Energy field intensity approach for probabilistic notch fatigue assessment under size effect

The development of modern engineering components and equipment features large size, intricate shape and long service life, which places greater demands on valid methods for fatigue performance analysis. Achieving a smooth transformation between small-scale laboratory specimens’ fatigue properties and full-scale engineering components’ fatigue strength has been a long-term challenge. In this work, two dominant factors impeding the smooth transformation — notch and size effect were experimentally studied, in which fatigue tests on Al 7075-T6511 (a very high-strength aviation alloy) notched specimens of different scales were carried out. Fractography analyses identified the evidence of the size effect on notch fatigue damage evolution. Accordingly, the Energy Field Intensity (EFI) initially developed for multiaxial notch fatigue analysis was improved by utilizing the volume ratio of the Effective Damage Zones (EDZs) for size effect correction. In particular, it was extended to a probabilistic model considering the inherent variability of the fatigue phenomenon. The experimental data of Al 7075-T6511 notched specimens and the model-predicted results were compared, indicating the high potential of the proposed approach in fatigue evaluation under combined notch and size effects.