Optimization of the chin bar of a composite-shell helmet to mitigate the upper neck force

The chin bar of motorcycl e full - face helmets is the most likely region of the helmet to sustain impact s during accident s , with a large percentage of these impacts lead ing to basilar skull fracture . Currently, helmet chin bars are designed to mitigate the peak acceleration at the c entre o f g ravity of isolated headforms , as required by standards, but they are not designed to mitigate the neck force, which is probably the cau se of basilar skull fracture, a type of head injury that can lead to fatalities . Here we test whether it is possible to increase the protection of helmet chin bars while meeting standard requirements. Fibre - reinforced composite shells are commonly used in helmets due to their lightweight and energy absorption charac teristics. W e optimize the ply orientation of a chin bar made of fibre - reinforced composite layers for reduction of the neck force in a dummy model using a computational approach . We use the fini te element model of a human head/neck surrogate and measure the neck axial force, which has been shown to be correlated with the risk of basilar skull fracture. The results show t hat by varying the orientation of the chin bar plies , thus keeping the helmet mass constant, the neck axial force can be reduced by approximately 3 0 % while ensuring that the helmet complies with the impact attenuation requirements prescribed in helmet standards

Assessment of the protective performance of neck braces for motorcycle riders: a finite-element study

Neck protective devices for motorcyclists have been introduced fairly recently but there is no standard method to evaluate their performance. The goal of this study is to compare the response of riders’ necks to direct impacts on the helmet with and without such a device. We investigate three common types of cervical injury mechanisms i.e. hyperflexion, hyperextension and lateral bending using finite-element method. The rotational movement of the head with respect to the torso, the neck shearing and axial loads and the stress distribution throughout the cervical vertebrae show that using the investigated type of neck protective device, which is designed to restrain the head–neck motion, can in some cases increase the risk of neck injury. Hence, the design of such devices needs further study and their assessment requires the introduction of relevant standards of evaluation

Feasibility study on the use of a hierarchical lattice architecture for helmet liners

Helmets are the most important piece of protective equipment for motorcyclists. The liner of the helmet is the main part of the helmet which dissipates the impact energy and mitigates the load transmitted to the head. Therefore, optimizing the material that absorbs most of the impact energy would improve the helmet\u2019s protection capacity. It is known that the energy absorption of the helmet liner can be optimized by means of using liners with varying properties through the thickness, however currently the majority of used liners exhibit constant properties through the thickness. Advances in the field of topology optimization and additive manufacturing provide the ability of building complex geometries and tailoring mechanical properties. Along those lines, in the present work the feasibility of using a hierarchical lattice liner for helmets was studied. Finite element method was employed to study whether a hierarchical lattice liner could reduce the risk of head injuries in comparison to currently used liner materials. The results show that using a hierarchical lattice liner has the potential of significantly reducing the risk of head injury compared to a helmet with traditional EPS liner and could potentially be considered as the new generation of energy absorbing liners for helmets

The effects of topology and relative density of lattice liners on traumatic brain injury mitigation

This paper evaluates the effects of topology and relative density of helmet lattice liners on mitigating Traumatic Brain Injury (TBI). Finite element (FE) models of new lattice liners with prismatic and tetrahedral topologies were developed. A typical frontal head impact in motorcycle accidents was simulated, and linear and rotational accelerations of the head were recorded. A high-fidelity FE model of TBI was loaded with the accelerations to predict the brain response during the accident. The results show that prismatic lattices have better performance in preventing TBI than tetrahedral lattices and EPS that is typically used in helmets. Moreover, varying the cell size through the thickness of the liner improves its performance, but this effect was marginal. The relative density also has a significant effect, with lattices with lower relative densities providing a better protection. Across different lattices studied here, the prismatic lattice with a relative density of 6% had the best performance and reduced the peak linear and rotational accelerations, Head Injury Criterion (HIC), brain strain and strain rate by 48%, 37%, 49%, 32% and 65% respectively, compared to the EPS liner. These results can be used to guide the design of lattice helmet liners for better mitigation of TBI

Multiscale modelling of cerebrovascular injury reveals the role of vascular anatomy and parenchymal shear stresses

Neurovascular injury is often observed in traumatic brain injury (TBI). However, the relationship between mechanical forces and vascular injury is still unclear. A key question is whether the complex anatomy of vasculature plays a role in increasing forces in cerebral vessels and producing damage. We developed a high-fidelity multiscale finite element model of the rat brain featuring a detailed definition of the angioarchitecture. Controlled cortical impacts were performed experimentally and in-silico. The model was able to predict the pattern of blood–brain barrier damage. We found strong correlation between the area of fibrinogen extravasation and the brain area where axial strain in vessels exceeds 0.14. Our results showed that adjacent vessels can sustain profoundly different axial stresses depending on their alignment with the principal direction of stress in parenchyma, with a better alignment leading to larger stresses in vessels. We also found a strong correlation between axial stress in vessels and the shearing component of the stress wave in parenchyma. Our multiscale computational approach explains the unrecognised role of the vascular anatomy and shear stresses in producing distinct distribution of large forces in vasculature. This new understanding can contribute to improving TBI diagnosis and prevention