This paper introduces a new model for the scuffing load capacity in heavily loaded contacts, concerned specifically with the effects of EP-additive oils. The scuffing limit for the additive condition will be closely related to the initial additive-free case, using the calculation method of Blok, solely on a referential level. The process thermodynamics involved at a friction contact will be related to a phenomenological integral relation, containing the necessary internal coordinate to describe the implicit dependence of the friction coefficient with time. The experimental response of the friction contact depends on a relaxant friction coefficient due to the additive effect. The simple calculation method requires only three input parameters for the prediction of the scuffing limit, and these can be obtained from a few experimental scuffing tests. All the tribology of the present scuffing model can be considered to be contained in a simple linear relationship, with the sliding speed as the dominant variable. The calculation criterion has shown to have predictive capability which agrees well with experiments.

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