3D-auxetic elastomeric cellular structures for impact protection

Abstract

Lightweight protective armour solutions have potential applications ranging from infrastructure cladding and damage tolerant aerospace composites to sports helmets and body armour. Elastomeric cellular structures are a promising candidate solution and with advances in 3D-printing technology, ever more complex geometries can be explored in the pursuit of enhanced performance. Auxetic structures, which exhibit negative Poisson’s ratio behaviour and reported improved mechanical properties are of interest. Recently, 3D-auxetic structures have demonstrated the potential to outperform their 2D counterparts. This work investigates the performance of four candidate elastomeric cellular structures, 3D-printed in thermoplastic polyurethane (TPU): one non-auxetic, two 2D-auxetic and one 3D-auxetic. The structures are subjected to quasi-static compression, cyclic compression and low-velocity impact tests. Energy absorption diagrams, based on quasi-static compression data, are produced which demonstrate that the choice of most efficient energy absorbing structure depends on the specific energy of the threat. It is found that the 3D-auxetic re-entrant honeycomb structure outperforms all others for specific energies greater than 13.3 mJ/cm3. Cyclic compression tests demonstrate excellent recoverability, and thus reusability of all structures. Hysteresis is observed for all specimens, increasing with increasing maximum strain. Generally, the 3D-auxetic structure provides the greatest energy dissipation. The behaviour observed in the low-velocity impact tests appear consistent with the trends identified in the quasi-static tests. The 3D-auxetic structure is the best choice for absorbing high impact energies since it results in a lower stress being transferred when subject to an impact energy which causes densification. This work demonstrates the potential for 3D-auxetic elastomeric cellular structures to provide superior protective performance.