Sensitivity study of multi-stable metamaterials applied in helmet liners

As additive manufacturing becomes more efficient, many opportunities arise where conventionally manufactured structures can be replaced by 3D printing systems with application-specific properties. In protective helmets, an impact is usually dampened by a foamed inlet that cannot be used again once subjected to a crash. While ranges of the foam microstructure distributions can be influenced by the manufacturing process, precise tailoring of the microstructure is unfeasible. In contrast, additive manufacturing enables the use of cellular structures with enhanced and tuned properties. In this study, the focus is on multi-stable metamaterials as these structures can achieve energy absorption through significant geometrical changes. High non-destructive energy absorption can be realised as the main energy absorption is provoked by elastic buckling, which may allow the helmet to be re-used. The properties highly depend on geometrical parameters. Instead of a foam inlay, we propose multi-stable hexagonal prisms for helmet applications. There, multi-stable elements with a specific shape are arranged in a hexagonal shape. Different configurations of the structures were designed and simulated to investigate the influence of geometric parameters on the multi-stable behaviour and energy absorption properties. The finite element simulations showed that the properties are highly adaptable. Tailoring and optimising the cell parameters can make the proposed structures well-suited for energy absorption in helmet applications.