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 extended to locations inaccessible to visual inspection. A first pattern of high radio contrast material is attached to or included in the sample. X-rays 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 material is stressed the Moire pattern changes, the degree of change indicating the degree of stress

Madaras, Eric I.

NASA Technical Reports Server

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US00548357 1A 
United States Patent [191 [ i l l  Patent Number: 5,483,571 
Madaras 1451 Date of Patent: Jan. 9,1996 
[54] RADIOGRAPHIC MOIRE 
[75] Inventor: Eric I. Madaras, Yorktown, Va. 
[73] Assignee: The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 251,434 
[22] Filed: May 31, 1994 
[51] Int. C1.6 ....................................................... G21K YO0 
[52] U.S. C1. ............................................... 37W145; 378/58 
[58] Field of Search ................................. 378/145, 62, 58 
1561 References Cited 
U.S. PATENT DOCUMENTS 
3,621,246 11/1971 Horsey. 
3,728,542 4/1973 Golfier . 
4,688,240 8/1987 Hosemann et al. 
5,125,016 6/1992 Korhonen et al. 
5,432,349 711995 Wood et al. .............................. 378143 
Primary Examiner-Craig E. Church 
Attorney, Agent, o r  Firm-George F. Helfrich; Robert C. E 
Perez 
[571 ABSTRACT 
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 
extended to locations inaccessible to visual inspection. A 
first pattern of high radio contrast material is attached to or 
included in the sample. X-rays 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 material is stressed the Moire pattern changes, the degree 
of change indicating the degree of stress. 
14 Claims, 3 Drawing Sheets 
https://ntrs.nasa.gov/search.jsp?R=20080004156 2019-08-30T02:25:15+00:00Z
U.S. Patent Jan. 9,1996 Sheet 1 of 3 5,48337 1 
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U.S. Patent Jan. 9,1996 Sheet 2 of 3 5,483,571 
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U.S. Patent Jan. 9,1996 Sheet 3 of 3 5,483,571 
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5,48357 1 
2 1 
RADIOGRAPHIC MOIRE 
ORIGIN OF THE 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 pur- 
poses without the payment of any royalties thereon or 
therefor. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
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 
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 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 monitor only a single point, the second is the need for 
cables running from the gage to its accompanying electron- 
ics. 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 con- 
structing 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 loca- 
tions. 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 materials that are substantially opaque to visible 
light, or interior regions that are not accessible making 
visible light Moire techniques unusable. 
The fiAt 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 material. This could 
include the belting of a radial tire or a pattern of metal dots 
fastened to or embedded in a specimen. Apattern 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:l with respect to the material being 
inspected. Alternatively the pattern could provide a radio 
opacity contrast of less than 2:l 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. 
5 It may be imposed over the detector so that the detected 
image already contains the Moire pattern. It could alterna- 
tively 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 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 substan- 
15 tially 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 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 
2o 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 of very thick wires. 
Both of the patterns could be attached to the material 
being inspected. If the patterns were attached at different 
25 depths, for example the first at the surface and the second 
within the material, this would allow observation of differ- 
ential motions within the material. 
The images produced are created by x-radiation. X-radia- 
tion's penetrative character allows for characterization of 
30 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 
method. It would be advantageous to make use of real time 
35 x-ray 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 
40 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. 
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 RTVO (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 
60 second is a 5 lb. load and the third is a 10 lb. load. 
DESCRIPTION OF THE PREFERRED 
EMBODIMENTS 
io 
45 
50 
55 
To produce a radiographic Moire pattern that is capable of 
65 demonstrating stress and other deformations in a rectangular 
matrix of RTVO rubber the present invention has been 
implemented in the following manner. 
5,483,571 
3 4 
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 RTVO rubber. Each wire was placed 0.020" 
from its neighbor and substantially parallel. An x-ray pho- 
tograph of this wire plus rubber test piece is shown in FIG. 5 
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, 5 lb. and 10 lb. An x-ray image was produced 10 
on film for each instance. These 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 place of parallel wires. In measuring material prop- 
erties 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 2o arranged into 
measurements. 
Another preferrcd embodiment is to make use of existing 
patterns 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. 
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 second patterns to the material being inspected. This 
allows observation of the motions of two different depths of 
the material to be made so that differential movements can 
be quantified. 40 observed with a dynamic radiography system. 
system. 
(e) observing a Moire pattern resulting from a combina- 
2. A method of inspecting materials that are substantially 
(a) attaching a f is t  pattern to an area of a material being 
inspected, said first pattern being chosen to provide a 
radio opacity contrast of at least 2: 1 with respect to the 
material being inspected, said first pattern consisting of 
an array of dots; 
(b) producing a second pattern at a detecting means, said 
second pattern consisting of substantially parallel lines; 
(c) projecting x-radiation through the area of the material 
containing said first pattern; 
(d) detecting an image resulting from the passage of the 
x-radiation through the area of the material containing 
said first pattern; 
(e) observing a Moire pattern resulting from a combina- 
tion of the first and second patterns. 
3. A method as recited in claim 2, wherein the dots are 
parallel lines. 
4. A method as recited in claim 2, wherein the dots are 
5. A method as recited in claim 2, wherein the second 
is produced by digitally scanning the x-ray image, 
25 the digital nature of the scanning providing the second 
pattern of substantially parallel lines. 
6. A method as recited in claim 1, wherein the image is 
observed using a real time radiography system. 
7. A method as recited in claim 6, wherein the real time 
30 radiography system is digital and the second pattern is 
produced by the digital nature of the real time radiography 
system. 
8. A method as recited in claim 2, wherein the image is 
observed using a real time radiography system. 
9. A method as recited in claim 8, wherein the real time 
radiography system is digital and the second Pattern is 
Produced by the digital nature of the real time radiography 
system. 
10. A method as recited in claim 1, wherein the image is 
11. A method as recited in claim 2, wherein the image is 
observed With a dynamic 
12. A method as recited in claim 1, wherein the radio 
opacity contrast is less than 2: 1 and the image is enhanced 
inspected, said first pattern being chosen to provide a 45 using signal processing techniques. 
radio opacity 13. A method as recited in claim 2, wherein the radio 
opacity contrast is less than 2: 1 and the image is enhanced material being inspected; 
using signal processing techniques. 
14. A method as recited in claim 1, wherein the second (b) producing a second pattern at a detecting means; 
(c) projecting x-radiation through the area of the material 50 pattern is attached to the material being inspected, said 
containing said first pattern; second pattern chosen to provide a radio opacity contrast of 
(d) detecting an image resulting from the passage of the at least 2: 1 with respect to the material being inspected. 
x-radiation through the area of the material containing 
tion of the first and second patterns. 
opaque to visible light, which comprises: 
15 
metal. 
35 
I claim: 
1. A method of inspecting materials that are substantially 
(a) attaching a first pattern to an area of a material being 
of at least 2:1 with respect to the 
opaque to visible light, which comprises: 
said first pattern; * * * * *  


Radiographic moire

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