(V) Assessing the Risk of Surface initiated Damage in Contact : An new original Approach

Many mechanical components (Rolling element bearings, Gear teeth, Cams and followers, ...), are subjected to contact stresses that are the seat of complex tri-axial state of stresses. Under dynamic, kinematic but also thermal working conditions, the contact seat will oversee some fatigue phenomenae that could lead to "true mechanism" of contact fatigue ("Subsurface fatigue cracks") but also "surface initiated" contact fatigue ("Surface fatigue cracks" or "Point Surface Origin Fatigue Cracks") and also some other complex fatigue mechanisms such as adhesive and abrasive wear (f.e. due to sliding speeds at the mating interface). The real practical working situations where sliding, rolling & repeated loading, deformation, partial lubrication and potentially materials defects can truly complexify the phenomenon, its understanding and its modelization. Intensive researches made by KOCH, PLANCK & WEBER of the Schaeffler Group concluded that the frictional energy flowing across the contacting parts may be a reliable indicator for jauging the occurrence of surface origin fatigue damages within contact pairs met in REB. Implementation of the lubrication and a mixed friction model was also considered in their modelization mainly for the cases of contacts met in rolling elements bearings. Those model and calculation revet a great importance in new Designs, not only to better understand the mechanisms and risk of surface initiated damages and their prevention but also in getting a better view of the frictional energy dissipated at the contact level and, by that way, helping in such to reduce the energy wastes and CO2 emission. This talk is a short summarized review of their interesting calculation model.