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Global application of bulk wear models,
originally developed for monolithic bodies, to predeposited thin films and
coatings can lead to the paradoxical prediction of wear removal rates exceeding
the rate of film introduction into the tribological contact. A thin-film wear model is developed which
resolves this paradox through differential wear model application, coupled with
the fractional nature of such thin films which may exist as they are worn
through and the corresponding fractional normal load that film supports. The model predicts the state of the wearing
film as a function of position within the contact. A corresponding description of friction coefficient of contacts
of such wearing fractional thin films is also developed, for purely sliding as
well as combined rolling/sliding contacts.
Furthermore, it is demonstrated that prediction of film state through
the contact, from inlet to exit, enables subsequent prediction of the evolving
global wear and friction behavior with time.
The model is compared to examples of experimental friction data for thin
films taken from the literature. The
manuscript closes with a discussion of extension of the model to cases where
such thin films are continuously replenished, such as in vapor phase
lubrication.
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