Energy-Absorbing Origami Structure for Crashworthiness Design

This thesis presents an experimental and numerical investigation on the novel origami-patterned tube which is recognised as a promising energy absorption device. Its peculiar buckling mode leads to high performances in terms of specific energy absorption (SEA) and crushing force efficiency (CFE). The mode is triggered by prefolding a polygonal tube following an origami pattern, which is designed to act as geometric imperfection and mode inducer, in order flatten the buckling force peak and to trigger a predictable and efficient “diamond crushing mode”. The current work represents the first step in evaluating a potential application of origami tubes as crashworthy components on a Personal Air Vehicle, currently under development at the hosting university. Two approaches are employed for this preliminary study: First, a series of quasi-static crushing tests are performed on origami tubes with different materials and geometrical features. Specimens in SUS316L and AlSi10Mg are produced through Additive Manufacturing (AM). It allows to conveniently produce few samples with a complex shape. Finite Element Analysis (FEA) and Direct Image Correlation (DIC) are employed for a better insight into the complex crushing behaviour. The Aluminium tube shows a brittle behaviour while SUS316L tubes have extremely promising performance until local crack happens. Limits stemming from the employment of AM are explored and a new geometry is designed to avoid cracking. Second, a numerical design exploration study is carried out to assess the sensitivity of origami pattern features over the energy-absorption performance. ANSYS Autodyn is utilized as explicit FE solver and the DesignXplorer tool for correlation and optimization. Benefits of new patterns are investigated through geometrical optimization, and an improved geometry is eventually proposed. The pattern stiffness is tuned to account for the external boundary conditions, resulting in a more uniform crushing behaviour. The optimised pattern force trend is maintained similar to the reference geometry while SEA is incremented by 51.7% due to a drastic weight reduction in areas with lower influence on post-buckling stiffness. The origami tube behaviour under dynamic loading, and the differences with the quasi-static case are also explored.