The continuous development of sport technologies constantly demands advancements
in protective headgear to reduce the risk of head injuries. This article
introduces new cellular helmet liner designs through two approaches. The first
approach is the study of energy-absorbing biological materials. The second
approach is the study of lattices comprised of force-diverting compliant
mechanisms. On the one hand, bio-inspired liners are generated through the study
of biological, hierarchical materials. An emphasis is given on structures in
nature that serve similar concussion-reducing functions as a helmet liner.
Inspiration is drawn from organic and skeletal structures. On the other hand,
compliant mechanism lattice (CML)-based liners use topology optimization to
synthesize rubber cellular unit cells with effective positive and negative
Poisson’s ratios. Three lattices are designed using different cellular unit cell
arrangements, namely, all positive, all negative, and alternating effective
Poisson’s ratios. The proposed cellular (bio-inspired and CML-based) liners are
embedded between two polycarbonate shells, thereby, replacing the traditional
expanded polypropylene foam liner used in standard sport helmets. The cellular
liners are analyzed through a series of 2D extruded ballistic impact simulations
to determine the best performing liner topology and its corresponding rubber
hardness. The cellular design with the best performance is compared against an
expanded polypropylene foam liner in a 3D simulation to appraise its protection
capabilities and verify that the 2D extruded design simulations scale to an
effective 3D design.
