Evaluation of a Combat Helmet Under Combined Translational and Rotational Impact Loading

Traumatic brain injury (TBI) is a health threat to military and civilian populations. Recent biomechanics research suggests that rotational kinematics are a significant cause of brain deformation during blunt impact events to the head. Military helmet blunt impact test methods evaluate protective capacity in terms of peak translational head acceleration using a drop impact format. This study investigated the utility of a different impact format based on a pneumatic ram to induce combined translational and rotational head motion to evaluate blunt impact protection in combat helmets. This test method has been adopted for certification tests related to professional and amateur football helmets. Impacts were performed on a Hybrid III head and neck assembly in the bareheaded and helmeted condition for a total of 126 impacts. Translational and angular acceleration was recorded along with high-speed video for each impact. A multibody model that relates the head kinematic response to brain strain, referred to as Diffuse Axonal Multi-Axis General Evaluation, was used to estimate the extent of injury resulting from impact. Results indicated that, on average, the Advanced Combat Helmet reduces headform translational and rotational kinematics compared to the response of the bareheaded case. Impacts to the rear of the head, for both bareheaded and helmeted impacts, resulted in the greatest predicted brain strain. Furthermore, rotational velocity showed a stronger correlation to predicted brain deformation than rotational acceleration under these impact conditions.