Bulging of Fatigue Cracks in a Pressurized Aircraft Fuselage (May 1991)

摘要

Fatigue crack growth and residual strength must be considered as part of thedamage problem of a pressurized aircraft fuselage. Longitudinal cracks offer problems because they occur in a curved thin sheet structure under biaxial loading conditions and internal pressure. The fatigue crack edges bulge outwards (out-of-plane deformation) which considerably complicates the fracture mechanics analysis. The problem is analyzed empirically and theoretically. Three test set-ups were developed respectively for (1) sheet specimens under biaxial loading, (2) tensile loading of curved sheet specimens, and (3) sheet specimens with a large radius of curvature loaded by internal air pressure and hoop stress. Fatigue crack growth and residual strength tests were carried out on aluminum alloy sheet specimens and some panels of new metal-sheet/fiber laminates (ARALL and GLARE). Analytical relations were developed to obtain K-values, which account for the non-linear behavior associated with sheet curvature and bulging-out of the crack edges. The predictions agree with the present test results, and with results from the literature obtained by FEM calculations for fuselages and in full-scale fatigue tests.