Development of new cycling helmet standard test for improved head impact protection

Cycling is a popular sport and an easy way of commuting with many health benefits, but also involves risks, like head injuries. Medical data and studies on accident reconstruction have established the common understanding that most cycling accidents involve oblique impacts which lead to injuries due to rotational loading conditions induced on the brain. Conventional helmets lack dedicated mechanisms that aim at rotational acceleration mitigation, since it is not yet a requirement in helmet testing standards. As a result, bicycle helmets need to evolve to better protect against such injuries. At the same time, certification processes should keep up by accurately replicating these accident conditions. Even though there are currently many different technologies available promising to reduce the effect of rotational acceleration during an impact, the lack of an official testing standard means that their evaluation is based on customised set-ups that may differ from each other and may not be sufficiently representative of real accident conditions. The goals of this PhD research were multiple as it is aiming to advance the pre-existing insights in oblique impact testing and standards in order to develop, verify and apply a designing method for bicycle helmets, compatible with these new testing standards. First, a novel testing set-up and process was further developed, where ordinary helmets but also more advanced helmets, designed for reducing rotational acceleration, can be tested. For its validation, motion tracking was utilized and combined with acceleration curves, leading to better repeatability and additional insights in the impact kinematics. The process defined is easy to use, but also capable of imitating the impact conditions during a bicycle accident. Second and in parallel with the first goal, different parameters that influence the biofidelity of the testing process were studied. The two most important that were investigated were the presence of a neckform and a scalp. Results showed that both parameters can have significant influence on the kinematics of the impact. They demonstrate the need for further research and development of biofidelic surrogates to corroborate and extend the current findings before implementing them into a final testing protocol. Third, the tools for a methodology to design bicycle helmets had to be developed, certifiable by the defined testing process, yet appealing and easily adopted by the consumers. Towards that end, the development and validation of a virtual FE model of an impacting helmet was essential, with the incorporation of adequate material models and data. This would require: 1) A newly developed test method to perform tensile tests on EPS foam at different strain rates. Results were used to define a density and strain rate dependent material model, applied in the FEA in combination with a crushable foam material model. 2) The development and verification of a FEA model of the head-helmet assembly, using impact experiments. Fourth, the developed methodologies and gained insights were applied into a novel concept. The concept was patented.

Jaar van publicatie:2021

Toegankelijkheid:Closed