University of Twente Student Theses


Development of Metamaterials for a Custom-fit Bicycle Helmet Liner

Moester, M.T. (2022) Development of Metamaterials for a Custom-fit Bicycle Helmet Liner.

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Abstract:Cyclists are still one of the most vulnerable road users and have a considerable higher fatality rate than other road users. Therefore, the bicycle helmet was introduced in 1975, to provide the user with head protection. Although bicycle helmets have been around for almost 50 years, the process to manufacture the helmets, and the approach to protecting the human head, has undergone only minor changes. To date, the majority of bicycle helmet liners are still manufactured with expanded polystyrene (EPS) foam. However, the foam is limited for energy absorption optimization due to its mechanical properties. Furthermore, the EPS liners are made for single-impact events and can not undergo multiple impacts at the same location. Large impact energies permanently deform the EPS liner after which the helmet must be discarded as it can no longer provide sufficient protection. The current helmets are commonly available in four standard sizes. However, in reality, every human head has its unique shape and dimensions. As a result, the improper fit causes discomfort and results in a reduction of the protection capabilities. A unique design was necessary to allow additional room for the liner’s performance while also increasing the helmet’s fit. Moreover, a design that was able to undergo multiple impacts while providing the same specific energy absorption. In this work, the origami-based metamaterial: Miura-Ori was investigated. It presented promising energy absorption capabilities and allowed more room for optimization. The design of the metamaterial was realized by creating a parametric design model based on Taguchi’s method L9. Nine distinctive samples were realized and additively manufactured via fused deposition modelling. The filament material, thermoplastic polyurethane, offered high specific energy absorption and allowed recoverable deformation. Prior to additive manufacturing, three geometrical parameters were selected: wall thickness, dihedral angle and cell wall ratio to investigate their influence on the energy absorption capabilities. This was accomplished by compressing the samples, out-of-plane, quasi-statically at a fixed strain rate. For improving the fit, 3D scanning equipment was used to capture the unique shape and dimensions of the human head. The 3D scans provided the fundamentals for the surface of the helmet liner. The final design presented a novel helmet liner that was able to undergo multiple impacts while offering recoverable specific energy absorption. Moreover, it showed more scope for optimization and the design demonstrated to provide an improved fit of the bicycle helmet.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
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