AIRCRAFT SANDWICH STRUCTURES WITH FOLDED CORE UNDER IMPACT LOAD

8th International Conference on Sandwich Structures ICSS 8 A. J. M. Ferreira (Editor) FEUP, Porto, 2008 AIRCRAFT SANDWICH STRUCTURES WITH FOLDED CORE UNDER IMPACT LOAD S. Heimbs * , P. Middendorf * , C. Hampf † , F. Hähnel † , K. Wolf † * EADS Innovation Works Germany 81663 Munich, Germany e-mail: [email protected], web page: http://www.eads.net † Institut für Luft- und Raumfahrttechnik Technische Universität Dresden Marschnerstraße 32, 01307 Dresden, Germany web page: http://www.tu-dresden.de/mwilr Key words: Sandwich structures, Folded core, Low velocity impact, Dynamic simulations. Summary. Folded structures made of composite materials have gained interest in the aerospace industry as a promising sandwich core structure. In this paper the mechanical behaviour of such a sandwich structure with a folded core made of carbon fibre-reinforced plastic under low velocity impact loads is investigated experimentally and numerically. At first the core properties under compressive and transverse shear loads are characterised building a basis for the validation of the simulation models. Low velocity impact tests under various energy levels are described with respect to the evaluated damage of face and core and are finally simulated with LS-DYNA. These simulations were used to investigate the influence of different parameters on the impact behaviour numerically. 1 INTRODUCTION Sandwich structures with composite faces and a cellular core are known for their outstanding weight-specific stiffness and strength properties and have therefore been used in aircraft structures for many decades. Examples are aerodynamic fairings (belly fairing, leading and trailing edge fairings) or control surfaces (rudders, ailerons) [1]. Since weight reduction is a main driver in aircraft design, the application of sandwich structures is constantly increasing. Even concepts for the utilisation of sandwich structures in the primary structure, i.e. the aircraft fuselage, have been developed in the past for large airliners [2]-[4] and have already been realised in smaller business jets [5]-[8]. One main issue is to identify an adequate sandwich core material for these purposes. Nowadays, Nomex ® honeycomb cores are prevalently used in aircraft sandwich structures because of their favourable mechanical and fire safety properties. But these closed honeycomb cells can lead to an inclusion and accumulation of condensation water, which increases weight and reduces the properties [8]- [10]. Therefore, folded sandwich core structures have gained interest of the aerospace industry in the past years as an alternative allowing for a ventilation through drainage 369

AIRCRAFT SANDWICH STRUCTURES WITH FOLDED CORE UNDER IMPACT LOAD

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sandwich structures

folded core

low velocity impact

dynamic simulations