Force Diverting Helmet Liner Achieved Through a Lattice of Multi-Material Compliant Mechanisms

Abstract

This work introduces the design of a lattice array of multi-material compliant mechanisms (LCM) that diverts the impact radial force into tangential forces through the action of elastic hinges and connecting springs. When used as the helmet liner, the LCM liner design has the potential to reduce the risk of head injury through improved impact energy attenuation. The compliant mechanism array in the liner is optimized using a multi-material topology optimization algorithm. The performance of the LCM liner design is compared with the one obtained by expanded polypropylene (EPP) foam, which is traditionally used in sport helmets. An impact test is carried out using explicit, dynamic, nonlinear finite element analysis. The parameters under consideration include the internal energy, the peak linear force, as well as von Mises stress and effective plastic strain distributions. Although there is a small increase in stress and strain values, the simulations show that the maximum internal of the LCM liner design is four times the one of the foam design while the peak linear force is reduced to about half. While the use of the LCM liner design is intended for sports helmets, this design may find application in other energy absorbing structures such as crashworthy vehicle components, blast mitigating structures, and protective gear.

Cellular Helmet Liner Design through Bio-inspired Structures and Topology Optimization of Compliant Mechanism Lattices

“…The polycarbonate shells are modeled as a linear elastic solid [49,50]. The model of the bio-inspired liners has their top and bottom surfaces attached to the adjacent sides of the outer and inner shells, respectively.…”

“…Engineered cellular materials have been developed for impact energy absorption in the form of honeycombs [40,41], microlattices [42], hollow spheres [43,44,45], and foams [46,47]; however, these cellular materials lack the ability to predictably redirect an impacting force and manage energy absorption [48]. In order to address this issue, this work expands on the design of a compliant mechanism lattice (CML) previously introduced by our group [49,50]. The CML redistributes an incoming radial force to tangential directions [51].…”

Towards concussion prevention in ice hockey: mechanical metamaterial liners and helmet assessment

“…Advancements in additive manufacturing and moulding methods, allowing fabrication of complex geometries, increased the possibilities to design and produce periodic cellular structures such as honeycombs and lattices [290][291][292][293]. Topology, base material properties, and relative density can be optimised to tailor impact behaviour and mass [294][295][296] using numerical analysis methods [294,295,[297][298][299][300][301][302][303]. Further advantages include the possibility to laterally spread impact energy more efficiently than conventional foams [294,304] or progressive layer-by-layer failure under dynamic loading, widening the range in which impacts can be managed [297,303].…”