Piezochromic Fluorescent Particles for Adhesive Bond Stress Evaluation

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Solution Overview

Problem

Current methods lack efficient and non-destructive techniques for evaluating the health and stress of adhesive bonds between composite materials in structural applications, such as in aerospace and automotive industries, which are critical for ensuring safety and reliability.

Innovation Solution

Incorporating piezochromic fluorescent particles into the adhesive layer between composite components, which change spectral intensity in response to stress, allowing for stress measurement through illumination with a specific wavelength of light and analysis of the emitted fluorescent light.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If adhesive bonding is used to connect composite components, then design simplicity and cost are improved, but inspection capability for bond health evaluation deteriorates

Engineering Contradiction:

Improvedesign simplicityVSAvoidbond health inspection capability

Core Design Contradiction:

Ease of manufactureVSDifficulty of detecting and measuring

Solution Approach 1:

Fluorescing particles are embedded within the adhesive layer during the bonding process, establishing the sensing capability before the bond is formed. This preliminary incorporation ensures that the inspection capability is built into the structure from the beginning, eliminating the need for post-bonding modifications while maintaining design simplicity.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Fluorescing particles act as an intermediary between the stress field in the adhesive and the optical measurement system. These particles convert mechanical stress into optical signals (fluorescence wavelength shifts) that can be non-destructively measured, bridging the gap between the hidden stress state and external detection capabilities.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Strength

If traditional inspection methods are used for adhesive bonds, then structural integrity is maintained, but measurement capability for stress evaluation deteriorates

Engineering Contradiction:

Improvestructural integrityVSAvoidstress measurement capability

Core Design Contradiction:

StrengthVSMeasurement precision

Solution Approach 1:

Traditional mechanical inspection methods (drilling, sectioning) are replaced with an optical measurement system. The fluorescing particles enable stress measurement through optical wavelength detection, eliminating the need to physically access or damage the bond while providing precise quantitative stress data.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The fluorescing particles exhibit stress-dependent wavelength shifts in their fluorescence emission. This optical property allows the particles to visually indicate stress levels through color/wavelength changes, providing direct measurement capability without compromising the bond's structural integrity.

Inventive Principle:

Principle #32Color changes

3Measurement precision

If fluorescing particles are embedded in adhesive, then stress measurement capability is improved, but adhesive properties may deteriorate

Engineering Contradiction:

Improvestress measurement capabilityVSAvoidadhesive bond strength

Core Design Contradiction:

Measurement precisionVSStrength

Solution Approach 1:

The fluorescing particles are distributed throughout the adhesive volume, providing localized stress measurement capability at multiple points within the bond. This distributed sensing approach enables comprehensive stress evaluation while maintaining the overall adhesive properties, as the particles are dispersed rather than concentrated in critical load-bearing regions.

Inventive Principle:

Principle #3Local quality

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

Enables non-destructive, efficient evaluation of bond stress by translating fluorescent light characteristics into stress data, providing a reliable method for assessing the health and integrity of composite material bonds.

Implementation Method 1

A layer of adhesive includes a plurality of embedded fluorescing particles which emit a first spectral intensity in an unstressed condition and a second spectral intensity in a stressed condition

Methodology Applied

Scientific EffectFluorescence: Fluorescence

Implementation Method 2

piezochromic fluorescing materials embedded within a composite bond line illuminated with light, having a wavelength less than the fluorescent wavelength allowing measurement of a wavelength at which the maximum intensity occurs and a wavelength shift at the maximum intensity

Methodology Applied

Scientific EffectPiezochromism: Photochromism

Data Source

PatentUS9612190B2Bond evaluation using piezochromic fluorescence

Publication Date: 2017.04.04 THE BOEING CO

AI summary

A composite bonded structure with integral stress sensing and bond evaluation system incorporates a bonded structure having a first component, a second component and a layer of adhesive bonding the first and second components. The layer of adhesive includes multiple embedded fluorescing particles which emit a first spectral intensity in an unstressed condition and a second spectral intensity in a stressed condition. A bond evaluation apparatus is then employed for measuring spectral intensity.