Effect of L-T and S-T orientations on fatigue crack growth in an aluminum 7050-T7451 plate

This study is focused on the anisotropic fatigue crack growth (FCG) behavior of an aluminum AA7050-T7451 plate. L-T and S-T orientations were studied in M(T) samples with W = 50 mm, in mode I loading, with R-ratio of +0.05. A numerical approach was used, assuming that crack tip plastic strain is the crack driving force. A purely kinematic elastic-plastic model was calibrated using experimental data from low cycle fatigue tests of smooth specimens in L and S orientations. The predicted FCG rates agree well with experimental trends in the Paris' regime, suggesting that cyclic plastic deformation is the main damage mechanism. The numerical model was used to estimate the stress ratio effect for both orientations, which was found to be linked with crack closure variations. However, the closure free predicted trends for both microstructural orientations at R = 0.05 are not overlapped, suggesting an effect of microstructure not linked to crack closure.

Automated summary

This study focuses on the anisotropic fatigue crack growth behavior of an aluminum AA7050-T7451 plate. A numerical model based on plastic strain at the crack tip as the driving force for crack growth was calibrated using experimental data from low cycle fatigue tests. The predicted crack growth rates agree well with experimental trends, suggesting that cyclic plastic deformation is the main damage mechanism. The model was also used to estimate the stress ratio effect and found a correlation with crack closure variations, but additional microstructural effects not linked to crack closure were observed at R=0.05.