Smart material and design solutions for protective headgears in linear and oblique impacts: column/matrix composite liner to mitigate rotational accelerations

Oblique impact is the most common situation that cyclists experience during traffic accidents during which the human head undergoes both linear and rotational (angular) accelerations. Angular acceleration of the head is known to be linked to the majority of traumatic brain injuries. This paper proposes various solutions to mitigate angular accelerations of which an anisotropic column/matrix composite foam design is the most effective. This smart design allows tailor-made adjustment of shear and compressive resistance of the foam liner. Regarding helmet shells, tough fiber-reinforced composite materials such as self-reinforced polypropylene (PP) (Curv®) and silk/high-density polyethylene (HDPE) were benchmarked against conventional brittle polycarbonate (PC). Results demonstrate the superior performance of silk/HDPE composite compared to PC in resisting perforation in localized impact involving sharp objects. Regarding the helmet liner, two configurations were studied particularly, a multi-layered and column/matrix design. Their efficacy was benchmarked against single-layer homogenous expanded polystyrene (EPS) foam of equivalent weight and thickness in linear and oblique impact using experimental and finite element methods. The results showed the superior behavior of the column/matrix configuration. Such smart design could be combined with other smart systems such as multi-directional impact protection system (MIPS) technology for possible synergy and enhanced performance in head protection.