Sports related injuries and in particular head injuries for American football players have been under intense public scrutiny in the recent years. The presented study was developed focusing on material system solutions that can be employed for impact mitigation purposes. The central hypothesis is that a multilayered structure can provide enhanced energy damping with respect to impact when impedance mismatch and energy dissipation mechanisms are tuned. Impedance mismatch between adjacent laminate layers of the structure influences the reflection of the propagating wave. Optimizing the impedance mismatch between the laminate layers creates a virtual echo chamber for the pressure wave generated by the impact: the high internal reflection potential of the structure enhances the residence of the energy within a viscoelastic material layer, where the energy dissipation mechanism contributes to the mitigation of the effects of the impact. The effects of these two mechanisms, impedance mismatch and energy dissipation, are quantified and presented. A novel and simple approach to evaluate impact mitigation parameters of material systems in a lab-scale environment is used: this employs a Newton's cradle to correctly and accurately account for all input and output energy components in an impact, therefore assessing the level of mitigation. All the laminates of this research are composed of commonly available polymeric materials. As much as 90% of the theoretical transferrable energy can be dissipated tuning impedance mismatch at the various interfaces and energy dissipation of the viscous material in multilayer specimens. Statistical analysis of transmission and dissipation data shows that these mechanisms are of primary importance for mitigating impact forces, while other factors are of secondary importance. The most significant model is obtained when both impedance mismatch and dissipation are accounted for. The effect of increasing internal reflection within the most dissipative layer of the structure results in the most significant variable for overall mitigation of energy transmission. A dynamic finite element analysis technique has also been developed that models the time evolution of energy within the laminate structure following an idealized impact, and verifies the experimental results.

Multi-layered structure approach for impact mitigation

2019 Spring National Meeting

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