The analytical models which describe the contacts, the stress field, the initiation of crack and the conditions to reach the surface spalling have led to establish four typical criteria regarding the endurance limit (H1, H2, H3 and H4).
The fatigue tests conducted either on simulated contacts or on full bearings have been evaluated from damage point of view. The endurance limit of several materials has been obtained through the residual stress analysis of a wide range of samples.
In order to predict the endurance limit in relation with the residual stress versus depth, a representative parameter has been created: the characteristic deformation number.
The effect of temperature has been also determined on these steels :
* 100Cr6, M50-NIL and CRONIDUR 30
The values found on M50 correlated the H1 limit obtained from the analysis.
A part of the tests was devoted to contacts in gears.
The Barkhausen noise technic was used. A good correlation was observed with residual stress on 100Cr6 steel.
Deviation between calculated lives and services lives is due to a combination of material improvements,inadequate representation of the stress mechanism that cause failures and general oversimplification embodied in the general power law assumption.
This project proposes:
1. To support a significant progress in the development of a new fatigue model based on a physical/metallurgical microscopic approach with a macroscopic approach of the stress tensor (continuum mechanics).
2. To conduct monitored test in order to evaluate the real endurance limit of actual bearing steels and to identify the weight of influencing parameters:
- hertzian stress
- hoop stress
- residual stress.
3. To achieve similar test in industrial situations,particularly in high speed conditions representing turbines engines applications.
4. To investigate damage effect on after service bearings and to correlate above analysis.
5. To investigate influence of similar parameters on the rolling/sliding contact subjected to similar fatigue phenomenon in gear applications.
Funding SchemeCSC - Cost-sharing contracts
92109 Boulogne Billancourt
BS12 7QE Filton