Fatigue and crack-growth analyses on 7075-T651 aluminum alloy coupons under constant- and variable-amplitude loading

This paper presents the results of small- and large-crack-growth-rate tests conducted on the 7075-T651 alloy over a wide range of constant-amplitude loading to establish the baseline crack-growth-rate curves for the fatigue analyses. Crack-growth behavior was found to be different in the thickness and in-plane directions. These test data are compared with results from a NASA/CAE Cooperative Program on small- and large-crack growth in a 7075-T6 thin-sheet alloy. Using inclusion-particle-cluster sizes and shapes, like those that are observed in tests, the fatigue and crack-growth lives are predicted on various specimens used to simulate details in a wing panel under either constant-amplitude or simulated wing spectrum loading. The predicted results compared well with the test data.