Isolated head-neck assemblies falling on guided rails do not recreate head impact kinematics of full body falls: an...

Fall induced traumatic brain injury (TBI) accounts for approximately 20% of reported TBI in military personnel. Consequently, evaluating military headgear with methods that provide an accurate representation of real-world falls is important to ensuring test fidelity. Guided drop towers aim to provide such a representation, yet are constrained to a single degree-of-freedom and, typically, exclude the mass of the full body from the system. The present work sought to test the hypothesis that guided falls and full dummy falls are kinematically similar. If not, then document key differences and implications for helmet assessment. An impact study was conducted for two impact velocities (3.0 m/s, 4.5 m/s) onto a rigid impact surface at 30° (body near supine) and 75° (body nearly upright, with head down) with measures of head center of gravity linear acceleration, angular acceleration, and angular velocity. A guided drop carriage with variable mass and Hybrid III head-neck were compared to a full Hybrid III mannequin, both simulating helmeted impacts. Results of the impact study showed that a guided drop tower yields varying estimations of peak kinematics, relative to a full surrogate. While the results do indicate that guided linear drops are adequate for assessing impact attenuation of military helmets, they do not recreate the helmet, head, and neck mechanics of a full ATD drop across all of the tested configurations for the measures of interest. Kinematically, a drop tower is not a direct substitute nor predictably correlated model for a full-sized dummy when assessing military helmets.