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.@en

Oblique impact is the most common accident situation that occupants in traffic accidents or athletes in professional sports experience. During oblique impact, the human head is subjected to a combination of linear and rotational accelerations. Rotational movement is known to be responsible for traumatic brain injuries. In this article, composite foam with a column/matrix composite configuration is proposed for head protection applications to replace single-layer uniform foam, to better attenuate rotational movement of the head during oblique impacts. The ability of composite foam in the mitigation of rotational head movement is studied by performing finite element (FE) simulations of oblique impact on flat and helmet shape specimens. The performance of composite foam with respect to parameters such as compliance of the matrix foam and the number, size and cross-sectional shape of the foam columns is explored in detail, and subsequently an optimized structure is proposed. The simulation results show that using composite foam instead of single-layer foam, the rotational acceleration and velocity of the headform can be significantly reduced. The parametric study indicates that using a more compliant matrix foam and by increasing the number of columns in the composite foam configuration, the rotation can be further mitigated. This was confirmed by experimental results. The simulation results were also analyzed based on global head injury criteria such as head injury criterion, rotational injury criterion, brain injury criterion and generalized acceleration model for brain injury threshold which further confirmed the superior performance of composite foam versus single-layer homogeneous expanded polystyrene foam. The findings of simulations give invaluable information for design of protective helmets or, for instance, headliners for the automotive industry.@en

Rotational acceleration experienced by the head during oblique impacts is known to cause traumatic brain injuries. It is hypothesized that shear properties of a foam layer, used for head protection (e.g., protective helmet liners, headliners in cars) can be related to the extent of rotational acceleration transmitted to the head. @en