25. Padding Dynamic Stiffness Using Impedance Modeling of Helmet-Head System

The dynamic performance of helmets in terms of the transmitted force from the helmet to the head is investigated in this paper using techniques in nonlinear vibration analysis. Impedance modeling is used to describe the interaction between the helmet and head-neck subsystems, which are each assumed to behave linearly. The focus of this study is on the influence of padding inside the helmets on the attenuation or amplification of forces applied to the helmet as these forces are transmitted through the padding into the head. The experimental results for vertical only excitation and response measurements indicate that dynamic stiffnesses (including both static and dynamic transfer impedance) for three types of padding were different with certain pads exhibiting less dynamic transfer impedance in certain frequency ranges. The experiments also indicate that these dynamic stiffnesses vary as a function of the amplitude of the forcing function suggesting that the padding behaves nonlinearly with respect to the amplitude of excitation.