Scale effects for surface-induced rolling fatigue

• Applicant: Dr.-Ing. Florian Pape
• Subject Area: Engineering Design, Machine Elements, Product Development
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 509725088

In particular, damage on rolling surfaces with buildup can significantly reduce fatigue life of components subjected to rolling stresses, especially rolling bearings. Such damage cannot be completely avoided during manufacturing, mounting and operation; an assessment of the expected adverse effects is urgently required, but has so far only been possible to a limited extent. It can be assumed that there is a significant size influence in the detrimental effect of impact marks and other surface damage in rolling contacts, which has not yet been recorded. The stressed volume increases with increasing bearing size, as does the number of inclusions in the stressed microstructure below the rolling contact, which can cause cracking even without surface defects. If the number of damages remains small, the proportion of the volume highly stressed by them also decreases in comparison to the total cyclically stressed volume. In addition, the stress field from the Hertzian stress on the undamaged surface moves further in depth and overlaps less with the stress field in the vicinity of the damage. Therefore, there is reason to believe that the same damage will increase the risk of failure significantly less for large bearings relative to the undamaged bearing. However, this size effect has not yet been systematically investigated and demonstrated experimentally, nor can it be reliably quantified based on verified computational models. The effect of surface damage on the fatigue life of rolling bearings, which is simulated by means of simulations, has so far only been experimentally verified on small cylindrical roller bearings with a bore diameter of 30 mm. For a reliable transfer to other dimensions, a deeper understanding of the significance of the various effects that interact in the damaging influence of surface defects on rolling fatigue is still lacking. In smaller bearings, residual stresses, local excess stresses due to the geometry of the throw-up and stresses below the surface due to Hertzian contact overlap in such a way that it is difficult to consider them separately. This results in the necessity to extend targeted experimental and theoretical investigations to significantly larger bearings.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr.-Ing. Gerhard Poll