Fatigue Crack Growth Assessment of Skin-Stringer Panels having Different Crack Scenarios

Skin-stringer structures are widely used in aerospace industry. Such structures are susceptible to initiation of fatigue cracks because of stress concentration around the rivet holes. In this study, experimental and numerical fatigue crack growth analysis of different crack scenarios in skin-stringer panels is investigated. Three 2024-T3 aluminum substructure test specimens are designed, fabricated and assembled well. The wire-cut machine is used to prepare initial flaws from rivet hole and under few number of constant amplitude cyclic loading the initial crack sizes are finalized. The scenarios include initial crack in the skin only (2a=10 mm), the previously described cracked skin besides one side cracked stringer (a=3.0 mm) and double side cracked skin (2a=6 mm) besides cracked stringer (a=3.0 mm). The tests are conducted under the same loading condition and the crack growth is monitored until failure of the specimens. The results of a-N are obtained for mode I cracks in skin and stringer. Also the stress intensity factors are extracted using ABAQUS commercial software and using walker equation the life of the structure are calculated. The numerical results are in good agreement with test data conservatively so the verified numerical procedure could be used for real structure. The comparison of results shows that existence of crack in both skin and stringer reduces the load carrying capability of the structure with respect to the state of crack in skin only. Also the stringer flange failure causes rapid crack propagation in skin and decrease the life of the structure.