SAMPE Journal - July/August 2022 - 47

test panels utilizing the processing parameters
identified from the photomicroscopy results of the
panels fabricated in the first set of experiments.
The photomicroscopy results are discussed in the
primary Results section. In the second set of process
experiments, two 50.8 cm x 25.4 cm (20 in x 10 in)
by 24 ply quasi-isotropic [45°/0°/-45°/90°]3S
panels
were fabricated using the same flat, heated tooling
and AFP head with four round spots, collimated,
diode lasers at the Electroimpact thermoplastic
development lab. The PEEK panel was fabricated
using a laser heating target temperature of 500°C,
a tool temperature of 120°C, and a placement
speed of 100 mm/s (236.2 in/min). The LM-PAEK®
panel was fabricated using a laser heating target
temperature of 450°C, a tool temperature of 80°C,
and a placement speed of 400 mm/s (944.8 in/min).
The compaction load applied by the AFP roller
for both panels was 1.1 kN (250 lbs). In addition
to fabricating the two mechanical test panels,
temperature data was collected again during
the second ICAT processing characterization
experiments to validate the predictions of the
thermal models under development.
ICAT Processing Trials Temperature
Measurements
In addition to fabricating thin laminates to
determine the placement quality, the ICAT
processing trials were also intended to collect
experimental temperature data to calibrate
the physics-based thermal models under
development. During both sets of trials, a FLIR
camera mounted on the front of the placement
head measured the temperature of the substrate
and incoming material prior to the nip point. The
FLIR camera was used to validate the substrate
temperature matched the tape target temperature
for the placement trials. During the first set of trials,
a thermocouple data acquisition (DAQ) system
(NI® cDAQ-9174, CompactDAQ chassis equipped
with a NI 9212 8-Channel Module) capable of
simultaneously measuring 95 samples/s/channel
was used to collect temperature measurements
at the maximum sample rate during each ply
laydown. During the first set of trials, it was
observed that 95 samples/s was not adequate to
accurately capture when the peak temperature
occurred and resulted in sparse data points during
heating and cooling of the material. For example, at
400 mm/s processing speeds, most of the heating
and cooling took place in ~0.3 s. During this time,
only 28 temperature measurements could be
captured. For these reasons, prior to the second
set of trials, a new DAQ was acquired (DATAQ®
www. sampe.org
Thermocouple (TC) #
TC0 and TC1
TC2 and TC3
TC4 and TC5
TC6 and TC7
TC8 and TC9
TC Location
Between tool and ply 1
Between ply 1 and ply 2
Between ply 14 and ply 15
Between ply 22 and ply 23
On top of ply 24 (final ply)
Table 2. Thermocouple locations in ply stack.
DI-2008) where up to two thermocouples could be
measured at 2000 samples/s/channel. This system
was used for the thermocouples on the surface of
the substrate as the robot placed material on top
of them. All thermocouples already in the material
were connected to the 95 samples/s/channel
DAQ. The thermocouples utilized were 40 AWG,
J-type
from Omega® (5TC-TT-J-40-36). These
thermocouples were selected based on their small
diameter (0.0799 mm (0.0031 in)) that results in
a low thermal mass and fast response time. The
thermocouple locations in the ply stack are listed
in Table 2.
ICAT Process Thermal Model Development
The relevant material thermal properties were
obtained from the suppliers and the open literature
such as polymer degradation and crystallization
kinetics. In addition, the ICAT process will be
optimized by understanding the physics underlying
the heating, compaction (intimate contact), and
autohesion (fusion-bonding) of the plies during
the in-situ fabrication process. As a first step in
this physics-based approach, thermal models have
been developed based on a one-dimensional (1D),
or through-the-thickness, closed-form analytical
solution of the relevant system of equations as well
as a 2D approximation of the thermal response
using the finite difference method.
Analytical Thermal Model Development
A heat transfer analysis of the laser heated
thermoplastic tape was performed to assess
the temperature profile during the in-situ AFP
consolidation of the thermoplastic composite.
Also, the temperature measurements from the
ICAT process builds were compared to the model
predictions. A simple one-dimensional thermal
analysis, sufficiently representative of the laser
heat transfer process of the tape in the vicinity
of the nip point of the consolidation roller,
is
considered here in order to provide a quick
estimate of the temperature range expected in
the in-situ thermoplastic panel builds. However,
JULY AUGUST 2022
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SAMPE Journal - July/August 2022

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