The application of the damage tolerance philosophy to aircraft fuselages in frequently based on the two-bay skin crack criterion. Due to the broken central stiffener the increased loading of the skin leads to fatigue crack propagation into the two adjacent bays. It has to be guaranted that the two crack tips do not become critical at least not until they reach the positions of the next stiffeners. Information on this is provided by so-called residual strength diagrams. The criterion is that the applied loading always should be smaller than the residual strength. The goal of the present paper is comparison of two R curve based methods for determining residual strength characteristics. This is done both for a small curved panel and for a fuselage detail. An overview on methods for determining the residual strength of thin wall configuration is provided. The KR concept (fracture resistance curve analyses) yielded higher residual strengths at crack lengths smaller than about 80 % of the stringer distance, s, for small panel and at crack lengths smaller than about 65 % for the fuselage detail. Above these values definite statements are not possible for different reasons although the impression is that KR, compared to SINTAP, yields at least no higher values anymore. one of the reasons for the uncertainty consists in the validity limits of the delta5 concept. Valid experimental R curves were obtained only up to a maximum stable crack extension of about 130 mm which accordingly limited the SINTAP residual strength curve of the fuselage detail. Another point was that for both geometries the KR calculations were terminated when the effective crack length became larger then the distance to the adjacent stringer, S.
Aspects of damage tolerance of aircraft fuselage structures
2008
7 Seiten, 10 Bilder, 6 Quellen
Aufsatz (Konferenz)
Englisch
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