Mechanical Behavior Laboratory University of Nevada, Reno


[J47] Zhao, T., Zhang, J., and Jiang, Y., 2008, "A Study of Fatigue Crack Growth of 7075-T651 Aluminum Alloy," International Journal of Fatigue, Vol.30, pp.1169-1181. doi: 10.1016/j.ijfatigue.2007.09.006

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Paper Abstract

Both standard and non-standard compact specimens were employed to experimentally study the crack growth behavior of 7075-T651 aluminum alloy in ambient air. The effects of the stress ratio (R), overloading, underloading, and high-low sequence loading on fatigue crack growth rate were investigated. Significant R-ratio effect was identified. At the same R-ratio, the influence of specimen geometry on the relationship between crack growth rate and stress intensity factor range was insignificant. A single overload retarded the crack growth rate significantly. A slight acceleration of crack growth rate was identified after a single underload. The crack growth rate resumed after the crack propagated out of the influencing plastic zone created by the overload or underload. A parameter combining the stress intensity factor range and the maximum stress intensity factor can correlate the crack growth at different stress ratios well when the R-ratio ranged from -2 to 0.5. The parameter multiplied by a correction factor can be used to predict the crack growth with the influence of the R-ratio, overloading, underloading, and high-low sequence loading. Wheeler's model cannot describe the variation of fatigue crack growth with the crack length being in the overload influencing zone. A modified Wheeler's model based on the evolution of the remaining affected plastic zone was found to predict well the influence of the overload and sequence loading on the crack growth.


Paper Figures

Fig. 3

Fig. 3. Stress intensity factor obtained from using Eq. (1) and that from the FE method for the standard compact specimen (Download data).

Fig. 4

Fig. 4. Stress intensity factor for the non-standard compact specimen obtained from the FE method (Download data).

Fig. 5

Fig. 5. Crack propagation under constant amplitude loading with the effect of the R-ratio (Download data).

Fig. 6

Fig. 6. Overload effect on crack growth (Download data).

Fig. 7

Fig. 7. Underload effect on crack growth (Download data).

Fig. 8

Fig. 8. Crack propagation under two-step high-low sequence loading (Download data).

Fig. 9

Fig. 9. Constant amplitude crack propagation with the effect of the R-ratio using Eq. (5) (Download data).

Fig. 10

Fig. 10. Prediction of crack growth rate after overloading using Wheeler's model (Download data).