TM 1-1500-204-23-11
Table 7-1.
General Description of Different Repair Types -- Continued
Constraints and
Description
Application
Type of Repair
Limitations
Wet Layup (External
Same as external stepped
Same as above.
Same as above.
Overlapped Patch)
patch described above
Overlapped patch involves
except the repair plies
larger iber eccentricities
are overlapped (made
than a stepped patch, but
successively larger in
may be less susceptible to
diameter).
edge peeling.
Thick carbon laminates
Wet Layup (Flush Scarfed
Circular or rectangular
Quality of the repair
with highly directional
Patch)
patches cut from woven
is sensitive to ply
layups..
and/or unidirectional
pattern uniformity,
carbon. Patches are
taper, concentricity,
custom tapered, i.e., each
iber orientation,
ply made successively
stacking sequence, and
smaller or larger in
impregnation quality.
diameter. Damage
Layup will generally
area in parent structure
duplicate the parent
scarfed to match taper
structure. Woven
of stepped repair plies.
materials will generally be
Patches laid up over
oriented 45 degrees
prepared damage area
relative to the axis
in prescribed sequence
at adjacent structural
and iber orientation and
members; unidirectional
impregnated with two-part
materials in the direction
epoxy/resin mixed at the
of the principal load.
repair site and applied
For lush repairs, the
by hand. For large-area
damaged part must
damage, restoration of the
be carefully scarfed to
structural shape of the part
match the taper of the
using foam or templates
patch. Uniform pressure,
may be necessary before
temperature, and cure
installing the repair.
cycle are important. If
Pressure applied and
the laminate thickness
repair cured at room
permits, anti-peel rivets
temperature or elevated
may be installed around
temperature depending
the edges of the cured
on the curing agent.
repair. Rivets may
be mandatory when
the damage involves
substructure. For
through-damage, access
to both sides is required to
clean up back surface and
provide support for layup.
Thick carbon laminates.
Wet Layup (Flush
Same as a lush scarfed
Same as above.
Double-scarfed Patch)
patch except that the
Two-sided access
damaged structure is
required.
scarfed inward from both
sides.
7-2
