The use of honeycomb in the design of innovative helmets

Motorbike riders are among the most vulnerable road users. The improvement of the protection offered by motorcycle helmets through use of non-conventional energy absorbing materials could significantly reduce the number of motorcyclists’ fatalities. This thesis investigates the coupling of hexagonal aluminium honeycomb with polymeric foams for the design of innovative and safer motorbike helmets. The compressive behaviour and energy absorption properties of two layered foam-honeycomb composites are assessed experimentally. The experiments include quasi-static and impact compressive tests. Experimental outcomes show an increase of the energy absorbed by the two-layered materials with respect to the one provided by foams currently used for the manufacturing of helmets, tested under the same conditions. A finite element model representing the two-layered materials is also proposed. The model is validated against the experimental results. An accurate reproduction of the experiments is attained. A commercially available helmet is then modified to accommodate aluminium honeycombs in the energy absorbing liner, and standard tests are performed. The investigation includes also the testing of unmodified helmets, presenting same geometry and material properties of the prototypes. The experiments consist of impacts against a flat and kerbstone surfaces, as prescribed by standards. The dynamical responses of the prototypes and their commercial counterparts are compared. It is found that for impacts against the kerbstone anvil, the prototypes offer a noticeable reduction of the accelerations transmitted to the head, compared to the commercial helmets. For impacts against the flat surface, commercial helmets generally provide better protection to the head, which highlights a non optimum design of the prototype helmet and the limitations of using aluminium honeycombs as reinforcement materials. Experimental findings are later used to validate a finite element model of the prototype, where the two-layered model presented in this thesis is implemented. Numerical results are in good agreement with experimental findings.EThOS - Electronic Theses Online ServiceGBUnited Kingdo