Fatigue crack growth in 7249-T76511 aluminium alloy under constant-amplitude and spectrum loading

Fatigue crack growth tests were conducted on compact, C(T), specimens made of 7249-T76511 aluminium alloy. These tests were conducted to generate crack growth rate data from threshold to near fracture over a wide range of load ratios (R). Four methods were used to generate near threshold data: (1) ASTM E-647 load reduction (LR), (2) compression pre-cracking constant-amplitude (CPCA), (3) compression pre-cracking LR, and (4) constant crack mouth opening displacement LR method. A crack closure analysis was used to develop an effective stress-intensity factor range against rate relation using a constraint factor (alpha = 1.85). Simulated aircraft wing spectrum tests were conducted on middle crack tension, M(T), specimens using a modified full-scale fatigue test spectrum. The tests were used to develop the constraint-loss regime (plane strain to plane stress; alpha = 1.85 to 1.15) behaviour. Comparisons were made between the spectrum tests and calculations made with the FASTRAN life prediction code; and the calculated crack growth lives were generally with +/- 10% of the test results.