Aspects of Self-Organization of Tribological Stressed Lubricating Greases

Abstract

Lubricating greases are markedly visco-elastic materials. Stressed by a friction process, this special material shows a drop of a measured shear stress or viscosity. This typical behaviour is observed in a number of papers and, therefore, is well known. Some different explanations can be found but most of them describe a structural degradation caused by the friction process. This paper attempts to elucidate the conditions that promote that structural change and understand this behaviour as an intrinsic response of the system.

Energy Dissipation in Tribological Stressed Greases

“…This assumption will now be followed up and indicators will be examined that enable instability and thus make self-organization probable. The analysis in [18] shows for the general case of lubricant friction…”

“…This seems explainable against the background that the bonds in the agglomerate are of a physical nature and during shearing the entire grease (base oil + thickener) is stressed. A more detailed investigation in [18] provided conditions for the initiation of instability. Several dissipation mechanisms were considered and, among others, a criterion with ∂γ critic ∂ϵ < 0 and ∂F f ∂ϵ > 0 (5) was found.…”

“…The general shear of the base oil, fragmentation of agglomerates and coagulation of particles after a collision were considered in [18].…”

“…The process of the occurrence of instability and a self-organization initiated by it, as studied by Prigogine [17], shows the possibility of checking tribological processes via this criterion.The assumption is made that self-organized processes can also be triggered in tribologically stressed lubricating grease films and lead to a new structural state [18]. In order to counteract the difficulty of experimentally observing the structural formation in tribologically stressed lubricating grease films, indirect indicators for the triggering of self-organized processes are investigated in this work.…”