SAMPE Journal - July/August 2020 - 34
FEATURE / REPAIR OF COMPOSITE STRUCTURES
Resin was positioned below the part in a holding
fixture, where water can be used to maintain resin
temperature if necessary for large part infusion.
The vacuum pump, heating setup, and temperature logger are seen in the background. The traveler
and work instructions are shown on the other half
of the tool for recording fabrication details. After
the part was infused, the valves were closed and
vacuum was disengaged from the part. The heating
pad was positioned over the repair between the inlet and outlet lines. The control thermocouple was
located off the part but still under the heater in order to allow the repair to heat beyond the heating
pad set temperature. A secondary bag was placed
over the setup to ensure good contact between the
heating pad and the part. The heating pad controller was then started, directing the heating pad to
reach the set point as fast as possible. Figure 9 is a
diagram of the final layup after infusion. Figure 10
shows the cured part of the first infusion trial. The
tool and bag sides showed no signs of porosity.
For all infusion trials, the part was heated to a
predetermined dwell temperature at 3-5°C/min,
maintained at the dwell temperature for 15 min,
and then allowed to cool to room temperature.
Because of the nature of the resin, the repair section built temperature faster and higher than the
set point. This allowed the repair zone to achieve
full cure without overheating the parent material.
In order to control the temperature of the repair
material, various parameters were controlled, such
as flow media type and location and the use of insulation. Discussion of these details is out of the
scope of this paper. Table 2 provides a summary
of five trials performed, including the maximum
temperatures reached at the scarf zone (see Figure 6). For all trials, the tool never exceeded 60°C 5
cm away from the part (and away from the heating
pad). Trial 5 was excluded from results because of a
processing failure.
Figure 9. Top view of final setup including heating
pad under secondary vacuum bag.
Figure 10. First infusion trial cured part (repair
side on left).
RESULTS
Microscopy
UDRI performed microscopy of the repair zone
cross section. The specimens were machined,
potted in resin, and polished before imaging. The
photomicrographs show the bondline diagonally through the image, with the repair zone on top
and the parent on the bottom. The bondline may
either rise or drop moving left to right depending
on how the specimen was prepared. The images in
Figure 11 and Figure 12 show that the parent material (bottom section of images) was free of voids,
Table 2. Process parameters for trials.
34
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SAMPE JOURNAL
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SAMPE Journal - July/August 2020
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