Bone-inspired elastomeric graded structures for impact protection

Lightweight protective armour solutions have potential applications ranging from infrastructure cladding to personal protective equipment including sports helmets and body armour. This study considers a novel, bio-inspired protective armour solution. Trabecular bone-inspired structures, manufactured from thermoplastic polyurethane, are examined and the role of density grading in enhancing energy absorption and dissipation behaviour is assessed. Six configurations are studied, including five bio-inspired designs, two incorporating through-thickness density grading, and a Body-Centered Cubic (BCC) structure for comparison. The specimens are subjected to quasi-static compression, cyclic loading and low velocity impact tests. Energy absorption diagrams, based on quasi-static compression data, reveal that the most efficient structure depends on the specific energy of the threat. The graded structures perform moderately well across a large range of energy levels, outperforming the medium and high density ungraded structures at low energies and the BCC and low density ungraded structures at high energies. This balanced performance is also observed in the cyclic and low velocity impact tests. These findings highlight the potential of density grading to provide versatile protective capability under variable threat conditions and demonstrate the promise of bio-inspired architectures in the development of lightweight, flexible protective armour.