Tribological Degradations in Conformal Contacts due to Impact-Friction

Because the wear laws do not account of evolving tribological conditions, they cannot predict the operating life of contacts between control rods and their guides in Pressurized Water Nuclear Reactors. This restriction is overcome by the study of the chain of tribological phenomena which control the third body flow and therefore the wear. The aim of this work is to predict this contact life. This problem cannot be studied 'in vivo', because of the radioactivity, implying the use of a simulator to attempt to reproduce the real contact geometry and conditions, to create specimens which serve as a reference. The lack of rheological data on the third body is overcome by a atlas relating morphology, cohesion and adherence of this third body. The atlas is established using calculations and tests on different rigs to study the parameters governing birth and life of the third body. The use of this atlas allows the reformation of the third body life, the contact behaviour, and the third body flow evaluation. One scenario of the contact behaviour is described and validated. It shows that the flow of wear particles depends on the third body reformation and its morphology is adapted to accommodate the velocity difference between guides and structures. The use of this atlas shows, through tests at different temperatures, that the variation of wear particle flow is due to the temperature influence on the operating conditions and not on the variations of the material properties. (author)