TM 1-1500-204-23-11
Figure 4-15. Overexpanded Honeycomb Core
(3) Flexible core cell coniguration ("lex--cor-
comparable hexagonal cores of equivalent density.
e") results in excellent formability in compound curva-
Flexible core is available in a variety of cell shapes
tures with reduced anticlastic (potato chip) curvature
and can be manufactured in most of the materials
and cell wall buckling. When formed into tight radii,
used for hexagonal honeycomb (see igure 4-16).
this type of core provides higher shear strengths than
Figure 4-16. Flexible Honeycomb Cores
(4) Honeycomb Core Selection. The following
for other aluminum cores, but not vice versa. See
criteria are applicable for repair core material selection.
the system speciic technical manual for core repair
requirements.
(a) Strength. To achieve the same strength,
(c) Service Temperature. Aluminum core is
replacement core should be of equal or higher density
than the part being repaired, be constructed of the
limited to 350 F. Some non-metallic core is limited
same material and match the part ribbon direction.
to temperatures no greater than 180 F. Glass fab-
When crossing a foam splice line, the replacement
ric reinforced polyimide core material has a service
core density should be equal to or higher than the
temperature of 500 F.
highest density on either side of the foam splice.
(d) Corrosion Protection. When repairing
(b) Material. Never use non-metallic core as
metallic honeycomb core, always use corrosion resis-
a repair core material for metallic core. Some alu-
tant aluminum core as the replacement core material.
minum cores may be used as a replacement core
