How the Geometry and Mechanics of Bighorn Sheep Horns Mitigate the Effects of Impact and Reduce the Head Injury Criterion
Male bighorn sheep (Ovis canadensis) participate in seasonal ramming bouts that can last for hours, yet they do not appear to suffer significant brain injury.Previous work has shown that the keratin-rich horn and boney horncoremay play an important role in mitigating brain injury by reducing brain cavity accelerations through energy dissipating elastic mechanisms. However, the extent to which specific horn shapes (such as the tapered spiral of bighorn sheep) may reduce accelerations post-impact remains unclear. Thus, the goals of this work were to 1) quantify bighorn sheep horn shape, particularlythe cross-sectional areal properties related to bending that largely dictate post-impact deformations, and 2) investigate theeffects of different tapered horn shapes on reducing post-impact accelerations in animpact model with finite element analysis. Cross-sectional areal properties indicate bighorn sheep horns have a medial-lateral bending preference at the horn tip (p=0.006), which is likely to dissipate energy through medial-lateral horn tip oscillations after impact. Finite element modeling showedbighorn sheepnative horn geometry reduced the head injury criterion (HIC15) by 48% compared to horns with cross-sections rotatedby 90 degrees to have a cranial-caudal bending preference, and by 125% compared to a circular tapered spiral model.These results suggest that the tapered spiral horn shape ofbighorn sheep is advantageous for dissipating energy through elastic mechanisms following an impact. These findingscan be used to broadly inform the design of improved safety equipment and impact systems.
Bioinspiration & Biomimetics
Wheatley, Benjamin; Gilmore, Emma C.; Fuller, Luca H.; Drake, Aaron M.; and Donahue, Seth W.. "How the Geometry and Mechanics of Bighorn Sheep Horns Mitigate the Effects of Impact and Reduce the Head Injury Criterion." (2023) .