Damage delocalisation in skeletal muscle-inspired hierarchical armoured structures for impact protection

We propose a skeletal muscle-inspired hierarchical structure for the alumina ceramic layer in ceramic composite armour structures to achieve greater energy dissipation under impact. We mimic the nano-architecture of skeletal muscle tissues by introducing hierarchy both with self-similarity using a fractal design, and without self-similarity in the hierarchical levels to explore the function of hierarchy in improving the protective capability of the armour structure. The numerical simulations showed that increasing the structural hierarchy can boost stress reduction by up to 30% for the third order hierarchical structure without self-similarity compared to the first order hierarchical structure with the same weight. The underlying mechanism that increases the impact resistance in the higher order hierarchical structures is the delocalisation of the damage over multiple crack paths in the different hierarchical levels. This bio-inspired concept can be used to generalise the design of future impact-resilient structures which optimise the suppression of stresses and reduce the associated weight penalty for use in protective gear and armoured structures.