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Method and apparatus for measuring strain using a luminescent photoelastic coating

a luminescent photoelastic coating and strain measurement technology, applied in the direction of force measurement, force measurement, force measurement, etc., can solve the problems of limited usefulness, difficult to determine the strain over an entire surface of a structure, and conventional brittle coating techniques can only test a part in one loading configuration, etc., to achieve the effect of improving accuracy

Inactive Publication Date: 2006-01-12
HUBNER JAMES P +5
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

Enables non-contact, non-destructive, full-field strain measurement with high sensitivity, suitable for complex geometries, and real-time monitoring of strain on mechanical components, improving the accuracy of strain data for structural analysis and design.

Problems solved by technology

Accordingly, these point methods can be cumbersome, making it difficult to determine the stresses over an entire surface of a structure.
Each of these methods can be useful for certain applications, but each have certain characteristics which limit their usefulness.
However, conventional brittle coating techniques can only test a part in one loading configuration and can only provide limited quantitative information.
Moreover, methods for automated data collection using conventional coating techniques are not presently available.
Conventional photoelastic coating techniques are typically cumbersome and time consuming to apply to large bodies.
Moiré methods are typically limited to flat objects and are not used on complex three-dimensional geometries.
Interferometric methods, such as holographic interferometry, electric speckle pattern interferometry and shearography, require sophisticated vibration isolation which greatly reduces their applicability.
Digital image correlation methods can lack the sensitivity required to test parts in the material linear range in regions of high strain gradients.

Method used

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  • Method and apparatus for measuring strain using a luminescent photoelastic coating
  • Method and apparatus for measuring strain using a luminescent photoelastic coating
  • Method and apparatus for measuring strain using a luminescent photoelastic coating

Examples

Experimental program
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Effect test

example 1

Method Flow Chart

[0103]FIG. 6 is a flow chart which lists steps generally used to measure the full-field shear strain and strain orientation on substrate surfaces. The flow chart includes descriptions for specimen preparation, coating, imaging, and analysis, using a typical luminescent photoelastic coating and a measurement system, such as system 100 shown in FIG. 1.

[0104] In step 610, the specimen to be tested is prepared. The specimen is sandblasted, degreased and cleaned. A black undercoat is then applied. In step 620, the specimen is coated. This step can involve applying a single luminescent-photoelastic coating and then curing. Alternatively, step 620 can comprise applying a luminescent undercoat, curing the undercoat, then applying a luminescent-photoelastic overcoat then curing the overcoat. For example, a RhoB / / polyurethane coating (60-80 μm) can be cured under normal room conditions (25 C, 50% -60% RH). A BGM overcoat (200-400 μm) can then be applied and be UV cured at n...

example 2

Luminescent Undercoat Polarized Emission

[0107] A single layer of luminescent photoelastic coating containing a blue emitting dye (0.1%), dissolved in an epoxy monomer (1 g), along with a photocure agent (1%), a thixotropic agent, chloroform (0.25 mL) and toluene (0.25 mL) solvents was sprayed onto a metal surface and cured using UV irradiation (365 nm). A set of four fluorescence spectral scans were performed using a spectrophotometer to determine the degree in which the luminescent photoelastic coating retained the polarization state of the excitation. The excitation (450 nm) was filtered with a linear polarizer in the vertical and horizontal positions. The coating emission was detected thorough a second polarizer in the vertical and horizontal positions relative to each excitation polarizer (a total of four cases: IVV, IVH, IHV, IHH). From the data, the wavelength dependent anisotropy can be calculated as shown in Eqs 4A and 4B: r=IVV-GIVHIVV+2⁢GIVH(4⁢A)G=IHVIHH(4⁢B)

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example 3

Shear Strain Data on a Flat Specimen

[0109] An aluminum bar (2.0″×0.5″ in cross-section) was degreased and prepared for undercoat and overcoat application of a two-coating luminescent photoelastic coating as described above. The specimen was placed in an apparatus such that it was simply supported from underneath and loaded with a downward force from above to create a three-point bend as shown in the image provided by FIG. 8A. The coating was excited using a blue LED lamp (λ=465 nm) coupled with a linear polarizer and quarter wave plate. A 600 nm (40 nm bandpass) interference filter was used on the CCD imager to detect and record the emission intensity analogous to system 100 shown in FIG. 1.

[0110] Images were acquired at four analyzer positions for each applied static load condition. FIG. 8A shows processed strain results for a given applied load. Regions of high shear are indicated by white and light gray areas. Clearly present is the spatially varying shear strain field. Beneath...

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Abstract

A method and apparatus for measuring strain on a surface of a substrate utilizes a substrate surface coated with at least one coating layer. The coating layer provides both luminescence and photoelasticity. The coating layer is illuminated with excitation light, wherein longer wavelength light is emitted having a polarization dependent upon stress or strain in the coating. At least one characteristic of the emitted light is measured, and strain (if present) on the substrate is determined from the measured characteristic.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of U.S. patent application Ser. No. 10 / 407,602, now U.S. Pat. No. 6,943,869 issued on Sep. 13, 2005, which was filed in the United States Patent and Trademark Office on Apr. 4, 2003 and claims the benefit of U.S. Provisional Application No. 60 / 416,105 entitled METHOD AND APPARATUS FOR MEASURING STRAIN, filed on Oct. 4, 2002, the entireties of which is incorporated herein by reference.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT [0002] Not applicable. FIELD OF THE INVENTION [0003] The invention relates to the field of strain measurement, more particular, to strain sensitive coatings which provide both photoelasticity and luminescence and methods for determining strain on surfaces coated with the same. BACKGROUND [0004] In the field of structural analysis, the ability to determine the stresses which a structural body experiences can provide important feedback in the design and construc...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): G01B11/16G01L1/24
CPCG01L1/241G01B11/18
Inventor HUBNER, JAMES P.IFJU, PETER G.SCHANZE, KIRK S.JIANG, SHUJUNLIU, YAOJENKINS, DAVID A.
Owner HUBNER JAMES P