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.
Highlights
Lubricating greases are markedly visco-elastical lubricants with the main task to separate solid surfaces in a tribo-contact
The effect of fluid friction leads to a structural degradation of lubricating greases
The mechanical degradation means a destruction of the thickener
Summary
Lubricating greases are markedly visco-elastical lubricants with the main task to separate solid surfaces in a tribo-contact. They consist of a base oil and a so-called thickener. This thickener (it is often a metal soap) forms a three-dimensional network and delivers the elastical part of the visco-elastical properties. The consequences of an applied friction stress can be indirectly observed by a change of the rheological and tribological behaviour. These are well known as thixotropic effects or even better as artificial thixotropy
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