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Wear mechanisms of polymeric surfaces

Our built-in microscratch apparatus, equipped with a specific optical system has been modified and tested during multiple repeated scratches along the same scratch path. By comparison with single scratch events at constant or progressive load test procedure, multiscratch tests provide much more comprehensive information about the build-up of irreversible phenomenon (yielding rate, plastic pile formation, formation of wear particles) and then damage (cracks). Such original surface procedure is more relevant of the wear behaviour of the tested polymeric surfaces, and then is more representative of the true solicitations in service for many applications.

First results have been obtained on PMMA surfaces and then extent to other transparent polymers and coated surfaces. A systematic study has to be carried out to show the influence of the contact pressure, the temperature or the sliding velocity or the nature and the roughness of the moving spherical tip, in order to plot wear or surface fatigue maps, describing as the evolution of the critical average contact pressure, related to a irreversible damage event, as a function of the cycle number.

With the modification of our tested microscratch system, such experiments may now conduct on non transparent and first results obtained on coated systems (thin titanium layer deposited on a PEHD polymeric substrate) are very interesting, proving that such study will be part of a larger effort to gain insight into the fundamentals of wear behaviours of polymeric surfaces and by extension of functionnalized surfaces, especially during first cycles at the initiation of the wear process.