Proporties of fiberglass

Can anyone tell me how fiberglass behaves when exposed to high heat for long periods of time?

For example, does the section directly above the exhaust system bake and become brittle over time, or does it sag, or does it warp... or what?

Does the resin used make a difference?

Chris,

Not sure about this one, but whilst checking over various Elsie's recently at a local dealers I found that many of the engine covers had heat bumps and ripples on them.

John S.

The glass part of the fiberglass does fine, I think. It is the resin used to make the whole composite that is more heat-sensitive.
Most fiberglass laminates that we see in cars are glassfiber cloth wet out with polyester resin. Poly resin is not particularly heat resistant, and it is not fireproof. Over long periods of time it gets brittle. When the resin loses its' strength it stops holding the fibers together and the laminate fails.
FRP (fiberglass reinforced plastic) structures made with better resins (epoxy, vinylester, or better polyester resins like isophthalic poly) are I think more heat-resistant. There are some laminating resins specifically designed to be heat-resistant- some of the better yacht builders use them when making fuel tanks which in good boats are fiberglass. Hope this is helpful. ALL these materials will burn and melt if they get hot enough.

Typical polyester and vinylester resins have "heat distortion temperatures" of between 80C and 100C. Above that temperature, there'll be some noticable change in the matrix's shape - waviness or glass print-through. Epoxies can go much higher, but the best performers are usually in pre-pregs, not hand-laminate resins. We use isophthalic tooling resin - it's got the highest distortion temperature of the non-epoxy laminating resins.

The bottom line is this: Keep exhaust heat away from the body any way you can.

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Originally posted by Bob Putnam -ERA-:
Typical polyester and vinylester resins have "heat distortion temperatures" of between 80C and 100C. Above that temperature, there'll be some noticable change in the matrix's shape - waviness or glass print-through. Epoxies can go much higher, but the best performers are usually in pre-pregs, not hand-laminate resins. We use isophthalic tooling resin - it's got the highest distortion temperature of the non-epoxy laminating resins.

The bottom line is this: Keep exhaust heat away from the body any way you can.<HR></BLOCKQUOTE>

(And) The continued heat cycling leads to further delamination due to the different expansion rates between the resin and the glass fibre. FWIW