Non Autoclaved Carbon Fiber

[pmatolcsy]

I copied this post from the Trevor Gore section
Hi all,

I'm considering some carbon fiber use in my next build. I built a Lotus 7 type car about 10 years ago , and when I did my reaearch , the consensus was that non autoclaved carbon fiber was more of a cosmetic thing over fine woven aircraft quality fiberglass when used with a high quality epoxy resin . Yes there is a strength gain by using the stronger fiber but the resin matrix will ultimately be what fails unless it cures more fully under heat and pressure like any reaction in plastics . Also in order to get the ultimate in stiffness to weight ratio the resin matrix(epoxy) needs to be used extremely sparingly. Thats what prepreg is all about. There is so little resin that its virtually undetectable on the partially cured pre impregnated cloth.
From my canoe building days , I am familiar with the need to fully saturate the fibers and then remove as much resin as you can to save weight. When reinforcing wood I imagine the same principal applies.
As an aside , Has anyone tried putting a piece of carbon fiber reinforced wood in a medical type autoclave during its setting reaction? I just happen to have access to one. What does every one think the effect on the wood would be of typical medical autoclave type conditions (121 - 134 C (250 - 272 °F) at 100 kPa (15 psi above atmospheric) at 100% relative humidity. Time can be varied . I was thinking of sealing the entire piece of wood with epoxy which could be sanded off afterwards. This would be applied first and allowed to fully cure at atmospheric conditions. Then the layer of CF and epoxy would be applied and put in the autoclave before the setting reaction happens. What do you think will it help?
Typical CF autoclave conditions are 5bar(75psi above atmospheric) and 250F/121C

Phil

[kiwigeo]

Trevor will chime in but if you ask me I'd say you're "micrometering the brick" and is a top complete with clamps ( I use a go bar deck) going to fit into autoclave?

[curly]

Hmm , there's a heap I can't answer in your post and a fair bit more that I'm just vague as to exactly what you mean . The little I've got something to say about is regarding how the timber will behave under autoclave conditions. Aside from the pressure the conditions sound similar to a commercial hardwood kiln reconditioning treatment . The effect of this is to swell the cell walls and intercellular voids to recover collapse. I expect the pressure would be running counter to this effect . What I'm not clear on is whether the epoxy is introduced before , after or during this treatment . Certainly the moisture and epoxy won't get along with each other .
Probably more successful would be to pull the epoxy into the timber in a vacuum as is done with thermocure resins in timber stabilisation . Best bet would be to run a second cycle after the resin was pulled into the timber by releasing the vacuum where the chamber was cleaned of resin with the objective of pulling the excess off before it cured .The process could be done in a heavy duty vacuum bag type get up which would negate the need for a go bar deck . The success would be contingent on the timbers density and structure . Details such as whether pores are blocked with tyloses would be crucial . Lots of commercial timber data includes how readily a species uptakes preservatives .
Pete
Curly timbers

[pmatolcsy]

The piece I am considering strengthening is is a is a block of Douglas fir 3"x 12" long 1.5 thick at centre tapering to .5" at each end that will serve as a combination upper transverse brace ,sound hole edge and neck block. I guess I could vacuum bag the part to protect it from humidity during autoclaveing. I would use some seperation cloth over the fiber so the resin had somewhere to go and didn't stick to the bag. I was asking if anyone thought that at atmospheric or medical autoclave conditions , partially cured west system epoyx( as quick as I can lay it up and get it bagged) would benefit from autoclave conditions , and if people thought that ther wa a significant advantage in strength and or weight under either of those curing conditions to using CF vs good quality aircraft grade fiberglass