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Design of Dual Layer Liner with Deformable Semi-Spherical Convex for Bicycle Helmet

Bicycle helmets aim to reduce the risk of injury due to impacts on the head. Generally, a bike helmet consists of the outer shell, liner, vents and straps. The liner helps absorb the effects of the impact to keep that force away from your head. To satisfy the functions of helmet liner, several criteria should be considered. The ideal liner would be stiffer in hard impacts, softer in lighter impacts, light, cheap, reliable to manufacture and easy to ventilate. Currently, there are many different design trends and concepts in the design of helmet liner. Researchers have tended to focus on the liner material. The Expended Polystyrene (EPS) foam is the most popular choice for liner material of helmet. The EPS foam is commonly used in helmets as an energy absorbing liner. However, EPS has some disadvantages, such as the difficulty to optimize energy absorbing in different areas of head and inferior effect of heat dissipation. Moreover, EPS is generally too brittle. In order to overcome its drawback, to search a better alternative is necessary. In this study, a dual layer liner is proposed to yield enhanced impact absorption, that is to say, the liner is constructed by two layers of polycarbonate with deformable semi-spherical convex. The energy absorbed by deformation of convexes which is described by a combination of folding and collapsing. The main advantages of this liner design not only show the energy absorbing capabilities like EPS foam but also gain a better optimization of energy absorbing for different sites. This study focuses on assessment of a helmet with dual layer liner based on the shock absorbing test of CPSC’s standard. Finite element method (FEM) is available contribution greatly to helmet test modeling. This study performs finite element analyses of helmet impact tests using LS-DYNA software. The simulation of helmeted headform drop test is implemented for the four kinds of liner thickness. To confirm the energy absorbing capabilities of dual layer liner, the resultant CG linear acceleration of the headform is measured from the helmet test simulation. According to the CPSC’s standard specification, the acceleration of headform should be less than 300 g's during the impact.