Towards concussion prevention in ice hockey: mechanical metamaterial liners and helmet assessment

Ice hockey has one of the highest concussion rates in sport. During player-to-player collisions, the most common concussive scenario, helmets have been shown to offer limited protection. Helmet testing that is representative of the broad range of potential head impacts requires extensive specialist equipment, while certification standards are currently not assessing the impact scenario that most commonly causes concussions in ice hockey. Consequently, helmets protect well in the scenario they are certified and designed for – falls onto stiff surfaces – but provide limited protection during other commonly occurring impacts, especially impacts with more compliant bodies. Due to the wide range of injurious head impacts in ice hockey, it is challenging to develop a helmet that protects well in all scenarios. The aim of this programme of research was to develop a simplified test method, capable of replicating common ice hockey head impacts. Then, to investigate the capabilities of a mechanical metamaterial to enhance protection during collisions without compromising protection during more severe head impacts. A novel test method, utilising laboratory equipment that is available to most researchers with an interest in impact protection, to replicate head impacts in ice hockey was developed and validated. It has been shown that a free-fall drop test method, with interchangeable impact surface orientation and compliance, can be used to create impact events that are representative of a range of common ice hockey head impacts. This newly developed test method can produce kinematic responses within less than 10% of key metrics obtained by current best practice methods to replicate ice hockey collisions and may facilitate widespread and more thorough testing in academic research and modifications to current test standard procedures. A series of investigations were conducted to assess the potential of a mechanical metamaterial, comprising bi-beam structures, with an adaptive response to specific impact scenarios. Testing and modelling of individual bi-beams, unit cells, and cellular structures of bi-beams suggest a cellular structure, comprising bi-beams, can be developed by arranging unit cells relative to each other between two stiff sandwich plates. It has been shown that controlling the direction of buckling and the associated contact situations, can cause an abrupt switch in stiffness (~155 – 180%) in axial direction. Applied as a liner in an ice hockey helmet, this could achieve enhanced protection against an additional cause of injury – collisions – without compromising the performance in the scenario the helmets are currently designed for – falls. Dimensional scalability facilitates a wide range of possible designs and fields of application. This programme of research contributes to the body of knowledge of head impact testing and helmet technologies to better protect players. Findings could help in developing better helmets that protect players against a wider range of head impacts which in turn would reduce concussions and make participation safer.