Predicting the kinematic response of a helmeted headform during oblique impacts

Abstract

A total of 160 oblique impact tests were performed to study the relationship between the kinematic response of a helmeted headform and the impact severity caused by a change in speed (Group 1) and anvil angle (Group 2). In this study, the kinematic response of a helmeted headform was evaluated by measuring its linear acceleration, rotational acceleration, and rotational velocity. In Group 1, a football helmet was tested at 45° anvil angle at four different impact speeds ranging from 4.5  to 7.4 m/s on five impact locations. The results showed that, for all cases, the relationship between the impact speed and helmeted headform kinematic response was linear, with an average R2 value of 0.98. At each impact location, a prediction line was generated using the data points for the lowest and highest speeds. For the speeds of 5.5  and 6.5 m/s, the prediction of the helmeted headform kinematic response was validated with an average error of 4.7%. In Group 2, the helmeted headform was tested at 5.5 m/s impact speed at six different anvil angles between 15° and 55°, and the response was fitted with a second-degree polynomial (curve) with an average R2 value of 0.96. The kinematic response of the higher and lower impact speeds was obtained experimentally for one angle, and the fitted curve for 5.5 m/s was offset to pass through the obtained kinematic response. The predicted helmeted headform kinematic response was experimentally validated, and the average error was found to be 8.3%. The results showed that it is possible to predict the kinematic response of a helmeted headform by interpolating or extrapolating the data without having to perform an additional impact test. An analysis of other research works also showed similar predictable behaviour for headform equipped with other helmet models. Therefore, the number of tests during the process of evaluating helmet performance can be reduced.