SAMPE Journal - September/October 2020 - 41
Table 1. Laminate stacking sequence of the repair patch. The 0 degree direction is defined as the axis
of the tube.
consists of a patch bonded to the underlying structure by single lap joints. The recommended overlap
(Llap) for single lap joints is 80t, where t denotes the
laminate wall thickness3. Over lamination was chosen to increase the total thickness of the patch (increasing the rigidity and strength of the repair) and
also to achieve an aesthetically pleasing symmetric
surface finish by overlapping the full tube circumference with the outermost plies.
The carbon fiber fabric chosen for the repair
was a plain weave of AS4 carbon (a standard modulus, high strength grade) in 3K tow. Dry fabric thickness was approximately 0.23 mm (9 mils). Four
plies were used for the scarf patch, and two for the
over lamination. The ply orientations and stacking
sequence are shown in Table 1, where ply 1 denotes
the first or bottom ply, and ply 6 denotes the outermost or surface ply. Four plies were oriented at
0/90° (the 0 degree direction is aligned with the axis
of the tube) and two were oriented at +/-45°. This
lay-up was based on observation of the stacking
sequence of the parent tube during abrasion. It appeared that the parent tube consisted primarily of
unidirectional plies oriented at 0°, along with a few
inner plies oriented at +/-45°. Each unidirectional
ply of the parent tube was approximately 0.13 mm
(5 mils) thick and the wall thickness was approximately 1.3 mm (50 mils). The dimensions of each
ply in the repair patch are given in Table 1. The outermost ply of the scarf patch measured 7 x 7 cm.
This dimension provided a scarf length of approximately 20t, which falls within the range used for
repair of composites in the aviation industry9 while
keeping the repair area relatively small.
w w w. s a m p e . o r g
Figure 14. Heat shrink tape was used to hold
the plies in place, provide compaction pressure,
squeeze out excess resin, and shield the epoxy
resin from air and moisture during cure. Excess
resin is visible exiting seams in the tape. Heat
shrink tape is easy to apply on tubular structures.
Figure 15. The patch was top coated with a fast
curing epoxy resin (West System 105/206) to inhibit amine blush. The top coat provides additional protection for the fibers and a smooth, glossy
finish.
S E P T E M B E R /O C TO B E R 2 0 2 0
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SAMPE JOURNAL
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41
http://www.sampe.org
SAMPE Journal - September/October 2020
Table of Contents for the Digital Edition of SAMPE Journal - September/October 2020
Table of contents
SAMPE Journal - September/October 2020 - Cover1
SAMPE Journal - September/October 2020 - Cover2
SAMPE Journal - September/October 2020 - Table of contents
SAMPE Journal - September/October 2020 - 2
SAMPE Journal - September/October 2020 - 3
SAMPE Journal - September/October 2020 - 4
SAMPE Journal - September/October 2020 - 5
SAMPE Journal - September/October 2020 - 6
SAMPE Journal - September/October 2020 - 7
SAMPE Journal - September/October 2020 - 8
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SAMPE Journal - September/October 2020 - Cover3
SAMPE Journal - September/October 2020 - Cover4
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