Talk Composites - The Forum for Advanced Composites

UD vs woven Prepreg

http://www.talkcomposites.com/Topic31379.aspx

By student00 - 12/24/2018 7:17:01 AM

I am trying to decide between using UD prepreg vs woven prepreg for a surfboard deck. I am leaning towards using a quad axial prepreg (one UD layer of 0,90,45,-45) as opposed to two layers of bi axial woven prepreg(one woven 0,90 and one -45,45 From my understanding:

1) UD being noncrimp has higher stiffness than woven
2) UD being flat has less chances of having resin rich pockets resulting in a laminate less prone to cracking

So essentially a laminate with 2 layers of UD (0,90) would have higher stiffness and lower weight (less resin) than a woven ply (0,90). So it seems like UD would be the more sensible choice, so then why is woven used so commonly? I understand if woven is used instead of one UD as it has fibers in both directions but what about biaxial UD vs woven? Note they are both prepreg, question being wouldnt 2 layers of UD prepreg yield better mechanical properties than one layer of woven prepreg?

I look forward to learning!
By Steve Broad - 12/27/2018 3:03:31 PM

 
f1rob - 12/27/2018 12:55:01 PM
 
Steve Broad - 12/27/2018 11:38:33 AM
 
f1rob - 12/24/2018 9:45:26 AM
Have you actually tried putting U/D down ? It's bloody hard soon as you get near a slight curve.
You will be slicing it to get it down an loose most of the strength
At the start all the f1 composite chassis were U/D
that soon changed an the only U/D you have now is inter laminar in flat/straight runs I.e across the back of the chassis from roll hoop to engine mount
Get yourself a 2x2 twill,little bit of heat an that will go round the edges of a board SO easy

I only use woven as, as you say, U/D can be a pain to work with.

Question. If laying down a 3 layer flat sheet using a 2x2 twill, is there any stiffening advantage in laying the centre layer at 45 degrees to the other two? 

LOT better in twist an also more balanced 

Cheers.