Blade Wrinkles Explained with Morten Handberg of Wind Power LAB

Allen Hall discusses the growing issue of blade wrinkles with
Morten Handberg, blade expert at Wind Power LAB. They delve into
the causes, consequences, and challenges of identifying and
repairing these minute deformities that can significantly reduce
blade life. Visit https://windpowerlab.com/! Sign up now for Uptime
Tech News, our weekly email update on all things wind technology.
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www.weatherguardwind.comIntelstor - https://www.intelstor.com Allen
Hall: Welcome to the special edition of the Uptime Wind Energy
podcast. I'm your host, Allen Hall, and if you have been following
the news lately, there are several ongoing campaigns by blade
manufacturers to deal with wrinkles in their blades. Even though
these wrinkles are minute in appearance, these fabric deformities
can create weaknesses that reduce blade life. And as you have seen
all over the news, these wrinkles are also expensive to remove and
repair. Our guest is Morton Handberg, Chief Blade Specialist and
Partner at Wind Power Lab, which is a blade consulting company
located in Copenhagen, Denmark. If you haven't heard Morten on our
podcast previously, Morten is our resident blade whisperer. In our
episode today, we'll be discussing how wrinkles are created, how
they produce stresses, and why they are difficult to eliminate
during manufacturing. Morten, welcome to the program. Morten
Handberg: Hi Allen, Allen Hall: it's nice to be back again. If we
can catch up a little bit, you and I talked to each other about
Blade Wrinkles several weeks ago now, and that topic has just
gotten progressively hotter and hotter. I thought, now's the time.
To get it out there about what's happening with wrinkles and why we
should care. Now, and at the same time, you sent me some pictures
and it would just scare the heck out of me because I thought these
wrinkles were relatively small coming from an aerospace background.
Wrinkles don't tend to be big. In aerospace products, but the
wrinkles you showed me are large. And I'm trying to understand like
what is the real threat here? Let's just start there. What's the
real threat. If a wrinkle is in a side of a blade, what does it
matter? Morten Handberg: So it really matters depending on the
location of the wrinkle. So is it in the structural spark cap or in
a heavy node, part of the bait, let's say the root or the
transition zone. Then even small wrinkles can actually turn into
very large cracks. And it doesn't really matter what the size is.
It's more, if it's in an area that allows it to grow into a crack,
because as soon as it does that, it will just continue growing at a
pace defined by the loading conditions, it can ultimately turn to a
blade failure. Obviously, the larger and more aggressive, the
cracking the wrinkles, meaning how how steep the angles are of the
wrinkles. So if this is the shape it matters that the wrinkles is
shaped like this or like this. Then how much stress it requires for
it to develop, because it's all about the, how much reduction that
it creates to the to the underlying blade structure. If you have
changes in the UD laminate and it starts to fold, it means that the
strength of the UD laminate is reduced. And then it's just about a
matter of time before it then turns into a structural crack. Allen
Hall: And the defect doesn't just apply to the plies where the
wrinkle is, it applies, it puts additional stress on the plies that
are around it? Is that the loading problem? Morten Handberg: Yeah,
because, if you remove the loading capacity of one area, it has to
be taken up by another, right? It doesn't, the loading doesn't go
away. It just, if you have a wrinkle that starts turning into a
crack, it means that all the UD fibers, they are essentially
removed from the equation. They're not taking up any blade loads
anymore. And that then creates more stress to the boundaries of the
crack, but it also creates more and more stress to the other
laminate areas of the blade, because now they have to take over
whatever part is this area of the blade, but this area of the
laminate was taken over. And this is also why some of these cracks
can turn into blade failures. Because at a certain point, then then
the amount of laminate that's been removed, that's not enough for
the rest of the blade to, to carry the load anymore. And then it
eventually fails. Allen Hall: What does this look like as the
wrinkle progresses into a larger defect? Is it a delamination that
happens? Is it a physical crack? Like you start breaking plies?
