SUMMARY

The fatigue performance of bearings is a function of many factors, including loading, material properties, and manufacturing processes. Crack nucleation, first spall generation and spall growth in rolling contact fatigue (RCF) are known to be highly sensitive to the heterogeneity of the microstructure. Yet the current state-of-the-art in the design of high performance bearing materials and microstructures is highly empirical requiring substantial lengthy experimental testing to validate the reliability and performance of these new materials and processes. The approach presented here is designed to determine the relative rolling contact fatigue performance as a function of microstructural attributes. Both an efficient geometric finite element model and an advanced two-phase material model were developed to address this complex problem. A fully 3D finite element modeling allows for end effects to be captured that were not previously possible with two-dimensional plane-strain models, providing for a more realistic assessment of inclusion morphology and arbitrary orientations. The scaling of the finite element models has been optimized to capture the cyclic microplasticity around a modeled inclusion accurately and efficiently. A microstructure-sensitive material model adds additional capability. A hybrid model that includes both martensite and austenite phases with additional internal state variable to track the volume fraction of retained austenite due to stress-assisted transformation were developed. Important links between microstructural features and fatigue indicator parameters (and thus relative fatigue performance) were determined. Demonstration cases show the relationship between inclusion orientation and relative fatigue performance. Also, increasing initial volume fraction of retained austenite was shown to reduce relative fatigue life. These tools allow for the investigation of many microstructural effects not previously possible with a numerical model.