Show notes
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/!
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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,