Washington | Scientists have developed a new lightweight, shock-absorbing football helmet system that effectively dissipates the energy from strong impacts and can better prevent brain injury. To dissipate energy, a helmet typically has to deform, like the bike helmets crack in a collision.
When a bike helmet breaks, it is absorbing impulse – a secondary effect of an initial force. Impulse, which gives objects momentum, transmits kinetic energy through a system. It takes into account not just force, but also how long that force was applied.
The prototype called Mitigatium developed by researchers from University of Michigan in US, could lead to a lightweight and affordable helmet for players of the American football – a full-contact sport in which injuries and concussions are relatively common.
For head protection to be most effective against the speeds and weights of players on a football field, it has to block impulse. Current helmets can not do this, and that is one of the reasons they are not 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, professor at the University of Michigan. But they don’t actually dissipate energy. They leave that to the brain, Arruda said.
Scientists do not fully understand how a blow to the head translates to brain injury, but the researchers say impulse is a big factor.
Researchers studied the mechanical features of impacts and blasts and how helmets and other armour might be designed to do a better job protecting sensitive structures. They built 2D mock cross-sections of materials that stood in for the brain and skull in various helmet shells. Then they use a table-top collision simulator to test the different samples and compared how much energy was transmitted through to the brain-type layer in their helmet system and the status quo. They used a high-speed camera to help them observe how the brain model deformed in both systems.
In their experiments, the conventional helmet model did little to block impulse. Mitigatium reduced impulse to just 20 per cent of what got through to the brain model in the conventional helmet. The prototype reduced peak pressure to 30 per cent. The helmet is made of three materials.
The first layer is similar to the hard polycarbonate that is 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 convert the frequency of that incoming pressure wave to a frequency that the next layer can dissipate by vibrating. This third visco-elastic layer has the consistency of dried tar.
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