Numerical and experimental investigation of a metallic fuselage stiffened panel loaded with a representative fuselage fatigue spectrum

A mission profile of a passenger airplane consists of several phases during which its structural components experience complex sequences of alternating loads. When focusing on a fuselage section, these sequences are usually consistent in format during the cruise flight phase. In the present work a full-scale stiffened fuselage panel was tested in static and fatigue by a novel experimental arrangement for panel-testing, after its numerical simulation in FE environment. The panel was manufactured using a 4th generation AL-Li alloy and its stiffeners were assembled by means of Friction-Stir-Welding (FSW). For the fatigue test, flaws were machined on different areas and the panel was subjected to a combination of pressure and axial loads that recreated realistic fuselage loading conditions. Load factor data from the related open literature, which have been recorded during typical flights were organized in exceedance diagrams, from which a fatigue spectrum representative of fuselage loading conditions was derived. The resultant spectrum consisted of pressurization-depressurization cycles, on which bending cycles were superimposed. FE static analyses were conducted to calibrate the spectrum's values. Subsequently, analytical predictions of crack growth were performed and successfully compared to experimental measurements of through-cracks located at critical locations.