Statistical Analysis of Energy Release Rate Evolution for Microstructurally Small Fatigue Cracks

ABSTRACT This study investigates the early propagation of microstructurally small fatigue cracks from micro‐defects in polycrystalline Inconel 718. A 3D conformal global/local finite‐element framework with adaptive remeshing is employed to explicitly resolve grain boundaries, and the energy release rate (ERR) is extracted along the crack front using the domain integral. By simulating statistically representative aggregates under linear elastic assumptions, the relative influence of microstructural features, including grain size, orientation, and topology, on the fracture driving force is quantified and ranked. Results demonstrate that the host‐grain crystallographic orientation exerts a critical first‐order influence: The [101] orientation increases the local ERR by +172 % on average compared to the [001] orientation. This significant sensitivity affects early propagation behavior, inducing pronounced scatter in fatigue life driven by the uncontrolled local microstructural neighborhood. However, this strong microstructural forcing is shown to be confined to the first few grains. Once the crack front length exceeds the characteristic grain size by an order of magnitude, local fluctuations spatially average out, and the homogenized approximation effectively recovers the propagation kinetics of randomly oriented microstructures.