Mechanical metamaterials for sports helmets: structural mechanics, design optimisation, and performance

Abstract

Sports concussions are a public health concern. Improving helmet performance to reduce concussion risk is a key part of the research and development community response. Head impacts with compliant surfaces that cause long duration moderate or high linear and rotational accelerations are associated with a high rate of clinical diagnoses of concussion. As engineered structures with unusual combinations of properties, mechanical metamaterials are being applied to sports helmets, with the goal of improving impact performance and reducing brain injury risk. Replacing established helmet material (i.e., foam) selection with a metamaterials design approach (structuring material to obtain desired properties) allows development of near optimal properties. Objective functions based on up to date understanding of concussion could be applied to topology optimisation regimes, when designing mechanical metamaterials for helmets. Such regimes balance computational efficiency with predictive accuracy, both of which could be improved under high strains and strain rates to allow helmet modifications as knowledge of concussion develops. Researchers could also share mechanical metamaterial data, topologies and computational models in open, homogenised repositories, to improve the efficiency of their development.

Focus on smart materials and structures for sporting protective equipment

“…The UK recently highlighted the importance of reducing sporting concussions in a review by a parliamentary select committee [1], and other nations and sporting governing bodies have raised concerns. As such, sports injuries, particularly concussions, and smart systems developed to help manage risks, are considered important by scientists, governments, governing bodies, and sports participants [2].…”

“…Adventure sports present a different challenge to team sports, in that environments and participant activity are harder to monitor and control. There have been calls amongst the scientific community for broader testing to reflect loading conditions in the wider range of potential collisions and falls [2]. For example, some climbing helmets offer better protection in locations that are impacted under more severe impacts during certification tests [4].…”

“…It is well known that clinical diagnosis of concussion is often associated with glancing blows and impacts with compliant surfaces. These induce longer duration, moderate head acceleration and rotation, that are often not measured in helmet certification standards [2]. While relatively linear acceleration over a short duration is well covered by helmets, there is a flourishing body of research and development around smart systems to adapt between different head impacts.…”

“…Processes to tune the response of helmets are key to their continued development [2]. Adams et al demonstrate an efficient approach to parametrically optimise a pre-buckled honeycomb structure using a finite element approach [7].…”

“…The focus issue highlighted the strong interest in smart materials for sporting impact protection. Noted challenges include adapting between the wide range of requirements; changing user groups, body types, and different types of impacts [2][3][4][5][6][7][8][9][10][11]. The impact or loading conditions and response that should be targeted when selecting or optimising effective smart material properties are developing with knowledge of injury risks [2][3][4]11].…”