Subcycle fatigue crack growth and equivalent initial flaw size model for fatigue life assessment under arbitrary loadings for Al-7075

A novel fatigue-life prediction methodology combining a subcycle fatigue crack growth (FCG) analysis and equivalent initial flaw size (EIFS) concept is proposed in this paper. This research focuses on extending a previously developed time-based subcycle fatigue crack growth model to a near-threshold regime and under multiaxial loadings. First, the threshold FCG behavior using subcycle FCG is discussed, and a new temporal kernel function to include intensity factor corresponding to the near-threshold region is proposed. Following this formulation, the multiaxial load case scenario is considered for mixed-mode FCG using a critical plane approach. Next, the general multiaxial loading is converted to an equivalent uniaxial loading for life prediction. Next, model predictions under arbitrary loadings (e.g., uniaxial and multiaxial, constant and variable amplitude loading, and random spectrums) are compared with experimental data from open literature and internal testing. Multiple conclusions and potential future work have been suggested using the proposed model.