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Hanaldo
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Hi all, I have come across an interesting problem that I've never seen before, was hoping someone might be able to give me some insight. I made a false floor for a Ford F1000 using one layer of 200g carbon on the surface, and one layer of 850g biaxial fibreglass. The part was infused with epoxy, as I always do and have done hundreds of times before. 0 micron drop over 24 hours registered on my digital vac gauge prior to infusion, so absolutely leak free. Infusion went perfectly, everything wet out nicely etc. Left to cure for 48-50 hours prior to demoulding. This is when the issue became apparent. I removed all the consumables as I normally do, then used compressed air to blow the part off the mould. As I blew the air into the gap between the part and the mould, this happened:  First thought was "s***, must have left the clear packing tape in there!" (the supplier I get the fibreglass from annoyingly insists on placing clear packing tape on the cut line when the cut some off the roll). Anyway, kept going with removing the part from the mould (I use Frekote, so it's not like much effort was required, it virtually fell out), and it just kept happening:   So I grabbed the offcut from the hole I cut in the centre, and the fibreglass peeled off the carbon easier than peel ply!  The 2 skins individually are very strong, the unidirectional fibreglass doesn't delaminate from the +45 degree layer when placed under load:  And the carbon is also strong, for 1 layer of carbon. So individually, the skins are performing very well and the resin is doing its job, it isn't delaminating from each skin. But there is just no interlaminar bond strength, I'm not exaggerating when I say it's harder to remove peel ply. These are materials and process that I have used many times, I'm not unfamiliar with any of it. But this is the first time I have seen this, and it's got me stumped. Anyone have any ideas?
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scottracing
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is there a binder on the fibreglass material? i cant think why it would have such little bond between the two materials if both have cured properly, unless one of the materials has got a unconventional binder that doesnt work with your chosen resin?
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Hanaldo
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It's a stitched biaxial, so there's no binder. In any case, I have used this same fibreglass previously with the same resin, and that part is still going strong today (was made 18 months or so ago). None of these are new materials, I've used all of them with each other successfully before, which is why I'm totally baffled.
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Warren (Staff)
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It can be quite easy to delaminate a layer once it has initially seperated, which initially could have been caused by a number of things. In essence, it's only the resin holding the layers together so a relatively fresh part would be easier to delaminate like that than something more fully cured. As you have mentioned it doesn't delaminate under load which is key. It does seem a little strange that it delaminates easier than peel ply.
Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant
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Hanaldo
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Individually the plies of fibreglass uni don't delaminate, but the carbon and the fibreglass do delaminate from each other under load. Give it any sort of flex and the fibreglass delaminates from the carbon all over the place.
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Matt (Staff)
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It's hard to say for sure because the biaxial glass (and possibly the carbon?) are not supplied by us but it does possibly point to something on the outside of the glass fabric that's encouraging delamination. You say the glass 'isn't new' so could it perhaps have some contamination on the outer layer; moisture ingress or silicone/oil mist contamination from a workshop environment?
As Warren says, you'd be amazed by how easily layers of reinforcement will delaminate from eachother; there's prcatically no difference between peeling peel-ply off your part and separating layers of laminate, which makes sense when you think about it - in either case you're simply breaking the resin-only bond between two layers of fabric.
It's possible that there is some contamination issue or it's possible that you simply didn't realise how easily laminates can be delaminated. If they don't get 'started' then you generally don't ever encounter a problem. The work of the part is done by the tensile strength (and modulus) of the reinforcement.
Compressed air is lethal when it comes to delaminating composites, much like trying to 'burst' through a laminate using a waterjet (which can delaminate even the best prepregs).
I hope this helps.
Matt Statham
Easy Composites / Carbon Mods - Technical Sales
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Hanaldo
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Thanks for the reply Matt. Indeed none of these materials are supplied by you, these are all local materials (except the carbon is from the States). I sort of agree with you that it must be something about the glass, however it has been stored for the past 18 months or so folded up in a cupboard at home, underneath various other types of fabric. So it for sure won't be oil or anything from a workshop environment, and I can't see it being dust. Moisture I guess is possible, but no more so than any of my other fabrics. I also have delaminated parts previously as you describe, but it's not at all like this. Previously, once I got an edge on a layer of a laminate it tended to snap the fibres before I could peel the entire skin off. It is the delamination under load that concerns me, any twisting or flexing of the panel causes more delamination, I don't have to pull at the fibres. Whatever is going on, it certainly isn't normal, there has to be something very wrong. I know compressed air can be a dangerous thing, but really, how many times does it cause total delamination of a laminate like this? I've certainly never seen it before, and I've used it to demould a fair few parts, often at times using a 100psi blast from a tyre cannon! There's no way the interlaminar void could be dry is there? It doesn't make sense to me and I'm sure it's not possible, but the laminate does look dry on the delaminated surface. Right down to the 'darker' spots between the weaves of carbon. The mould surface is totally wet out, no dry spots or pin holes. The only reason I am questioning this is because I calculated the laminate would use 550 grams of resin, but it only used 350. The part is 0.25sqm, so 350 grams for one layer of 200g, one layer of 850g, and the flow media... It doesn't seem enough...
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Hanaldo
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Just to update this; I investigated this issue further with the supplier after I did various tests and all came out with the same delamination issues. I was able to rule out spray adhesive being an issue, as delamination occured on 2 independent flat sheets that were laid up in the same schedule as the original part, but minus the spray adhesive. The only laminates that I had any issues with were those that included the 850g biaxial glass in it. In light of this, the supplier asked me to bring the fibreglass back to them, and we have concluded that the issue is very likely to have been caused by over application of the sizing agent in the manufacturing process. The material had always been very cardboard-like, very stiff and dry (a bit similar to 3D PET core, but was able to conform under vacuum). The supplier has replaced the fibreglass from a new roll of 850g biaxial, and the difference is worlds apart. Had I known how flexible and soft the fabric was supposed to feel, I would have raised this issue a long time ago, I just put it down to being a heavy-weight uni-directional fabric. Panels with the new fibreglass have so far been perfect, no delamination issues at all.
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scottracing
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good to hear you found the problem with the material!
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Matthieu Libeert
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nice to read your investigation, We had some same problems while building a boat, we first thought it was the removed peelply surface not giving enough bond for the following layers
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