The behaviour of lubricants in elastohydrodynamic contacts

Abstract Difficulties once found in accounting for the tractional behaviour of lubricants in elastohydrodynamic (EHD) contacts have largely been resolved. A wealth of research stimulated by this problem has gradually unravelled the underlying rheological complexities and laid the basis for a coherent physical explanation. The understanding achieved and the problems that remain are briefly reviewed. Despite the advances made in rheological modelling, developments are not readily taken up by those engaged in theoretical investigations. Although computational complexity must inevitably rise when lubricants are modelled realistically, the penalty for not doing so must be clearly understood. The implications can be readily devined from previous research findings. Progress made in the exploration of EHD film thickness is also examined. Similarities and differences in film-forming behaviour in thick film (> 0.1 μm) and thin film (< 0.1 μm) regimes are identified and consideration given to the interpretational difficulties that may arise as EHD and boundary regimes begin to merge. Finally, a few observations are made on the value of EHD lubrication studies to automotive engineering.