Usage of composite materials above Tg
Usage of composite materials above Tg
(OP)
Has anyone has any experience in using composite material above its Tg. If one could characterise its mechanical properties (at temperature >Tg and ignoring non linear failure behaviour), can one use them for FE analysis i.e. does the FE result applicable or appropriate??
n/b: the component will not be reused once it is being subjected to the temperature
n/b: the component will not be reused once it is being subjected to the temperature





RE: Usage of composite materials above Tg
Many thermoset composites can be slightly thermoformed at temperatures above Tg. Shape-memory composites use this effect.
RE: Usage of composite materials above Tg
I suggest that if you 'get away with' using a composite above Tg, you're working in someone else's safety factor, which doesn't sound like a real good idea to me.
Mike Halloran
Pembroke Pines, FL, USA
RE: Usage of composite materials above Tg
RE: Usage of composite materials above Tg
RE: Usage of composite materials above Tg
Wes C.
------------------------------
No trees were killed in the sending of this message, but a large number of electrons were terribly inconvenienced.
RE: Usage of composite materials above Tg
On a more practical note and assuming your question is regarding an application and not just theoretical, I would recommend you look for a material that is below its Tg and therefore capable of bearing load.
As an example, there are special epoxies that retain almost full modulus above Tg and all the way up to 300C.
Chris DeArmitt
"Knowledge has no value except that which can be gained from its application toward some worthwhile end."
Think and Grow Rich - Napoleon Hill
RE: Usage of composite materials above Tg
The properties drop off rapidly within a few degrees of the nominal dry Tg; 10 or 20 deg C (depends on how the Tg is measured) sees the modulus well below 10%, and heading for 1%, and any significant deformation is likely to be permanent. A laminate whose matrix is above its Tg is quite likely to deform under its own weight, as MikeHalloran describes, and its deformation is time dependent as Demon3 says.
If you must try to predict its behaviour then you need to do some fairly serious material-nonlinear work, and you're quite likely to get it wrong anyway.
If it's a one-time thing as part of manufacture, then try to arrange for tooling to support the part. If it's a rare service case then that's tricky... What will it cost/break if it's bad?
You can, of course, suck it and see with a test. That might be cheaper than analysis. If it's a service case than the laminate will probably need to be wet, which lowers the Tg a lot, and complicates testing even more.
RE: Usage of composite materials above Tg
Thanks again
RE: Usage of composite materials above Tg
Mike Halloran
Pembroke Pines, FL, USA