Matthias Waimer

Dynamic testing and modelling of composite fuselage frames and fasteners for aircraft crash simulations

In crash simulations of composite aircraft fuselage sections, frame breaking, skin bending and failure of mechanically fastened joints can typically be identified as major contributors to crash energy absorption. In order to generate a database for model validations, corresponding static and dynamic tests have been performed on coupon and structural element level to characterise the rate-dependent failure behaviour and energy absorption. Skin-bending, frame-bending and joint-failure tests under pull-out, bearing and peeling loads were performed on 977-2/HTS carbon fibre/epoxy specimens. On the one hand, effects of loading rate on the frame-bending behaviour could be observed. On the other hand, fastener failure did not appear to be depending on loading rate for the test speeds up to 10 m/s involved in this study. Adequate modelling methods in Abaqus/Explicit were derived and validated, and finally applied to a global aircraft crash simulation model.

Investigation of a crash concept for CFRP transport aircraft based on tension absorption

Transport aircraft made of carbon fibre reinforced plastics (CFRP) have to provide an equivalent crashworthiness compared to todays aluminium aircraft designs. However, CFRP structures typically show brittle failure behaviour under complex loading conditions and little energy absorption, whereas aluminium structures provide comparably high energy absorption due to their ductile failure characteristics. Improved crashworthiness for CFRP fuselages can be obtained by the installation of special crash devices, which are designed for energy absorption by progressive failure in compression, tension or bending. The realisation of crashworthy CFRP fuselage designs with the focus on compression or bending absorbers is often associated with significant mass penalty compared to the purely static sizing of the corresponding fuselage structure. In this context, an alternative crash kinematics was developed and numerically investigated in which most of the kinetic energy is dissipated by tension absorption in the sub-cargo area of a fuselage structure. The numerical study was performed on the basis of a purely vertical impact with a two-bay fuselage section using the explicit finite element (FE) solver Abaqus/Explicit. The simulation results show for the developed crash kinematics several advantages, e.g. reduced mass penalty, with the tension absorption concept compared to crash concepts that use energy absorption by progressive crushing in the sub-cargo area.

Crash concepts for CFRP transport aircraft – comparison of the traditional bend frame concept versus the developments in a tension absorbers concept

ABSTRACT Due to their inherently brittle behaviour, carbon fibre reinforced plastics (CFRP) structures demand for a specific design to achieve appropriate crash energy absorption compared to classical metallic fuselage designs. In this paper, experimental as well as numerical studies on two different crashworthy designs are presented. The first concept aims to absorb the crash energy by crushing of CFRP components below a reinforced cargo cross beam in combination with further energy absorbing devices in the lower side shell. The feasibility of this concept was in the meantime proven by tests at the coupon and structural element level. An alternative crash concept making use of energy absorption in so-called tension absorbers in the passenger and cargo floor structure was developed and assessed with the focus on a reduction of structural mass in combination with improved concept robustness. This paper provides a summary of the performed research work and discusses the context of the concept development. Details on the individual research tasks can be found in further publications which are given in the references.