F01 A study into the feasibility of replicating and improving the mechanical properties of the Wavecel helmet liner using additively manufactured auxetic structures

Abstract

In the event of a cycling accident, there is evidence supporting the bicycle helmet’s role in reducing the risk of traumatic brain injury (TBI). Despite this, there is ambiguity surrounding the effectiveness and integrity of specific helmet liner technologies which claim to reduce concussion risk, such as Wavecel. This research project seeks to explore the feasibility of replicating the mechanical properties of the Wavecel metamaterial using an additively manufactured (AM) honeycomb structure. Wavecel, introduced in 2019 by Trek Bicycle Co. as part of the Bontrager sub-brand, is a helmet liner technology. Consisting of a collapsible cellular metamaterial, it functions through a network of interconnected shock absorbers that link the user’s head to the helmet shell. Upon its announcement, Wavecel claimed that its cellular lattice structure helmet liner is up to 48× more effective at preventing concussion than a standard helmet, reducing the likelihood of concussion to 1.2% during a laboratory simulated head impact (Bliven et al., 2019, Acc Analysis Prev, 124, 58-65). As one of the most commercially successful metamaterial helmet liners available on the consumer market, Wavecel is a clear demonstration that a metamaterial protection system can be mass-produced, well received by consumers and profitable for a business. To conduct this research, the properties of the Wavecel liner will be defined through impact testing. Computer-aided design (CAD) will then be used to produce several prototypes of a honeycomb structure. These prototypes will then undergo identical impact tests, aiming to replicate the mechanical properties of the Wavecel helmet liner. Comparisons will include elastic stiffness, column buckling, and response to off-axis impact. The collected data will serve as evidence for evaluating the performance and mechanical attributes of these structures, contributing to the advancement of next-generation helmet liners and sports personal protective equipment (PPE). The findings will also benefit businesses looking to develop helmets incorporating metamaterials in their liner technology.