TYPICAL DAMAGE AND ASSESSMENT
5-1. OVERVIEW. Most damage to aircraft occurs on
impart greater damage than originally sustained to
the ground during aircraft servicing, maintenance and
the composite material.
handling. Impacts from dropped tools, forklifts, main-
tenance stands, dropped panels and in light foreign
c. Damage Growth Potential. Whenever damage
objects are major causes of damage. This chapter
is left in disrepair, the potential for damage growth
addresses the critical procedures for determining how
becomes a concern. A large amount of research has
much damage has been sustained. It covers visual
been directed toward the potential growth of unde-
inspection, tap testing, and Nondestructive Inspection
tected small damages. Growth of damage between
(NDI) techniques. Although visual inspection and tap
testing technically are structures NDI methods, this
several ways. Cracking in metal is similar to delami-
document treats them as techniques to be used by
nation in advanced composite structures. Penetration
the composite technician, not the NDI technician. The
damage becomes critical in advanced composites due
task of repair begins when it has been determined
to the non-isotropic nature of the material design.
that a structure has been damaged and the damage
Keep in mind that the potential for damage growth is
is suficient to require the structure to be repaired.
peculiar to each component on each weapon system.
The existence of damage may be obvious for a skin
penetration, gouge or dent. Conversely, proper iden-
5-2. INSPECTION METHODS. The following nonde-
tiication and classiication of the damage may be
structive methods are used to inspect composite struc-
dificult owing to the brittle or elastic nature of com-
tures to evaluate damage. The ultrasonic inspection
posite laminate materials. For example, ibers may
techniques may also be used following a bonded
break upon impact but then spring back leaving little
repair to evaluate the adequacy of the performed
visible indication of damage.
repair. Detailed information on non-destructive inspec-
tion can be found in TM 1-1500-204-23-7.
a. Steps to Identify Damage. There are three dis-
tinct steps involved in damage assessment. The irst
a. Visual Inspection. Visual inspection will always
step is to locate the damage. The second is to evalu-
play a key role in determining the extent of structural
ate the defect to determine such information as defect
damage. Visual inspection has the distinct advantage
type, depth, and size. This information is important
in that it is inexpensive, easy, and fast. Internal
because the method of repair will vary depending
laws such as delaminations or disbonds are not
on this information. The third step is to reevaluate,
readily detectable and require the use of ultrasonic
after defect removal (as applicable), to determine that
or tap inspection techniques. In addition, closed
all damaged material has been removed. While the
surface cracks and edge delaminations may not be
search for improved methods is continuing, a sat-
detectable. Visual inspection aids such as lashlights,
isfactory job of ield inspection can be done using
mirrors, borescopes, and magniiers may be used to
visual and tap test inspection techniques combined
increase access or detectably of the suspect area.
with inexpensive, easy to operate, pulse-echo ultra-
Photographs can be helpful in providing a record
of visual inspection results. Penetration damage is
readily apparent. The presence of dents requires a
b. Causes of Damage. Damage comes from a
closer look and can be aided by using a straight
great many causes, such as scratching, gouging,
edge over a suspected dent area and comparing
impact, abrasion, erosion, local chemical attack or
the suspected dent area with the surrounding part.
overheating, may affect only a few surface plies over
The presence of cracks and edge delaminations may
a large area or a depth of many plies in a smaller area.
sometimes be detected by wiping the edge of the
Failure to use protective devices, such as padded
part with a solvent. If the edge is delaminated,
ixtures and sacriicial plies, may cause additional
the solvent will wick into the delaminated area. The
damage. Inadvertent or accidental impact may occur
solvent will evaporate on the undelaminated edge area
during the handling of parts during maintenance. The
leaving a "wet" mark along the delaminated edge.
types of damage range from small surface scratches
NDI penetrants should not be used as they may
to more severe defects that would include punctures.
contaminate surface cracks or edge delaminations,
Once damage is identiied, the extent of damage
foiling subsequent repair attempts. Internal laws
must be determined and then it can be classiied
such as delaminations not open to an edge and skin
to determine the disposition of the defective part.
disbonds cannot be detected using visual methods.
Improper damage removal and repair techniques can
If the inspection is performed in the presence of
hazardous conditions or materials, such as aircraft fuel