Thermal damage and fatigue estimation in heavily loaded lubricated rolling/sliding contacts with Micro-Geometry

A previously developed model for heavily loaded Elastohydrodynamically lubricated (EHL) contacts with surface micro-geometry for the calculation of surface distress (micropitting), based on high-cycle fatigue and mild wear competition, is herewith further extended. It now includes the effects of frictional heating with a sharp temperature rise developed in the rolling contact. For this, a new surface damage model, originated in creep modelling, is included. With this modification, the detrimental effect of high temperature developed in the rolling/sliding contact can now be accounted for. This model can consider sharp or moderate surface temperature rise during over-rolling is found in bearings and gears operating at high speeds or under the combination of speeds, loads and unfavourable environmental aspects. The present model introduces a threshold limit made of the combination of temperature and (heating time under stress) load cycles above which the conditions in the rolling contact are deemed damaging for the steel microstructure and the tribological functionality of the rolling contact. The surface damage model is first compared with laboratory experiments in rolling/sliding conditions and then applied to study combinations of loads, sliding speeds and the effect in rolling bearings. The ability of the present model to include damaging mechanisms, other than classical metal fatigue, increases the flexibility in contact surface damage modelling and allows for the accounting of phenomena up to now excluded from better estimation of the machine elements surface life.