Bike helmets work by absorbing impact energy that would otherwise be passed through to the wearer's head. An experimental new helmet is claimed to do so better than conventional models, thanks to a special resin.
With a few notable exceptions, bicycle helmets typically consist of an outer plastic shell that dissipates impact energy by cracking, along with an underlying expanded polystyrene foam liner that compresses to absorb impact energy, further reducing the amount that reaches the rider's head.
Led by Assoc. Prof. Leong Kah Fai, scientists at Singapore's Nanyang Technological University (NTU) are developing a helmet in which the shell is instead made of carbon fiber impregnated with a thermoplastic resin known as Elium.
Made by French materials company Arkema, Elium gradually hardens into a solid at room temperature, unlike other resins that have to be heated in order to cure. This quality, along with its low viscosity, reportedly allows it to more thoroughly impregnate the carbon fibers, boosting the toughness of the resulting composite.
According to NTU, the Elium-infused shell of its prototype helmet is tougher, stiffer and less brittle than a traditional polycarbonate shell, allowing it to absorb more impact energy over a longer period of time (in other words, over a larger number of milliseconds per impact).
As a result, lab tests indicate that whereas the foam liner of a polycarbonate-shelled helmet has to absorb about 75 percent of the total impact energy, the liner of the Elium-shelled helmet only has to absorb about 35 percent. Additionally, the composite shell should be cheaper to manufacture than those made of traditional thermoplastics, which have to be molded at high temperatures.
It should be noted that the present prototype helmet is about 20 percent heavier than its conventional counterparts. The researchers hope to address this shortcoming by replacing the carbon fiber with lighter-weight polypropylene fabric.
Source: Nanyang Technological University
