The Third Body Flows Approach
- Wear of Filled PTFE
International Tribology Conference - Nagasaki
2000 - October 29 / November 2
L. Mahé and Y. Berthier
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 . 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 , and thus cannot be easily tranposed to an industrial
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 .
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.
 TANAKA, K., UCHIYAMA, Y. and TOYOOKA,
S. The mechanism of wear of polytetrafluoroethylene.
Wear, 1973, vol. 23, p. 153-172
 MAKINSON, K.R. and TABOR, D.
The friction and transfer of polytetrafluoroethylene. Proc.
Roy. Soc. London, Ser. A, 1964, vol. 281, p. 49-61
 ARCHARD, J.F. and HIRST, W. The
wear of metals under unlubricated conditions. Proc. Roy. Soc.,
A, 1956, vol. 236, p. 397-410
 GODET, M. The third body
approach, a mechanical view of wear. Wear, 1984, vol. 100,
 BERTHIER, Y. Maurice Godet's third body.
Proceedings of the 22nd Leeds-Lyon Symposium on Tribology,
Lyon, September 5-8 1995. p. 21-30