SAMPE Journal - September/October 2020 - 36
FEATURE / BONDED STRUCTURAL REPAIR
Figure 3. Significant impact damage may appear minor at the surface or be nonvisible.
may only damage the outermost plies, whereas a
slightly higher energy impact may result in full delamination across the wall thickness. In either case,
damage at the surface may appear minor or be
nonvisible, as illustrated in Figure 3. Before a repair
patch is bonded to the structure, all of the damaged
material should be removed so that no impact-induced cracks or delaminations will remain underneath the patch, where they could propagate and
possibly lead to a fatigue failure. Damaged material
is removed by abrasion, either in the form of sanding (with abrasive pads or paper) or grit blasting.
The depth and extent of damage can be evaluated
during the abrasion process by periodically repeating the tap test as material is removed. In this case,
the tap test was repeated several times as the tube
wall was sanded increasingly thin, and the structure continued to respond with a dull thud, indicating that the entire wall thickness was delaminated. Eventually, the wall thickness was completely
abraded leaving an opening approximately 2.5
cm (1 in.) across, as shown in Figure 4. Tap testing
around the periphery of the opening indicated that
the remaining material was undamaged. Additional sanding was performed around the opening to
form gradually tapered edges.
SURFACE CREATION AND PREPARATION
After removal of all damaged material, a roughly
2.5 x 2.5 cm (1.0 x 1.0 in) opening surrounded by
tapered edges was present in the previously damaged area. Lay up of a composite patch requires a
mold surface, so, in this case, a new surface had to
be fabricated in place of the opening. This was accomplished by filling the damaged section of tube
with polyurethane (PU) foam. First, a foam casting
was made, from which a plug was carved and inserted into the tube as shown in Figure 5.
With the plug in place, a freshly mixed batch of
foam was poured directly into the damaged section
Figure 4. Removal of all damaged material by abrasion left an opening of approximately 2.5 cm (1 in.)
across in the tube wall. This opening
would need to be filled prior to applying a patch.
36
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SAMPE Journal - September/October 2020
Table of Contents for the Digital Edition of SAMPE Journal - September/October 2020
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SAMPE Journal - September/October 2020 - Cover1
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SAMPE Journal - September/October 2020 - Table of contents
SAMPE Journal - September/October 2020 - 2
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SAMPE Journal - September/October 2020 - Cover3
SAMPE Journal - September/October 2020 - Cover4
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