Multiaxial fatigue behavior and life prediction of 7075-T651 aluminum alloy under two-step loading
Section snippets
Material and specimens
7075-T651 aluminum alloy was used in this work with the chemical composition shown in Table 1. The mechanical properties of 7075-T651 aluminum alloy are listed in Table 2, and the specimen geometry is shown in Fig. 1.
Multiaxial fatigue tests
Multiaxial fatigue tests are stress-controlled by SDN100/1000 electro-hydraulic servo fatigue testing machine with the sinusoidal loading wave of 5 Hz. The tests are carried out under completely reversed and in-phase tension-torsion loading. The axial and shear stress amplitudes
Review of constant amplitude loading tests
This part of the experiments was reported in reference [23]. A review is presented to make the research complete.
With stress amplitude ratio remaining , multiaxial fatigue life decreases gradually with the increase of equivalent stress amplitude. As presented in Fig. 2, average specimen life is 83,123 cycles under 250 MPa of while it reduces to 11,423 cycles when equals to 350 MPa. Fig. 3 shows the relation between stress amplitude ratio and multiaxial fatigue life under 300 MPa of
Criterion for constant amplitude loading tests
Basquin [38] proposed a criterion which described the relation between stress amplitude and fatigue life and was applied to stress-controlled uniaxial fatigue life prediction. Which is,
In which, is half of the variation of normal stress, which equals to axial stress amplitude . is the tensile fatigue strength, b is the tensile fatigue strength coefficient. Based on Basquin’s criterion, a modified criterion is developed to predict stress-controlled multiaxial fatigue
Conclusions
- (1)
Under stress amplitude ratio of , multiaxial fatigue life of 7075-T651 aluminum alloy decreases with the increase of equivalent stress amplitude. While under fixed equivalent stress amplitude, the multiaxial fatigue life raises with the increase of stress amplitude ratio. Considering stress amplitude ratio effects, a modified Basquin’s criterion is proposed, which could predict the constant amplitude multiaxial fatigue life.
- (2)
Fatigue damage accumulation rate is decreased by the two-step loading
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors gratefully acknowledge the financial support of the Fundamental Research Funds for the Central Universities (Grant No. 3122019194).
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