BOND EVALUATION USING PIEZOCHROMIC FLUORESCENCE

• US 20140202239A1
• Filed: 01/23/2013
• Published: 07/24/2014
• Est. Priority Date: 01/23/2013
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Hull, John R., Davis, Keith J., Bossi, Richard H.
• Granted Patent: US 9,612,190 B2
• Time in Patent Office: Days
• US Class Current: 73/150.A
• CPC Class Codes: G01L 1/24 by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
• CPC Class Codes: G01N 19/00 Investigating materials by mechanical methods G01N3/00 - G01N17/00 take precedence
• CPC Class Codes: G01N 19/04 Measuring adhesive force between materials, e.g. of sealing tape, of coating
• CPC Class Codes: G01N 21/00 Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light G01N3/00 - G01N19/00 take precedence
• CPC Class Codes: G01N 21/62 Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light

Abstract

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.

Claims

1. A process for bond stress measurement comprising:

identifying fluorescing particles sensitive to stress;

mixing the fluorescing particles within adhesives subsequently used in a bond between two layers of material;

providing a stimulus light of appropriate wavelength;

observing characteristics of fluorescent light emitted from the fluorescing particles, said emitted light being indicative of the stress experienced by the fluorescing particles; and

translating the fluorescent light characteristics into stress data.

2. The process of claim 1 wherein fluorescing particles are first dispersed within small diameter transparent fiber, chopping the fiber into small lengths and mixing the fibers with the adhesive.

3. The process as defined in claim 1 wherein at least one of the two layers of material contains at least one hole allowing transmission of the stimulus light and fluorescent light emissions.

4. The process as defined in claim 3 wherein the hole is either open, filled with a transparent polymer, or filled with a glass fiber.

5. The process as defined in claim 1 wherein the step of translating the fluorescent light characteristics includes:

measuring a spectral intensity of the fluorescent light with the fluorescing particles in an unstressed condition; and

,

measuring a shifted spectral intensity of the fluorescent light with stress present in the bond.

6. The process as defined in claim 1 further wherein the step of observing the fluorescent light includes scanning the light source or the detector across the two layers of material and the bond to measure localized stress.

7. A composite bonded structure with integral stress sensing and bond evaluation system comprising:

a bonded structure having

a first component;

a second component;

a layer of adhesive bonding the first and second components, said layer of adhesive incorporating a plurality of fluorescing particles embedded therein, said fluorescing particles emitting a first spectral intensity in an unstressed condition and a second spectral intensity in a stressed condition; and

,

a bond evaluation apparatus for measuring spectral intensity.

8. The composite bonded structure with integral stress sensing and bond evaluation system of claim 7 wherein the bond evaluation apparatus comprises:

a light source emitting light for inducing fluorescence in the fluorescing particles;

a light detector receiving fluorescent light emitted from the fluorescing particles; and

,

a spectrum analyzer measuring the spectral intensity of the fluorescent light, the spectral intensity proportional to stress in the adhesive bond.

9. The composite bonded structure with integral stress sensing and bond evaluation system of claim 8 wherein the light source is a laser.

10. The composite bonded structure with integral stress sensing and bond evaluation system of claim 9 wherein the light source or detector is scanned over the bonded structure.

11. The composite bonded structure with integral stress sensing and bond evaluation system of claim 7 wherein the fluorescing particles are quantum dots.

12. The composite bonded structure with integral stress sensing and bond evaluation system of claim 7 wherein the fluorescing particles are created from material selected from the set of cadmium selenide (CdSe), difluoroboron complex BF₂AVB or crystals of [(CH₃)₄N]₂MnCl₄ or [(CH₃)₄N]₂MnBr₄.

13. The composite bonded structure with integral stress sensing and bond evaluation system of claim 7 wherein at least one of said first and second components is transparent to the light emitted from the light source and fluorescent light emitted from the fluorescing particles.

14. The composite bonded structure with integral stress sensing and bond evaluation system of claim 7 wherein at least one of said first and second components incorporates at least one hole extending through the component to the bond layer.

15. The composite bonded structure with integral stress sensing and bond evaluation system of claim 14 wherein the at least one hole is filled with transparent polymer.

16. The composite bonded structure with integral stress sensing and bond evaluation system of claim 14 wherein the at least one hole is filled with a glass fiber.

17. The composite bonded structure with integral stress sensing and bond evaluation system of claim 16 wherein the glass fiber has a curved end proximate the bond joint.

18. The composite bonded structure with integral stress sensing and bond evaluation system of claim 7 wherein at least one of said first and second components has at least one transparent fiber proximate and parallel to the bond joint.

19. The composite bonded structure with integral stress sensing and bond evaluation system of claim 7 further comprising at least one transmission fiber in the bond joint.