Re-Entrant Helmet Liner Geometry for Rotational Impact Protection
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Solution Overview
Problem
Current energy absorbing systems in helmets, particularly those used in sports, are inadequate in reducing both linear and rotational brain acceleration during impacts, leading to traumatic brain injuries, and lack advanced geometries to effectively manage sub-concussive impacts, with most designs relying on homogeneous, bulk materials and simple circular or axisymmetric elements.
Innovation Solution
A flexible energy absorbing system comprising a plurality of cells with re-entrant geometries and varying orientations to provide anisotropic behavior, allowing for differential performance in different directions, thereby reducing both linear and rotational accelerations, and incorporating elastomeric materials for improved comfort and breathability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If homogeneous bulk materials with simple circular or axisymmetric elements are used, then manufacturing is easier and structure is simpler, but protection against both linear and rotational brain acceleration is inadequate
Solution Approach 1:
The energy absorbing system is divided into multiple cells with different geometries (re-entrant, cylindrical, conical, pyramidal, etc.) arranged in a structured pattern. Each cell type contributes differently to energy absorption mechanisms, with re-entrant cells providing negative Poisson's ratio behavior for rotational impact protection and other cells providing complementary energy absorption for linear impacts.
Solution Approach 2:
Different cell geometries are strategically positioned within the helmet liner to provide localized protection characteristics. The re-entrant cells are distributed throughout to provide rotational acceleration protection, while variations in cell density, size, and type are used in different regions to optimize protection for both linear and rotational impacts throughout the head.
2Strength
If EPS density is increased to pass high speed test standards, then high speed impact protection is improved, but protection against sub-concussive and slow speed impacts deteriorates
Solution Approach 1:
The system uses multiple cell types with different geometric parameters to provide a range of energy absorption characteristics. The re-entrant cells with their negative Poisson's ratio behavior provide protection at lower impact speeds by expanding laterally to absorb energy, while denser cells provide protection at higher speeds, creating a multi-regime protection system that addresses both sub-concussive and high-speed impacts.
Solution Approach 2:
The helmet liner combines multiple cell geometries within a single foam structure, effectively creating a composite energy absorbing system. The re-entrant cells, cylindrical cells, conical cells, and pyramidal cells work together to provide a broad spectrum of energy absorption mechanisms that protect against both low-speed sub-concussive impacts and high-speed impacts.
3Reliability
If traditional foam materials are used, then material simplicity is maintained, but ability to reduce rotational acceleration is insufficient
Solution Approach 1:
The re-entrant cells feature curved, non-linear geometries that enable them to expand laterally when compressed, creating a negative Poisson's ratio effect. This curvature allows the cells to absorb rotational impact energy by expanding in directions perpendicular to the applied load, providing rotational acceleration protection that traditional linear foam structures cannot achieve.
Solution Approach 2:
The helmet liner is constructed as a porous foam structure with interconnected cells. The re-entrant cell geometry creates a porous structure that allows for controlled deformation and energy absorption. The porous nature enables the material to undergo large deformations while maintaining structural integrity, which is essential for absorbing both linear and rotational impact energies.
4Volume of moving object
If helmet size is reduced to create slimmer designs, then aerodynamic performance and comfort are improved, but energy absorption capacity deteriorates
Solution Approach 1:
The liner is segmented into multiple cell types with different energy absorption characteristics, allowing for optimized distribution of protection within a reduced volume. The re-entrant cells provide rotational protection with compact geometry, while other cell types provide linear impact protection, enabling comprehensive protection in a slimmer profile.
Solution Approach 2:
The cell geometry parameters are optimized to maximize energy absorption efficiency per unit volume. The re-entrant cells are designed with specific dimensions and wall thicknesses that enable them to absorb rotational energy effectively in a compact form factor, allowing the helmet to maintain protection capabilities while reducing overall size and weight.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively reduces peak linear and rotational accelerations by up to 23% and enhances protection against sub-concussive impacts, offering improved comfort and performance in various directions, applicable not only to helmets but also to other personal protective equipment and body armor.
Implementation Method 1
a first plurality of cells comprising a first re-entrant geometry and a second plurality of cells comprising a second, different geometry, wherein the first plurality of cells and the second plurality of cells comprise an elastomeric material
Implementation Method 2
comprise an elastomeric material
Data Source
Figure 1a~1c
Figure 2a~2c
Figure 3a~3d
AI summary
The present disclosure relates to flexible energy absorbing systems and body armour, helmets and protective garments incorporating flexible energy absorbing systems. A flexible energy absorbing system comprises a first plurality of cells comprising a first re-entrant geometry and a second plurality of cells comprising a second, different geometry. The first plurality of cells and the second plurality of cells comprise an elastomeric material. Cells in the first plurality are located in a first area of the system and cells in the second plurality are located in a second, different area of the system. Cells in the first area are packed at a higher density to cells in the second area