A normalized equivalent initial flaw size model to predict fatigue behavior of metallic materials

A normalized equivalent initial flaw size method is proposed based on the updated Kitagawa–Takahashi diagram considering the small crack growth behavior, which is essential to accurately predict the fatigue crack initiation and propagation. Meanwhile, the updated Kitagawa–Takahashi diagram indicates that small cracks can propagate even with an applied stress below the fatigue limit, which is consistent to the experimental observations. A new fatigue life prediction model is proposed by considering the fatigue crack growth from the normalized equivalent initial flaw size to normalized final crack length when the failure occurs. The parameters of the proposed model have clear physical meaning and can be determined from experiments. Experimental data for aluminum alloys and steels under different test conditions are adopted to verify the proposed model, the theoretical predictions show good agreement compared with the experimental results.