SAMPE Journal - July/August 2022 - 49

(5)
Additionally, the grid element dy is chosen to be
about the same order of magnitude as the surface
smoothness deviations and no smaller than the
distance between each fiber in the tows (below
which point the composite assumption breaks
down and fiber and resin would need to be treated
as separate regions).
One domain is used for the substrate, another
for the current tape layer being applied, & a third for
the thermal condition of the roller itself, Figure 7.
The domain for the roller is approximated as a
slab of the same length as the circumference of the
roller, and all three domains are set to this length.
The boundary condition on the bottom (i.e., the
tool surface in contact with the substrate) is set to
a constant temperature (i.e., the tool temperature),
enforced each time step. The boundary condition
of the inside of the roller is also a constanttemperature
condition set at or near room
temperature. Side boundaries are set to insulating.
The boundaries between the three domains are set
as a region of adjustable thermal conductivity, set
to zero when the surfaces are not in contact and
set to some value between zero and one when in
thermal contact. Convection and radiation are not
used in the current implementation, but this could
be added as a boundary condition. First-order
estimates show single-digit percentage impacts on
the heat distribution during the actual simulation.
However, convection and radiation over longer
periods (such as between passes of the head) can
create a thermal gradient in the substrate and
roller, particularly for thicker parts.
Laser energy for welding the tape to the
substrate is added as a constant flux to both the
top surface elements of the substrate and the
bottom surface elements of the incoming tape.
The ratio between the two fluxes can be varied.
While nominally this is modeled as a constant
flux for the duration of the laser pass, the flux can
follow any arbitrary positive function, such as an
increasing ramp or an increasing ramp followed
by a decreasing ramp. The length of the laser
pass on the top and bottom can be adjusted. No
sophisticated optics are modeled, but a separate
optical model could be used to provide a function
for the laser input power.
On each time step, any thermal energy from
the laser is input into the substrate and tape grid
elements according to a vector representing the
current position of the laser impinging region.
Temperature conditions at constant-temperature
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Figure 7. Schematic of the finite difference model
boundaries in relation to the nip-point materials.
boundary conditions are enforced. Grid elements
within each region exchange heat with elements
immediately adjacent. The vectors representing
the distribution of intimate contact are advanced
to correspond to the position of the roller. Grid
elements on the edges of regions exchange heat
with elements of regions adjacent according to the
degree of intimate contact set.
SUPPLIED TAPE QUALITY EVALUATION
The quality of the supplied thermoplastic tapes
currently available from Toray and Victrex were
evaluated. As a part of that ongoing effort, crosssections
were taken from the supplied Toray
TC1200® and the Victrex AE250/IM7® slittape.
The specimens were potted, polished, and
photographed using a digital microscope at 100X
magnification. Figures 8 and 9 show the results of
the photomicroscopy for the TC-1200 and AE250/
IM7 slit-tape, respectively.
Figure 8. Photomicroscopy of Toray TC-1200 slit-tape.
Figure 9. Photomicroscopy of Victrex AE250/IM7 slit-tape.
JULY AUGUST 2022
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SAMPE JOURNAL | 49
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SAMPE Journal - July/August 2022

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