Comparison of damage characteristics of adhesively bonded and rivet-connected evtol wing under bird-strike

The advent of electric aircraft, including urban mobility vehicles, has brought renewed attention to the structural integrity of associated lightweight composite airframes. The evolution of composite passenger aircraft demonstrates the advantages of the use of these lightweight materials yet there are still certain structural components which are more susceptible to off-design loading than their metallic counterparts. For example, wing and empennage leading edges, are particularly susceptible to bird strike and are usually still made out of aluminium. Nonetheless, there are certain advantages in pursuing a composite leading edge, such as further weight reduction and enhanced laminar flow. In doing so, it becomes imperative to ensure that its energy absorption characteristics are well understood and can be predicted using computational modelling to reduce the extent of physical testing. For the case of fixed leading edges, energy absorption is likely to be dependent on the way that this leading edge is assembled and attached to the front spar, since the joint itself is a potential energy-absorbing mechanism. In this computational study two approaches are investigated; (i) the leading edge is adhesively-bonded, and (ii) riveted (Fig 1). Soft body impact, to simulate a bird strike, is achieved using Smooth Particle Hydrodynamics (SPH) which is preferred over the Arbitrary Lagrangian Eulerean (ALE) method. The analyses in this study are performed using an explicit finite element solver LS-DYNA. In this article, a composite sandwich wing model, made of unidirectional carbon-fibre polymer composite and a phenolic-based honeycomb core material, is impacted with a soft body mass in accordance with international standards and special conditions given by EASA. These standards are CS-25.631 and the special conditions for eVTOLs. The lay-up of the wing model includes unidirectional prepreg materials pertain to the face and back skin as well as the aforementioned attachment region which connects the spar and the leading edge. The substitute bird model (soft body mass) is configured using a well-defined equation of state model and the properties of homogenous gelatin.