Mechanical Behavior Laboratory University of Nevada, Reno

Paper

[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.

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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).

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