Fatigue Crack Growth under Flight Spectrum Loading with Superposed Fuselage Cabin Pressure

ABSTRACT. Pressurized transport aircraft fuselage panels see the combined action of gust loading and internal pressurization that causes a rather complex biaxial cyclic loading action. In an attempt to investigate fatigue crack growth under such conditions, cruciform test coupons cut from 2.7 mm thick 2024-T3 Al-Cu alloy were tested under a modified TWIST load spectrum superposed with biaxial quasi-static load simulating internal cabin pressure. The TWIST spectrum was modified into blocks of load cycles re-arranged so as to serve as microscopic markers of crack growth over 50 flights. Further, the magnitude of transverse load from pressurization was changed in a controlled sequence as a function of block count or crack size so as to induce changes in load biaxiality whose effect may be discernible at both the microscopic and macroscopic level