Auxetic Foam Impact Attenuation via Negative Poisson Ratio

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Solution Overview

Problem

Existing impact absorbing materials in helmets, such as those with positive Poisson's ratios, require increased thickness to effectively absorb blunt impacts, which can lead to increased rotational inertia and a higher risk of traumatic brain injury.

Innovation Solution

The use of auxetic foam substrates with negative Poisson's ratios, which can be converted from non-auxetic closed-cell foams through a process involving heat and pressure, allowing for effective impact attenuation with reduced thickness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the thickness of energy absorbing materials is increased to guard against blunt impacts, then impact protection performance is improved, but helmet weight and rotational inertia increase

Engineering Contradiction:

Improveimpact protection performanceVSAvoidhelmet weight

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

The patent applies parameter changes by transforming the foam material's Poisson's ratio from positive to negative through controlled cell collapse during manufacturing. This fundamental material parameter change enables the foam to exhibit auxetic behavior, allowing thinner sections to provide equivalent or superior impact protection compared to thicker conventional foam, thereby reducing helmet weight while maintaining protection performance.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite structure by combining auxetic foam with traditional helmet components (shell, liner, padding layers). This composite approach integrates the unique energy absorption characteristics of auxetic foam into the existing helmet system, optimizing overall protection performance while minimizing weight penalties through strategic placement and thickness reduction.

Inventive Principle:

Principle #40Composite materials

2Reliability

If the thickness of impact absorbing articles is increased to absorb blunt impacts, then impact attenuation is improved, but the size and rotational inertia of the helmet increase

Engineering Contradiction:

Improveimpact attenuationVSAvoidhelmet size

Core Design Contradiction:

ReliabilityVSLength of stationary object

Solution Approach 1:

By changing the Poisson's ratio parameter to negative values through auxetic conversion, the foam material fundamentally alters its deformation characteristics. This enables the material to expand laterally when compressed, creating a more efficient energy absorption mechanism that requires less thickness to achieve the same impact attenuation, thereby reducing helmet size without compromising protection.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent inverts the conventional foam behavior by creating auxetic foam with negative Poisson's ratio. Instead of contracting laterally when compressed like traditional materials, the auxetic foam expands laterally, reversing the deformation pattern. This inversion creates more efficient stress distribution and energy absorption in thinner sections, reducing the required thickness and overall helmet size.

Inventive Principle:

Principle #13The other way round (Inversion)

3Ease of manufacture

If conventional foam with positive Poisson's ratio is used, then manufacturing is straightforward, but increased thickness is required to achieve effective impact absorption

Engineering Contradiction:

Improvefoam manufacturingVSAvoidfoam thickness

Core Design Contradiction:

Ease of manufactureVSLength of stationary object

Solution Approach 1:

The patent applies parameter changes by modifying the foam's Poisson's ratio through controlled cell collapse during the manufacturing process. By adjusting manufacturing parameters (heat, pressure, expansion ratios), the foam transitions from positive to negative Poisson's ratio, fundamentally changing its mechanical behavior. This enables thinner foam sections to provide equivalent impact absorption, reducing thickness while maintaining ease of manufacture through established foam processing techniques.

Inventive Principle:

Principle #35Parameter changes

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 auxetic foam substrates effectively dissipate forces from localized impacts, maintaining peak acceleration below 150 G, even with reduced thickness, thereby reducing the risk of traumatic brain injury and improving helmet design.

Implementation Method 1

the plurality of closed cells each have a negative Poisson's ratio

Methodology Applied

Scientific EffectNegative Poisson's ratio effect: Auxetic Materials

Implementation Method 2

configured to dissipate forces delivered through the bottom surface associated with localized impacts delivered to the top surface

Methodology Applied

Scientific EffectImpact force dissipation: Impact Force

Implementation Method 3

The auxetic foam substrate is configured to increase in density, temporarily, in response to the localized impact being delivered to the outer surface of the shell

Methodology Applied

Scientific EffectCompression: Compression

Data Source

PatentUS12201176B2Auxetic conversion of foam for impact attenuation

Publication Date: 2025.01.21 GENTEX CORP

AI summary

An impact absorbing article including an auxetic foam substrate having a top surface, a bottom surface opposite the top surface, and a thickness extending from the top surface to the bottom surface. The auxetic foam substrate is comprised of a plurality of closed-cells and configured to dissipate forces delivered through the bottom surface associated with localized impacts delivered to the top surface of the auxetic foam substrate. The plurality of closed cells each have a negative Poisson ratio.