Fabrication of grid-domed textile composite and its application in safety helmets

Safety helmet, such as bicycle helmet is one of the most important devices that could protect the human head from injury. In the last few years, a research team at HKUST and HK Poly U has developed a new type of textile composites, that is, the grid-domed cellular textile composite, which possesses higher specific energy absorbing capacity compared to the conventional polymer foams, such as Expanded Polyurethane (EPU). In this study, the potential of using this material as the energy absorbing liner of bicycle helmet has been evaluated. The composite composes of weft knitted nylon fabric with Epokite 815 resin added on and Carboxyl Terminated Butadiene Nytrile (CTBN) as the toughening agent. The selection of the resin materials was carried out through comparing the fracture toughness, yield strength and ductility of different resin mixtures. The tensile properties of the composite along different direction and with various pre-conditioning environment has also been studied. The geometry of the samples also plays a vital role that affects the energy absorption capacity and the deformation mode of the composite liner. A large amount of experiments were carried out in order to investigate the deformation mechanisms of the composite. Fabric stretching induced during the forming process was assessed, while the large deformation mechanism of the flat-topped conical shell has been modeled. In accordance with the relevant international standards, such as the Consumer Product and Safety Commission and the EN1078 standards, comprehensive impact tests were carried out to evaluate the energy absorption capacity of the composite liners. Several liner configurations, including a single-layer composite with a PU outer shell, and a double-layer (e.g. interlock) textile composite, are fabricated and developed into helmet prototypes. The failure mechanisms of each helmet prototype are also identified and analyzed. Finally, a testing protocol has been developed for the comfort assessment on the helmet prototypes