Evidence of Plug Flow in Rolling–Sliding Elastohydrodynamic Contact

The existence of shear bands, boundary slippage or shear localization was observed several times by various researchers. At the same time, the concept of limiting shear stress is almost exclusively used for traction modeling without clear explanation of physical phenomena that it is associated with. Despite it, the classic linear distribution of speed through-film profile is often considered in current numerical analyses and in our thinking about experimental results. It seems there is a small effort to unify our approaches to meet general concept that can explain a wide range of phenomena. This paper presents experimental results that point out on irregular distribution of through-film speed profile. The observations show an existence of cohesive core of entrainment speed surrounded by two shear zones located closely to the surfaces. This result represents experimental evidence for plug flow mechanism in highly loaded rolling–sliding elastohydrodynamic contact. Possible mechanisms of shear localization are discussed.