SAMPE Journal - July/August 2020 - 20

FEATURE / FIBER BED ARCHITECTURE
Goals
The main goal of this study is to experimentally
observe the effects of the macro-level details of a
variety of fiber beds on the spreading of fluid on
the surface. Particularly, details such as tow edges,
overlaps/underlaps, and pinholes will be observed.
These will be compared to fluid flow on a unidirectional fiber bed as well.
The following parameters will be measured:
height of the droplet above the fabric surface over
time, surface area coverage over time, and the
shape of surface coverage over time. As this is anempirical study, observations of these parameters
will be made, but no specific model or analytical
predictions will be developed.
EXPERIMENTAL METHODS
Materials - Fluid Selection
While the motivation behind this study is to understand the flow of resin on the fiber bed surface,
working with resin and controlling its viscosity
carefully can be difficult, in this case requiring
carefully controlling the temperature of the resin
reservoir, the fiber bed, and the air through which
the droplet travels. Therefore, a facsimile fluid is selected instead.
The resin of choice for the previous iterations
of USCPreg3-5 was selected as the basis for this
study as well. This is an epoxy resin developed by
Patz Materials & Technologies (PMT-F4A). Using
the suppliers filming procedure, the minimum viscosity achieved during deposition was obtained.
Per the supplier, the filming temperature cycle is
the following: Resin is pre-melted at 65-68°C (150155°F) for 30-60 minutes. Then, filming is done at

68-72°C (155-162°F), which takes 30 minutes. Using a pre-filming sample of the resin provided by
the supplier, a rheology test was done following the
maximum temperatures allowed within this cycle
and can be seen in Figure 1.
From this test, the minimum viscosity value
during the filming process was found to be 27.1Pas. Therefore, a facsimile fluid of 30Pa-s was selected
as it is the closest standard viscosity to the minimum achieved. The facsimile fluid selected is a silicone viscosity standard with a viscosity of 30Pa-s
(±1%) (General Purpose Silicone, Brookfield Ametek). This fluid is ideal for these tests, as it the variation in viscosity due to the temperature at values
near room temperature are a minimum.
It is worth noting, however, that the fluid is
transparent, and in further studies, attempts will
be made at either obtaining a colored fluid or dying
the viscosity standard, as the transparency leads to
difficulties in observation of the fluid.
Materials - Fabrics
The baseline fiber bed, for which the others will be
compared to, will be a 305gsm (9.0 oz/sq.yard) unidirectional non-crimp fabric (UD-NCF). This fabric
was selected as it is currently the fabric of choice
for manufacturing through-thickness permeable
prepreg2,4,5. Alongside this, three different weaves
were also selected: A plain weave (PW) fabric with
an areal weight of 119 gsm (3.5 oz/sq.yard); a 2x2
twill (TW) fabrics with areal weights of 193 gsm
(5.7 oz/sq.yard) and two other unidirectional fabrics, a 137 gsm (4.0 oz/yard) matching the 305gsm
UD-NCF, and a heavier 756 gsm (22.3 oz/sq. yard)
quilted unidirectional fabric.

Figure 1. Rheology test for an un-filmed sample of PMT-F4A, following the
filming process thermal cycle at the highest temperatures allowed.

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SAMPE Journal - July/August 2020

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