Experimental study on the effect of load on the residual fatigue life of 7050-T7451 aluminum alloy structures containing crack damage

Fatigue tests were conducted on 7050-T7451 aluminum alloy, a commonly used material in aircraft, under various stress levels utilizing a random load spectrum. The crack extension data were statistically analyzed to determine the mean remaining fatigue life and the dispersion coefficient for structures with different crack damage sizes. The analysis reveals that the mean remaining fatigue life of structures decreases as the crack damage size increases. At the same crack damage size, higher stress levels result in a shorter remaining fatigue life. Furthermore, as the damage size increases, the difference in the effect of varying stress levels on the remaining fatigue life diminishes. The dispersion coefficient of the remaining fatigue life also increases with the crack damage size. Under the same crack damage conditions, higher stress levels correspond to larger dispersion coefficient values, and the difference in dispersion of the remaining fatigue life between different stress levels increases with larger damage sizes. Considering the dispersion factor, the remaining fatigue life decreases with increasing damage size, with the dispersion coefficient rising sharply beyond a certain damage size. Specifically, the remaining fatigue life of a test specimen with a 5 mm crack damage size decreases to 2.8% of that of a specimen with a 0.5 mm damage size at a medium stress level. A critical crack size of 5 mm is identified, which is less than 50% of the critical size designed for conventional fracture control.