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Two-stage fatigue life evaluation of an aircraft fuselage panel with a bulging circumferential crack and a broken stringer

The article presents two-stage fatigue life evaluation of a stiffened aluminium aircraft fuselage panel, subject to ground-air-ground pressure cycles, with a bulging circumferential crack and a broken stringer. As a worst-case scenario, it is assumed that double cracks start at the edge of a rivet hole both in the skin and in the stringer simultaneously. In the first stage, fatigue crack growth analysis is performed until the stringer is completely broken with the crack on the fuselage skin propagating. After the stringer is completely broken, the effect of bulging crack on the fatigue life of the panel is investigated utilizing the stress intensity factors determined by the three-dimensional finite element analyses of the fuselage panel with the broken stringer. It is concluded that bulging of the skin due to the internal pressure can have significant effect on the stress intensity factor, resulting in fast crack propagation after the stringer is completely broken.