Investigation into soft body impact on laminated composites

Abstract

The impact of soft bodies such as birds on aircraft structures is a significant threat that leads to serious structural damage and economic loss to the aircraft industry. The leading edges are the foreparts of the aircraft and are always under the possibility of a bird strike. Leading edges are typically fabricated with GLARE laminate, tailored with alternatively arranged aluminium alloy and glass fibre epoxy layers. The approach followed in designing the leading edge is to design it to have a higher energy absorption capacity, thereby transferring less force to the supporting structure. Moreover, the deformation of the leading edge also to be reduced to protect its internal components. The present research aims to improve the bird impact resistance of fibre metal laminates used to fabricate the leading edges. This research is conducted in two parts; the first part is the optimization of the aluminium alloy parameters of the leading edge skin subjected to bird impact. The second part is the analysis of the strength and damage characteristics of different GLARE laminates under soft body impact. For this research, different bird modelling approaches are analysed to establish a soft body model consistent with theoretical and experimental predictions of actual bird strike events. The SPH soft body model with Mie-Grüneisen equation of state parameters exhibited a good correlation with an experimental test based on deformation patterns and pressure distribution characteristics. Then, the soft body impact simulation on the aluminium alloy (AA 2024-T3) wing leading edge is validated with a bird impact experimental test. Soft body impact simulations showed that the material parameters which influence the energy absorbing characterises of aluminium alloys are static yield limit, elastic modulus, strain hardening modulus and hardening exponent. The selected material parameters are optimized and validated with soft body impact analysis on the wing leading edge using Taguchi's L16 design of experiments with grey relational analysis. Quasi-static tension test simulations demonstrate that the mechanical properties of the optimized aluminium alloy are increased 20.84% yield strength, 20% tensile strength, and 25% deformation energy compared to AA 2024-T3. The tension test simulations on different GLARE laminates tailored with optimized aluminium alloy showed an average improvement of 20.87% aluminium alloy yield strength and 20.22% matrix failure strength compared to GLARE laminates tailored with AA 2024-T3. Observations of the soft body impact analysis concluded that the GLARE laminate with the glass/epoxy layers arranged between thinner aluminium alloy layers is most suitable for designing the leading edges.