Biaxial testing of cruciform specimens representing characteristics of a metallic airplane fuselage section

Based on biaxial tests with cruciform specimens, the scenario of fatigue cracks in the upper fuselage section between the wings and the tail unit of a commercial single aisle aircraft has been studied. Two different types of specimen were designed, namely for the scenario of a circumferential crack across a broken stringer and for a longitudinal crack parallel to the stringers. With crack length up to 2a ≈ 610 mm, maximum mode I stress intensity factors of 160 MPa√m were obtained for the commercial aluminum alloys AA2024-T351 and AA5028-H116. All experiments were supported by digital image correlation to obtain the actual deformation fields of the specimens. Based on these data stress intensity factors and J integrals were computed with a line integral procedure. Furthermore, plastic zone and crack closure effects were studied.