To ensure the safety and of reducing the costs of maintenances in railways systems, it is necessary to evaluate the life prediction of fatigue crack initiation in rolling contact fatigue starting from the defects. The influence of defects on the rolling contact fatigue was studied, we simulated two types of geometry of defect (circular and elliptic) and also we studied the influence of defects clusters. The stresses and deformations were analyzed in the vicinity of the defect. Calculations were carried out with four levels of loading with the code of finite elements ABAQUS-standard (version 6.3). The fatigue impact was evaluated by using the multiaxial fatigue parameter to estimate the rolling contact fatigue life.
During machining processes, materials undergo severe deformations that lead to different behavior than in the case of slow deformation. The microstructure changes, as a consequence, affect the materials properties and therefore influence the functionality of the component. Developing material models capable of capturing such changes is therefore critical to better understand the interaction process-materials. In this paper, we introduce a new physics model associating Mechanical Threshold Stress (MTS) with Dislocation Density (DD) models. The modeling and the experimental results of a series of large strain experiments on polycrystalline copper (OFHC) involving sequences of shear deformation and strain rate (varying from quasi-static to dynamic) are very similar to those observed in processes such as machining. The Kocks-Mecking model, using the mechanical threshold stress as an internal state variable, correlates well with experimental results and strain rate jump experiments. This model was compared to the well-known Johnson-Cook model that showed some shortcomings in capturing the stain jump. The results show a high effect of rate sensitivity of strain hardening at large strains. Coupling the mechanical threshold stress dislocation density (MTS-DD), material models were implemented in the Abaqus/Explicit FE code. The model shows potentialities in predicting an increase in dislocation density and a reduction in cell size. It could ideally be used in the modeling of machining processes.
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