Crash concept for composite transport aircraft using mainly tensile and compressive absorption mechanisms

Abstract

Current design concepts for transport aircraft aim at increasing the aircraft efficiency and performance by the introduction of advanced composite materials, such as carbon fibre reinforced plastics (CFRP). These novel transport aircraft designs may show dissimilar dynamic response behaviour due to differences in failure modes and energy absorption characteristics compared with the current transport aircraft designs made of aluminium alloys. For that reason, crash concepts are being developed to utilise the high specific energy absorption of composite materials for predefined load conditions. In the context of this paper, crash concepts for future CFRP transport aircraft were developed in which most of the kinetic energy is absorbed by tension energy absorbers integrated in the cabin and cargo floor, and by crushing energy absorbers integrated in the cabin floor support struts. The developed crash concepts define mainly parallel activation of different crash devices to achieve smooth energy absorption for different crash load scenarios. Crushing of the energy absorbers integrated in the cabin floor support struts is controlled by a novel structural design in this fuselage area. So far, this research is limited to conceptual studies performed on the basis of a generic CFRP fuselage design. Numerical simulations using the explicit finite-element (FE) code Abaqus/Explicit were performed to derive qualitative and quantitative results for an assessment of the crash concepts. A hybrid FE/macro model approach was used that combines typical FE discretisation with macro models for main failure representation. Two different crash kinematics were considered which distinguish between the failure patterns of the frame structure of the lower fuselage shell. The simulation results presented in this paper in terms of energy plots, passenger accelerations, and crash sequences identify favourable crash performance for a load scenario with fully loaded cabin and an impact velocity of 9.1 m/s (30 ft/s). Significant amount of kinetic energy could be absorbed by tension loads. Parallel activation of crash devices resulted in smooth crash kinematics with reduced trigger loads. By utilisation of the cabin floor support strut area as an energy absorption zone, sufficient energy absorption capacity could be provided even for load scenarios with increased impact energies. The results, presented in this paper, are the basis for further detailed research work on this tension crash concept.