SAMPE Journal - May/June 2016 - 10
Feature Article
Figure 2. Micro-CT image of OoA prepreg after hand lay-up.
4. Abrupt geometrical changes. The flat-bottom
depression in the double-curvature region, combined
with the nearby honeycomb core inserts required
significant material deformation during lay-up. This
deformation may alter the resin-fibre distribution
and the warp/weft reinforcement interlacements,
possibly lowering the in-plane air permeability.
The possible manufacturing induced defects for this
part were identified, and are summarized in Table 1.
Defects in the monolithic laminate regions are likely
to form in the areas with small radii and abrupt
geometry changes5-7. The prepreg material was
within the manufacturer's recommended out-time8
and a suitable thermal profile was chosen to ensure
resin viscosity is sufficiently low to saturate the dry
reinforcement9. The part was laid-up in a temperature
and humidity controlled clean-room, limiting
moisture induced defects10. The combined distance
to edge breathing, in-plane permeability, vacuum
quality and vacuum hold time should evacuate most
gasses from the prepreg, minimizing the likelihood of
interply voids11-14.
The most likely defects in the honeycomb regions
are attributed to a rise in the honeycomb core
pressure, which in turn will reduce the applied
consolidation pressure. For honeycomb inserts, a
prepreg must form a connected macro-porosity
network in the core regions in order to evacuate
the core15,16. If the material's through-thickness
permeability is negligible or too low, spiking can be
used to increase the air permeability17. Prepregs with
low through-thickness permeability will likely lead
to high-voidage honeycomb skins18, and surfacing
film can suppress surface porosity4. Non-metallic
honeycomb cores absorb moisture very quickly, and
this moisture can easily diffuse from the thin cell walls
during processing, increasing the pressure within the
honeycomb core19.
Materials
A micro-Computed Tomography (micro-CT) image
of the OoA prepreg material used in this study is shown
in Figure 2. The image was obtained using a procedure
outlined in20. The plain weave reinforcement was
196 g/m2, and contained 36% resin by weight. The
8-ply sample shown in Figure 2 was laid-up by hand
and scanned at 7 µm/pixel. The light-grey regions
show the resin, the dark grey regions show the dry
reinforcement, and the black regions are empty space
(voids). The unsaturated region of the reinforcement
was estimated at 16.5%. A 294 g/m2 areal weight
adhesive film was used to co-cure the prepreg layers
Figure 3. Pressure measurements
for 4-ply skins (using prepreg
shown in Figure 2).
The insert shows the porcupine
roller in use in a different study.
10
SAMPE Journal, Volume 52, No. 3, May/June 2016
Table of Contents for the Digital Edition of SAMPE Journal - May/June 2016
Contents
SAMPE Journal - May/June 2016 - Cover1
SAMPE Journal - May/June 2016 - Cover2
SAMPE Journal - May/June 2016 - Contents
SAMPE Journal - May/June 2016 - 2
SAMPE Journal - May/June 2016 - 3
SAMPE Journal - May/June 2016 - 4
SAMPE Journal - May/June 2016 - 5
SAMPE Journal - May/June 2016 - 6
SAMPE Journal - May/June 2016 - 7
SAMPE Journal - May/June 2016 - 8
SAMPE Journal - May/June 2016 - 9
SAMPE Journal - May/June 2016 - 10
SAMPE Journal - May/June 2016 - 11
SAMPE Journal - May/June 2016 - 12
SAMPE Journal - May/June 2016 - 13
SAMPE Journal - May/June 2016 - 14
SAMPE Journal - May/June 2016 - 15
SAMPE Journal - May/June 2016 - 16
SAMPE Journal - May/June 2016 - 17
SAMPE Journal - May/June 2016 - 18
SAMPE Journal - May/June 2016 - 19
SAMPE Journal - May/June 2016 - 20
SAMPE Journal - May/June 2016 - 21
SAMPE Journal - May/June 2016 - 22
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SAMPE Journal - May/June 2016 - 28
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SAMPE Journal - May/June 2016 - 31
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SAMPE Journal - May/June 2016 - 33
SAMPE Journal - May/June 2016 - 34
SAMPE Journal - May/June 2016 - 35
SAMPE Journal - May/June 2016 - 36
SAMPE Journal - May/June 2016 - 37
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SAMPE Journal - May/June 2016 - 108
SAMPE Journal - May/June 2016 - Cover3
SAMPE Journal - May/June 2016 - Cover4
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