Optimising the tether angle of a head and neck restraint

Abstract

This study used models of a helmeted human and Hybrid III anthropomorphic test device (HIII ATD) head and neck to analyse the effects of changing the helmet to device tether angle on a head and neck restraint (HNR). Models were validated against literature before attaching a linear spring tether. Bayesian optimisation determined the optimal design parameters for three different tether setups. The validation results show that the human model may underestimate injury risk, even though it predicts a greater risk than the HIII ATD model. Therefore, the underestimated values of the human model may represent a conservative approach when used for device versus baseline comparative analysis. Conversely, the HIII ATD model underestimates the maximum head displacement. Since head displacement is required for the tethers to reduce injury risk, the human model may yield more beneficial results. Overall, improvements could be made to both models, but it is more important to tailor each model to the specific test environment. It was found that the human model’s optimal tether angle is 8.83 degrees below the horizontal and that there is 13 degrees’ difference between the optimal tether angles of the human and HIII ATD models. Therefore, HNR designs focused on the results from HIII ATD testing may be less effective for humans. Additionally, increasing the height of the tether’s attachment point on the helmet by approximately 35 mm may improve the HNR’s ability to further reduce the injury risk. Future work may include testing oblique impacts or using finite element models.