to record it on film. Defects in material essentially
existence of damage may be obvious, such as a skin
change the thickness of the material, thus changing the
penetration, a gouge, or a dent. Conversely, the proper
degree of absorption of radiation. More radiation
identification and classification of the damage may be
passes through the thinner area of a part, and shows up
difficult. Because of the brittle, elastic nature of
as a darkened area on the developed film.
composite laminate materials, for example, the fibers
may break upon impact, but then spring back, leaving
little visible indication of damage.
There are three distinct steps involved in damage
Ultrasonic inspections use sound wave frequencies
assessment. The first step is to locate the damage. The
higher than the human hearing level, above 20,000
second step is to evaluate the defect to determine such
hertz, to penetrate the part. It measures the time the
information as the defect type, depth, and size. This
transmitted sound waves take to pass through the object
information is important because the method of repair
and return to the receiver. The signals are changed into
will vary, depending on this information. The third step
a display on a cathode-ray tube that provides a means of
is to re-evaluate, after defect removal (as applicable),
interpreting defects. Accurate results are dependent on
the area being repaired.
an experienced operator, clean surface, known
standards of part construction, and repeatability of
DAMAGE INSPECTION METHODS
Advanced composite materials consist of a
There are many methods available for locating and
combination of what materials?
evaluating the damage. Ideally, the fastest method that
will reliably find the appropriate type and size of defect
What type of inspection is used to analyze the
should be employed since recurring costs will probably
extent of the damage and effectiveness of
outweigh nonrecurring equipment procurement costs.
repair to composite materials?
Some of these inspection methods are visual
What types of fibers are golden yellow in
inspection, tap test, X-ray, and ultrasonic inspections.
color and are used in many secondary
structures replacing fiber glass or as a hybrid
with fiber glass?
Visual inspections are a methodical search for
What is used as a single-ply arrangement of
defects, checking for obvious damages. Be suspicious
unidirectional or woven fibers in a matrix?
of any nick, dent, or paint chip because there may be
Crazing and cracking of composite materials
underlying damage. Many types of defects, such as
by ultraviolet radiation is categorized as what
impact damage, corrosion, and delamination, cannot be
type of damage?
detected by visual inspections alone.
What type of damage inspection method is
limited to finding defects close to the surface
in composite materials?
A tap test is used in conjunction with a visual
inspection, and is an elementary approach to locating
What does a dark area on the developed film
delaminations, disbonds, core damage, water, or
indicate when viewing an X-ray of composite
corrosion. Tapping should be done with a small
hammer about the weight of a US 50-cent coin. A dull
or dead sound indicates that some delamination or
disbond exists. A clear, sharp sound indicates a solid
All damage must be classified to determine what
structure. Tap testing is limited to finding defects close
repair action should be taken. Ultimately, all
to the surface, and is ineffective in areas of sharp
discrepancies will be placed into one of three
contours and changes in shape.
categories--negligible damage, nonrepairable damage,
or repairable damage. The decision concerning
disposition must be made considering the requirements
X-ray inspections use the same basic process as a
of the aircraft, the particular parts involved, the
dentist uses to X-ray teeth. The penetrating power of
limitations that can be placed on the repaired aircraft,
the radiation is used to reveal the interior of objects and