Crashworthy response of fibre metal laminate top hat structures

Abstract

The axial crushing response of fibre metal laminates (FML), in particular GLARE top-hat structures, has been investigated using experimental and numerical techniques, which are reported in this paper. Crushing performance (crush force, energy absorption) was evaluated for formed GLARE top-hat structures as an analogue for an energy absorbing aircraft sub-floor structure. A numerical simulation methodology was established which could accurately predict the crushing performance of GLARE top hat structures using commercial explicit finite element (FE) analysis tool LS-DYNA. Material characterisation at coupon level was conducted to measure the appropriate material properties required for the model to achieve good predictability. The successful demonstration of GLARE energy absorbing structures widens options to enhance crashworthiness; numerous applications of such GLARE structures could be envisaged, including reinforcement of aircraft sub-floors.The crushing modes of GLARE top-hat structures were found to be complex, exhibiting mixed-mode failure which was a combination of the individual constituent failure modes. The metallic layers plastically deformed by folding and tearing while the composite layer failed with a wide range of failure patterns i.e. splaying, delamination and cracking. The top hat structures, most importantly, crushed in a stable progressive manner making them suitable for energy absorbing (EA) applications. The GLARE top hat structure’s crushing response is superior to its bare metal equivalent.Given the complexity of the FML crushing process, there is tremendous scope for optimisation of the laminate parameters to maximise energy absorption. The good agreement obtained between the numerical and experimental results highlights the benefits of using simulation to predict the overall crashworthiness of FMLs.