MECHANOCHEMICAL MODEL - REACTION TEMPERATURES IN A CONCENTRATED CONTACT

Successful boundary lubrication is essential in the design and operati on of many mechanical components. The lubrication process is complex a nd it involves contact mechanics, fluid mechanics, tribochemistry, and material deformation and fracture. Two schools of thought have emerge d over the years in examining the mechanisms and modeling of boundary lubrication. The chemical school believes that chemical reactions at t he rubbing surfaces control the efficacy of the lubrication process. T he mechanical school believes that while chemistry is a factor, hydrod ynamics, elastohydrodynamics (EHD), and micro-EHD can account for most of the load-bearing mechanisms, so at least in design, they are the p rincipal issues. This paper attempts to bring the two schools together to examine a common set of experimental data. The experiments involve running wear tests on a four-ball wear tester using microliters of lu bricant until seizure. Lubricant degradation and breakdown are therefo re a factor in the wear test. Eventually we would like to compare the chemical kinetic model with the mechanical contact model in describing and predicting the effectiveness of the lubrication process, i.e. the time to seizure. The chemical kinetics model assumes that oxygen cons umption by the lubricant to make friction polymers controls the proces s. The mechanical model suggests that if temperatures in the contact e xceed a certain limit, scuffing will occur. The key to both models is the temperatures in the contact. This paper describes the two models a nd focuses on the temperatures in the contact. The temperatures calcul ated from the two models differ significantly. The temperatures predic ted by chemical kinetics are about 100-degrees-C higher than the mecha nical model. The identification of the discrepancy and the magnitude o f the difference highlight the difference between the two approaches. It is hoped that this paper will bring forth further research effort t o this critical issue. Various possible explanations were offered for the temperature difference. A plausible explanation was proposed and i nitial calculations suggest that by taking into account of the wear pr ocess, the temperatures calculated by the mechanical model can reach t he temperatures estimated by the chemical model.