Abstract 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.

中文翻译：

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用于预测金属材料疲劳行为的归一化等效初始缺陷尺寸模型

摘要 考虑到小裂纹扩展行为，基于更新的北川-高桥图提出了一种归一化等效初始缺陷尺寸方法，这对于准确预测疲劳裂纹的萌生和扩展至关重要。同时，更新后的 Kitagawa-Takahashi 图表明，即使施加的应力低于疲劳极限，小裂纹也可以传播，这与实验观察结果一致。考虑失效发生时从归一化等效初始裂纹尺寸到归一化最终裂纹长度的疲劳裂纹扩展，提出了一种新的疲劳寿命预测模型。所提出模型的参数具有明确的物理意义，可以通过实验确定。