January/February 2023 - 19

honeycomb, the adhesive sometimes fails, " he said.
" You get fatigue damage... Although composites are
extremely strong in fatigue, over time there can
become some micro cracking into the laminate
due to the high cycles of either it is on skims or it
could be in different areas that are very dynamic
on the aircraft. "
The other types of damage Thouin said to watch
for are stress cracking and erosion.
For repairing composite material there are two
main types of repairs: cocure and voltage.
" A cocure repair is typical for a skin that can be
scarfed. And what we mean by scarfed is, there's
a damage area which will be completely removed
and then there's a tapering area in the surrounding
which you do very gradually, and then you go place,
essentially, what you could consider a patch back
onto that area by respecting the same gradient that
you scarfed to. That's typically done using heat and
vacuum, " Thouin said.
Voltage repairs are typical for a thick laminate
that cannot be scarfed.
" So we would essentially, just as is stated, bolt a
new skin or both a new part onto the existing
part. But I think it's important to notice that
all repairs start out with the guidance of the
designer, the OEM, whoever is responsible
for that aircraft. And that's known as the
structural repair manual, " Thouin said.
Dorworth said common mistakes are not
removing enough of the damage and bonding
materials together that aren't compatible.
" For instance, honeycomb core has what
we call a pronounced ribbon direction, and
you have to match the original ribbon direction
with the core. So sometimes you'll get
technicians that don't match that properly
or they're 90 degrees off on that core replacement.
The other part is that people, after they
do the scarf repair, sometimes that part,
they'll do slight damage in the structure
and just assume that they can cover that up
with a repair patch and nobody will know, "
he continued.
A Future of Growth
With aircraft becoming more and more composite-based,
both Thouin and Dorworth
agreed that the adoption rate of composites
is going to grow over the coming years, but
neither think there will ever be a 100 percent
composite aircraft.
" I think adoption will continue to increase. It will
forever be a multi-material solution. I don't think
we'll ever come to a point where we have an airplane
that's run 100 percent composites because there are
still some applications where metals are either more
efficient or either more performant or sometimes
just more efficient to put together. So yes, I think
we're going to continue to see adoption throughout
the next decade, " Thouin said.
" The Boeing 777 has a wing box, portions of the
fuselage, those sorts of things. 787 included. So
we're seeing that. Over in Europe, the A350 has
a fuselage wing, empennage sections. They're all
composites. So they're going to composites in a
big way in the future here. So whether we see all
composite or not, I think that's going to be probably
not. We're going to see a lot of mixed materials,
where it's more efficient to have a titanium fitting
or titanium product or an aluminum product.
That's what we're going to see, is a combination of
materials. But the bulk of the structure and the
ability to lightweight is found in composites, "
added Dorworth.
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January/February 2023

Table of Contents for the Digital Edition of January/February 2023
