Fatigue crack growth under flight spectrum loading with superposed biaxial loading due to fuselage cabin pressure

Pressurized transport aircraft fuselage panels see the combined action of gust loading and internal pressurization that causes a rather complex biaxial pseudo-random cyclic loading action. Stress biaxiality is also known to affect constant amplitude fatigue. Fatigue crack growth was studied using cruciform test coupons under constant amplitude and a modified TWIST load spectrum superposed with biaxial quasi-static load simulating internal cabin pressure. The experiments were performed on a specially designed four-actuator biaxial test system suited for high frequency in-phase and out-of-phase constant amplitude loading as well as biaxial pseudo-random spectrum loading. Observed crack growth rates were correlated with stress intensity values, corrected for biaxiality.