Fatigue Behaviour of Stringers in Stiffened Panels.
Final technical rept.,
PISA UNIV (ITALY) INST OF AERONAUTICS
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The investigation reported upon in this report was undertaken to study methods for evaluating stringer fatigue endurance in riveted stiffened panels which crack in the sheet cover under constant amplitude fatigue loading. The methods are aimed to correlating the crack length in the sheet cover 1, at which a stringer begins to crack, with the load conditions, the relevant panel geometric dimensions and the type of material. Two different approaches have been tried, both based on the use of the Miners rule. The first is based on the assumption that a stringer in a cracked stiffened panel resembles a lap joint as far as its fatigue behaviour is concerned. The proposed approaches were than evaluated on the basis of the results of fatigue tests on 59 riveted stiffened panels differing in geometric shape dimensions and load conditions. The panels were constructed of 2024-T3 and 7075-T6 aluminum alloys utilizing different types of stringers single, double strip and formed section stringers. All the stringers were hand riveted to the sheet cover utilizing round head as well as machine countersunk rivets. The experimental data indicate that the lap-joint approach work satisfactorily on the contrary the other approach requires further improvement, particularly a better understanding of the rivet forces redistribution caused by local plastic deformation around some rivet hole.
- Structural Engineering and Building Technology