Tribological Stress of Lubricating Greases in the Light of System Entropy

Abstract

Lubricating greases show a structural degradation due to friction stress. The shear process dissipates energy. This results in a breakdown of the thickener structure, heat and entropy generation. Tribo-systems are energy driven systems. The stressed lubricating grease is modeled as a subsystem and presents an open thermodynamic system. Investigations were made to obtain more information about the correlation of system entropy and structural degradation of a lubricating grease. Experimental studies were done to estimate the role in terms of entropy transport for the open system. The degradation-entropy theorem was applied with the help of an empirical model to describe the correlation between degradation process and entropy production for the special case of a closed and stationary system.

Aspects of Self-Organization of Tribological Stressed Lubricating Greases

“…In recent years, the general investigations of friction and wear were transferred to the special material and lubricant-lubricating grease. This means that, in addition to the friction investigations, irreversible structural changes, as an intrinsic reaction, are also of interest [6,11,[18][19][20][21].…”

Tribological Investigation on the Friction and Wear Behaviors of Biogenic Lubricating Greases in Steel–Steel Contact

“…Moreover, some studies [29,30] attempted to assess the selected materials in terms of wear resistance, as well as in terms of energy using Fleischer's wear model in pin-disk test devices. In addition, the influence of entropy transport on the ability of a system to resist tribological stress [31,32] relates to the apparent friction energy density.…”

The Use of Entropy in Modeling the Mechanical Degradation of Grease

“…Because of these two major issues, developing a model that can predict grease life for a general case and allow the user to update the model through monitoring methods would be a significant step forward in preventing machine failure due to poor lubrication. Promising new approaches for assessing grease degradation that allows both the prediction of grease life and several updates of this estimate have been recently introduced [13,[17][18][19][20][21][22][23][24]. This approach involves the application of irreversible thermodynamics to model the irreversible changes that happen to the grease's microstructure during use.…”