Bell Helmets Boosts Impact Protection
is launching an important first for the company this month with the addition of the Moto-9 Flex, an offroad helmet with a new approach to impact protection. The company is using what it calls “progressive layering technology” in the Moto-9 Flex liner to manage high-, medium- and low-speed impacts, as well as rotational impacts.
The system incorporates three protective materials, each designed to address specific impact velocities. Bell has discovered Expanded Polyolefin (EPO), which works in tandem with the often used Expanded Polypropylene (EPP) and Expanded Polystyrene (EPS) layering systems. EPO is a soft and flexible low-density polymer that, when placed between the EPP and EPS layers, dampens low-threshold impacts. Bell has addressed rotational energy management by engineering a “slip zone” within the liner which allows for subtle movement between the inner layers in an effort to reduce rotational energy transfer from angular impacts.
There are two different types of forces at play whenever an impact occurs:
- A LINEAR FORCE, which is caused by a straight and direct impact (such as when a ball hits a wall without rotating); it consists firstly of blunt compression (the hit) and then a reaction (the bounce) causing direct injury to the point of impact and potential further injuries following a straight line into the brain.
- A ROTATIONAL FORCE is slightly oblique and causes the head to rotate around its point of articulation at the top of the spine as it is hit.
Rotational head injury is startlingly common, but often under-recognized as a threat. It is the principal cause of brain injury from motorcycle and motor vehicle accidents. It happens because the head rotates around its point of articulation, which is the neck. This causes the brain to rotate within the skull tearing the veins and causing bleeding which results in a subdural hematoma. Because the head is not perfectly round, the brain not only spins as a whole but some parts within it spin at different rates. This sets up additional shear forces inside the brain itself. This stress within the brain results in the tearing of nerve fibers and tiny veins within the brain. This is called Diffuse Axonal Injury (DAI).
“We’ve seen so much attention and discussion being given to specific impact scenarios, and that concerned us, because off-road motorcycling can be completely unpredictable. A proper helmet needs to protect the rider in the widest array of situations they might encounter,” said Chris Sackett, Bell Helmets vice president.
Tags: accident reconstruction, failure analysis, forensic engineering, motorcycle accident reconstruction