Understanding Energy Dissipation
Helmets are designed to manage the kinetic energy generated during an impact, preventing it from directly harming the brain. When an object strikes a helmet, the helmet’s materials are engineered to absorb and distribute this energy over a larger area and a longer period. This process transforms the impact’s sudden force into a more controlled event.
The outer shell, for instance, spreads the force across a wider surface, reducing the localized pressure on the skull. Beneath the shell, a crucial energy-absorbing liner, often made of materials like expanded polystyrene (EPS) foam, compresses and deforms irreversibly upon impact. This deformation works to dissipate the energy, preventing a significant portion of it from transferring to the head.
This controlled deformation is a key mechanism, as the helmet essentially “sacrifices” itself by crushing or fracturing to absorb the kinetic energy. By extending the time and increasing the area over which the force is applied, the helmet significantly reduces the peak acceleration experienced by the head. This reduction in acceleration protects the brain.
Essential Helmet Components
A helmet typically consists of several integrated components, each serving a specific protective function. The rigid outer shell, often made from materials such as polycarbonate or fiberglass composites, forms the first line of defense. This shell prevents localized penetration and protects against sharp objects.
Beneath the outer shell lies the energy-absorbing liner, the most critical component for impact protection. This liner, commonly composed of expanded polystyrene (EPS) foam, dissipates kinetic energy, preventing it from reaching the wearer’s head and brain.
Further inside, comfort padding and a fit system ensure the helmet stays securely in place. While primarily for comfort and stability, these elements ensure the energy-absorbing liner is positioned correctly to function effectively during an impact. Together, these layers manage and mitigate the forces on the head during a collision.
Protecting Against Rotational Forces
Beyond direct impacts, head injuries can also result from rotational forces, which cause the brain to twist within the skull. These forces can lead to injuries such as concussions and diffuse axonal injury. Traditional helmets excel at managing linear impacts but offered less protection against these rotational movements.
Modern helmet designs have evolved to address this type of injury by incorporating features that mitigate rotational forces. Technologies like slip planes or multi-directional impact protection systems (MIPS) are integrated into the helmet’s design. These systems involve a low-friction layer between the helmet’s outer shell and the comfort padding.
During an oblique impact, this low-friction layer allows the helmet’s outer shell to rotate independently around the head. This slight independent movement redirects the rotational energy, reducing the amount of twisting force transferred to the brain. By allowing the head to move relative to the helmet during angled impacts, these innovations provide additional protection against brain injuries.