SAMPE Journal - May/June 2016 - 46

Feature Article

Figure 1. Schematic of
bagging layup.

An aluminum mold was cleaned of surface defects
using sand paper, and a non-porous Ethelyne
tetrafluoro ethelyne (ETFE) release film was placed.
The prepreg layers were cut into required dimensions
and laid up according to the required facesheet
configuration. Rollers along with hand pressure were
used to press the prepregs, starting from the center
of the layup and moving progressively towards the
edges. This process was repeated for all the prepreg
layers to remove entrapped air as well as folds or
wrinkles. The tool-side and bag-side facesheet layups
were debulked at room temperature under full
vacuum for 60 minutes to ensure good compaction.
The schematic of the bagging procedure employed
for the OOA process is shown in Figure 1. The
compacted tool side facesheet layup was laid on the
aluminum mold which was covered with the ETFE
release film. A layer of film adhesive was placed on
the prepreg layup. The honeycomb core was placed
on the adhesive layer followed by the bag-side
adhesive layer and facesheet stack. Edge breathing
using EB1590 edge bleeder was used to evacuate
entrapped air from the sandwich layup. A layer of
ETFE release film was placed on the sandwich layup
followed by an aluminum caul plate. Airweave N10
breather was used to distribute the vacuum pressure
evenly. The entire layup was sealed using a double
vacuum bagging scheme.
The layup was debulked at 49°C (120°F) for two
hours. The sample was cured according to the cure
cycle shown in Figure 2, and allowed to cool down
to room temperature. This was followed by a freestanding post-cure at 232°C (450°F) for two hours.
The prepreg cure cycle was used to manufacture the
sandwich panel. The samples did not exhibit warping
following post cure.
46

Experiments
Thermogravimetric Analysis
Outgassing of prepreg and adhesive during cure
can lead to voids in facesheets and adhesive fillets.
These volatiles need to be removed during cure. The
evolution of volatiles from the prepreg and adhesive
was studied using Thermogravimetric analysis (TGA).
The adhesive was removed from storage and allowed
to warm up to room temperature. A small sample was
removed and the prepreg cure cycle was simulated in
a TGA. Air at a flow rate of 40 mL/min. was used as the
sample purge gas and the weight loss was recorded.

Flatwise Tensile Test
Flatwise tensile (FWT) strength primarily serves
as a quality control parameter for bonded sandwich
panels. This test produces information on the quality
and strength of the core-to-facing adhesive bond. The
flatwise tensile test for sandwich samples was done
according to ASTM C297. Sandwich samples had a
facesheet configuration of [0°/90°]s. This test method
consists of subjecting a honeycomb sandwich samples
to a uniaxial tensile force normal to the plane of the
sample. Honeycomb sandwich samples of 50.4 mm x
50.4 mm (2 in. x 2 in.) were cut from the manufactured
panel. The sample edges were polished progressively
using 80-220 grit sandpaper. The facings of the
samples were lightly roughened using 80 grit sand
paper. For RT testing, aluminum blocks of 50.4 mm x
50.4 mm x 50.4 mm (2 in. x 2 in. x 2 in.) were bonded
to the sample facings using a high strength epoxy, 3M
Scotch-Weld DP-460NS. The adhesive was allowed
to cure at room temperature for 24 hrs and was post
cured at 121°C (250°F) for two hours. Samples for
elevated temperature testing at 177°C (350°F) were
bonded to aluminum blocks using Metlbond 2550
film adhesive. Test samples were conditioned at
177°C (350°F) in the thermal testing chamber for 2
hours prior to testing. Average relative humidity was
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
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