CHAPTER 3. FIBERGLASS AND PLASTICS
SECTION 1. REPAIR OF LIGHT LOAD LAMINATE STRUCTURES
3-1. GENERAL. There is a wide variation
in the composition and structural application
of laminates, and it is essential that these factors be given major consideration when any
restoration activities are undertaken. To a
similar extent, there also exist many types of
laminatestructure repairs that may or may not
be suitable for a given condition. For this reason, it is important that the aircraft or component manufacturer’s repair data be reviewed
when determining what specific type of repair
is permissible and appropriate for the damage
NOTE: Review Material Safety Data
Sheets for material to be used. When
handling materials, prepreg fabrics,
or partswith prepared surfaces, observe shelf life. Latex gloves and approved masks must be worn.
a. The materials used in the repair of
laminate structures must preserve the strength,
weight, aerodynamic characteristics, or electrical properties of the original part or assembly.
Preservation is best accomplished by replacing
damaged material with material of identical
chemical composition or asubstitute approved
by the manufacturer.
b. To eliminate dangerous stress concentrations, avoid abrupt changes in
cross-sectional areas. When possible, for scarf
joints and facings, make small patches round
or oval-shaped, and round the corners of large
repairs. Smooth and properly contour aerodynamic surfaces.
c. Test specimens should be prepared
during the actual repair. These can then besubjected to a destructive test to establish the
quality of the adhesive bond in the repaired
part. To make this determination valid, the
specimens must be assembled with the same
adhesive batch mixture and subjected to curing
pressure, temperature, and time identical to
those in the actual repair.
3-2. FIBERGLASS LAMINATE REPAIRS. The following repairs are applicable
tofiberglass laminate used for non-structural
fairing, covers, cowlings, honeycomb panel
facings, etc. Prior to undertaking the repair,
remove any paint by using normal dry sanding
methods. Bead blasting may be used but caution must be exercised not to abrade the surfaces excessively.
Chemical paint strippers
must not be used.
NOTE: These repairs are not to be
used on radomes or advancedcomposite components, such as graphite
(carbon fiber) or Kevlar.
CAUTION: Sanding fiberglass laminates gives off a fine dust that may
cause skin and/or respiratory irritation unless suitable skin and respiration protection is used. Sanding also
creates static charges that attract dirt
or other contaminants.
a. Check for voids and delamination by
tap testing. (See chapter 5.) When the surfaceof a fiberglass laminated structure is scratched,
pitted, or eroded; first wash with detergent and
water to remove all of the dirt, wax, or oxide
film. Then scrub the surface with an acceptable cleaner. After the surface is thoroughly
cleaned, sand it with 280-grit sandpaper, and
again use an acceptable cleanser to remove any
sanding residue and moisture.
essential, as any moisture remaining on the
surface will inhibit the cure of the resin. Dry
the fiberglass laminate thoroughly prior to
bonding repair. Mix enough resin, using the
manufacturer’s instructions, to completely
cover the damaged area, and apply one or two
coats. Cover the resin with a peel ply to exclude all air from the resin while it is curing.
After the resinhas cured, remove the film and
file or sand the surface to conform to the original shape of the part. Ensure that all edges of
the laminate part are sealed to prevent water
absorption. Then refinish it to match the rest
of the structure.
FIGURE 3-1. Typical laminate (facing) repair.
b. Superficial scars, scratches, surface
abrasion, or rain erosion can generally be repaired by applying...