Composites 101 technical questions by SAM

[mdcfab]

I will start posting pictures and literature on composites, mostly carbon fiber and fiber glass. I am visiting some friends at swift engineering and will take picture and post a race car composites shop on Thursday

The first know how
Matrix also known as resins. The matrix is what holds the fibers together(glue)

most commonly used resins

1. polyester resin cheapest, week, brittle,shrinks
2. Vinyl ester resin stronger less brittle shrinks less cost more
3. epoxy resin is about 3 times cost of polyester,epoxy stronger harder and
more stable very little shrinkage.holds up again higher heat

when you here people say its prepreg 95% of the time its going to be epoxy



Any questions on composites I would be more than happy to answer. :biggrin:

 

[UnhuZ]

the friend of mine that i talked about in Procar's thread, uses epoxy, but he is always trying to find a better one.

he managed to do, vacuum bagged, Integra Type R DC2 and Civig EG9 hoods, with a weight a little south of 3Kg, with 2 layers of carbon on top and 2 on bottom with some kind of foam (i think it's the correct name) in the middle, with the under structure only at edges all arround the hood, and you can't imagine the strengh of them... we could even jump up and down on top of them that almost nothing happened but a few scratchs ont the clear coat.

that's one of the things that impressed me about his work.

he also made replicas out of Recaro's Pole Position (but in Carbon kevlar), and the shell was strong...very strong...and light....very light....

 

[mdcfab]

Yeah you describing a panel (sandwich) panel the core material can be a great deal of variations foam,aluminum-nomex honey come even balsa wood works fantastic it just depends on application and cost. But, composites are a beautiful thing I was at swift engineering tonight and looked at some of the new tub and wings the are beautiful work of art I'll post up some pictures
why is your friend trying to use a different epoxy ??? cost or quality or hard to use ???

 

[mdcfab]

here are some photos just visiting old friends and my old Job at swiftengineering
left to right
peter and me on left acting like we are pulling a mold with a nose for an open wheel car the 016 to be exact from a small to mid size autoclave

then the autoclave closed
next picture is a few old champ cars sitting around. one of those Robby Gorden used to race.
mext is the new car swift has designed prototype and building for the Japan grand prix cars that pictures shows the the top part of the tub (where the drive sits the main body) being prepared for assembly with the bottom have you can see the aluminum jig fixtures custom made just to put these together
the last picture is the toyota atlantic open wheel race cars some what apart
other wise known as the 016 :biggrin:
hope you guys enjoy these I have a lot more pics I can share on prime

 

[UnhuZ]

why is your friend trying to use a different epoxy ??? cost or quality or hard to use ???

he always just try to find a better epoxy...he test it and if he have better results, he uses that from that point on...

i'll try to find pictures of some of his work to post here. i think i already did post the picts of the recaro PP shells.

 

[Jeff@Carbon6]

Sam,

I'm still just a composite hobbiest but starting to make some structural parts. Wanted to get you opinion on this. I use a Dow 600 cps epoxy that has a tensile stength of about 10,000 psi. I make a special under pan for my widebody that incorporates the subframe under the battery, The first one I made I built up 12 layers in the recesses and 7 layers everywhere else (4x4 twill 8.5oz CF). I used an infusion and saturated the material about 50/50 resin to cloth (by weight). The part is super strong but creaks when I roll 1 wheel off my driveway at a time. Would it be stronger to wrap the cloth around a core material? I don't seem to have any twist with it now but it seems like it would be beneficial to be as strong as possible.

Pic of the mold:

 

[mdcfab]

can you give me more details sounds like its making noise where it mounts to I don't thinks its the actual panel more pics please

 

[Jeff@Carbon6]

can you give me more details sounds like its making noise where it mounts to I don't thinks its the actual panel more pics please

I agree, the noise is coming from the attaching hardware. I guess I can simplify the questions by just asking if it would be more ridged if I wrapped a core material in a tubular shape or kept it as a flat lamination. I was thinking of trying a test with some cf sleeves wrapped around divinimat and laminated inside the whole part (vip).

 

[mdcfab]

I agree, the noise is coming from the attaching hardware. I guess I can simplify the questions by just asking if it would be more ridged if I wrapped a core material in a tubular shape or kept it as a flat lamination. I was thinking of trying a test with some cf sleeves wrapped around divinimat and laminated inside the whole part (vip).

yeah adding core will make a huge difference in the stiffness but do you have the clearance ??? a cheap secrete :biggrin: buy white cheap styrofoam a thin layer maybe 1/2 inch thick if it fits . so you would example 3 layer of carbon then styrofoam then 3 more layers carbon also are you rotating the carbon to change the warp and fill directions ??? that also matters a lot if I leave DF early enough tonight I will draw up a layup schedule for you and post it up :smile: also I have samples of wing sections from race cars cut outs of the tunnel and tub and other piece I can give out to who ever request them. divinimat is better though just more money.

P.S. styrofoam only works with epoxy and urethanes do not try it on polyester will melt

 

[Jeff@Carbon6]

I use the Divinimat for core material because I can vacuum infuse it. I've tried styrene and urethane foam and it causes voids. Also the Divinimat will not deform under 30 atmospheres of vacuum. I think it's made from vinyl.

 

[mdcfab]

I use the Divinimat for core material because I can vacuum infuse it. I've tried styrene and urethane foam and it causes voids. Also the Divinimat will not deform under 30 atmospheres of vacuum. I think it's made from vinyl.

yeah possible most likely its polyurethane
and not to correct you but its 30 hg inches of mercury and one full atmosphere
14.7 psi is our atmosphere :biggrin: I only correct to educate sorry don't mean to nit pick. Yeah great job infusing by the way not many people get it. I am impressed

 

[Jeff@Carbon6]

yeah possible most likely its polyurethane
and not to correct you but its 30 hg inches of mercury and one full atmosphere
14.7 psi is our atmosphere :biggrin: I only correct to educate sorry don't mean to nit pick. Yeah great job infusing by the way not many people get it. I am impressed

Oops, yeah meant to say inches of mercury, My bad. If you don't mind me asking, what is the viscosity of the resins you use for production parts? do you use pre-preg on anything?

 

[ScienceofSpeed]

I agree, the noise is coming from the attaching hardware. I guess I can simplify the questions by just asking if it would be more ridged if I wrapped a core material in a tubular shape or kept it as a flat lamination. I was thinking of trying a test with some cf sleeves wrapped around divinimat and laminated inside the whole part (vip).

I think bushing your panel with rubber would eliminate the noise from the chassis flexing. Use a high density rubber or neoprene washer between the chassis and the panel. Looks nice!

Cheers,
-- Chris

 

[mdcfab]

Oops, yeah meant to say inches of mercury, My bad. If you don't mind me asking, what is the viscosity of the resins you use for production parts? do you use pre-preg on anything?

we use a lot of vinyl ester resin more expensive than polyester but the quality is a lot better I just picked up 2 freezers from swift engineering (we got a good deal:wink: ) and have some prepgreg we are going to start using .. eventually all our products will be epoxy
100-200 centipoises on some of our resins