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with performing a tap test on other composite
components, the tap test uses acoustic
sounds produced when a small metal
object is tapped on the surface. Mechanics
are looking for a clear, sharp sound. A dull
thud would indicate a void or delamination.
Here are a few things to consider
when performing a tap test.
Familiarize yourself with the structure
you are inspecting. A change in the sound
does not necessarily indicate a defect.
For example, if tapping different areas of
the wing, you would get a slightly different
sound for areas that are sandwiched
laminate, non-sandwiched laminate, and
transition areas between the two. Corrie
Volinkaty, a technical instructor for Cirrus,
shares, “You will get slightly different
sounds as you transition between different
areas of the aircraft depending on the
structure. The thing to remember is that
a delamination will not be just a different
sound, it will be a dull sound or a thud.
Knowing the structure beneath is very
helpful when performing tap tests.”
• When performing a tap test, locate an
undamaged area with similar structure
to that of the area with suspected
damage. Tap the known good structure
and use that as a reference when
tapping the suspect area.
• Use a consistent rate and force when
tapping the structure.
• When performing the tap test, mark
the outer edge of the damaged area
with a Sharpie.
Damage classification
Now that we have used visual and coin
tap tests to evaluate the damaged area, we
need to classify it. Damage can be classified
into four classes: cosmetic, secondary
bond, solid laminate, and sandwich structure
damage. Always refer to the Cirrus
maintenance manual for damage classification.
Here are some highlights of the different
classifications.
Cosmetic
Cosmetic damage is non-structural damage.
It includes minor gouges, scratches,
dents, or other defects. Cosmetic defects
are defined to the surface protection of the
laminate.
Secondary bond damage
This is when disbonding occurs between
two pre-cured components. This could be
structural or non-structural in nature.
Solid laminate damage
This is structural or non-structural damage
which extends beneath the surface
protection and affects the solid laminate
structure underneath. This could be either
penetrating or non-penetrating.
Penetrating. This includes fractures and
penetration through the laminate.
Non-penetrating. This includes abrasions,
delaminations, surface impact, or
gouges through one laminate surface.
Sandwich structure damage
As the name implies, this is damage to
composite sandwich structures.
Visual inspection tips
The Cirrus maintenance manual offers the following guidelines for performing
visual inspections:
1. To enhance familiarization with fuselage construction, examine the
Aircraft Zone Diagrams.
2. If necessary, remove surface coat around damaged area.
3. Examine component tactually by running hands over surface of suspect
repair area to feel for surface imperfections and anomalies.
4. Paint is generally more brittle than the composite and will crack
before the laminate is damaged.
5. Cracked paint does not indicate the extent of the damage, only that
damage has occurred.
6. While dimple and dent damage is similar in appearance to hail
damage on a metal surface, delamination and disbanding is more
difficult to detect. It is sometimes possible to feel this type of damage
by pressing on the area. A disband or delamination may feel soft and
movement between the separated layers may be detected.
7. If possible, use a back light to reveal internal defects and delaminations.
8. Examine exposed laminate for stress whitening.
9. If possible, the backside of the suspected area should be examined.
A borescope can be a helpful tool to examine interior areas. A tip for
inspecting interior structure — interior surfaces are usually not painted
and damage to glass-fabric structures will show up as a white area.
10. Use a Sharpie to mark suspect areas found to facilitate coin tap test.
18 July 2006 • Aircraft Maintenance Technology • www.AMTonline.com • www.AMTSociety.org
Ai r f rame Technology
Laminate only. This is damage
to only one side of the sandwich
structure with no core damage.
This type of damage to the sandwich
structure can be identified
using the solid laminate damage
classifications.
Laminate and core. This is when
there is damage to one side of the
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