Evaluation of an Elastomeric Honeycomb Bicycle Helmet Design to Mitigate Head Kinematics in Oblique Impacts.

Head impacts in bicycle accidents are typically oblique to the impact surface and transmit both normal and tangential forces, causing linear and rotational head kinematics, respectively. Traditional EPS foam helmets are effective at preventing many head injuries, especially skull fractures and severe TBIs (primarily from normal contact forces). However, the incidence of concussion from collisions (primarily from rotational head motion) remains high, indicating need for enhanced protection. An elastomeric honeycomb helmet design is proposed as an alternative to EPS foam to improve TBI protection and be potentially reusable for multiple impacts, tested using a twin-wire drop tower. Small-scale normal and oblique impact tests showed honeycomb had lower oblique strength than EPS foam, beneficial for diffuse TBI protection by permitting greater shear deformation and had the potential to be reusable. Honeycomb helmets were developed based on the geometry of an existing EPS foam helmet, 3D-printed with thermoplastic polyurethane, and full-scale flat and oblique drop tests performed. In flat impacts, honeycomb helmets resulted in a 34% higher peak linear acceleration, and 7% lower HIC15 than EPS foam helmets. In oblique tests, honeycomb helmets resulted in a 30% lower HIC15, and 40% lower peak rotational acceleration compared to EPS foam helmets. This new helmet design has the potential to reduce the risk of TBI in a bicycle accident, and as such, reduce its social and economic burden. Also, the honeycomb design showed potential to be effective for repetitive impact events without the need for replacement, offering benefits to consumers.