE), two types of investigation were carried out on its wear behaviour. The first deals with the wear interpretation based on the surfaces observation after sliding [1,2]. In spite of the quality of the microscopic or macroscopic static observations, it is not easy to extrapolate the dynamic view of wear phenomena. In the other hand, the second investigation is related to the establishment of wear laws [3]. The wear rate represented by the worn volume or lost weight, is connected to some specific mechanical parameters. Unfortunately, these laws are generally strongly linked to the test appartus [4], and thus cannot be easily tranposed to an industrial mechanism.

These investigations led to the development of a tribological process where the whole of the tribological triplet is taken into account. From this concept, it has been defined the following conceptual tools : the velocity accommodation mechanisms and the tribological circuit [5].

The tribological triplet consists on the mechanism (test machine), the first bodies (filled PTFE, glass) and the third body. The wear is caracterized in term of third body flows. The different flows of the tribological circuit are the source flow (detachment of particles), the internal flow (third body circulation in the contact), the recirculation flow and finally the wear flow (third body definitively lost from the contact).

In order to identify these flows, this work is based on in situ dynamic view (video) during visualization tests through a glass (first body) and on a static view after sliding (photonic and scanning electronic microscopes). The contact life scenario is reconstitued thanks to the conceptual tools on the basis of a fine analysis from these observations. This scenario shows the influence of the initial geometrical profile and as well as the initial physico-chemical surface state, on the trapping of the first detached particuls. It shows also the influence of the rheology of the third body on the flows nature. Afterwards concerning the link between this scenario and the wear and friction evolution a discussion is open.

[1] TANAKA, K., UCHIYAMA, Y. and TOYOOKA, S. The mechanism of wear of polytetrafluoroethylene. Wear, 1973, vol. 23, p. 153-172

[2] MAKINSON, K.R. and TABOR, D. The friction and transfer of polytetrafluoroethylene. Proc. Roy. Soc. London, Ser. A, 1964, vol. 281, p. 49-61

[3] ARCHARD, J.F. and HIRST, W. The wear of metals under unlubricated conditions. Proc. Roy. Soc., A, 1956, vol. 236, p. 397-410

[4] GODET, M. The third body approach, a mechanical view of wear. Wear, 1984, vol. 100, p. 437-452

[5] BERTHIER, Y. Maurice Godet's third body. Proceedings of the 22nd Leeds-Lyon Symposium on Tribology, Lyon, September 5-8 1995. p. 21-30