Friction-velocity characteristics of a paper-based wet friction material in low sliding velocity (Part 1): boundary film model supposing eyring viscosity

摘要

By supposing Eyring viscosity model which shows an non-Newtonian viscosity characteristic as rheology of boundary film, numerical simulations have been carried out to estimate the tangential force (friction) velocity characteristics of a paper-based wet friction material in low sliding velocity region probably under boundary lubrication conditions in automatic transmission fluid (ATF). The results of the simulations for one period of reciprocating friction are consistent with feature of data from the experiments. Also, the relations between shear stress and shear rate, and between apparent viscosity and shear rate have been represented by non-dimensional expression. These results show the influence of characteristic stress and characteristic viscosity of Eyring viscosity and boundary film thickness on friction characteristics. It is clarified from the examination of the characteristic of apparent viscosity that shear thinning phenomenon obtained under conventional thin film lubrications in so-called nanotribology is the same characteristic as the Eyring viscosity. Moreover, it is shown that characteristic stress determines the slope of tangential force coefficient-velocity (φ-logV) diagram for a wide range of sliding velocity and the change in a ratio of characteristic viscosity to film thickness makes a diagram shift in parallel. As a result, the influence of temperature on tangential force (friction force) characteristics can be explained by the characteristic stress and characteristic viscosity.