Application of Mechanical Metamaterials for Head Impact Protection in Recreational Snowsports

The 2022 Beijing Winter Olympics reached an audience of over 2 billion worldwide, boosting participation in recreational skiing and snowboarding to over 120 million people [1]. Due to its high-speed and technical nature, injuries have been found to be as high as 3.49 injuries per 1000 participation days [2]. Head injuries can account for anywhere between 20-54% of all snowsports injuries and are the most common cause of snow-sport fatalities [3,4]. Helmets have been shown to reduce the likelihood of a head injury by up to 60% [5]. Helmets currently used in skiing and snowboarding act in the same manner as those used in other sports, such as cycling, climbing and motorsport, by using a crushable layer (typically expanded polystyrene (EPS)) that reduces peak acceleration of the head during an impact. This crushable layer is less effective when subjected to oblique impacts. This is due to the foam being relatively resistant to shearing, increasing peak rotational accelerations. Recent advances in manufacturing and computer simulations have led to the possibility of designing helmets made from mechanical metamaterials. Within the world of metamaterials lie auxetic materials; these display a negative Poisson’s ratio and have previously demonstrated efficient impact energy absorption [6,7]. Additionally, the increased fracture toughness and synclastic curvature of auxetic metamaterials may be beneficial in sports helmets [8,9].