Reliability-Based Model for Fatigue Notch Effect

This paper proposes a probabilistic analysis framework incorporating material fatigue response models at the microstructural scale to predict the scatter in damage behavior for an ensemble of test specimen. The material fatigue response model uses micromechanical fatigue analysis to properly account for the multiple stages of early fatigue damage that drives the scatter in fatigue response. Observations from the open literature are used to determine fatigue damage accumulation mechanisms at the microstructural level for an α-β Ti-6Al-4V alloy. The fatigue stages of crack nucleation, small crack growth and long crack growth are explicitly considered. Theoretical and semi-empirical models that relate the damage to the fatigue response are developed for each stage. The statistics of the microstructural variables that govern the scatter in the fatigue response are estimated. A Monte Carlo Simulation algorithm is developed to combine the three stages of damage accumulation to predict the total life of test specimens. The predictions compare favorably with test data.