Anisotropic Fatigue Crack Growth in High-Strength Aluminium Alloys

摘要

Production rates of civil airliners are reaching unprecedented numbers. To reduce recurring cost of future large-series airframes, more integrated light-alloy primary structure is needed. Over-conservative fatigue crack growth assumptions can lead Analysts and Designers to add weight to such integrated components. A method is needed that can predict the actual crack path, accounting not only for the specifics of integral structures, but also for the high-strength aluminium alloys they will be made of. These alloys can show pronounced fracture orthotropy, with low-ductility "delamination"-fracture occurring along the plane perpendicular to the ST-direction of the wrought material. This paper reports on fatigue crack growth testing performed on coupons cut from 100mm thick plates of AA7010 T7451 and AA2050 T84. Fracture mechanisms are discussed. Two models to predict crack paths are presented, and their predictions compared to the test results. Using the above as well as new insights from recent literature, a third, improved model is formulated.