FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 5. Nondestructive Inspection (NDI) | 9. Acoustic Emission | 5-113. Applications
AC 43.13-1B
9/8/98
5-113. APPLICATIONS. A wide variety of
structures and materials, such as: wood, plas-
tic, fiberglass, and metals can be inspected by
the acoustic-emission technique by applying
stress on the test material. The emis-
sion-producing mechanism in each type of
material may differ, but characteristic acous-
tic-emissions are produced and can be corre-
lated to the integrity of the material. Acous-
tic-emission technology has been applied quite
successfully in monitoring proof tests of pres-
sure vessels and tests of fiber-reinforced plas-
tic structures of all kinds. There are now
ASTM standards and ASME codes applying to
its use in testing gas cylinders and both metal
and fiber-reinforced plastic vessels, tanks, and
piping.
For a welded structure such as a pressure ves-
sel, acoustic-emission testing works well with
relatively simple instrumentation. However,
slight movement of bolted or riveted joints can
also generate acoustic signals. Thus a complex
structure may have many acoustic sources be-
sides flaws in its components. These un-
wanted emission sources greatly complicate
acoustic-emission tests of complex structures.
The difficulties are not prohibitive, but they
put a premium on the intelligent use of signal
processing and interpretation. Therefore, be-
cause of the complexity of aircraft structures,
application of acoustic-emission testing to air-
craft has required a new level of sophistication,
both in testing techniques and data interpreta-
tion. Research and testing programs are cur-
rently in progress to determine the feasibility
of acoustic-emission testing on several differ-
ent types of aircraft.
5-114.5-119. [RESERVED.]
SECTION 10. THERMOGRAPHY
5-120. GENERAL. Thermography is an NDI
technique that uses radiant electromagnetic
thermal energy to detect flaws. The presence
of a flaw is indicated by an abnormal tem-
perature variant when the item is subjected to
normal heating and cooling conditions inherent
to the in-service life, and/or when artificially
heated or cooled. The greater the material’s
resistance to heat flow, the more readily the
flow can be identified due to temperature dif-
ferences caused by the flaw.
5-121.5-126. [RESERVED.]
SECTION 11. HOLOGRAPHY
5-127. GENERAL. Holography is an NDI
technique that uses visible light waves cou-
pled with photographic equipment to create a
three-dimensional image. The process uses
two laser beams, one called a reference beam
and the other called an object beam. The two
laser beams are directed to an object, between
beam applications the component is stressed.
The beams are then compared and recorded
on film, or other electronic recording medium,
creating a double image. Indications of ap-
plied stresses or defects are shown as virtual
images with a system of fringe lines overlay-
ing the part. Holography is most commonly
used for rapid assessment of surface flaws in
composite structures.
5-128.5-133. [RESERVED.]
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