Design of micro- and macro-scale impact mitigating material toward the development of helmet padding design criteria

Each year an estimated 1.7 million people suffer from traumatic brain injury (TBI), of which 52,000 die, 275,000 are hospitalized, and 1.365 million are treated and released from an emergency department. Approximately 75% of all reported TBIs that occur are concussions or other forms of mild traumatic brain injury (MTBI). Concussions in football have recently received heightened attention due to prevalence at the professional, collegiate, and high school levels. With research pushing the boundaries of understanding the long-term effects of neurotrauma, there is high demand to develop better protections against traumatic brain injury. Current helmet designs are limited by a lack of novel energy-absorptive materials and outdated testing standards, which focus on a single parameter for design, as opposed to a systems approach. Ideally, energy-absorption material should be customizable to the impact energy needs in both the time domain and the frequency domain. In this research, silicone and graphite impregnated silicone are developed and characterized for use as energy-absorbing material in helmet padding. Both materials are shown to have customizable properties, including shear modulus, bulk modulus, natural frequency, damping coefficient, and strain energy by using micro- and macro-scale techniques. Furthermore, systematic material characterization has led to the development of a comprehensive set of design criteria for football helmet padding