Abnormal Effect of Initial Crack Size on Fatigue Crack Propagation Rate of High‐Strength Al Alloys

The fatigue crack propagation (FCP) behavior of high‐strength Al alloys is crucial to ensuring the in‐service safety of aircraft components. This study found that, during the mesoscopic long crack propagation stage, high‐strength Al alloys with short initial crack sizes exhibit significantly lower FCP rates compared to those with long initial crack sizes, which is contrary to the common behavior observed in short cracks. Besides, this phenomenon has not been observed in other high‐strength materials such as Ti alloys and steels. A possible explanation has been proposed based on dislocation shielding effects, that is, through dislocation emission, the crack tips with short initial crack sizes can release a larger proportion of stress concentration under cyclic loading, thereby effectively reducing the accumulation of cyclic plastic deformation damage. Additionally, this work introduces a normalization quantitative method for the mesoscopic long crack propagation stage, showing that the exponent in the power‐law relationship between the stress intensity factor and the crack size increases gradually as the crack grows.