NASA CASE NO.

PRINT FIG.

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The invention disclosed in this document resulted from research in aeronautical and

space activities performed under programs of the National Aeronautics and Space

Administration. The invention is owned by NASA and is, therefore, available for

licensing in accordance with the NASA Patent Licensing Regulation (14 Code of

Federal Regulations 1245.2).

To encourage commercial utilization of NASA-owned inventions, it is NASA policy to

grant licenses to commercial concerns. Although NASA encourages nonexclusive

licensing to promote competition and achieve the widest possible utilization, NASA

will provide the necessary incentive to the licensee to achieve early practical

application of the invention.

Address inquiries and all applications for license for this invention to NASA Patent

Counsel, Langley Research Center, Code 143, Hampton, Virginia 23681-0001.

Serial No.: 08/251,434

05/31/94 LaRC

(NASA-Case-EAR-15104-1)

RADIOGRAPHIC MOIRE Patent

App|ication (NASA- Langley

Research Center} 12 P

N95-1383_

Unc|as

G3/38 0029862
RADIOGRAPHIC 

w 

MOIRE 

NASA Case No. LAR 1 51 04-1 

Existing methods for strain measurements on materials have a variety of drawbacks. 

Strain gages take point measurements and require wires leading to the electronics 

controlling the gage. Optical methods allow only for surface measurements or interior 

measurements only for transparent materials. It is the object of this invention to 

allow for materials characterization in situations where the forgoing methods are 

impractical. 

The invention achieves this object by making use of the Moire effect along with the 

penetrative and remote nature of x-radiation. A pair of patterns is employed to 

produce a third, Moire pattern. At least one of the first two patterns is attached to 

the specimen to be analyzed. The second may be imposed at the detection stage or 

at some post-detection stage. The nature of the third pattern depends on the nature 

of the first two. As the test object is stretched, rotated or otherwise loaded the third 

pattern will change to reflect the load. 

The novelty of the invention lies in combining Moire techniques which are old in the 

optical art and the penetrative nature of x-radiation. It is useful for inspecting large 

areas of opaque materials and may be particularly useful in the inspection and 

characterization of viscoelastic materials like rubber and solid rocket fuel, materials 

which to this point are not well modeled. 

Inventor: Eric lrvine Madaras 

Address: 202 Aspen Blvd. 

Yorktown, VA 23690 

Employer: LaRC 

Evaluator: Joseph S. Heyman 

Serial No.: 081251,434 

Filed: 513 1 194 
LAR 15104-1 -1 PATENT APPLICATION

RADIOGRAPHIC MOIRE

Origin of 1;he Invention

The invention described herein was made by an employee of the

United States Government and may be manufactured and used by or for

the Government for governmental purposes without the payment of any

royalties thereon or therefor.

10 Background of the Invention

1___. Field of the Invention

15

The invention relates to the field of x-ray inspection, more

particularly to x-ray inspection of macroscopic phenomena such as

stresses in a material.

2_= Description of the Related Art

20 Moire inspection is widely known in use for inspection of areas

accessible to visible light. X-rays are widely known for use in observation

of areas that cannot be penetrated by visible light. Numerous methods

for examining strain are available including electronic and optical strain

gages and optical methods such as holography, shearography and speckle

25 interferometry. The present invention allows for the inspection of areas

that cannot be observed with optical methods. The interior of materials

that are not transparent to visible light cannot be observed with the

optical methods enumerated above.

Strain gages have two large limitations, the first is that they

30 monitor only a single point, the second is the need for cables running
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5104-1 -2 PATENT APPLICATION

from the gage to its accompanying electronics. It is sometimes

impractical when examining the interior of structures to have cables

leading from the interior to the exterior. It would be difficult to prevent

leakage from a high pressure tire, for example, if there were a cable

running from its interior. The first limitation can be overcome by

constructing the pattern of this method such that it covers a large area of

the inspected object. The second is overcome as the remote nature of

this method allows for the elimination of any such cables.

There are some systems that make use of both x-rays and the

Moire effect in diffraction measurements. These make use of reflection

patterns to make measurements at the surface of a material. They are

useful mostly on a very small scale and again fail to allow measurements

at remote locations. The claimed method allows for remote

measurements and large scale investigations.

Summary of the Invention

The present invention is a method for using x-rays and the Moire

effect to characterize materials. Its advantage lies in its use with

20 materials that are substantially opaque to visible light, or interior regions

that are not accessible making visible light Moire techniques unusable.

The first step involves attaching a first pattern to the material being

inspected. By attaching is meant the process of attaching to the exterior,

embedding within the material, or using a pattern already extant in the

25 material. This could include the belting of a radial tire or a pattern of

metal dots fastened to or embedded in a specimen. A pattern could also

be attached first to an intermediate object that would in turn be attached

to a specimen to be tested. The pattern used as the first pattern should

be chosen to provide a radio opacity contrast of at least 2:1 with respect

30 to the material being inspected. Alternatively the pattern could provide a
LAR 15104-1 -3 PATENT APPLICATION

radio opacity contrast of less than 2:1 and the resulting image could be

enhanced using signal processing techniques.