What does it look like? Morten Handberg: If you have a wrinkle as I
said, it's like a fold inside the laminate. If the, if that fold is
creating a wave like this, then at, on the top of the ridge, you
are, you're consistently, the wrinkle is trying to stretch itself
out during operation. So it's trying to do like this and that
creates a lot of stress on the top part of the ridge. And that's
where you create the crack. But on the lower side where you have
the slopes, they are trying to lift they're lifting themselves out,
out of the laminate, essentially, that that's what's going on. Is
it and that then means that it de bonds from the from the lower
from the laminate. What we typically see is that on the lower
boundaries of the wrinkle, we create delamination and then on the
ridge, we create a crack in the direction of the wrinkle. Wow.
Okay. Allen Hall: So you, depending on where you're looking, you
may see a DLAM or you may see a crack on either side of it, but you
probably have both? Morten Handberg: If you have in a very
sensitive area where you have very high loading, maybe one or the
other is more than maybe the crack is more. Aggressive than the
wrinkle. So the crack will progress faster than the delamination
develops. If you're in a low unloaded zone, then maybe it's the
delamination that is the most prominent one developing. So you
can't really say that with, for whatever, whenever you see a
brinkle or you see a brinkle in development, that. It will be the
crack that will be the dominating or it will be the the
delamination. But if you're in the Spark app laminate, then you
would cut away the laminate layers before the delamination becomes
anything significant. And then the crack will be the be the measles
finger. Allen Hall: So the blade manufacturers today, when they, if
they have blades out in service and they realize that they may have
wrinkles, is it easy to detect how, if you're on a turbine, this
blade is on a turbine, can they find wrinkles simply or is there a
way to do that? Or is this get really complicated for them to
identify where the wrinkles are? What is normally done when the
blade is produced? Morten Handberg: Is that after the, after it's
been demolded. Either the shell or the full blade, depending on the
manufacturer. A QC technician will go through the entirety of the
blade on the outside and on the inside and look for waviness or
rises in the laminate to see are there any wrinkles here and then
get those fixed if they're outside of factory specification. Allen
Hall: How are they identifying those? Is it an ultrasound? Is it a
flashlight? Is it a tap test, what's involved there? Morten
Handberg: A Tap test wouldn't make any sense because see, it's
still solid laminate, so there's no no, no deep bonding that you
could detect from a Tap test you can use ultrasonic to see you, you
typically do that for the low carrying path of the lathe, for the
spark caps. Not all OEMs are doing that. And that is a problem
because often what some of the wrinkles that we see leading to
major structural damages or blade failures, Is because the the
quality checks at factory were not sufficient. We're not not
carried out in a way that would allow for them. But skilled quality
technicians, they would be able to see them either visually, just
by looking at it, by knowing how does a healthy laminate look from
a laminate with a distortion. You can also, to some extent, use a
you use a light dispersion test by holding over a flashlight over
an area and see how the light passes through it. If there's any
major changes to lemme structure that will show in, in, in that
way, but it requires some skill to detect it that way. So again,
it's not something that you would send out any guy on the street
and he would be able to find it. You need to know what you want to
look for at the factory. The best way to do it is to use entity but
that's typically only applied to the main load carrying parts of
the blade, because that's what you're mainly concerned about, but
wrinkles can happen anywhere. It's not something we can say it
always at six meters. It's only on the leading edge. It's only in
the spike gaps. They can occur anywhere where you have a laminate
stack. Allen Hall: And then, so in the factory, easier to identify
because the blade's sitting there and you can have probably the
proper tools, Once you're in service though, what happens, is it
only ultrasonic? For the inner third of Morten Handberg: the blade,
you could still, you can still walk in, do a manual inspection to
check if there's any changes to the, any, if there's any visible
changes in the laminate structure. Not seeing a damage yet, just by
seeing if there's a, if there, there's a certain rise in the blade
suddenly without any need for it. That typically indicates that
there's a wrinkle in this area. They can either be longitudinal,
they can be transverse. Typically longitudinal,