Rolling Contact Fatigue Life Prediction Incorporated With Machined Surface Integrity

The importance of Rolling Contact Fatigue (RCF) has been widely recognized among manyindustries such as aeronautics, automotive, mechanics and etc. This phenomenon is actuallyrecognized as the first root of failure for most mechanical components under cyclic loadings.The main failure mechanism for hard-turned bearing steel particularly subjected to RCF isrecognized as subsurface initiated spalling. The machining process of hard-turning is widelyused in replacement of the grinding process as finishing machining process thanks to itseconomic, technical and environmental advantages.This thesis aims to incorporate the surface integrity most important factors into an analyticalmodel for improving the accuracy of rolling contact fatigue life prediction regarding hard-turned bearing steels. It particularly focuses on High Cycle Fatigue (HCF) and AISI52100steels. In that purpose a review of the phenomenon of rolling contact fatigue with its mostimportant characteristics is provided. The analysis of the models in literature and theirlimitations in terms of surface integrity consideration has permitted to determine an analyticalmodel for rolling contact fatigue life prediction.The surface integrity significance has been demonstrated by means of the description ofsurface integrity factors and their influence on Rolling Contact Fatigue life. Surface Integrityrefers to: the surface roughness, residual stress, micro-hardness and phase transformationinduced from hard-turning process. The fundamental inhomogeneity characteristic of thematerial has also being put forward. The residual stress distribution below the machinedsurface has been identified as the major factor to influence the RCF life of hard-turnedbearing steels. Hard turning is more favorable for generating compressive stresses thangrinding process. However, few methods have been developed to evaluate precisely theresidual stress profiles for the hard-turning of bearing steels and their direct influence onfatigue life. An optimized profile of residual stress could be achieved through the selection of appropriate cutting conditions. The residual stresses will therefore be input in the model toevaluate its influence and give a more accurate prediction of RCF life.The developed model considers elastic-plastic deformation during rolling contact anddistinguishes the crack initiation and crack propagation life. The crack initiation life is basedon a dislocation theory and the crack propagation life based on a plasticity model. Anidentification and calibration of the model parameters are given as well as a procedure topredict rolling contact fatigue life. The residual stress profile is incorporated both in the crackinitiation and propagation life through the maximum shear stress parameter.This RCF life prediction model is verified by the exploitation of residual stress profilesprovided by the measurement of AISI52100hard-turned steels. This surface integrity factor istherefore treated as the internal variable to reduce or increase fatigue life.The study suggests that the fatigue life decreases with increasing external loads. However, thefatigue life will be increased due to the presence of mostly compressive residual stress in thehard-turned bearing steels as the residual stress is incorporated into the life prediction model.The analytical model shows that compressive residual stresse decreases the maximum shearstress and therefore elongates both the crack initiation and propagation life. The study showsthat by the residual stress, the maximum shear stress can be reduced up to31%and thus thefatigue life can be increased by more than40%by incorporating the residual stresses. Finally,the analytical model incorporating the integrity factor of residual stresses presents a betteraccuracy prediction by more than10%than that without considering residual stress.