Innovation provides a single system flexible enough to test objects ranging from large amplitude displacement and/or velocities down to extremely small displacements and/or velocities by making only a few minor adjustments in the component arrangements

Kurtz, R. L.

English

NASA Technical Reports Server

July 1972	 B72-10351 
•	 NASA TECH BRIEF Marshall Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Composite Mobile System For Holographic

Nondestructive Testing 
.
The most promiing application of holography at 
present appears to be in the area of nondestructive 
testing. This subject has been widely discussed by work-
ers in the field of holography and is fast becoming a 
field in its own right. There are basically three main 
types of nondestructive testing, namely, real time 
analysis, the double exposure method, and the time 
averaging process. 
In real-time holography, a single exposure is made 
with the object in equilibrium. After development, the 
holographic plate is replaced in the recording position 
and is illuminated with the reference beam. Any defor-
mation of the object slightly changes the phase of the 
reflected light, and destructive interference takes place 
for points whose phase is changed by an odd multiple of 
180 degrees, i.e., a path length change equal to one-half 
wavelength of the laser light. This destructive inter-
ference is evidenced by dark bands or fringes which 
appear across the virtual image. The frequency and the 
position of these fringes can be analyzed to determine 
the magnitude and the direction of the deformation. As 
long as the object is not displaced more than a few wave-
lengths of light, any number of different deformations 
may be analyzed and photographically recorded. Macro-
scopic movement of any system component, however, 
destroys the real-time fringes. 
Interference fringes are also observed with double-
exposure holography, but their origin is different. In the 
double-exposure method, an exposure is made with the 
object in equilibrium as in the real-time method, but the 
object is stressed, and a second exposure is made before 
the plate is removed. The hologram is then developed 
and illuminated by the reference beam. Two virtual-
images are formed because two exposures were made. 
Any deformation in the object between exposures causes 
the phases of the reflected light to differ, which results
in the same type of interference fringes mentioned 
above. 
Time-average holography is most useful in the analysis 
of periodic deformations of an object caused by vibra-
tion. With this technique, two positions of the object 
are recorded because a periodically vibrating object is 
located at or near the two peaks of the vibration the 
majority of the time. Upon reconstruction, interference 
between the wave fronts from the two virtual-images 
again causes fringe formation. The analysis of the 
fringes yields information on the shape and the ampli
-
tude of the vibrating areas. 
In all cases the quantitive information is obtained by 
the analysis of the interference fringes which occur in 
the vicinity of the reconstructed image of the object 
under study. The major difference between these three 
main types of nondestructive testing lies in the ampli-
tude or velocity of the motion of the test object, in that 
this deformation results in path length change of the 
illuminating object beam. Therefore, the user must first 
determine which method should be used and then set 
about to arrange a particular set up for his particular 
test. If he decides to investigate his object using a differ-
ent method of nondestructive testing, he must set up a 
completely different arrangement, dependent on his first 
choice of component placement. 
It is the general purpose of the present innovation to 
provide a single system for nondestructive testing which 
will have the capability of being mobile (used outside of 
the laboratory) and the versatility to allow any one of 
the three main nondestructive test methods to be used. 
It thereby provides the user with a system flexible 
enough to test objects ranging from large amplitude 
displacement and/or velocities down to extremely small 
displacements and/or velocities by making only a few 
minor adjustments in the component arrangements. 
S
(continued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19720000350 2020-03-17T03:30:15+00:00Z
Notes: 
I. Information concerning this innovation may be of 
interest to optical companies or any company using 
nondestructive test methods. 
2. Requests for further information may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Code A&TS-TU 
Huntsville, Alabama 35812 
Reference: B72-10351
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to: 
Patent Counsel 
Marshall Space Flight Center 
Code A&TS-PAT 
Huntsville, Alabama 35812
Source: R. L. Kurtz
Marshall Space Flight Center

(MFS-2 1704) 
B72-10351	 Category 03, 02
	
•


Composite mobile system for holographic nondestructive testing

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