Probabilistic framework for a microstructure-sensitive fatigue notch factor

To advance fatigue life prediction algorithms, more comprehensive knowledge of the intensity and distribution of slip within microstructure at the notch root is desired to quantify notch size effects. This study utilizes 3D computational crystal plasticity to assess the degree of heterogeneity of cyclic plastic deformation as a function of notch size and notch root acuity for notch root strain amplitudes near and below the macroscopic yield strain (high cycle fatigue) and for several realizations of aggregates of grains with random orientation distribution at the notch root for polycrystalline OFHC Cu. By using different notch root radii and microstructure realizations of aggregates of grains, statistical information regarding the distributions of stress/strain gradients and fatigue indicator parameters provides useful insight into the microstructure dependence of driving forces for fatigue crack formation at the scale of mean grain size. Results from simulations within a quantitatively defined notch root damage process zone are used along with a probabilistic mesomechanics approach to quantify notch size effects by defining a new microstructure-sensitive fatigue notch factor that considers the probability distribution of the high cycle fatigue strength.