Volume 2, Issue 2 (February 2005)
Rheological 3-D Modeling of Scuffing for the EP-Additive Condition
A rheology-based new model for predicting the scuffing limit in heavily loaded contacts, concerned especially with effects of EP-Additive Oil (Antiwearbasis Sulfure phosphore Zinc Nitrogen and Zincdithio phosphare) is developed here. The theoretical framework is sustained on the main assumption that all of the effects of additives can be modeled by the use of a combined friction-temperature variable, introduced in the theoretical known Blok's calculating criterion. The analytical step-jump method3 is used to expand the rearranged form of Blok's Flash Temperature expression, to yield a constitutive integral equation in order to describe a generalized friction process. The particular solution found is assumed to be representative for the rheological behavior of contacts, in the Additive Containing Condition (ACC), thus representing the linear step response contribution of protective layers due to tribochemical action. The improvement of the scuffing capacity with speed is influenced radically by the derived thermorheological friction-function, which at least turns out to be explicitly a function of the sliding speed. Physically, the friction-function represents the rheological response of the lubricated contact to the operating conditions. Mathematically, it is equivalent to the relaxation modulus in viscoelasticity. Thereafter, the scuffing capacity depends on the sliding speed as a dominant variable and markedly on two experimental response coefficients containing all the tribology of the model. Additionally, a short and economical method for determining experimentally the scuffing limit is suggested for the FZG-rig . This study is concerned with Blok's calculating method and its extension to the ACC  and also with the view to incorporate the model into a code to form a general predictive capability for the design of gearing .