To produce a Moire pattern a second pattern is necessary. This

second pattern could be produced in a number of ways. It may be

5 imposed over the detector so that the detected image already contains

the Moire pattern. It could alternatively be imposed after the detecting

step, for example by digitally scanning a film image into a computer, the

line density of the digital scanner providing the second pattern.

The nature of the two patterns need not be important, any two

10 patterns are capable of producing a Moire pattern, however for them to

be useful in making quantitative measurements it is preferable that they

be regular, for example, sets of substantially parallel lines with

substantially constant separation distances. In addition, it is well known

in the art that the geometry of an x-ray set up limits the resolution of that

15 system. It is beneficial to detect an image as close as possible to the

object being imaged. The size of the pattern elements and the sizes of

their images will in turn govern the final resolution of the data produced

through the present method. That is, a pattern of thin wires will be able

to produce an image that will provide more detailed information than one

20 of very thick wires.

Both of the patterns could be attached to the material being

inspected. If the patterns were attached at different depths, for example

the first at the surface and the second within the material, this would

allow observation of differential motions within the material.

25 The images produced are created by x-radiation. X-radiation's

penetrative character allows for characterization of areas that are

inaccessible. The x-radiation should be beamed through the area of the

material containing the first pattern and may be detected by any means.

Film is an inexpensive detecting means and thus it lends itself to this

30 method. It would be advantageous to make use of real time x-ray
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5104-1 -4 PATENT APPLICATION

detecting methods to save the time necessary to develop film as well as

reduce sample irradiation time. Digital real time radiography systems are

capable of directly transferring detected images to a computer, by

controlling the density of the imaging the Moire image can be produced

and stored directly. Dynamic or flash x-ray systems are capable of even

faster imaging that would allow dynamic measurements to be made and

very short x-ray exposure times.

10

15

20

Brief Description of the Drawings

FIG. 1 is a drawing prepared from an x-ray photo of a test object

used to implement the invention, an RTV ® (GE Polymer Division) rubber

matrix with a grid of 0.005" diameter steel wires attached and spaced

0.020" apart.

FIG. 2 is a drawing prepared from a computer image created by

digitally scanning an x-ray photo into a computer. The image represents

the Moire pattern produced by the test object of FIG. 1 as the object is

bent around a cylinder 8" in diameter.

FIG. 3 is a drawing prepared from a computer image created by

digitally scanning x-ray photos into a computer. Each of the three images

represents the Moire pattern produced by the test object of FIG. 1 when a

particular tensile load is applied. The first represents zero load, the

second is a 5lb. load and the third is a 10lb. load.

25 Description of the Preferred Embodiments

3O

To produce a radiographic Moire pattern that is capable of

demonstrating stress and other deformations in a rectangular matrix of

RTV ® rubber the present invention has been implemented in the following

manner.
LAR 15104-1 -5 PATENT APPLICATION

The first pattern as set out in the claims was in the form of a series

of 0.005" diameter steel wires that were fixed to the matrix of RTV ®

rubber. Each wire was placed 0.020" from its neighbor and substantially

parallel. An x-ray photograph of this wire plus rubber test piece is shown

5 in FIG. 1 (note that in the test piece four wire positions were

unintentionally crossed, causing the two dark bands).

The test piece underwent various deformations including inducing a

curvature of diameter 8", and applying a tensile load of zero, 5lb. and

10lb. An x-ray image was produced on film for each instance. These

10 images were then digitally scanned into a computer. The line resolution

of the digital scanning provided the second pattern necessary to produce

a Moire pattern. The resulting Moire patterns are shown in FIGS. 2 and 3

respectively.

Another preferred embodiment is to use a series of metal dots in

15 place of parallel wires. In measuring material properties it is desirable not

to include the properties of the device used for measuring. By the

substitution of dots the tensile properties of the wires are eliminated from

any measurements.

Another preferred embodiment is to make use of existing patterns

20 contained in the workpiece such as the belts of a tire.

Another preferred embodiment is to make use of real time

radiography to produce images quickly, eliminating the film stage.

Further, with proper setting of the resolution the digital display will act as

the second pattern and the Moire image will be captured directly.

25 Another preferred embodiment is to make use of a flash x-ray or

dynamic radiography system. This operates at a higher rate of speed

than real time radiography and could be used to make measurements on a

specimen under dynamic loads.

Another preferred embodiment is to attach both the first and

30 second patterns to the material being inspected. This allows observation
LAR 15104-1 -6 PATENT APPLICATION

of the motions of two different depths of the material to be made so that

differential movements can be quantified.
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RADIOGRAPHIC MOIRE

PATENT APPLICATION

Abstract

5 A method for the x-ray inspection of materials making use of the

Moire effect is described. The Moire effect results when two patterns are

superimposed, a third pattern is produced. Any change in either of the

first two patterns creates a change in the third. Moire inspection is

common with visible light, this invention allows the technique to be

10 extended to locations inaccessible to visual inspection. A first pattern of

high radio contrast material is attached to or included in the sample. Xrays are projected through the sample. A second pattern is imposed at

the observation point, either before or after the formation of the x-ray

image. The two patterns interact to create a third, Moire, pattern. As the

15 material is stressed the Moire pattern changes, the degree of change

indicating the degree of stress.

FIG. 2
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