SAMPE Journal - January/February 2023 - 57

Test Procedures
Specimen Volume by Fluid Displacement
To find the volume fraction of printed specimens,
first the volume of the specimens needed to be
determined. These printed structures exhibited a
rough texture on the sides of the print. However,
no modifications to the specimens such as
sanding, or polishing were performed to preserve
the as-printed properties of the specimens.
Therefore, the volume of the specimens was
determined using a fluid displacement method
based on ASTM 79211
. The mass of each sample
was weighed, in air, using a laboratory precision
scale accurate to 10 micrograms. Then the mass
of each sample, submerged in a solution of known
density, consisting of 1 part RedLine Water Wetter
surfactant and 32 parts deionized (DI) water, was
measured using a hanging basket apparatus. The
water wetter was added to the DI water to lower
the surface tension in an attempt to minimize the
formation of air bubbles on the sample surfaces
that could alter the measurements. Through the
Archimedes' principle it can be stated that the
weight of a submerged objects is reduced, due to
buoyancy effects, by its volume multiplied by the
density of the fluid. Using this principle, the volume
and density of each specimen was calculated.
Volume Fraction by Matrix Burn Off
To determine the fiber volume fraction and void
volume fraction of the E-glass fiber reinforced PET
specimens, a matrix burn off test was performed
according to ASTM D3171-1512
. Specimens were
placed in ceramic crucibles and positioned in a
furnace. The furnace temperature was then raised
to 600°C and the specimens were kept at that
temperature for at least 2 hours to ensure that the
matrix was completely removed. After the furnace
was turned off and cooled to room temperature,
the crucibles containing the specimen fibers
were again placed into the 70°C drying oven with
desiccant for 1 hour. The mass of the reinforcement
fibers for each specimen was measured using the
precision laboratory scale. The mass of the matrix
was then determined by calculating the difference
between the total specimen dry mass and the mass
of the reinforcement fibers. The volume of the
fibers and the matrix were determined by dividing
the previously determined masses by known
constituent material densities of the commingled
material given by the feedstock manufacturer.
The given constituent material densities for the
E-Glass fibers and the PET matrix fibers were 2.62
g/cm3
and 1.27 g/cm3
, respectively. To determine
the volume of voids in the samples, the volume
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of the reinforcement fibers and the matrix were
subtracted from the measured volume of the
samples found during Archimedes' testing. Finally,
the fiber volume fraction and void volume fraction
of each sample was determined by dividing the
calculated volume of the reinforcement fibers and
the voids by the total volume of the sample.
Microscopic Inspection
A micrograph evaluation was performed on the high
aspect ratio stiffener rib composite to qualitatively
evaluate the reinforcement distribution, determine
the void locations, and to support the constituent
material concentration measurements. Due to the
complete consumption of the matrix in burn off
testing, micrographs of constituent content tested
samples could not be obtained. Thus, samples
were taken from material adjacent to that which
was used for constituent content testing. Short
samples were cut from the remaining loop print
material using a diamond saw, as shown in yellow
in Figure 5. It should be noted that the side of the
sample that was polished and imaged was the
side adjacent to the constituent content testing
samples, suggesting that the micrographs are
consistent with the microstructure of section 5, as
defined in Figure 4. The samples were suspended
in an acrylic mounting media which was left to
cure for 24 hours before polishing. Polishing was
performed by hand using polishing wheels and
various grinding and polishing media.
Consolidation Force Measurement
To measure the consolidation force experienced
throughout the manufacturing of a stiffener beam
the consolidation force measurement system was
used. Because the first 80-layer stiffener beam
sample was manufactured prior to the installation
of the consolidation force measurement system, a
second stiffener beam sample was manufactured.
The consolidation force experienced during the
manufacturing of the second stiffener beam
sample was measured using the consolidation
force measurement system. The second stiffener
beam sample was manufactured using the
same processing parameters as were used to
manufacture the first sample. This was done so
that consolidation force data acquired during
printing of the new stiffener beam sample could
be directly compared to the volume fraction data
gathered from the original stiffener beam sample.
The Arduino controlling the 4 cantilever load cells
was programmed to output the summation value
of the 4 load cell readings using a HX711 load cell
measurement code modified to accommodate 4
JANUARY FEBRUARY 2023
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SAMPE JOURNAL |
57
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SAMPE Journal - January/February 2023

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