Bicycling is a popular activity around the world and a frequent source of head injury. Traditional expanded polystyrene (EPS) foam helmets reduce the risk of skull fracture (caused by the radial contact forces), but do not reduce the risk of diffuse traumatic brain injury (TBI), such as concussion (caused by rotational motion of the head from the tangential forces). Hexagonal honeycomb could be suitable for head protection due to its energy absorbing capabilities and anisotropy, where it is weaker under shear loading to reduce rotation. Therefore, a helmet design was proposed that is made of hexagonal honeycomb with 5-7 defects to accommodate the curvature of the head and made of thermoplastic polyurethane (TPU) to be potentially reusable for multiple impacts.

The properties of flat honeycomb samples were explored, where 3D-printing was employed for rapid prototyping. Two arrangements of 5-7 defects were tested and shown to decrease the strength of the honeycomb. A relative density most suitable for head protection was determined based on the results of quasi-static compression and shear testing.

As real-world accidents occur at higher rates, dynamic impact tests were performed on the chosen honeycomb design, with various impact conditions. Honeycomb showed greater anisotropy than EPS foam, which is beneficial for diffuse TBI protection, and potential to be reusable. The results were used to scale the honeycomb design for dynamic impact conditions. A helmet model was developed based on the geometry of an existing EPS foam helmet and helmet prototypes were 3D-printed to be used in future drop tower impact tests.

This work presented a new helmet design that has potential to reduce the risk of sustaining TBI in a bicycle accident, and as such, reduce its social and economic burden. As well, the honeycomb helmet design showed potential for reusability, which would have substantial benefits to consumers.