TM 1-1500-204-23-11
components. The structural concept is the same, and
the requirements for a sound repair do not differ. The
only new requirement that accompanies the use of
composite skins is the need to pay attention to iber
DO NOT sand into laminate near patch edge
direction.
when sanding adhesive squeeze out.
a. Moisture Ingression. Moisture has long been,
(m) If applicable, repair the outer lightning
and will continue to be, a problem in sandwich struc-
mesh according to paragraph 7-12 and
ture. Moisture, either present in the repair environment
the system speciic technical manual.
or absorbed by the parent structure or any of the
materials used in the repair, is still the major source
(n) Reinish.
of trouble. Nonmetallic core is subject to rapid mois-
ture absorption, which if present during the repair
1
Sand the area smooth with 180 grit
cure, can destroy adhesion of the laminate to the
abrasive paper. Vacuum the repair
core surface by creating porosity in the repair material
area and then wipe with clean wip-
and bondline. All moisture must be removed prior to
ing cloth to remove sanding dust.
initiating and completing a repair. See paragraph 6-6
for information and procedures.
Apply inish system in accordance
2
with paragraph 7-13b or the system
b. Core Repairs. Core damage may be repaired
speciic technical manual.
by either a plug made of the same or suitable
substitute core material or by core potting, which
d. Full Thickness Bonded Repair. Full thickness
uses a paste compound to ill in the core cutout
bonded repairs follow the same procedures as para-
area. Parts made with X-Cor cannot be repaired
graph 7-3, partial thickness bonded repairs. The only
with X-Cor and a different core material, such
differences are for machining out the damaged area
as Rohacell or honeycomb, must be used. Never
according to paragraph 6-4 and a backside seal is
under any circumstances should non-structural illers
required according to paragraph de prior to iller appli-
be used to ill the void of removed core, the core
cation.
material must securely attach the two face sheets
together. Refer to the system speciic technical manual
or engineering for the required replacement core.
7-5. SANDWICH DAMAGE. A large proportion of
There are three methods for replacing damaged core
composite structures currently in production are of
sections: the core potting method, the paste adhesive
sandwich construction. For this reason, and because
method and the ilm/foam method. The core potting
the thin skins on sandwich components are easily
method is limited by damage size. Selection of the
damaged, many structural repairs will be on sandwich
paste adhesive or ilm/foam method is based on
components. The basic repair principles that apply to
strength and weight considerations. These methods
metal-skinned sandwich structures apply to composite
for core replacement are shown in paragraph 7-9. The
sandwich components as well. MIL-HDBK-337, Adhe-
rationale for method selection is discussed below.
sive Bonded Aerospace Structure Repair, covers core
repair of metal-bonded structures in detail and should
be referenced for core repair of composite sandwich
7-19
