Examination of Geometric Effects on Stress Wave Propagation and Applications in Football Helmet Design

A recent study of college and high school football players demonstrated that 5.1% sustained at least one concussion in a single season. Considering the number of individuals that participate in football in the United States, this percentage equates to a staggering number [1]. The information and attention dealing with concussions and traumatic brain injury (TBI) has greatly increased recently, and represents a need for more advanced helmets that can eliminate concussions as well as other forms of TBI. In order to obtain this goal, lessons can be learned from high speed impacts in nature, particularly the shock-mitigating effects of the bighorn sheep’s (or ram’s) horn and woodpecker’s hyoid bone. For instance, during fights between male bighorn sheep, the rams clash together at speeds up to 5.5 m/s, causing forces up to 3400 N [2]. Even while undergoing these tremendous forces, the animals are rarely injured, which leads to the notion that the horn geometry plays a role in mitigating the shock wave. The woodpecker’s hyoid bone extends around the skull in a spiral shape. It aids the woodpecker in extending its tongue and helps bypass vibrations generated from drumming, which protects the brain from shock [3]. Does the reoccurrence of this curious (tapered spiral) shape throughout nature have some significance in regards to energy dissipation and shock absorption abilities inherent to its geometry? Answering this was the primary goal of this study.