SAMPE Journal - January/February 2020 - 10

FEATURE / THERMAL INSPECTION
ethernet connection using the industry standard
GigEVision protocol. The camera communicates
to a data acquisition computer at the operator's
station via an ethernet switch on the AFP head
itself, which then passes the ethernet through the
slip ring/tool changer assembly at the end effector
of the robot. The thermal camera is mounted near
the existing visible light camera, which is used by
the operators to monitor the roller. Both cameras
point to a region directly behind the compaction
roller to observe the material right after lay up as
it passes underneath the roller. The placement of
the camera coupled with the installed 50 mm lens
enabled the capture of a 7.62 cm x 10.16 cm region
behind the roller, giving a 4232 pixel/cm2 density.
Tow Steered Composite Experiments
NASA LaRC collaborated with Generation
Orbit Launch Services (GO) to investigate the
feasibility of fabricating reduced-mass composite
rocket bodies using AFP tow-steering. Tow steering
is a method with which design engineers can
efficiently tailor the strength of a structure by
orienting the fibers in the direction of loading.
Tow steering is performed by rotating the direction
of the AFP roller during the layup of individual
courses, instead of keeping a straight path as is
seen in traditional layups. Normally these types
of rocket bodies are built with a quasi-isotropic
stacking sequence to produce a composite with a
strength that is uniform throughout the cylinder.
By steering the fiber direction to where it is most
needed the overall amount of material needed can
be reduced. The collaborative project designated
GO-1 designed the tow-steered cylinder seen in
Figure 4A. The strength of the structure is tailored
to a series of mounting hard points on the crown
of the cylinder. This was to ensure the hard points
could support the entire launch vehicle, enabling

the rocket to be mounted and launched from the
wing hard point of an aircraft11. The final cylinder
designed was 1.85 m tall with a 0.61 m diameter.
Despite the potential mass savings of tow
steering, uptake in aerospace applications have
been limited. Intuitively we see that, during a tow
steer, the tows at the outer edge of the curve will
cover more distance than tows at the inside edge
of the curve. This is accounted for in the tow feed
rates during a tow steer; however, each tow has a
finite width. Thus, it is difficult to make a tow bend
about its width (in plane) without the edge peeling
up from the ply or buckling on the respective sides
of each tow. Tow misalignment leading to overlaps
and gaps is also a concern, as tows may slip out of
place due differences in tow tension and loss of
adherence11.
To investigate the likelihood of these defects
and how well they could be mitigated through
process control, the GO-1 team designed a tow
steered panel based on the design of the GO-1
cylinder (Figure 4B). We acquired thermography
data during both the panel and the subsequent
cylinder builds. The results generated from testing
on the tow steered panel contributed directly into
the process development and build plan of the
cylinder.
Additionally, we recently rebuilt the GO-1
cylinder using a modified stacking sequence and
process parameters. The intent was to characterize
the effects of sub-optimal compaction on the
thermal data acquired during the build. This work
is still on going, but preliminary results will be
presented in the following section.

Figure 4. (A) Design of the GO-1 tow-steered cylinder. (B) Diagram of the tow steered panel used for risk mitigation study, and
the section of the cylinder it was built to imitate.

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SAMPE Journal - January/February 2020

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