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or begins to shear apart causing the fiber to finally
crack. Fracture lines can advance through layers breaking
fibers into shorter sections creating fiber bundles
(PHOTOS 25 and 26). Most of the synthetic fibers will
shear, buckle or bend creating irregular fiber fracture
surfaces at the break. The original fiber diameter will be
retained (PHOTOS 27 and 28). Kevlar® is one fiber that
responds differently. A fracture produces a surface layer
of fibrils instead of cracking. The parent fiber divides into
smaller size fibers called fibrils. The original diameter of
the parent fiber has been changed by the creation of fibrils
and the fibrils have smaller size diameters than the original
parent fiber diameter.
(b) SANDWICHED LAMINATE. In addition to the damage
described for the solid laminate, a sandwiched panel
can develop separations between the surface layers and
the core. The core can be crushed and torn. (PHOTO
30)
(c) FILAMENT WOUND LAMINATE. Matrix and fiber
cracking occurs as explained for the solid laminate. Layers
separate creating fiber/matrix strips. The winding pattern
unravels revealing each individual winding layer.
(PHOTO 31)
(d) DEBRIS TYPES. Using the terms described in paragraph
3.7.b.1, the type of physically-damaged debris that
can be produced are fragments, strips, and dust. The
dust includes fiber bundles, minute amount of single fibers,
resin and fiber particulate. The particulate does
not linger in the air (excluding detached Kevlar® fibrils).
Fibers are exposed on the surfaces and at the ends of
the broken pieces. Small fiber bundles and dust will be
laying on the surfaces of the damaged pieces and in the
immediate area. There may not be any surface indications
that reveal internal damage. Material failure due to
excessive load doesn’t shatter the material that is common
for impact damage.
(e) FIBER PATTERN EFFECTS. The finished form of
the material affects the way the composite releases broken
and separated debris. Fibers are held tightly together
in a fabric or filament wound part. The fabric weave and
complex winding patterns inhibits movement of the fracture
surfaces and fiber layers. In comparison to the unidirectional
tape layer, less fraying and fiber separation is
observed and the weave sustains for the most part.
(f) HEALTH CONCERNS. Generally, released particulate
concentrations remain close to their point of origin.
In the case of localized damage, the particulate concentration
will be right at the fracture surface. Extensive damage
will produce particulate that will be dispersed in close
vicinity of the shattered piece. Wind and site conditions
will influence the dispersion while handling the broken
TO 00-105E-9
3-24
pieces. The exposure concerns are: sensitization response
from dermal contact with the dust, puncture
wounds from fiber bundles, eye and throat irritation from
internal and surface particulate.
(3) FIRE DAMAGE
(a) EFFECTS OF HEAT AND FIRE. There are physical
and chemical changes that occur to the materials
within the composite system. Fuel fires such as JP-8
fires create extremely high temperatures that can exceed
2000°F. As the heat penetrates the layers, the coatings
are burned off and the resin layers are thermally and
oxidatively attacked. Heat causes the cured resin or plastic
to break apart into smaller and smaller size molecules
creating char material and volatiles (an analogy would
be the refining of crude oil to obtain lighter grades of fuel
oil). When volatile concentrations reach combustion levels,
flaming combustion occurs.
When the resin no longer seals and supports the fiber,
the composite layers become unattached. Without the
solid matrix, air can move between the fibers within and
between the layers. A fiber layer without resin is very
light and the thermal column within the flame can release
surface layers outside of the burn area. Fibers decompose
or melt. Fibers that melt are Spectra® and glass.
Kevlar® and carbon fiber are oxidatively attacked and
decomposes. Boron fiber surfaces oxidize causing a
change in color.
A heat source is needed to ignite a composite. Ignition
temperature depends on the resin type and will vary.
When the composite does ignite some resin systems
become a source of fuel and add heat to the JP-8 flame.
Some resins give off more dense black smoke than others
but liquid fuels like JP-8 will be the major contributor
to smoke density in a composite fire. Char formation will
also depend on the resin type.
Most epoxy formulations will start to burn around 440-
　
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