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cited By 0; Mechanical contacts in rolling element bearings and gears are increasingly loaded nowadays. In high temperature applications, surface treatments such as gas-nitriding are used to increase their rolling contact fatigue life. This study focuses on the prediction of the location of crack initiation for gas-nitrided steels subjected to rolling contact fatigue taking into account the material property gradients induced by the nitriding process. Several approaches based on the Dang Van criterion are compared to experimental data to find the most reliable prediction model. © 2019 Elsevier Ltd

International audience; In rolling contact fatigue (RCF), failure mechanisms are known to be very sensitive to material microstructure. Yet, among the different numerical models developed to predict the RCF life, few models use a microstructure representation. A granular cohesive finite element model has been developed to simulate progressive damage of a structure subject to RCF and to investigate failure initiation mechanisms. This paper focuses on the implementation of crystal elasticity in the model. The numerical analysis of a representative volume element (RVE) validates the use of cubic elasticity to represent crystal behavior. The influence of the RVE size and the influence of boundary conditions applied on the RVE are evaluated in the finite element approximation framework. As regards the implementation of cubic elasticity in the RCF model, the generation of stress singularities at triple junctions is first highlighted. Then the average value of the intergranular shear stress is proved to be mesh size independent and therefore can be used as damage criterion. Finally, the influence of crystal elasticity on micro-cracks distribution is presented.

The study of rolling contact fatigue in spur gears requires a good comprehension of all the phenomena occurring at the material scale. On a numerical point of view, a realistic representation of the material and of the load repartition function of the local micro-geometries is needed. However the resulting models are often complex and time-consuming. So, this work aims at developing a model meeting these specificities. Thus, different sections of the spur gear material granular geometry are simulated first. Secondly, the contact pressure fields are computed accurately relatively to the simulated surface microgeometry. Then, the influence of several parameters on their rolling contact fatigue life is highlighted. Among friction, sliding coefficient, load variation and roughness, these individual or combined parameters are taken into account in the model, tested and their impact stressed out. Finally, a fatigue criteria based on rolling contact fatigue micro-cracks nucleation at grain boundaries is proposed in order to compare simulations and influencing parameters to the reference.

Colloque avec actes et comité de lecture. Internationale.; International audience; Les mécanismes d'initiation de fissures en fatigue de contact sont fortement liés à la microstructrure du matériau. Cependant, la plupart des modèles utilisés pour prédire la durée de vie en fatigue de contact se situent à l'échelle macroscopique. Un modèle basé sur une représentation de type Voronoi des grains (échelle mésoscopique) est développé afin d'analyser les mécanismes d'initiation. Le concept d'endommagement est appliqué aux joints de grain modélisés par la méthode des zones cohésives (CZM). La représentativité du modèle a été améliorée par la modélisation de l'anisotropie cristalline. Enfin, une nouvelle méthode d'application de l'endommagement aux joints de grain a permis de rendre les résultats plus cohérents en termes d'estimation de la durée de vie.