If you use prepreg to produce parts, but happen to have some dry carbon fabric that you want to use, how successful would the parts come out if you decided to lay down dry fabric (200gsm 2x2 or 200gsm UD) onto the prepreg? Would it work/fail on both the surface and in the middle of a laminate?
I would imagine you’d have to use prepreg with a higher resin content, say 42% stuff to have some sort of success?
Thanks,
Kyle.
Wouldn’t work at all, it would come out very dry and the interlaminar bond would be very weak so they layers would delaminate very easily.
You could however do it with the use of a resin film. You would need to work out how much resin you need to add, and it may affect the void content of the pre-preg, but it would work!
Ah right, ok. That’s kinda what I thought. Thank you Hanaldo.
As for the resin film you mention - how/where would I find some? Whenever I’ve looked, the only stuff I’ve come across is what you use for bonding cores.
Thanks wobcomp.
Maybe you want to use the dry fabric as a core between the layers of pre preg? Anyway,I don’t think it could work.
My thinking was that if I used prepreg to make parts, but bought inexpensive carbon fabric whenever it was on offer and added that into the laminate.
Realistically, it’s going to end up being a more expensive way to go about things by the time you get it to work.
If you use a layer of kevlar between other two of carbon, the result is pretty good, and Kevlar is not so expensive as you could think (anyway you have also to wet it as you do with carbon). I did once in this way during the making of my several bottle cages for bicycle.
I can’t imagine that any prepreg would have enough resin to properly wet out a dry fabric placed against it.
I have done this with a really light 70g kevlar and it worked ok. I have also seen others do this with glass pre preg and 160g kevlar. Also seen soric successfully sandwiched in glass pre preg too.
You need enough layers of pre preg to ensure enough resin or you can also plan for the technique by ordering your pre preg with a higher resin content.
Yes indeed, I don’t think the resin used to wet the prepreg could be good enough to impregnate the dry fabric.
Thanks for the responses!
It could be one of those things to experiment with using scrap pieces.
The point of prepreg is to tightly control the resin content at a minimum. Resin isn’t even close to the strength of the fibers so the less resin the stronger the part (by weight). So any prepreg you use will have as little resin as it can hold so if you add dry fabric you’ll starve the prepreg of resin and almost certainly not fully saturate the dry fabric.
And if you add saturated fabric to prepreg layup then you’ll want to make sure the two resins are compatible from a chemical and cure standpoint.
Bottomline- don’t do it for anything you care about.
If you order larger quantities you can adjust the resin content. Sometimes this is used to bond cores in stead of using glue films. I also know it is used in very specific applications to wet out dry fibre in the layup, for instance to get some air flow/extraction in the laminate,or use materials which are not very easy to pre-impregnate. It will require some testing to get to the right panel specifications, and maybe a different curecycle as well. But I can’t really think of a reason to create this possible points of failure in the manufacturing process, unless absolutely necessary.
Even using the higher resin content to bond to the core, as some find cheaper because it is less work, creates a very “fat” prepreg , which is harder to work with, it leaves resin everywhere, is more sticky, and creeps away more while laminating, so in my eyes gives a less controllable process, where quality will suffer. Working with prepregs usually means high performance products, in which sub optimal parts will either be resulting in more weight, or failure in the range of normal working loads or reduced safety margin.