Researchers at the University of Michigan in Ann Arbor are developing a shock-absorbing football helmet they say is lightweight, affordable, and can effectively dissipate the energy from a hit to the head.
"Today's football helmets are designed to prevent skull fractures by reducing the peak force of an impact," says Ellen Arruda, professor of mechanical engineering and biomedical engineering at U-M. "And they do a good job of that. But they don't actually dissipate energy. They leave that to the brain."
Arruda says for a helmet to dissipate energy, it typically has to deform, like how a bike helmet cracks in a collision. But she says disposable helmets aren't practical for football players. She says bike helmets absorb impulse, the secondary effect of the initial force. For head protection to be effective, it has to block impulse. The researchers say in their experiments, the current football helmet model did little to block impulse.
Arruda says the U-M-developed helmet system, called Mitigatium, is made of three materials. She says the first layer is similar to the hard polycarbonate that's the shell of present-day helmets. The second layer is plastic, and combined with the first layer, the substances reflect most of the initial shock wave from a collision. They also convert the frequency of the incoming pressure wave to a frequency the next layer can grab ahold of and dissipate by vibrating, called the "visco-elastic” layer. The material has the consistency of dried tar.
"We've come up with a totally new concept of how to make efficient, impact-mitigating structures that could dissipate energy without being damaged," says Michael Thouless, professor of mechanical engineering and materials science at U-M.
Sponsors include the National Football League, Under Armour, General Electric, and the National Institute of Standards and Technology.
A paper on some of the findings, called Design of armor for protection against blast and impact, is published in the Journal of the Mechanics and Physics of Solids.