Finite element-based optimisation of an elastomeric honeycomb for impact mitigation in helmet liners

Abstract

Finite element simulation was used to analyse the response of an elastomeric pre-buckled honeycomb structure under impact loading, to establish its suitability for use in helmet liners. A finite element-based optimisation was performed using a search algorithm based on a radial basis function. This approach identified optimisation configurations of a pre-buckled honeycomb structure, based on structural bounds subject to impact loading conditions. Furthermore, the influence of objective function, peak acceleration and head injury criterion was analysed with respect to the resultant mechanical behaviour of the structure. Numerical results demonstrate that this class of structure can exceed the performance threshold of a common helmet design standard and minimise the resultant injury index. Experimental testing, facilitated through laser sintering of thermoplastic polyurethane powder, validated the output of the numerical optimisation. When subject to initial impact loading, the fabricated samples satisfied their objective functions. Successive impact loading was performed to assess the performance and degradation. Samples optimised for peak acceleration demonstrated superior performance after stabilisation, relative to their initial response. The culmination of this study establishes a numerical design pathway for future optimisation of candidate structures for head impact protection. Furthermore, the optimised pre-buckled honeycomb structure represents a new class of energy absorbing structure, which can exceed the thresholds prescribed by the design standard.