Carbon weave, fiber density, etc >> what is ideal for high stress member?

General Composites Discussions Composites Talk
#1

What is the ideal mix of weave , fiber density, for acheiving the strongest component. I am looking to use vacuum bagging to make my part (motorcycle sub-frame) and leaning toward 3K twill. I realize that 6K would allow quicker build-up but would how much more structural integrity is gained by using it? (I imagine that 2 plys of 3K would be stronger then 1 ply of 6K, is my assumption correct?)

Should I be using HS, Plain, or twill weave? How much/ how does the weave effect the strength? For a given # of layers of 3K vs 6K what is the strength benefit?

I am really concerned about strength of the component as I said before, because it has to be able to bear the load of my ass and any road bumps etc.

Also, for mounting the component it has to be bolted on the bike. Should I lay the fiber in a way to allow a hole for the bolt to pass through, or should I just use a high speed drill to carefully drill through the cured component? :confused:

Thanks in advance.

#2

I am thinking of making exactly the same part, but for off road bikes. Probably looking at using a carbon-kevlar hybrid, infused with epoxy resin system. Not looked at dealing with bolt hole areas yet, but may reinforce them with titanium sheet.

#3

that sounds like a good projct. In my case , garage project , using Ti would be out of the question. How does one deal with the bolt-on issues? do you take the threadded metal piece and lay it with the fabric and resin? or do you drill after curing and just tighten the carbon part to the frame with nut and bolt?:confused:

#4

I would put riv-nuts into small pieces of titanium sheet, and bond them to layup with epoxy, after it has cured.

#5

I have seen such things as the chasis of cars use epoxy and bolts to hold the car together(lotus elise I think) but how strong is any epoxy that the puplic can get their hands on?

How durable would a Ti sheet mounted to the cured surface of a composite material be? wouldn’t that run the risk of delaminating the composite part where the sheet is bonded to the CF component?

I have no doubt that the modern adhesive has some astounding strength but I still have trouble getting over the idea of “gluing” parts together (but composites are just that :smiley: ) you know what I mean?

#6

just a thought, i had seen an article on making fiberglass/composite parts where bolts are needed, the put the bolts into the part they were making so that when it cured the part had the proper threading in it. as for the car being held together by resin and bolts, its a special resin that is made for aluminum and its also riveted, im sure you could get a hold of similar strength resins, not necisarily that one as that is specific to and developed by lotus’ aluminum provider.
hope this helps some
john

#7

Thanks for the input

#8

We don’t worry about fiber sytles much, so I can’t help ya. however, our bolt hardpoints are normally a block of G10 (compressed fiberglass i think), drilled out and helicoils put in…simple as hell. I know there are specific hardpoints made for putting in composite plys. Whatever you use, I’m sure it’s a good idea to wrap in fiberglass before putting layers of carbon on it, so you don;t have corrosion.

#9

When I worked on V-22’s, since most of the airplane is composite, they had things we called “click studs” bonded to the surface for attaching parts. I was not a structers person, though I wish I had talked to those guys more now, but only rarely did the click stud come off of the composite and delam it. For years we had problems with them popping off. The key is having an adhesive that is not quite as strong as the resin matrix used in the composite, therefore the adhesive fails before it delams the composite.

#10

I always hated Heli-coils and favor Keen serts! There are a pop rivet type of a threaded insert too and they are called Brute Thread serts…I’ll shoot and post a picture later on today.

OK, I’ll admit it. I’m an aerospace fastener junkie! I go to these surplus fastenor stores and spend all my hard earn money there!

#11

Yeah, but I bet you put them to good use.

#12

why not just bond in a small section of stainless sheet and use some rivnuts?

Or epoxy in a dowel with double shoulders and then use a nut and bolt to affix it to the frame…you have 4 mounting points…and it really doesnt bear much load.

Thickness? Id imagine youd need 20 layers to make the thing super strong and still light.

#13

Sounds like good advice guys keep any ideas comin.

That sounds like a good idea, it would probably be easiest to do the nut and bolt suggestion. THanks.

#14

Ok, here’s a pict of some of the fasteners I was talking about. The red ones at the bottom are the real composites ones but maybe more for Honeycomb type panels. One has a captured nut and both and stepped for the clearance hole and oversize washer head to clamp down properly.

#15

What is the red part made out of aluminum or plastic?

#16

google “rivnuts” I think thats what is on the top in the pic.

#17

The top ones are the Brute and may also go by Rivnuts too! Many versions of them too…Macfadden Dale & MacMaster Carr has them.

The red ones are anodized alum and if you want a few to test them, I might be able to mail you a few sets…for a donation to keep this forum going…

Most of these aerospace surplus places I go to sell these types of fastenors by a $1 or $2 a pound (US)!

#18

Hoping for a bit of a clarification with the process…I have read that there are significant losses in strength if you drill the cured composite to make the hole. Wouldn’t it be much stronger to either cure the rivit into the part or to make the hole before curing the part somehow?

#19

I’m no specialist in that field but in my mind, if you add extra plies in those areas it would be stronger drilled and compression fitted that trying to lay up around a fastener.