Dynamic behaviour of bicycle helmets under impact

Bicycle helmet is a useful personal device for protecting bicyclist's head and brain during accidents. Nowadays most bicycle helmets are made of polymer foams such as expended polyurethane and expended polystyrene. The current polymer foams used mostly have closed cells structure, resulting in poor ventilation. This can only be improved by adding the ventilation slots (vents), with the cost of the reduction in the impact protection. A research project concentrating on the impact strength, the effectiveness of the ventilation and the selection of alternative materials had been conducted for two years. This thesis summarizes the investigation results of the project. Polymer foam has been widely used in bicycle helmets as an efficient energy-absorption material. This study examines the energy-absorbing capacity and various failure modes of polymer foam laminated structure by a series of static and impact experiments using both MTS and Dynatup 8250. When a head is subjected to an impact, violent force and moment caused by sudden deceleration of the head are applied to the brain. Wearing a helmet substantially reduces the risk of head injury in a crash. Therefore, the highest head acceleration, the energy-absorbing capacity and the failure analysis of bicycle helmets under specially designed Impact Test Rig have been studied on various anvils. To improve the design of bicycle helmets, a mechanics model has been proposed which is capable of estimating the acceleration - time curve and predicting the energy absorbed by the bicycle helmet. The predictions have shown good agreement with the experimental measurements. Based on our experimental studies and modeling, some improvements in the alternative selection of materials has also been suggested. It has been found that the grid-domed textile composites possess outstanding impact energy-absorption capacity and good ventilation. This has raised a possibility of employing this new type of material as the cushioning layer (i.e. liner) in bicycle helmets of new generation