Fluid rheology, traction/creep relationships and friction in machine elements with rolling contacts
Creators: name: Poll, G.W.G.
name: Wang, D.
Publisher: name: London : SAGE Publications Ltd.
Year: 2012
Subjects: subject: limiting shear stress
subject: Lubricant rheology
subject: rolling contacts
subject: traction-creep relationship
subject: viscoelasticity
subject: Angular contact ball bearing
subject: Boundary lubrications
subject: Contact pressures
subject: Experimental data
subject: Fluid rheology
subject: Friction torque
subject: Hydrodynamic films
subject: Limiting case
subject: Limiting shear stress
subject: Linear relationships
subject: Machine element
subject: Mixed lubrication
subject: Molecular dynamics simulations
subject: Phenomenological models
subject: Rheological property
subject: Roller rigs
subject: Roller test
subject: Rolling contacts
subject: Rolling Element Bearing
subject: Rolling speed
subject: Rolling/sliding contact
subject: Slide-to-roll ratio
subject: Slope change
subject: Threshold pressures
subject: Toroidal drive
subject: Traction characteristics
subject: Traction drive
subject: Ball bearings
subject: Elasticity
subject: Elastohydrodynamic lubrication
subject: Electric drives
subject: Forecasting
subject: Lubricants
subject: Molecular dynamics
subject: Rheology
subject: Rolling
subject: Shear stress
subject: Strip mills
subject: Tribology
subject: Viscoelasticity
subject: Friction
subject: Dewey Decimal Classification::600 | Technik::620 | Ingenieurwissenschaften und Maschinenbau::621 | Angewandte Physik

description: The correct prediction of shear stresses in lubricants applied to concentrated rolling/sliding contacts has been an issue of intense debate for many years. Traction testers of various kinds such as two-disc roller rigs or ball on disc apparatus have been extensively used in order to obtain experimental data, as well as, more recently, molecular dynamics simulations. Several, partly competing, phenomenological models have been developed to describe the dependence of shear stresses on various parameters. Evidently, the importance lies in the need to predict and reduce friction, or, more accurately, resistance to motion of rolling element bearings in order to increase efficiency of machines and vehicles. Also, it plays a crucial role in design and performance of traction drives. As a prerequisite, experimental data for a wide variety of fluids were obtained from two-disc roller tests with a wide variation of contact pressures, rolling speeds and slide-to-roll ratios. Following earlier investigations, the amount of slip created by the elastic deformation of the discs was separated from the contribution of the fluids and their rheological properties. In accordance with experiments of Jacobson a threshold pressure in the fluid was identified which marks the onset of a nearly linear relationship between a limiting shear stress and pressure. However, this threshold does not appear to be constant but rather declining with decreasing hydrodynamic film thickness respective of rolling speed, while the slope changes to a lesser extent. When measurements were extended far into the mixed lubrication regime close to the limiting case of boundary lubrication, the shear stress/pressure relationship became quasi-Coulomb with a virtually zero threshold pressure. These results have successfully been used to predict the friction torque of angular contact ball bearings and the traction characteristics in toroidal drives. © IMechE 2012.