Modeling of Elastohydrodynamically Lubricated Contacts with Chemical Degradation of Polymer Additives

Kettering University, Flint MI

Investigators

Abstract

9912501 Kudish Chemical degradation of polymer additive molecules in lubricated tribological contacts may significantly alter the lubricant rheology and contact film properties. This study is a theoretical study of the coupling between elastohydrodynamic behavior of a lubricated contact and the strain and temperature induced polymer degradation reactions which occur in the contact. A statistical modeling of polymer alignment and bond cleavage as a function of polymer chain length, molecular structure, and local shear and strain rates at different locations within a contact zone will be performed. In particular, a kinetics equation describing polymer chemical degradation will be derived, analyzed, and solved under different assumptions. This equation is based on a probabilistic approach. The predictions derived from the kinetics equation will be linked to elastohydrodynamic lubrication calculations through lubricant viscosity in order to formulate a new coupled chemo-elastohydrodynamic treatment of lubricated contacts. This formulation will be used to asymptotically and numerically model lubrication in the presence of chemical degradation. The effects of pressure, temperature, strain, and polymer chain length on polymer degradation will be studied. The major difference of this formulation from the ones for non-Newtonian lubricant fluids is that the polymer and lubricant chemical changes are irreversible. The results will be compared with direct experimental measurements of lubricant properties to be performed at Lubrizol. The results are expected to establish the conditions under which polymer additive degradation can be expected to significantly affect film formation (thickness, temperature, strain, etc.) in lubricated contracts and thus, to contribute to further thermal, mechanical, and chemical degradation. That allows to further the understanding of the tribochemical behavior of lubricants in various machine elements and joints such as engines, bearings, and gears. ***