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Advanced structure concepts for closed metallic stringer geometries regarding lower and upper fuselage structures

: Dittrich, D.; Brenner, B.; Kirchhoff, G.; Reim, A.; Horst, P.; Sähn, M.; Hackius, J.

VDI-Wissensforum GmbH:
EUCOMAS 2009, 2nd European Conference on Materials and Structures in Aerospace. CD-ROM : 1-2 July 2009, Augsburg, Germany
Augsburg, 2009
ISBN: 978-3-00-027303-2
15 S.
European Conference on Materials and Structures in Aerospace (EUCOMAS) <2, 2009, Augsburg>
Fraunhofer IWS ()
Finite Elemente Methode (FEM); Flugzeugrumpf; Knicken; Längsversteifung; Laserstrahlschweißen; Schweißbarkeit; Schweißverbindung; statische Ermüdung; statische Festigkeit; Struktureffekt; Struktureigenschaft

Future metallic structures will not just compete for reduced weight and lowered manufacturing costs, but also for satisfying overall structure requirements which will become likewise challenging. On the stringer side, Airbus successfully established laser beam welded L-stringer-skin-joints in the lower fuselage for about a decade. Within the german LUFO III research program, the work package IMER was used to develop and test advanced laser weldable future panel designs containing unconventional stringer. Current L-stringer were designed with the objective of weldability and the capability of structural weight saving. New fuselages skins will be thinner and the stiffeners will be exposed to higher loads in the lower fuselage considering buckling scenarios. On the upper fuselage, damage tolerance requirements of welded stringer-skin-connections emerge as an engineering challenge for an integral structure. This paper presents the results of an interdisciplinary research project, that combined FE-modeling for structural stringer geometry optimization, the evaluation of manufacturing requirements regarding welding technologies and the experimental characterization of the structure behavior. It can be shown, that advanced structures containing so called Y- and Ustringers will provide higher static capacity against buckling as well as a better damage tolerance behavior compared to the state of the art L-stringer. Particular attention was paid to FE-modeling to optimize structural geometries before production of hardware and mechanical experiments as well as to explain final results. The higher stiffness against bending and buckling of the Y- and U-stringer compared to the L-stringer would allow reducing the total amount of stringer in the structure by increasing the pitch distance. That would also lead to a shorter manufacturing process and would save manufacturing costs. Additionally, the improvement of tolerance against welding defects for laser beam welding would also help to reduce the manufacturing costs by shortening the process chain about the repair step.