Helmet uses physics to prevent brain injury

February 9, 2016

A shock-absorbing football helmet uses physics to prevent head injuries.

University of Michigan researchers made a prototype that dissipates the energy from hits on the field. Current helmets can’t do this, and that’s one of the reasons they aren’t very good at preventing brain injury.

“Today’s football helmets are designed to prevent skull fractures by reducing the peak force of an impact,” said Ellen Arruda, U-M professor of mechanical engineering and biomedical engineering. “And they do a good job of that. But they don’t actually dissipate energy. They leave that to the brain.”

To dissipate energy, a helmet typically has to deform, like the bike version cracks in a collision. And disposable helmets aren’t practical for football players.

When a bike helmet breaks, it’s absorbing what’s called “impulse” — a secondary effect of an initial force. For head protection to be most effective against the speeds and weights of players on a football field, these researchers say it has to block impulse.

The new helmet is made out of three layers. The first layer is similar to the hard polycarbonate that’s the shell of present-day helmets. The second is a flexible plastic. Together these substances reflect most of the initial shock wave from a collision — most of the initial force. They also allow the third layer to absorb the remaining force. The third “visco-elastic” layer has the consistency of dried tar.

Late last year, the U-M team was one of five winners of the Head Health Challenge III, a competition to support the development of materials that better absorb or dissipate impact. Aside from the NFL, sponsors are Under Armour, GE and the National Institute of Standards and Technology. The U-M researchers received US$250,000 to take their technology to the full prototype stage. Doctoral candidate Tanaz Rahimzadeh is also contributing to this project.

A paper on some of these findings, titled “Design of armor for protection against blast and impact,” is published in the Journal of the Mechanics and Physics of Solids. Rahimzadeh is the first author.

Tags: featured