FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 5. Nondestructive Inspection (NDI) | 7. Ultrasonic Inspection | 5-95. Bond Testing Instruments
AC 43.13-1B
9/8/98
(1) Standards for Types I, II, III, and IV
unbonds can be prepared by placing discs
of 0.006 inch thick (maximum) Teflon sheets
over the adhesive in the areas selected for un-
bonds. For Type II unbonds, the Teflon is
placed between the core and adhesive. The
components of the standard are assembled and
the assembly is then cured.
(2) Types I, II, and III standards can
also be produced by cutting flat-bottomed
holes of a diameter equal to the diameter of the
unbonds to be produced. The holes are cut
from the back sides of bonded specimens, and
the depths are controlled to produce air gaps at
the applicable interfaces. When using this
method, patch plates can be bonded to the rear
of the reference standard to cover and seal
each hole.
(3) Type II standards can be produced
by locally undercutting (before assembly) the
surface of the core to the desired size unbond.
The depth of the undercut should be sufficient
to prevent adhesive flow causing bonds be-
tween the undercut core and the skin.
(4) Type IV standards can be produced
by removing the adhesive in selected areas
prior to assembly.
(5) Type V standards can be produced
by drilling small holes in the back of the stan-
dard and injecting varying amounts of water
into the cells with a hypodermic needle. The
small holes can then be sealed with a small
amount of water-resistant adhesive.
suggested methods contained in figure 5-21
and table 5-7 are for reference only. Details of
the inspection coverage and inspections for a
particular assembly should be obtained from
the OEM’s manuals, or other FAA-approved
requirements.
h. Inspection Methods. Table 5-8 lists
the various inspection methods for bonded
structures along with advantages and disad-
vantages of each inspection method.
5-95. BOND TESTING INSTRUMENTS.
Standard ultrasonic inspection instruments can
be used for bond testing as previously noted;
however, a wide variety of bond testing in-
struments are available for adaptation to spe-
cific bonded structure inspection problems.
a. General Principle. Two basic operat-
ing principles are used by a variety of bond
testers for single-sided bond inspection.
(1) Ultrasonic resonance. Sound waves
from a resonant transducer are transmitted into
and received from a structure. A disbond in
the structure will alter the sound wave charac-
teristics, which in turn affect the transducer
impedance.
(2) Mechanical impedance. Low-
frequency, pulsed ultrasonic energy is gener-
ated into a structure. Through ultrasonic me-
chanical vibration of the structure, the imped-
ance or stiffness of the structure is measured,
analyzed, and displayed by the instrumenta-
tion.
g. Inspection Coverage. Examples of
several different configurations of bonded
structure along with suggested inspection cov-
erages with standard ultrasonic test instru-
ments are shown in figure 5-21. In many
cases, access limitations will not permit appli-
cation of the suggested inspections in all of the
areas shown. The inspection coverages and
b. Operation. In general, operation of the
adhesive bond test instruments noted is simi-
lar. The test probe is moved over the surface
in smooth overlapping strokes. The direction
of the stroke with regard to the surface is gen-
erally immaterial; however, when using the
Sondicator models, the direction of the stroke
becomes critical when the test probe is
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