Stretch-Dominated Hollow-Cell Helmet Liner for Uniform Impact Absorption

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Solution Overview

Problem

Conventional impact-absorbing structures in helmets, such as those with unitary foam liners, face limitations in effectively managing energy absorption in curved surfaces due to non-uniform contact areas, leading to increased peak forces and accelerations, which can compromise brain injury protection.

Innovation Solution

A stretch-dominated hollow-cell structure, such as a hexagonal honeycomb lattice, is used to dissipate energy more uniformly by employing 'hard' deformation modes like compression and tension, allowing for higher energy absorption per volume with lower relative density, thus reducing peak acceleration and force.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If conventional unitary foam liners are used in helmets, then the structure is simple and easy to manufacture, but the energy absorption is non-uniform leading to increased peak forces and accelerations

Engineering Contradiction:

Improveease of manufactureVSAvoidpeak force

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The foam liner is divided into multiple cellular compartments with varying densities and stiffness properties. Each cell can be independently optimized for specific impact scenarios, allowing uniform energy distribution and reduced peak forces while maintaining manufacturability through modular assembly processes

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the helmet liner are assigned different foam densities and cellular structures tailored to local impact risks. High-density cells are placed in areas prone to severe impacts, while lower-density cells are used in less critical zones, optimizing energy absorption uniformity without excessive overall weight

Inventive Principle:

Principle #3Local quality

2Object-affected harmful factors

If more impact-absorbing material is added to the helmet, then the impact protection is improved, but the helmet weight increases

Engineering Contradiction:

Improveimpact protectionVSAvoidhelmet weight

Core Design Contradiction:

Object-affected harmful factorsVSWeight of moving object

Solution Approach 1:

The foam material properties are dynamically optimized by varying density, cell size, and stiffness parameters across different helmet regions. This parametric optimization allows achieving required impact protection levels with minimal material quantity, reducing overall helmet weight while maintaining protective performance

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The helmet liner combines multiple foam materials with different mechanical properties in a composite structure. This allows synergistic energy absorption characteristics where each material contributes its strengths, providing superior impact protection per unit weight compared to homogeneous foam designs

Inventive Principle:

Principle #40Composite materials

3Weight of moving object

If the helmet is made lighter by reducing material, then the comfort and wearability is improved, but the impact absorption capability is compromised

Engineering Contradiction:

Improvehelmet weightVSAvoidimpact absorption

Core Design Contradiction:

Weight of moving objectVSObject-affected harmful factors

Solution Approach 1:

The foam liner incorporates dynamic response characteristics through varying cell structures that adapt to impact magnitude and rate. Under normal conditions, the lightweight structure provides comfort, but during impacts, the cellular structure activates energy absorption mechanisms that provide adequate protection despite reduced overall material quantity

Inventive Principle:

Principle #15Dynamics

4Ease of manufacture

If conventional foam structures are used on curved surfaces, then the manufacturing is simple, but the contact area is non-uniform leading to increased peak accelerations

Engineering Contradiction:

Improveease of manufactureVSAvoidpeak acceleration

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The foam liner cells are designed with curved geometries that conform to the helmet's outer shell curvature. This curved cellular architecture ensures uniform contact area distribution across the curved surface during impacts, distributing forces evenly and reducing peak accelerations while maintaining manufacturability through specialized molding techniques

Inventive Principle:

Principle #14Spheroidality (Curvature)

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 stretch-dominated structure achieves improved impact absorption by maintaining a uniform plateau force and increasing energy dissipation, meeting or exceeding safety standards while reducing the risk of traumatic brain injury and minimizing helmet weight.

Implementation Method 1

employing 'hard' deformation modes like compression and tension

Methodology Applied

Scientific EffectCompression: Compression

Implementation Method 2

employing 'hard' deformation modes like compression and tension

Methodology Applied

Scientific EffectTension: Tension

Data Source

PatentEP3253243B1An impact absorbing structure and a helmet comprising such a structure

Publication Date: 2020.04.01 OXFORD UNIVERSITY INNOVATION LTD

Figure 1A~1C
Figure 2A~2B
Figure 3~4

AI summary

An impact absorbing structure comprises a unitary material formed as a stretch-dominated hollow cell structure and a helmet comprising such a structure as an inner impact resistant liner.